Cognitive And Cooperative Relay Transmission For Wireless Communication Systems

Recently, Cognitive Radio (CR) has been proposed as a brand-new way of efcientspectrum usage for wireless communications. It allows unlicensed Secondary Users toopportunistically access the spectrum band authorized to Primary Users (PUs), whileavoiding harmful interference to PUs. For SUs, spectrum access opportunities or spec-trum holes lie in multiple domains, such as time, frequency and space etc. In CR sys-tems, one of the key problems is how to fully explore and dynamically access multi-dimensional spectrum holes to improve the Quality of Service (QoS) for SUs. The pre-vious work on Opportunistic Spectrum Access (OSA) mainly focused on fully exploit-ing temporal spectrum holes rather than using multi-dimensional spectrum holes. Theimpacts of the burstiness of secondary trafcs and the randomness of wireless channelfading are rarely considered. This paper will investigate the way of improving the OSAperformance with the aid of cooperative relaying in CR systems.This paper proposes a cooperative beamforming based cognitive and cooperativerelay transmission strategy. It can not only achieve cooperative diversity gain for com-bating wireless channel fading, but also realize directional tranmsissions for accessingspatial spectrum holes. Thus, it can greatly reduce the average outage probability of SUs.Based on this approach, we design optimal OSA schemes according to the characteristicsof secondary trafcs. At first, this paper proposes an optimal OSA scheme with priorityfor serving real-time secondary trafcs. By an absorbing Markov chain model, we de-rive the probability of queueing timeout due to the presence of PUs on the channel. Wethen analyze the probability of delay-limited outage, which is caused by both wirelesschannel fading and the presence of PUs. Secondly, this paper proposes a delay-optimalqueue-length based OSA scheme for serving non-real time secondary trafcs with burstarrival patterns. By modeling it as a tandem queueing system, we analyze the maxi-mum arrival rate and the average delay using the Matrix-Geometric solution. Thirdly, byadopting incremental relaying, this paper proposes an efcient cognitive and cooperativerelay transmission scheme for serving non-real time backlogged trafcs. The averagethroughput is derived for two Hybrid Automatic Repeat reQuest (HARQ) protocols. Us-ing the cross-layer optimization method, we can further optimize the performances of the proposed schemes by optimizing their scheduling parameters.Through elaborate scheme design and rigorous theoretical analysis, this paper inves-tigates the impacts of secondary trafc characteristics, PUs' behaviors and wireless chan-nel fading on the system performance. It also gives the optimal transmission schemes fordiferent system parameters. This paper studies a new combining way of CR and cooper-ative relaying technologies and the OSA performance gain brought by such combination.The proposed schemes and algorithms are easy and feasible, and the performance gain issignificant. Hence, our work has the prospect for application.