Multi-Antenna Transceivers and Cooperative Relaying Protocol Designs for Wireless Networks
Multiple antennas technique is an important means to improve the capacity and reliability of wireless communication systems. It is widely understood that in rich scattering and reflection environments, the use of multiple antennas technique, e.g. multiple-input-multiple-output (MIMO), in a system allows us to have: higher capacity throughput and more reliable communication links, compared to the conventional single-input-single-output (SISO) systems. Spatial multiplexing provided by MIMO technique is beneficial especially in the bandwidth-limited systems, since it supports higher data throughput by the parallel spatial channels with given bandwidth. On the other hand, multiple antenna technique also offers diversity to combat the severe channel fading to improve the reliability of wireless communications. In addition, resource allocation plays a critical role in the performance improvement of the wireless communication systems. However, the direct application of existing multiple antennas technique might be infeasible to provide the potential benefits in certain wireless networks, e.g., airborne wireless network with strong LoS components, or the cost-limited network where each terminal has only single antenna. In this dissertation, we first analyze the potential capacity performance improvement of MIMO technique in the application of airborne/Light-of-Sight (LoS) wireless communications, which was rarely studied unlike the scenario of the rich scattering and reflection environments. First, we systematically investigates the capacity of airborne MIMO wireless communication systems with arbitrary alignments of general antenna array structures, i.e. planar (2D) antenna array and 3D antenna array. We determine the capacity upper bound of general airborne MIMO system as well as a necessary and sufficient condition for such a system to achieve the upper bound. However, for arbitrary alignments of planar or 3D transceiver antenna arrays, the achievability of the upper bound is not always guaranteed, and even difficult to identify by the necessary and sufficient condition. Then, based on the concept of proper Tx-Rx pairing pattern, we propose a design for general 2D or 3D airborne MIMO system which achieve a substantial achievable capacity by adjusting the antenna separations, compared to the conventional SISO systems. Interestingly, the achievable capacity analysis with proper Tx-Rx pairing patterns provides practical design guideline of 2D or 3D transceiver antenna arrays, which can achieve substantial Airborne MIMO capacity and in some scenarios can reach the capacity upper bound. Multiple antennas technique not only offers high data throughput of wireless communication systems, but also provides reliable link connection especially in severe fading channels. However, due to space and cost limitation, terminals equipped with multiple antennas might not be available in some applications. As an alternative, cooperative relaying is a promising technology to improve the system performance through "virtual array''. We start from the cooperative relaying protocols design with optimum power and time allocation in the Point-to-Point communication scenario. we obtain an asymptotically optimum strategy of power and time allocations in the ideal cooperative protocol, where the system can use arbitrary re-encoding methods at the relay and adjust time allocation arbitrarily. It shows that in order to minimize the outage probability of the protocol, one should always allocate more energy and time to the source than the relay. Then, with more realistic consideration, we design a practical cooperative relaying protocol based on optimum linear mapping, i.e. using linear mapping as the re-encoding method at the relay and considering integer time slots in the two phases. The theoretical results from the ideal cooperative protocol serve as guideline and benchmark in the practical cooperative protocol design. Simulation results show that, with optimum power and time allocation, the performance of the proposed cooperative relaying protocol based on the optimum linear mapping is close to the performance benchmark of the ideal cooperative protocol. Different from the Point-to-Point relaying communication scenario, the performance analysis for Broadcast/Multicast relaying network is more complicated due to the fact that the number of relays is unknown. We propose a cooperative multicast scheme with randomized space-time code (RSTC) technique. To increase the received signal-to-noise ratio (SNR) of the proposed scheme, we put forward a class of orthogonal space-time codes (OSTC) with desired structure, which enable RSTC technique to use joint detection of all received signals. We derive the closed-form formulation of its average outage probability and observe that the optimization of power allocation can be solved by single-variable numerical search. We further derive the asymptotically tight approximation to study the asymptotic behaviour, which shows that the scheme can achieve diversity order K + 1, where K is the size of OSTC used in the multicast scheme. Simulations show that the distributed cooperative multicast scheme with RSTC can better utilize user cooperation to reduce the outage probability, especially in the high SNR region. (Abstract shortened by UMI.)
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