On The Transmission Mechanism Analysis And Optimized Design Of Wireless Relaying Networks

With the wide applications of wireless networks, such as satellite, WIFI, cellular networks, wireless sensing and control networks (WSCN), and so on, wireless service have more stringent requirements on the network capacity, end-to-end (E2E) delay, reliability performance. However, there are trade-offs among the capacity, delay, reliability, e.g., a larger capacity will results in lower reliability or longer delay, and a higher reliability is at the cost of smaller capacity or longer delay. Popular wireless networks prefer a larger capacity and lower delay while WSCNs prefer higher reliability and lower delay. In wireless networks, there are two key technologies:relaying which can extend the transmission range, improve network capacity and reduce the costs, and multi antennas (also known as multi-input multi-output, MIMO) which provide multiplexing and diversity gains. On the other hand, WSCN uses anypath routing to improve the E2E reliability and reduce the E2E delay. In this thesis, we focus on improving the capacity performance and design for one-way relaying and multi-way relaying networks, as well as improving the E2E reliability in the E2E delay bound for the WSCNs.Firstly, a MIMO one-way relaying network is considered. In the network, the source s communicates wirelessly to the destination d via the help of an amplify-and-forward (AF) relay r. Previous studies are almost exclusively based on the assumptions of equal time-duration phases for s-r and r-d transmission and equal number of multiple antennas for every node, and the results concerning arbitrary time scheduling and arbitrary anten-na arrays are not yet known. To achieve the best E2E data rate, this thesis considers joint source and relay beamforming design combined with time scheduling and subchannel pairing, in accordance to respective link conditions. We first propose a practical beam-forming framework that is inspired by the optimal MIMO relay beamforming structure. It is shown that in this framework, after subchannel pairing, the joint beamforming de-sign problem can be transformed to a joint optimal power allocation problem. Numerical results show that the E2E data rate can be significantly improved by appropriate time scheduling, subchannel pairing, and power allocation.Secondly, full message exchange in a restricted multi-way relay (MWR) network with K users, each equipped with Mu antennas, and a single relay equipped with Mr anten-nas is considered. a). the achievable rate region (ARR) for a multi-antenna restricted MWR with the decode-and-forward (DF) cooperative strategy with and without user-user connections is investigated. It is shown that the ARR of MWR can be increased with appropriate scheduling of time and users, and can be further extended when the user-user connection is present. b). In MIMO MWR networks, the complexity of multi-user detection is exponential. To tackle this problem and reduce the complexity, a scheme which is based on the idea of interference alignment is proposed. In the scheme, each user only utilizes its individual channel state information (CSI) to perform aligned transmis-sion, and the signals from the users are aligned at the relay. At the users, all the signals from the others can be recovered with its own message, the recovering approach is the well-known successive interference cancellation. The outage performance is approximately analyzed and it is proposed that the performance is improved by optimal power allocation at the relay. c). relay selection is considered for multi-relay MWR networks, specifical-ly, we consider the case of K= 2. Previous relay selection schemes require full CSI of all the relaying channels thus incurring high overhead in the network. In this paper, a low complexity switch-and-stay relaying selection scheme is proposed. The outage and diversity performance of the scheme is analyzed and it is shown that optimal outage and diversity performance can be achieved with lower complexity. Simulations are provided to corroborate the theoretical analysis.Thirdly, a delay-constrained wireless sensing and control network is considered. The WSCN consists of multiple sources and a gateway (destination), all the source messages are delay constrained and reliability sensitive. Due to the high data load, contention-based scheduling schemes results in high delay and energy consumption, and low reliability, while anypath routing and offline TDMA-based scheduling have more advantage in providing predictable delay, reliability and energy performance. Based on anypath routing, TDMA-based offline scheduling schemes named dedicated scheduling and shared scheduling are proposed, and the performance of the schemes are analyzed asymptotically. Extensive simulation experiments are performed to illustrate their effectiveness in improving the E2E reliability of packet delivery under different network settings.In all, the study on one-way and multi-way relaying network shows that an appro-priately designed transmission mechanism improves the network capacity with the same time, antenna, and power consumptions; similarly, the work on WSCNs show that a well developed schedule takes a good trade-off in delay and reliability.