Relaying strategies and protocol designs for buffer-aided cooperative relaying networks

In this thesis, a new technique named buffer-aided relaying is studied to enhance the performance of wireless relaying networks. In particular, the transmission strategies that can improve diversity gain, maximize the system throughput and reduce the information delay are investigated. First, we apply the buffer-aided relaying scheme into a space-shift-keying (SSK) based relaying system and propose a novel link adaptation method. The average symbol-error performance of the proposed link adaptation scheme is investigated and it is shown that the proposed scheme can achieve a diversity order of 2. In addition, the delay of the information packets at the relay node (RN) is investigated and two link adaptation schemes with reduced delay are proposed. It is shown that by jointly considering the buffer state, the proposed link adaptation schemes can achieve a relative small packet delay at the expense of a little performance loss. Subsequently, a buffer-state based relay selection scheme is proposed for a bufferaided multiple RNs system to reduce the average delay. Different from the existing relay selection schemes which select the RNs only based on the channel quality, our proposed relay selection scheme selects a RN based on both the channel quality and the buffer state of the RNs. The outage probability of the proposed relay selection scheme is obtained in a closed-form expression and it is shown that the proposed relay ii selection scheme can outperform the existing relay selection schemes. In addition, analytical results also show that our proposed relay selection scheme has lower average packet delay as compared with the existing buffer-aided relay selection schemes. Moreover, the application of the buffer-aided relaying scheme in a wireless-powered relaying system is also investigated. By assuming that the RNs of the system have no embedded power supply and are charged by the radio frequency (RF) signal transmitted by a power beacon (PB), a joint node-and-mode selection scheme is proposed. For the general system setup, some analytical results are obtained which provide useful insights in finding the optimal joint node-and-mode selection scheme. Following this, theoretical analysis is conducted for two specific systems, namely the single RN system and the multiple RNs system with a symmetric channel. For these system setups, the system throughput is obtained in closed-form expressions. Numerical results show that the system throughput can be improved by using the proposed transmission schemes. Finally, we extend the buffer model into a wireless-powered cooperative communication network (WPCCN) and treat the battery of the SN as an energy queue. Based on this model, we investigate the long-term throughput of two proposed block-wise cooperative protocols, namely the block-wise harvest-and-transmit (BW-HaT) protocol and the block-wise mode adaptation (BW-MA) protocol. For the BW-HaT protocol, the throughput expression is obtained in closed form. For the BW-MA protocol, the optimal mode adaptation method that maximizes the throughput of the system is presented and the maximum throughput is given for different system setups. It is shown that the proposed transmission schemes can significantly increase the system throughput.