Massive MIMO uplink transmission with pilot extension and system-level analysis

In this paper, a novel pilot extension scheme is proposed for massive MIMO uplink transmission, and its performance is evaluated analytically. Specifically, we divide the cell users into two groups, namely near users and far users, according to their distances to the service base stations. The far users are more motivated to mitigate the inter-cell interference than the near users at the price of data transmission opportunity, it is proposed to schedule one more pilot sequence to each far user, and share the pilot knowledge of strong interfering users via backhauls. Then the interference from the latter can be mitigated significantly. We also develop a general analysis framework for both conventional and proposed schemes, where the bounds on the cumulative distribution function of the uplink signal-to-interference ratio are derived instead of complex system-level simulations. It is shown by numerical simulations that the analytical bounds are tight and the proposed scheme could effectively improve the uplink signal-to-interference ratio for far users. Besides, significantly throughput gain can also be achieved for far users with reasonable length of coherent fading block.