A Linear-Time Grouping Algorithm for F-RANs with Index Coding and Cache-Aided NOMA

Both index coding and non-orthogonal multiple access (NOMA) are useful techniques for a transmitter to send information to multiple cache-enabled receivers. In former works, either index coding or cache-aided NOMA is applied in the system, while the combination of index coding and cache-aided NOMA has not been fully investigated. This work is the first attempt to integrate these two techniques. A two-phase transmission algorithm is proposed to first partition receivers into index coding groups and next pair these groups up for superposition coding. Cache-aided interference cancellation (CIC) is employed at the receiver. This new method is applied to a cache-enabled fog radio access network (F-RAN). Besides, a distinct-file caching scheme with imbalanced cache size at fog access points (F-APs) is proposed. For this particular caching scheme, the two-phase algorithm can be fine-tuned in a way so that its time complexity becomes linear in the number of F-APs, which is very fast and particularly desirable from a practical viewpoint. Furthermore, simulation results show that our proposed method can significantly reduce the power consumption for transmissions over the fronthaul link of the F-RAN.