In this paper, the edge caching problem in fog radio access network (F-RAN) is investigated. By maximizing the overall cache hit rate, the edge caching optimization problem is formulated to find the optimal policy. Content popularity in terms of time and space is considered from the perspective of regional users. We propose an online content popularity prediction algorithm by leveraging the content features and user preferences, and an offline user preference learning algorithm by using the online gradient descent (OGD) method and the follow the (proximally) regularized leader (FTRL-Proximal) method. Our proposed edge caching policy not only can promptly predict the future content popularity in an online fashion with low complexity, but also can track the content popularity with spatial and temporal popularity dynamic in time without delay. Furthermore, we design two learning based edge caching architectures. Moreover, we theoretically derive the upper bound of the popularity prediction error, the lower bound of the cache hit rate, and the regret bound of the overall cache hit rate of our proposed edge caching policy. Simulation results show that the overall cache hit rate of our proposed policy is superior to those of the traditional policies and asymptotically approaches the optimal performance.

Abstract-In this paper, the edge caching problem in fog radio access networks (F-RAN) is investigated. By maximizing the cache hit rate, we formulate the edge caching optimization problem to find the optimal edge caching policy. Considering that users prefer to request the contents they are interested in, we propose to implement online content popularity prediction by leveraging the content features and user preferences, and offline user preference learning by using the "Follow The (Proximally) Regularized Leader" (FTRL-Proximal) algorithm and the "Online Gradient Descent" (OGD) method. Our proposed edge caching policy not only can promptly predict the future content popularity in an online fashion with low computational complexity, but also can track the popularity changes in time without delay. Simulation results show that the cache hit rate of our proposed policy approaches the optimal performance and is superior to those of the traditional policies.Index Terms-F-RAN, edge caching, cache hit rate, content popularity, user preference.

In this paper, a joint transmitter and receiver design for pattern division multiple access (PDMA) is proposed.At the transmitter, pattern mapping utilizes power allocation to improve the overall sum rate, and beam allocation to enhance the access connectivity. At the receiver, hybrid detection utilizes a spatial filter to suppress the interbeam interference caused by beam domain multiplexing, and successive interference cancellation to remove the intra-beam interference caused by power domain multiplexing. Furthermore, we propose a PDMA joint design approach to optimize pattern mapping based on both the power domain and beam domain. The optimization of power allocation is achieved by maximizing the overall sum rate, and the corresponding optimization problem is shown to be convex theoretically. The optimization of beam allocation is achieved by minimizing the maximum of the inner product of any two beam allocation vectors, and an effective dimension reduction method is proposed through the analysis of pattern structure and proper mathematical manipulations. Simulation results show that the proposed PDMA approach outperforms the orthogonal multiple access and power-domain non-orthogonal multiple access approaches even without any optimization of pattern mapping, and that the optimization of beam allocation yields a significant performance improvement than the optimization of power allocation. Index TermsPattern division multiple access, pattern mapping, power allocation, beam allocation. I. INTRODUCTIONWith the new challenges of explosive mobile data growth, tremendous increase in the number of connected devices, and continuous emergence of new service requirements, future communication systems with high spectral efficiency are needed. In order to efficiently support unprecedented requirements for system sum rate and access connectivity, researchers from both industry and academia are focusing on the design of next-generation multiple access techniques, particularly non-orthogonal multiple access (NOMA)[1], [2].In mobile communications systems, the design of multiple access schemes is of great importance to increase the sum rate in a cost-effective manner. In general, multiple access schemes can be classified into orthogonal and non-orthogonal ones based on the way wireless resources are allocated to the users.Orthogonal multiple access (OMA) schemes, such as orthogonal frequency division multiple access (OFDMA) in downlink and single-carrier frequency division multiple access (SC-FDMA) in uplink, are adopted in the 4G mobile communication systems such as Long-Term Evolution (LTE) and LTE-Advanced (LTE-A) [3]. In order to attain further enhancements in sum rate and access connectivity, more advanced multiple access schemes need to be developed. Actually, NOMA schemes are optimal in the sense of achieving the capacity region of the broadcast channel [4]. In NOMA schemes, multi-user signals are superposed in the same time and frequency resources via code domain and/or power domain multiplexing at the transmitter, a...

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