Hình 6,32 Hiệu suất giảm lưới hỗ trợ phát hiện cho hệ thống QPSK với NT = NR = 4 (rắn đậm dòng: MLD thực hiện, in đậm dòng tiêu tan: máy dò tuyến tính) Kết quả mô phỏng Bây giờ, chúng ta muốn so sánh hiệu suất của cách tiếp cận LR giới thiệu để phát hiện kỹ thuật đã được mô tả trong Chương 5. | MULTIPLE ANTENNA SYSTEMS 317 Figure Performance of lattice reduction aided detection for QPSK system with At Ar 4 solid bold line MLD performance bold dashed line linear detectors Simulation Results Now we want to compare the performance of the introduced LR approach to the detection techniques already described in Chapter 5. We consider multiple antenna systems with an identical number of receive and transmit antennas. Moreover uncorrelated flat Rayleigh fading channels between different pairs of transmit and receive antennas are assumed. Note that no iterations according to the turbo principle are carried out so that we regard a one-stage detector. If the loss compared to the maximum likelihood detector is large the performance can be improved by iterative schemes as shown in Chapter 5. Figure compares the BER performance of an uncoded 4-QAM system with At Ar 4 antennas at the transmitter and receiver. Figure summarizes the zero-forcing results. The simple decorrelator bold dashed curve based on the original channel matrix H shows the worst performance. It severely amplifies the background noise and cannot exploit diversity and so the slope of the curve corresponds to a diversity degree of D Ar At 1 1. The ZF-SQLD-SIC detection gains about 7 dB at 10 2 compared to the decorrelator but is still far away from the maximum likelihood performance. It can only partly exploit the diversity as will be shown in Figure . The decorrelator based on the reduced channel matrix Hred labeled LR performs slightly worse than the ZF-SQLD-SIC at low SNRs and much better at high At an error rate of 2 10 3 the gain already amounts to 4 dB. On the one hand the LR-aided decorrelator does not enhance the background noise very much owing to the nearly orthogonal structure. On the other hand it fully exploits the diversity in all layers as indicated by the higher slope of the error rate curve. Since the reduced channel matrix Hred is not perfectly orthogonal .
