On Cooperative Communications and Its Application to Mobile Multimedia

University dissertation from Karlskrona : Blekinge Institute of Technology

Abstract: With the rapid growth of multimedia services, future generations of wireless communications require higher data rates and a more reliable transmission link while keeping satisfactory quality of service. In this respect, multipleinput multiple-output (MIMO) antenna systems have been considered as an efficient approach to address these demands by offering significant multiplexing and diversity gains over single-antenna systems without increasing requirements on radio resources such as bandwidth and power. Although MIMO systems can unfold their huge benefit in cellular base stations, they may face limitations when it comes to their deployment in mobile handsets. In particular, the typically small-size of mobile handsets makes it impractical to deploy multiple antennas. To overcome this drawback, the concept of cooperative communications has recently been proposed and gained large interest in the research community. The key idea is to form a virtual MIMO antenna array by utilizing a third terminal, a so-called relay node, which assists the direct communication. After receiving the source’s message, the relay processes and forwards it to the destination. With this approach, the benefits of MIMO systems can be attained in a distributed fashion. Furthermore, cooperative communications can efficiently combat the severity of fading and shadowing effects through the assistance of relay terminals. It has been shown that using the relay can extend the coverage of wireless networks. In this thesis, we focus on the performance evaluation of such cooperative communication systems and their application to mobile multimedia. The thesis is divided into five parts. In particular, the first part proposes a hybrid decode-amplify-forward (HDAF) relaying protocol which can significantly improve the performance of cooperative communication systems compared to the two conventional schemes of decode-and-forward (DF) and amplify-and-forward (AF). It is interesting to see that the performance gain of HDAF over DF and AF strictly depends on the relative value of channel conditions between the two hops. The second part extends HDAF to the case of multiple relays. It is important to note that the gains are saturated as the number of relays tends to be a large value. This observation motivates us to use a small number of relays to reduce network overhead as well as system complexity while the obtained gains are still as much as in the large-number case. In the third part, we analyze the performance of DF relaying networks with best relay selection over Nakagami-m fading channels. Besides the diversity gain, we show that the spatial multiplexing gain can be achieved by cooperative communications. We analyze the performance of cooperative multiplexing systems in terms of symbol error rate and ergodic capacity over composite fading channels. Finally, in the fifth part, we exploit the benefit of both diversity and multiplexing gain by proposing an unequal error transmission scheme for mobile multimedia services using cooperative communications.