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WiMAX is a standards-based engineering easing the proviso of last mile radio broadband entree as an surrogate to wired broadband similar to overseas telegram and DSL. WiMAX offers inactive, going, ready to hand and, shortly, nomadic radio broadband connectivity with no demand for consecutive line-of-sight with a base station. For fixed and portable entree applications, WiMAX systems can be anticipated to transport capacity of equal to 40 Mega spots per second for each channel, in a usual cell radius deployment of 3 to 10 Km. This is sufficient bandwidth to at the same time keep 100 of concerns with T-1 velocity connectivity and 1000 of places with DSL velocity connectivity. Mobile web deployments are estimated to give equal to 15 Mega spots per seconnd of capacity in a usual cell radius deployment of equal to 3 Km.

WiMAX is intended to go a “ Following Large Thing ” because regulative bureaus and criterions groups around the Earth accept this criterion and it is built on unfastened criterions.

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1.2 PROBLEM STATEMENT

The job with WiMax is to supply thebetter Quality of service equivalent to that of the wired engineering. Though the WiMax has constitutional quality of service architecture but in existent deployment it does non supply the promised quality of service to stop users over longer distances.

1.3 Aim

The chief aims of this thesis are to give basic apprehension of this emerging engineering by depicting its quality of service mechanisms that are used at the PHY and MAC beds, optimising quality of service parametric quantities ( hold, burden and throughput ) , which will assist in bettering the broadband WiMAX services.

1.4 METHODOLOGY

  • Detailed survey of the related subjects and literature.
  • Planing the different simulation based practical theoretical account scenarios of a WiMax web to imitate different QoS parametric quantities ( latency, jitter, hold, throughput etc ) that may impact the QoS in radio webs.
  • Model based solution will be proposed which will turn to these QoS parametric quantities and the obtained consequences will optimise the public presentation of the web derived from different designed simulation theoretical accounts.

1.5 ORGANIZATION of the THESIS

This thesis consists of six chapters. Chapter 2 contains the elaborate debut of the standard IEEE 802.16 ( WiMax ) , the different versions of the standard IEEE 802.16, its operation manners, and the protocol architecture of 802.16. Chapter 3 describes the use theoretical accounts ( fixed and portable ) , the characteristics and the usage scenarios. The WiMAX criterion addresses a wide assortment of applications and use scenarios which are assembled into 2 big classs, private webs and public webs. Chapter 4 describes the QoS mechanisms precise to 802.16. It explains how QoS is provisioned in 802.16. It besides equates the QoS abilities of 802.16 with the rival engineerings. Chapter 5 discusses the WiMAX web simulation scenarios developed in OPNET 14.5 simulation tool. Chapter 6 concludes the consequences obtained.

Chapter 2

LITERATURE REVIEW and INTRODUCTION to WIMAX ( IEEE 802.16 )

2.1 LITERATURE REVIEW

2.2 Introduction

The IEEE 802.16 Working Group on Broadband Wireless Access Standards was initiated in a meeting held by the National Institute of Standards and Technology ( NIST ) . The working group has formed new criterions for broadband radio metropolitan country webs. The 1st edition of the IEEE 802.16 criterion is 802.16-2001 agreed in December 2001 and in print in April 2002.

The IEEE 802.16 criterion and its amendments depict the air interface specifications together with a common MAC bed and physical beds ( PHY ) covering with the Data Link bed and Physical bed of Open Systems Interconnection ( OSI ) theoretical account [ 4 ] . The criterions screen frequence ranges of 2-66 GHz, both licensed and license-exempt sets. The channel entree method supports both Frequency Division Duplexing ( FDD ) and Time Division Duplexing ( TDD ) .

At the beginning, the intend of IEEE 802.16 media entree control bed was to back up PMP broadband radio entree ( BWA ) system. Subsequently Mesh manner is added to back up operating in mesh webs. It is anticipated to turn to high spot rate communications with assorted services. The IEEE Std 802.16 [ 5 ] defines three MAC sub-layers.

Service-specific Convergence Sub-layer ( CS )

The Service-specific CS receives exterior web informations via the convergence sub-layer SAP, transforms the information to media entree control SDUs, and sends the media entree control SDUs to the media entree control service entree point. The classification of upper-layer protocol informations units ( PDUs ) and directing those PDUs to the proper media entree control service entree point is the its key undertaking. The standard specifies convergence sub-layer for ATM and packet-based protocols. The supported packet-based protocols are IEEE 802.3 standard/Ethernet, IEEE standard 802.1Q-1998 practical local country web ( VLAN ) , and Internet Protocol ( IP ) , both IPv4 and IPv6 [ 5 ] .

MAC Common Part Sub-layer ( CPS )

The MAC CPS receives MAC SDUs through the MAC SAP from the Service-specific CS. It provides method for entree to the system, allotment of bandwidth, constitution and care of connexion. Presently, it supports PMP and Mesh manners [ 5 ] .

Security Sub-layer

The hallmark, secure cardinal exchange, and encoding is provided by an encapsulation protocol and a cardinal direction protocol contained in Security Sub-layer. The PHY defines several specifications for different frequence scopes and applications [ 5 ] .

2.3 Benefits

The followers are some benefits given by the IEEE Std 802.16 and its amendments.

Large coverage

Compared to prior radio engineering, the IEEE Std 802.16 provides much larger country of coverage. In line-of-sight ( LOS ) environment, the coverage distance is up to 50 kilometres. In NLOS environments, a base station covers the radius of up to 8 kilometres [ 6 ] . The larger coverage needs few base Stationss, shorter installing clip, and less cost.

High informations capacity

It delivers up to 70 Mb/s in a individual wireless frequence ( RF ) channel. ( This is theoretically maximal value under ideal fortunes. Practically it delivers less. ) By utilizing Orthogonal Frequency Division Multiplexing ( OFDM ) technique, the criterion increases informations capacity. Using multiplexing technique a wide channel is divided into several narrower channels with different frequences. Therefore, we can at the same time direct several messages via a wide channel [ 6 ] .

NLOS environment support

The IEEE Std 802.16a plants in 2 to11 GHz frequence sets. Its low frequence and three new PHY specifications facilitate the IEEE Std 802.16a to back up working in NLOS environments. The needed PHY functionalities to run under NLOS conditions are the advanced power direction techniques, intervention mitigation/coexistence, and multiple aerials [ 6 ] .

Flexible channel sizes

The IEEE Std 802.16 allows an operator to utilize flexible channel sizes. It optimizes the usage of spectrum. For illustration, an operator pays for 14 MHz spectrum and wants to utilize all of granted spectrum. If the system can be deployed merely with 6 MHz channels, they attain 2 channels and waste 2 MHz of spectrum. What they wish for is a system which can work on 7 MHz, 3.5 MHz, or 1.75 MHz channels [ 2 ] .

Mesh manner

The IEEE Std 802.16a-2003 provides full mesh networking capableness with Mesh manner. In Mesh manner, a package can be routed non merely among the base station ( BS ) and subscriber Stationss ( SSs ) but besides among two SSs. The Mesh manner operates with OFDM PHY bed and TDD.

Mobile user support

The IEEE Std 802.16e-2005 specifies a criterion for nomadic broadband radio entree at vehicle velocities.

Table 2.1 shows comparing of the IEEE 802.16 and other radio engineering criterions.

Table 2.1: Comparison of radio engineerings

Characteristic

IEEE Std 802.15 ( Bluetooth )

IEEE Std 802.11

( Wi-Fi )

IEEE Std 802.16

( WiMAX )

Application

WPAN

Wireless local area network

WMAN

Maximum

Coverage country

100 m ( Class 1 )

10 m ( Class 2 )

1 m ( Class 3 )

105 m ( Outdoors )

45 m ( Office )

50 kilometer ( LOS )

8 kilometer ( NLOS )

Peak informations rate

1 Mbps ( Version 1.2 )

3 Mps ( Version 2 with

Enhanced informations rate )

11 Mbps ( 802.11b )

54 Mbps ( 802.11a/g )

70 Mbps

Frequency set

2.4 – 2.485 GHz

2.4 GHz ( 802.11b/g )

5 GHz ( 802.11a )

2 – 66 GHz

2.4 APPLICATIONS

The IEEE 802.16 working group does non take to replace the IEEE Std 802.11 with the IEEE Std 802.16, instead the IEEE Std 802.16 serves as a complement of the IEEE Std 802.11. The IEEE Std 802.16 is planned for WMANs, whereas the IEEE Std 802.11 is planned for WLANs. Therefore, the IEEE Std 802.16 enables users to entree into wireless web on a larger graduated table. Because of its better coverage, faster velocity, and larger figure of supported users per base station, the IEEE Std 802.16 tends to be used extensively as backhaul and last-mile solutions for Wi-Fi webs. A radio web dwelling Wi-Fi entree points could utilize the IEEE Std 802.16 solution as a backhaul to present signal to the nucleus web. As a last-mile solution, an cyberspace service supplier ( ISP ) could put in the IEEE 802.16 engineering, alternatively of overseas telegrams, DSL, and T1, to present services to endorsers. It gives advantages over the traditional wired engineering in instance that telegraphing is non executable or excessively expensive, for illustration, implementing in rural countries or developing states where deficiency wired web substructures [ 12 ] .Figure 2.1 shows an illustration of the IEEE 802.16 web.

Two usage theoretical accounts of the IEEE Std 802.16. The IEEE Std 802.16 base station provides wireless entree services to fixed and portable endorsers. The fixed endorsers could be residential endorsers or concerns in edifices. For residential endorsers, the criterion provides broadband radio entree as a last-mile solution, in topographic point of utilizing overseas telegram modem. The IEEE 802.16 engineering can be a replacement to DSL or leased line services for little and average size concerns, every bit good as a replacement to T1/E1 degree services for endeavors. Users in the edifices can fall in to the web via Ethernet/IEEE 802.3 or WLAN/IEEE 802.11 criterions. For nomadic users, the IEEE Std 802.16e which is an amendment to IEEE Std 802.16-2004 adds the capableness to supply services. The users can straight attach to the web utilizing devices, such as personal digital helpers ( PDAs ) , smart phones, and nomadic laptops.

2.5 OVERVIEW of WiMAX

The IEEE 802.16 criterion is commercially known as WiMAX, which is an acronym for Worldwide Interoperability for Microwave Access. WiMAX is a wireless metropolitan-area web engineering that provides interoperable broadband radio connectivity to fixed, portable and mobile users. It covers up to 50- kilometres of service country, license users to obtain broadband connectivity with no demand of direct line-of-sight to the base station, and provides entire informations rates up to 75 Mbps, plenty bandwidth to simultaneously support 100s of concerns and places with a individual base station [ 2 ] .

WiMAX covers a wide spectrum of bandwidth from a few hundred MHzs to 10s of GHz. This encompasses far more spectrum than any earlier criterion. WiMAX is intended to go a “ Following Large Thing ” correspondent to the impact of the Internet because WiMAX is built on unfastened criterions and is extensively accepted by regulative bureaus and criterions groups around the Earth. This cosmopolitan degree of blessing agencies that merchandises can be prepared that will work wheresoever comparable service is provided.

It has been developing by the WiMAX Forum working groups. The WiMAX Forum established in June 2001 and is a non-profit-making organisation. The intend of the organisation, similar to Wi-Fi Alliance, is to do certain the compatibility and interoperability of merchandises conforming to the IEEE Std 802.16 and European Telecommunications Standards Institute ( ETSI ) HiperMAN criterions. WiMAX plays a function as a complement of the IEEE Std 802.16. The IEEE 802.16 working group defines the criterion for working, whereas the WiMAX Forum coordinates companies to do certain that equipment from each company can well run with one another.

The WiMAX Forum creates system profiles and defines test suite for conformity and interoperability. “WiMAX Forum CERTIFIEDa„?” text and logo will be used by the equipment that passes the trial and will be certified. The hallmarks are shown in Figure 2.2. The enfranchisement is non provided to constituents but to the equipment. The trial is done by WiMAX research lab. The first official enfranchisement research lab chosen by the WiMAX Forum is Cetecom in Malaga, Spain [ 2 ] .

However, if equipment conforms to the 802.16 and ETSI HiperMAN criterions, it might non accomplish WiMAX enfranchisement. To go through the trial programme, it does non necessitate merely conformity with the criterion but besides interoperability with equipment from other companies. There are at nowadays more than 300 companies fall ining the WiMAX Forum from different industries, such as web equipment makers, service suppliers, and bit makers.

2.6 VERSIONS of the IEEE 802.16 STANDARD

The IEEE 802.16 Working Group has been following a figure of undertakings to enlarge the IEEE Std 802.16 functionality. This subdivision provides the general thought of the IEEE 802.16 criterion and its amendments as of January 2006 [ 21 ] .

2.6.1 IEEE Std 802.16-2001

The IEEE 802.16-2001 criterion is first edition of the IEEE 802.16 criterion. It was accepted on 23 rd December 2001 and in print in April 2002. MAC and PHY are defined by the criterion for fixed PMP BWA systems. The MAC construction support multiple PHY specifications. A system can supply multiple services for its endorsers through PMP connexions [ 21 ] . It operates in the 10-66 GHz sets. Because of its high frequences, the criterion can work merely in LOS environments to diminish multipath deformation.

2.6.2 IEEE Std 802.16c-2002

The first alteration to the IEEE Std 802.16-2001standard is IEEE standard 802.16c-2002. The alteration specifies the complete system profiles for working in 10-66 GHz. It standardizes the radio engineering in more inside informations. Namely, it defines aggregations of facets and maps used in executing [ 21 ] . These defined sets boost the consistence and interoperability between equipment from different companies.

2.6.3 IEEE standard 802.16a-2003

The 2nd alteration for the IEEE standard 802.16-2001 is IEEE standard 802.16a-2003. It supports working at the 2-11 GHz frequences, both licensed and license-exempt sets. The standard improves PMP MAC and defines new PHY specifications. By MAC functionality, the criterion introduces a figure of characteristics, such as a specific quality of service ( QoS ) to optimise informations, picture, and voice services, Automatic Retransmission Request ( ARQ ) to acquire better end-to-end public presentation. The MAC in add-on defines optional Mesh manner which enables every node to straight link to others through multipoint-to-multipoint air interface and as a consequence extends the coverage of communicating. Because low frequences have capableness to perforate barriers, the IEEE 802.16a criterion can work in close LOS and NLOS environments enabled by the new PHY functionality [ 21 ] .

2.6.4 IEEE Std 802.16-2004

The alteration and consolidation of the IEEE standard 802.16-2001, the IEEE standard 802.16a-2003, and the IEEE standard 802.16c-2002 is IEEE standard 802.16-2004. It is intended for both accredited and un-licensed frequences. In 10 to 66 GHz sets, it requires LOS environment, whereas, in frequences below 11 GHz, it provides the installation to back up NLOS environment. The MAC supports both PMP and Mesh manners [ 21 ] .

2.6.5 IEEE standard 802.16f-2005

The alteration of the IEEE standard 802.16-2004 is IEEE standard 802.16f-2005. It defines a direction information base ( MIB ) for the media entree control, PHY, and direction processs to do criterion for web direction of the IEEE 802.16 webs.

2.6.6 IEEE standard 802.16e-2005

The alteration of the IEEE standard 802.16-2004 is IEEE standard 802.16e-2005. The extension defines the criterion for nomadic endorsers traveling at vehicular velocities. It provides handover map among BSs. Although nomadic functionalities are added into the amendment, fixed SSs can work with the IEEE Std 802.16e-2005 BSs. The set used in the amendment is limited to below 6 GHz licensed sets [ 21 ] .

2.7 OPERATION MODES

The two manners of operation supported by IEEE 802.16 are, Point-to-Multipoint and Mesh manner.

2.7.1 PMP manner

Figure 2.3 shows a web working in PMP manner. An IEEE 802.16 nexus is handled through a BS and a sectorized aerial. Multiple sectors can be handled at the same time. The traffic in PMP manner occurs merely among the BS and the SSs. The signal could be sent to or from the BS. Downlink is the way from the base station to the SSs. Conversely, the way from a subscriber station to the base station is uplink. In a FDD strategy, uplink and downlink signal transmittals are coincident. In a TDD strategy, transmittal clip is divided into uplink and downlink periods. The downlink is normally broadcast. The SSs which have connexions to an aerial sector by agencies of a given frequence channel receive the same signal transmittal [ 12 ] . The uplink bandwidth to the BS is shared by the SSs. Depending on the category of service utilized, the IEEE Std 802.16 defines the bandwidth allotment and petition mechanisms.

2.7.2 Mesh manner

The Mesh manner has been introduced in IEEE 802.16 in add-on to PMP. It allows the IEEE 802.16 nodes to make mesh webs. In mesh web a communication node connects to other nodes. If each node in a web straight connects to every other node, it is called a “fully meshed network” . Otherwise, it is a “partial meshed network” [ 11 ] . The mesh topology is shown in Figure 2.4.

Figure 2.5 shows a web working in Mesh manner. The traffic in Mesh manner can go on from a SS to another SS or other SSs. The Mesh manner allows signal to be routed through SSs, whereas the PMP manner allows signal to be routed merely from the BS or to the BS. That means a node is non merely a SS, but besides a BS [ 11 ] . When a message is sent from the beginning, if a message does non get at its finish, the node forwards it to another neighbour. Choosing the following node depends on every node ‘s routing tabular array.

2.8 SUMMARY of IEEE 802.16

Table 2.2: Summary of IEEE 802.16 Standards

Standard

802.16

802.16-2004

802.16e

Completed

End 2001

802.16a: Jan 2003

802.16-2004: End 2004

Early 2006?

Spectrum

10 to 66 GHz

2.5 – 11 GHz

2.5 – 6 GHz

Channels

Line-of-sight

Non line-of sight

Non line-of-sight

Bit Rate

32 to134 Mbps

up to 75 Mbps

up to 15 Mbps

Transition

QPSK,

16 QAM,

64 QAM

OFDM256, OFDMA, 64 QAM, 16 QAM, QPSK, BPSK

OFDM 256, OFDMA, 64 QAM, 16 QAM, QPSK, BPSK

Mobility

Fixed

Fixed and portable

Mobility, regional roaming

Channel BW

20, 25 or 28 Megahertzs

1.25 to 20 Megahertzs with up to16 logical sub-channels cchannels

1.25 to 20 Megahertzs with up to

16 logical sub- channels

Typical Cell

Radius

2 to 5 Km

5 to 8 Km ( max 50 Km )

2 to 5 Km

2.9 PROTOCOL LAYERS

802.16 IEEE criterion consists of a protocol stack with chiseled interfaces. It works on two beds Common Medium Access Control Layer ( MAC ) of Data Link Layer and Physical Layer [ 5 ] . MAC bed consists of three sub-layers. Service Specific Convergence Sub-layer ( MAC CS ) , the MAC Common Part Sub-layer ( MAC CPS ) and the privateness sub-layer.

The Service Specific Convergence Sub-layer is the sub-layer that permits CS to pass on with higher beds and converts higher-level informations services to MAC layer service flows and connexions. There are two types of CS sub-layer: ATM Convergence Sub-layer which is used for ATM webs and services, and package Convergence Sub-layer which is used for package services like Ethernet, Point to Indicate protocol ( PPP ) , IPv4, IPv6, and practical local country web ( VLAN ) .

The MAC Common Part Sub-layer ( MAC CPS ) is the bosom of the criterion. This sub-layer defines the regulations for connexion direction, bandwidth allotment and mechanism for system entree. Besides uplink programming, bandwidth petition and grant, connexion control, and automatic repetition petition ( ARQ ) maps are defined. In the MAC layer the communicating among the CS and the MAC CPS is done by MAC service Access Point ( MAC SAP ) . Communication is really easy as merely four basic actions can be used: creative activity of connexion, alteration of connexion, omission of connexion and conveyance of informations over the connexion.

The sub-layer among MAC CPS and Physical Layer ( PHY bed ) is Privacy Sub-layer. It is the sub-layer that is accountable for the encoding and decoding of informations that is incoming and go forthing the PHY bed and is besides used for hallmark and procure cardinal exchange.

PHY bed is the bed which is chiefly adaptable to the demands of the protocol. This means that the flexibleness of the protocol permits the interior decorators to do alterations to it refering transition, an illustration is the add-on of the 2-11 GHz set and the OFDM transition in the 802.16a-2003 criterion [ 5 ] . The PHY bed besides supports different frontward mistake corrections ( FEC ) like Reed-Solomon GF ( 256 ) with mutable block size and mistake rectification capablenesss and Block Turbo Codes. Layering of 802.16 protocol is shown in the figure 2.6.

From a security perspective the most important beds in the MAC sub-layer are the MAC Common Part Sub-layer and Privacy Sub-layer. IEEE when refers to “the MAC” by and large means the MAC CPS so from this point when MAC is referred, it implies the MAC CPS [ 3 ] .

2.9.1 MAC bed

The karyon of the criterion is MAC sub-layer. It functions in the similar manner to IEEE 802.11. There are several subscriber Stationss and one Base Station ( BS ) . The BS is seen as the Access Points ( AP ‘s ) in 802.11, while the both criterions are wholly dissimilar in the manner that they use the airwaves. MAC is designed to back up point to multipoint engineering [ 24 ] . On the contrary to 802.11 CSMA/CA strategy, 802.16 brand usage of UL and DL maps to vouch crash free entree. To portion uplink, subscriber Stationss use Time Division Multiple Access ( TDMA ) , whereas base station make usage of TDM. UL and DL agendas are swapped in each frame by agencies of UL-MAP and DL-MAP messages [ 3 ] [ 24 ] .

2.9.1.1 MAC connexions

IEEE 802.16 media entree control is connexion oriented. Each service is mapped to a connexion, and each connexion is identified through 16-bit connexion identifier and might necessitate invariably contracted bandwidth on demand [ 9 ] [ 24 ] . Media entree control layer links can be seen in a manner similar to TCP links. Similar to TCP links, where a computing machine might hold at the same clip tonss of separate active links in diverse ports, in MAC links the endorser station might hold several links to a base station for diverse services such as direction of web or conveyance of user informations ( The direction messages are carried by direction links and where as other traffic, usually user informations is carried by conveyance links. Though the chief differentiation is that in MAC links, each nexus might hold dissimilar parametric quantities for bandwidth, security and precedence. Each nexus is recognized via its connexion identifier that is allotted via the base station [ 24 ] . As links are unidirectional, so bi-directional nexus uses two CIDs. Three CIDs, When a endorser station joins the web, are given to it each with different QoS necessities used by different direction degrees: Basic, Primary Management and Secondary Management links [ 24 ] .

Basic nexus transmits brief, time-critical MAC and radio nexus control ( RLC ) messages. Primary Management nexus conveyances longer, more latency broad messages like enrollment petitions and privateness and cardinal direction messages- messages that are used for hallmark and connexion apparatus [ 24 ] . Secondary Management nexus will allow a peculiar protocol being run at a higher bed to transport standards-based direction messages, for case ( DHCP ) , ( TFTP ) , and Simple Network Management Protocol ( SNMP ) . Extra connexions are served by MAC for other grounds such as to convey the UL and DL transmittal agendas. A connexion identifier might transport traffic for several different upper-layer Sessionss [ 24 ] .

2.9.1.2 MAC message format

Base station MAC and subscriber station MAC barter messages known as Protocol Data Units. The messages comprise of three parts: the fixed length MAC heading, the changeable-length Payload and the Cyclic Redundancy Code. There are two types of MAC heading. The first is the Generic MAC heading ( GMH ) used to transport about all the standard MAC Management messages. The 2nd is the Bandwidth Request Header ( BRH ) , it is sent entirely, with no warhead. Demuring Bandwidth Request PDUs ( with no warhead ) MAC PDUs might keep either MAC direction messages or convergence sub-layer data- MAC Service Data Unit ( MSDU ) . Payload is optional besides. CRC is optional excessively and is used merely when SS petition for it in its QoS parametric quantities [ 24 ] . MSDUs are fragmented and packed within MPDUs which are so transmitted on air.

Transport CID in GMH Payload

GMH

MSDU ( may be packed, fragmented,

Carry an ARQ feedback warhead, or

any combination therefore )

CRC

Transport CID

in GMH Payload

GMH

MAC direction message

CRC

BRH

2.9.1.3 Generic MAC heading format

Figure 2.8 shows the format of the GMH. HT stands for Header Type, this is used to stipulate whether the heading is generic or bandwidth petition. For generic heading HT spot is set to zero. Encoding control ( EC ) spot specifies whether the warhead is encrypted or non. If set to zero specifies that warhead is non encrypted and set to one agencies warhead is encrypted. For generic heading it is set to one. The information sing which direction message is saved in the warhead is contained in Type field. CRC index ( CI ) shows the being of optional CRC at the stoping of MPDU. CI=0 indicates no CRC is appended, CI=1 indicates CRC is appended to the PDU. Encryption cardinal sequence field ensures that BS and SS are synchronized while doing usage of traffic encoding keys and Initializing Vectors ( IV ) . This field is merely important when EC spot is set to1. 11 spot LEN field is used to stipulate the length in bytes of MAC PDU consisting heading and CRC. Connection identifier ( CID ) 16 spot field is used to stipulate which connexion the MPDU is serving. Header cheque sequence ( HCS ) is an 8 spot field used to place mistakes in the heading field.

HT=0 ( 1 )

EC ( 1 )

Type ( 6 )

Rsv ( 1 )

CI ( 1 )

EKS

( 2 )

Rsv ( 1 )

LEN

MSB ( 3 )

LEN ( LSB ) ( 8 )

CID ( MSB ) ( 8 )

CID ( LSB ) ( 8 )

HCS ( 8 )

2.9.1.4 Bandwidth petition PDU

A 6-Byte bandwidth petition heading is transmitted to inquire for the alterations for given features of a connexion. Format of BRH is shown in figure 2.9. The HT spot is set to 1 to demo that the heading is a bandwidth petition. The EC spot is set to 0. The 6-bit type field can get value 0 to demo an incremental bandwidth petition or a value of 1 to demo a corporate petition. The bandwidth petition ( BR ) field shows the figure of uplink bytes of bandwidth being requested. The CID field shows the connexion for which the bandwidth petition is being made. The HCS field is used to place the mistakes in the heading field ( first 5 bytes ) .

HT=1

EC=0

TYPE ( 6 )

BR ( MSB ) ( 8 )

BR ( LSB ) ( 8 )

CID ( MSB ) ( 8 )

CID ( LSB ) ( 8 )

HCS ( 8 )

2.9.2 Privacy sub-layer

The full security of 802.16 prevarications in the privateness sub-layer. It provides entree control and confidentiality of the informations nexus. Following constituents are involved in the security of 802.16: Security Associations ( SA ) , X.509 certifications, Privacy Key Management mandate protocol ( PKM mandate ) , Privacy and Key Management ( PKM ) .

Security Associations ( SA )

Itmaintains the security province of every connexion. 802.16 utilizations two SA, Data SA and Authorization SA. The information SA protects the communicating among SSs and BS. When a new conveyance connexion is created, SS begins a information SA with a create connectionrequest. Multiple CIDs may be served by a individual information SA. When the SS joins the web, automatically a SA is assigned to it for the secondary direction channel. Then each SS has either one SA for uplink and downlink conveyance connexions together, or one SA for uplink conveyance connexions and one for downlink conveyance connexions. Besides if there is a multicast group it requires a SA to portion among group members.

The mandate SA is shared among a BS and a SS. The Authorization Key ( AK ) should be treated by BS and SS as a secret. BS uses the mandate SAs to configure the informations SAs on the SS.

The X.509 Certificates

The X.509 Certificates are used to acknowledge the communication parties. It comprises of the undermentioned Fieldss:

  • X.509 certification format version
  • Certificate consecutive figure.
  • Certificate issuer ‘s signature algorithm Public Key.
  • Cryptography Standard 1-that is, RSA encoding with SHA1 hashing.
  • Certificate issuer.
  • Certificate cogency period.
  • Certificate topic or certification holder ‘s individuality, ( station ‘s MAC reference ) .
  • Subject ‘s public key or certification holder ‘s public key.
  • Signature algorithm identifier
  • Issuer ‘s signature

The standard operates with two certification types: maker certifications and SS certifications. The maker of an 802.16 device is identified by Manufacturer certifications. It could either be issued by a 3rd party or be self-signed. Single SS is identified by SS certifications and capable field contains MAC reference of the SS. SS certifications are normally issued and signed by makers. BS verifies the SS certification by utilizing maker ‘s public key.

The PKM Authorization Protocol

This protocol makes the BS to acknowledge SS. There are three stairss in mandate protocol: two messages are sent from SS to BS and after that one message is sent from BS to SS.

  • Measure 1: A message is sent by SS to BS, that includes a X.509 certification acknowledging SS ‘s maker. BS uses this message so as to do a determination if the peculiar SS is a sure device.
  • Measure 2: A 2nd message is sent by SS without waiting for an reply from BS. The SS ‘s X.509 certification and its public key, the SSs security capablenesss and its SAID ( alone SA identifier ) are contained in this 2nd message. BS make usage of X.509 certifications to cognize if the SS is authorized, and to retrace the replying message BS make usage of SS ‘s public key.
  • Measure 3: Third message is sent by BS when if it determines that SS is authorized, this message initiates a SA among BS and SS. An mandate key ( AK ) is sent to SS that is encrypted with the public key of the SS. SS so additions the mandate to entree the WMAN channel if AK is used decently. 802.16 design supposes that merely BS and SS portion the AK-AK must ne’er be disclosed to another entity.

Privacy and Key Management Protocol

This protocol establishes a information SA among BS and SS. This is accomplished, via two or three messages sent between BS and SS.

  • Measure 1: This measure is non-compulsory and this message is sent merely if BS wishes to coerce rekeying of a information SA or to do a new SA. BS after calculating HMAC ( 1 ) ( hash function-based message hallmark codification ) permits SS to acknowledge disproof.
  • Measure 2: United states secret service petitions SA parametric quantities by directing a message to BS. SS must do usage of the SAID from the mandate protocol SAID list. SS sends a separate 2nd message for each information SA. SS computes HMAC ( 2 ) excessively to allow BS to acknowledge disproof. BS can strongly authenticate SS by HMAC ( 2 ) .
  • Measure 3: BS sends message 3 when if it finds that HMAC ( 2 ) is valid and SAID is surely one of the SS ‘s SA. Message 3 includes the old TEK ( temporal encoding key ) that is used to repeat the active SA, the new TEK is used after the termination of the bing TEK.

2.9.3 Physical bed

Initially IEEE 802.16 criterion supported tonss of physical medium interfaces. In 2001 merely individual bearer transition was supported by the standard 802.16 but now Orthogonal Frequency Division Multiplexing ( OFDM ) is besides supported, which is a multi-carrier transition strategy. There are two OFDM-based manners in 802.16 criterion: OFDM and OFDMA. Depending on distance and noise, these engineerings permit sub-carriers to be modulated ( QPSK, 16-QAM, 64-QAM ) adaptively. The scalability options in OFDMA offer higher efficiency in bandwidth use. Besides in the imploring criterion merely used 10-66 GHz sets, but now 2 to11 Gega Hertz and 10 to 66 Gega Hertz sets are used besides. This has to make with the modularity of the criterion, that permits alterations to go on in the Physical bed with really few fluctuations to the remainder of the protocol [ 24 ] .

In 10 to 66 Gega Hertz 802.16 PHY bed specification, line-of-sight transmittal was an indispensable. Single-carrier transition was chosen for that ground. The air interface in that instance, is known as “Wireless MAN-SC” . Base station sends out TDM signal and SSs assigned with a clip slot serially. Uplink although, is carried by TDMA [ 24 ] . Afterward, another profile was adopted, based on the demand for burst design. This one permits both TDD, in which channel is shared by uplink and downlink but transmittal is non coincident, besides FDD, where different channels are used for uplink and downlink, sometimes at the same time.

The 2 to11 Gega Hertz 802.16 PHY bed specification addresses both the accredited and un-licensed sets. The demand of None Line of Sight operation motivated this design. The two air interface specifications up to now are [ 10 ] Wireless MAN-OFDM which make usage of OFDM with 256-point transform. It is accessed through TDMA. This is mandatory interface for un-licensed sets [ 24 ] . Wireless MAN-OFDMA which make usage of OFDMA with a 2048-point transform. In this system, to offer multiple entree, a subset of the assorted bearers to single receiving systems is addressed.

2.9.3.1 TDD frame format

On air transmittal clip is divided into frames by 802.16 PHY. Every frame is of a fixed length, and is foremost divided into the Downlink Sub-frame and after that the Uplink Sub-frame. Two types of transmittal duplexing are at that place: Time Division Duplexing and Frequency Division Duplexing. In TDD, the full DL sub-frame is sent by BS, that starts with downlink-MAP and uplink-MAP which explain the contents of the downlink and the uplink [ 24 ] ( DL-MAP and UL-MAP are the directories of slot locations )

Preamble

DL- MAP

UL- MAP

Traffic

Burst

Scheme

a

Traffic

Burst

Scheme

Bacillus

Traffic

Burst

Scheme

C

Tx/Rx Gap

Ranging contention

Contention

BW Request contention

Contention

SS a Uplink

Burst

SS B Uplink

Burst

SS c Uplink

Burst

Empties

Tx/Rx Gap

Downlink Sub-frame Adaptive Uplink Sub-frame

Figure. 2.10: TDD frame format [ 10 ]

During the downlink, BS informs SS when it is planned to travel transmittal explosion strategy. During UL, every SS is informed by the agenda that when it will be permitted sole usage of the transmittal spectrum [ 24 ] . In FDD, while DL-MAP and UL-MAP still schedule the transmittals, UL and DL transmittals occur at the same time, on dissimilar frequences.

Downlink Sub-frame

In downlink sub-frame, foremost there is a preamble. The map of this is to ease the SS to synchronise to the frame, because it may hold lost synchronism towards the terminal of the preceding frame. Following this preamble there is DL-MAP and UL-MAP. The entree to the downlink information is defined by the DL-MAP. It tells every United states secret service about timings when alterations in transition and cryptography will take topographic point. The subscriber station listens to all the information it is able to until it reaches information for itself. The entree to the uplink channel is defined by the UL-MAP. In this, a explosion profile and a clip for every SS are specified to convey their informations. The BS transmits its TDM information following this DL-MAP and UL-MAP. The hardiness of the transmitted information is decreased in footings of the explosion profile. The ground for this is so that a SS does non drop synchronism.

Uplink Sub-frame

In Uplink sub-frame foremost there are runing contention chances. This is to allow any SS, which have non antecedently registered to direct a ranging petition message. The map of this message for a SS, which is non registered, is to find web hold and to discourse a explosion profile or power alteration. Since this is the first communicating this SS is holding with the BS, there are no pre-defined uplink chances. All SS ‘s, with no such uplink chances, transmit their scope petition in this initial runing contention chance clip. There is BW Request Contention following this runing contention chance, which is used to direct BW petition message, and following this the SSs transmit their informations through TDMA, in the clip slot given to them by the UL-MAP.

2.10 ESTABLISHING a Connection

Upon installing, in order to observe an operating channel, SS begins to scan its frequence. After observing the channel SS may be programmed to register with a certain BS it wants to fall in ; SS tries to synchronise to the downlink transmittal. Then SS will wait for the sporadically broadcast downlink channel form ( DCD ) and uplink channel form ( UCD ) messages to larn the transition and the FEC strategies used on the bearer.

After larning what parameters it must utilize for initial runing transmittal, SS will scan the UL-MAP to acquire an chance to execute the ranging since it is really indispensable to state SS about when to direct the ranging, if assorted SS would seek to fall in the web at the same clip, that would hold an highly bad consequence on the web efficiency. SS will try to direct the petition ( RNG-REQ ) with minimal power, and if it does n’t happen any answer, so will seek with progressively higher transmittal power. BS replies to SS ( RNG-RSP ) with a timing progress and a power accommodation. Furthermore BS uses this message to state SS about the Basic and the Primary Management CIDs [ 10 ] .

After finding the timing progresss of the SS transmittals, SS and BS maintain on interchanging RNG-REQ and RNG-RSP until a satisfactory wireless nexus is established. The basic system capablenesss can be negotiated by utilizing the direction messages over the direction connexions.

The following measure to come in the web is SS hallmark and Registration. PKM protocol is used for this ground. Certificates and RSA public key methods are used by PKM to authenticate SS to a BS. Once the SS is successfully authenticated, it will register with the web. After that it will put up the secondary Management connexion and it will be assigned to its Secondary Management CID. To have criterion based secondary messages for different services this CID so is used for the SS. Dynamic Host Configuration Protocol ( DHCP ) is one of those. Through DHCP so, SS is attained with an IP reference and besides is given the reference of the Trivial File Transfer Protocol ( TFTP ) waiter from which SS can inquire for a constellation file. The web clip of twenty-four hours through Internet Time Protocol is the last portion of the SS low-level formatting.

Chapter 3

WiMAX as a METRO-ACCESS DEPLOYMENT & A ; its POTENTIAL FEATURES

3.1 Use Model

WiMAX being a planetary enfranchisement addresses interoperability across IEEE 802.16 standards-based merchandises. The two use theoretical accounts addressed by the IEEE 802.16 criterion with precise alterations are:

  • Fixed
  • Portable

3.1.1 Fixed

The IEEE standard 802.16-2004 ( that modifies and reinstates IEEE 802.16a and 802.16REVd versions ) is intended for static-access use theoretical accounts. This criterion might be known as “fixed wireless” since at the endorser ‘s site it uses a mounted aerial. Alike to a satellite Television dish, the aerial is set up on a roof or mast. The indoor installing is besides addressed by the IEEE 802.16-2004, but it is non as lasting in as out-of-door installings. The wireless solution for inactive broadband Internet entree is the standard 802.16-2004, supplying an interoperable, last mile carrier-class solution. For inactive entree, the Intel WiMAX solution works in accredited 2.5-GHz, 3.5-GHz and un-licensed 5.8-GHz sets. The overseas telegram modem, digital endorser lines of any type ( xDSL ) , transmit/exchange ( Tx/Ex ) circuits and optical bearer degree ( OC-x ) circuits [ 11 ] can be substituted with this radio engineering [ 25 ] .

3.1.2 Portable

The standard IEEE 802.16e is a alteration to the 802.16- 2004 base specification. The nomadic market with adding up portability and the installation for nomadic users with IEEE 802.16e arrangers to acquire connected straight to the WiMAX web, is its mark. OFDMA is used by the 802.16e criterion, that is correspondent to OFDM in that bearers are divided into many sub-carriers. OFDMA, though, is a measure progress where many sub-carriers are grouped into sub-channels. The full sub-channels contained in bearer infinite may be used by a individual user or SS for transmittal, or several users may convey with every one devising usage of a fraction of the entire figure of sub-channels at the same clip. The standard IEEE 802.16-2004 makes better last-mile bringing in legion cardinal characteristics:

  • Multi-path intervention
  • Delay spread
  • Robustness

The multi-path intervention and hold spread enhance public presentation in state of affairss When there is no consecutive LOS way among the BS and the SS. The MAC direction messages contained in 802.16 specification license the BS to ask the SS, but a definite sum of clip hold is involved at that place. TDD is used by WiMAX merchandises working in un-licensed sets, merchandises working in accredited sets will utilize either TDD or FDD [ 25 ] .

3.2 RANGE and SCALABILITY

The standard 802.16-2004 is dependent on a grant-request entree protocol that does n’t allow informations hits, as is in contention-based entree used in 802.11 and, accordingly, the available bandwidth is utilized more efficaciously. The BS synchronizes full communicating [ 25 ] . Further features of the standard 802.16-2004 comprise:

Improved user connectivity

The 802.16-2004 criterion maintains more users connected due to its flexible channel breadths and adaptative transition. Since it uses channels narrower alternatively of fixed 20-MHz channels used in 802.11, lower data-rate endorsers can be served by the 802.16-2004 criterion without misapplying bandwidth. When endorsers come across noisy conditions or low signal strength, they might be dropped but the adaptative transition strategy keeps them connected.

Higher quality of service

This criterion besides facilitates WISPs to vouch QoS for clients who need it and to orient service degrees to run into different client demands. For illustration, the 802.16-2004 criterion can assure high bandwidth to concern clients or low latency for voice and picture applications, whereas residential Internet surfboarders can merely be provided with best-effort and lower-cost service.

Full support for WMAN service

In contrast to last-mile executions based on the 802.11g criterion, 802.16-2004 is capable of back uping more users and present faster information rates at longer distances.

Robust carrier-class operation

The criterion was intended for carrier-class operation. As more users join, they have to portion the cumulative bandwidth and their single throughput reduces linearly. The decrease, nevertheless, is non every bit dramatic as experient under 802.11. This ability is termed “efficient multiple access.”

3.3 FLEXIBLE CHANNEL BANDWIDTH

When endorser moves by walking or driving in a auto, the distance among a endorser and the base station ( or AP ) increases, so it becomes more hard for that endorser to convey successfully at a given power degree back to the base station. For power-sensitive devices such as laptop computing machines or hand-held devices, if the channel bandwidth is wide, so it ‘s non possible for them to convey to the base station over long distances. To do possible transmittal over longer scopes and to different types of endorser devices, 802.16 has elastic channel bandwidths between 1.5 and 20 MHz. In add-on, this flexibleness of channel bandwidth is besides of import for cell planning, peculiarly in the accredited spectrum. For scalability, an operator with 14 MHz of accessible spectrum, may hold multiple sectors ( transmit/receive braces ) on the same base station by spliting that spectrum into four sectors of 3.5 MHz. With a dedicated aerial, each sector can supply users with more throughput over longer scopes as compared to an omni-directional aerial.

3.4 SMART ANTENNA SUPPORT

Smart antennas heighten the spectral denseness ( the figure of spots communicated over a given channel in a given clip ) and besides hike the signal-to-noise ratio for both Wi-Fi and WiMAX solutions. Because of public presentation and engineering, several adaptative smart aerial types supported by the 802.16-2004 criterion include [ 21 ] :

Receive spacial diverseness aerials

Involves more than one aerial having the signal. To map expeditiously, the aerials have to be placed no less than half a wavelength apart. Note that wavelength can be found by taking the opposite of the frequence. Keeping this smallest distance makes certain that the aerials are incoherent, that is, additive/subtractive effects of signals geting by agencies of multiple waies impact on them otherwise.

Simple diverseness aerials

The signal strength of the multiple ( two or more ) aerial attached is detected and that aerial is switched into the receiving system. The possibility of acquiring a strong signal will be higher if choice is from more incoherent aerial.

Beam-steering aerials

The antenna array form is shaped to bring forth high additions in the utile signal way or notches that reject intervention. High antenna gain enhances the signal, noise and rate. The intervention is attenuated out of the chief beam with directional forms. If multi-path constituents arrive with a adequate angular separation, selective attenuation can be alleviated.

Beam-forming aerials

Permit the country to be divided around a base station into sectors, leting extra frequence reuse between sectors. The figure of sectors can be every bit few as four to every bit many as 24. Base Stationss which smartly manage sectors have been used for a long clip in mobile-service base Stationss.

3.5 BNEFITS and CHALLENGES

The WiMAX footing benefits are:

  • Built-in QoS
  • High public presentation
  • Standards-based
  • Smart antenna support [ 25 ]

For WiMAX the most of import challenge is that it ‘s a fresh engineering with emerging support.

3.6 FEATURES

The WiMAX is designed with assorted purposes in head. Below is the sum-up of possible characteristics of WiMAX:

Flexible Architecture

Numerous system architectures are supported by WiMAX, dwelling P2P, P2MP, and ubiquitous coverage. The clip slot for every SS are scheduled through WiMAX MAC to back up Point-to-Multipoint and omnipresent service. When there is merely one SS in the web, the WiMAX BS uses Point-to-Point service to pass on with the SS. In P2P constellation to cover longer distances a BS might utilize a narrower beam aerial.

High Security

WiMAX encrypts the links among the base station and the endorser station to supply privateness ( loath to listen ining ) and safety across the broadband radio nexus to the users. With security operators can be protected loath to stealing of service.

WiMAX QOS

WiMAX is dynamically optimized for transporting mix of traffic. WiMaX supports four service types: UGS, rtPS, nrtPS, BE Services.

Quick Deployment

WiMAX needs small or no external works building as compared with the deployment of wired solutions, For illustration, delving to back up the trenching of overseas telegrams is non needed. Operators do non hold to subject farther applications to the Government that have acquired licences to utilize one of the accredited sets, or that wish to utilize one of the unaccredited sets. Once the installing of aerial and equipment is complete and they are powered, WiMAX is ready for service. In most instances, deployment of WiMAX web can be deployed with in hours, as compared to other solutions that take months for deployment.

Multi-Level Service

The QoS provisioning is by and large based on the Service Level Agreement ( SLA ) among the service supplier and the end-user.

Interoperability

WiMAX is based on international, vendor-neutral criterions, which facilitate end-users to go and utilize their SS at different locations, or with different service suppliers. Interoperability protects the initial investing of an operator as it can take equipment from diverse equipment sellers, and it will protract to convey the costs of equipment down as a consequence of mass acceptance.

Portability

Like current cellular systems, one time the WiMAX SS is powered up, it recognizes itself, finds out the features of the nexus with the BS, provided that the SS is registered in the system database, and so its transmittal features are negotiated by it consequently.

Mobility

To back up mobility, cardinal characteristics have been added in IEEE 802.16e amendment. The OFDM and OFDMA physical beds have been improved to back up devices and services in a nomadic environment. The criterion has familial OFDM ‘s better NLOS ( Non-Line Of Sight ) public presentation and multipath-resistant operation, so it is extremely appropriate for the nomadic environment.

Cost-efficient

The costs of the criterion will drive down well due to mass acceptance of the criterion, and the usage of low-cost, mass-produced chipsets, and the eventful competitory pricing will show important cost nest eggs for service suppliers and end-users.

Wider Coverage

Multiple transition degrees are supported by WiMAX including BPSK, QPSK, 16-QAM, and 64-QAM. WiMAX systems cover big geographic country when outfitted with a high-power amplifier and working with a low-level transition ( BPSK or QPSK ) and when the way among the BS and the SS is unhampered.

High Capacity

End-users can be provided important bandwidth by doing usage of higher transition ( 64-QAM ) and channel bandwidth from ( 1.25MHZ to 20 MHz ) .

3.7 USAGE SCENARIOS

WiMAX engineering will overhaul the manner we communicate. The people who are extremely nomadic are provided freedom and will remain connected with voice, informations and picture services. The WiMAX criterion addresses a big scope of applications and use scenarios which are grouped into two wide classs, private webs and public webs.

3.7.1 Private webs

Single organisation, establishment or concern utilizations private webs to supply dedicated communicating links for the secure and dependable transportation of voice, informations and picture. High precedence is by and large given to quick and easy deployment, and constellations are typically Point-to-Point or Point-to-Multipoint [ 21 ] .

3.7.1.1 Cellular backhaul

The cellular services market is going increasingly competitory. For cellular operators to remain in the concern, they must look for ways to take down operating costs. Backhaul costs for cellular operators represent a considerable part of their recurring costs. WiMAX can supply Point-to-Point links of up to 30 stat mis ( 50 kilometer ) , with informations rates capable of back uping multiple E1/T1s. WiMAX equipment can therefore be used by cellular operators for backhauling Base Station traffic to their Network Operation and Switching Centers, as shown in figure 3.3..

The constitutional QoS property of WiMAX is extremely suited for cellular traffic which is a mix of voice and informations. Backhaul installations leased from local telephone companies can be excessively expensive, and put ining a fiber solution, can be both dearly-won and drawn-out. For supplying cellular backhaul, wired solutions are non frequently cost-efficient in rural or suburban countries, and most versions of DSL and overseas telegram engineering can non show the needed bandwidth, peculiarly for backhauling 3G webs.

3.7.1.2 Wireless service supplier backhaul

WiMAX equipment is used by wireless Service Providers ( WSPs ) for backhauling traffic from BS in their entree webs, as shown in figure 3.4.

WiFi, WiMAX or some proprietary wireless entree engineering might be used as an entree web. As WSPs usually proffer voice, informations and picture, the WiMAX constitutional QoS property will help in prioritizing and optimising the backhauled traffic. The on the job outgo are raised for engaging backhaul services from the local telephone company, and deploying a fibre web can be improbably expensive and entails considerable long clip. Furthermore, in countrified and suburban countries, fibre, DSL and overseas telegrams are non money-making, and the capacity necessary for these webs might non be offered by DSL and overseas telegram engineerings.

3.7.1.3 Banking webs

The subdivisions and ATM sites of big Bankss transporting voice, informations and picture traffic can be connected to their regional office through a private WiMAX web as shown in figure 3.5. These Bankss require high safety and bandwidth to pull off the traffic as they are normally spread over a big country.

To support against unsought break and direction of sensitive banking traffic WiMAX information encoding offers superb link security. Due to big coverage and high capacity, a immense no: of variously situated subdivision offices and ATM sites can be linked to the bank ‘s regional office.

3.7.1.4 Education webs

School board office can link the schools with their office by doing usage of Private WiMAX web as shown in figure 3.6.

Using QoS, the complete scope of communicating necessities, consisting telephony voice, runing informations ( for illustration records of pupils ) , email, Internet and intranet entree ( informations ) , and distance instruction ( picture ) can be delivered by the instruction webs based on WiMAX, among the school board office and all of the schools in the scope, and among the schools themselves [ 26 ] .

3.7.2 Public webs

In public web, resources are accessed and shared by both concerns and private persons. In Public networks the users place is neither predictable nor inactive so they normally need a cost-efficient agencies of supplying ever-present coverage. Voice and informations communicating are the major applications of public webs, while video communicating is going more and more popular. As several users portion the web, security is a critical demand. These concerns are addressed by informations encoding and built-in VLAN support. Quite a few public web usage scenarios are discussed below [ 21 ] .

3.7.2.1 Wireless service supplier entree web

WiMAX webs are used by Wireless Service Providers to offer connectivity to both lodging ( voice, informations and picture ) and concern ( mainly voice and Internet ) [ 26 ] clients, as shown in figure 3.7.

3.7.2.2 Rural connectivity

WiMAX webs are used by Service suppliers to convey service to underserved markets in rural countries and the suburban outer borders of metropoliss, as shown in figure 3.8.

In many developing states and underserved countries of developed states, the bringing of rural connectivity is critical, where small or no substructure is available. Rural connectivity brings much-needed voice telephone and Internet service. Because of the drawn-out coverage of WiMAX solution, it is a greatly more cost-efficient solution as compared to wired engineering in countries with lower population densenesss. WiMAX solutions can be installed quickly, supplying communicating links to these underserved countries, supplying a more safe environment, and assisting to acquire better their local economic systems.

Chapter 4

QUALITY of SERVICE in IEEE 802.16

4.1 QUALITY of SERVICE ( QoS )

QoS refers to the web ‘s capableness to offer improved service to elected web traffic over several engineerings. The purpose of QoS engineerings is to prioritise ( consisting committed bandwidth to pull off jitter and hold ) assorted real-time and synergistic traffic, while guaranting that in making so the other traffic does n’t halt working [ 25 ] . In licensed-exempt sets deployment is by and large unfastened to everyone, so they can be capable to QoS issues. However, there are advancements in the associated criterions and engineerings, that aid relieve injuries with licensed-exempt sets, for illustration multi-path intervention [ 14 ] .

On the Internet and in other webs, the thought behind QoS is to cipher, enhance, and, to some grade, assure the transmittal rates, mistake rates, and other features in progress. QoS is of peculiar concern for the nonstop transmittal of high-bandwidth. The radio engineering ‘s capableness to expeditiously convey high value services for illustration voice and picture is determined by Quality of Service. Latency, jitter, package loss, burden and throughput are the main disparagers to good QoS.

WiMAX nowadayss lower hold across the radio extent. There are many sellers holding merchandises with hold less than 10ms from BS to client premises equipment and frailty versa. Keeping that in head, hold have to be calculated end-to-end. VoIP, for case, is highly vulnerable to detain. If hold go beyond 150ms for illustration, the conversation quality starts draging. At or beyond 200ms, conversation might be meaningless for several viewing audiences.

The figure 4.1 shows that delay on the web ‘s radio subdivision is smallest compared to that on web ‘s wired subdivision.

4.2 IEEE 802.16 QoS MECHANISMS at PHY LAYER

The 802.16 criterion incorporates legion QoS mechanisms at the PHY bed, for illustration Time Division Duplex ( TDD ) , Frequency Division Duplex ( FDD ) and Orthogonal Frequency Division Multiplexing ( OFDM ) . All can help in supplying QoS. TDD can dynamically administer uplink and downlink bandwidth, based on their demands [ 19 ] . For case, more bandwidth can be assigned to uplink traffic when it is more, and when there is less uplink traffic bandwidth can be taken off. This is illustrated in Figure 4.2. Every 802.16 TDD frame is one downlink sub-frame and one uplink sub-frame, separated by a guard slot. 802.16 adaptively assigns the figure of slots for each, based on their bandwidth demands.

Guard Slot

In FDD, transmittal occurs on different sub-bands, and hence there is less opportunity of interfere among Stationss. This permits for even more bandwidth distribution flexibleness. And, OFDM offers better spectral efficiency, and alleviates intervention with its tighter beam breadth and its distribution of informations across different frequences.

There are a twosome of QoS attributes that are specific to OFDM. Forward Error Correction ( FEC ) builds redundancy into the transmittal by retroflexing a few of the information spots, so bits that are lost or in mistake can be repaired at the having terminal. with no FEC, mistake rectification would affect full frames to be retransmitted, ensuing in latency and hapless QoS. The other manner OFDM assists with QoS is with interleaving [ 19 ] . As OFDM make usage of multiple sub-carriers, a fraction of each information spot can be auto

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