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Tham khảo tài liệu 'advanced transmission techniques in wimax part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Hybrid ARQ Utilizing Lower Rate Retransmission over MIMO Wireless Systems 141 multiplication of hh H SMNolj with Hh takes eight CMLs and finally hhH SMNolj Hhy needs further four CMLs. Hence there are 1344 CMLs in total. To recapitulate our proposed scheme reduces the complexity by about 50 and 70 as compared to VSTBC-MRC with SLC and soft LMMSE with BLC respectively. 5. Lower Rate Retransmission LRR combined with Modulation Step Up LRRMSU scheme There are several pros of the LRR scheme such as 1. a robust retransmission because the inter-stream interference is reduced 2. the transmitter side acquires additional transmit power gain for each retransmitted stream 3. frequency and spatial diversity is gained because different resource allocation will be automatically guaranteed. However one possible cons the total retransmitted bits will be reduced as compare to number of bits in initial transmission might degrade its performance in high coding rate scenarios. To overcome this deficiency higher order modulation or called modulation step up is introduced and combined with the LRR scheme in Figure 8. In the initial transmission the transmission mode operates with 4 transmission antennae with QPSK in each stream. In retransmission the number of transmission antennae is reduced to 3 but the modulation order is step up to 16 QAM. Therefore we keep the number of retransmission bits very close to that of traditional scheme. Fig. 8. LRRMSU retransmission scheme 142 Advanced Transmission Techniques in WiMAX 6. Numerical results In order to verify the superiority of the proposed scheme the simulation based on a low correlation MIMO model WiMAX 2007 with Mt Mr 2 is undertaken here. In particular we show two examples of comparison in this paper VSTBC in SLC v.s. SFBC in BLC and SFBC in BLC v.s. SM in BLC. The delay profile of each path is evaluated under ITU-R ITU-R 2000 Pedestrian Type-B 3km hr PB3 or Vehicular Type-A 60km hr VA60 . Furthermore PUSC with 10Mhz bandwidth is .