Research On Cooperative Communications Based On Two-way Relaying Systems

The channel fading is one of the main factors which affect reliability and validityin wireless communication systems. Cooperative relay technology can resist the impactof multi-path fading to improve the coverage, reliability and validity, and has become animportant research field of wireless communications. However, the half-duplexlimitation of relay causes the loss of spectral efficiency in traditional one-way relayingsystems. In recent years, two-way relaying technique has emerged and been extensivelystudied. The two-way relaying can improve the throughput and make up the spectruminefficiency of the traditional one-way relaying system. Currently, the two-way relayingtechnology has become one of the hot research areas in wireless communications. Inthis thesis, focusing on two-way amplify-and-forward (AF) relaying system, we designnovel low-implementation complexity relay selection schemes and investigate thesystem performance. The main contributions of this paper are summarized as follows:1. The relay selection scheme in symmetric two-way AF relaying systemsIn symmetric two-way multiple AF relaying systems, a relay selection schemebased on distributed time technology is proposed. The scheme has lowerimplementation complexity. In addition, the outage performance of the scheme isinvestigated in Rayleigh fading, and the integral and closed-form expressions of thelower bound are obtained. Simulations demonstrate that the signal-to-noise ratio (SNR)gap between the lower bound and the exact value is less than0.5dB. Moreover, theperformance gap between the proposed scheme and the existing outage-optimal relayselection scheme is very small. Thus the proposed scheme has both good outageperformance and lower complexity, and can be widely applied in practical systems.2. The relay selection scheme in asymmetric two-way AF relaying systemsIn asymmetric two-way multiple AF relaying systems, a relay selection schemebased on distributed time technology is proposed. The scheme has lowerimplementation complexity. In addition, the integral and closed-form expressions of thelower bound for the outage probability in Nakagami-m fading are derived. Simulationsdemonstrate that the obtained theoretical results are very consistent with the exactvalues in all SNR regions. Moreover, the performance gap between the proposedscheme and the existing outage-optimal relay selection scheme is very small. Thus theproposed scheme has good outage performance.3. The performance analysis of asymmetric two-way AF relaying systemsIn asymmetric two-way AF relaying systems, we propose an outage analysis method based on inequality equivalence deformation. Using the method, one can readilyevaluate the outage probability based on the cumulative distribution function of thechannel gain, requiring very low mathematical complexity. Moreover, the proposedmethod is applicable to a variety of wireless channels and has wide applications.According to the method, the closed-form expressions of the outage probability ofasymmetric single relaying, multiple relaying and multi-user two-way AF cooperationcommunication systems are derived in Rayleigh and Nakagami-m fadings, respectively.Simulations indicate that the obtained theoretical results are very consistent with theexact values in middle and high SNR regions.4. The performance analysis of cognitive two-way AF relaying with underlayspectrum sharingFocusing on cognitive two-way AF relaying with underlay spectrum sharing, theoutage and bit error probabilities are derived in Rayleigh fading, respectively.Simulations indicate that the obtained theoretical results coincide well with the exactvalues. Moreover, the deducing method can easily be extended to evaluate the systemperformance over other fading channels.