Detection techniques for alternate-relayingcooperative communications systems

Cooperative technology constitutes a breakthrough in the design of wireless communication systems. This is due to its relatively simple implementation and its significant performance gains in terms of link reliability, system capacity, and transmission range. In cooperative communications, multiple terminals in a network cooperate by relaying each other’s information, forming a virtual antenna array, and, thus realizing spatial diversity in a distributed fashion. It is not surprising that cooperative communications have become a strong candidate for many wireless applications, such as cellular networks, wireless local area network, mobile ad-hoc networks, and wireless sensor networks. However, cooperative technology is not without challenges. A major problem in this technology is the reduction in spectral efficiency, which results from the half-duplex constraint at the relays and orthogonal relay transmission. This has spurred researchers to investigate cooperative strategies to recover the spectral efficiency loss. Such strategies can be classified into three main categories. One category supposes that each source transmits a ’superimposed’ signal, which consists of its own data and relaying information. This superposition can be performed in code or in modulation domain. Obviously, if the relay does not have its own data, a full-rate transmission can not be achieved. The second category is to employ adaptive modulation techniques where the spectral efficiency is improved by changing modulation size with fixed symbol rate. However, the transmitter needs to know the channel signal-to-noise (SNR) such that the best suitable modulation is chosen and the receiver must be informed on the used modulation in order to decode the information. This leads to an increased overhead in the system as compared with a fixed modulation system, and will increase the complexity of the receiver too. The third one utilizes two-relay, which alternatively transmit and receive. A key feature of this category is that the source continues to transmit data, while the two relays take turns in receiving and transmitting the data from the source. Due to the simultaneous transmission of the data streams through both direct and one of relay channels, harmful interference occurs at the relays and destination. The interference occurred at the relays and destination represents a drawback in this case, though. According to our best knowledge, no previous research was done to develop the optimal detectors for alternate-relaying cooperative (ARC) systems. Further, all the previous works for ARC systems have in common that they do not exploit any properties of the underlying error correcting codes. It is therefore necessary to propose optimal detection techniques for uncoded and coded two-relay systems. This motivated us to do this research. In this thesis, we proposed optimal and suboptimal detectors to mitigate the influence of the interference signal for the uncoded and coded decode-and-forward (DF) ARC systems.