Spatial Interweave LTE-TDD Cognitive Radio Communication

This presentation highlights the capabilities of the EURECOM OpenAirInterface platform in terms of long term evolution-time division duplex (LTE-TDD) reciprocity. To this end, we introduced a cognitive radio scenario including two secondary users and two primary users in a system based on LTE-TDD specification. Specifically, we study the problem of beamforming design for a cognitive radio system in which multiple-input multiple-output (MIMO) secondary link, wants to opportunistically communicate without harming the primary SISO system. In the proposed solution the opportunistic user designs its beamformer in order to zero-force at the primary receive antenna, thus lying in the spatial whitespace of the primary system, causing no interference to the latter. To solve this beamforming design problem, the knowledge of channel state information at the transmitter is crucial. In our model we do not require any priori knowledge of the channel information but we rely on channel reciprocity in TDD transmission. We provide a beamformer design algorithm and channel estimation procedures which allow the secondary communication without cooperation from the primary system. To compensate the channel mismatch we introduce a new calibration algorithm that outperforms the performance of previously proposed solutions for MIMO channels.