Multi-Antenna System Design with Bright Transmitters and Blind Receivers
  This paper considers a scenario for multi-input multi-output (MIMO) communication systems when perfect channel state information at the transmitter (CSIT) is given while the equivalent channel state information at the receiver (CSIR) is not available. Such an assumption is valid for the downlink multi-user MIMO systems with linear precoders that depend on channels to all receivers. We propose a concept called dual systems with zero-forcing designs based on the duality principle, originally proposed to relate Gaussian multi-access channels (MACs) and Gaussian broadcast channels (BCs). For the two-user N*2 MIMO BC with N antennas at the transmitter and two antennas at each of the receivers, we design a downlink interference cancellation (IC) transmission scheme using the dual of uplink MAC systems employing IC methods. The transmitter simultaneously sends two precoded Alamouti codes, one for each user. Each receiver can zero-force the unintended user's Alamouti codes and decouple its own data streams using two simple linear operations independent of CSIR. Analysis shows that the proposed scheme achieves a diversity gain of 2(N-1) for equal energy constellations with short-term power and rate constraints. Power allocation between two users can also be performed, and it improves the array gain but not the diversity gain. Numerical results demonstrate that the bit error rate of the downlink IC scheme has a substantial gain compared to the block diagonalization method, which requires global channel information at each node. 
Liangbin Li and Hamid Jafarkhani
cs.IT math.IT