D2D Assisted Multi-Antenna Coded Caching

Abstract

A device-to-device (D2D) aided multi-antenna coded caching scheme is proposed to improve the average delivery rate and reduce the downlink (DL) beamforming complexity. Novel beamforming and resource allocation schemes are proposed where local data exchange among nearby users is exploited. The transmission is split into two phases: local D2D content exchange and DL transmission. In the D2D phase, subsets of users are selected to share content with the adjacent users directly. In this regard, a low complexity D2D mode selection algorithm is proposed to find the appropriate set of users for the D2D phase with comparable performance to the optimal exhaustive search. During the DL phase, the base station multicasts the remaining data requested by all the users. We identify scenarios and conditions where D2D transmission can reduce the delivery time. Furthermore, we demonstrate how adding the new D2D phase to the DL-only scenario can significantly reduce the beamformer design complexity in the DL phase. The results further highlight that by partly delivering requested data in the D2D phase, the transmission rate can be boosted due to more efficient use of resources during the subsequent DL phase. As a result, the overall content delivery performance is greatly enhanced, especially in the finite signal-to-noise (SNR) regime.INDEX TERMS Multi-antenna communications, coded caching, multicast beamforming, D2D communication.

Low-Complexity Multi-Antenna Coded Caching Using Location-Aware Placement Delivery Arrays

“…In this section, we explain the optimal design of precoding vectors v k (n) in ( 6) to enhance the finite-SNR performance. Unlike the conventional max-min beamforming problem addressed in previous works such as [29], [32], [54], we consider a weighted-max-min (WMM) beamforming approach to enable multi-rate transmission. In this regard, we alter the iterative approach presented in [54], with a slight modification to account for the weighted beamforming requirements, wherein the weights reflect the non-uniform quantities of data transmitted to different users.…”

“…Later, the analysis in [29] showed that an optimized multi-antenna precoder design is necessary for the CC scheme to perform well also in the low-SNR regime. Soon, device-to-device (D2D) CC schemes were proposed (e.g., [30]- [32]) to increase the network throughput. Despite exciting theoretical gains, the real-world implementation of CC schemes has been restricted by a wide range of practical issues, which are highlighted below.…”

“…The PDA structure provides a set of conditions (reviewed for MISO systems in Section III) that allows a given matrix to be used for both content placement and delivery of a CC scheme, thus translating the subpacketization reduction problem to finding a small-dimension matrix satisfying PDA conditions. Interestingly, authors in [33] demonstrated that all the schemes in [19], [26]- [32] could also be presented as PDAs. Motivated by the generalized framework in [33], various PDA-based CC schemes were later proposed for different settings, aiming for reduced subpacketization [34]- [36].…”

“…A major breakthrough in subpacketization reduction was achieved with the introduction of signal-level CC schemes in [37]. In contrast to bit-level CC schemes [19], [26]- [32], where file fragments intended to different users are combined/separated using bit-wise XOR operations in the finite field, signal-level CC schemes rely on the superposition of all precoded data terms in the signal domain and the regeneration and cancellation of the unwanted parts at the physical layer of each receiver (see [2] for a more detailed explanation). As a result, the design flexibility is greatly increased compared with bit-level schemes, enabling the subpacketization requirement of MISO-CC setups to be even smaller than their comparable SISO-CC settings [37].…”

STAR-RIS Empowered NOMA Systems With Caching and SWIPT

“…Compared to the former [41], exploiting the latter approach [42] yields more flexible and efficient communications as it does not require any overhead for network deployment. As a consequence, research on caching-based individual nodes has been showing its feasibility in a variety of contexts to enhance the system's spectrum utilization [43]- [46] and cell-edge users' performance [47]- [50] From the aforementioned discussions, it is clear that caching is a key part of future communication networks and remains relatively unexplored in conjunction with emerging technologies, such as NOMA, STAR-RIS, and SWIPT. In particular, as shown in [44], [45], exploiting caching at nearby users in coordinated NOMA systems can efficiently mitigate the impact of inter-relaying interference.…”