The outage performance of realtime transmission in multiple asynchronous relays enhanced OFDM system

This paper¹ considers the outage performance of multiple relays transmission in Orthogonal Frequency Division Multiplexing (OFDM) systems. Relaying has been suggested in general to improve the reliability of wireless systems significantly and is therefore a candidate for wireless industrial communication systems that need to meet tough latency and outage requirements. Different from previous works, this paper takes synchronization mismatch of hardware processing time at multiple relays into account and characterizes the performance impact of such asynchronous relays on the reliability of the system. We focus especially on the case where the transceivers do not have instantaneous channel state information but still need to fullfill tough reliability and latency constraints. We find that with respect to this scenario the synchronization mismatch can lead to a significant loss of reliability even if the individual mismatch of relays is relatively small compared to the cyclic prefix of the OFDM symbol. Consequently, this paper devises countermeasures to efficiently combat the synchronization issues either by introducing a longer cyclic prefix or by decreasing/adjusting the number of active relays. We find that all proposed countermeasures have their application domains which are determined by the average SNR and the severity of synchronization errors.