A Combined Symbol-Based Closed-Loop Orthogonal Space-Time Block Code for four transmit antennas

We propose the CS-CL-OSTBC (Combined Symbol-Based Closed-Loop Orthogonal Space-Time Block Code) for four transmit antennas. In the multiple antenna systems, the CS-CL-OSTBC not only achieves full rate and full diversity with the linear MLD (maximum-likelihood detection) but also obtains higher feedback gain than existing CL-OSTBCs due to more efficient use of channel feedback information. In the proposed closed-loop feedback scheme, each complex value of channel coefficients is rotated to a positive real value by the exact channel phase feedback. As a result, the channel gain can be expressed as the square of the sum of all positive real values and obtains the maximum value without any channel loss. Simulation results on bit error rate performance show that the CS-CL-OSTBC outperforms existing CL-OSTBCs for various spectral efficiencies.