Random Access Strategy in Hierarchical OFDMA Wireless Networks

As a promising multiple access technique for B3G cellular networks, OFDMA provides high resource granularity, but has a limitation that, in case of high mobility, it cannot perform coherent detection due to the long symbol transmission time. Therefore we present an advanced model of a hierarchical cellular system that combines multiple access techniques of OFDMA and FH-OFDMA with micro and macrocells, which handle various cases efficiently considering user mobility and traffic class. We consider the issue of designing an appropriate reuse factor for random access channels in order to overcome the intercell interference problem in hierarchical OFDMA environments. Our finding is that full sharing, i.e., a reuse factor of 1, performs best for given random access channels in flat multicell environments. Applying this result to hierarchical cellular systems, we can use random access channels for micro and macrocells separately without coordination among neighboring cells. To achieve load balancing between micro and macrocells, we devise a random access strategy combined with an admission control scheme.