In this paper, the authors study the problem of distributed relay beamforming for a bidirectional cognitive relay network which consists of two secondary transceivers and K ognitive relay nodes and a primary network with a transmitter and receiver, using underlay model. For effective use of spectrum, they propose a Multiple Access BroadCasting (MABC) two-way relaying scheme for cognitive networks. The two transceivers transmit their data towards the relays and then relays re-transmit the processed form of signal towards the receiver. Their aim is to design the beamforming coefficients to maximize Quality of Service (QoS) for the secondary network while satisfying tolerable interference constraint for the primary network. They show that this approach yields a closed-form solution.