Do tiềm năng cho các tình huống nghiêm trọng gần xa trong mạng lưới quảng cáo đặc biệt, tần số nhảy phương pháp tiếp cận thường thích hợp hơn. Vì vậy, chúng tôi tập trung vào thông qua mạng cho các hệ thống FHMA. | MULTIUSER DETECTION 147 Parallel Interference Cancellation The main drawback of the SIC receiver is that in the presence of equal received powers the BER performance is poor for the signals that are detected early. In fact the SINR for the first detected signal is equivalent to the matched filter. This can be seen explicitly for linear SIC from equation with k 1 and Q 1 r v p1 N i p1 02 g_ p1 N A p1 -1 1-1 N Ê 1 Nm 2 2 -1 Ne 2 Eb -1 K - n N where we have used ơ2 N 2Tb and the result is the same as the matched filter given in . A third type of non-linear receiver structure the PIC receiver alleviates this problem by providing equal cancellation benefit to all signals 58 108-110 . This structure is plotted in Figure . PIC detectors use matched filters to estimate the data from all signals in parallel. The estimates for each user can then be used to reduce the interference to and from the other signals by subtracting the estimate of each interferer from the desired user s signal. Ideally this would allow the elimination of all interference from the desired user. Formally Ĩ bk sgn yk Aibipi k where again we have assumed perfect channel knowledge . Ai . Of course in practice this must also be estimated. Additionally during this development we have assumed equal phase between users for notational simplicity. However in practice there are clearly phase differences between users. This must also be estimated and used in the cancellation process. In such a case we can consider Ai to be complex containing both amplitude and phase. Further the final decision statistic would have to be phase rotated prior to making a decision. The above formulation assumes the implementation of cancellation directly on the matched filter outputs sometimes referred to as a narrowband implementation . Since cancellation and despreading are linear operations we can perform cancellation prior to despreading with no change in performance. If cancellation is performed
