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

The conventional TDoA (Time Difference of Arrival)-based and RSS (Received Signal Strength)-based location schemes create large positioning errors because of the various wireless channel effects such as path loss, shadowing, and NLoS (Non-Line-of-Sight) components of the multipath channels. In this paper, we propose an improved wireless location scheme which performs a weighted combination of the TDoA and RSS location schemes to improve a detection probability in the mobile-WiMAX femto-cell environments.

We present a simple bit allocation scheme based on adaptive coding for MIMO-OFDM (Multiple Input Multiple Output - Orthogonal Frequency Division Multiplexing) systems with V-BLAST (Vertical-Bell laboratories LAyered Space-Time) detector. The proposed scheme controls the code rate of the channel coding and assigns the same modulation and coding to the set of selected sub-channels, which greatly reduces the feedback burden while achieving good performance. Simulation results show that the proposed scheme with minimal feedback provides significant performance improvement over other systems.