Effect of secondary transmission on primary pilot carriers in overlay cognitive radios

Cognitive radio aims to increase spectral efficiency by exploiting information about the environment and activity of other transmitters. It allows access to temporary and/or spatially unused TV spectrum, white space, or overlay on the TV transmission. In this paper we consider an overlay cognitive radio in DVB-T coverage area, TV black space. We analyze the performance of a simple sequential interference cancellation algorithm at secondary receiver in presence of channel estimation error. The channel estimation quality depends on how the overlay signal disturbs the primary pilots. We compare two Orthogonal-Frequency Division Multiplexing based overlay cognitive radio schemes having secondary with: 1) modified WLAN frame structure avoiding secondary transmission on primary pilots. 2) LTE-type frame structure that uses all the DVB-T carriers. A prototype system was implemented on hardware platform to validate analytical results and study implementation limitations. Simulation and measurement results show that overlay interference on primary pilots does not have significant impact on primary reception. However, unlike scheme (1), in scheme (2) signal-to-interference plus noise ratio at secondary receiver was found to be severely limited by interference level on pilot carriers.