Space-time block coding in MIMO cognitive networks with known channel correlations

We consider a spectrum sharing based cognitive radio network where a secondary mulitple-input multiple-output (MIMO) communication link coexists with a primary user by opportunistically utilizing the transmit spectrum originally allocated to the primary user. The secondary link employs orthogonal space-time block coding (OSTBC) at the transmitter and maximum likelihood (ML) decoding at the receiver. For this system, we focus on designing linear precoders assuming the knowledge of the transmit antenna fading correlations for both the secondary-transmitter to primary-receiver (ST-PR) and secondary-transmitter to secondary-receiver (ST-SR) links at the secondary transmitter. Given a limited power budget of the secondary transmitter, the precoder is designed to minimize the minimum-distance average pair-wise error probability (PEP) of the secondary user subject to the average interference-power constraint at the primary receiver. We present two sub-optimal solutions based on the eigen-beamforming on ST-SR channel and interference nulling on ST-PR channel. Simulation results are shown to compare the performance of these precoding schemes.