  Base station (BS) cooperative transmission, also known as coordinated
multi-point transmission (CoMP), is an effective way to avoid inter-cell
interference in universal frequency reuse cellular systems. To gain the
promised benefit, however, huge feedback overhead is in demand to gather the
channel information. In this paper, we analyze the impact of channel asymmetry,
which is inherent in CoMP systems, on downlink BS cooperative transmission with
limited feedback. We analyze the per-user rate loss of a multi-user CoMP system
led by quantization. Per-cell quantization of multicell channels is considered,
which quantizes the local channel and cross channel separately and is more
feasible in practice. From both the analytical and simulation results, we
provide a whole picture on various critical factors that lead to the
performance loss. Specifically, we show that the per user rate loss led by
limited feedback depends on the location of its paired users, except for
relying on its own signal to noise ratio and the quantization errors as in
single cell multi-user multiple antenna systems. This implies that the
quantization accuracy required for local and cross channel of each user depends
on the locations of its own as well as its paired users.
