OFDMA techniques in multicellular networks with total frequency reuse

Orthogonal frequency division multiple access (OFDMA) techniques are investigated in this paper. Five subchannel allocation algorithms are analysed and their performance in a multicellular environment is evaluated with simulations. Four schemes of lower complexity, suitable for the early deployment of wireless systems, are compared with a more computationally demanding scheme with respect to their blocking probability, loading factor and offered bit rate. The channel condition of each carrier is calculated and its knowledge is used for power controlled adaptive modulation, as an essential feature of the OFDMA technique. The general radio resource management process is divided into two steps: in the first step a base station allocates carriers to users while in the second step the modulation and power levels for each allocated carrier are defined. The simulation results demonstrate that a wireless system in its early deployment phase (up to 15-30% blocking probability) can employ simple OFDMA techniques capable of achieving high throughput. Furthermore, it is demonstrated that two of the proposed lower complexity schemes, (those based on cell coordination), offer good performance gain for higher data rate services. Nevertheless, these schemes achieve relatively lower gains with adaptive modulation, when compared with the techniques which exploit interference averaging or adaptive interference mitigation.