Research On Radio Resource Optimization Mechanism In OFDM Cooperative Relaying Networks

Orthogonal Frequency Division Multiplexing (OFDM) cooperative relayingnetworks have received intensive attentions recently due to the advantages ofenhancing network capacity, end-to-end transmission reliability, coverage range, etc.,as well as due to the flexibility on design and deployment. In such networks,cooperative relaying strategies and radio resource allocation are the key researchelements in terms of providing proper system performance or even further enhancingthe system performance. And, because of the ever-increasing various high-speedhigh-bandwidth wireless applications and services, the contradictions between thelimited supply of wireless radio resources and the need from wireless users becomeeven more intensified. Also, the energy consumptions on wireless communicationsare increasing rapidly, urging the deployment of green networks. Therefore, how toenhance the capability of wireless networks on spectrum efficiency, energy efficiencyand the support of heterogeneous services turns into one of the key concerns about theenhancement of wireless networks and the relief of pressure from the high-volumeapplications. In this dissertation, we study the radio resource optimization issues inOFDM cooperative relaying networks with the focus on the enhancement of spectrumefficiency, energy efficiency and the support of heterogeneous traffic, expecting toobtain schemes with high spectrum-energy efficiency and strong-enhanced support ofapplications, so as to provide theoretical suggestions for future research anddeployment on resource-optimization-centric application systems, and to makepositive contributions to solve the mentioned concern above. The major researchworks carried out in this dissertation can be summarized as follows:(1) The related work on wireless cooperative networks are analytically surveyedand summarized. Considering on the two key research elements, i.e., cooperativerelaying strategies and radio resource allocations, we category and survey the relatedwork on OFDM wireless cooperative networks from the following aspects:cooperative relaying strategies, resource allocation schemes for relay-assisted uni-directional relaying networks, relay-assisted bi-directional relaying networks anduser cooperative based relaying networks, as well as system implementation schemes.We also compare and analyze the features of some selective related works from theaspects of the involved network elements and the design considerations. Then, wegive some suggestions on the unsolved problems, and point out the importance ofnetwork coding, imperfect channel state information (CSI) and multi-objectoptimization on obtaining practical radio resource allocation schemes with highspectrum-energy efficiency.(2) The issue of heterogeneous traffic enhancement and spectrum efficiencyoptimization is studied in uni-directional multi-user multi-relay OFDM networks.Considering on the minimum required transmission rate for real-time traffic,subcarrier-pairing based subcarrier assignment, power allocation and relay-user pairing,etc., and with the aim of maximizing the overall transmission rate of non-real-timetraffic, we study the subcarrier-pairing based adaptive radio resource allocation issue,so as to enhance the support of heterogeneous traffic and optimize the spectrumefficiency. We propose two asymptotic optimal resource allocation schemes for totalnetwork power constraints and individual power constraints, respectively. Thesimulation results validate the performance of the proposed schemes.(3) The issue of spectrum efficiency is investigated in bi-directional multi-relayOFDM networks with dynamic network coding. We first analyze the advantages ofnetwork coding on increasing spectrum efficiency and energy efficiency, and thenemphasize the benefits of dynamic network coding over static network coding. Next,considering on the probabilistic estimation error in imperfect CSI, we formulate aworst-case optimization problem, and propose a robust resource allocation scheme.Simulation results validate the effectiveness of the proposed scheme on resistance ofimperfect CSI, by comparing with the performance of the scheme with perfect CSIassumption when the actual obtained CSI has an error part. The advantages ofdynamic network coding are also confirmed by simulation results.(4) The issue of trade-off optimization between energy efficiency and trafficquality of experience (QoE) is studied in bi-directional multi-relay OFDM networkswith dynamic network coding. We study the trade-off optimization between energy efficiency and QoE to obtain the best balance between the two performance metrics.We propose a new metric, QEE (QoE-Energy), to indicate the QoE profit per energyincrease, and prove that QEE is quasi-concave with QoE, which implies the existenceof a unique global optimal point for the formulated quasi-concave optimizationproblem. By transforming the problem into a series of convex optimization feasibilityproblems, we propose an efficient linear-complexity optimization framework. Withthe framework, we develop asymptotic optimal resource allocation schemes fordecode-and-forward (DF) and compute-and-forward (CPF) relaying strategies.Simulation results validate the theoretical findings and the performance of theproposed schemes. Inspired by this research, we further develop a resource allocationscheme with flexible adjustment of QoE-energy trade-off degree, through introducingweighted factors for QoE and energy. This scheme allows network operators adjustthe QoE-energy tradeoff level easily.(5) A preliminary implementation proposal is presented to establish an OFDMcooperative relaying network test-bed. With GNU Radio/USRP open-source cognitiveradio research platform, we try to present an initial proposal to build a test-bed forOFDM cooperative relaying network with network coding, so as to provide someguides and suggestions for future detailed implementation. Specifically, we presentthe function requirements and the hardware configurations of the potential test-bed,and then design software architectures and communicating procedures for userstations and relays. Then, we analyze the major required functions in the cognitiveOFDM physical layer, including spectrum detecting, multi-band filtering,multi-packet transmitting and multi-packet receiving with single antenna,configurable physical interfaces for OFDM parameters (i.e., physical API), etc. Wealso present a synchronized medium access control (MAC) protocol, showing theframe structures, MAC statuses and protocol coordination procedures, which can beused as a carrier to implement and evaluate advanced functions such as the resourceallocation schemes and network coding schemes in the future.