Comparing random access protocols in UWB based wireless sensor networks

In this paper we compare impulse-radio ultra wideband (IR-UWB) physical layer related medium access control (MAC) protocols, Slotted Aloha and optional preamble mode six of IEEE 802.15.4-2011, and preamble sense multiple access when the events of false alarm and miss-detection are introduced. Furthermore, a generalized multi-slot channel access scheme is proposed that can, with a proper selection of slots, represent any of the above MAC protocols. As a result of the generalization, an efficiency factor is then proposed, which allows for the protocols to be compared efficiently. At present, the challenge of designing a random access protocol suitable for IR-UWB is however, not completely solved. The generalized multi-slot model and efficiency factor help in determining the optimal number of slots, given certain preamble lengths and channel conditions. While there does not exist a globally optimal solution for all combinations of preamble length and signal-to-noise ratio, this paper shows that dividing the maximum MAC protocol data unit from 4 to 8 equally-sized slots, each with their own preamble, provides the best solution in all but the extreme cases.