Downlink/uplink Configuration Identification of TD-LTE Primary Systems in Cognitive Radios

When the cognitive radios are coexisting with time division duplex systems, it should firstly find out the link directions of the primary systems for the separate design and implementation of the followed spectrum sensing and access. However, in the present studies, this information is assumed as prior information of the cognitive radios, which in fact is not practical in common scenarios. In this paper, a method based on the power levels on both links of TD-LTE is proposed to identify the link directions of subframes and the downlink/uplink configuration in the TD-LTE. This method needs not the cooperation between the primary and secondary systems. Simulations show that the method can meet a high accuracy when a few of frames and SUs are participated in the identification.