Centralized Coded Caching for Wireless Networks with Heterogeneous Channel Conditions

In this paper, we focus on mobile wireless networks comprising of a powerful communication center and a multitude of mobile users. We investigate the propagation of deadline-based content in the wireless network characterized by heterogeneous (time-varying and user-dependent) wireless channel conditions, heterogeneous user mobility, and where communication could occur in a hybrid format (e.g., directly from the central controller or by exchange with other mobiles in a peer-to-peer manner). We show that exploiting double opportunities, i.e., both time-varying channel conditions and mobility, can result in substantial performance gains. We develop a class of double opportunistic multicast schedulers and prove their optimality in terms of both utility and fairness under heterogeneous channel conditions and user mobility. Extensive simulation results are provided to demonstrate that these algorithms can not only substantially boost the throughput of all users (e.g., by 50% to 150%), but also achieve different consideration of fairness among individual users and groups of users.

This paper studies device to device (D2D) coded-caching with information theoretic security guarantees. A broadcast network consisting of a server, which has a library of files, and end users equipped with cache memories, is considered. Information theoretic security guarantees for confidentiality are imposed upon the files. The server populates the end user caches, after which D2D communications enable the delivery of the requested files. Accordingly, we require that a user must not have access to files it did not request, i.e., secure caching. First, a centralized coded caching scheme is provided by jointly optimizing the cache placement and delivery policies. Next, a decentralized coded caching scheme is developed that does not require the knowledge of the number of active users during the caching phase. Both schemes utilize non-perfect secret sharing and one-time pad keying, to guarantee secure caching. Furthermore, the proposed schemes provide secure delivery as a side benefit, i.e., any external entity which overhears the transmitted signals during the delivery phase cannot obtain any information about the database files. The proposed schemes provide the achievable upper bound on the minimum delivery sum rate. Lower bounds on the required transmission sum rate are also derived using cut-set arguments indicating the multiplicative gap between the lower and upper bounds. Numerical results indicate that the gap vanishes with increasing memory size. Overall, the work demonstrates the effectiveness of D2D communications in cache-aided systems even when confidentiality constraints are imposed at the participating nodes and against external eavesdroppers.

In the coded caching problem apart from transmission rate, reducing the number of packets $F$ ia also meaningful for practical implementation for coded caching scheme. Yan et al. reformulate the centralized coded caching schemes as designing a corresponding placement delivery array (PDA). In this letter, we propose two concatenating constructions by concatenating some known PDAs to obtain new PDAs therefore new code caching schemes with low sub-packetization level. Further, the comparison and analysis of parameters between our new schemes and known schemes is also performed.

Aided by scalable video coding, multirate multicast has become a promising technique of providing differentiated quality of experience (QoE) for massive numbers of video subscribers operating in heterogeneous channel conditions. Nevertheless, due to the time-varying nature of wireless channels and the subscribers’ diverse requirements, it is challenging to dynamically control the video rate in the light of the available radio resource to achieve the best QoE. To elaborate a little further, the time scale of resource scheduling is of short-term nature, which determines the short-term video quality variation, but from a service provider’s perspective the design objective is to optimize the long-term QoE for all subscribers. Despite its importance, this problem has not been considered before. Explicitly, we formulated this problem as a time-averaged stochastic optimization problem which avoids the impact of both the short- term channel quality fluctuation and that of the video bitrates, whilst maintaining both inter- and intra- group fairness. The stratified structure of the problem inspires us to decompose it into a two-phase optimization: coarse grained assignment for each user group and fine grained assignment for each subgroup. We propose an adaptive multicast algorithm based on Lyapunov’s optimization theory for solving this problem, by striking a compelling trade-off between the system’s utility and its queue stability. We quantify the achievable performance of our proposed solution based on realistic video traces.

Authentication is a primary component for secure delivery of multimedia content in many consumer networking applications: to guarantee the integrity of the received data stream. Meanwhile, consumer networks increasingly used for multimedia information and commercial content delivery, are destined to be heterogeneous. To provide QoS, it is necessary to adapt the multimedia stream to the heterogeneous network channel conditions and device capabilities. This new adaptation requirement, together with the 'best effort' and 'error prone' characteristics of IP and wireless networks, and the 'real time playback' property of streaming media impose challenges in the design of the streaming media authentication schemes. Conventional message authentication schemes do not offer suitable scalability or loss resilient capability for this new set of applications. A suitable authentication scheme must allow the recipient to authenticate the received data faster than the packet receiving rate, with means to adapt to channel conditions and device capability, despite any losses or transmission errors. In this paper we study the design of loss resilient scalable media stream authentication and present a scheme that is scalable and loss resilient.

Rateless codes can be advantageously used to provide Application Layer Forward Error Correction (AL-FEC) with a distinct advantage that an infinite number of packets can be generated on the fly from the source packets. For heterogeneous users and/or variable channel conditions, significant adaptation features and improvement in the video quality can be achieved by partitioning the video data into different priority classes. Such partitioned data can be unequally protected using appropriate FEC scheme based on its contribution to video reconstruction. Expanding Window Random Linear Codes (EW RLC) are a simple unequal error protection fountain coding scheme which can adapt to the prioritized data transmission. In this paper, EW RLC are proposed for broadcasting the H.264/Advanced video coding partitioned with the data partitioning feature. The results show viability of the EW RLC for multimedia broadcast applications to suit different data rates and channel conditions.

This paper studies coverage probabilities of randomly deployed radio nodes in single-destination networks. Such networks are typically operated for data aggregation in machine-to-machine (M2M) communication scenarios. In large-scale deployments, diverse environments usually result in heterogeneous propagation channels. We address the question to which extent an increased medium access can compensate for impaired propagation conditions. Based on superimposed Poisson Point Processes and a strongest interferer approximation, we propose a closed-form solution for the probability of a successful packet transmission under heterogeneous channel conditions. The applicability of the framework is demonstrated for an exemplary network configuration with a given latency constraint. Jointly optimising the medium access probabilities can either increase the network coverage area (e.g. by factor two) or reduce the overall networks power consumption by up to more than 30% in sufficiently dense deployments.

We propose a simple unified analytical model to analyze the IEEE 802.11 DCF infrastructure BSS performance in terms of MAC delay, PLR, and throughput efficiency under non-homogeneous and non-saturation conditions. Our model accounts for: (i) asymmetric traffic load between an AP and its associated STAs of an infrastructure BSS; (ii) transition from the non-saturation to saturation mode (and vice-versa) from an AP perspective; (iii) heterogeneous traffic flows between STAs; and (iv) heterogeneous wireless channel conditions between BSSs of a multi-AP hotspot scenario, all in a single unifying framework. More specifically, we integrate a Markov chain model in conjunction with a finite queueing model to analyze the QoS performance of DCF infrastructure BSS, which will be useful for capacity analysis and the design of network control mechanisms. Extensive analyses and simulations have unveiled that the improper modeling or ignorant of backoff freezing for an infrastructure BSS will result in overly conservative bounds which will lead to low network utilization when deployed as admission control, particularly, in heavy load scenarios.

A coded caching scheme for efficient storage and access of medical data is discussed in this paper. Being an inspiring technology for improving the availability and sharing of medical data, the coded caching scheme for medical data is not only convenient for the medical staffs to grasp the patients’ health conditions and treatment history in time, but also effective for the patients to obtain improved quality of medical services. In this paper, the coded caching scheme for the combination network which is the model for the medical data sharing is studied. In the combination network, the server communicates with the users via multiple relays, and the relays as well as the users have cache memories. Using the maximum distance separable codes and placement delivery array (PDA) algorithm, the coded placement phase and delivery phase for combination networks are designed. In addition, for combination networks that satisfy the resolvability property, we extend the PDA algorithm to the case where the users’ priority is considered. The proposed scheme greatly reduces the subpacketization level with slightly increasing the transmission rate. The users with higher priority can get the requested content faster. We demonstrate that relays with cache memories can reduce the data transmission in peak time. The gap between the upper bound and lower bound of the transmission rate is gradually decreased with the increase in the users’ memories. The proposed scheme will shorten the latency time of the system and improve system efficiency for storage and access of medical data.

Coded caching was introduced as a technique of systematically exploiting locally available storage at the clients to increase the channel throughput via coded transmissions. Most known coded caching schemes in literature enable large gains in terms of the rate, however at the cost of subpacketization that is exponential in $K^{\frac{1}{r}}$ ($K$ being the number of clients, $r$ some positive integer). Building upon recent prior work for coded caching design via line graphs and finite-field projective geometries, we present a new scheme in this work which achieves a subexponential (in $K$) subpacketization of $q^{O((\log_{q}{K})^2)}$ and rate $\Theta\left(\frac{K}{(\log_{q} {K})^2}\right)$, for large $K$, and the cached fraction $\frac{M}{N}$ being upper bounded by a constant $\frac{2}{q^{\alpha-1}}$ (for some prime power $q$ and constant $\alpha \geq 2$) . Apart from this asymptotic improvement, we show that through some numerical comparisons that our present scheme has much lower subpacketization than previous comparable schemes, however with an increased rate and some increase in cache size required. For instance, we obtain practically relevant subpacketization levels such as $10^2 - 10^7$ for $10^2 - 10^4$ number of clients. Leveraging prior results on adapting coded caching schemes for the error-free broadcast channel to device to device (D2D) networks, we obtain a low- subpacketization scheme for D2D networks also, and give numerical comparison for the same with prior work.

Videoconferencing transmission over wireless channels presents relevant challenges in mobile scenarios at vehicular speeds. Previous contributions are focused on the optimization of the transmission of multimedia and delay‐sensitive applications over the forward link. In this paper, a new Quality of Service (QoS) parameter adaptation scheme is proposed. This scheme applies the Cross‐Layer Design technique on the reverse link of an 1xEV‐DO Revision 0 channel. As the wireless channel parameters and the vehicle speed have significant influence in the network layer packet loss rate, it is proposed that the data rate generated by the application adapts itself to the throughput offered by the lower layers as a function of such packet loss rate. Simulations of the proposed model show a significant reduction in losses caused by wireless channel impairments and vehicle mobility, resulting in an improvement in the performance of the mobile videoconferencing session.

Stereoscopic video multicast over wireless network is a challenging issue due to large bandwidth requirement, limited resource, and heterogeneous user channel conditions. Recently, most existing me...

Data delivery in low power and lossy networks like Wireless Sensor Networks (WSN), which has a significant role in Internet of Things (IoT), is vital due to the high probability of packet loss due to wireless and constrained environment. Data caching and transmission rate control are independent ways of improving the performance of transport protocols in WSN by immediately responding to packet losses in the network. However, a suitable rate control for cache-based transport protocols is not yet investigated. This work developed a dynamic cache-aware rate control algorithm that uses a transmission window rate as a function of cache size allocation used by intermediate nodes and utilizes cache elimination policy to notify packet losses in the network. A baseline cache-based transport protocol called DTSN+ is used to implement the rate control algorithm and evaluated under different network scenarios. Results show that the cache-aware approach improves the performance of the baseline transport protocol during high level of packet losses in the network in terms of cache utilization especially at lower cache size value. The algorithm also obtained outstanding throughput, transmission time and fairness performance as compared with original DTSN+ and DTC protocols. In the future, these results can serve as an underlying support in designing a new cache-aware congestion control framework that can be integrated in a transport protocol to mitigate packet losses in WSN.

The allocation of communication power consumption and computing rate is inherently one of the cross-layer problems in wireless distributed computing networks (WDCNs). This paper exploits a subgradient approach to choose the optimal power-rate pair for maximizing the network computing capability and minimizing the power consumption. The impact of heterogeneous channel conditions for different nodes are modeled as a penalty term in the objective function to balance the performance and power consumption, and increase the amount of the power for the computing task. Simulation results show that both energy efficiency and the distributed computing power ratio (DCPR) can be increased by considering the wireless channel conditions. These results provide some guidelines for designing the protocol dedicated to WDCNs.

We consider a cache network, where a single server is connected to multiple users via a shared bottleneck link. The server has a set of files, which can be cached by each user in a prefetching phase. In a following delivery phase, each user requests a file and the server delivers user demands as efficiently as possible by taking into account their cache contents. We focus on an important and commonly used class of prefetching schemes, where the caches are filled with uncoded data. We provide the exact characterization of rate-memory tradeoff for this problem, by deriving both the minimum average rate (for a uniform file popularity) and the minimum peak rate required on the bottleneck link for a given cache size available at each user. We propose a novel caching scheme, which strictly improves the state of the art by exploiting commonality among user demands. We then demonstrate the exact optimality of our proposed scheme through a matching converse, by dividing the set of all demands into types, and showing that the placement phase in the proposed caching scheme is universally optimal for all types. Using these techniques, we can also fully characterize the rate-memory tradeoff for a decentralized setting, in which users fill out their cache content without coordination.