Traffic capacity of multi-cell WLANs

Performance of wlans has been extensively studied during the past few years. While the focus has mostly been on isolated cells, the coverage of wlans is in practice most often realised through several cells. Cells using the same frequency channel typically interact through the exclusion region enforced by the rts/cts mechanism prior to the transmission of any packet. In this paper, we investigate the impact of this interaction on the overall network capacity under realistic dynamic traffic conditions. Specifically, we represent each cell as a queue and derive the stability condition of the corresponding coupled queuing system. This condition is then used to calculate the network capacity. To gain insight into the particular nature of interference in multi-cell wlans, we apply our model to a number of simple network topologies and explicitly derive the capacity in several cases. The results notably show that the capacity gain obtained by using m frequency channels can grow significantly faster than m, the rate one might intuitively expect. In addition to stability results, we present an approximate model to derive the impact of network load on the mean transfer rate seen by the users.