On synchronization requirements and performance limitations for CoMP systems in large cells

We consider coordinated multi-point systems where multiple base stations apply a joint signal processing in the uplink and downlink. Large distances between the base stations result in unavoidable differences in time of arrival between the users´ signals which in turn lead to inter-symbol interference in OFDM systems if the cyclic prefix length is exceeded. Moreover, carrier frequency offsets which are caused by imperfect oscillators lead to inter-carrier interference and are in particular a problem in the downlink due to the feedback delay of the measured channel state information. In this paper we derive metrics for evaluating the impact of time and frequency asynchronisms in CoMP systems with large base station distances. We compare performance results for CoMP and single user transmission techniques in a selected transmission scenario where we use a 3GPP/LTE baseline system.