Low-Latency Multichannel ALOHA With Fast Retrial for Machine-Type Communications

In this paper, for low-latency transmissions in machine-type communications, we study multichannel ALOHA with fast retrial that can shorten the access delay by immediate retransmissions of collided packets. To analyze the access delay of multichannel ALOHA with fast retrial, we employ an erasure channel model, which is equivalent to the widely used collision model, and study the effective capacity and the quality of service (QoS) exponent. Through the asymptotic analysis, we show that the QoS exponent grows logarithmically with the system dimension (i.e., the number of subchannels), which implies that multichannel ALOHA with fast retrial can effectively shorten the average access delay by increasing the system dimension. However, the growth rate of the effective capacity is shown to be slower than linear when the system dimension increases, which becomes the cost of improved access delay. In particular, the effective capacity is proportional to (N/lnN), where N is the number of subchannels. From the QoS exponent, the tail probability of queue is obtained and compared with simulation results, which confirms that the theoretical results from the derived QoS agree with the simulation results for large systems.