Impact of Traffic Load on OFDMA Femtocells Interference Mitigation

The primary challenge in heterogeneous cellular networks is mitigating intercell interference, particularly in dense deployments of residential femtocells. Traditionally, interference in wide-area cellular networks has been studied from a multicell resource-allocation perspective, where radio resources, e.g., power and bandwidth, in each cell are centrally managed to reduce interference. This approach generally assumes a fully loaded network (i.e., many simultaneous active users in a cell) where the system performance is insensitive to the activity of a single user. This assumption is not suitable for femtocells, which are designed to serve very few users and thus lack the presumed traffic aggregation. In this paper, we quantify the impact of the user activity factor by comparing the performance of centralized resource-allocation schemes represented by a highly idealized power control protocol to that of a simple random access protocol. Our analysis shows that, with a high probability, a simple un-optimized random access protocol would perform much better than a fair optimized power-controlled network in most of the unsaturated traffic scenarios. If the network is saturated, then a fixed orthogonal partitioning of the channel bandwidth among femtocells would be the best strategy to handle the interference. This result highlights the importance of modeling the random user activities and traffic patterns in the design and analysis of femtocell interference mitigation solutions.