Spectrum Occupancy Estimation in Wireless Channels with Asymmetric Transmitter Powers

In proposed cognitive radio schemes, channel occupancy is often offered as the metric to determine if a channel is free to open a new communication channel. Channel occupancy is the time average of detected transmissions above a certain power level. In many systems the transmission power between the uplink side and down-link side are asymmetric. If a single power threshold is used, then a system may underestimate channel occupancy on the low power down-link side. This results in an increased probability of interference in an existing channel if a listen-before-talking scheme is used. To avoid this hidden terminal problem, cognitive radios need to better understand the receiver properties of existing wireless channels.