overview of wimax

7/30/2019 Overview of Wimax

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WiMAX/802.16

(Overview)


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Evolution of Wireless Broadband.1.Wireless Local Loop system (WLL).

First application of wireless: Alternative for Voice telephony.

Ex: DECT, CDMA.Internet was commercialized in 1993.

WLL systems had to offer additional value to be competitive.

few hundred of kilobits per second data rate in 900Mhz,

1900Mhz, 2.4Ghz.

2. First Generation Broadband system.DSL and Cable modem began to deployed.

Multichannel Multipoint Distribution Services (MMDS) band

at 2.5Ghz.

This enabled LOS coverage.

3. Second Generation Broadband System.

NLOS coverage using OFDM, CDMA and multichannelantenna processing.


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4. Emergence of Standards - Based technology .In 1998,IEEE formed a group called 802.16 to develop a

standard for WMAN.

Focused on developing 10Ghz to 66Ghz band.Standard approved in December 2001.

This standard (Wireless MAN-SC), specified a physical layer

that used single-carrier modulation techniques AND a Media

Access Control (MAC) layer with a burst time division

multiplexing (TDM) structure that supported both Frequency

Division Duplexing(FDD) and Time Division Duplexing(TDD).

After that, standard work on extending it in the 2Ghz to

11Ghz and IEEE 802.16a, was completed in 2003. this enabled

NLOS coverage also.

Further revisions to 802.16a made and completed in

2004.this revised standard ,IEEE 802.16-2004 replaces 802.16,

802.16a-d.


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In order to develop interoperable solutions using the 802.16

family of standards, the scope of the standard had to be

reduced by establishing consensus on what options of the

standard to implement and test for interoperability.

The Worldwide Interoperable for Microwave Access

(WIMAX) forum was formed to solve this problem and to

promote solutions based on the IEEE 802.16 standards.

NOTE:

WiFi based on the 802.11 family of standards and primarily

a local are networking (LAN) technology designed to provide

in-building Broadband coverage.


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Overview Of Wimax


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Protocol Layers and topologies.802.16 standard applies the OSI seven layer model.

In 802 standard Data Link layer split in to two sub layers.


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In Wimax/802.16 only first two layers defined.

MAC layer

PHYsical layer

The MAC Layer is itself made of three sub layers.

Convergence sublayer (CS)

Common part sublayer (CPS)

Security Sublayer

PHYsical Layer :In 802.16 standard the MAC layer can be

used with OFDM PHY or OFDMA PHY layer.


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Wimax topologies.Point to Multipoint (PMP) topology.

traffic may take place only between a BS and its SSs


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Mesh topology/Mesh mode.

Traffic can be routed through other SSs. Mesh topologyis not yet part of a WiMAX certification profile


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Wimax PHYsical Layer.

Wimax PHYsical Layer based on OFDM and OFDMA.

Wimax/802.16 use digital modulation.Four modulations are supported by the IEEE 802.16 standard:

BPSK, QPSK, 16-QAM and 64-QAM.


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Generation of OFDM signal (simplified)


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Cyclic prefix insertion in an OFDM symbol

TG = Guard time,

Ts = OFDM symbol time,Td = Data duration,

G = T G/T d


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802.16-2004 using following parameters for single carrier.Number of Orthogonal subcarriers (N):256

Number of used Orthogonal subcarriers (N used ):192

Number of Pilot subcarriers:8

Number of Left & Right guard subcarriers:55

Direct Current (DC), null subscribers:1

Max. Data Rate = number of uncoded bits per symbol

OFDM symbol duration


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Wimax MAC Layer.


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MAC layer consist with three sublayers.

Service Specific Convergence Sublayer(CS) is the Top sublayer of

the MAC Layer in WiMAX/802.16

CS accepts higher-layer PDUs from the higher layers and transmitsthem to the MAC CPS.

Payload Header Suppression (PHS), Classifying and mapping the

MSDUs into appropriate CIDs (Connection IDentifier) also done by

the CS .

The Common Part Sublayer (CPS) resides in the middle of the MAC

layer

Bandwidth allocation, connection establishment, maintenance of

the connection between the two sides are functions of CPS.

Security Sublayer providing authentication, secure key exchange,

encryption and integrity control


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Classification and Mapping based on two fundamental concepts. Connection:

MAC Level connection between a BS and an MS or inversly.

unidirectional mapping between a BS and an SS MAC peers

for the purpose of transporting a service flow's traffic.A

connection is identified by a CID (Connection IDentifier),

an information coded on 16 bits

Service flow:

A Service Flow (SF) is a MAC transport service that

provides unidirectional transport of packets on the

uplink or on the downlink. A service flow is identifiedby a 32-bit SFID (Service Flow IDentifier).


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Service flow allocation


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Classification & Mapping;

A classifier is a set of matching criteria applied to each packet

entering the WiMAX/802.16 network.


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QoS ParametersScheduling service type:BE (default), nrPS, rtPS and UGS

Traffic priority:The value of this parameter specifies the priority

assigned to a service flow

Maximum sustained traffic rate: peak information rate of the

service

Maximum traffic burst: maximum burst size that is accommodated

for the service

Minimum reserved traffic rate: minimum rate reserved for this

service flow

Tolerated jitter: maximum delay variation (jitter) for the

connection


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Maximum latency: maximum latency between the reception of

a packet by the BS or SS on its network interface and the

forwarding of the packet to its RF interface and the forwardingof the packet to its RF interface.

Fixed-length versus variable-length SDU indicator:The value of

this parameter specifies whether the SDUs on the service flow

are of a fixed length or variable length

SDU size: length of the SDU for a fixed-length SDU service flow

overview of wimax

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