Performance of rateless codes in ALOHA WANETs

In this paper, we study the performance of wireless adhoc networks (WANETs) that employ rateless error correction codes. We consider a WANET which uses constant power for all transmissions and adapts the pure ALOHA as the channel access protocol. The locations of nodes are modeled by a homogeneous space time Poisson point process with Rayleigh fading. The paper quantifies the rate density and the dynamic variations of packet transmission time by deriving an upper bound on the CCDF of the packet transmission time. The rate density of rateless codes is compared to two benchmarks, the ergodic rate density (ERD) and the rate density of fixed rate codes. The considered rateless coding scheme is attractive, as it does not require time diversity, and each packet is transmitted within a single coherence time. Yet the derived bound shows that the rate density of rateless codes can be quite close to the ergodic rate density. Thus, the presented network has near ERD performance while maintaining shorter delays. We also demonstrate that rateless codes achieve a higher rate density than fixed rate codes.