Analysis of a Cooperative Caching-Multicast Strategy in D2D-Aided Networks

Due to characteristics of video request, i.e., request-repeatability and group-orientation, we propose a cooperative caching-multicast strategy in typical Device-to-Device (D2D)-aided networks to improve the timeliness and space coverage of video services. First, based on the request cumulative time window (RCTW), a multicast-scale based caching resource allocation scheme is presented and videos whose corresponding multicast groups have larger probabilities to be non-empty are allocated more caching spaces. Second, a collaborative transmission scheme is presented, where base station opportunistically multicasts blocks of the requested video to group while failed receivers can obtain the missing blocks from successful receivers with the aid of D2D joint transmission. Finally, the tractable expressions for the average transmission coverage rate and the system average transmission delay are derived. The effectiveness of the proposed strategy when the video popularity distribution is in the general dip range is verified by numerical examples. Simulation results demonstrate that a reasonable RCTW can balance the relationship between the service probability of more users through one multicast transmission and the system transmission delay.