On MSE Balancing in the MIMO Broadcast Channel with Unequal Targets

Average mean square error (MSE) balancing in a multiple-input multiple-output (MIMO) scenario was studied for multiple streams per-user and even for various power limitations that bound the achievable performance, but usually with equal MSE targets. We now focus on the case where the user MSE targets are different. In this situation, only a subset of the receivers may be served at the solution. At low transmit power, users with low target values are strictly prioritized and transmission to users with large MSE targets can even be switched off. That way, MSE balancing distinguishes from signal-to-interferenceplus- noise (SINR) and rate balancing optimizations, where transmission to all users is always active. The transmission to users dependent on the balancing level leads to several practical and theoretical questions that we address here.