Bandwidth and routing optimization in wireless cellular networks with relays

Abstract

Abstract-This paper aims to quantify the performance improvement due to the use of fixed relays in the uplink of a wireless cellular network. Consider an orthogonal frequency division multiplex (OFDM) based cellular network in which each cell consists of a base station, multiple mobile users, and a number of relays. The questions of which frequency tones each link should use, whether the mobile station should communicate directly to the base station or though a relay, and how much power should be allocated on each frequency tone, form a simultaneous routing, frequency planning, and power allocation problem. This paper presents a dual decomposition approach to this problem and illustrates that while the use of relays does not necessarily increase the total cell throughput, it significantly improves the minimum common rate achievable across all the mobile users. Thus, the main benefit for deploying relays is in the improvement in fairness, rather than the total throughput. I. INTRODUCTIONThe use of relays to improve the performance of wireless cellular systems has been a subject of intense research activities in recent years. Relays have been shown to be capable of improving the capacity, coverage, and reliability of wireless connections in various settings (e.g. [1]- [7]). However, the deployment of relays in a cellular network also introduces significant practical challenges. Not only does the use of relays increase deployment cost, the network planning and resource allocation problem in relay networks also becomes more complicated. This paper aims to quantify the performance improvement due to the use of relays from a system point of view by considering a resource allocation problem in the uplink of a wireless cellular network with fixed relay infrastructure. We consider an orthogonal frequency division multiple access (OFDMA) based system and dynamically optimize which frequency tones each mobile station (MS) and relay station (RS) should use, whether the MS should communicate directly to the base station (BS) or though a relay, and how much power should be used on each frequency tone. We use a dual decomposition technique and show that such a simultaneous routing, frequency planning, and power allocation problem can be solved efficiently. Further, by comparing with traditional networks while taking deployment cost and fairness across the users into account, we illustrate that the main benefit of relay deployment is in improving the minimum supportable data rate rather than the overall throughput.Resource allocation issues for wireless cellular networks with relays have been considered extensively in the literature.