  Cellular systems that employ time division duplexing (TDD) transmission are
good candidates for implementation of interference alignment (IA) in the
downlink since channel reciprocity enables the estimation of the channel state
by the base stations (BS) in the uplink phase. However, the interfering BSs
need to share their channel estimates via backhaul links of finite capacity. A
quantization scheme is proposed which reduces the amount of information
exchange (compared to conventional methods) required to achieve IA in a TDD
system. The scaling (with the transmit power) of the number of bits to be
exchanged between the BSs that is sufficient to preserve the multiplexing gain
of IA is derived.
