In this paper, we propose statistically robust design for multiuser multiple-input multiple-output (MIMO) relay systems with direct source-destination links and imperfect channel state information (CSI). The minimum mean-squared error (MMSE) of the signal waveform estimation at the destination node is adopted as the design criterion. We develop two iterative methods to solve the nonconvex joint source, relay, and receiver optimization problem. Simulation results demonstrate the improved robustness of the proposed algorithms against CSI errors.
In underwater acoustic (UWA) communication, Doppler effect is particularly severe due to the slow velocity of sound and the complex variant UWA channel environment. Carrier frequency offset (CFO) can result in extension and compression of the received signal in time domain and has a direct effect on the performance of decoding. In this paper, we propose a new scheme of CFO estimation and compensation for a high speed UWA communication system. There are three steps including coarse CFO estimation, fine CFO estimation and linear interpolation, which are taken to estimate and compensate the CFO. The scheme can eliminate the phenomenon of ambiguous phase and tolerate quick random variation of the CFO in UWA channel. A UWA communication experiment was carried out in December 2012 in the Indian Ocean, off Rottnest Island, Western Australia. With the proposed algorithm in this paper, the UWA system can achieve an average of 1.95% uncoded BER with QPSK modulation at the 1km range and 5.57% with BPSK at the 10km range.
Wireless video broadcast plays an important role in multimedia communication with the emergence of mobile video applications. However, conventional video broadcast designs suffer from a cliff effect due to separated source and channel encoding. The newly proposed SoftCast scheme employs a cross-layer design, whose reconstructed video quality is proportional to the channel condition. In this paper, we provide the performance evaluation and the parameter optimization of the SoftCast system. Optimization principles on parameter selection are suggested to obtain a better video quality, occupy less bandwidth and/or utilize lower complexity. In addition, we compare SoftCast with H.264 in the LTE EPA scenario. The simulation results show that SoftCast provides a better performance in the scalability to channel conditions and the robustness to packet losses.
In this paper, we generalize the iterative algorithms proposed by Khandaker to amplify-and-forward multiuser Multiple-Input Multiple-Output (MIMO) relay communication systems with the source-destination links. Compared with the conventional algorithms, where the source-destination links are ignored, the evolved Tri-Step method and Bi-Step method are derived for the new system model with the source-destination links for more spatial diversity gain. From the theoretical derivation of the Minimum Mean-Squared Error (MMSE) of the signal waveform estimation at the destination node, we show that the existence of the source-destination links bring benefits no matter how weak they are. Numerical examples demonstrate that the evolved algorithms perform much better than the original algorithms and other existing ones in terms of both MSE and Bit-Error-Rate (BER).
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