C PDU contains multiple ARQ blocks. The number of ARQ blocks in a MAC PDU is equal to the number of ARQ connections multiplexed in the MAC PDU. The ARQ blocks of a connection are sequentially numbered. The ARQ block Sequence Number (SN) is included in the MAC PDU using FPEH or MEH headers. The original MAC SDU ordering is maintained [2]. In the legacy system, the size of the ARQ blocks is fixed and the length of the ARQ blocks is specified by the serving BS for each connection and signaled through MAC management messages [1]. In that case, if the length of the MAC SDU is not an integer multiple of ARQ block size, the last ARQ block may be padded. The MAC SDU partitioning into ARQ blocks remains in effect until all ARQ blocks are received and acknowledged by the receiver [1]. As shown in Figure 7-3, if the initial transmission of an ARQ block fails, a re-transmission is scheduled with or without rearrangement. In the case of ARQ block re-transmission without MAC SDU 1 MAC SDU 2 MAC SDU 3 MAC SDUs ARQ Block 1 ARQ Block 2 ARQ Blocks Sub-block Sub-block Sub-block Sub-block Sub-block Sub-block Sub-block ARQ Block1 ARQ Block2 ARQ Sub-blocks Block 1 Block 1 Block 1 Block 2 Block 2 Block 2 Block 2 MAC PDU 1 MAC PDU 2 Sub Fragment of olock Sub-block Sub-blo2k Eragmentof ARQb-block Sub-block MAC PDUs SN 1) ARQ Block 1ARQ SN 2) Block ARQ Block 2RQ (1st Transmissions) Block 1 Block 1 Block 1 Block 2 Block 2 Block 2 Block 2 Successful Transmission Failed Transmission MAC PDU 3 MAC PDU 4 REPEH Sub-block Sub-block Sub-block (SN 2 Sub-block Sub-block (SN 2. SSN 1) SSN 3Y Block 1 Block 2 Block 2 Block 2 Block 2 Re-transmission of MAC PDU 2 with Rearrangement MAC PDU 3 Sub-block Sub-blo2nd Fragment of ARQb-block Sub-block (SN 2) ARCBlock 1 +ARQ Block 2RQ Block 1 Block 2 Block 2 Block 2 Block 2 Re-transmission of MAC PDU 2 without Rearrangement FIGURE 7-3 ARQ block initial transmission and re-transmission [2] CHAPTER 7 The IEEE 802. 16m MAC CPS (Part II) rearrangement, the MAC PDU contains the same ARQ block and corresponding fragm