WiMAX-Physical (PHY) Layer

 WiMAX-Physical (PHY) Layer:

In order to support duplexing, WiMAX adapted a burst design that allows Time Division Duplexing (TDD) and Frequency Division Duplexing (FDD). 

In TDD the uplink and downlink share a channel but do not simultaneously transmit. In FDD the uplink and downlink operate on different channels and sometimes simultaneously. Half-duplex FDD subscribers can also be accommodated. The TDD and FDD duplexing support addresses the varying wore worldwide regulations.

Must Read>> WiMAX Technology: Principles and Layers

WiMAX-PHY layer specification has been standardized keeping in view the 10-66 GHz (LOS) and 2-11 GHz (NLOS) bands. The 2-11 GHz band specification is given in the IEEE 802.16a standard.

Three types of air interfaces are supported in this band. They are: 

  1. WirelessMAN SC2: It uses a single carrier modulation format. It is to support existing networks and protocols.
  2. WirelessMAN OFDM: It uses Orthogonal Frequency Division Multiplexing with 256 point transform. Access is by TDMA. This air interface is mandatory for license-exempt bands.
  3. WirelessMAN OFDMA: It uses Orthogonal Frequency Division Multiplexing with a 2048 point transform. In this system, multiple access is provided by addressing a subset of the multiple carriers to individual receivers.

Because the WiMAX-physical layer is quite flexible, data rate performance varies based on the operating parameters. Parameters that have a significant impact on the physical layer data rate are channel bandwidth and the modulation and coding scheme used. Other parameters, such as the number of subchannels, OFDM guard time, and oversampling rate, also have an impact. 

Following is the PHY layer data rate at various channel bandwidths, as well as modulation and coding schemes.

WiMAX-Physical (PHY) Layer

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