Praise for Fundamentals of WiMAX

9.2 MAC PDU Construction and Transmission 313SDU 1 SDU 21 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17ARQ BlockFragment 1 Fragment 2 Fragment 1 Fragment 2Header Fragment 1 Header Fragment 2 Fragment 1 Header Fragment 2PDU 1 PDU 2 PDU 3Downlink or Uplink BurstFigure 9.4 Segmentation and concatenation of SDUs in MAC PDUsindicates that the ARQ block has been received without errors. A cumulative ACK for a givenBSN, on the other hand, indicates that all blocks with sequence numbers less than or equal tothe BSN have been received without error.Each MAC PDU consists of a header followed by a payload and a cyclic redundancy check(CRC). 3 The CRC is based on IEEE 802.3 and is calculated on the entire MAC PDU; the headerand the payload. WiMAX has two types of PDUs, each with a very different header structure, asshown in Figure 9.5.1. The generic MAC PDU is used for carrying data and MAC-layer signaling messages. Ageneric MAC PDU starts with a generic header whose structure is shown in Figure 9.5 asfollowed by a payload and a CRC. The various information elements in the header of ageneric MAC PDU are shown in Table 9.2.2. The bandwidth request PDU is used by the MS to indicate to the BS that more bandwidthis required in the UL, due to pending data transmission. A bandwidth request PDU consistsonly of a bandwidth-request header, with no payload or CRC. The various informationelements of a bandwidth request header are provided in Table 9.3.3. The CRC is mandatory for the SCa, OFDM, and OFDMA PHY. In the case of SC PHY, the CRCis optional.