In this paper, we consider a full-duplex multiple-input multiple-output (MIMO) relaying network with the decode-and-forward (DF) protocol. Due to the full-duplex transmissions, the self-interference from the relay transmitter to the relay receiver degrades the system performance. We thus propose an iterative beamforming structure (IBS) to mitigate the self-interference. In this method, the receive beamforming at the relay is optimized to maximize the received signal-to-interference-plus-noise-ratio (Max-SINR), while the transmit beamforming at the relay is optimized to maximize the signal-to-leakage-plusnoise-ratio (Max-SLNR). To further improve the performance, the receive and transmit beamforming matrices are optimized between Max-SINR and Max-SLNR in an iterative manner. Furthermore, in the presence of the residual self-interference, a low-complexity whitening-filter (WF) maximum likelihood (ML) detector is proposed. In this detector, a WF is designed to transform a colored interference-plus-noise to a white noise, while the singular value decomposition is used to convert coupled spatial subchannels to parallel independent ones. From simulations, we find that the proposed IBS performs much better than the existing schemes. Also, the proposed low-complexity detector significantly reduces the complexity of the conventional ML (CML) detector from exponential time (an exponential function of the number of the source transmit antennas) to polynomial one while achieving a slightly better BER performance than the CML due to interference whitening.

In wideband multi-pair two-way relay networks, the performance of beamforming at a relay station (RS) is intimately related to the accuracy of the channel state information (CSI) available. The accuracy of CSI is determined by Doppler spread, delay between beamforming and channel estimation, and density of pilot symbols, including transmit power of pilot symbols. The coefficient of the Gaussian-Markov CSI error model is modeled as a function of CSI delay, Doppler spread, and signal-to-noise ratio, and can be estimated in real time. In accordance with the real-time estimated coefficients of the error model, an adaptive robust maximum signal-to-interferenceand-noise ratio (Max-SINR) plus maximum signal-to-leakage-and-noise ratio (Max-SLNR) beamformer at an RS is proposed to track the variation of the CSI error. From simulation results and analysis, it is shown that: compared to existing non-adaptive beamformers, the proposed adaptive beamformer is more robust and performs much better in the sense of bit error rate (BER); with increase in the density of transmit pilot symbols, its BER and sum-rate performances tend to those of the beamformer of Max-SINR plus Max-SLNR with ideal CSI.

In this paper, spatial channel pairing (SCP) is introduced to coherent combining at the relay in relay networks. Given SCP, the closed-form solution to the optimal coherent combining is derived. Given coherent combining, the approximate SCP solution is presented. Finally, an alternating iterative structure is developed. From simulation results and analysis, we find: given symbol error rate and data rate, the proposed alternating iterative structure achieves several signal-to-noise ratio gains over existing schemes in maximum ratio combining (MRC) plus matched filter, MRC plus antenna selection, and distributed space-time block coding due to the use of SCP and iterative structure.

本文根据DFT的一个性质为OFDM通信系统构造了一种通用信道估计模型。该模型利用系统子信道中的一部分专门进行信道估计，适用于慢消失信道。该模型同最小平方差(LS)和最小均方差(LMMSE)相结合分别形成两种信道估计方法，并从理论角度分别分析它们的计算复杂性和均方差性能。对多径信道仿真表明，基于LS的方法误符号率性能比基于LMMSE的方法差2-3dB，但是计算复杂度较低。总之，此信道估计模型的计算复杂度和性能随着用于信道估计的子信道数目增加而增加，当所用子信道数目是周期头长度的两倍时，达到计算量和估计性能的最佳平衡。

该文提出一种基于频域的幅度两电平的DAPSK+OFDM，并讨论该调制方式在频域的差分调制和解调，然后给出它在白高斯信道的误比特性能公式，最后在典型的调幅(AM)波段信道对它和基于时域的DAPSK+OFDM的误比特性能进行了仿真。结果表明：在短波信道，频域的DAPSK+OFDM比时域的DAPSK+OFDM性能好；在中波信道，时域的DAPSK+OFDM比频域的DAPSK+OFDM性能好。因此，数字调幅广播系统在短波信道可采用频域DAPSK+OFDM，在中长波信道可采用时域DAPSK+OFDM。