We propose a network architecture that enables spectrum sharing between a primary TV broadcast system and a secondary cellular broadband system. To compensate for the interference caused by overlay transmissions, the cognitive cellular base station cooperates with the TV system. We base our encoding approach on prior theoretical results and demonstrate how the cognition can be enabled in the TV spectrum. We show the performance gains of the proposed overlay approach for both the downlink and uplink of the cellular system. While the proposed approach requires that a cellular base station spends a part of its power to cooperate with the TV system, at the same time, it opens up frequency bands with favorable propagation properties, otherwise unavailable to cellular systems. This approach can thus bring benefits to both cellular and TV network operators in terms of performance and increased capacity.