A short feasibility study of a cognitive TV black space system

This paper evaluates the feasibility of overlaying a secondary system on a digital TV (DTV) system. We denote this type of approach TV black space (in contrast to TV white space). In this type of operation the secondary transmitter transmits on the same spectrum resources as the DTV system. Particularly, we consider the case where the secondary transmitter is collocated with the DTV transmitter and uses the same antennas. The fraction of the total transmitted power that is used for the secondary signal is set low enough so that the DTV receivers are always able to decode the DTV signals. The black space receivers decode the TV signal component and cancel it from the total received signal which results in an improved SINR of the secondary signal in the residual. Numerical evaluations show that this type of overlay in the DTV spectrum is feasible only when the secondary system is satisfied with relatively low SINR values of around 5 to 10 dB. A critical parameter when determining the secondary signal SINR after DTV signal cancellation is the SINR requirements by the primary system: DVB-T systems typically require SINR values above 20 dB and then overlay becomes less feasible since the fraction of power left for the secondary signal becomes very low. Additionally, realistic levels of TX EVM noise (around 6% to 8%) at the transmitter causes low achievable SINR values for the secondary signal even after DTV signal cancellation at the receiver side.