Performance Study on Cooperative Relaying Topologies in beyond 3G Systems Eike REETZ, Rainer HÖCKMANN, Ralf TÖNJES University of Applied Sciences Osnabrueck, P.O. Box 1940, 49009 Osnabrueck, Germany Tel: +495419693251, Fax: +4954196913251, Email: e.reetz@fh-osnabrueck.de Abstract: Relaying has been proposed to support users suffering from high shadowing or high interference and therefore being not able to receive high data rates. With adaptive relaying, a higher Modulation and Coding Scheme (MCS) can be used in order to increase the feasible data rate. The investigation of relaying techniques widely has concentrated on information theoretical methods. Instead, this paper focuses on system level simulations to analyse the achievable results within a realistic environment. The question where to locate the Relay Stations is investigated and the achievable system performance is outlined. We show that relaying techniques can improve the median cell throughput and decrease the outage probability. Cooperative relaying results in the lowest outage probability, whereas the introduced concept of Dynamic Resource Relaying (DRR) offers a higher cell throughput. For the investigated LTE (3GPP Long Term Evolution) system with a frequency re-use factor of one, the outage probability can be decreased by using relaying and no further frequency planning is required. Keywords: Cooperative relaying, relaying topologies, LTE. 1. Introduction Next generation mobile communication networks require advanced transmission schemes to achieve their intended performance targets. Utilising the commonly supposed multiple access technique OFDMA (Orthogonal Frequency Division Multiple Access), 3GPP LTE (Long Term Evolution) offers the highest data rates only to users close to the Base Stations (BS). In order to increase the cell throughput, one option is to increase the BS density. But this would result in increased deployment and operational costs. However, the introduction of Relay Stations (RS) is an approach for cost efficient and fair resource allocation for users in larger coverage areas. The first analysis of the three node relay channel was performed by van der Meulen [1]. Cover et al. [2] proceeded by proving capacity theorems for the relay channel. The extension of cooperation was introduced by Sendonaris et al. [3][4], showing that the capacity for the user increases with cooperative strategies and the transmission becomes more robust to channel variations. Laneman et al. [5][6] investigated Space Time Block Coding (STBC) together with relaying techniques. Additional cooperative protocols were introduced by Nabar et al. [7] exploiting parallel transmissions of signals from the BS and the RS at the same time. This results in efficient utilisation of frequency/time resources but requires additional orthogonal radio resources. Some simple cooperative protocols were proposed by Herhold et al. [8][9] proving that they can increase end to end spectral efficiency. Weiss et al. [10] investigated relay-enhanced topologies and compared them with conventional cellular systems. They showed that the spectrum efficiency can be increased with relay enhanced cells. A general overview of relaying concepts is given by Pabst et al. [11].