Stability and Delay Analysis of Buffered Aloha Networks

In this paper, a unified analytical approach is developed to characterize the stability and delay performance of buffered Aloha networks. It is demonstrated that a buffered Aloha network can be stabilized if backoff parameters are properly selected. The stable region of backoff factor q is derived and shown to be enlarged by increasing the cutoff phase K. With Geometric Retransmission (K{=}1), for instance, the stable region rapidly diminishes as the number of nodes n increases, implying that a slight change of network size may lead to instability if the backoff factor q is not updated accordingly. In contrast, a buffered Aloha network with Exponential Backoff (K{=}∞) is much more robust as the stable region becomes insensitive to the number of nodes n. The improvement on stability performance is, nevertheless, achieved at the cost of severe delay jitter. The delay analysis further reveals that the second moment of access delay of Head-of-Line (HOL) packets rapidly grows with the cutoff phase K when the network is saturated. In spite of an improved stable region, an excessively large K will lead to significant degradation of queueing performance.