Opportunistic Transmission for Heterogeneous Cognitive Cellular Networks

Heterogeneous cellular structure is a potential scheme in the sixth generation (6G) network, where macro and micro base stations (BSs) are collaborated to improve quality of service (QoS) for users. For the conventional heterogeneous cellular networks, data of users is transmitted at one frequency band and perfect channel state information (CSI) is required to beamforming. However, adjacent frequency interference and imperfect CSI decrease the spectrum efficiency (SE) of cellular network and QoS of users. In order to deal with performance loss of SE and QoS, this paper proposes a cognitive radio (CR)-based heterogeneous cellular networks, where opportunistic scheme is applied to improve QoS of users with imperfect CSI. Then, an optimization problem is established, considering both resource allocation and user selection under the constraints of users' QoS requirements. For the convenience of solving, we divide the optimization problem into two suboptimal issues and use an iterative method to approximate the global optimal solution. Numerical results reveal that the proposed scheme can achieve higher SE than the conventional scheme in heterogeneous cellular networks.