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Performance Evaluation of IEEE 802.15.4 OQPSK and CSS PHY in the Presence of Interference

Industrial environments often exhibit harsh propagation conditions for wireless transmissions. This paper investigates the influence of different interference characteristics on the performance of IEEE 802.15.4 using the OQPSK and Chirp Spread Spectrum (CSS) PHY. Bit error rates are determined for AWGN, Rayleigh fading and self-interference scenarios. GNU Radio, a Software Defined Radio framework, serves as simulation environment. In addition to the implementation of the CSS transmitter and receiver, a low-complexity synchronization algorithm, which only consists of a correlator and a second order Phase Locked Loop (PLL), and its limitations are presented. Furthermore, MAC layer simulations are performed for beacon-enabled (slotted) as well as nonbeacon- enabled (unslotted) mode to make a statement about achievable throughput and latency in the presence of interference. It shows that the CSS PHY clearly surpasses the OQPSK PHY in throughput. Moreover, the simulation results are confirmed by the derivation of the theoretical maximum throughput for the investigated PHY layers.