A bidirectional multi-symbol phase estimation (BD-MSPE) scheme for differentially encoded optical signals, which can realize high-speed processing with superior BER characteristics, is proposed. Conventional MSPE needs decision feedback to correct phases of past symbols, so it is not suitable for parallelization. BD-MSPE, in contrast, uses tentative decision to avoid feedback. Due to the tentative decision, both past and future symbols can be utilized for phase estimation. Moreover, BD-MSPE can be organized in multistage when the decision result of the first stage of MSPE is used as the second tentative decision result for the next stage. Simulation results show the bit-error-rate (BER) curve of the proposed scheme asymptotically approaches that obtained by coherent detection.
This paper studies the effects of imperfect feedback cancellation on the design of amplify-and-forward full-duplex relay system. The lower and upper bounds of relay-transmit power as well as the upper bound of a feedback channel estimation error, guaranteeing improved performance than point-to-point transmission, are derived. Then, we propose the strategy controlling relay-transmit power within bounds. The computer simulations confirm the analysis.
In this paper, we present an efficient differential quasi-orthogonal space-time block code (ED-QOSTBC) system. In particular, it is shown that our proposed system performs symbol-wise complex symbol decoding with the maximum likelihood (ML) receiver. From the performance evaluations, it is demonstrated that the ED-QOSTBC system has the same performance compared to conventional D-QOSTBC transmission in terms of bit-error-rate (BER), and it reduces decoding complexity proportional to the cardinality of the constellation set.