Hybrid TDD Access Scheme with Confidence Factor Based Weighted Cooperative Sensing in Massive MIMO System

In this paper, a hybrid time-division duplex access scheme with confidence factor based weighted cooperative sensing for the femtocells has been proposed in cognitive massive multiple-input multiple- output (massive MIMO) system to improve the detection performance and achieve the high throughput while alleviate the influence to the macrocell users as little as possible. In the cognitive massive MIMO system, femtocell base stations (FBSs) sense the spectrum through cooperative scheme and decide whether to access the channel or not. Firstly, all the FBSs sense the macrocell users in the uplink channel and the macrocell BS in the downlink channel, and make dynamical clustering based on the channel conditions. After the information exchange within each cluster, the FBSs in each cluster update their confidence factors (CFs) and weight factors (WFs) according to the detection results. With consideration of the CFs and WFs, more accurate sensing results would be obtained. Simulation results and theoretical analysis show that the proposed scheme can get more accurate sensing results and better throughput tradeoff for the femtocells.