1 Adaptive Resource Allocation in Cooperative Cellular Networks

1.1 Introduction The cellular structure is a central concept in wireless network deployment. A wireless cellular network is comprised of base-stations geographically located at the centre of each cell serving users within its cell boundary. The assignment of users to base-stations depends on the relative channel propagation characteristics. As a mobile device can usually observe signals from multiple base-stations, the mobile is typically assigned to the base-station with the strongest signal; signals from all other base-stations are then regarded as intercell interference. However, at the cell edge, it is often the case that the propagation path losses from two or more base-stations are similar. In this case, the signal-to-noise-and-interference ratio (SINR) would have been close to 0dB, even if the mobile is assigned to the strongest base-station. To avoid excess intercell interference in these cases, traditional cellular networks employ a fixed frequency reuse pattern so that neighbouring base-stations do not share the same frequency. In this manner , neighbouring cells are separated in frequency so that cell-edge users do not interfere with each other. The traditional fixed frequency reuse patterns are effective in minimizing inter-cell interference, but it is also resource intensive in the sense that each cell requires substantial amount of nonoverlapping bandwidth, so that only a fraction of the total bandwidth can be made available for each cell. Consequently, many standards for future wireless systems have targeted on maximal frequency reuse, where all cells use the same frequency everywhere. In these systems, it is crucial to manage intercell interference using dynamic power control, frequency allocation, and rate allocation methods. Wireless channels are fundamentally impaired by fading, by propagation loss, and by interference. In the past decade, intense research has focused on the mitigation of short-term fading, where spatial, temporal and frequency diversity techniques have been devised to combat the short-term variation of the channel over time. Large-scale fading, propagation loss and intercell interference, however , call for different approaches. As large-scale channel and noise characteristics can often be estimated at the receivers and made available at the transmitter, rather than combating large-scale fading the right approach is to adapt to it.