WiMAX Basic Theory Level III

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    WiMAX Basic Theory

    WiMAX Basic Theory

    Level III

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    WiMAX Basic Theory

    Version Date Author Approved By Remarks

    V1.0 2010/12/23 Not open to the Third Party

    2010 ZTE Corporation. All rights reserved.ZTE CONFIDENTIAL: This document contains proprietary information of ZTE and is not to bedisclosed or used without the prior written permission of ZTE.Due to update and improvement of ZTE products and technologies, information in this documentis subjected to change without notice.

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    CONTENT

    1 Chapter1 Introduction to WiMAX.....................................................................71.1 Wireless Introduction...........................................................................................71.1.1 Wireless Network Topologies..............................................................................21.1.2 Wireless Technologies ........................................................................................21.1.3 Kinds of Wireless Networks ................................................................................21.1.4 Wireless Broadband Access (WBA)....................................................................31.2 Related Organization ..........................................................................................31.2.1 IEEE....................................................................................................................31.2.2 WiMAX Forum.....................................................................................................41.3 What is WiMAX ...................................................................................................41.3.1 What is WiMAX ...................................................................................................5

    1.3.2 What is 802.16d ..................................................................................................51.3.3 What is 802.16e ..................................................................................................51.3.4 WiMAX Speed and Range ..................................................................................61.3.5 Why WiMAX........................................................................................................61.3.6 WiMAX Goals......................................................................................................71.4 Salient Features of WiMAX.................................................................................71.4.1 OFDM-based physical layer................................................................................71.4.2 Very High Peak Date Rate ..................................................................................81.4.3 Scalable bandwidth and rate support..................................................................81.4.4 Adaptive modulation and coding (AMC)..............................................................81.4.5 Link-layer retransmissions ..................................................................................81.4.6 Support for TDD and FDD...................................................................................8

    1.4.7 Orthogonal frequency division multiple access (OFDMA)...................................91.4.8 Flexible and dynamic per user resource allocation .............................................91.4.9 Support for advanced antenna techniques .........................................................91.4.10 Qulity of service support......................................................................................91.4.11 Robust security .................................................................................................101.4.12 Support for mobility ...........................................................................................101.4.13 IP-based architecture........................................................................................10

    2 Chapter2 OFDM & OFDMA .............................................................................112.1 OFDM System Description................................................................................112.2 Difference between OFDMA and OFDM...........................................................132.3 OFDM Orthogonality .........................................................................................142.4 How to Overcome Inter Symbol Interference (ISI) ............................................142.5 How to Overcome Inter Carrier Interference (ICI) .............................................15

    3 Chapter3 Physical Layer Description............................................................163.1 OFDMA Basics..................................................................................................163.2 OFDMA SymbolStructure and Sub-Channelization .........................................173.3 Scalable OFDMA ..............................................................................................193.4 TDD Frame Structure........................................................................................203.5 Other Advanced PHY Layer Features...............................................................21

    4 Chapter4 WiMAX MAC Layer .........................................................................23

    4.1 Common MAC Concepts ..................................................................................244.1.1 CS Sublayer......................................................................................................24

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    4.1.2 MAC CPS Sublayer...........................................................................................244.2 Quality of Service (QoS) Support......................................................................294.3 MAC Scheduling Service ..................................................................................31

    4.4 Mobility Management ........................................................................................324.4.1 Power Management ..........................................................................................324.4.2 Handoff..............................................................................................................33 4.5 Security .............................................................................................................34

    5 Chapter5 WiMAX Advanced Features ...........................................................355.1 Smart Antenna Technologies............................................................................355.2 Fractional Frequency Reuse.............................................................................37

    5.3 Multicast and Broadcast Service (MBS)............................................................39

    6 Chapter6 WiMAX Network Architecture........................................................40

    6.1 WiMAX Network Architecture............................................................................40

    7 Chapter7 WiMAX Channel Estimation ...........................................................447.1 Introduction .......................................................................................................447.2 Channel Estimation...........................................................................................447.2.1 Transmitter........................................................................................................457.2.2 Channel.............................................................................................................46 7.2.3 Receiver............................................................................................................49

    8 Chapter8 WiMAX Major Benefi ts ...................................................................518.1 WiMAX Major Benefits ......................................................................................518.1.1 Benefits to Component Makers.........................................................................51

    8.1.2 Benefits to Equipment Makers ..........................................................................518.1.3 Benefits to Operators ........................................................................................518.1.4 Benefits to Consumers......................................................................................51

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    FIGURESFigure 2-1 OFDM description in both time and frequency division ......................................11

    Figure 2-2 Orthogonal subcarriers.......................................................................................12

    Figure 2-3 Comparing of FDMA and OFDM ........................................................................12

    Figure 2-4 Compirement of OFDM and OFDMA .................................................................13

    Figure 2-5 Subcarriers and multipath component shown ....................................................15

    Figure 2-6 Cyclic prefix ........................................................................................................15

    Figure 3-1 Basic Architeture of OFDMA system..................................................................17

    Figure 3-2 OFDMA Sub-carrier Structure ............................................................................18

    Figure 3-3 DL Frequency Diverse Sub-Channel..................................................................18

    Figure 3-4 Tile Structure for UL PUSC ................................................................................19

    Figure 3-5 OFDMA Scalablity Parameters...........................................................................20

    Figure 3-6 OFDMA Frame Structure....................................................................................21

    Figure 4-1 MAC PDU format................................................................................................24

    Figure 4-2 MAC header format ............................................................................................25

    Figure 4-3 MAC management message format...................................................................25

    Figure 4-4 Composition of Burst and MAC PDU..................................................................29

    Figure 4-5 Mobile WiMAX QoS Support ..............................................................................30

    Figure 5-1 Adaptive Switching for Smart Antennas .............................................................37

    Figure 5-2 Multi-Zone Frame Structure................................................................................38

    Figure 5-3 Fractional Frequency Reuse ..............................................................................38

    Figure 5-4 MBS Zones.........................................................................................................40

    Figure 6-1 IP-Based WiMAX Network Architecture .............................................................41

    Figure 7-1 Simulated Doppler spectrum ..............................................................................47

    Figure 7-2 Rayleigh fading channel .....................................................................................48

    Figure 7-3 The Block Diagram.............................................................................................50

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    TABLESTable 3-1 Supported Code and Modulations .......................................................................22

    Table 3-2 PHY Data Rates with PUSC Sub-Channel ..........................................................22

    Table 4-1 MAC management messages .............................................................................26

    Table 4-2 Mobile WiMAX Application and Quality of service ...............................................30

    Table 5-1 Advanced Antenna Options.................................................................................36

    Table 5-2 Data Rates for SIMO/MIMO Configurations ........................................................36

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    1 Chapter1 Introduction to WiMAX

    Knowledge

    zWhat is WiMAX ------------------------------------------------------------------Level 1 2

    zWiMAX Benefits -----------------------------------------------------------------Level 1 2

    z Salient Features -------------------------------------------------------------------Level 1 2

    1.1 Wireless Introduction

    Wireless means transmitting signals using radio waves as the medium instead of

    wires. Wireless technologies are used for tasks as simple as switching off the

    television or as complex as supplying the sales force with information from an

    automated enterprise application while in the field. Now cordless keyboards and

    mouse PDAs, pagers and digital and cellular phones have become part of our

    daily life.

    Some of the inherent characteristics of wireless communications systems which

    make it attractive for users are given below.

    Mobility: A wireless communications system allows users to access information

    beyond their desk and conduct business from anywhere without a cable

    connectivity.

    Reachability: Wireless communications systems enable people to be better

    connected and reachable without any limitation of any location.

    Simplicity: Wireless communication system is easy and fast to deploy incomparision of cabled network. Initial setup cost could be a bit high but other

    advantages overcome that high cost.

    Maintainability: Being a wireless system, you do no need to spend too much to

    maintain a wireless network setup.

    Roaming Services: Using a wireless network system you can provide service any

    where any time including train, busses, airoplans etc.

    New Services: Wireless communications systems provide new smart services like

    SMS and MMS.

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    1.1.1 Wireless Network Topologies

    There are basically three ways to setup a wireless network.

    Point-to-point bridge: As you know a bridge is used to connect two networks. A

    point-to-point bridge interconnects two buildings having different networks. For

    example, a wireless LAN bridge can interface with an Ethernet network directly to a

    particular access point.

    Point-to-multipoint bridge: This topology is used to connect three or more LANs

    that may be located on different floors in a building or across buildings.

    Mesh or ad hoc network: This network is an independent local area network that is

    not connected to a wired infrastructure and in which all stations are connected

    directly to one another.

    1.1.2 Wireless Technologies

    Wireless technologies can be classified in different ways depending on their range.

    Each wireless technology is designed to serve a specific usage segment. The

    requirements for each usage segment are based on a variety of variables,

    including Bandwidth needs, Distance needs and Power.

    1.1.3 Kinds of Wireless Networks

    Wireless Wide Area Network (WWAN):

    This network enables you to access the Internet via a wireless wide area network

    (WWAN) access card and a PDA or laptop.

    These networks provide a very fast data speed compared with the data rates of

    mobile telecommunications technology, and their range is also extensive. Cellular

    and mobile networks based on CDMA and GSM are good examples of WWAN.

    Wireless Personal Area Network (WPAN):

    These networks are very similar to WWAN except thier range is very limited.

    Wireless Local Area Network (WLAN): This network enables you to access the

    Internet in localized hotspots via a wireless local area network (WLAN) access card

    and a PDA or laptop.

    It is a type of local area network that uses high-frequency radio waves rather than

    wires to communicate between nodes.

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    These networks provide a very fast data speed compared with the data rates of

    mobile telecommunications technology, and their range is very limited. Wi-Fi is the

    most widespread and popular example of WLAN technology.

    Wireless Metropolitan Area Network (WMAN):

    This network enables you to access the Internet and multimedia streaming

    services via a wireless region area network (WRAN).

    These networks provide a very fast data speed compared with the data rates of

    mobile telecommunication technology as well as other wireless network, and their

    range is also extensive.

    1.1.4 Wireless Broadband Access (WBA)

    Broadband wireless is a technology that promises high-speed connection over the

    air. It uses radio waves to transmit and receive data directly to and from the

    potential users whenever they want it. Technologies including 3G, Wi-Fi, WiMAX

    and UWB work together to meet unique customer needs.

    BWA is a point-to-multipoint system which is made up of base station andsubscriber equipment. Instead of using the physical connection between the base

    station and the subscriber, the base station uses an outdoor antenna to send and

    receive high-speed data and voice-to-subscriber equipment.

    BWA offers an effective, complementary solution to wireline broadband, which has

    become globally recognized by a high percentage of the population.

    1.2 Related Organization

    1.2.1 IEEE

    IEEE802.16 is a broadband radio MAN technology intended to provide a fixed

    broad radio access system with an efficient, applicable, and interoperable access

    means. Its protocol is focused on the contents on the MAC layer and physical

    layer.

    IEEE 802.16e defines the physical layer and MAC layer of the air interface for the

    radio broadband access system that supports mobility, and at the same time,

    includes the definition of PKMv2 encryption.

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    1.2.2 WiMAX Forum

    WiMAX Forum (WMF) is a nonprofit production group founded on April 9, 2001 byequipment and device suppliers that adopt the 802.16 standard, with an intention

    to coordinate world-wide broadband radio technologies and promote development

    of the WiMAX industry chain.

    With increasing concern for the WiMAX technologies in this industry, WiMAX

    Forum has more and more members, and has set up in succession Certification

    Work Group (CWG), Technology Work Group (TWG), Regulatory Work Group

    (RWG), Market Work Group (MWG), Service Provider Work Group (SPWG),

    Network Work Group (NWG), and Application Work Group (AWG). Accordingly,

    this organization is extending its objectives gradually. Apart from certification, it is

    devoted to requirement analysis, application scenario exploration, and WiMAX

    network architecture research with regard to the operable broadband radio access

    system, thus promoting powerfully the development of the broadband radio access

    technologies and market.

    WiMAX has become an alias of compliance with the 802.16 specification system.

    1.3 What is WiMAX

    WiMAX is one of the hottest broadband wireless technologies around today.

    WiMAX systems are expected to deliver broadband access services to residential

    and enterprise customers in an economical way.

    Loosely, WiMAX is a standardized wireless version of Ethernet intended primarily

    as an alternative to wire technologies ( such as Cable Modems, DSL and T1/E1

    links ) to provide broadband access to customer premises.

    More strictly, WiMAX is an industry trade organization formed by leading

    communications component and equipment companies to promote and certify

    compatibility and interoperability of broadband wireless access equipment that

    conforms to the IEEE 802.16 and ETSI HIPERMAN standards.

    WiMAX would operate similar to WiFi but at higher speeds, over greater distances

    and for a greater number of users. WiMAX has the ability to provide service even in

    areas that are difficult for wired infrastructure to reach and the ability to overcome

    the physical limitations of traditional wired infrastructure.

    WiMAX was formed in April 2001, in anticipation of the publication of the original

    10-66 GHz IEEE 802.16 specifications. WiMAX is to 802.16 as the Wi-Fi Alliance is

    to 802.11.

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    1.3.1 What is WiMAX

    z Acronym for Worldwide Interoperability for Microwave Access

    z Based on Wireless MAN technology.

    z A wireless technology optimized for the delivery of IP centric services over a

    wide area.

    z A scaleable wireless platform for constructing alternative and complementary

    broadband networks.

    z A certification that denotes interoperability of equipment built to the IEEE

    802.16 or compatible standard. The IEEE 802.16 Working Group developsstandards that address two types of usage models:

    A fixed usage model (IEEE 802.16-2004).

    A portable usage model (IEEE 802.16e).

    1.3.2 What is 802.16d

    This is targeted to provide a broadband internet connection to indoor users. The

    SS operating on this standard use indoor antenna and a limited mobility (portabledevices) is allowed. 802.16d uses orthogonal frequency division multiplexing

    (OFDM) as its physical layer specification to enable NLOS communication below

    11 GHz. Since OFDM is used, the receiver is made simple by elimination of bulky

    equalizer. The other features have nearly been kept similar in all the physical

    profiles of the standards Variable FFT size and symbol time is specified, which

    could be fixed depending on type of environment and allocated bandwidth.. FEC

    includes concatenated RS-CC followed by interleaving. Similar to 802.16a, AAS,

    STC schemes are provided but are kept optional.

    1.3.3 What is 802.16e

    Specifications are provided such that mobility of the SS at 125 KMPH is allowed.

    Orthogonal frequency division multiple access (OFDMA) is used as the physical

    layer scheme.. Data is randomized and interleaved to avoid loss of carrier recovery

    and burst errors. In addition to AAS, STC, optional multi input multi output (MIMO)

    scheme has been specified. Code division multiple access (CDMA) codes are used

    along with the random window length based contention control algorithm for initial

    ranging, periodic ranging, bandwidth request and handoff. The inter BS

    communications have been defined, which will be used as a backbone network

    between the BSs to aid the inter-cell mobile subscriber station (MSS) handoff. This

    ensures fast and accurate synchronization at the cost of slightly increased

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    complexity. Similar to 802.16d, variable FFT size and symbol time is provided

    which could be set depending on the environment and allocated bandwidth.

    Put together, the 802.16 technology would enable the SS to get broadband

    wireless access (BWA) at all times in all locations, either when stationary, or at

    pedestrian speed or when traveling at 125 KMPH.

    Few of the difference between 802.16d and 802.16e are presented here. In OFDM,

    SS uses all the available subcarriers for the allocated time, but in OFDMA, user is

    allocated region having definition in both time and frequency. The subcarrier

    mapping is different in both the standards, resulting in channel estimation done in

    802.16d being complex, but done less number of times. In 802.16e the channel

    estimation is simple, but more frequently done (because data considered, per

    iteration is less Channel is flat only over limited subcarriers). Another difference

    is use of CDMA codes for ranging in 802.16e, the receiver performs correlation to

    detect the user, and hence more processing is involved.

    1.3.4 WiMAX Speed and Range

    WiMAX is expected to offer initially up to about 40 Mbps capacity per wireless

    channel for both fixed and portable applications, depending on the particular

    technical configuration chosen, enough to support hundreds of businesses with T-1

    speed connectivity and thousands of residences with DSL speed connectivity.

    WiMAX can support voice and video as well as Internet data.

    WiMAX will be to provide wireless broadband access to buildings, either in

    competition to existing wired networks or alone in currently unserved rural or thinly

    populated areas. It can also be used to connect WLAN hotspots to the Internet.

    WiMAX is also intended to provide broadband connectivity to mobile devices. It

    would not be as fast as in these fixed applications, but expectations are for about

    15 Mbps capacity in a 3 km cell coverage area.

    With WiMAX users could really cut free from today.s Internet access arrangements

    and be able to go online at broadband speeds, almost wherever they like from

    within a MetroZone.

    WiMAX could potentially be deployed in a variety of spectrum bands: 2.3GHz,

    2.5GHz, 3.5GHz, and 5.8GHz

    1.3.5 Why WiMAX

    z WiMAX can satisfy a variety of access needs. Potential applications include

    extending broadband capabilities to bring them closer to subscribers, filling

    gaps in cable, DSL and T1 services, Wi-Fi and cellular backhaul, providing

    last-100 meter access from fibre to the curb and giving service providers

    another cost-effective option for supporting broadband services.

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    z WiMAX can support very high bandwidth solutions where large spectrum

    deployments (i.e. >10 MHz) are desired using existing infrastructure keeping

    costs down while delivering the bandwidth needed to support a full range of

    high-value, multimedia services.

    z WiMAX can help service providers meet many of the challenges they face due

    to increasing customer demands without discarding their existing

    infrastructure investments because it has the ability to seamlessly interoperate

    across various network types.

    z WiMAX can provide wide area coverage and quality of service capabilities for

    applications ranging from real-time delay-sensitive voice-over-IP (VoIP) to

    real-time streaming video and non-real-time downloads, ensuring that

    subscribers obtain the performance they expect for all types of

    communications.

    z WiMAX, which is an IP-based wireless broadband technology, can be

    integrated into both wide-area third-generation (3G) mobile and wireless and

    wireline networks, allowing it to become part of a seamless anytime, anywhere

    broadband access solution.

    Ultimately, WiMAX is intended to serve as the next step in the evolution of 3G

    mobile phones, via a potential combination of WiMAX and CDMA standards called

    4G.

    1.3.6 WiMAX Goals

    A standard by itself is not enough to enable mass adoption. WiMAX has stepped

    forward to help solve barriers to adoption, such as interoperability and cost of

    deployment. WiMAX will help ignite the wireless MAN industry, by defining and

    conducting interoperability testing and labeling vendor systems with a "WiMAX

    Certified" label once testing has been completed successfully.

    1.4 Salient Features of WiMAX

    WiMAX is a wireless broadband solution that offers a rich set of features with a lot

    of flexibility in term of development options and potential services offerings. Some

    of the more salient features that deserve hightlighting are as follows:

    1.4.1 OFDM-based physical layer

    WiMAX physical layer (PHY) is based on the orthogonal frequency division

    multiplexing, a schem that offers good resistance to multipath, and allows WiMAX

    to operate in NOL-Sight conditions. OFDM is now widely recognized as the method

    for mitigating mutipath for broadband wireless.

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    1.4.2 Very High Peak Date Rate

    WiMAX is capable of supporting very high peak data rate. In fact, the peak data

    rate can reach 74Mbps when operationg using 20MHz wide spectrum. More

    typically, using a 10MHz spectrum operating using TDD schem with a 3:1

    downlink-to-uplink ratio, the peak PHY data rate is 25Mbps and 6.7Mbps for

    downlink and uplink, respectively. These peak data rate are achieved when using

    64 QAM moduration with rate 5/6 err-correcting coding. Under viry good signal

    condition, even higher data rate may be achieved using multiple antennas and

    spatial multiplexing.

    1.4.3 Scalable bandwidth and rate support

    WiMAX has a scalable physical layer architecture that allows for the date rate to

    scal easily with available channel bandwidth. This scalability is supported in the

    OFDMA mode, where the FFT(fast fourier transform) size may be scaled based on

    the available bandwidth. For example, a WiMAX system may use 128-, 512-,

    1,024bit FFTs based on whether the channel bandwidth is 1.25MHz, 5MHz,

    10MHz, respectively. This scaling may be done dynamically to support user

    roaming across different network that may have different bandwidth allocations.

    1.4.4 Adaptive modulation and coding (AMC)

    WiMAX supports a number of modulation and forward effort correction (FEC)

    coding schemes and allows the schemes to change on per user and per frame

    bisis, based on the channel conditions. AMC is an effective mechanism to

    maximize the throughput in a time-varying channel. The additive algorithm typically

    calls for the use of the highest modulation and coding scheme that can be

    supported by the signal-to-nosie and inteference ratio at the receiver such that

    each user is provided with the highest data rate that can be suppotted in their

    respective links.

    1.4.5 Link-layer retransmissions

    For connections that require henced reliability, WiMAX supports automatic

    retransmission requests (ARQ) at the link layer. ARQ-enabled connections require

    each transmitted packet to be acknowledged by the receiver; unacknowledged

    packets are assumed to be lost and are retransmitted. WiMAX also optionally

    support hybrid-ARQ(HARQ), which is an effective hybrid between ARQ and FEC.

    1.4.6 Support for TDD and FDD

    IEEE 802.16 2004 and IEEE 802.16 2005 both support time division duplexing and

    frequency division duplexing as well as a half duplex FDD, which allows a low-cost

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    system implementation. TDD is favored by a majority of implementions because of

    its advantages:

    (1) flexibility to choose downlink-to-uplink date rate rato.

    (2) ability to exploit channel reciprocity.

    (3) ability to implement nonpaired spectrum and less complex transceiver

    design.

    1.4.7 Orthogonal frequency division multip le access (OFDMA)

    Mobile WiMAX use OFDM as a multi-acess technique, whereby different users can

    be allocated different subsets of the OFDM tones. OFDMA facilitates theexploitation of frequency diversity and multiuser divisity to significantly improve the

    system capcity.

    1.4.8 Flexible and dynamic per user resource allocation

    Both uplink and downlink resource allocation are controlled by a scheduler in the

    base station. Capicity is shared among multiple users on a demand basis, using a

    burst TDM scheme. When using the OFDMA-PHY mode, multiplexing is

    additionally done in the frequency dimension, by allocating different subsets of

    OFDM subcarriers to different users. Resources may be allocated in the spatialdomain as well when using the optional advanced antenna system (AAS). The

    standard allows for bandwidth resources to be allocated in time, frequency, and

    space and has a flexible mechanism to convey the resource allocation information

    on a frame-by-frame basis.

    1.4.9 Support for advanced antenna techniques

    The WiMAX solution has a number of hooks built into the physicl-layer design,

    which allows for the use of multiple-antenna techniques, such as beamforming,

    space-time coding, and spatial multiplexing. These shemes can be used to

    improve the overall system capacity and spectral efficiency by deploying mulitiple

    anttenas at the transmitter and/or receiver side.

    1.4.10 Qulity of service support

    The WiMAX MAC layer has a connection-oriented architechtrue that is design to

    support a variety of applications, including voice and multimedia services. The

    system offers support for constant bit rate, real-time, and non-real-time time traffic

    flows, in addition best-effort data traffic. WiMAX MAC is designed to support a

    large number of users, with multiple connections per terminal, each with its own

    Qos requirement.

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    1.4.11 Robust securi ty

    WiMAX support strong encryption, using Advanced Encryption Starded (AES), and

    has a robust privacy and key-management protocol. The system also offers a very

    flexible authentication architecture based on Extensible Authentication Protocol

    (EAP), which allows for a variety of user credentials, including username/password,

    digital certificates, and smart cards.

    1.4.12 Support for mobi lity

    The mobile WiMAX variant of the system has mechanisms to support secure

    seamless handovers for deley-tolerant full-mobility applications, such as VoIP. The

    system also has built-in support for power-saving mechanisms that extend the

    battery life of handheld subscriber devices. Physical-layer enhancements, such asmore frequent channel estimation, uplink subchannelization, and power control, are

    also specified in support of moble applications.

    1.4.13 IP-based archi tecture

    The WiMAX Forum has defined a reference network architecture that is based on

    an all-IP platform. All end to end services are delivered over an IP architecture

    relying on IP-based protocols for end-to-end transport, Qos, session management,

    security, and mobility. Reliance on IP allows WiMAX to ride the declining

    costcurves of IP processing, facilitate easy convergence with other networks, and

    exploit the rich ecosystem for application development that exsits for IP.

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    2 Chapter2 OFDM & OFDMA Knowledgez OFDM System Basics-------------------------------------------------------------Level 1 2

    z OFDM Orthogonality -------------------------------------------------------------Level 1 2

    z Overcome ISI-----------------------------------------------------------------------Level 1 2

    z Overcome ICI----------------------------------------------------------------------Level 1 2

    2.1 OFDM System Descript ion

    z OFDM = Orthogonal Frequency Division Multiplexing .

    z OFDM converts a high rate broadband signal into many parallel low rate

    narrowband signals.

    z Low rate signals have large symbol periods, which make OFDM signal

    resistant to multipath delay spread.

    z OFDM uses a Fast Fourier Transform (FFT) to allow overlap in frequency of

    individual narrowband signals.

    z More efficient than conventional multi-carrier.

    Figure 2-1 OFDM description in both time and frequency division

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    OFDM is a multi carrier transmission scheme where the information is transmitted

    on multiple subcarriers, with a lower data rate, instead of one high data rate carrier

    Figure 2-2 Orthogonal subcarriers

    Figure 2.1-2

    Figure 2-3 Comparing of FDMA and OFDM

    The major disadvantage of an OFDM system is its requirement of perfect

    synchronization in time and frequency. But the advantages of using OFDM are far

    more and provide enough reasons for the popularity of the OFDM systems. A

    typical channel fade will degrade only a few of the subcarriers, which in most cases

    can be compensated by use of efficient interleaving and channel coding. OFDM

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    systems can be implemented very efficiently by using the Inverse Fast Fourier

    transform (IFFT) at the transmitter and Fast Fourier transform (FFT) at the receiver.

    The overall complexity and its increase with data rate in OFDM systems is far less

    than the single carrier systems, hence OFDM is becoming a widely accepted

    technology and more prominent to be used in future mobile wireless

    communication standards.

    2.2 Difference betweenOFDMA and OFDMIEEE 802.16d (fixed service) uses Orthogonal Frequency Division Multiplexing

    (OFDM). IEEE 802.16e (mobile) uses Orthogonal Frequency Division Multiple

    Access (OFDMA). So, whats the difference between the two, and why is there adifference?

    Figure 2-4 Compirement of OFDM and OFDMA

    OFDM allows only one user on the channel at any given time. To accommodate

    multiple users, a strictly OFDM system must employ Time Division Multiple Access

    (TDMA) (separate time frames) or Frequency Division Multiple Access (FDMA)(separate channels). Neither of these techniques is time or frequency efficient:

    TDMA is a time hog and FDMA is a bandwidth hog.

    OFDMA is a multi-user OFDM that allows multiple access on the same channel (a

    channel being a group of evenly spaced subcarriers, as discussed above). WiMAX

    uses OFDMA, extended OFDM, to accommodate many users in the same channel

    at the same time.

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    2.3 OFDM Orthogonality

    For successful operation of OFDM system, it is required that the subcarriers should

    never loose orthogonality between each other at any time. The advantage of an

    OFDM system is lost when the subcarriers are no longer orthogonal to each other.

    This puts forward quite stringent requirements to be fulfilled by the transmitter and

    the receiver.

    0dt(2f)tsin2ft2sin

    T

    0

    = where T = f1

    Ideally, to maintain orthogonality we need that the symbol duration be exactly

    inverse of the subcarrier spacing and the FFT be considered over symbol duration

    such that it covers integer number of cycles. Moreover, the consecutive subcarriers

    differ by 1 full cycle only (Figure 3.1). If the system is to operate in a multipath

    environment, then each subcarrier should experience a flat fading, hence the

    subcarrier spacing should be less than the coherence bandwidth and each symbol

    should experience a time-invariant channel, hence the symbol time should be less

    than the coherence time else the complexity of receiver increases when

    overcoming the fading effect.

    2.4 How to Overcome Inter Symbol Interference(ISI)

    A guide time is added.

    Reduction of inter symbol interference, which would require bulky equalizer to be

    constructed at the receiver in a single carrier system, is overcome by the use of

    guard time in an OFDM system. A guard time is added in time domain between two

    OFDM symbols and the FFT is considered over duration such that there is no

    component from the previous or next symbol, (Figure 3.3) which nulls the ISI and

    thus avoiding the bulky equalizer. ISI is completely eliminated when the multipath

    signal delay is within the guard time. When designing an OFDM system proper

    values are selected depending on the environment so as to satisfy the above

    condition.

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    Figure 2-5 Subcarriers and multipath component shown

    2.5 How to Overcome Inter Carr ier Interference (ICI)

    Cyclic prefix is fiiled.

    Multi carrier systems have the problem of inter carrier interference (ICI), whichresults from loss of orthogonality between the subcarriers. This happens when the

    FFT is considered over duration where the subcarrier is not present (non-integer

    number of cycles), which would be the case when multipath is present and the

    guard time has amplitude zero. This is reduced by use of cyclic prefix, where we

    transmit a copy the last part of the symbol followed by the symbol itself. This

    ensures orthogonality over the FFT period in case of delayed multipath

    Figure 2-6 Cyclic prefix

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    3 Chapter3 Phys ical Layer Description Knowledge

    z OFDMA Basics -----------------------------------------------------------------Level 1 2

    z OFDMA Symbol Stucture-----------------------------------------------------Level 1 2

    z Scalable OFDMA---------------------------------------------------------------Level 1 2

    z TDD Frame Structure----------------------------------------------------------Level 1 2

    z Advanced PHY Features------------------------------------------------------Level 1 2

    z Difference between OFDMA and OFDM-----------------------------------Level 1 2

    3.1 OFDMA Basics

    z OFDMA = Orthogonal Frequency Division Multiple Access

    z In Scalable OFDMA, subcarrier spacing is independent of bandwidth

    z FFT size is scaled with bandwidth

    z Subchannel size is fixed and independent of bandwidth and other modes

    of operation

    z The number of subchannels scales with FFT size rather than with the

    capacity of subchannels

    Orthogonal Frequency Division Multiplexing (OFDM) is a multiplexing technique

    that subdivides the bandwidth into multiple frequency sub-carriers.

    In an OFDM system, the input data stream is divided into several parallel

    sub-streams of reduced data rate (thus increased symbol duration) and each

    sub-stream is modulated and transmitted on a separate orthogonal sub-carrier. The

    increased symbol duration improves the robustness of OFDM to delay

    spread. Furthermore, the introduction of the cyclic prefix (CP) can

    completely eliminate Inter-Symbol Interference (ISI) as long as the CP duration is

    longer than the channel delay spread. The CP is typically a repetition of the last

    samples of data portion of the block that is appended to the beginning

    of the data payload as shown in Figure 3. The CP prevents inter-block

    interference and makes the channel appear circular and permits low-complexity

    frequency domain equalization. A perceived drawback of CP is that it

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    introduces overhead, which effectively reduces bandwidth efficiency.

    While the CP does reduce bandwidth efficiency somewhat, the impact

    of the CP is similar to the roll-off factor in raised-cosine filtered single-carrier

    systems. Since OFDM has a very sharp, almost brick-wall spectrum, a large

    fraction of the allocated channel bandwidth can be utilized for data

    transmission, which helps to moderate the loss in efficiency due to the cyclic

    prefix.OFDM exploits the frequency diversity of the multipath channel by coding

    and interleaving the information across the sub-carriers prior to transmissions.

    OFDM modulation can be realized with efficient Inverse Fast Fourier Transform

    (IFFT), which enables a large number of sub-carriers (up to 2048) with low

    complexity. In an OFDM system, resources are available in the time domain by

    means of OFDM symbols and in the frequency domain by means of sub-carriers.

    The time and frequency resources can be organized into sub-channels for

    allocation to individual users. Orthogonal Frequency Division Multiple Access(OFDMA) is a multiple-access/multiplexing scheme that provides multiplexing

    operation of data streams from multiple users onto the downlink sub-channels and

    uplink multiple access by means of uplink sub-channels

    Figure 3-1 Basic Architeture of OFDMA system

    3.2 OFDMA Symbol Structu re and Sub-Channelization

    The OFDMA symbol structure consists of three types of sub-carriers.

    z Data sub-carriers for data transmission

    z Pilot sub-carriers for estimation and synchronization purposes

    z Null sub-carriers for no transmission; used for guard bands and DC carriers

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    Figure 3-2 OFDMA Sub-carrier Structure

    Active (data and pilot) sub-carriers are grouped into subsets of sub-carriers called

    subchannels.The WiMAX OFDMA PHY supports sub-channelization in both DL

    and UL. The minimum frequency-time resource unit of sub-channelization is one

    slot, which is equal to 48 data tones (sub-carriers).

    There are two types of sub-carrier permutations for sub-channelization; diversity

    and contiguous. The diversity permutation draws sub-carriers pseudo-randomly to

    form a sub-channel. It provides frequency diversity and inter-cell interference

    averaging. The diversity permutations include DL FUSC (Fully Used Sub-Carrier),

    DL PUSC (Partially Used Sub-Carrier) and UL PUSC and additional optional

    permutations. With DL PUSC, for each pair of OFDM symbols, the available or

    usable sub-carriers are grouped into clusters containing 14 contiguous sub-carriers

    per symbol, with pilot and data allocations in each cluster in the even and odd

    symbols

    Figure 3-3 DL Frequency Diverse Sub-Channel

    A re-arranging scheme is used to form groups of clusters such that each group is

    made up of clusters that are distributed throughout the sub-carrier space. A

    sub-channel in a group contains two (2) clusters and is comprised of 48 data

    sub-carriers and eight (8) pilot subcarriers. Analogous to the cluster structure for

    DL, a tile structure is defined for the UL PUSC .

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    Figure 3-4 Tile Structure for UL PUSC

    The available sub-carrier space is split into tiles and six (6) tiles, chosen from

    across the entire spectrum by means of a re-arranging/permutation scheme, aregrouped together to form a slot. The slot is comprised of 48 data sub-carriers and

    24 pilot sub-carriers in 3 OFDM symbols.

    The contiguous permutation groups a block of contiguous sub-carriers to form a

    subchannel.The contiguous permutations include DL AMC and UL AMC, and have

    the same structure. A bin consists of 9 contiguous sub-carriers in a symbol, with 8

    assigned for data and one assigned for a pilot. A slot in AMC is defined as a

    collection of bins of the type (N x M = 6), where N is the number of contiguous bins

    and M is the number of contiguous symbols. Thus the allowed combinations are [(6

    bins, 1 symbol), (3 bins, 2 symbols), (2 bins, 3 symbols), (1 bin, 6 symbols)]. AMCpermutation enables multi-user diversity by choosing the sub-channel with the best

    frequency response.

    In general, diversity sub-carrier permutations perform well in mobile applications

    while contiguous sub-carrier permutations are well suited for fixed, portable, or low

    mobility environments. These options enable the system designer to trade-off

    mobility for throughput.

    3.3 ScalableOFDMA

    The IEEE 802.16e Wireless MAN OFDMA mode is based on the concept of

    scalable OFDMA (S-OFDMA). S-OFDMA supports a wide range of bandwidths to

    flexibly address the need for various spectrum allocation and usage model

    requirements. The scalability is supported by adjusting the FFT size while fixing the

    sub-carrier frequency spacing at 10.94 kHz. Since the resource unit sub-carrier

    bandwidth and symbol duration is fixed, the impact to higher layers is minimal

    when scaling the bandwidth. The SOFDMA parameters are listed in Table 1. The

    system bandwidths for the initial planned profiles being developed by the WiMAX

    Forum Technical Working Group for Release-1 are 5 and 10 MHz .

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    Figure 3-5 OFDMA Scalablity Parameters

    3.4 TDD Frame Struc ture

    The 802.16e PHY supports TDD, FDD, and Half-Duplex FDD operation; however

    the initial release of Mobile WiMAX certification profiles will only include TDD. With

    ongoing releases, FDD profiles will be considered by the WiMAX Forum to address

    specific market opportunities where local spectrum regulatory requirements either

    prohibit TDD or are more suitable for FDD deployments.

    To counter interference issues, TDD does require system-wide synchronization;

    nevertheless, TDD is the preferred duplexing mode for the following reasons:

    z TDD enables adjustment of the downlink/uplink ratio to

    efficiently support asymmetric downlink/uplink traffic, while with FDD,

    downlink and uplink always have fixed and generally, equal DL and UL

    bandwidths.

    z TDD assures channel reciprocity for better support of link adaptation,

    MIMO and other closed loop advanced antenna technologies.

    z Unlike FDD, which requires a pair of channels, TDD only requires a single

    channel for both downlink and uplink providing greater flexibility foradaptation to varied global spectrum allocations.

    z Transceiver designs for TDD implementations are less complex and

    therefore less expensive.

    Figure 3-6 illustrates the OFDM frame structure for a Time Division Duplex (TDD)

    implementation. Each frame is divided into DL and UL sub-frames separated by

    Transmit/Receive and Receive/Transmit Transition Gaps (TTG and RTG,

    respectively) to prevent DL and UL transmission collisions. In a frame, the following

    control information is used to ensure optimal system operation:

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    z Preamble: The preamble, used for synchronization, is the first OFDM symbol

    of the frame.

    z Frame Control Head (FCH): The FCH follows the preamble. It provides the

    frame configuration information such as MAP message length and coding

    scheme andusable sub-channels.

    z DL-MAP and UL-MAP: The DL-MAP and UL-MAP provide sub-channel

    allocation and other control information for the DL and UL sub-frames

    respectively.

    z UL Ranging: The UL ranging sub-channel is allocated for mobile stations (MS)

    to perform closed-loop time, frequency, and power adjustment as well as

    bandwidth requests.

    z UL CQICH: The UL CQICH channel is allocated for the MS to feedback

    channelstate information.

    z UL ACK: The UL ACK is allocated for the MS to feedback DL HARQ

    acknowledgement.

    Figure 3-6 OFDMA Frame Structure

    3.5 Other Advanced PHY Layer Features

    Adaptive modulation and coding (AMC), Hybrid Automatic Repeat Request (HARQ)

    and Fast Channel Feedback (CQICH) were introduced with Mobile WiMAX to

    enhance coverage and capacity for WiMAX in mobile applications.

    Support for QPSK, 16QAM and 64QAM are mandatory in the DL with Mobile

    WiMAX. In the UL, 64QAM is optional. Both Convolutional Code (CC) and

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    Convolutional TurboCode (CTC) with variable code rate and repetition coding are

    supported. Block Turbo Code and Low Density Parity Check Code (LDPC) are

    supported as optional features Table 4.2 summarizes the coding and modulation

    schemes supported in the Mobile WiMAX profile the optional UL codes and

    modulation are shown in italics.

    Table 3-1 Supported Code and Modulations

    The combinations of various modulations and code rates provide a fine resolution

    of data rates as shown in Table 3 which shows the data rates for 5 and 10 MHz

    channels with PUSC sub-channels. The frame duration is 5 milliseconds. Each

    frame has 48 OFDM symbols, with 44 OFDM symbols available for data

    transmission. The highlighted values indicate data rates for optional 64QAM in the

    UL.

    Table 3-2 PHY Data Rates with PUSC Sub-Channel

    The base station scheduler determines the appropriate data rate (or burst profile)

    for each burst allocation based on the buffer size, channel propagation conditions

    at the receiver, etc. A Channel Quality Indicator (CQI) channel is utilized to provide

    channel-state information from the user terminals to the base station scheduler.

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    Relevant channel-state information can be fed back by the CQICH including:

    Physical CINR, effective CINR, MIMO mode selection and frequency selective

    sub-channel selection. With TDD implementations, link adaptation can also takeadvantage of channel reciprocity to provide a more accurate measure of the

    channel condition (such as sounding). Hybrid Auto Repeat Request (HARQ) is

    supported by Mobile WiMAX. HARQ is enabled using N channel Stop and Wait

    protocol which provides fast response to packet errors and improves cell edge

    coverage. Chase Combining and optionally, Incremental Redundancy are

    supported to further improve the reliability of the retransmission. A dedicated ACK

    channel is also provided in the uplink for HARQ ACK/NACK signaling.

    Multi-channel HARQ operation is supported. Multi-channel stop-and-wait ARQ with

    a small number of channels is an efficient, simple protocol that minimizes the

    memory required for HARQ and stalling [8]. WiMAX provides signaling to allow fully

    asynchronous operation. The asynchronous operation allows variable delaybetween retransmissions which gives more flexibility to the scheduler at the cost of

    additional overhead for each retransmission allocation. HARQ combined together

    with CQICH and AMC provides robust link adaptation in mobile environments at

    vehicular speeds in excess of 120 km/hr.

    Knowledge

    4 Chapter4 WiMAX MAC Layer

    z Kinds of Qos ----------------------------------------------------------------Level 1 2

    z MAC Scheduling Service--------------------------------------------------Level 1 2

    z Mobility Management------------------------------------------------------Level 1 2

    z Security-----------------------------------------------------------------------Level 1 2

    The 802.16 standard was developed from the outset for the delivery of broadband

    services including voice, data, and video. The MAC layer is based on the

    time-proven DOCSIS standard and can support bursty data traffic with high peak

    rate demand while simultaneously supporting streaming video and

    latency-sensitive voice traffic over the same channel. The resource allocated to

    one terminal by the MAC scheduler can vary from a single time slot to the entire

    frame, thus providing a very large dynamic range of throughput to a specific user

    terminal at any given time. Furthermore, since the resource allocation information

    is conveyed in the MAP messages at the beginning of each frame, the scheduler

    can effectively change the resource allocation on a frame-by-frame basis to adapt

    to the bursty nature of the traffic.

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    4.1 Common MAC Concepts

    The MAC layer consists of Convergence Sublayer, MAC CPS, and SecuritySublayer.

    4.1.1 CS Sublayer

    CS is a transition sublayer, on which the SAP is used to receive data from external

    networks, and then transfer or map the data. This operation involves classifying of

    external network SDUs, and assignment of an appropriate MAC-layer SFID and

    CID to each classification. It also includes the PSH function.

    The CS is used to process the objects of upper-layer data packets (core network

    PDU) and upper and lower-layer QoS features.

    The CS is used to implement the classifier and PHS functions.

    4.1.2 MAC CPS Sublayer

    The CPS sublayer receives data from different CSs through the MAC SAP, and

    classifies the data to specific MAC connections. Through QoS scheduling,

    bandwidth is allocated, and SDUs are formed into PDUs. In each PUD MAC

    header, the CID field is used to identify connection.

    The formed PDUs are transferred to the PHY layer through the PHY SAP.

    4.1.2.1 MAC-Layer PDU Format

    A MAC message consists of a MAC header, MAC data, and CRC.

    For OFDMA, CRC is a required part.

    Figure 4-1 MAC PDU format

    The MAC header takes the format as follows:

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    Figure 4-2 MAC header format

    4.1.2.2 MAC-Layer Management Message

    A MAC-layer management message takes the format as follows:

    Figure 4-3 MAC management message format

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    MAC-layer management messages are listed in the table below. The applications

    of MAC messages are detailed in each optimization topic.

    Table 4-1 MAC management messages

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    4.1.2.3 Composition of Burst and MAC PDU

    The MAC-layer messages will be ultimately mapped to the Burst and transferred

    on the physical layer, as shown in the figure below.

    Figure 4-4 Composition of Burst and MAC PDU

    Burst

    MAC Msg 1

    MAC PDU 1

    MAC Msg n

    MAC PDU nPad

    MAC HeaderMAC msg payload

    (optional)

    CRC

    (optional)

    4.2 Quality of Servi ce (QoS) Support

    With fast air link, symmetric downlink/uplink capacity, fine resource granularity and

    a flexible resource allocation mechanism, Mobile WiMAX can meet QoS

    requirements for a wide range of data services and applications.

    In the Mobile WiMAX MAC layer, QoS is provided via service flows as illustrated in

    Figure 4-5. This is a unidirectional flow of packets that is provided with a particular

    set of QoS parameters. Before providing a certain type of data service, the base

    station and user-terminal first establish a unidirectional logical link between the

    peer MACs called a connection. The outbound MAC then associates packets

    traversing the MAC interface into a service flow to be delivered over the connection.

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    The QoS parameters associated with the service flow define the transmission

    ordering and scheduling on the air interface.

    The connection-oriented QoS therefore, can provide accurate control over the air

    interface. Since the air interface is usually the bottleneck, the connection-oriented

    QoS can effectively enable the end-to-end QoS control. The service flow

    parameters can be dynamically managed through MAC messages to

    accommodate the dynamic service demand. The service flow based QoS

    mechanism applies to both DL and UL to provide improved QoS in both directions.

    Mobile WiMAX supports a wide range of data services and applications with varied

    QoS requirements. These are summarized (Table 4-2).

    Figure 4-5 Mobile WiMAX QoS Support

    Table 4-2 Mobile WiMAX Application and Quality of service

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    4.3 MAC Scheduling Servi ce

    The Mobile WiMAX MAC scheduling service is designed to efficiently deliver

    broadband data services including voice, data, and video over time varying

    broadband wireless channel. The MAC scheduling service has the following

    properties that enable the broadband data service:

    z Fast Data Scheduler: The MAC scheduler must efficiently allocate availableresources in response to bursty data traffic and time-varying channel

    conditions. Thescheduler is located at each base station to enable rapid

    response to traffic requirements and channel conditions. The data packets are

    associated to service flows with well defined QoS parameters in the MAC

    layer so that the scheduler can correctly determine the packet transmission

    ordering over the air interface. The CQICH channel provides fast channel

    information feedback to enable the scheduler to choose the appropriate

    coding and modulation for each allocation. The adaptive modulation/coding

    combined with HARQ provide robust transmission over the timevarying

    channel.

    z Scheduling for both DL and UL: The scheduling service is provided for both

    DL and UL traffic. In order for the MAC scheduler to make an efficient

    resource allocation and provide the desired QoS in the UL, the UL must

    feedback accurate and timely information as to the traffic conditions and QoS

    requirements. Multiple uplink bandwidth request mechanisms, such as

    bandwidth request through ranging channel, piggyback request and polling

    are designed to support UL bandwidth requests. The UL service flow defines

    the feedback mechanism for each uplink connection to ensure predictable UL

    scheduler behavior. Furthermore, with orthogonal UL sub-channels, there is

    no intra-cell interference. UL scheduling can allocate resource more efficiently

    and better enforce QoS.

    z Dynamic Resource All ocation: The MAC supports frequency-time resource

    allocation in both DL and UL on a per-frame basis. The resource allocation is

    delivered in MAP messages at the beginning of each frame. Therefore, the

    resource allocation can be changed on frame-by-frame in response to traffic

    and channel conditions. Additionally, the amount of resource in each allocation

    can range from one slot to the entire frame. The fast and fine granular

    resource allocation allows superior QoS for data traffic.

    z QoS Oriented: The MAC scheduler handles data transport on a

    connection-byconnection basis. Each connection is associated with a single

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    data service with a set of QoS parameters that quantify the aspects of its

    behavior. With the ability to dynamically allocate resources in both DL and UL,

    the scheduler can provide superior QoS for both DL and UL traffic. Particularly

    with uplink scheduling the uplink resource is more efficiently allocated,

    performance is more predictable, and QoS is better enforced.

    z Frequency Selective Scheduling: The scheduler can operate on different

    types of sub-channels. For frequency-diverse sub-channels such as PUSC

    permutation, where sub-carriers in the sub-channels are pseudo-randomly

    distributed across the bandwidth, sub-channels are of similar quality.

    Frequency-diversity scheduling can support a QoS with fine granularity and

    flexible time-frequency resource scheduling. With contiguous permutation

    such as AMC permutation, the sub-channels may experience different

    attenuation. The frequency-selective scheduling can allocate mobile users to

    their corresponding strongest sub-channels. The frequency-selective

    scheduling can enhance system capacity with a moderate increase in CQI

    overhead in the UL.

    4.4 Mobil ity Management

    Battery life and handoff are two critical issues for mobile applications. Mobile

    WiMAX supports Sleep Mode and Idle Mode to enable power-efficient MSoperation. Mobile WiMAX also supports seamless handoff to enable the MS to

    switch from one base station to another at vehicular speeds without interrupting the

    connection.

    4.4.1 Power Management

    Mobile WiMAX supports two modes for power efficient operation Sleep Mode and

    Idle Mode. Sleep Mode is a state in which the MS conducts pre-negotiated periods

    of absence from the Serving Base Station air interface. These periods are

    characterized by the unavailability of the MS, as observed from the Serving BaseStation, to DL or UL traffic. Sleep Mode is intended to minimize MS power usage

    and minimize the usage of the Serving Base Station air interface resources. The

    Sleep Mode also provides flexibility for the MS to scan other base stations to

    collect information to assist handoff during the Sleep Mode. Idle Mode provides a

    mechanism for the MS to become periodically available for DL broadcast traffic

    messaging without registration at a specific base station as the MS traverses an air

    link environment populated by multiple base stations. Idle Mode benefits the MS by

    removing the requirement for handoff and other normal operations and benefits the

    network and base station by eliminating air interface and network handoff traffic

    from essentially inactive MSs while still providing a simple and timely method

    (paging) for alerting the MS about pending DL traffic.

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    4.4.2 Handoff

    There are three handoff methods supported within the 802.16e standard HardHandoff (HHO), Fast Base Station Switching (FBSS) and Macro Diversity

    Handover (MDHO). Of these, the HHO is mandatory while FBSS and MDHO are

    two optional modes. The WiMAX Forum has developed several techniques for

    optimizing hard handoff within the framework of the 802.16e standard. These

    improvements have been developed with the goal of keeping Layer 2 handoff

    delays to less than 50 milliseconds.

    When FBSS is supported, the MS and BS maintain a list of BSs that are involved in

    FBSS with the MS. This set is called an Active Set. In FBSS, the MS continuously

    monitors the base stations in the Active Set. Among the BSs in the Active Set, anAnchor BS is defined. When operating in FBSS, the MS only communicates with

    the Anchor BS for uplink and downlink messages including management and traffic

    connections.

    Transition from one Anchor BS to another (i.e. BS switching) is performed without

    invocation of explicit HO signaling messages. Anchor update procedures are

    enabled by communicating signal strength of the serving BS via the CQI channel. A

    FBSS handover begins with a decision by an MS to receive or transmit data from

    the Anchor BS that may change within the active set. The MS scans the neighbor

    BSs and selects those that are suitable to be included in the active set. The MS

    reports the selected BSs and the active set update procedure is performed by the

    BS and MS. The MS continuously monitors the signal strength of the BSs that are

    in the active set and selects one BS from the set to be the Anchor BS. The MS

    reports the selected Anchor BS on CQICH or MS initiated HO request message. An

    important requirement of FBSS is that the data is simultaneously transmitted to all

    members of an active set of BSs that are able to serve the MS.

    For MSs and BSs that support MDHO, the MS and BS maintain an active set of

    BSs that are involved in MDHO with the MS. Among the BSs in the active set, an

    Anchor BS is defined. The regular mode of operation refers to a particular case of

    MDHO with the active set consisting of a single BS. When operating in MDHO, the

    MS communicates with all BSs in the active set of uplink and downlink unicast

    messages and traffic. A MDHO begins when a MS decides to transmit or receive

    unicast messages and traffic from multiple BSs in the same time interval. For

    downlink MDHO, two or more BSs provide synchronized transmission of MS

    downlink data such that diversity combining is performed at the MS. For uplink

    MDHO, the transmission from a MS is received by multiple BSs where selection

    diversity of the information received is performed.

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    4.5 Security

    Mobile WiMAX supports best in class security features by adopting the best

    technologies available today. Support exists for mutual device/user authentication,

    flexible key management protocol, strong traffic encryption, control and

    management plane message protection and security protocol optimizations for fast

    handovers.The usage aspects of the security features are:

    z Key Management Protocol: Privacy and Key Management Protocol Version

    2 (PKMv2) is the basis of Mobile WiMAX security as defined in 802.16e. Thisprotocol manages the MAC security using PKM-REQ/RSP messages. PKM

    EAP authentication, Traffic Encryption Control, Handover Key Exchange and

    Multicast/Broadcast security messages all are based on this protocol.

    z Device/User Authentication: Mobile WiMAX supports Device and User

    Authentication using IETF EAP protocol by providing support for credentials

    that are SIM-based, USIM-based or Digital Certificate or

    UserName/Password-based. Corresponding EAP-SIM, EAP-AKA, EAP-TLS

    or EAP-MSCHAPv2 authentication methods are supported through the EAPprotocol. Key deriving methods are the only EAP methods supported.

    z Traffic Encryption: AES-CCM is the cipher used for protecting all the user

    data over the Mobile WiMAX MAC interface. The keys used for driving the

    cipher are generated from the EAP authentication. A Traffic Encryption State

    machine that has a periodic key (TEK) refresh mechanism enables sustained

    transition of keys to further improve protection.

    z Control Message Protection: Control data is protected using AES based

    CMAC, or MD5-based HMAC schemes.

    z Fast Handover Support:A 3-way Handshake scheme is supported by Mobile

    WiMAX to optimize the re-authentication mechanisms for supporting fast

    handovers. This mechanism is also useful to prevent any

    man-in-the-middle-attacks.

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    5 Chapter5 WiMAX Advanced Features Knowledge

    z AntennaTechnolegies Basics-------------------------------------------------Level 1 2

    z FFR-------------------------------------------------------------------------------Level 1 2

    z MBS------------------------------------------------------------------------------Level 1 2

    5.1 Smart Antenna Techno log ies

    Smart antenna technologies typically involve complex vector or matrix operations

    on signals due to multiple antennas. OFDMA allows smart antenna operations to

    be performed on vector-flat sub-carriers. Complex equalizers are not required to

    compensate for frequency selective fading. OFDMA therefore, is very well-suited to

    support smart antenna technologies. In fact, MIMO-OFDM/OFDMA is envisioned

    as the corner-stone for next generation broadband communication systems. Mobile

    WiMAX supports a full range of smart antenna technologies to enhance system

    performance. The smart antenna technologies supported include:

    z Beamforming: With beamforming, the system uses multiple-antennas to

    transmit weighted signals to improve coverage and capacity of the system and

    reduce outage probability.

    z Space-Time Code (STC): Transmit diversity such as Alamouti code is

    supported to provide spatial diversity and reduce fade margin.

    z Spatial Multiplexing (SM): Spatial multiplexing is supported to take

    advantage of higher peak rates and increased throughput. With spatialmultiplexing, multiple streams are transmitted over multiple antennas. If the

    receiver also has multiple antennas, it can separate the different streams to

    achieve higher throughput compared to single antenna systems. With 2x2

    MIMO, SM increases the peak data rate two-fold by transmitting two data

    streams. In UL, each user has only one transmit antenna, two users can

    transmit collaboratively in the same slot as if two streams are spatially

    multiplexed from two antennas of the same user. This is called UL

    collaborative SM.

    The supported features in the Mobile WiMAX performance profile are listed in the

    following table 5-1.

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    Table 5-1 Advanced Antenna Options

    Mobile WiMAX supports adiptive switching between these options to maximize the

    benefit of smart antenna technologies under different channel conditions. For

    instance, SM improves peak throughput. However, when channel conditions are

    poor, the Packet Error Rate (PER) can be high and thus the coverage area where

    target PER is met may be limited. STC on the other hand provides large coverage

    regardless of the channel condition but does not improve the peak data rate.

    Mobile WiMAX supports adaptive switching between multiple MIMO modes tomaximize spectral efficiency with no reduction in coverage area.

    Figure 5-1 shows the architecture for supporting the smart antenna feature. The

    following table provides a summary of the theoretical peak data rates for various

    DL/UL ratios assuming a 10 MHz channel bandwidth, 5 ms frame duration with 44

    OFDM data symbols (out of 48 total OFDM symbols) and PUSC subchannelization.

    With 2x2 MIMO, the DL user and sector peak data rate are doubled. The maximum

    DL peak data rate is 63.36 Mbps when all the data symbols are dedicated to DL.

    With UL collaborative SM, the UL sector peak data rate is doubled while the user

    peak data rate is unchanged. The UL user peak data rate and sector peak datarate are 14.11 Mbps and 28.22 Mbps respectively when all the data symbols are

    dedicated to UL. By applying different DL/UL ratio, the bandwidth can by adjusted

    between DL and UL to accommodate different traffic pattern. It should be noted

    that the extreme cases such as all DL and all UL partition are rarely used. WiMAX

    profile supports DL/UL ratio ranging from 3:1 to 1:1 to accommodate different traffic

    profiles. The resulting peak data rates that will typically be encountered are in

    between the two extreme cases.

    Table 5-2 Data Rates for SIMO/MIMO Configurations

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    (For 10 MHz channel, 5 ms frame, PUSC sub-channel, 44 data OFDM symbols)

    Figure 5-1 Adaptive Switching for Smart Antennas

    5.2 Fractional Frequency Reuse

    Mobile WiMAX supports frequency reuse of one, i.e. all cells/sectors operate on

    the same frequency channel to maximize spectral efficiency. However, due to

    heavy cochannel interference (CCI) in frequency reuse one deployment, users at

    the cell edge may suffer degradation in connection quality. With Mobile WiMAX,

    users operate on subchannels, which only occupy a small fraction of the whole

    channel bandwidth; the cell edge interference problem can be easily addressed by

    appropriately configuring subchannel usage without resorting to traditional

    frequency planning.

    In Mobile WiMAX, the flexible sub-channel reuse is facilitated by sub-channel

    segmentation and permutation zone. A segment is a subdivision of the available

    OFDMA sub-channels (one segment may include all sub-channels). One segment

    is used for deploying a single instance of MAC.

    Permutation Zone is a number of contiguous OFDMA symbols in DL or UL that use

    the same permutation. The DL or UL sub-frame may contain more than one

    permutation zone as shown in the following figure 5-2

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    Figure 5-2 Multi-Zone Frame Structure

    The sub-channel reuse pattern can be configured so that users close to the base

    station operate on the zone with all sub-channels available. While for the edge

    users, each cell or sector operates on the zone with a fraction of all sub-channels

    available. In Figure 5-3, F1, F2, and F3 represent different sets of sub-channels in

    the same frequency channel. With this configuration, the full load frequency reuse

    one is maintained for center users to maximize spectral efficiency and fractional

    frequency reuse is implemented for edge users to assure edge-user connection

    quality and throughput. The sub-channel reuse planning can be dynamically

    optimized across sectors or cells based on network load and interferenceconditions on a frame by frame basis. All the cells and sectors therefore, can

    operate on the same frequency channel without the need for frequency planning.

    Figure 5-3 Fractional Frequency Reuse

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    5.3 Multi cast and Broadcast Service (MBS)

    Multicast and Broadcast Service (MBS) supported by Mobile WiMAX combines the

    best features of DVB-H, MediaFLO and 3GPP E-UTRA and satisfies the following

    requirements:

    z High data rate and coverage using a Single Frequency Network (SFN)

    z

    Flexible allocation of radio resources

    z Low MS power consumption

    z Support of data-casting in addition to audio and video streams

    z Low channel switching time

    The Mobile WiMAX Release-1 profile defines a toolbox for initial MBS service

    delivery. The MBS service can be supported by either constructing a separate

    MBS zone in the DL frame along with unicast service (embedded MBS) or the

    whole frame can be dedicated to MBS (DL only) for standalone broadcast service.

    Figure 5-4 shows the DL/UL zone construction when a mix of unicast and

    broadcast service are supported. The MBS zone supports multi-BS MBS mode

    using Single Frequency Network (SFN) operation and flexible duration of MBS

    zones permits scalable assignment of radio resources to MBS traffic. It may be

    noted that multiple MBS zones are also feasible. There is one MBS zone MAP IE

    descriptor per MBS zone. The MS accesses the DL MAP to initially identify MBS

    zones and locations of the associated MBS MAPs in each zone. The MS can then

    subsequently read the MBS MAPs without reference to DL MAP unless

    synchronization to MBS MAP is lost. The MBS MAP IE specifies MBS zone PHY

    configuration and defines the location of each MBS zone via the OFDMA Symbol

    Offset parameter. The MBS MAP is located at the 1st sub-channel of the 1st

    OFDM symbol of the associated MBS zone. The multi-BS MBS does not require

    the MS be registered to any base station. MBS can be accessed when MS in Idle

    mode to allow low MS power consumption. The flexibility of Mobile WiMAX to

    support integrated MBS and uni-cast services enables a broader range of

    applications.

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    Figure 5-4 MBS Zones

    6 Chapter6 WiMAX Network Architecture

    Knowledge

    z Network Architecture ----------------------------------------------------------Level 1 2

    6.1 WiMAX Network Architecture

    The IEEE 802.16e-2005 standard provides the air interface for WiMAX but does

    not define the full end-to-end WiMAX network. The WiMAX Forum's Network

    Working Group (NWG), is responsible for developing the end-to-end network

    requirements, architecture, and protocols for WiMAX, using IEEE 802.16e-2005 as

    the air interface.

    The WiMAX NWG has developed a network reference model to serve as an

    architecture framework for WiMAX deployments and to ensure interoperability

    among various WiMAX equipment and operators.

    The network reference model envisions an unified network architecture for

    supporting fixed, nomadic, and mobile deployments and is based on an IP service

    model. Below is simplified illustration of an IP-based WiMAX network architecture.

    The overall network may be logically divided into three parts:

    (1) Mobile Stations (MS) used by the end user to access the network.

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    (2) The access service network (ASN), which comprises one or more base

    stations and one or more ASN gateways that form the radio access

    network at the edge.

    (3) Connectivity service network (CSN), which provides IP connectivity and all

    the IP core network functions.

    The network reference model developed by the WiMAX Forum NWG defines a

    number of functional entities and interfaces between those entities. Fig below

    shows some of the more important functional entities.

    Figure 6-1 IP-Based WiMAX Network Architecture

    z Base station (BS): The BS is responsible for providing the air interface to the

    MS. Additional functions that may be part of the BS are micromobility

    management functions, such as handoff triggering and tunnel establishment,

    radio resource management, QoS policy enforcement, traffic classification,

    DHCP (Dynamic Host Control Protocol) proxy, key management, session

    management, and multicast group management.

    z Access service network gateway (ASN-GW): The ASN gateway typically

    acts as a layer 2 traffic aggregation point within an ASN. Additional functions

    that may be part of the ASN gateway include intra-ASN location management

    and paging, radio resource management and admission control, caching of

    subscriber profiles and encryption keys, AAA client functionality,

    establishment and management of mobility tunnel with base stations, QoS

    and policy enforcement, foreign agent functionality for mobile IP, and routing

    to the selected CSN.

    z Connectivity service network (CSN): The CSN provides connectivity to the

    Internet, ASP, other public networks, and corporate networks. The CSN is

    owned by the NSP and includes AAA servers that support authentication for

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    the devices, users, and specific services. The CSN also provides per user

    policy management of QoS and security. The CSN is also responsible for IP

    address management, support for roaming between different NSPs, location

    management between ASNs, and mobility and roaming between ASNs.

    The WiMAX architecture framework allows for the flexible decomposition and/or

    combination of functional entities when building the physical entities. For example,

    the ASN may be decomposed into base station transceivers (BST), base station

    controllers (BSC), and an ASNGW analogous to the GSM model of BTS, BSC, and

    Serving GPRS Support Node (SGSN).

    z R1: Between MS and ASN

    Protocols and Procedures as per the air interface

    MAY include additional protocols related to the management plane

    z R2: Between the MS and CSN

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    Authentication, Services Authorization and IP Host Configuration

    management.

    z R3: Between the ASN and CSN

    Control plane Protocols support AAA, policy and mobility management

    capabilities.

    z R4: between ASNs and ASN-GWs.

    Control and Bearer plane Protocols

    Originating / terminating various functional entities of an ASN that

    coordinate MS mobility

    z R6: between the BS and the ASN-GW.

    Control and Bearer plane protocols for communication

    z R8: between the base stations

    Control plane message flows

    Optionally Bearer plane data flows

    Ensure fast and seamless handover.

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    7 Chapter7 WiMAX Channel Estimation Knowledgez Introduction -----------------------------------------------------------------------Level 1 2

    z Uplink Transmission--------------------------------------------------------------Level 1 2zChannel Estimation_Transmitter------------------------------------------------Level 1 2z Channel Estimation_Channel----------------------------------------------------Level 1 2z Channel Estimation_Receiver----------------------------------------------------Level 1 2

    7.1 Introduction

    A general communication system consists of two blocks, a transmitter and receiver,

    connected by a channel. The information transmitted by the transmitter passes

    through the channel and then reaches the receiver. If the channel does not distort

    the transmitted signal, then the receiver can retrieve the transmitted information

    successfully, but in practice the channel alters the transmitted information making

    the task difficult for the receiver. The main aim of the designer is to reduce thenumber of errors made at the receiver. To achieve this, information is required at

    the receiver, as to how the channel alters the information, so that the channel

    impairments can be mitigated.

    When the user is mobile, the channel characteristics do not remain constant for a

    very long time. Hence the channel parameters need to be tracked, so that the

    effect can be mitigated and reconstruct the transmitted data. This part deals with

    the requirements of Channel estimation at the Base station (BS) for an 802.16e

    uplink. Symbol time has an effect on system performance depending on the

    channel conditions. Different symbol times are proposed in and each one has been

    simulated and compared for various channel condition. In addition a solution

    proposed by Intel coop. has also been analyzed. It is concluded that the

    performance of the system, for few proposed symbol times, is relatively good in all

    conditions.

    7.2 Channel Estimation

    The Block diagram (Figure 7-3) represents the whole system model or the signal

    chain at base band. The block system is divided into 3 main Chapters namely the

    transmitter, receiver and the channel. The model has been tested with and without

    the channel coding (part in doted box representing the channel coding and

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    decoding). The bit error rate (BER) plots have been obtained for at least 2000

    errors to get