A Survey on Next Generation Mobile WiMAX Networks:Objectives,Features and

Technical Challenges

Ioannis Papapanagiotou,Graduate Student Member,Dimitris Toumpakaris,Member,Jungwon Lee,Member,

Michael Devetsikiotis,Senior Member

Abstract—In order to meet the requirements of4G mobile networks targeted by the cellular layer of IMT-Advanced,Next Generation Mobile WiMAX devices based on IEEE802.16m will incorporate sophisticated signal processing,seamless handover functionalities between heterogeneous technologies and advanced mobility mechanisms.This survey provides a description of key projected features of the physical(PHY)and medium access con-trol(MAC)layers of802.16m,as a major candidate for providing aggregate rates at the range of Gbps to high-speed mobile users. Moreover,a new uni?ed method for simulation modeling,namely the Evaluation Methodology(EVM),introduced in802.16m,is also presented.

Index Terms—IEEE802.16m,Mobile WiMAX Networks,Next Generation Wireless Networks,Broadband Wireless Access, Evaluation Methodology.

I.I NTRODUCTION

D ESPIT

E the challenges faced when transmitting data

through varying wireless channels,broadband metropoli-tan area wireless systems are becoming a reality,partly thanks to the increasingly sophisticated designs that are being em-ployed.Such designs have been made possible by theoretical advances and also by improvements in technology that have led to faster and cheaper implementations compared to older systems.Currently,the focus is on developing4G systems in the framework of IMT-Advanced[1],an ITU platform on which the next generation of wireless systems will be built.This paper is a survey of some of the state-of-the-art characteristics of the physical(PHY)and medium access control(MAC)layers of802.16m,one of the major candidates for Next Generation Wireless Systems.The concepts and algorithms that are implemented in802.16m will very likely be used in IMT-Advanced systems,either as they will appear in the802.16m standard or in similar,and possibly more sophisticated versions.Therefore,it is of interest not only to present these concepts and the ways that they address the needs of future systems,but also to identify technical Manuscript received9October2008;revised8February2009.

I.Papapanagiotou and M.Devetsikiotis are with the Department of Electri-cal&Computer Engineering,North Carolina State University,Raleigh,NC 27695USA.e-mail:{ipapapa,mdevets}@https://www.wendangku.net/doc/591875974.html,.

D.Toumpakaris is with the Wireless Telecommunications Laboratory, Department of Electrical&Computer Engineering,University of Patras,265 00Rio Achaias,Greece.e-mail:dtouba@upatras.gr.

J.Lee is with Marvell Semiconductor,Santa Clara,CA95054,USA.e-mail:jungwon@https://www.wendangku.net/doc/591875974.html,

Digital Object Identi?er10.1109/SURV.2009.090402.challenges that will have to be tackled in order for Next Generation Wireless Systems to meet the objectives set by IMT-Advanced.

IMT-Advanced is the continuation of IMT-2000,the global standard for3G wireless communications.The goal of IMT-2000was“to provide a framework for worldwide wireless access by linking the diverse systems of terrestrial and/or satellite based networks”[2].IMT-2000comprised a range of activities both inside and outside the ITU by partnerships such as3GPP and3GPP2.The main ambition of IMT-2000was to combat fragmentation and to unify different services(such as voice and multimedia)over a common platform.This way, operators should be able to provide seamless connectivity to users anytime and https://www.wendangku.net/doc/591875974.html,pared to earlier,2G systems, IMT-2000systems aimed at higher transmission rates for both mobile and?xed users.Therefore,IMT-2000standards needed to combine?exibility,affordability,modular design,and be backwards compatible with existing systems.Five IMT-2000 radio interfaces were approved in1999.A sixth one,namely IP-OFDMA TDD WMAN was added in2007.As will be explained below,IP-OFDMA TDD WMAN is a subset of the IEEE802.16standard and the WiMAX speci?cation. Similar to IMT-2000,IMT-Advanced aims at providing the platform on which4G wireless systems will be built,although it is not guaranteed that all4G systems will be compliant with IMT-Advanced.Moreover,it is possible that the capabilities of4G systems extend beyond IMT-Advanced.Naturally,the requirements of IMT-Advanced are more stringent compared to IMT-2000,and new services have been provisioned.4G systems are expected to provide higher rates(up to100 Mbps and1Gbps aggregate rates for mobile and?xed users, respectively),and a wide range of services and service classes in order to meet Quality of Service(QoS)requirements. Another notable feature of4G systems is that an all-IP network architecture will be used,at least in the near future. Currently,both3GPP and the IEEE aim at developing standards to ful?ll the goals of IMT-Advanced.The3GPP partnership has started work on LTE-Advanced,and Release 10will likely target IMT-Advanced[3].The IEEE has formed the802.16m Task Group for the development of the next amendment to the802.16standard[4].However,3GPP has as a modus operandi to provide a closed standard,whereas the IEEE802.16m task group is developing a free standard.This survey focuses on the evolution of the IEEE WirelessMAN

1553-877X/09/$25.00c 2009IEEE

standard,although several of the principles will likely also be applied to the design of LTE-Advanced systems.

Several articles that focus on Mobile WiMAX networks complying to the IEEE802.16e standard have appeared re-cently[6]–[10].This survey shifts the focus to IEEE802.16m-based Next Generation Mobile WiMAX,the recent design advances and the requirements as set by IMT-Advanced. An attempt is made to identify the new challenges of Next Generation wireless systems,and provide the reader with a unifying overview of the most important design improvements and changes in802.16m compared to802.16e.For this reason, an effort has been made to

?provide a survey of some of the state-of-the-art technolo-gies used in Wireless Next Generation Networks,?identify current bottlenecks and technical challenges and propose solutions or present already proposed ap-proaches,

?decompose the Broadband Wireless Access technology to its parameters and present their correlations,and ?present the IEEE802.16m Evaluation Methodology that aims at facilitating the collaboration of partners involved in the standardization of a complex system such as IEEE 802.16m.

The remainder of this survey is organized as follows:Sec-tion II contains a brief overview of WirelessMAN standards culminating to the development of IEEE802.16m that is currently under way.Section III discusses some of the changes and enhancements that are expected in the OFDMA PHY layer of IEEE802.16systems in order for Next Generation802.16m systems to meet IMT-Advanced requirements,whereas Section IV focuses on the Medium Access Control(MAC)layer.The Evaluation Methodology that is being developed for802.16m systems is presented separately in Section V.Finally,Section VI contains concluding remarks.

II.B RIEF O VERVIEW OF PREVIOUS IEEE802.16

STANDARDS AND REQUIREMENTS FOR802.16M

The IEEE802.16task group has been developing a fam-ily of standards for Wireless Metropolitan Area Networks (WMANs).WiMAX systems are based on IEEE802.16. However,strictly speaking,a WiMAX system is certi?ed by the WiMAX forum,an industry-led organization[11]. Certi?ed systems should conform to speci?ed parts of the 802.16standard and pass speci?c performance tests.That said,the terms IEEE802.16and WiMAX are often used interchangeably.The?rst802.16standard was approved in 2001.It employs Single-Carrier(SC)modulation in the10-66 GHz band and targets Line-of-Sight(LOS)scenarios.802.16a, the?rst amendment,was rati?ed in2003.It added support for non-LOS environments in order to support last-mile?xed broadband access.For this reason,Orthogonal Frequency Division Multiplexing(OFDM)and Orthogonal Frequency Di-vision Multiple Access(OFDMA)were introduced as options for the implementation of the physical(PHY)layer.802.16d that followed802.16c,a minor amendment,superseded all previous802.16standards(in the form of802.16-2004)and is frequently referred to as Fixed WiMAX[12].The success of OFDM-based WLANs and the gradual appearance of802.16d-based products triggered work on a new amendment that would support constant mobility in cellular networks that resulted in802.16e-2005,commonly referred to as Mobile WiMAX[7],[13].

Similar to previous amendments,802.16e-2005comprises different options for the implementation of the physical layer, depending on the radio frequency and the deployment envi-ronment.However,the main focus of802.16e in the physical layer is OFDMA(the IP-OFDMA TDD WMAN part of the standard).More speci?cally,compared to802.16d,more Fast Fourier Transform(FFT)sizes are supported and the FFT size is variable(Scalable OFDMA)in order for systems to be able to adapt to different conditions and requirements. 802.16e was the?rst802.16amendment to use MIMO spatial multiplexing(in addition to Alamouti transmit precoding that had appeared in802.16d),therefore increasing the maximum spectral ef?ciency.The use of multiple antennas coupled with channel feedback also makes possible the use of beamforming as a means of focusing to speci?c users while,at the same time,protecting others from interference.This capability is expected to be exploited more in the future to implement interference avoidance schemes,not only in a speci?c cell, but also among users belonging to different cells.Moreover, Hybrid ARQ,a retransmission scheme that can trade off delay for improved link reliability was included in the standard. Such improvements augment the capacity of systems in terms of users and allow802.16e systems to support mobile users moving at speeds up to120km/h.Finally,in each OFDMA frame of802.16e systems,different modulation can be used in different groups of subcarriers(subchannels)allocated to different users.This way,the available system resources can be utilized more ef?ciently.As mentioned previously,the OFDMA implementation option of the802.16e standard is now the sixth approved standard of IMT-2000of the ITU.

In order to meet IMT-Advanced goals,several enhance-ments and new capabilities are being studied for inclusion in the Physical Layer of802.16m.The aim is to use re-sources more ef?ciently,increase capacity,improve reliability in highly mobile environments,and accommodate users with different requirements.One change that is being studied is the decoupling of the subchannel permutations from the transmis-sion modes,and also the use of a common basic unit for the permutations.This is explained in more detail in the following section.The goal is to reduce overhead,improve?exibility and facilitate channel estimation.In802.16e systems,MIMO has mainly been addressed from the single-user perspective,and subcarriers are allocated to a given base station-mobile station pair.However,when many antennas are available at the base station,they can be used to transmit to more than one users simultaneously in each https://www.wendangku.net/doc/591875974.html,e of beamforming and other Multi-user(MU-MIMO)techniques,such as Dirty Paper Coding[14],can increase the capacity of the system and/or improve reliability.Hence,algorithms are needed that allocate subcarriers and users and calculate the transmit vectors de-pending on the Quality of Service(QoS)requirements of each session.Design of such algorithms requires a good theoretical background,but also depends on practical considerations,the most important being the feedback of channel information to the base station.In high doppler speeds channel information may not be reliable.Moreover,even when channel variations

SGORA and VERGADOS:A SURVEY ON NEXT GENERATION MOBILE WIMAX NETWORKS:OBJECTIVES,FEATURES AND TECHNICAL CHALLENGES5

are not an issue,the amount of overhead that is required for channel feedback should be kept to reasonable levels.The performance of WiMAX systems can be enhanced further by performing the allocation of frequency and spatial resources at the inter-cell rather than the intra-cell level.This way, adaptive and?exible frequency reuse can be implemented and the available spectrum can be redistributed depending on the requirements and the locations of the https://www.wendangku.net/doc/591875974.html,ing cooperation among neighboring cells,interference avoidance techniques can also be employed,especially for users near the cell boundaries.Finally,the reliability of transmission can be improved by devising and incorporating HARQ designs that take into account the performance of HARQ in practical MIMO scenarios.Such possible enhancements and additions to the Physical Layer of the802.16standard are discussed in Section III.

Regarding the MAC Layer,in order to achieve energy conservation and support mobility in rural environments,an ef?cient handover mechanism and power saving method has been standardized in802.16e,which allows discontinuous reception of data from the base station.Moreover,in order to accommodate the new application demands,Quality of Service has been an essential part of all new WMAN standards.The IEEE802.16-2004standard mainly included QoS functional-ities from the DOCSIS standard(multiple QoS classes)[5]. In IEEE802.16e an additional QoS class has been introduced that would support real-time applications with variable bit rate. Many other mobility features,such as those related to paging and location update,were also introduced by the IEEE802.16e workgroup[6].

In order to comply with4G standards,IEEE802.16m allows handover with service continuity for Radio Access Tech-nologies(speci?c interest being paid on IEEE802.11,3GPP GSM/EDGE,UTRA,E-UTRA and3GPP2CDMA2000)and support of IEEE802.21Media Independent Handover(MIH) services.The IEEE802.21standard allows optimal wireless network selection,seamless roaming to maintain data connec-tions and lower power operation for multi-radio devices.Some other operational requirements include multi-hop relaying(as introduced in IEEE802.16j),synchronization among all base stations and mobile stations and self-organizing mechanisms. Moreover,IEEE802.16m focuses on supporting legacy de-vices and cooperation among other802.16standards.

IEEE802.16m will comprise three documents:A Sys-tem Requirements Document(SRD)[15],a System De-scription Document(SDD)[16],and an Evaluation Method-ology Document(EMD)[17].As its name suggests,the System Requirements Document contains high-level require-ments for802.16m-compliant systems,including,among oth-ers,rates,throughput,coverage,mobility support,operating bandwidths and frequencies,QoS,latency,handover and se-curity.The main goal is to meet the cellular layer demands of IMT-Advanced,and,at the same time,support legacy WirelessMAN-OFDMA equipment.A list of some of the main requirements for IEEE802.16m is given in Table I.These requirements are compared with IEEE802.16e,the legacy standard for Mobile WiMAX.

The System Description Document contains all the details on the implementation of802.16m.It should be noted that the focus is on the de?nition of the signals emitted from the transmitter.The implementation details of the transmitter,as well as the design of the receiver are left to the manufacturers. The SDD speci?es the Physical(PHY)layer and the Medium Access Control(MAC)layer and is currently in a preliminary stage.

A new element in802.16m compared to previous amend-ments is the Evaluation Methodology Document.The EMD was introduced in order to provide a common baseline that will enable the evaluation and the comparison of different technol-ogy proposals.For this reason,both link-level and system-level simulation models and metrics are de?ned.Because of the projected complexity of802.16m systems and the diverse environments and scenarios in which they will be deployed,it could be argued that the development of a methodology that will lead to reliable evaluation is itself a challenge.In this survey,a separate section is dedicated to the EMD,in order to provide more details on the work in this area.

III.P HYSICAL L AYER ENHANCEMENTS

This section contains an overview of some Physical Layer enhancements that are currently being considered for inclusion in future systems.Because the development of the802.16m standard is still in a relatively early stage,the focus is on presenting the concepts and the principles on which the proposed enhancements will be based,rather than on providing speci?c implementation details.Although the exact degree of sophistication of the new additions to the standard cannot be safely predicted,it is expected that the additions will make some use of the concepts described below.

A.Flexibility enhancements to support heterogeneous users Because the goal of future wireless systems is to cater to needs of different users,ef?cient and?exible designs are needed.For some users(such as streaming low-rate appli-cations)link reliability may be more important than high data rates,whereas others may be interested in achieving the maximum data rate even if a retransmission,and,therefore, additional delay,may be required.Moreover,the co-existence of different users should be achieved with relatively low control overhead.For these reasons,the frame format,the subcarrier mapping schemes and the pilot structure are being modi?ed for802.16m with respect to802.16e.

Each802.16e frame consists of a downlink(DL)and an uplink(UL)part separated in time by an OFDMA symbol and is of variable size.The(downlink or uplink)frame begins by control information that all users employ to synchronize and to determine if and when they should receive or transmit in the given frame.Control information is followed by data transmission by the base station(in the downlink subframe)or the mobile stations(in the uplink subframe).For each mobile station,transmission or reception happens in blocks that are constructed from basic units called slots.Each slot can be thought of as a two-dimensional block,one dimension being the time,the other dimension being the frequency.In general, a slot extends over one subchannel in the frequency direction and over1to3OFDMA symbols in the time direction, depending on the permutation scheme.The subchannels are

6IEEE COMMUNICATIONS SURVEYS &TUTORIALS,VOL.11,NO.4,FOURTH QUARTER 2009

TABLE I

M OST IMPORTANT FEATURES AND SYSTEM REQUIREMENTS OF M OBILE W I MAX STANDARDS

Requirement IEEE 802.16e IEEE802.16m

Aggregate Data Rate 63Mbps

100Mbps for mobile stations,1Gbps for ?xed

Operating Radio Frequency

2.3GHz,2.5-2.7GHz,

3.5GHz

<6GHz.Duplexing Schemes TDD and FDD

TDD and FDD

MIMO support

up to 4streams,no limit on antennas

4or 8streams,no limit on antennas 3km,5-30km and 30-100km,

Coverage

10km depending on scenario

Handover Inter-frequency

Interruption Time 35-50ms 30ms Handover Intra-frequency

Interruption Time Not Speci ?ed

100ms

From legacy serving BS to legacy target BS Handover between 802.16standards From 802.16m serving BS to legacy target BS (for corresponding mobile station)From 802.16e serving BS to 802.16e target BS

From legacy serving BS to 802.16m target BS From 802.16m serving BS to 802.16m target BS

IEEE 802.11,3GPP2,GSM/EDGE,(E-)UTRA (LTE TDD)Handover with other technologies

Not Speci ?ed Using IEEE 802.21Media Independent Handover (MIH)

Indoor:10km/h

Mobility Speed Vehicular:120km/h Basic Coverage Urban:120km/h

High Speed:350km/h

Location Determination Latency:30s

Position accuracy

Not Speci ?ed

Handset based:50m (67-percentile),150m (95-percentile)Network based:100m (67-percentile),300m (95-percentile)

IDLE to ACTIVE state transition 390ms

50ms

Quality of Service Classes

UGS,nrtPS,ertPS,rtPs,BE

UGS,nrtPS,ertPS,rtPs,BE

groups of OFDMA subcarriers.The number of subcarriers per subchannel and the distribution of the subcarriers that make up a subchannel in the OFDMA symbol are determined based on the permutation scheme.As explained in more detail below,the subcarriers of a given subchannel are not always consecutive in frequency.Downlink and uplink subframes can be divided into different zones where different permutation schemes are used.

In the Partial Usage of Subchannels (PUSC)zone that is mandatory,the priority is to improve diversity and to spread out the effect of inter-cell interference.Each slot extends over 2OFDMA symbols,and a subchannel consists of 24data subcarriers that are distributed over the entire signal bandwidth (OFDMA symbol).Thus,each subchannel has approximately the same channel quality in terms of the channel gain and the inter-cell interference.To reduce the effect of the inter-cell interference,when PUSC is used,the available subchannels are distributed among base stations so that adjacent base stations not use the same subchannels.

When the inter-cell interference is not signi ?cant,as in the case of mobile stations located closely to a base station,it may be advantageous to employ Full Usage of Subchannels (FUSC).The goal of the FUSC permutation scheme is similar to PUSC,i.e,to improve diversity and to spread out the effect of inter-cell interference.However,as the name suggests,in the FUSC zone all subchannels are used by a base station.For this reason,the design of the pilot pattern for the FUSC zone is slightly more ef ?cient compared to PUSC.A subchannel in the FUSC permutation zone consists of 48data subcarriers and the slot only comprises one OFDMA symbol.

For users with high rate requirements,the Adaptive Mod-ulation and Coding (AMC)zone is employed instead of PUSC or FUSC.AMC makes it easier to exploit multiuser diversity by using adjacent subcarriers to form a subchannel.Subchannels made of adjacent subcarriers vary in quality across the frequency spectrum.Therefore,the system can employ opportunistic schemes that do not perform well when the transmission bandwidth is averaged (as is the case when subcarriers are spread out).A subchannel in the AMC zone consists of 16data subcarriers.For the 2×3AMC mode,each slot extends over 3OFDMA symbols.

Therefore,in addition to requiring overhead to transition between zones inside a frame,in IEEE 802.16e the size of the basic data unit (the slot)depends on the permutation zone.The frame structure is being rede ?ned in 802.16m to make the allocation of transmission resources between the downlink and the uplink more ?exible [16].802.16m consists of a 20-ms superframe,divided in equally sized 5-ms radio frames using either Time-Division Duplexing (TDD)or Frequency-Division Duplexing (FDD).Each 5-ms frame is further divided in 8subframes when OFDMA is used.Each subframe is assigned to either downlink or uplink transmission,the allocation decision being based on QoS.If more capacity is required for the downlink,then the scheduler allocates more subframes to the downlink.Moreover,latency requirements can be satis ?ed via proper subframe allocation between the downlink and the uplink.Although some additional control overhead will be needed to signal the transitions between downlink and uplink and,vice versa,overall the system can bene ?t from the improved ?exibility in rate allocation and latency guarantees.Moreover,in order to reduce the overhead that is required for the placement of different zones in a frame,an effort is under way in 802.16m to de ?ne the same basic unit for all permutation schemes and to improve the ?exibility of the system.This will be achieved by separating the subcarrier allo-cation mode from the transmission scheme.More speci ?cally,a localized (contiguous)and a distributed (non-contiguous)resource unit permutation mode are de ?ned for 802.16m [16].As the name suggests,the localized (contiguous)permutation mode employs groups of contiguous subcarriers,whereas for the distributed (non-contiguous)permutation mode the subcarriers of each group are spread out.A given transmission

SGORA and VERGADOS:A SURVEY ON NEXT GENERATION MOBILE WIMAX NETWORKS:OBJECTIVES,FEATURES AND TECHNICAL CHALLENGES7

scheme(such as SISO,beamforming or space-time coding using many transmit antennas etc.)can be used with both localized and distributed permutation modes.Having only two modes will also simplify channel estimation.Clearly,some control overhead is still needed to signal the subchannels that are assigned to each user and the subframe allocation. However,it is expected that this overhead will be reduced compared to802.16e.

The possible modi?cation of the permutation modes will also have an impact on the position of the pilot subcarriers that are used for channel estimation.In fact,this is a good opportunity to devise good subcarrier placements for more than two transmit antennas,especially because the goal of Next Generation WiMAX seems to be to support up to at least 4downlink streams,possibly up to8streams.In802.16e,the number of pilots per subchannel is constant.Therefore,when two transmit antennas are employed,the pilots are typically divided between the two transmit antennas.This means that the channel estimates may be less accurate when two transmit antennas are used at the base station instead of one.For more than two antennas,the estimation quality drops further,since the available pilots will need to be distributed to more an-tennas.Although the802.16e standard contains provision for more than two antennas at the base station,Mobile WiMAX systems currently employ two antennas.The design of pilots for802.16m is already under way.The current proposal uses the same pattern for localized and distributed resource units. It has been reported that the required overhead is smaller compared to802.16e and that the estimation performance is better.In order to improve support for two downlink streams, it is proposed that the number of pilots be twice as large compared to when only one stream is used(12within each resource unit i.e.,6pilots per stream)[16].For4streams,16 pilots per resource unit are being proposed(or,equivalently, 4per stream).Although the quality of channel estimation is expected to be inferior to the2-stream case,4streams will be used in better channel conditions where the quality of the estimation may be less crucial to the system performance. The?exibility of802.16m systems can also be improved by allowing use of more than one Radio Frequency(RF) bands when such bands are available.By including multi-carrier support,the available bandwidth,and,consequently, the system capacity,can increase.The RF bands do not need to be adjacent.In order to support multiple carriers without lowering the ef?ciency of the system,the distance between carriers will need to be an integer multiple of the subcarrier spacing to eliminate the need for additional guard bands. Moreover,the MAC should be modi?ed in order to provide multi-carrier support.

Finally,it is important that802.16m systems be backwards compatible with legacy standards so that other802.16de-vices be supported and coexist with new802.16m-compliant equipment.802.16m will contain provisions for backwards compatibility,coexistence and also handover with IMT-2000 and IMT-Advanced systems(such as LTE).This is discussed in more detail in Section III-D.B.Extending use of MIMO transmission

Multiple-Input Multiple-Output(MIMO)communication is already a reality in wireless systems.It will be supported by the IEEE802.11n amendment to the802.11WLAN standards that is expected to be rati?ed in the near future.Similarly, 802.16e includes support for MIMO downlink and uplink transmission.As MIMO technology matures and implementa-tion issues are being resolved,it is expected that MIMO will be widely used for wireless communication.

Current Mobile WiMAX pro?les include support for up to 2transmit antennas even though the IEEE802.16e standard does not restrict the number of antennas,and allows up to4 spatial streams.The current aim for Next Generation WiMAX systems is to support at least up to8transmit antennas at the base station,4streams and Space-Time Coding. Moreover,although some other MIMO features of802.16e, such as closed-loop MIMO,have not appeared in Mobile WiMAX pro?les yet,it is expected that they will be included in new802.16m-based systems.More speci?cally,it has been already decided to support closed-loop MIMO using Channel Quality Information,Precoding Matrix Index and rank feedback in future systems[18].

In802.11systems,as well as in the802.16e standard, MIMO transmission is used to increase the data rate of the communication between a given transmitter-receiver pair and/or improve the reliability of the link.It is expected that802.16m and future3GPP systems will extend MIMO support to Multi-user(MU-)MIMO.More speci?cally,use of multiple antennas can improve the achievable rates of users in a network with given frequency resources.In information-theoretic terms,the capacity region of the uplink and the downlink increases,in general,when MIMO transmission is employed[14].In many cases,a large portion of this capacity increase can be achieved using relatively simple linear schemes(transmit beamforming at the downlink and linear equalizers at the uplink).Therefore,the achievable rates can be increased without the need for sophisticated channel coding. If larger complexity can be afforded,even higher gains can be attained using successive decoding at the uplink and Dirty Paper Coding schemes at the downlink.

An overview of the projected MIMO architecture for the downlink of802.16m systems is given in the System De-scription Document(SDD),and is repeated in Fig.1for convenience.

One of the major theoretical advances of recent years was the characterization of the Gaussian MIMO uplink(a Mul-tiple Access Channel)and the Gaussian MIMO downlink(a Broadcast Channel).More speci?cally,for the uplink,the ca-pacity is achieved by the receiver decoding users successively, whereas,in the downlink,capacity-achieving codes are created by superimposing encoded streams destined for each mobile station.The encoded streams are created successively using Dirty Paper Coding(DPC)techniques[19].In the uplink,the optimality of successive decoding at the receiver holds when the transmitted signals are Gaussian.Moreover,the codes should be suf?ciently long in order for the probability of error of each user that is decoded successively to be arbitrarily close to zero.Similarly,in the downlink,capacity is achieved

8IEEE COMMUNICATIONS SURVEYS&TUTORIALS,VOL.11,NO.4,FOURTH QUARTER

2009 Fig.1.MIMO architecture for the downlink of802.16m systems.

by employing suf?ciently long codes and encoded signals

with Gaussian distribution.In practice,codes of reasonable encoding and decoding complexity are needed,both for the uplink and for the downlink.The encoding schemes may also

affect the implementation of the receiver.Linear beamforming schemes[20],[21]that avoid the use of DPC have been shown

to perform reasonably well in practical scenarios and could be a good candidate for802.16m systems.

WiMAX and3GPP networks employing MU-MIMO will need to calculate which users should transmit and receive

during each frame,as well as the best achievable rate that corresponds to each user based on their QoS requirements, the number of users in each cell and their position.Although

the information-theoretic capacity has been characterized,this is not an easy task,even for narrowband systems,and it is even more challenging when all subcarriers of the OFDMA system

are considered.Therefore,ef?cient algorithms will be needed at the base station for user selection that will also determine

the beamforming?lters for the downlink,the receiver?lters for the uplink and the required power allocation at the base station and each mobile station.

The performance of MU-MIMO also depends on what is

known about the channel at the transmitter.When the doppler speeds are high,the channels may be changing faster than the speed with which the transmitter can track the channel.

Even in low speeds,obtaining perfect channel knowledge may not be desirable from a practical point of view,especially in MIMO systems.For example,a base station with N t antennas

wishing to obtain channel information corresponding to K mobile stations each with N r antennas will need to collect

information for K·N t·N r channel coef?cients.This consumes part of the bandwidth that would otherwise be allocated to data communication.Moreover,as was mentioned previously,the

pilot structure should be such that the channel measurement be obtained with suf?cient reliability.Therefore,in addition to well-designed pilot patterns,it is very likely that base stations of future systems will have to rely on imperfect and partial channel information.802.16e already includes ?ve different mechanisms for channel feedback ranging from the mobile station only reporting to the base station which antennas should be used(Antenna Selection)to the mobile station sending to the base station exact information about the MIMO channel(Channel Sounding).The channel feedback mechanisms will need to be extended to the case of MU-MIMO and algorithms will be needed in order for the mobile stations to determine what information to send back to the base station.For this reason,the performance of MU-MIMO with partial channel information at the transmitter,and the mechanisms to obtain channel information at the receiver and feed it back to the transmitter are currently topics of considerable theoretical and practical interest[18],[22]–[24].

C.Resource allocation and multi-cell MIMO

In cellular networks careful frequency planning is required in order to achieve communication with small outage probabil-ity and,at the same time,minimize interference among users of neighboring https://www.wendangku.net/doc/591875974.html,ers near the cell edges are particu-larly vulnerable,because they receive signals of comparable strength from more than one base stations.For this reason, different parts of the frequency spectrum are typically assigned to neighboring cells.1The assignment in current systems is static and can only be changed by manual re-con?guration of the system.Changes to the frequency allocation can only be performed periodically and careful cell planning is required in order not to affect other parts of the system.Frequen-cies are reused by cells that are suf?ciently far away so that the interference caused by transmissions on the same frequencies is small enough to guarantee satisfactory Signal-to-Interference and Noise Ratios(SINRs).Although static frequency reuse schemes greatly simplify the design of cellular systems,they incur loss in ef?ciency because parts of the spectrum in some cells may remain unused while,at the same 1CDMA systems are an exception to this scenario although the system still needs to guarantee that the chip sequence assigned to a given user is not employed by any other user that communicates with the same base stations.

SGORA and VERGADOS:A SURVEY ON NEXT GENERATION MOBILE WIMAX NETWORKS:OBJECTIVES,FEATURES AND TECHNICAL CHALLENGES9

time,other cells may be restricting the rates of their mobile stations or even denying admission to new users.Moreover, the handover process is more complicated for mobile stations since communication in more than one frequencies is required. In order for future wireless systems to attain the high rate and reliability requirements of IMT-Advanced,ef?cient management of the system resources is needed.Ideally,sys-tems should be able to re-allocate dynamically the available spectrum among different cells.As discussed previously,by using beamforming,MIMO systems can transmit to more than one user in a given frequency,in general.So,it is possible, and it may actually also be desirable,to allow more than one users of the same or of different cells to transmit or receive on the same frequency.In general,MU-MIMO transmission and resource allocation are closely linked to each other,as can also be seen in Fig.1.For optimal performance,resource allocation (frequency,power,antennas and users)should be made by a central controller that receives information from all base stations of all cells.Clearly,this is very complicated,since the amount of information that needs to be transferred to the central controller and the complexity involved in performing resource allocation can be very large.

In order to improve the ef?ciency of resource allocation with reasonable complexity,distributed approaches can be used.For example,resource allocation can be seen as a non-cooperative game among different base stations.Each base station attempts to allocate resources to satisfy the QoS requirements of the users in the cell it serves,but,at the same time,gets penalized for the amount of resources that are being used[25].If information on the interference caused to users of other cells can be conveyed to the base station, the cost function could include the effect of the choices of the base station on the transmissions occurring in neighboring cells.Simpler approaches can also be used.As an example,a dynamic scheme is being developed for802.16m that divides the frequency band into4sub-bands[16].Three sub-bands use a frequency reuse factor of1/3,whereas the frequency reuse factor in the fourth sub-band is equal to1.The size of the sub-bands can be changed dynamically,thus changing the overall frequency reuse factor of the system.This dynamic Fractional Frequency Reuse scheme could be a?rst step towards fully dynamic frequency reuse schemes.

Finally,as the infrastructure improves,cellular systems could also take advantage of communication between the base stations.As mentioned above,exchange of information regarding the interference caused by neighboring cells can improve the ef?ciency of resource allocation.If user data can also be communicated,in addition to channel measurements, the system performance at the cell edge could be potentially improved by processing jointly the data of users that are received by more than one base stations.Other open-and closed-loop multi-cell MIMO transmission schemes are also being considered for802.16m,but the development is still in a very early stage for safe predictions to be made on what will be included in the standard.

An example of transmission depending on the level of inter-cell cooperation is given in Fig.2where,in each cell i,a base station BS i communicates with a mobile station

MS i.In Fig.2(a),a traditional system with static

frequency https://www.wendangku.net/doc/591875974.html,munication and resource allocation depending on level of inter-cell cooperation.

reuse and no inter-cell cooperation is considered.Even if the base stations have many antennas,different parts of the available spectrum are used by each cell for transmission because BS1does not have access to information regarding the frequencies used by BS2to transmit to MS2,and vice-versa.In Fig.2(b),BS1and BS2exchange information on the beamforming vectors and the frequencies that are used for transmission.This way,they can avoid interfering with each other.This can be achieved by choosing different frequencies from a shared pool of frequencies,or,if this is possible,use the same frequency,but pick beamforming vectors that minimize interference between the two links.When the interference between the mobile stations is weak,or when the rates requested by the corresponding users are suf?ciently small, a given frequency may be shared even if no beamforming is used(for example at the uplink,when each mobile station has a single antenna).Finally,in Fig.2(c),the base stations can also share the received symbols(or,equivalently,they can send them to a central processor).This way,an equivalent,virtual

10IEEE COMMUNICATIONS SURVEYS &TUTORIALS,VOL.11,NO.4,FOURTH QUARTER 2009

Downlink:TDM 29 OFDM Symbols Uplink: FDM

Frame 5ms

Legacy Zone

Legacy Zone

a)

b)

Fig.3.

Supported 802.16connections and IEEE 802.16m frame structure with TDM Downlink and FDM Uplink.

Multiuser-MIMO system is created between the combination

of the antennas of BS1and BS2and the mobile stations of both cells.Clearly,this last architecture is the most ef ?cient in terms of resource usage,but also the most complicated,especially as the number of cells that are coupled together increases.

It is important to note that,most likely,the future WiMAX standards will not describe in detail how resource allocation should be performed,and it will be up to the manufacturers to devise ef ?cient and practical schemes.For example,802.16e does not specify how subcarriers and transmit matrices are allocated to users in a cell.The base station performs resource allocation based on information that is received from mobile stations and then informs mobile stations when each should transmit and receive.What is important is to ensure that future amendments contain the mechanisms that will enable the transmission and exchange of the necessary information for the implementation of resource allocation mechanisms.Changes in the MAC layer may also be needed if mobile stations need to communicate simultaneously with more than one base stations.

D.Interoperability and coexistence.

In order for the standard to be able to support either legacy base and mobile stations or other technologies (e.g.LTE),the concept of the time zone,an integer number (greater than 0)of consecutive subframes,is introduced.

Interoperability among IEEE 802.16standards :The 802.16m Network Reference Model permits interoperability of IEEE 802.16m Layer 1and Layer 2with legacy 802.16standards.The motivation for ensuring interoperability comes from the fact that WiMAX networks have already been deployed,and it is more realistic to require interoperability instead of an update of the entire network.Another advantage is that each 802.16standard provides speci ?c functionalities in a WiMAX network.The goal in 802.16m is to enable coexistence of all these functionalities in a network without

the need to create a new standard that contains all of them.The supported connections and frame structure are summarized in Fig.3.The legacy standard can transmit during the legacy zones (also called LZones),whereas 802.16m-capable stations can transmit during the new zones.The Uplink (UL)portion shall start with the legacy UL zone,because legacy base stations,mobile stations or relays expect IEEE 802.16e UL control information to be sent in this region.When no stations using a legacy 802.16standard are present,the corresponding zone is removed.The zones are multiplexed using TDM in the downlink,whereas both TDM and FDM can used in the uplink.In each connection,the standard that is in charge is showcased.The Access Service Network can be connected with other network infrastructures (e.g.802.11,3GPP etc.)or to the Connectivity Service Network in order to provide Internet to the clients.

Adjacent Channel Coexistence with LTE TDD :802.16m-compliant devices may coexist with LTE devices (E-ULTRA TDD)in adjacent channels.This is accomplished by insert-ing either idle symbols within the 802.16m frame or idle subframes.Thus,the 802.16m system shall be capable of applying an operator con ?gurable delay or offset such that the 802.16m UL shall start at the same subframe as the LTE frame.Hence,both standards can coexist and be synchronized.Similarly,802.16m-compliant devices can coexist with other technologies such as ULTRA LCR (TD-SCDMA)etc.

IV.M EDIUM A CCESS C ONTROL L AYER

In contrast to contention-based WiFi networks where each station needs to compete for access to the medium,the IEEE 802.16standard is a connection-oriented wireless network.A scheduling algorithm allocates resources (either in speci ?c grants or contention periods)to each service ?ow (or con-nection)taking into account the Quality of Service needs.Further extensions to the initial design of IEEE 802.16-2004included mobility (i.e.,functionalities associated with han-dover and energy-ef ?cient algorithms),relaying [26],ef ?cient

SGORA and VERGADOS:A SURVEY ON NEXT GENERATION MOBILE WIMAX NETWORKS:OBJECTIVES,FEATURES AND TECHNICAL CHALLENGES11

Network Layer

Newest features of Mobile WiMAX networks, from IEEE 802.16e to IEEE 802.16m

Fig.4.MAC layer architecture of IEEE802.16m.

localization and several other MAC layer features.In this section,the MAC layer enhancements of IEEE802.16m that aim at meeting the IMT-Advanced requirements are presented.

A basic understanding of connection-oriented and WiMAX network architectures is assumed in the following.For more information on this subject,see,for example,[28].

The MAC of802.16m is divided into three sublayers:?Convergence sublayer(CS)

?Radio Resource Control and Management(RRCM)sub-layer

?Medium Access Control(MAC)sublayer

The general architecture of the MAC layer of802.16m is shown in Fig.4.The purpose of the sublayers is to encapsulate wireline technologies such as ETHERNET,ATM and IP on the air interface,and to introduce the state-of-the-art connection-oriented features.In the following these three sublayers are discussed in more detail.

A.Convergence sublayer

The Convergence sublayer(CS)resides on top of the MAC CPS(Common Part Sublayer).The Packet CS is responsible for accepting data units from higher layers,classifying,pro-cessing based on classi?cation,and delivering CS Protocol Data Units(PDU)to the appropriate MAC SAP(Service Access Point).In reality,it is the sublayer that unites the IEEE802.16MAC with the network layer.The MAC CPS

creates its Protocol Control Information(MAC header)and is responsible for the delivery of MAC PDUs to its peer MAC-CPS according to the Quality of Service(QoS)requirements

of the particular Service Flow(SF).Those functionalities,as provided by the current form of the CS of IEEE802.16m,are

similar to the ones of legacy802.16systems.

B.RRCM sublayer

The RRCM sublayer includes functionalities that determine the performance of the service?ow.The functionalities are indicated in the boxes of Fig.4.New functionalities are shown

in grey boxes.The functionalities of RRCM are the following.?Relay Functions.They are described in detail in[26]and include methodologies referred to as“Mobile Multihop

Relay”(MMR).The basic idea behind MMR is to allow WiMAX base stations that do not have a backhaul connection to communicate with base stations that do(in order to increase network coverage).A technical survey for the nonexpert can be found in[27].

?Radio Resource Management,that adjusts radio network parameters related to the traf?c load,and includes some other QoS-related functionalities,such as load,admission and interference control.

?Mobility Management,that is related to handover.

12IEEE COMMUNICATIONS SURVEYS&TUTORIALS,VOL.11,NO.4,FOURTH QUARTER2009

?Network Management,that is in charge of initialization procedures.

?Location and Idle Mode Management,responsible for supporting location-based services and for controlling Idle Mode operation,respectively.The system require-ments for location-based Services(LBS)are identi?ed in Table I.

?Since security is one of the most important issues in wireless networks,Security Management provides secure communication between the mobile station and the base station by handling encryption and authentication.?Broadcast control messages,such as the downlink/uplink channel descriptor(DCD/UCD),are generated from the System Con?guration Management block.

?MBS(Multicast and Broadcasting Service)controls man-agement messages and coordinates with the base station to schedule the transmission related to MBS data.?Connection Management allocates connection identi?ers (CID)during initialization,handover and service?ow creation procedures.

?Self Organization includes the procedures to request that mobile stations report measurements for self-con?guration and optimization.

?A Multi-carrier block,that enables a common MAC en-tity to control a PHY spanning over multiple frequencies. The way that a speci?c service?ow will be handled by the MAC layer is based on the performance of the scheduler.Con-trary to the802.16e standard,the IEEE802.16m workgroup does not provide amendments on the service?ow management part.Five QoS categories are de?ned to handle different types of applications.

?UGS(Unsolicited Grant Service)is designed to support real-time uplink service?ows that generate?xed-size packets on a periodic basis.For this reason,the base station generates periodically?xed-size data grants to minimize the overhead and the latency.It includes V oIP applications without silence suppression and also handles T1/E1.

?rtPS(Real-time Polling Service)supports variable-size data packets,such as MPEG video.The base station offers real-time periodic unicast request opportunities and allows the mobile station to specify the size of the desired grant.

?Extended rtPS(Extended Non-Real-time Polling Service) provides unicast grants with variable size in an unso-licited manner.It is supposed to be the service?ow that combines the advantages of both UGS and rtPS.?nrtPS(Non Real-time Polling Service)is designed to sup-port non real-time uplink service?ows,where the base station issues unicast request opportunities on a regular basis.During the request interval,the mobile stations contend and the base station allocates resources accord-ingly.It may also support unicast request opportunities.

This service?ow may provide access to applications that do not require strict QoS guarantees,even during network congestion.

?BE(Best Effort)is based on a Request/Transmission policy where the mobile stations are contending for

request opportunities.It is the only scheduling service where no mandatory QoS parameters are set because it handles only best-effort traf?c.

C.MAC sublayer

The functionalities of the MAC sublayer are related to PHY control(cross-layer functionalities,such as HARQ ACK/NACK etc).The Control Signaling block is responsible for allocating resources by exchanging messages such as DL-MAP and UL-MAP.The QoS block allocates the input traf?c to different traf?c classes based on the scheduling and resource block,according to the SLA guarantees.The name of other blocks,such as fragmentation/packing,multi-radio coexistence and MAC PDU formation,clearly describes their function. The MAC sublayer also deploys state-of-the-art power saving and handover mechanisms in order to enable mobility and make connections available to speeds up to350km/h. Since newer mobile devices tend to incorporate an increasing number of functionalities,in WiMAX networks the power saving implementation incorporates service differentiation on power classes.A natural consequence of any sleeping mech-anism is the increase of the delay.Thus,delay-prone and non delay-prone applications are allocated to different classes, such that the energy savings be optimized,while satisfying the appropriate QoS(e.g those that support web page downloading or emails).

MAC addresses play the role of identi?cation of individual stations.IEEE802.16m introduces two different types of addresses in the MAC sublayer.1)The IEEE802MAC address that has the generic48-bit format and2)two MAC logical addresses that are assigned to the mobile station by management messages from the base station.These addresses are used for resource allocation and management of the mobile station and are called“Station Identi?ers”(assigned during network entry)and“Flow Identi?ers”(assigned for QoS purposes).

1)MS state:The mobile station can be in four different states based on the MAC functionalities,namely Initialization, Access,Connected and Idle State.The states are shown in Fig.5.The Initialization State is where the mobile station performs the scanning and synchronization based on the base station preamble.As soon as it acquires the system con?gu-ration information,it is ready to perform the ranging process and transition to the Access State.If the mobile station cannot perform BCH information decoding(that usually involves the evaluation of the error locating polynomial)and cell selection, it goes back to scanning and DL synchronization.

In the Access State,MOB?RNG-REQ and MOB?RSP-REG MAC messages2are exchanged in order to initiate the ranging process and Uplink(UL)synchronization,respec-tively.For security purposes,Authentication and Authorization is performed before mobile station registration to the target 2Since802.16networks are connection-oriented,the base station and mo-bile station communicate with management messages.Starting from802.16e these messages are of the form MOB?XXX-YYY,where MOB stands for Mobility and the rest for each functionality(e.g.XXX can be REG: Registration,RNG:Ranging,SCN:Scanning,SLP:Sleep mode functionality message and YYY REQ:Request Message,RSP:Response message,ADV: Advertisement).

SGORA and VERGADOS:A SURVEY ON NEXT GENERATION MOBILE WIMAX NETWORKS:OBJECTIVES,FEATURES AND TECHNICAL CHALLENGES13

Idle State

Connected State

Fig.5.IEEE802.16m mobile station state transition diagram.

base station.During the registration,the mobile station is associated with a MAC Connection Identi?er(CID)and an IP address.The dashed arrows in Fig.5denote the case where the mobile station moves back to the Initialization step because of failure.

The Connected State comprises three different modes. Traf?c is transmitted and handover is performed when on Active Mode.For moving from Active to Sleep Mode,the standard de?nes speci?c messages that are exchanged between the mobile station and the base station.The mobile station also needs to scan for other available base stations,and for that it must move to the Scanning Mode(MOB?SCN-REQ and MOB?SCN-RSP messages are exchanged for this transaction),thus the Scanning Mode State.

As mentioned before,in order to conserve energy and to prolong the battery lifetime of the mobile station,a Sleep Mode is de?ned.The Sleep Mode is further divided into a sleep interval and a listen interval.This mechanism takes advantage of the idle transmission intervals of the BS when there are no packets destined to the MS in the output buffer of the BS.Therefore,the sleep interval is the amount of time during which the radio interfaces are periodically shut down. After that,a listen interval follows,in which the mobile station synchronizes with the serving base station and receives a small amount of data or a traf?c indication message(called TIM; it indicates the existence of a packet in the buffer of the base station).However,because packets are buffered when the radio is shut down multiple times,an optional Idle State was introduced in IEEE802.16e.When in Idle State,the mobile station can monitor the link channel,transition to the Active Mode and perform handover.This can be done in the Paging Listening Mode using MOB?PAG-ADV messages. However,monitoring is not performed in Paging Unavailable Mode.The advantage of this implementation is that battery life can be prolonged,and the delay is maintained below the agreed levels.For higher QoS classes,such as constant bit rate V oIP,the sleep interval is usually in-between the packets, whereas for best-effort traf?c classes an exponential algorithm is implemented for the sleep intervals[33].

2)Hybrid ARQ:Hybrid Automatic Repeat reQuest (HARQ)is an extension of ARQ.When the receiver detects a corrupted packet,a retransmission is requested from the receiver.The standard retransmission strategies of ARQ(such as stop-and-wait,go-back-N and selective-repeat)can also be used for HARQ.The difference from ARQ is that HARQ uses all received copies of a given packet for decoding.HARQ transmission can improve the throughput of a communication link,and for this reason it is supported in802.16e.Two vari-ants of HARQ have been developed.When Chase-Combining HARQ(CC-or Type I HARQ)is employed,the same packet is sent after each request.Incremental Redundancy HARQ(IR-or Type II/III HARQ)is more general:retransmitted packets

14IEEE COMMUNICATIONS SURVEYS&TUTORIALS,VOL.11,NO.4,FOURTH QUARTER2009

may contain different bits of an encoded stream,or a different encoder may be used.In general,the use of different encoders and/or different bits provides a coding gain,and,for this reason,IR-HARQ performs better than CC-HARQ.However, there are some cases of fading channels where CC-HARQ may outperform IR-HARQ[29].Moreover,the architecture of transceivers that employ CC-HARQ is simpler.The pro?les of Mobile WiMAX only support CC-HARQ,although IR-HARQ was included in the802.16e standard.IR-HARQ is now being considered for Next Generation systems and code designs are being developed.

In the following,some issues related to the application of HARQ in802.16m systems are discussed.

?MIMO HARQ:When HARQ is used in MIMO systems, the implementation of the receiver may have substantial im-pact on the performance of HARQ.Transmission is affected by Gaussian noise and the fading channel,but also from the interference among streams received at different antennas. When Maximum-Likelihood(ML)decoding is too complex to implement in terms of operations and/or required storage, simpler architectures need to be employed.When CC-HARQ is used,the decoder can be simpli?ed without loss in perfor-mance by combining the received modulated symbols at each antenna.However,in general,the bit-to-symbol mapping may not be constant in IR-HARQ.Suboptimal approaches such as decoding after each retransmission and combining of the decoded soft bits may result in signi?cant performance loss. In some cases,for schemes used in802.16e,use of a practical receiver may result in IR-HARQ transmission performing worse than CC-HARQ[30].Therefore,it is important to develop codes that will exhibit good coding gains and will be robust to suboptimal operations at the receiver.One approach to obtaining a good complexity-performance tradeoff is to include mechanisms that enable IR-HARQ that preserves the alignment between bits and the symbol vectors that are transmitted at the base station[31].This allows reduction of complexity and storage without a penalty in performance. However,care has to be taken in the design of the IR-HARQ scheme to combine constant bit-to-symbol vector alignment with suf?cient coding gains so that IR-HARQ still have an advantage over CC-HARQ.It should be noted that, although constant bit-to-symbol vector alignment can lead to considerable simpli?cation of the receiver,optimal receivers for IR-HARQ will be more complex than their counterparts for CC-HARQ.However,for a future WiMAX system where ef?ciency is very important,the additional gain provided by IR-HARQ may be required,and,therefore,simpli?cation of a receiver capable of supporting IR-HARQ will be very bene?cial.Another approach is to design IR-HARQ coding schemes that take the MIMO nature of the system into account [32].Again,the complexity of the receiver will depend on the scheme,and,inversely,will impact the performance of HARQ.?Synchronous and Asynchronous HARQ:One of the latest developments on the HARQ technology is to classify the HARQ operations in terms of retransmission timing.However, it is still being debated whether synchronous or asynchronous HARQ or a combination of both will be used.In synchronous HARQ the retransmission timing accurately de?nes the exact period in which HARQ retransmission processes will be ex-changed between the mobile station and the base station.The advantage of this mechanism is that less signaling overhead is required during retransmissions.In asynchronous HARQ,

the retransmissions can take place at any time.Because of the usage of explicit signaling,the overhead is increased,but this allows more?exibility on the decisions of the scheduler.?Adaptive/Non-adaptive HARQ:Adaptive HARQ provides more?exibility in scheduling,because transmission attributes (such as modulation order,code rate etc)may be changed

during retransmissions.However,adaptive HARQ also re-quires more signaling overhead in order to inform the receiver of any changes on the transmission attributes every time a retransmission occurs.Non-adaptive HARQ does not allow any changes on the transmission attributes,and,therefore, requires less signaling overhead.However,the gain is smaller compared to adaptive HARQ.

3)Handover:Next Generation Mobile WiMAX networks

will include advanced handover functionalities(low transition delay for fast moving mobile stations in combination with sleep mode operations).Handover occurs when the received signal quality at the mobile station is not adequate to provide the Quality of Service required by an application,in which case it is handed over to another base station.The mechanism is divided into two phases,Network Topology Acquisition, during which the mobile station obtains information about the neighboring base stations through several advertisement messages and scanning processes,and the Handover Process. An excellent description of the functionalities required for handover in Mobile WiMAX systems is given in[34]. Apart from the fast handover requirements[15],the IEEE 802.16m standard includes handover support between femto base stations and base stations,and legacy Mobile WiMAX systems and Inter-RAT handover procedures.Femto cells are designed for residential or business environments and may en-hance the coverage of indoor locations.Although the speci?c functionalities of femto base station handover support are not yet de?ned,it is required that the mobile station be allowed to cache the information when making a handover to the speci?c femto cell.The handover support for legacy systems includes a new method for Network Topology Acquisition.The YBS3 advertises the system information to its neighbor YBSs and to the LZones of its neighbor ABSs.4The ABS does the same for its neighbors’YBSs in both its LZone and its802.16m zone.Finally,the ABS advertises the system information to its neighbor ABSs in the802.16m zone only.In the Network Topology Advertisements,the ABS may indicate its support for802.16m mobile stations.LZones and802.16m zones are used in a similar way during the handover from802.16m to 802.16e(and from802.16e to802.16m).

One of the goals of IMT-Advanced,as described in the introduction,is seamless handover between Radio Access 3Yardstick BS:Base station compliant with the WirelesMAN-OFDMA reference system.Similarly,in IEEE802.16m,new abbreviations have been introduced for YMS(Yardstick MS):Mobile station compliant with the WirelessMAN-OFDMA reference system,AMS(Advanced MS):Mobile station capable of acting as a YMS and additionally implementing the protocol de?ned in IEEE802.16m,and ABS(Advanced BS),the base station equivalent of AMS.

4Details on the LZones are not repeated here because they have been discussed in Section III-D.

SGORA and VERGADOS:A SURVEY ON NEXT GENERATION MOBILE WIMAX NETWORKS:OBJECTIVES,FEATURES AND TECHNICAL CHALLENGES15

Technologies.Therefore,Network Topology Acquisition for Inter-RAT handover includes the advertisement of information about other RATs to assist the mobile station with network discovery and selection.IEEE802.16m systems provide a mechanism for the mobile station to obtain information from a base station about other access networks in its vicinity,either by making a query or by listening to information broadcasts. Moreover,other mechanisms are introduced for conducting inter-RAT measurements and reporting.Based on whether the mobile station supports a dual transmitter/dual receiver,it may connect to both an ABS and a base station operating on another RAT simultaneously during handover.

V.E VALUATION METHODOLOGY

The Evaluation Methodology of IEEE802.16m de?nes a uni?ed method of simulation models and associated param-eters that can be used when introducing new proposals for IEEE802.16m or when presenting new research results.As shown in Fig.6,the simulation components can introduce results both from the link-level perspective,when only one base station and one mobile station exist in the network topology scenario,and from the system-level perspective when multiple base stations and mobile stations communicate.Some aspects of the document that are related to the physical layer are discussed?rst,followed by a description of the handover evaluation.More details on other components of the evaluation methodology(such as antenna and traf?c patterns)can be found in the Evaluation Methodology Document(EMD)of the IEEE802.16m workgroup[17].

A.System-level evaluation methodology and link-to-system mapping using Effective SINR

Because WiMAX systems can employ various constellation sizes,subchannel permutation schemes,coding methods and MIMO modes,and may be based on different transmitter and receiver hardware and implementations,a set of representative and widely acceptable scenarios needs to be de?ned.This is expected to enable the developers present their systems using a common language.Moreover,the scienti?c and business communities will be able to assess independently the submit-ted proposals.Some of the most important sets of parameters de?ned in the Evaluation Methodology Document(EMD)for system simulation are the following.

1)System-level simulation assumptions for the downlink

and the uplink,including the constellation size,the du-plexing scheme,the subchannelization method,the pilot structure,the number of transmit and receive antennas, the interference cancelation method at the receiver,the channel coding scheme,the scheduling method and the frequency reuse pattern.

2)Test scenarios,including the carrier frequency,the site-

to-site distance,the power transmitted by the base sta-tion and the mobile stations,the path loss and shadowing model and the mobile speeds.

3)Base station and mobile station equipment model pa-

rameters,including the number of transmit and receive antennas and the number of sectors,the spacing among antennas,the transmit power and the noise?gure.

4)OFDMA parameters,including the FFT size,the sam-

pling frequency,the subcarrier spacing,the total band-width,the length of the Cyclic Pre?x and the frame length.

Moreover,the simulations should be performed over agreed channel models.The channel models need to be representative of the different radio environments and propagation scenarios in which802.16m systems will be deployed[17].In addition to the so-called“Baseline Test Scenario”that is mandatory and part of the system-level simulations speci?cation as described above,seven additional optional test scenarios are de?ned for802.16m:Urban Macrocell,Suburban Macrocell,Urban Microcell,Indoor Small Of?ce,Outdoor to Indoor,Indoor Hotspot and Open Rural Macrocell,each corresponding to different cell sizes,propagation conditions,and number and density of mobile stations.Each model is associated with speci?c path loss,shadowing,and Cluster-Delay-Line(CDL) models.

An additional goal of the EMD is to create a PHY abstrac-tion that will allow accurate prediction of the performance of the link layer in a computationally simple way.The abstraction needs to accurately re?ect the fact that the PHY layer becomes increasingly dynamic and adapts to the changing channel conditions.Therefore,evaluating the performance based on the expected topology and average Signal-to-Noise ratios may not be suf?cient.One methodology that is used in the EMD is Effective SINR mapping(ESM).ESM consists of calculating an effective SINR SINR eff based on the SINR of each subchannel where a given coded block is transmitted.Then, the calculation of the expected Block Error Rate(BLER) is based on a single value SINR eff.There are several approaches for the exact mapping of the subchannel SINRs to SINR eff,some of them taking into account the case of MIMO transmission.ESM can also be applied when HARQ (CC-or IR-)or repetition coding is used.The PHY link-to-system mapping procedure as depicted in the EMD and is given in Fig.7for convenience.

The BLER that is calculated based on SINR eff is then used to compute the Packet Error Rate(PER),based on the number of blocks that comprise a packet.

B.System Simulation of Handover

High Speed Mobility scenarios require low delay handover so as not to degrade the end-user experience when moving from one cell to another.For the comparison of different handover schemes,a speci?c evaluation methodology was developed in IEEE802.16m,where latency and data loss rate are taken into account as key metrics,since both have a direct impact on the QoS as perceived by the user.Thus, two handover evaluation methods are introduced.The?rst method is based on a single moving mobile station with all other users at?xed locations,whereas in the second method all users move randomly.

1)Single Moving MS:In order to reduce complexity and provide simple handover results,a single moving mobile station scenario can be used.Mobility speeds can be chosen among three different scenarios:Stationary-Pedestrian0-10 km/h(optimized),Vehicular10-200km/h(graceful degra-dation)and High Speed Vehicular120-350km/h(maintain

16IEEE COMMUNICATIONS SURVEYS&TUTORIALS,VOL.11,NO.4,FOURTH QUARTER2009

Fig.6.Simulation Components for Evaluation

Methodology.

Fig.7.PHY link-to-system mapping procedure.

connection).The simulation scenario may include either a two-cell topology were the mobile station is moving from Cell 1to Cell2following the trajectories of Fig.8,or a single moving mobile station in a10-cell scenario.Each cell has three sectors and frequency reuse is modeled by planning frequency allocation in different sectors.Path loss and fading are updated (based on location and velocity)and the simulation statistics are measured on the moving mobile station.

The trajectories in the single moving mobile station scenario are the following:

?Trajectory1:Begins from the center of cell1and ends at the center of cell2.The purpose is to evaluate a case where the mobile station is moving from a high signal strength position with respect to cell1(low with respect to cell2)to a low signal strength position(high with respect to cell2).

?Trajectory2:The mobile station is moving along the boundary of two adjacent sectors and until it reaches the midpoint of the cells boundary.

?Trajectory3:The mobile station is now moving from the center of cell2,along the boundary of two adjacent sectors and towards the center of cell1.

2)Multiple Moving MS:In the Multiple Moving MS scenario the mobile stations are uniformly distributed over a19-cell topology.Each initial angle trajectory is again chosen randomly,at the beginning of the call,where angle0 corresponds to the North of the simulation environment.The mobility speed can take one of the values described in the single moving mobile station,and the mobile station users remain at that speed and direction for the duration of the simulation drop.

In order to model the interference from other cells,the total network topology requires7clusters,each cluster consisting of19cells.Depending on the con?guration,the impact of the outer six cells may be neglected and only the central cluster is modeled.Thus,the simulation parameters and distribution of the nodes are set for the central cluster(cluster-0).The six outer clusters are exact copies of cluster-0,so that the corresponding cells have the same antenna con?gurations, traf?c,fading,etc.except for the location.

Since each mobile station is associated with a serving cell, a two-step algorithm is employed to identify the sector/cell to which the mobile station belongs.First,the19shortest dis-tance cells for each mobile station from all seven logical cell clusters are determined.Then the mobile station is associated

SGORA and VERGADOS:A SURVEY ON NEXT GENERATION MOBILE WIMAX NETWORKS:OBJECTIVES,FEATURES AND TECHNICAL CHALLENGES 17

Average Radio Layer Latency =

N HO success

i =1

(T 2,i ?T 1,i )

N HO success

,

(1)Average Network Entry and Connection Setup Time = N HO success

i =1

(T 3,i ?T 2,i )

N HO success

,and

(2)

Fig.8.EVM Handover Trajectories.

with the cell/sector that has the best link quality based on path loss and shadowing.

3)Handover Performance Metrics:For the evaluation of the performance of different handover schemes the following statistics/measurements shall be kept,for the entire simulation time,and are calculated based on the number of success-ful handovers N HO success ,the number of failed handovers N HO fail ,and the number of handover attempts N attempt =N HO success +N HO fail [17].See Equations (1)and (2)above.

Handover Interruption Time =T 3,i ?T 2,i ,

(3)

where T 1,i is the time instant that a mobile station transmits to the serving base station its commitment to handover (the time the mobile station disconnects from the serving base station for Hard Handover);T 2,i is the time instant that the mobile station successfully synchronizes with the target base station;and T 3,i is the time instant of the start of transmission of the ?rst data packet between the mobile station and the target base station.The Handover Interruption Time represents the time interval during which a mobile station cannot receive service from any base station during handover.Two additional performance metrics are

Data Loss = N HO success

i =1

(D T X,i ?D RX,i )

N HO success

and (4)Handover Failure Rate =

N HO fail

N attempt

,

(5)

where D T X,i and D RX,i correspond to the number of bits transmitted and received during the handover process i .It is useful to mention that a handover failure will happen if the handover is executed while the reception conditions are inadequate on either the downlink or the uplink such that the mobile station would have to move to a Network Entry State.

VI.C ONCLUSION

The recent proliferation of quadruple-play services (High Quality V oice and Video,the Internet and mobility)has led not only to an increase in the demand for bandwidth for broadband access networks,but also to the requirement of ?exible Next Generation Wireless Systems.To address these needs,IEEE

802.16m appears as a strong candidate for providing aggregate rates to high-speed mobile users at the range of Gbps,while guaranteeing ?exibility and backwards compatibility with ex-isting systems.Although these issues have been addressed by several scienti ?c groups,this is typically done either from the research or the engineering perspective.In this survey an attempt was made to combine these approaches into a uni ?ed view.

The main focus of this survey was to outline the evolution of several parameters and the way that they can be uni ?ed in order to build the structure of IEEE 802.16m systems.From the PHY layer perspective,the focus was on ?exibility enhancements,aiming at supporting heterogeneous users,on extensions of MIMO transmission and resource allocation techniques,and on ways to guarantee interoperability with other access technologies.A collection of MAC layer func-tionalities was also analyzed whose goal is to combine energy conservation and security algorithms,as well as handover and relaying mechanisms with Quality of Service requirements.Because the combination and interdependence of multiple pa-rameters increases the complexity when introducing research results or when submitting new proposals,the fundamentals of a uni ?ed way of simulation modeling and corresponding pa-rameters,namely the IEEE 802.16m Evaluation Methodology,were also discussed.

Clearly,several unresolved issues remain to this date and,at this stage,it is not possible to predict accurately when the 802.16m standard will be rati ?ed and to what extent the new approaches will be incorporated in its ?nal form.Therefore,it is hoped that this survey will serve as a reference on the most relevant technical issues and that it will assist the interested reader in identifying the most challenging and interesting parts of the algorithmic design of Next Generation Wireless Systems.

R EFERENCES

[1]http://www.itu.int/md/R07-IMT.ADV-C [2]http://www.itu.int/home/imt.html

[3]https://www.wendangku.net/doc/591875974.html,/article/lte-advanced [4]

https://www.wendangku.net/doc/591875974.html,/tgm/

18IEEE COMMUNICATIONS SURVEYS&TUTORIALS,VOL.11,NO.4,FOURTH QUARTER2009

[5]Data Over Cable Service Interface Speci?cation(DOCSIS3.0),Third-

generation transmission systems for interactive cable television services -IP cable modems,ITU-T Recommendation J.222

[6] B.Li,Y.Qin,C.P.Low,and C.L.Gwee,“A Survey on Mobile WiMAX,”

in IEEE Commun.Mag.,vol.45,no.12,pp.70–75,Dec.2007.

[7]K.Etemad,“Overview of Mobile WiMAX Technology and Evolution,”

in IEEE Commun.Mag.,vol.46,no.10,pp.31–40,Oct.2008

[8]P.Taaghol,A.K.Salkintzis and J.Iyer,“Seamless Integration of Mobile

WiMAX in3GPP Networks,”in IEEE Commun.Mag.,vol.46,no.10, pp.74–85,Oct.2008

[9]M.Riegel,“Ethernet Services over Mobile WiMAX,”in IEEE Commun.

Mag.,vol.46,no.10,pp.86–93,Oct.2008

[10] F.Wang,A.Ghosh,C.Sankaran,P.J.Flemming,F.Hsieh,and S.J.

Benes,“Mobile WiMAX Systems:Performance and Evolution,”in IEEE Commun.Mag.,vol.46,no.10,pp.41–49,Oct.2008

[11]https://www.wendangku.net/doc/591875974.html,/

[12] A.Ghosh,D.R.Wolter,J.G.Andrews,and R.Chen,“Broadband

Wireless Access with WiMAX/802.16:Current performance benchmarks and future potential,”in IEEE Commun.Mag.,vol.43,no.2,pp.129–136,Feb.2005.

[13]IEEE Std802.16e-2005,“IEEE Standard for local and metropolitan

area networks,part16:air interface for?xed broadband wireless access systems,amendment2:physical and medium access control layers for combined?xed and mobile operation in licensed bands,”Feb.2006. [14] D.Tse,and P.Viswanath,“Fundamentals for Wireless Communication,”

Cambridge University Press,2005.

[15]M.Cudak,ed.,“IEEE802.16m System Requirements Document,draft

IEEE802.16m-07/002r9,”Sep.2009.

[16]S.Hamiti,ed.,“IEEE802.16m System Description Document,draft

IEEE802.16m-09/0034r2,”Sep.2009.

[17]R.Srinivasan,ed.,“IEEE802.16m Evaluation Methodology Document

(EMD),draft IEEE802.16m-08/004r5,”Jan.2009.

[18] D.J.Love,R.W.Heath,https://www.wendangku.net/doc/591875974.html,u, D.Gesbert, B. D.Rao,

and M.Andrews,“An Overview of Limited Feedback in Wireless Communication Systems,”in IEEE J.Select.Areas Commun.,vol.26, no.8,pp.1341–1365,Oct.2008.

[19]H.Weingarten,Y.Steinberg,and S.Shamai,“The Capacity Region

of the Gaussian Multiple-Input Multiple-Output Broadcast Channel,”in IEEE https://www.wendangku.net/doc/591875974.html,rm.Theory,vol.52,no.9,pp.3936–3964,Sep.2006.

[20]G.Dimic,and N.D.Sidiropoulos,“On Downlink Beamforming with

Greedy User Selection:Performance Analysis and a Simple New Algo-rithm,”in IEEE Trans.Signal Processing,pp.3857–3868,vol.53,no.

10,Oct.2005.

[21]T.Yoo,and A.Goldsmith,“On the Optimality of Multiantenna Broad-

cast Scheduling Using Zero-Forcing Beamforming,”in IEEE J.Select.

Areas Commun.,pp.528–541,vol.24,no.3,Mar.2006.

[22]Samsung Corp.,“Downlink MIMO for EUTRA,R1-060335,”3GPP

TSG RAN WG1Meeting#44,Denver,USA,Feb2006.

[23]S.Saur,H.Halbauer, A.Rueegg,and F.Schaich,“Grid-of-Beams

(GoB)Based Downlink Multi-User MIMO,IEEE C802.16m-08/487,”

May2008.

[24]W. C.Wong,and S.Talwar,“Interference mitigation using down-

link transmit beamforming with nulling techniques,IEEE C802.16m-08/653r2,”Jul.2008.

[25]H.Kwon,and B.G.Lee,“Distributed Resource Allocation through

Noncooperative Game Approach in Multi-Cell OFDMA Systems,”in Proc.IEEE https://www.wendangku.net/doc/591875974.html,mun.(ICC),Istanbul,June2006.

[26]IEEE Std802.16j-2006,“IEEE Standard for local and metropolitan

area networks,part16:air interface for?xed broadband wireless access systems,Air Interface for Fixed and Mobile Broadband Wireless Access Systems-Multihop Relay Speci?cation,”March2006.

[27]S.W.Peters and R.W.Health Jr.“The future of WiMAX:Multihop

Relaying with IEEE802.16j,”in IEEE Commun.Mag.,vol.47,no.1, pp.104–111,Jan.2009.

[28]S.Ahson and M.Ilyas,“The WiMAX Handbook.V ol:Standards and

Security,”CRC Press,Taylor&Francis Group,2007.

[29]J.-F.Cheng,“Coding Performance of Hybrid ARQ schemes,”,in IEEE

https://www.wendangku.net/doc/591875974.html,mun.,vol.54,no.6,pp.1017–1029,June2006.

[30] D.Toumpakaris,J.Lee,A.Matache,and H.-L.Lou,“Performance of

MIMO HARQ Under Receiver Complexity Constraints,”in Proc.IEEE Globecom2008,New Orleans,USA,Dec.2008.

[31]J.Lee, D.Toumpakaris,H-L.Lou,E.W.Jang,and J.M.Ciof?,

“Transceiver Design for MIMO Wireless Systems Incorporating Hybrid ARQ,”in IEEE Commun.Mag.,vol.47,no.1,pp.32–40,Jan.2009.[32]Z.Ding,and M.Rice,“Hybrid-ARQ code combining for MIMO using

multidimensional space-time Trellis codes,”in in Proc.IEEE ISIT’07, Glasgow,Scotland,UK,Jun.2007.

[33]G.S.Paschos,I.Papapanagiotou and T.M.Bohnert,“Power Saving

Mechanisms in IEEE802.16e Wireless Networks,”Chapter in“WiMAX Networks Planning and Optimization,”Auerbach Publications,CRC Press,2009.

[34]H-H.Choi and D-H.Cho,“Mobility Support for IEEE802.16e System,”

Chapter in“WiMAX Standards and Security,”pp.103–128,CRC Press, 2008.

Ioannis Papapanagiotou[S05]received his Diploma in Electrical& Computer Engineering from the University of Patras,Greece in2006,and his MS in Electrical Engineering from North Carolina State University,in 2009,where he is currently a PhD student.His main research interests lie in the area of Network Design&Dimensioning,network pricing and Wireless NGNs.Ioannis has received the Best Paper Award,the NSF Student Travel Grant Award in IEEE GLOBECOM2007,and is supported by the Academy of Athens.

Dimitris Toumpakaris[S’98,M’04]received his Diploma in Electrical and Computer Engineering from the National Technical University of Athens, Greece in1997,and his MS and PhD degrees in Electrical Engineering from Stanford University in1999and2003,respectively.He was a Senior Design Engineer in Marvell Semiconductor Inc.,Santa Clara,California from2003to2006.He has also worked as an intern for Bell-Labs,CERN and France Telecom,and as a consultant for Ikanos Communications and Marvell Semiconductor Inc.He is currently an Assistant Professor in the Wireless Telecommunications Laboratory,Department of Electrical&Com-puter Engineering,University of Patras,Greece.His current research interests include information theory with emphasis on multi-user communications systems,digital communication,synchronization and estimation,and cross-layer optimization.

Jungwon Lee[S00,M05]received his BS degree in Electrical Engineering from Seoul National University in1999,and he received his MS and PhD degrees in Electrical Engineering from Stanford University in2001and 2005,respectively.From2000to2003,he worked as an intern for National Semiconductor,Telcordia Technologies,and AT&T Shannon Labs Research and as a consultant for Ikanos Communications.Since2003,he has worked for Marvell Semiconductor Inc.,Santa Clara,California,where he is now a Se-nior Manager/Principal Engineer leading algorithm development and system architecture design for the next generation wireless communication network. His research interests lie in wireless and wireline communication theory with emphasis on multi-input multi-output(MIMO)orthogonal frequency division multiplexing(OFDM)system design.

Michael Devetsikiotis[S1985,M1993,SM2004]received his Diploma in Electrical Engineering from the Aristotle University of Thessaloniki Greece, in1988,and the M.Sc.and Ph.D.degrees in Electrical Engineering from North Carolina State University,Raleigh,in1990and1993,respectively.He became a faculty in the Department of Systems and Computer Engineering at Carleton University in April1995,and then joined the Department of Electrical and Computer Engineering at NC State where he is now a full Professor.He is also an active member of the Operations Research faculty, and an associate member of the faculty of Computer Science at NC State. He recently?nished his stint as Chairman of the IEEE Communications Society Technical Committee on Communication Systems Integration and Modeling.He is an Area Editor of the ACM Transactions on Modeling and Computer Simulation and a member of the editorial board of the Journal of Internet Engineering,the IEEE Communication Surveys and Tutorials and the International Journal of Simulation and Process Modeling.Michael was recently selected to become an IEEE/Communications Society Distinguished Lecturer for the period2008-2009.

html标签以及属性大全

...普通卷动 ...滑动 ...预设卷动 ...来回卷动 ...向下卷动 ...向上卷动 向右卷动 向左卷动 ...卷动次数 ...设定宽度 ...设定高度 ...设定背景颜色 ...设定滚动速度 ...设定卷动时间 ...鼠标经过上面时停止滚动...鼠标离开时开始滚动 字体效果

...

标题字(最大)

...

标题字(最小) ...粗体字 ...粗体字(强调) （同上效果略同） ...斜体字 ...斜体字(强调) ...斜体字(表示定义) ...底线 ...底线(表示插入文字) ...横线 ...删除线 ...删除线(表示删除) ...键盘文字 ... 打字体 ...固定宽度字体(在文件中空白、换行、定位功能有效) ...</plaintext>固定宽度字体(不执行标记符号) <listing>...</listing> 固定宽度小字体 <font color=00ff00>...</font>字体颜色 <font size=1>...</font>最小字体 <font style =’font-size:100 px’>...</font>无限增大 区断标记 <hr>水平线 <hr size=’9’>水平线(设定大小) <hr width=’80%’>水平线(设定宽度) <hr color=’ff0000’>水平线(设定颜色) <br>(换行) <nobr>...</nobr>水域(不换行)</p><h2>HTML语言复习题</h2><p>1.下面设定网页15秒后自动跳转到哈尔滨师范大学网站首面的正确代码是（C ）。 A. <Meta Name=ReFresh content=15 HREF=https://www.wendangku.net/doc/591875974.html,> B. <Meta http-Equiv=15 URL= https://www.wendangku.net/doc/591875974.html,> C. <Meta http-Euiqv=ReFresh Content=15 URL=https://www.wendangku.net/doc/591875974.html,> D. <Meta http-Euiqv=ReFresh Content=15 SRC=https://www.wendangku.net/doc/591875974.html,> 2.在HTML页面中插入半角的大于号>，应使用的代码是（D）。 A. &plusmn; B. &cent C. &lt; D. &gt; 3.下面的文字修饰标记中，可以给文字加删除线的标记是（B）。 A. <Strong> B. <Strike> C. <TT> D. <Big> 4.下面表示文件的地址中，属于相对地址的是（. A）。 5.中国大陆常用的字符集是（A）。 A. GB2312 B. BIG5 C. ASCII D. ISO8859-1 6.HTML的颜色属性值中，RED的代码是（ D ） A．″#808080″B．″#0000FF″C．″#00FF00″D．″#FF0000″ 7.在HTML页面中输入半角的空格，应使用的代码是（A）。 A. &nbsp; B. #nbsp; C. &Space; D. #Space; 8.下面的文字修饰标记中，可以令文字用显示为下标的标记是（D）。 A. <SUP> B. <Strike> C. <Small> D. <SUB> A. contents/1_1.html B. FTP://192.168.0.222 C. https://www.wendangku.net/doc/591875974.html, D. /WebSites/News/Index.html 9.在HTML文档中，排列内容的最佳手段是使用（C）。 10.要从为文字“转至第3章第2节”建立超连接，以实现单击该文字后在新窗口中打开文档Chapt3.html（该文档与当前文档在同一目录下），并定位到书签“Sect_2”，正确代码是（B）。 A. <a Url=Chapt3.html#Sect_2 TarGet=_Blank>第3章第2节</a> B. <a Href= Chapt3.html#Sect_2 TarGet=_Blank>第3章第2节</a> C. <a Src= Chapt3.html#Sect_2 TarGet=_Blank>第3章第2节</a> D. <a Href= Sect_2#Chapt3.html#Sect_2 TarGet=_Blank>第3章第2节</a> 11.在HTML文档中，要定义一个宽400像素，高200像素的表格，正确的<table>标记是（D）。 A. <Table Border=400 High=200> B. <Table Length=400 High=200> C. <Table Size=400 Height=200> D. <Table Width=400 Height=200> 12.在使用表格标记<Table Border=3 Frame=Rhs>，则下面说法正确的是（B）。 A. 表格显示上下外边框 B. 表格只显示右边框 C. 表格只显示左边框 D. 表格显示左右边框 13.把窗口分割成上下两个框架，高度分别为40%和60%，正确的代码是（D）。 A. <Frameset Cols=40,60><Frame><Frame></Frameset> B. <Frameset Rows=40,60><Frame><Frame></Frameset> C. <Frameset Cols=40%,*><Frame><Frame></Frameset> D. <Frameset Rows=40%,*><Frame><Frame></Frameset> 14 网页的基本构成元素不包括（ D ）。 A 文本 B 图像 C 超连接 D 角本</p><h2>【IT专家】在2×2的方块中放置4个图像,以在HTML-CSS中占据页面的一半。</h2><p>本文由我司收集整编，推荐下载，如有疑问，请与我司联系在2×2的方块中放置4 个图像，以在HTML/CSS 中占据页面的一半。 在2×2的方块中放置4 个图像，以在HTML/CSS 中占据页面的一半。 [英]Having trouble putting 4 images in a 2 by 2 square to fit on half of the page in HTML/CSS I’ve tried everything. Need Help PLEASE! Wanting to get the wire frame images in a 2 by 2 on the right side of the page. Being able to be responsive at the sametime. 我试着一切。需要帮助请!想要在页面右边的2×2的帧中获取线框图像。能够及时 响应。 any help will be appreciated soo much! 任何帮助都将被感激的多! div Creating an app designed for mobile devices (smart phones and tablets). Able to use the smart phones camera or tablet to view the picture in real-time. Jager is centred around the old-style game of I Spy/Scavenger hunt played usually by kids. This focus would be part of the Mahuki Gamelab team. Creating games used for education in fun ways to help get children involved in the seasonal museum exhibitions. br br h1 Abstract /h1 br br To create a game for mobile devices, tablets and smart phones. An app that uses augmented reality technology to involve users in the environment around them. The game is a scavenger hunt / I SPY type of game played using your smart phone or tablet’s built-in camera to view the world through. The app will generate an object to make the user search for from a list of pre-programmed items and paths. The app will give users a hint or a clue to the general area or direction of the object. A timer and a score will be used</p><h2>HTML第二部分作业(含答案)</h2><p>HTML4-7章作业 1、CSS样式表不可能实现( )功能。 A将格式和结构分离 B．一个CSS文件控制多个网页 C.控制图片的精确位置 D．兼容所有的浏览器 2、可用来在一个网页中嵌入显示另一个网页内容的标记符是（） A.<Marquee> B. <Iframe> C.<embed> D.<object> 3.我们想要在框架中加入一个叫做list.htm的文件，应该在HTML中如何描述它？ A、frame page="list.htm" B、frame target="list.htm" C、frame src="list.htm" D、frame framepage="list.htm" 4.我们想要在页面中加入一个层，可以使用哪些HTML标记来描述它？(选择2项) A、<floor> B、<div> C、<span> D、<level> 5 . 下列哪种CSS样式定义的方式拥有最高的优先级？ A、嵌入 B、行内 C、链接 D、导入 6 . 以下的HTML中，哪个是正确引用外部样式表的方法？ A、 <style src="mystyle.css"> B、 <link rel="stylesheet" type="text/css" href="mystyle.css"> C、 <stylesheet>mystyle.css</stylesheet> 7. 在HTML文档中，引用外部样式表的正确位置是？ A) 文档的末尾 B) <head>部分 C) 文档的顶部 D) <body>部分 8. 哪个HTML标签可用来定义内部样式表？ A) <style> B) <script> C) <css> 9. 哪个HTML属性可用来定义内联样式？ A) font B) class C) styles</p><h2>JavaScript_脚本代码的位置</h2><p>JavaScript脚本代码的位置可以有以下三种情况： 一、在网页文件的<script></script>标签对中直接编写JavaScript脚本代码； 二、将JavaScript脚本程序代码放置在一个单独的文件中，在网页文件中引用这个脚本程序。 三、将脚本程序代码作为某个元素的事件属性值或超链接的href属性。 第一种情况： 在网页文件的<script></script>标签对中直接编写JavaScript脚本代码。这是用得最多的情况，<script></script>标签对的位置并不是固定的，可以出现在<head></head>或<body></body>的任何位置。 对于JS在什么时候应该包含在head中，什么时候应当包含在body中，人们有着不同的看法。但下面的规则是适用的： 1. 当JavaScript要在页面加载过程中动态建立一些Web页面的内容时，应将JavaScript放在body中。 2. 定义为函数并用于页面事件的JavaScript应当放在head标记中，因为它会在body之前加载。 放置脚本的一个很好的经验规则是：仅当页面载入期间脚本会建立一些Web页面内容时，才将脚本嵌入在body中；否则，将其放在head元素中。采用这种方法，页面就不会被脚本搞得一团糟，在每个页面中，总可以在同一个位置找到脚本。有种方法可以避免将JavaScript插入到body中，即使用DOM生成一个新内容，再将其附加给一个页面元素。 在一个HTML文档中可以有多段JavaScript代码。每段JavaScript代码可以相互访问，这与将所有代码放入同一对<script></script>之间的效果是一致</p><h2>html标签属性大全总结</h2><p>html标签属性大全 html标签属性大全是朋友们整理常用的html标签，和大家更好的交流沟通。学习html标签属性大全html标签< <marquee>...</marquee>普通卷动 <marquee behavior=slide>...</marquee>滑动 <marquee behavior=scroll>...</marquee>预设卷动 <marquee behavior=alternate>...</marquee>来回卷动 <marquee direction=down>...</marquee>向下卷动 <marquee direction=up>...</marquee>向上卷动 <marquee direction=right></marquee>向右卷动 <marquee direction=’left’></marquee>向左卷动 <marquee loop=2>...</marquee>卷动次数 <marquee width=180>...</marquee>设定宽度 <marquee height=30>...</marquee>设定高度 <marquee bgcolor=FF0000>...</marquee>设定背景颜色 <marquee scrollamount=30>...</marquee>设定滚动速度 <marquee scrolldelay=300>...</marquee>设定卷动时间 <marquee onmouseover="this.stop()">...</marquee>鼠标经过上面时停止滚动 <marquee onmouseover="this.start()">...</marquee>鼠标离开时开始滚动 <!>字体效果 <h1>...</h1>标题字(最大) <h6>...</h6>标题字(最小) <b>...</b>粗体字 <strong>...</strong>粗体字(强调) （同上效果略同） <i>...</i>斜体字 <em>...</em>斜体字(强调) <dfn>...</dfn>斜体字(表示定义) <u>...</u>底线 <ins>...</ins>底线(表示插入文字) <strike>...</strike>横线 <s>...</s>删除线 <del>...</del>删除线(表示删除) <kbd>...</kbd>键盘文字 <tt>...</tt> 打字体 <xmp>...</xmp>固定宽度字体(在文件中空白、换行、定位功能有效) <plaintext>...</plaintext>固定宽度字体(不执行标记符号) <listing>...</listing> 固定宽度小字体 <font color=00ff00>...</font>字体颜色 <font size=1>...</font>最小字体 <font style =’font-size:100 px’>...</font>无限增大 区断标记 <hr>水平线</p><h2>HTML文件的基本结构</h2><p>1.1 HTML文件的基本结构 HTML的英文全称是Hyper Text Markup Language，它是网页超文本标记语言的缩写，是Internet 上用于编写网页的主要语言。HTML中每个用来作为标记的符号都可以看作是一条命令，它告诉浏览器应该如何显示文件的内容。 1.1.1 HTML文件结构 一个完整的HTML文件由标题、段落、表格和文本等各种嵌入的对象组成，这些对象统称为元素，HTML使用标记来分隔并描述这些元素。实际上整个HTML文件就是由元素与标记组成的。 下面是一个HTML文件的基本结构。 <html>文件开始标记 <head>文件头开始的标记 ……文件头的内容 </head>文件头结束的标记 <body>文件主体开始的标记 ……文件主体的内容 </body>文件主体结束的标记 </html>文件结束标记 从上面的代码可以看出，HTML代码分为3部分，其中各部分含义如下。 <html>…</html>：告诉浏览器HTML文件开始和结束的位置，其中包括<head>和<body>标记。HTML文档中所有的内容都应该在这两个标记之间，一个HTML文档总是以<html>开始，以</html>结束。 <head>…</head>：HTML文件的头部标记，在其中可以放置页面的标题以及文件信息等内容，通常将这两个标签之间的内容统称为HTML的头部。 <body>…</body>：用来指明文档的主体区域，网页所要显示的内容都放在这个标记内，其结束标记</body>指明主体区域的结束。 1.1.2 使用记事本手工编写HTML页面 编写HTML文件有两种方法，一种是利用记事本编写，另一种是在可视化网页制作软件中编写，如Dreamweaver，下面分别进行讲述。 HTML是一个以文字为基础的语言，并不需要什么特殊的开发环境，可以直接在Windows自带的记事本中编写。HTML文档以.html为扩展名，将HTML源代码输入记事本并保存，可以在浏览器中打开文档以查看其效果。使用记事本手工编写HTML页面的具体操作步骤如下。 （1）在Windows系统下，执行“开始”→“所有程序”→“附件”→“记事本”命令，新建一个记事本，在记事本中输入代码，如图1-1所示。 （2）编写完HTML文件后，执行“文件”→“保存”命令，弹出“另存为”对话框，在对话框</p><h2>HTML中CSS样式标签大全及用法</h2><p>CSS 网页样式大全如下： 字体属性：(font) 大小font-size: x-large;(特大) xx-small;(极小) 一般中文用不到，只要用数值就可以，单位：PX、PD 样式font-style: oblique;(偏斜体) italic;(斜体) normal;(正常) 行高line-height: normal;(正常) 单位：PX、PD、EM 粗细font-weight: bold;(粗体) lighter;(细体) normal;(正常) 变体font-variant: small-caps;(小型大写字母) normal;(正常) 大小写text-transform: capitalize;(首字母大写) uppercase;(大写) lowercase;(小写) none;(无) 修饰text-decoration: underline;(下划线) overline;(上划线) line-through;(删除线) blink;(闪烁) 常用字体：(font-family) "Courier New", Courier, monospace, "Times New Roman", Times, serif, Arial, Helvetica, sans-serif, Verdana 背景属性：(background) 色彩background-color: #FFFFFF; 图片background-image: url(); 重复background-repeat: no-repeat; 滚动background-attachment: fixed;(固定) scroll;(滚动) 位置background-position: left(水平) top(垂直); 简写方法background:#000 url(..) repeat fixed left top; 区块属性：(Block) 字间距letter-spacing: normal; 数值 对齐text-align: justify;(两端对齐) left;(左对齐) right;(右对齐) center;(居中) 缩进text-indent: 数值px; 垂直对齐vertical-align: baseline;(基线) sub;(下标) super;(下标) top; text-top; middle; bottom; text-bottom; 词间距word-spacing: normal; 数值 空格white-space: pre;(保留) nowrap;(不换行) 显示display:block;(块) inline;(内嵌) list-item;(列表项) run-in;(追加部分) compact;(紧凑) marker;(标记) table; inline-table; table-raw-group; table-header-group; table-footer-group; table-raw; table-column-group; table-column; table-cell; table-caption;(表格标题) 方框属性：(Box) width:; height:; float:; clear:both; margin:; padding:; 顺序：上右下左 边框属性：(Border) border-style: dotted;(点线) dashed;(虚线) solid; double;(双线) groove;(槽线) ridge;(脊状) inset;(凹陷) outset; border-width:; 边框宽度 border-color:#; 简写方法border：width style color; 列表属性：(List-style)</p><h2>HTML标记单词表</h2><p>HTML标记含义 1.<html>…</html>:html文档标记 2.<head>…</head>:文档头标记 3.<title>…</title>:文档标题标记 4.<body bgcolor=? Background=? >…</body>:文档正文标记 Bgcolor :背景颜色 Background :背景图片 5.<a href=? T arget=?>热点</a> :超链接标记 Href:指定链接目标 T arget: 指定要在其中打开文档的框架的名称 _Self: 指定在当前页面或当前框架中打开 _Blank: 指定在新窗口中打开 _Parent: 定在当前文档的父框架组中打开 _T op: 指定链接在当前页面打开，破坏当前框架6.<a name=#?>主题名称</a> :锚标记 Name:锚点名称 7.<p align=?>… :分段标记 Align:对齐方式 Center:居中对齐 Left:左对齐 Right:右对齐 8.<br> :换行标记 9.<h1>…</h1>:1号标题标记 10.<blockquote>…</blockquote>:缩进式段落标记 11.<pre>…</pre>:原样显示标记 12.<ul type=?>…</ul>:无序列表 <li type=?>…</li>:列表项标记 T ype:列表项符号类型 Disc:实心圆 Circle:空心圆 Square:方形 13.<ol type=? start=?>…</ol>:有序列表标记 Start:第一个列表项的起始序号 <li type=?>…</li>:列表项标记 T ype:列表项序列类型 a :小写字母 A:大写字母 I:大写罗马数字 i:小写罗马数字 默认为阿拉伯数字 14.<dl>…</dl>:定义列表标记 <dt>…</dt> :定义术语标记 <dd>…</dd>:定义解释标记 15.<b>…</b>:加粗标记</p><h2>HTML基本结构标签</h2><p>基本结构标签: <HTML>,表示该文件为HTML文件</HTML>,<HTML>的结束标志 <HEAD>,包含文件的标题,使用的脚本,样式定义等</HEAD>,<HEAD>的结束标志 <TITLE>---</TITLE>,包含文件的标题,标题出现在浏览器标题栏中 <BODY>,放置浏览器中显示信息的所有标志和属性,其中内容在浏览器中显示. </BODY>,<BODY>的结束标志 其它主要标签 以下所有标志用在<BODY></BODY>中: <A,HREF="…"></A>,链接标志,"…"为链接的文件地址<IMG,SRC="…">,显示图片标志,"…"为图片的地址 <BR>,换行标志<P>,分段标志<B></B>,采用黑体字<I></I>,采用斜体字<HR>,水平画线<FONT></FONT>,字体样式标志 <TABLE></TABLE>,定义表格,HTML中重要的标志 <TR></TR>,定义表格的行,用在<TABLE></TABLE>中<TD></TD>,定义表格的单元格,用在<TR></TR>中 属性: 属性是用来修饰标志的,属性放在开始标志内.例:属性bgcolor="BLACK"表示背景色为黑色. 引用属性的例子: <BODY,bgcolor="BLACK"></BODY>表示页面背景色为黑色; <TABLE,bgcolor="BLACK"></TABLE>表示表格背景色为黑色. 常用属性: 对齐属性，范围属性:，色彩属性: ALIGN=LEFT,左对齐(缺省值), ALIGN=CENTER,居中，ALIGN=RIGHT,右对齐<center>表示绝对居中. WIDTH=象素值或百分比,对象宽度. HEIGHT=象素值或百分比,对象高度. COLOR=#RRGGBB,前景色,参考色彩对照表. BGCOLOR=#RRGGBB,背景色. <table></table>表格标识的开始和结束. 属性: cellpadding=数值单位是像素,定义表元内距cellspacing=数值单位是像素,定义表元间距border=数值单位是像素,定义表格边框宽度width=数值单位是像素或窗口百分比,定义表格宽度background=图片链接地址,定义表格背景图 <tr></tr>表格中一个表格行的开始和结束; <td></td>表格中行内一个单元格的开始和结束 属性: Colspan="",单元格跨越多列; Rowspan="",单元格跨越多行; Width="";定义表格宽度Height="";定义表格高度Align="";对齐方式Valign="" ; Border="",边框宽度; Bgcolor="",背景色; Bordercolor="",边框颜色; Bordercolorlight="",边框明亮面的颜色; Bordercolordark="",边框暗淡面的颜色; Cellpadding="",内容与边框的距离(默认为2); Cellspacing="",单元格间的距离(默认为2); <br>强制换行 <font></font>文本标识的开始和结束 属性: face=字体color=颜色 <b></b>加粗文字标识的开始和结束 属性: style=font-size:40pt;,用样式表方式控制字体大小,这里是40点 <div></div>,分区标识的开始和结束 属性: align=|center|left|right|水平对齐方式 <marquee></marquee>动态标识的开始和结束,如标识内放置贴图格式则可实现图片滚动 属性: scrollamount=1~60,滚动速度direction=|left|right|up|down|,滚动方向scrolldelay=滚动延时,单位:毫秒 <P>段落标识, 空格符, <img>贴图标识 属性: src=../../图片链接地址,贴图标识必备属性style=filter:Alpha(opacity=100,style=2); filter:样式表滤镜; Alpha:透明滤镜, opacity:不透明度100(0~100); style:样式2(0~3), rules="none"不显示内框" <embed,src="…">多媒体文件标识 属性: SRC="../../FILENAME", 设定音乐文件的路径,文件类型除了可以播放.rm;.mp3;.wav等音频,还可播放.swf和.mov等视频. AUTOSTART=TRUE/FALSE,是否要音乐文件传送完就自动播放,TRUE是要,FALSE是不要,默认为FALSE LOOP=,设定播放重复次数,LOOP=6表示重复6次,true或-1为无限循环,false为播放一次即停止.</p><h2>HTML常用标签使用位置及重要属性</h2><p>标签总结 标签名称 标签作用标签属性使用位置html 超文本标记语言-- 文本最开始和最后head 头-- 紧接html之后 body 体Bgcolor、 background、font、紧接head之后并且和head 并列 title 网页标题在head之内 h1~h6 文本小标题在body之中从一到六表示 六级标题 link 连接外部样式表Rel="stylesheet" ty pe="text/css" href= "theme.css" 在head之内 style 连接行内样式Type="text/css" 在head之内和link并列作 为样式的引入 form 把提交的数据包起来action="" method= “” 紧接body，但在body之内div 用于布局紧接body，但在body之内pre 转换段落（与输入一致）在body内</p><p>table 建立表格Border(边框)="1" b 以下均在body内 gcolor、background th 建立表头Width="" height=" " tr 建立行Width="" height=" " td 建立列Width="" height=" " rowspan="" colsp an="" a 超链接Href="地址/#锚名"t arget="_blank/_self " title="" Name="锚名" embed 插入flash Src="" width="" he ight="" type="appl ication/x-shockwav e-flash" hr 分隔线 br 换行 span 行级元素 input 插入各种输入框Type="text" Type="Password"</p><h2>HTML标签单词汇总0717</h2><p>HTML标签含义 1.<html>…</html>:html文档标记 2.<head>…</head>:文档头标记 3.<title>…</title>:文档标题标记 4.<body bgcolor=? Background=? >…</body>:文档正文标记 Bgcolor :背景颜色 Background :背景图片 5.<a href=? Target=?>热点</a> :超链接标记 Href:指定链接目标 Target: 指定要在其中打开文档的框架的名称 _Self: 指定在当前页面或当前框架中打开 _Blank: 指定在新窗口中打开 _Parent: 定在当前文档的父框架组中打开 _Top: 指定链接在当前页面打开，破坏当前框架6.<a name=#?>主题名称</a> :锚标记 Name:锚点名称 7.<p align=?>… :分段标记 Align:对齐方式 Center:居中对齐 Left:左对齐 Right:右对齐 8.<br> :换行标记 9.<h1>…</h1>:1号标题标记 10.<blockquote>…</blockquote>:缩进式段落标记 11.<pre>…</pre>:原样显示标记 12.<ul type=?>…</ul>:无序列表 <li type=?>…</li>:列表项标记 Type:列表项符号类型 Disc:实心圆 Circle:空心圆 Square:方形 13.<ol type=? start=?>…</ol>:有序列表标记 Start:第一个列表项的起始序号 <li type=?>…</li>:列表项标记 Type:列表项序列类型 a :小写字母 A:大写字母 I:大写罗马数字 i:小写罗马数字 默认为阿拉伯数字 14.<dl>…</dl>:定义列表标记 <dt>…</dt> :定义术语标记 <dd>…</dd>:定义解释标记 15.<b>…</b>:加粗标记</p><h2>html标签属性大全</h2><p><!> 跑马灯 <marquee>...</marquee>普通卷动 <marquee behavior=slide>...</marquee>滑动 <marquee behavior=scroll>...</marquee>预设卷动 <marquee behavior=alternate>...</marquee>来回卷动 <marquee direction=down>...</marquee>向下卷动 <marquee direction=up>...</marquee>向上卷动 <marquee direction=right></marquee>向右卷动 <marquee direction=’left’></marquee>向左卷动 <marquee loop=2>...</marquee>卷动次数 <marquee width=180>...</marquee>设定宽度 <marquee height=30>...</marquee>设定高度 <marquee bgcolor=FF0000>...</marquee>设定背景颜色 <marquee scrollamount=30>...</marquee>设定滚动速度 <marquee scrolldelay=300>...</marquee>设定卷动时间 <marquee onmouseover="this.stop()">...</marquee>鼠标经过上面时停止滚动<marquee onmouseover="this.start()">...</marquee>鼠标离开时开始滚动 <!>字体效果 <h1>...</h1>标题字(最大) <h6>...</h6>标题字(最小) <b>...</b>粗体字 <strong>...</strong>粗体字(强调)（同上效果略同） <i>...</i>斜体字 <em>...</em>斜体字(强调) <dfn>...</dfn>斜体字(表示定义) <u>...</u>底线 <ins>...</ins>底线(表示插入文字) <strike>...</strike>横线 <s>...</s>删除线 <del>...</del>删除线(表示删除) <kbd>...</kbd>键盘文字 <tt>...</tt> 打字体 <xmp>...</xmp>固定宽度字体(在文件中空白、换行、定位功能有效) <plaintext>...</plaintext>固定宽度字体(不执行标记符号) <listing>...</listing> 固定宽度小字体 <font color=00ff00>...</font>字体颜色 <font size=1>...</font>最小字体 <font style =’font-size:100 px’>...</font>无限增大 区断标记 <hr>水平线 <hr size=’9’>水平线(设定大小) <hr width=’80%’>水平线(设定宽度)</p><h2>html标签属性大全(完美版)</h2><p>html标签属性大全（完美版） html标签属性大全是朋友们整理常用的html标签，和大家更好的交流沟通。学习html标签属性大全 html标签< <marquee>...</marquee>普通卷动 <marquee behavior=slide>...</marquee>滑动 <marquee behavior=scroll>...</marquee>预设卷动 <marquee behavior=alternate>...</marquee>来回卷动 <marquee direction=down>...</marquee>向下卷动 <marquee direction=up>...</marquee>向上卷动 <marquee direction=right></marquee>向右卷动 <marquee direction=’left’></marquee>向左卷动 <marquee loop=2>...</marquee>卷动次数 <marquee width=180>...</marquee>设定宽度 <marquee height=30>...</marquee>设定高度 <marquee bgcolor=FF0000>...</marquee>设定背景颜色 <marquee scrollamount=30>...</marquee>设定滚动速度 <marquee scrolldelay=300>...</marquee>设定卷动时间 <marquee onmouseover="this.stop()">...</marquee>鼠标经过上面时停止滚动 <marquee onmouseover="this.start()">...</marquee>鼠标离开时开始滚动 <!>字体效果 <h1>...</h1>标题字(最大) <h6>...</h6>标题字(最小) <b>...</b>粗体字 <strong>...</strong>粗体字(强调) （同上效果略同） <i>...</i>斜体字 <em>...</em>斜体字(强调) <dfn>...</dfn>斜体字(表示定义) <u>...</u>底线 <ins>...</ins>底线(表示插入文字) <strike>...</strike>横线 <s>...</s>删除线 <del>...</del>删除线(表示删除) <kbd>...</kbd>键盘文字 <tt>...</tt> 打字体 <xmp>...</xmp>固定宽度字体(在文件中空白、换行、定位功能有效) <plaintext>...</plaintext>固定宽度字体(不执行标记符号) <listing>...</listing> 固定宽度小字体 <font color=00ff00>...</font>字体颜色 <font size=1>...</font>最小字体 <font style =’font-size:100 px’>...</font>无限增大 区断标记 <hr>水平线</p><h2>HTML常用标记</h2><p>《HTML常用标记》 一、HTML文档结构 ＜html＞//网页解析开始 ＜head＞//网页头部定义开始 ＜title＞标题＜title＞//定义标题显示于浏览器的标题栏内 ＜/head＞//网页头部定义结束 ＜body＞//网页主体定义开始 网页主体内容 ＜/body＞//网页主体定义结束 ＜/html＞//网页解析结束 以下是具体标记说明。 1.文件标题 ＜title＞..........＜/title＞ 2.文件更新--＜meta＞ 【1】10秒后自动更新一次 ＜meta http-equiv="refresh"content=10＞ 【2】10秒后自动连结到另一文件 ＜meta http-equiv="refresh"content="10；URL=欲连结文件之URL"＞ 二、文字标记 预设的基准路径--＜base>＜base href="放置文件的主机之URL"＞ 版面 1.标题文字＜h#＞..........＜/h#＞#=1~6；h1为最大字，h6为最小字 2.字体变化＜font＞..........＜/font＞ 【1】字体大小＜font size=#＞..........＜/font＞#=1~7；数字愈大字也愈大 【2】指定字型＜font face="字型名称"＞..........＜/font＞ 【3】文字颜色＜font color=#rrggbb＞..........＜/font＞取值为十六进制数 r：表红色（red）色码 g：表绿色（green）色码 b：表蓝色（blue）色码 3.显示小字体＜small＞..........＜/small＞ 4.显示大字体＜big＞..........＜/big＞ 5.粗体字＜b＞..........＜/b＞ 6.斜体字＜i＞..........＜/i＞ 7.打字机字体＜tt＞..........＜/tt＞ 8.底线＜u＞..........＜/u＞ 9.删除线＜strike＞..........＜/strike＞ 10.下标字＜sub＞..........＜/sub＞ 11.上标字＜sup>..........＜/sup＞ 12.文字闪烁效果＜blink＞..........＜/blink＞ 13.换行＜br＞ 14.分段＜p＞ 15.文字的对齐方向＜p align="#"＞#号可为left：表向左对齐（预设值）center：表向中对齐right：表向右对齐P.S.＜p align="#"＞之後的文字都会以所设的对齐方式显示，直到出现另一个＜p align="#"＞改变其对齐方向，或遇到＜hr＞或＜h#＞标签时会自动设回预设的向左对齐。 16.水平线（分隔线）＜hr＞注：多个属性可以同时写。 【1】分隔线的粗细＜hr size=点数＞ 【2】分隔线的宽度＜hr size=点数或百分比＞</p><h2>HTML常用标签以及特殊符号</h2><p>HTML常用标签以及特殊符号 常用属性： color 颜色(#ff0000 #ff8000 #ffff00 #00ff00 #0080ff #0000a0 #8000ff #000000 #c0c0c0) width 宽度%(百分比) / px(pixels) height 高度%(百分比) / px(pixels) aligh 水平对其位置left center right top bottom middle(垂直居中) texttop(向文字顶部对齐) baseline(向文字底部对齐) absmiddle(绝对居中) absbottom(绝对置下) valigh 垂直对齐位置baseline top middle bottom justify char border 边框宽bordercolor bordercolordark(右和下暗边框的颜色) bordercolorlight(左和上亮边框的颜色) 常用标签： &lt;HTML&gt; 表明这是一个HTML文件 &lt;head&gt; 标明网页头部分 &lt;title&gt; 网页题目总长不超过85个Character &lt;meta&gt; (单标记) 用法: &lt;meta http-quive="content-type" content="text/html;</p><p>charset=GB-2312"&gt; 说明网站的格式及编码方式 &lt;meta contents="关键字一, 关键字二, 关键字三.."&gt; 中间用逗号隔开总长不超过1000个Character(40个字) &lt;meta contents="整个网站的描述&#8230;&gt; 不超过200个Character (约15个字) &lt;meta content="ALL,NONE,INDEX,NOINDEX,FOLLOW,NOFOL LOW"&gt; 告诉搜索引擎的Spider哪些网页要摘哪些不摘，一般设为All(默认值) &lt;body&gt; 主体标签bgcolor background text link vlink alink &lt;br&gt; 强制断行标签 &lt;p&gt; 强制分段标签(比断行多隔一行) left center right &lt;hr&gt; 普通分隔线color width size(厚度) aligh noshade(实心分割线无阴影) &lt;center&gt; 置中标签 &lt;blockquote&gt; 每加一个这个标签向右缩排一个单位 &lt;pre&gt; 保存原始格式标签(显示出如代码中所显示的格式) &lt;h1&gt;&lt;h2&gt;&lt;h3&gt;&lt;h4&gt;&lt;h5&gt;&lt;h6&gt; 标题标签h1字体最大该行字自占一行</p></div> </div> <div> <div>相关文档</div> <div class="relatedtopic"> <div id="tabs-section" class="tabs"> <ul class="tab-head"> <li id="12173700"><a href="/topic/12173700/" target="_blank">初三生活作文800字</a></li> <li id="22041728"><a href="/topic/22041728/" target="_blank">html标签位置的放置</a></li> </ul> </div> </div> </div> </div> <div class="category"> <span class="navname">相关文档</span> <ul class="lista"> </ul> <span class="navname">最新文档</span> <ul class="lista"> <li><a href="/doc/0719509601.html" target="_blank">幼儿园小班科学《小动物过冬》PPT课件教案</a></li> <li><a href="/doc/0e19509602.html" target="_blank">2021年春新青岛版(五四制)科学四年级下册 20.《露和霜》教学课件</a></li> <li><a href="/doc/9319184372.html" target="_blank">自然教育课件</a></li> <li><a href="/doc/3019258759.html" target="_blank">小学语文优质课火烧云教材分析及课件</a></li> <li><a href="/doc/db19211938.html" target="_blank">(超详)高中语文知识点归纳汇总</a></li> <li><a href="/doc/af19240639.html" target="_blank">高中语文基础知识点总结(5篇)</a></li> <li><a href="/doc/9919184371.html" target="_blank">高中语文基础知识点总结(最新)</a></li> <li><a href="/doc/8b19195909.html" target="_blank">高中语文知识点整理总结</a></li> <li><a href="/doc/8019195910.html" target="_blank">高中语文知识点归纳</a></li> <li><a href="/doc/7f19336998.html" target="_blank">高中语文基础知识点总结大全</a></li> <li><a href="/doc/7a19336999.html" target="_blank">超详细的高中语文知识点归纳</a></li> <li><a href="/doc/6719035160.html" target="_blank">高考语文知识点总结高中</a></li> <li><a href="/doc/6a19035161.html" target="_blank">高中语文知识点总结归纳</a></li> <li><a href="/doc/4d19232289.html" target="_blank">高中语文知识点整理总结</a></li> <li><a href="/doc/3a19258758.html" target="_blank">高中语文知识点归纳</a></li> <li><a href="/doc/2519396978.html" target="_blank">高中语文知识点归纳(大全)</a></li> <li><a href="/doc/2419396979.html" target="_blank">高中语文知识点总结归纳(汇总8篇)</a></li> <li><a href="/doc/1f19338136.html" target="_blank">高中语文基础知识点整理</a></li> <li><a href="/doc/ef19066069.html" target="_blank">化工厂应急预案</a></li> <li><a href="/doc/bc19159069.html" target="_blank">化工消防应急预案(精选8篇)</a></li> </ul> </div> </div> <script> var sdocid = "5190a2b8960590c69ec376c7"; </script> <div class="footer"> <p><a href="/tousu.html" target="_blank">侵权投诉</a> &nbsp;&copy; 2013-2023 www.wendangku.net &nbsp;<a href="/sitemap.html">站点地图</a>&nbsp;|&nbsp;<a href="https://m.wendangku.net">手机版</a></p> <p><a href="https://beian.miit.gov.cn" target="_blank">闽ICP备11023808号-7</a>&nbsp;&nbsp;本站文档均来自互联网及网友上传分享，本站只负责收集和整理，有任何问题可通过上访投诉通道进行反馈</p> </div> <script type="text/javascript">foot();</script> </div> </body> </html>