Experiment on MIMO cognitive radio using Tx/Rx beamforming

Spatial spectrum sharing with MIMO cognitive radio is efficient and attractive for wireless systems with limited communication resources. MIMO cognitive radio is a kind of cognitive radios using MIMO beamforming techniques to avoid interference to other nodes. There are many theoretical works on this topic but validation of the algorithm on real hardware has not been realized. Most of these works assume perfect CSI though it is always obtained with errors in practice, especially CSIT. It is known that MIMO beamforming techniques are sensitive to CSI errors and their performance might severely be degraded in practice. Despite the fact that cognitive radio with MIMO beamforming techniques is powerful in terms of spatial efficiency as shown by theoretical results, the feasibility of such systems in real environment have never been studied before. Therefore, we attempt to provide the first implementation of a MIMO cognitive radio system using Tx/Rx beamforming and prove the feasibility by measuring its throughput performance. In this paper, we will explain our implementation and measurement results. In the measurement, we measure achievable throughput of both primary and secondary system. As a result, we found that this system works effectively when transmit power of primary nodes is large enough while that of the secondary nodes is relatively small.