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Tham khảo tài liệu 'advanced transmission techniques in wimax part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 116 Advanced Transmission Techniques in WiMAX OFDMA Air Interface and System Level configuration Subcarrier Permutation Distributed PUSC and Contiguous Band AMC FFT length CP 2048 12.5 of used subcarriers 1728 Modulation 4 16 64 -QAM Channel coding1 Turbo coding with rates 1 3 1 2 2 3 Channel model Rayleigh and ITU Pedestrian A Channel estimation CQI Ideal without any delay Frame duration Tftame 5ms DL UL rate 2 1 OFDM symbols in the DL 30 Number of transmit antennas M 1 2 4 Number of receive antennas N 1 2 4 MIMO detector MMSE Rate spectral efficiency 2 4 8 bits per channel use bpcu Table 1. TACS evaluation framework system parameters where for each realization a tile or a subchannel specified in each analysis is transmitted. In case of Partial Usage Subcarrier permutation PUSC the tile is formed by 4 subcarriers and 3 symbols where 4 tones are dedicated to pilots as defined in IEEE 802.16e 17 . For the Band Adaptive Modulation and Coding AMC permutation scheme each bin equivalent to the tile concept is comprised by 9 subcarriers where 1 tone is used as pilot. Perfect channel estimation is assumed at the receiver. Every log2 Z bits are mapped to one symbol. The channel models used are uncorrelated Rayleigh H CN 0 1 and the ITU Pedestrian A 38 . In both cases the channel is considered constant within a tile block fading channel model . In case of uncorrelated Rayleigh the channel between tiles is uncorrelated whereas in the ITU PedA case the channel is correlated both in frequency and time. 4.4.3 MIMO reference and simulation results In Fig. 6 the reference performance for a fixed rated is depicted for N 2 when no transmit antenna selection neither code selection are used. For uncorrelated Rayleigh channel we can observe that for low data rate i.e. R 2 4 the Alamouti code outperforms the rest of the schemes. This is strictly related to the diversity order that G2 achieves equal to gd N M 4 whereas the SM and the Golden code with a linear receiver get a diversity .
