Secure content delivery over device‐to‐device communications underlaying cellular networks

Content delivery via device‐to‐device (D2D) communications is a promising technology for offloading the heavy traffic for future mobile communication networks. As security is a critical concern for the users, we focus on improving the secrecy capacity for content dissemination in D2D communications. In this work, we explore the inherent characteristics of wireless channels to prevent eavesdropping. Firstly, we propose a power control scheme to obtain the optimal transmission powers for the D2D links without violating secrecy requirement of cellular users. Then, we formulate the problem as a stochastic optimization problem, aiming at maximizing the secrecy capacity gain of D2D communications. By solving the expected value model for the stochastic optimization problem, the optimal D2D links are selected to realize maximal ergodic secrecy capacity gain. Specifically, a weighted conflict graph is formulated according to the protocol model. Thus, the optimization problem has been transformed to the maximum weighted independent set problem, which is solved by a greedy weighted minimum degree algorithm. Simulation results demonstrate that the content dissemination scheme with power control can bring high secrecy capacity gain to the network. Copyright © 2016 John Wiley & Sons, Ltd.     

Location‐based distributed caching for device‐to‐device communications underlaying cellular networks

Device‐to‐device (D2D) communications have been viewed as a promising data offloading solution in cellular networks because of the explosive growth of multimedia applications. Because of the nature of distributed device location, distributed caching becomes an important function of D2D communications. By taking advantage of the caching capacity of the device, in this work, we explore the device storage and file frequent reuse to realize distributed content dissemination, that is, storing contents in mobile devices (named helpers). Specifically, we first investigate the average and lower bound of helper amount by dividing the network into small areas where the nodes are within each other's communication radius. Then, optimal helper amount is derived based on average helper amount and network topology. Subsequently, a location‐based distributed helper selection scheme for distributed caching is proposed based on the given optimal helper amount. In particular, nodes are selected as helpers according to their locations and degrees, and contents are placed in the manner for maximizing total user utility. Extensive simulation results demonstrate the factors that affect the optimal helper amount and the total user utility. Copyright © 2015 John Wiley & Sons, Ltd.     

Proactive content caching by exploiting transfer learning for mobile edge computing

To address the vast multimedia traffic volume and requirements of user quality of experience in the next‐generation mobile communication system (5G), it is imperative to develop efficient content caching strategy at mobile network edges, which is deemed as a key technique for 5G. Recent advances in edge/cloud computing and machine learning facilitate efficient content caching for 5G, where mobile edge computing can be exploited to reduce service latency by equipping computation and storage capacity at the edge network. In this paper, we propose a proactive caching mechanism named learning‐based cooperative caching (LECC) strategy based on mobile edge computing architecture to reduce transmission cost while improving user quality of experience for future mobile networks. In LECC, we exploit a transfer learning‐based approach for estimating content popularity and then formulate the proactive caching optimization model. As the optimization problem is NP‐hard, we resort to a greedy algorithm for solving the cache content placement problem. Performance evaluation reveals that LECC can apparently improve content cache hit rate and decrease content delivery latency and transmission cost in comparison with known existing caching strategies.     

Energy‐efficient resource allocation in D2D communications for energy harvesting–enabled NOMA‐based cellular networks

In this paper, we propose an energy‐efficient power control and harvesting time scheduling scheme for resource allocation of the subchannels in a nonorthogonal multiple access (NOMA)–based device‐to‐device (D2D) communications in cellular networks. In these networks, D2D users can communicate by sharing the radio resources assigned to cellular users (CUs). Device‐to‐device users harvest energy from the base station (BS) in the downlink and transmit information to their receivers. Using NOMA, more than one user can access the same frequency‐time resource simultaneously, and the signals of the multiusers can be separated successfully using successive interference cancellation (SIC). In fact, NOMA, unlike orthogonal multiple access (OMA) methods, allows sharing the same frequency resources at the same time by implementing adaptive power allocation. Our aim is to maximize the energy efficiency of the D2D pairs, which is the ratio of the achievable throughput of the D2D pairs to their energy consumption by allocating the proper subchannel of each cell to each device user equipment (DUE), managing their transmission power, and setting the harvesting and transmission time. The constraints of the problem are the quality of service of the CUs, minimum required throughput of the subchannels, and energy harvesting of DUEs. We formulate the problem and propose a low‐complexity iterative algorithm on the basis of the convex optimization method and Karush‐Kuhn‐Tucker conditions to obtain the optimal solution of the problem. Simulation results validate the performance of our proposed algorithm for different values of the system parameters.     

Bio-inspired power control and channel allocation for cellular networks with D2D communications

With the tremendous increment of traffic in the next generation mobile networks, device to device (D2D) communication is proposed to relieve the traffic burden of the base station and improve the overall network capacity. It supports direct communications between devices and could reuse the resources of cellular users (CUs). Despite the advantages, D2D communications bring great challenges in interference management. In this paper, we study the power control and channel allocation problems in three scenarios: (1) one CU and one D2D pair; (2) one CU and multiple D2D pairs; (3) multiple CUs and multiple D2D pairs. The goal is to coordinate the mutual interferences and maximize the overall network capacity. We derive sufficient conditions to guarantee the efficiency of D2D communications in scenarios with one CU and one D2D pair. We propose the bio-inspired PSO-P power control algorithm for the scenarios with one CU and multiple D2D pairs, and the PSO-CP algorithm for the scenarios with multiple CUs and multiple D2D pairs to jointly assign channels and powers. Simulation results show that the proposed algorithms are efficient in improving the overall network capacity.

     

Replication schemes for peer‐to‐peer content in wireless mesh networks with infrastructure support

Many mobile devices (e.g., smart phones, PDAs, portable computers) and wireless routers (e.g., WiFi access points) nowadays are equipped with ad hoc transmission mode. In a dense environment such as a college/office campus, this creates the possibility of forming a wireless mesh network (WMN) in which mobile users communicate with each other through multiple wireless hops. This allows mobile users to exchange (share) files over the free access WMN rather than a carrier frequency such as 3G and WiMax. We consider a peer‐to‐peer (P2P) content sharing setting in a WMN, wherein the mesh network operator over‐provision a number of mesh routers in the network with additional storage capacity and P2P‐aware devices that are programmed to cache and store P2P content. Those mesh routers act as caches and participants in P2P content sharing. The aim of this setting is to both reduce the cost of communications between peers within the WMN (i.e., reduce bandwidth and energy that P2P traffic consumes in the network), and enhance the performance of P2P content sharing (i.e., reduce the average P2P content download delay). Our main contribution in this paper is an optimum P2P content replication strategy at the participating mesh routers. In particular, we determine the optimum number of replicas for every P2P file such that the average access cost of all files in the network is minimized. We propose a centralized algorithm that enables the participating mesh routers to implement the optimal strategy. We further propose a distributed (low cost) algorithm for P2P content replication at the participating mesh routers, and show that the distributed algorithm mimics the optimal strategy very well. The analytical and simulation results show that our replication strategy significantly reduces the average overall cost of accessing P2P files in the WMN as compared with other commonly used replication strategies. Copyright © 2013 John Wiley & Sons, Ltd.     

带有特征感知的D2D内容缓存策略

设备到设备通信(D2D)可以有效地卸载基站流量,在D2D网络中不仅需要共享大众化内容还需要个性化内容缓存。该文对缓存内容选择问题进行了深入研究,提出一种结合特征感知的内容社交价值预测(CSVP)方法。价值预测不仅可以降低时延也可以减少缓存替换次数降低缓存成本。首先结合用户特征和内容特征计算内容当前价值,然后通过用户社交关系计算未来价值。微基站根据内容的价值为用户提供个性化内容缓存服务,宏基站则在每个微基站的缓存内容中选择价值较大部分的内容。仿真结果表明,该文提出的缓存策略可以有效缓解基站流量,与其他方法相比降低时延约20%～40%。     

Cache‐at‐relay: energy‐efficient content placement for next‐generation wireless relays

Uploading and downloading content have recently become one of the major reasons for the growth of Internet traffic volume. With the increasing popularity of social networking tools and their video upload/download applications, as well as the connectivity enhancements in wireless networks, it has become a second nature for mobile users to access on‐demand content on‐the‐go. Urban hot spots, usually implemented via wireless relays, answer the bandwidth need of those users. On the other hand, the same popular contents are usually acquired by a large number of users at different times, and fetching those from the initial content source each and every time makes inefficient use of network resources. In‐network caching provides a solution to this problem by bringing contents closer to the users. Although in‐network caching has been previously studied from latency and transport energy minimization perspectives, energy‐efficient schemes to prolong user equipment lifetime have not been considered. To address this problem, we propose the cache‐at‐relay (CAR) scheme, which utilizes wireless relays for in‐network caching of popular contents with content access and caching energy minimization objectives. CAR consists of three integer linear programming models, namely, select relay, place content, and place relay, which respectively solve content access energy minimization, joint minimization of content access and caching energy, and joint minimization of content access energy and relay deployment cost problems. We have shown that place relay significantly minimizes the content access energy consumption of user equipments, while place content provides a compromise between the content access and the caching energy budgets of the network. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhancing quality of experience using peer‐to‐peer overlay on device‐to‐device communications

With the recent development of LTE‐A/5G technologies, data sharing among mobile devices offer an attractive opportunity to reduce Internet access. However, it requires smart strategies to share the data with low trade‐offs in time, cost, and energy. Several existing schemes offer a super‐peer‐based two‐tier model using a distributed hash table (DHT) organization for smart devices having device‐to‐device (D2D)/Bluetooth/WiFi capabilities. The primary focus of these schemes has been to reduce Internet usage by increased D2D content sharing. However, the real challenge is not in creating a two‐tier model, but evolving an efficient overlay that offers enhanced opportunities for D2D content sharing over the existing model. In this paper, we formulated a P‐median‐based selection of tier‐1 devices in a distribution network and solved it using the Lagrangian relaxation method. The tier‐2 devices become clients seeking content sharing services from tier‐1 devices. A strong motivation in this work is to raise a user's perception of the grade of service known as quality of experience (QoE). We analyzed the challenge for QoE assessment in resource‐constrained smartphones under the proposed model of enhanced D2D communication. Our focus is to establish a framework to evaluate QoE for applications and services over LTE‐A/5G networks with an improved D2D communication level. The simulation and the experimental results validate the claim that substantial improvements in QoE are possible with the proposed mathematical model for selecting and placing tier‐1 mobile devices and maintaining a DHT for D2D communication.     

Incentive edge caching in software‐defined internet of vehicles: A Stackelberg game approach

In this paper, we investigate an incentive edge caching mechanism for an internet of vehicles (IoV) system based on the paradigm of software‐defined networking (SDN). We start by proposing a distributed SDN‐based IoV architecture. Then, based on this architecture, we focus on the economic side of caching by considering competitive cache‐enablers market composed of one content provider (CP) and multiple mobile network operators (MNOs). Each MNO manages a set of cache‐enabled small base stations (SBS). The CP incites the MNOs to store its popular contents in cache‐enabled SBSs with highest access probability to enhance the satisfaction of its users. By leasing their cache‐enabled SBSs, the MNOs aim to make more monetary profit. We formulate the interaction between the CP and the MNOs, using a Stackelberg game, where the CP acts first as the leader by announcing the popular content quantity that it which to cache and fixing the caching popularity threshold, a minimum access probability under it a content cannot be cached. Then, MNOs act subsequently as followers responding by the content quantity they accept to cache and the corresponding caching price. A noncooperative subgame is formulated to model the competition between the followers on the CP's limited content quantity. We analyze the leader and the follower's optimization problems, and we prove the Stackelberg equilibrium (SE). Simulation results show that our game‐based incentive caching model achieves optimal utilities and outperforms other incentive caching mechanisms with monopoly cache‐enablers whilst enhancing 30% of the user's satisfaction and reducing the caching cost.     

雾网络中基于统计分布的内容缓存与交付方案

作为5G中的一种重要模型，雾无线接入网络(Fog Radio Access Network, F-RAN)通过设备到设备通信和无线中继等技术获得了显著的性能增益，而边缘设备中合适的缓存则可以让内容缓存用户(Caching Users, CUs)向内容请求用户(Requesting Users, RUs)直接发送缓存内容，有效减小前传链路的负担和下载延迟。考虑一个F-RAN模型下用户发出请求并获得交付的场景，将每个CU的内容请求队列建模为独立的M/D/1模型，分析导出CUs缓存命中率和平均下载延迟关于内容缓存与交付方案的表达式，证明CUs缓存命中率与内容统计分布之间的联系有助于实现前者的近似最优解。针对在一段时间内的期望视角下建立的优化问题，提出了基于统计分布的算法并注意了执行时的交付控制。仿真结果表明，相较于现有缓存策略，优化内容整体统计分布的方案能够最大化CUs缓存命中率，同时减小平均下载延迟。     

The User-level Security of Mobile Communication Systems

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Deep reinforcement learning-based resource allocation for D2D communications in heterogeneous cellular networks

Device-to-Device (D2D) communication-enabled Heterogeneous Cellular Networks (HCNs) have been a promising technology for satisfying the growing demands of smart mobile devices in fifth-generation mobile networks. The introduction of Millimeter Wave (mm-wave) communications into D2D-enabled HCNs allows higher system capacity and user data rates to be achieved. However, interference among cellular and D2D links remains severe due to spectrum sharing. In this paper, to guarantee user Quality of Service (QoS) requirements and effectively manage the interference among users, we focus on investigating the joint optimization problem of mode selection and channel allocation in D2D-enabled HCNs with mm-wave and cellular bands. The optimization problem is formulated as the maximization of the system sum-rate under QoS constraints of both cellular and D2D users in HCNs. To solve it, a distributed multiagent deep Q-network algorithm is proposed, where the reward function is redefined according to the optimization objective. In addition, to reduce signaling overhead, a partial information sharing strategy that does not observe global information is proposed for D2D agents to select the optimal mode and channel through learning. Simulation results illustrate that the proposed joint optimization algorithm possesses good convergence and achieves better system performance compared with other existing schemes.     

Radio resource management scheme and outage analysis for network-assisted multi-hop D2D communications

In a cellular network it's very difficult to make spectrum resource more efficiently. Device-to-Device (D2D) technology enables new service opportunities, and provides high throughput and reliable communication while reducing the base station load. For better total performance, short-range D2D links and cellular links share the same radio resource and the management of interference becomes a crucial task. Here we argue that single-hop D2D technology can be used to further improve cellular networks performance if the key D2D radio resource management algorithms are suitably extended to support multi-hop D2D communications. Aiming to establish a new paradigm for the analysis and design of multi-hop D2D communications, We propose a radio resource allocation for multi-hop D2D routes based on interference avoidance approach in LTE-A networks. On top of that, we investigate the outage probability of D2D communication. We first introduce a new definition of outage probability by considering the maximum distance to be allowable for single-hop transmission. Then we study and analyze the outage performance of a multi-hop D2D route. We derive the general closed form expression of outage probability of the multi-hop D2D routes. The results demonstrate that the D2D radio, sharing the same resources as the cellular network, provide higher capacity compared to pure cellular communication where all the data is transmitted through the base station. They also demonstrate that the new method of calculation of D2D multi hop outage probability has better performance than classical method defined in the literature.     

Extending P2PMesh: topology‐aware schemes for efficient peer‐to‐peer data sharing in wireless mesh networks

Wireless mesh networks (WMNs) have emerged as a promising technology that provides low‐cost broadband access to the Internet for fixed and mobile wireless end users. An orthogonal evolution in computer networking has been the rise of peer‐to‐peer (P2P) applications such as P2P data sharing. It is of interest to enable effective P2P data sharing in this type of networks. Conventional P2P data sharing systems are not cognizant of the underlying network topology and therefore suffer from inefficiency. We argue for dual‐layer mesh network architecture with support from wireless mesh routers for P2P applications. The main contribution of this paper is P2PMesh: a topology‐aware system that provides combined architecture and efficient schemes for enabling efficient P2P data sharing in WMNs. The P2PMesh architecture utilizes three schemes: (i) an efficient content lookup that mitigates traffic load imbalance at mesh routers; (ii) an efficient establishment of download paths; and (iii) a data transfer protocol for multi‐hop wireless networks with limited capacity. We note here that the path establishment and data transfer schemes are specific to P2P traffic and that other traffic would use routes determined by the default routing protocol in the WMN. Simulation results suggest that P2PMesh has the potential to improve the performance of P2P applications in a wireless multi‐hop setting; specifically, we focused on data sharing, but other P2P applications can also be supported by this approach. Copyright © 2011 John Wiley & Sons, Ltd.     

Modeling and implementation of 5G edge caching over satellite

The fifth‐generation (5G) wireless networks have to deal with the high data rate and stringent latency requirements due to the massive invasion of connected devices and data‐hungry applications. Edge caching is a promising technique to overcome these challenges by prefetching the content closer to the end users at the edge node's local storage. In this paper, we analyze the performance of edge caching 5G networks with the aid of satellite communication systems. First, we investigate the satellite‐aided edge caching systems in two promising use cases: (a) in dense urban areas and (b) in sparsely populated regions, eg, rural areas. Second, we study the effectiveness of satellite systems via the proposed satellite‐aided caching algorithm, which can be used in three configurations: (a) mono‐beam satellite, (b) multi‐beam satellite, and (c) hybrid mode. Third, the proposed caching algorithm is evaluated by using both empirical Zipf‐distribution data and the more realistic Movielens dataset. Last but not least, the proposed caching scheme is implemented and tested by our developed demonstrators which allow real‐time analysis of the cache hit ratio and cost analysis.     

D2D通信中一种基于FFR的动态功率控制方案

工作在underlay方式下的D2D(device-to-device)通信利用资源复用共享蜂窝网络中的资源,在提高频谱资源利用率、降低移动终端功耗的同时,会给已有蜂窝网络带来干扰。在保证D2D用户和蜂窝用户的服务质量的前提下,研究了蜂窝用户和D2D用户的功率控制和资源分配问题。首先引入部分频率复用(FFR)实现蜂窝用户和D2D用户之间的资源划分和复用;然后以系统吞吐量最大化为原则,建立优化目标。结合部分功率控制(FPC)的基本思想,进而提出了一种动态功率控制(DPC)策略。仿真结果表明,所提出的方案能够有效地提高多小区系统的性能。     

D2D通信中的基于联盟形成博弈的能量有效的无线资源共享机制

D2D(Device-to-Device)通信作为蜂窝网中的一种新型的通信方式,因其在提高传输速率和改善能效性能等方面的无可比拟的优势,受到人们越来越多的关注。但是,D2D通信技术在带来令人无法抗拒的优势的同时,亦会产生棘手的干扰问题。鉴于此,本文从降低干扰的不利影响、提高网络能效性的角度出发,综合蜂窝用户共享资源的主观性和客观性因素,探讨了无线资源共享机制的设计问题,即联合模式选择和链路资源分配。首先,分析了D2D通信中的两种通信模式下用户的能量有效性。其次,将能量有效的无线资源共享问题建模为效用不可转移联盟形成博弈,分析了博弈性质,并基于合并-拆分准则和帕累托偏好关系提出一种分布式算法,依此确定无线资源共享策略。最后给出并分析了数值仿真结果,以验证所提机制的可行性。      

Cooperative caching for content dissemination in vehicular networks

The explosive growth of mobile data traffic has made cellular operators to seek low‐cost alternatives for cellular traffic off‐loading. In this paper, we consider a content delivery network where a vehicular communication network composed of roadside units (RSUs) is integrated into a cellular network to serve as an off‐loading platform. Each RSU subjecting to its storage capacity caches a subset of the contents of the central content server. Allocating the suitable subset of contents in each RSU cache such that maximizes the hit ratio of vehicles requests is a problem of paramount value that is targeted in this study. First, we propose a centralized solution in which, we model the cache content placement problem as a submodular maximization problem and show that it is NP‐hard. Second, we propose a distributed cooperative caching scheme, in which RSUs in an area periodically share information about their contents locally and thus update their cache. To this end, we model the distributed caching problem as a strategic resource allocation game that achieves at least 50% of the optimal solution. Finally, we evaluate our scheme using simulation for urban mobility simulator under realistic conditions. On average, the results show an improvement of 8% in the hit ratio of the proposed method compared with other well‐known cache content placement approaches.     

Graph-Based Radio Resource Sharing Schemes for MTC in D2D-based 5G Networks

Apart from the the increasing demand of smartphones in human-to-human (H2H) communications, the introduction of machine-to-machine (M2M) devices poses significant challenges to wireless cellular networks. In order to offer the ability to connect billion of devices to propel the society into a new era of connectivity in our homes, officies and smart cities, we design novel radio resource sharing algorithms in a H2H/M2M coexistence case to accommodate M2M communications while not severely degrading existing H2H services. We propose group-based M2M communications that share the same spectrum with H2H communications through device-to-device (D2D) communication, as one of the technology components of 5G architecture. First, we formulate radio resource sharing problem as a sum-rate maximization, problem for which the optimal solution is non-deterministic polynomial-time hard (NP-hard). To overcome the computational complexity of the optimal solution, we model the resource sharing problem as a bipartite graph, then propose a novel interference-aware graph-based resource sharing scheme using a fixed M2M transmit power. To further enhance the protection of H2H services, we introduce an adaptive power control mechanism into the interference-aware graph-based resource sharing scheme. M2M transmit power is efficiently adjusted using one among the two following alternative controllers, namely, either the proportional integral derivative (PID) or the fuzzy logic. The latter is proposed within the aim to assure the desired quality-of-service (QoS) of H2H users and increase the efficiency of M2M spectrum usage. In both cases (fixed and adaptive), a centralized and a semi-distributed instantiations are given. Simulation results show that adaptive M2M radio resource sharing scheme using fuzzy logic is the one that achieves the best compromise. In fact, it guarantees H2H performance in terms of throughput and fairness while maximizing the efficiency of M2M spectrum usage. Simulation results also show that in spite of its quite good performance, semi-distributed M2M resource sharing instantiation achieves them with a decline of up to 10% in terms of H2H throughput compared to the centralized instantiation. This is achieved through a markedly lower communication overhead.