Synchronization requirements for OFDM-based cellular networks with coordinated base stations: Preliminary results

Coordinating base stations is envisioned as a key component in future multi-user cellular networks. While the capacity limits of such networks are becoming well understood and promise high spectral efficiency gains, there is still little knowledge about the performance degradation that may result from imperfect synchronization among bases and mobiles. We study this problem for the downlink of basecoordinated networks that use OFDM for the air interface. Transmissions are impaired by carrier frequency offset and sampling frequency offset. We derive an accurate signal model that captures the effect of both impairments and compute the interference caused by them. We find that the carrier frequency offset requirement for base stations is an order of magnitude stricter than for mobile terminals and that the required precision can only be attained with rubidium oscillators or by high quality oven-controlled crystal oscillators stabilized by GPS.