Praise for Fundamentals of WiMAX

2.3 WiMAX Physical Layer 45OFDM Symbol Number (time)DL-MAPUL-MAP (Contd.)DL Burst #2UL Burst #1UL Burst #2DL SubframeDL-PHY PDU CR CBRFrameUL SubframeUL-PHYPDU. . .UL PHYPDUS u b c a rrie rs (f req u en c y )Prea mbleDL-MAPUL-MAPDLBurst#1DLBurst#3DL Burst #4DL Burst #5UL Burst #3UL Burst #4UL Burst #5RangingPreamble FCHDLFPDL Burst#1DL-MAP,UL-MAP,DCD, UCD. . .MAC PDUDL Burst#nMACPDUMACHeaderCR: Contention RegionCBR: Contention for Bandwidth RequestPreambleMSDUUL BurstMACPDUPADCRCDownlink Subframe Uplink SubframeGuardFigure 2.1 A sample TDD frame structure for mobile WiMAXWiMAX is quite flexible in terms of how multiple users and packets are multiplexed on asingle frame. A single downlink frame may contain multiple bursts of varying size and type carryingdata for several users. The frame size is also variable on a frame-by-frame basis from 2 msto 20 ms, and each burst can contain multiple concatenated fixed-size or variable-size packets orfragments of packets received from the higher layers. At least initially, however, all WiMAXequipment will support only 5 ms frames.The uplink subframe is made up of several uplink bursts from different users. A portion ofthe uplink subframe is set aside for contention-based access that is used for a variety of purposes.This subframe is used mainly as a ranging channel to perform closed-loop frequency,time, and power adjustments during network entry as well as periodically afterward. The rangingchannel may also be used by subscriber stations or mobile stations (SS/MS) 7 to make uplinkbandwidth requests. In addition, best-effort data may be sent on this contention-based channel,particularly when the amount of data to send is too small to justify requesting a dedicated channel.Besides the ranging channel and traffic bursts, the uplink subframe has a channel-quality7. The subscriber terminal mobile station (MS) is mobile WiMAX, and subscriber station (SS) isfixed WiMAX. Henceforth, for simplicity, we use MS to denote both.