Study on spectrum sharing method based on distance estimation for cognitive radio networks

We investigate a method to set the maximum allowable transmit power (MATP) for a secondary base station (SB) in dynamic spectrum sharing among secondary users (SUs) and primary users (PUs). In conventional methods, location information is assumed to be available. Thus, the MATP can be set by considering the shadowing between the SB and the PU receivers to satisfy a constraint. Specifically, probability that the interference caused by SB exceeds the allowable interference level should be less than the constrain target probability (CTP). We assume that the location information is not available at secondary network. Instead, the SB uses the received signal strength (RSS) from the PU transmitter for distance estimation. In this case, we have to consider shadowing not only between the SB and the PU receivers, but also between the PU transmitter and the secondary receiver(s). In addition, we also need to account for the uncertainty of the distance. Furthermore, we consider multipath fading. In order to satisfy the CTP, we proposed a two-step approach to setting the MATP where a transmission decision margin and a transmit power margin are utilized. To reduce these margins, we also proposed cooperative MATP setting method utilizing also RSS values from several SUs. Simulation results confirm the effectiveness of the proposed cooperative MATP setting method.