Carrier aggregation/channel bonding in next generation cellular networks: Methods and challenges

To provide cellular systems with additional spectral resources, the wireless industry is considering the aggregation of frequency carriers in licensed, unlicensed, and shared access (SA) bands. In this article, we focus on reliable carrier aggregation/channel bonding (CA/CB) techniques, in which when CA/CB between the licensed, unlicensed, and SA carriers is performed, the licensed carrier is used for the primary and secondary carriers, and the unlicensed and SA carriers operate as additional secondary carriers. We provide a taxonomy of the use of CA/CB in cellular networks and highlight the differences between different CA/CB approaches. We make the case that although the licensed primary carrier can give reliable transmission of control signaling, due to the nature of unlicensed and SA bands, for the efficient aggregation of secondary carriers there is a need for new CA/CB methods. To illustrate our case for novel CA/CB methods, we provide examples for different network environments where intelligent CA/CB decisions can increase throughput compared to the traditional CA/CB methods. Finally, we highlight challenges in the design of novel CA/CB techniques in unlicensed and SA bands.