Overlay spectrum reuse in a broadcast network: Covering the whole grayscale of spaces

In this paper we address the problem of allowing secondary access to the spectrum assigned to a broadcast operator. We assume that the secondary transmitter knows of the primary message but is not able to apply interference cancellation techniques due to the lack of channel state information. Thus, interference cancellation can only be performed at the secondary receivers, provided they are able to decode the primary message. Unlike previous approaches, which study the particular cases of secondary access in a white space (far away from the influence of the primary transmitter) or a black space (inside the primary coverage zone), we present an analysis which is valid for any position of the secondary operation area. An interesting result arises from the study of gray spaces (a region which is near the primary coverage area), where the optimum power allocation for the secondary transmitter can increment the primary coverage area, thus benefiting the primary system.