Resource allocation for OFDMA cognitive radios under channel uncertainty

A weighted sum-rate maximization problem is considered for an access point (AP) allocating resources to wireless cognitive radios (CRs) communicating using orthogonal frequency-division multiple access (OFDMA). To protect the incumbent primary user (PU) system operating over the same frequency band, the interference inflicted to the PU receiver must be regulated. Since the channel gain estimates from the AP to the PU receiver may well be inaccurate in practice, a probabilistic interference power constraint is adopted. Although the latter translates to a second-order cone constraint, the overall optimization problem for joint transmit-power and subcarrier allocation is non-convex, and coupled over all subcarriers in general. To circumvent this hurdle, a tight polyhedral approximation of the second-order cone is employed. A near-optimal solution can then be efficiently obtained using the dual method.