Research On Key Technologies Of Two-way Relaying Cooperative Communications

The requirement of the validity and reliability of wireless communication system is growing with the wide application of wireless communication technology. Cooperative communication is an effective technology to overcome multi-path fading of wireless channel. An idle node is used as a relay in cooperative communication and the virtual multi-antenna system is realized. Based on physical layer network coding technique, the two-way relay system can solve the problem of mutual interference between nodes under the certain condition and improve spectrum efficiency, which has been extensively studied in recent years. This thesis highlights the key technologies of two-way DF relaying based on physical-layer network coding. The main contributions of the thesis are summarized as follows:(1) In order to improve the performance of the multiple-input multiple-output (MIMO) two-way DF relay system based on physical-layer network coding, the minimum mean square error (MMSE) detection is applied after the relaying node receives the signal. When the channels between the relay and the two stations are symmetric, the bit error rate (BER) and channel capacity are analyzed. The simulation results show that the two-way relay system based on MMSE detection can facilitate more reliable transmission and improve the throughput.(2) The two channel qualities between the relay and the stations of MIMO two-way DF relay system are not always symmetric. When the two channel qualities of the broadcast phase of two-way relay systems are asymmetric, the data transfer rates from the relay are limited by the weaker link of the two stations and the channel gain of the stronger link is not fully used. A novel transmission scheme is proposed in order to fully use every channel gain. By using the prior bit information, the weaker link receiver exploits a known bit information in each transmission symbol and decodes on a subset of the transmit symbol constellation which causes different minimum Euclidean distance. The two links can respectively transmit signal at different data rates corresponding to link quality and reach the requirement of the same bit error rate. In order to attain the same BER requirements for any channel quality, the scheme based on adaptive modulation is proposed. The modulation mode is adaptively adjusted by the channel qualities between the relay and two source nodes. The signal-to-noise ratio (SNR) region between the relay and two source nodes are divided into four regions. The modulation mode is adaptively adjusted according to the region of the SNR of the link. Simulation results show that the proposed transmission schemes can be applied to the practical scenarios.(3) The interruption of communication in wireless network of the weak channel quality is common. In this paper, we investigate the outage performance of a two-way DF relay network in the presence of co-channel interference (CCI) at the source/destination terminals and channel estimation errors. First, we define the SNR and signal-to-interference ratio (SIR). The outage probability expression is changed into the function of multiple variables. Then, the cumulative density function (CDF) and Probability Density Function (PDF) of the variables are concluded. We derived the closed-form expressions of the outage probability for the system under the symmetrical and asymmetrical cases. Based on the analytical expressions, we perform asymptotic analysis in the case where the power of relay becomes infinite. Simulation results not only validate our analytical results, but also reveal how the channel estimation errors and the interferers affect the outage performance.(4) The Nakagami-m fading is a more general distribution of channel fading. In this paper, we investigate the outage performance of a two-way DF relay network in an interference-limited Nakagami-m fading environment.Specifically, the presence of Nakagami-m faded multiple co-channel interferers at the source/destination terminals is assumed. First, the appropriate Nakagami-m fading parameters are attained by using moment-based estimators and the CDF and PDF of the variables are concluded. Then, the closed-form approximate expression of the outage probability is derived. Based on the approximate expressions, we perform asymptotic analysis in the case that the power of relay becomes infinite and the channel fading parameters are set as 1. Simulation results demonstrate that our analytical result is in excellent agreement with the Monte Carlo simulation.