An Analysis on Downlink Capacity of Multi-Cell OFDMA Systems Under Randomized Inter-cell/sector Interference

An analysis on downlink capacity of multi-cell OFDMA (orthogonal frequency division multiple access) systems is presented in this paper under a model of randomized multiple access interference, which is a result of applying random sub-carrier allocation among different cells/sectors. The analysis shows that the system capacity is either in the bandwidth-limited or power-limited region and that optimum tradeoff between capacity and coverage is achievable in a sense that given a required capacity the maximum coverage can be determined. The capacity is evaluated for different system setups, which are characterized by cell radius, reuse factor and types of antenna system with and without spatial division multiple access (SDMA). Three types of antenna are considered including omni-directional antenna, 3-sector antenna and switched-beam smart antenna. Numerical results show that the use of 3-sector and switched-beam smart antenna can enlarge the bandwidth-limited region and achieves a better capacity and coverage tradeoff.