Estimation of Time and Frequency Offsets in LTE Coordinated Multi-Point Transmission

We address the impact, estimation and compensation of time and frequency offsets in LTE CoMP. In LTE CoMP, transmissions may come from a different transmission point in every subframe of one millisecond. Due to propagation delay differences and time-frequency synchronization imperfections between the transmission points, the user equipment (UE) receiver is thus exposed to different time- frequency offsets in every subframe. In this paper we illustrate both analytically and numerically the impact of these time and frequency offsets on channel estimation performance and finally on LTE CoMP link-level demodulation performance. Furthermore, we study the applicability of existing LTE reference signals to the time-frequency offset estimation problem. In particular we compare two approaches in which the UE is either aware or unaware of the exact transmission point. Finally, we show with LTE link-level simulations that using the proposed approaches the impacts of time-frequency offsets can be almost perfectly compensated.