For Massive Access With Sporadic Traffic in M2M Communication: Collision Avoidance or Collision Resolution

To meet the increased requirement of machine-to-machine (M2M) communication, the potential to support massive access with sporadic traffic in uplink of two typical methods, one is the collision avoidance (CA) method at the user side, and the other is the collision resolution (CR) method at the base station (BS) side, is explored under grant-free protocol in this paper. A comprehensive study from MAC layer is conducted under the proposed distributed queue model, which describes the queue behavior of each device and the interaction between devices under grant-free protocol. The upper bounds of the throughput and the success probability of CA method are derived and the closed forms of the throughput and the success probability of a typical CR method, known as power domain multiple access (PDMA), are derived. The performance is further analyzed besides delay and stability. Through simulations, we validate that there is a hopeful upper bound for CA method, and the performance of PDMA can be flexibly improved with variable power level, which has a similar effect with channel extension. On the other hand, we note that grant-free protocol is suitable for access when the input traffic is below a critical threshold, otherwise packets would be blocked at the queue and the delay would increase infinitely.