  In theory coordinated multi-point transmission (CoMP) promises vast gains in
spectral efficiency. But industrial field trials show rather disappointing
throughput gains, whereby the major limiting factor is proper sharing of
channel state information. Many recent papers consider this so-called limited
feedback problem in the context of CoMP. Usually taking the assumptions: 1)
infinite SNR regime, 2) no user selection and 3) ideal link adaptation;
rendering the analysis too optimistic. In this paper we make a step forward
towards a more realistic assessment of the limited feedback problem by
introducing an improved metric for the performance evaluation which better
captures the throughput degradation. We find the relevant scaling laws (lower
and upper bounds) and how that they are different from existing ones. Moreover,
we provide a robust iterative interference alignment algorithm and
corresponding feedback strategies achieving the obtained scaling laws. The main
idea is that instead of sending the complete channel matrix each user fixes a
receive filter and feeds back a quantized version of the effective channel.
Finally we underline our findings with simulations for the proposed system.
