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Computation offloading is a proven successful paradigm for enabling resource-intensive applications on mobile devices. Moreover, in view of emerging mobile collaborative application, the offloaded tasks can be duplicated when multiple users are in the same proximity. This motivates us to design a collaborative offloading scheme and cache the popular computation results that are likely to be reused by other mobile users. In this paper, we consider the scenario where multiple mobile users offload duplicated computation tasks to the network edge, and share the computation results among them. Our goal is to develop the optimal fine-grained collaborative offloading strategies with caching enhancements to minimize the overall execution delay at the mobile terminal side. To this end, we propose an optimal offloading with caching-enhancement scheme (OOCS) for femto-cloud scenario and mobile edge computing scenario, respectively. Simulation results show that compared to six alternative solutions in literature, our single-user OOCS can reduce execution delay up to $42.83$ % and $33.28$ % for single-user femto-cloud and single-user mobile edge computing, respectively. Our multi-user OOCS can further reduce $11.71$ % delay compared to single-user OOCS through users’ cooperation. [ABSTRACT FROM AUTHOR]

In this paper, we concentrate on the robust multi-objective optimization (MOO) for the tradeoff between energy efficiency (EE) and spectral efficiency (SE) in device-to-device (D2D) communications underlaying heterogeneous networks (HetNets). Different from traditional resource optimization, we focus on finding robust Pareto optimal solutions for spectrum allocation and power coordination in D2D communications underlaying HetNets with the consideration of interference channel uncertainties. The problem is formulated as an uncertain MOO problem to maximize EE and SE of cellular users (CUs) simultaneously while guaranteeing the minimum rate requirements of both CUs and D2D pairs. With the aid of $\varepsilon$ -constraint method and strict robustness, we propose a general framework to transform the uncertain MOO problem into a deterministic single-objective optimization problem. As exponential computational complexity is required to solve this highly non-convex problem, the power coordination and the spectrum allocation problems are solved separately, and an effective two-stage iterative algorithm is developed. Finally, simulation results validate that our proposed robust scheme converges fast and significantly outperforms the non-robust scheme in terms of the effective EE-SE tradeoff and the quality of service satisfying probability of D2D pairs. [ABSTRACT FROM AUTHOR]

In this paper, a social-aware virtual medium access control (SV-MAC) is devised to integrate virtualization and social awareness to D2D communications underlying heterogeneous cellular networks. SV-MAC is a converged network layer. Through SV-MAC, heterogeneous networks can be unified in a single protocol stack, providing a common abstraction for users and mobile network operators (MNOs) to share their network resources. Leveraging users’ social information, SV-MAC can realize social-aware D2D discovery, association, and resource allocation for improved D2D communication efficiency. In order to validate the advantages of the proposed SV-MAC protocol, we study the cellular and D2D resource allocation problems under the SV-MAC protocol. The problems are formulated as maximizing the cellular and D2D energy efficiency (EE). The cellular resource allocation problem is first solved considering its priority to D2D users. The resource allocation problem for D2D users is solved after cellular users to control the D2D-to-cellular interference within a tolerable threshold. In the simulation, we introduce real mobile user traces to simulate the user social information. Simulation results show that the proposed SV-MAC resource allocation schemes obtain a beneficial EE improvement comparing with conventional schemes. [ABSTRACT FROM AUTHOR]

Synchronization of bio-inspired pulse-coupled oscillators is receiving increased attention due to its wide applications in sensor networks and wireless communications. However, most existing results are obtained in the absence of malicious attacks. Given the distributed and unattended nature of wireless sensor networks, it is imperative to enhance the resilience of pulse based synchronization against malicious attacks. To achieve this goal, we propose a new pulse based interaction mechanism to improve the resilience of pulse based synchronization. We rigorously characterize the condition for mounting stealthy attacks under the proposed pulse based interaction mechanism and prove analytically that synchronization of legitimate oscillators can be achieved in the presence of multiple stealthy attackers even when the initial phases are unrestricted, i.e., randomly distributed in the entire oscillation period. This is in distinct difference from most existing attack-resilient synchronization algorithms (including the seminal paper from L. Lamport and P. M. Melliar-Smith, “Synchronizing Clocks in the Presence of Faults,” J. ACM, vol. 32, no. 1, pp. 52–78, 1985), which require a priori (almost) synchronization among legitimate nodes. Numerical simulations are given to confirm the theoretical results. [ABSTRACT FROM AUTHOR]

In this paper, we study the energy efficiency (EE) optimization for simultaneous wireless information and power transfer in multiple-input-multiple-output two-way amplify-and-forward relay networks, where the energy-constrained relay harvests energy from two sources’ signals by power splitting (PS) scheme to forward the information of two sources. Our objective is to jointly design the sources and relay precoding matrices and the PS ratio to maximize the EE of the network, under the transmit power constraints at sources and relay and the minimum spectral efficiency requirement. We transform the nonconvex precoding and PS design problem into a difference of convex programming and propose an efficient iterative algorithm based on the constrained concave convex procedure to obtain a local optimum. To reduce computational complexity, we propose a generalized singular value decomposition based channel diagonalization scheme to simplify the optimization into a joint source and relay power allocation problem. The alternating optimization method is employed to solve this problem and a suboptimal solution to the EE maximization problem is obtained. Simulation results demonstrate the effectiveness of the proposed schemes. [ABSTRACT FROM AUTHOR]

In this paper, we focus on wireless coverage extension and nodes' cooperation. We propose a new protocol based on an incentive approach and a scheduling algorithm to reward cooperative nodes. The cost of cooperation can be prohibitively expensive in terms of quality of service (QoS) and energy consumption, which does not motivate some nodes to cooperate. Therefore, we introduce a percentage of cooperation and QoS parameters in the scheduling algorithm called coverage extension based on incentive scheduling to incite potential mobile relaying nodes to cooperate and, in turn, extend the wireless areas. We use the cross-layer approach to optimize the QoS parameters. The proposed solution not only incites the nodes to cooperate but enhances the QoS by increasing the average throughput and decreasing the delay as well. The simulation results show that the proposed solution not only gives better results than the well-known scheduling algorithms, such as maximum signal-to-noise ratio (MaxSNR) and weighted fair opportunistic (WFO), but allows the cooperative mobile nodes to increase their own throughput by around 114% as well. The total amount of data transmitted out of the cell to extend the coverage can be increased by around 59% compared with the scheduling algorithm MaxSNR. [ABSTRACT FROM PUBLISHER]

This paper investigates retransmission (RT) mechanisms in wireless regenerative multirelay networks. Conventionally, the RT can be realized in a cooperative manner with the assistance of all available relays. However, this may result in high overall power consumption due to the RT of the same packets across the nodes, particularly when the number of relays is large. We propose a cooperative RT (CR) scheme based on relay cooperation (RC) and binary xor operations to significantly reduce the number of packets retransmitted to produce a more power-efficient system with nonoverlapped RTs. Significantly, we also derive the error probability of RT decisions at the source and relays and show that the proposed CR scheme improves the reliability of the RTs. Furthermore, by deriving the average number of packets to be retransmitted at the source and relays, we not only show that the proposed CR scheme reduces the number of RTs and removes overlapped retransmitted packets but determine the optimized number of relays used for the RT phase as well. Finally, simulation results are presented to demonstrate the validity of the analytical expressions. [ABSTRACT FROM PUBLISHER]

Wireless sensor networks are mainly designed for environment surveillance, wherein wireless sensor nodes cooperate to get their job done. Generally, wireless sensors are battery powered; therefore, it is crucial for them to efficiently use their battery resources. Most of the existing power-saving protocols achieve power savings by periodically putting sensor nodes to sleep. Such a regular sleep/awake mechanism fails to adjust a sensor node's sleep duration based on its traffic load, thus causing either lower power efficiency or higher latency. Furthermore, sensors may be deployed in hostile environments and may thus unexpectedly fail. Most power-saving protocols do not promptly react to such link breakage, resulting in long transmission delays. In this paper, we propose a quorum-basedmedium access control (QMAC) protocol that enables sensor nodes to sleep longer under light loads. Since traffic flows toward the sink node in wireless sensor networks, a new concept, i.e., the next-hop group, is also proposed to reduce transmission latency. Simulation results verify that the proposed QMAC saves more energy and keeps the transmission latency low. [ABSTRACT FROM AUTHOR]

A new cluster-based approach to increase the overall network lifetime of the wireless sensor networks is proposed in this paper. We first consider a strategic deployment especially when there are heterogeneous sensor nodes to be deployed. With the strategic deployment, the cluster header selection scheme is proposed. Unlike conventional approaches, we develop our scheme by designing the network with multiple-sized fixed grids while taking into account the arbitrary-shaped area sensed by the sensor nodes. Our simulation results show that the proposed scheme alleviates high energy consumption and a short lifetime of the wireless sensor networks supported by existing schemes. [ABSTRACT FROM AUTHOR]

This paper proposes task-scheduling algorithms designed to save energy in ad hoc networks by using a novel concept of "affinity" as the scheduling metric. This notion of affinity is used to represent the task-linking topology. For one-hop ad hoc networks, we define three types of affinity measures: node affinity, task affinity, and weighted affinity. Node affinity is defined as the weighted sum of incoming and outgoing task flows at each node, and task affinity as the sum of node affinities of source and destination nodes for each task. Based on these affinity measures, we consider three heuristic scheduling algorithms that are executable in real time: 1) affinity-first shortest task scheduling Qat; 2) task-size-first affinity-based scheduling Qta; and 3) task-size weighted-affinity scheduling Qwa. These algorithms have the advantage of making the total duration of the doze state of all the nodes in the network longer than in other conventional schemes, thereby achieving significant power saving (PS). Our simulation experiments suggest that the PS performance of Qwa is comparable to optimal scheduling (which is not implementable in practice for realistic link topologies). We also present a framework for a PS medium-access-control (MAC) protocol in which our scheduling algorithm can be deployed, and we describe how to enhance the existing 802.11 PS MAC to implement our framework. Simulation results demonstrate that our enhanced PS MAC protocol combined with affinity-based scheduling improves power efficiency and throughput significantly over other existing schemes. [ABSTRACT FROM AUTHOR]

Access efficiency and energy conservation are two critical performance concerns in a wireless data broadcast system. We propose in this paper a novel parameterized index called the exponential index that has a linear yet distributed structure for wireless data broadcast. Based on two tuning knobs, index base and chunk size, the exponential index can be tuned to optimize the access latency with the tuning time bounded by a given limit, and vice versa. The client access algorithm for the exponential index under unreliable broadcast is described. A performance analysis of the exponential index is provided. Extensive ns-2-based simulation experiments are conducted to evaluate the performance under various link error probabilities. Simulation results show that the exponential index substantially outperforms the state-of-the-art indexes. In particular, it is more resilient to link errors and achieves more performance advantages from index caching. The results also demonstrate its great flexibility in trading access latency with tuning time. [ABSTRACT FROM AUTHOR]

Wireless Body Area Network (WBAN) in recent years have received significant attention, due to their potential for increasing efficiency in healthcare monitoring. Typical sensors used for WBAN are low powered single transceiver devices utilizing a single channel for transmission at the Medium Access Control (MAC) layer. However, performance of these devices usually degrades when the density of sensors increases. One approach to counter this performance degradation is to exploit multiple channels at the MAC layer, where optimal usage of the channels is achieved through cooperation between the sensor nodes. In this paper we propose a cooperative WBAN environment that supports multi-hop transmission through cooperation involving both environmental sensors and WBAN nodes. Our solution extends the cooperation at the MAC layer to a cross-layered gradient based routing solution that allows interaction between WBAN and environmental sensors in order to ensure data delivery from WBANs to a distant gateway. Extensive simulations for healthcare scenarios have been performed to validate the cooperation at the MAC layer, as well as the cross-layered gradient based routing. Comparisons to other cooperative multi-channel MAC and routing solutions have shown the overall performance improvement of the proposed approach evaluated in terms of packet loss, power consumption and delay. [ABSTRACT FROM PUBLISHER]

Energy-efficient wireless communication is very important for battery-constrained mobile devices. For mobile devices in a cellular system, uplink power consumption dominates the wireless power budget because of RF power requirements for reliable transmission over long distances. Our previous work in this area focused on optimizing energy efficiency by maximizing the instantaneous bits-per-Joule metric through iterative approaches, which resulted in significant energy savings for uplink cellular OFDMA transmissions. In this paper, we develop energy efficient schemes with significantly lower complexity when compared to iterative approaches, by considering time-averaged bits-per-Joule metrics. We consider an uplink OFDMA system where multiple users communicate to a central scheduler over frequency-selective channels with high energy efficiency. The scheduler allocates the system bandwidth among all users to optimize energy efficiency across the whole network. Using time-averaged metrics, we derive energy optimal techniques in "closed forms" for per-user link adaptation and resource scheduling across users. Simulation results show that the proposed schemes not only have low complexity but also perform close to the globally optimum solutions obtained through exhaustive search. [ABSTRACT FROM AUTHOR]

In this paper, we consider the exact top-k query problem in wireless sensor networks, i.e., where one seeks to find the k highest reported values as well as the complete set of nodes that reported them. Our primary contribution in this context is EXTOK, a provably correct and topology-independent new filtering-based algorithm for processing exact top-k queries. As a secondary contribution we confirm a previous result of ours by showing that the efficiency of top-k query processing algorithms, including EXTOK, can be further improved by simply choosing a proper underlying logical tree topology. We examine EXTOK's performance with respect to a number of parameters and different logical tree topologies while using both synthetic and real data sets. Our simulation reveal that EXTOK consistently outperforms the current state-of-the-art algorithm by a very significant margin and regardless of the underlying logical tree topology. [ABSTRACT FROM AUTHOR]

In this paper we propose an efficient cooperation scheme to increase transmission throughput in a 60GHz 3D HD (high definition) video transmission system. A 3D HD video transmission system usually requires high transmission throughput with low power consumption. The proposed cooperation scheme achieves high transmission speed by reducing the data size using a relay and low transmission power by using path diversity. The efficiency of the scheme is demonstrated both analytically and by Monte-Carlo simulations in environments varying the number of relays. The proposed scheme has increased costs in terms of computational complexity at the relay and the destination. [ABSTRACT FROM AUTHOR]