Coexistence of SRD CSMA-based systems with DC-based systems and LTE

Abstract

Short Range Devices (SRDs) operate in unlicensed spectrum, and though there are some rules to control the sharing of radio resources, there is no limit to the geographical density of devices. Therefore, efficient radio resource utilization is of paramount importance to guarantee the expected performance, even in high contention situations. It is also necessary to guarantee that the growing number of SRDs operating in the adjacent band of Long Term Evolution (LTE) do not degrade its performance, and vice-versa. In this work, the operation of SRDs in a building automation application scenario is assessed using a Carrier Sense Multiple Access (CSMA) channel access scheme for multiple SRD densities. CSMA is considered both as a standalone access scheme and in coexistence with another random channel access scheme — Duty Cycle (DC). Simulation results have shown that the SRD system underperforms if the transmission power is too low or too high, which means that, in order to obtain the best performance, the transmission power of CSMA nodes needs to be carefully adjusted taking into account the operating area. Moreover, CSMA is proven to successfully operate in the presence of dozens of DC sensors, although at the cost of more energy required for retransmissions. Finally, with respect to the LTE and SRD coexistence scenario, the analysis shows that the LTE User Equipment (UE) emissions may impair the SRD system; on the other hand, the impact of SRD emissions on LTE UEs is insignificant.