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The end-to-end throughput of multi-hop communication in wireless ad hoc networks is affected by the conflict between forwarding nodes. It has been shown that sending more packets than maximum achievable end-to-end throughput not only fails to increase throughput but also decreases throughput owing to high contention and collision. Accordingly, it is of crucial importance for a source node to know the maximum end-to-end throughput. The end-to-end throughput depends on multiple factors, such as physical layer limitations, medium access control (MAC) protocol properties, routing policy, and nodes’ distribution. There have been many studies on analytical modeling of end-to-end throughput but none of them has taken routing policy and nodes’ distribution as well as MAC layer altogether into account. In this paper, the end-to-end throughput with perfect MAC layer is obtained based on routing policy and nodes’ distribution in 1-D and 2-D networks. Then, imperfections of IEEE 802.11 protocol are added to the model to obtain precise value. An exhaustive simulation is also made to validate the proposed models using ns-2 simulator. Results show that if the distribution to the next hop for a particular routing policy is known, our methodology can obtain the maximum end-to-end throughput precisely. [ABSTRACT FROM AUTHOR]

A distributed storage system (DSS) is one of the most vital components of a cloud computing system used for storing and sharing big data among authorized users. A typical DSS consists of ${ n}$ storage nodes each with a storage capacity of ${\alpha }$ units of data such that the entire file stored on the DSS can be recovered by accessing any ${k < n}$ nodes. The objective of this paper is to construct fractional repetition (FR) codes with applications in DSSs. FR codes are the key to constructing a class of distributed storage codes with exact repair by transfer (i.e., upon failure, a failed storage node is exactly regenerated through simple downloading). A major drawback of existing FR codes is that they are insufficiently flexible to adapt adequately to system changes in DSSs. To address this problem, this paper introduces a new type of FR codes, called pliable FR codes, in which both the per-node storage ${\alpha }$ and repetition degree ${ \rho }$ can easily and simultaneously be adjusted. In addition, this paper presents several constructions of pliable FR codes and provides a relatively comprehensive analysis of the constructed pliable FR codes, which reveals the following versatile properties of the codes: 1) the transposed codes of the constructed codes are also pliable FR codes; 2) the constructed codes attain a tight upper bound on the file size with equality at least for ${1 \le k < \min (3, k' + 1)}$ , where ${k'}$ is the smallest value of ${k}$ such that ${k \alpha - (k - 1) > \frac {n - 1}{\rho - 1}}$ ; 3) the constructed codes also meet a Singleton-like bound on the minimum distance at least for ${1 \le k < 3}$ , which demonstrates their optimality; 4) the computational complexity necessary for determining the file size or the minimum distance of the constructed codes can be greatly reduced when it is hard to exactly determine them; and 5) the constructed codes can be used as fractional repetition batch codes to provide load balancing in DSSs, for which the batch size (i.e., the number of symbols that can be read in parallel) can be exactly determined. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of primary network interference on the performance of cognitive multihop secondary network under various multiple-input multiple-output (MIMO) approaches per hop. Specifically, the cognitive system involves a secondary network with MIMO relays that use the amplify-and-forward protocol, and each of which shares the same spectrum resources of multiple primary users (PUs) transmit and receive stations. Two different receive array conditions, and hence processing approaches, per hop in the secondary network are treated separately, which are maximal ratio combining for sufficiently spaced receive antennas to provide receive diversity gain and interference cancellation (IC) for insufficiently spaced antennas to reduce the effect of PUs interference. The latter approach involves two different algorithms that vary in terms of complexity and achieved performance, which are dominant receive IC and adaptive receive IC. Moreover, for both approaches, the transmit array gain is achieved per hop through the low-complexity transmit antenna selection. In doing so, new analytical results for multihop secondary network’s end-to-end outage probability are developed. Moreover, simple asymptotic results for this outage performance in high SNR regime are provided, from which the achieved diversity and coding gains and the diversity-multiplexing tradeoff can be extracted. In addition, to further enhance the secondary network, optimal power allocation among hops is obtained based on the asymptotic outage performance under the constraints of transmit power of a secondary transmit station and interference limit on the primary network. The developed analytical results in this paper are validated through numerical and simulation results. [ABSTRACT FROM AUTHOR]

In this paper, we aim to improve the connectivity, scalability, and energy efficiency of machine-type communication (MTC) networks with different types of MTC devices (MTCDs), namely Type-I and Type-II MTCDs, which have different communication purposes. To this end, we propose two transmission schemes called connectivity-oriented machine-type communication (CoM) and quality-oriented machine-type communication (QoM), which take into account the stochastic geometry-based deployment and the random active/inactive status of MTCDs. Specifically, in the proposed schemes, the active Type-I MTCDs operate using a novel Bernoulli random process-based simultaneous wireless information and power transfer (SWIPT) architecture. Next, utilizing multi-user power-domain non-orthogonal multiple access (PD-NOMA), each active Type-I MTCD can simultaneously communicate with another Type-I MTCD and a scalable number of Type-II MTCDs. In the performance analysis of the proposed schemes, we prove that the true distribution of the received power at a Type-II MTCD in the QoM scheme can be approximated by the Singh-Maddala distribution. Exploiting this unique statistical finding, we derive approximate closed-form expressions for the outage probability (OP) and sum-throughput of massive MTC (mMTC) networks. Through numerical results, we show that the proposed schemes provide a considerable sum-throughput gain over conventional mMTC networks. [ABSTRACT FROM AUTHOR]

Locally repairable codes (LRCs) have been recently proposed and used in real-world distributed storage systems (DSSs) such as Microsoft Azure Storage and Facebook HDFS-RAID (Hadoop Distributed File System-Redundant Array of Independent Disks). Since information in DSSs is changed frequently, reducing update complexity (UC) of LRCs is of great interest. In this paper, we propose code design algorithms that can reduce UC of existing LRCs without sacrificing their important code parameters such as minimum distance, code rate, or locality. We establish bounds on UC, and use them to show that our algorithms can achieve optimal or near optimal UC for a large class of LRCs. [ABSTRACT FROM AUTHOR]

The next generation of cellular networks (5G) will provide dense millimeter-wave backhaul architectures to wirelessly forward heterogeneous data traffic in a multihop fashion. In this paper, we present a general optimization framework for the design of delay-aware (DA) policies in multihop wireless networks, providing proportional prioritization of traffic. We develop three throughput-optimal DA algorithms (BP-DA, BPE-DA, and HD-DA) for joint dynamic routing and dynamic link-scheduling problems with good to optimal average network delay performance. Our DA framework considers both the classical back-pressure (BP) and the recent heat-diffusion (HD) algorithms, since queue back-pressure algorithms are being considered for mmWave backhauling management. We provide analytical results for the throughput-optimality of the proposed policies and average delay minimization of HD-DA within the class of DA policies. These are policies that make decisions at each timeslot based only on current channel state, current network queue sizes, and flow priorities. We discuss the applications of our proposals to backhaul management of mmWave cellular networks in light of recent works in the literature. Finally, we present extensive simulations of our proposed algorithms, which confirm the theoretical results and show how the algorithms effectively differentiate data traffic in terms of delay while satisfying flow rate requirements. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a decode-and-forward-based wireless multihop network with a single source node, a single destination node, and $N$ intermediate nodes. To increase the spectral efficiency and energy efficiency of the system, we propose a cooperative multihop communication protocol with spatial reuse, in which interference is treated as noise or can be canceled. The performance of a spatial-reused space–time-coded cooperative multihop network is analyzed over Rayleigh fading channels. In particular, the exact closed-form expression for the outage probability at the $n$th receiving node is derived when there are multiple interference sources over non-i.i.d. Rayleigh fading channels. Furthermore, the outage probability expressions are derived when nodes are equipped with more than one antenna. In addition, to reduce the effect of interference on multihop transmission, we propose a simple power control scheme that is only dependent on the statistical knowledge of channels. In the second approach for managing the interference, linear interference cancelation schemes are employed for both noncooperative and cooperative spatial-reused multihop transmissions. Finally, the analytic results were confirmed by simulations. Simulation results show that the spatial-reused multihop transmission outperforms the interference-free multihop transmission in terms of energy efficiency in low- and medium-signal-to-noise scenarios. [ABSTRACT FROM PUBLISHER]

The performance of distributed computing is restricted by the slowest worker nodes, known as stragglers, in the system. Coded computation has emerged as an efficient technique to mitigate the straggler effects in distributed computing. Most existing works only considered the computation straggler for single-hop networks. However, in multi-hop networks, the straggler effects will occur not only on worker nodes but also on relay nodes. In this paper, we consider a heterogeneous multi-hop network. The nodes in the network are heterogeneous, i.e., their computation capacities and transmission capacities are different. We propose a hierarchical coding scheme for such a network. Firstly, we reorganize it into a hierarchical network containing multiple layers. Each layer in the network consists of several groups. Then, a new hierarchical coding scheme is proposed, where coding is applied to each group to mitigate the stragglers. By taking both the computation time and transmission time into consideration, the overall task completion time is derived. To improve the performance of the network, heterogeneous hierarchical coded computation (HHCC) algorithm is proposed to provide an asymptotically optimal task allocation strategy. Compared with existing uniform uncoded, load balanced uncoded, and heterogeneous coded matrix multiplication schemes, HHCC has significant improvement. [ABSTRACT FROM AUTHOR]

Underwater acoustic (UWA) networks are a key form of communications for human exploration and activities in the oceanographic space of the earth. A fundamental issue of UWA communications is large propagation delays due to water medium, which has posed a grand challenge in UWA network protocol design. Conventional wisdom of addressing this issue is to live with this disadvantage by inserting a guard interval to introduce immunity to propagation delays. Recent advances in interference alignment (IA) open up a new direction to address this issue and promise a great potential to improve network throughput by exploiting large propagation delays. In this paper, we investigate propagation delay-based IA (PD-IA) in multi-hop UWA networks. We first develop a set of simple constraints to characterize PD-IA feasible region at the physical layer. Based on the set of PD-IA constraints, we develop a distributed PD-IA scheduling algorithm to greedily maximize interference overlapping possibilities in a multi-hop UWA network. Simulation results show that the proposed PD-IA algorithm yields higher throughput than an idealized benchmark algorithm without propagation delays, indicating that large propagation delays are not adversarial but beneficial for network throughput performance. [ABSTRACT FROM AUTHOR]

This paper analyzes the performance of a buffer-aided multi-hop relaying system using the max-link relay selection scheme for decode-and-forward cooperative networks. A Markov chain approach is adopted to analyze the state transition matrix that models the evolution of the status of relay buffers. Analytical expressions for the steady-state probability vector are obtained for a three-hop buffer-aided system, and through these expressions, we observe that states with the same probabilities can be clustered, thus reducing the size of the state transition matrix. We propose a state-clustering-based method to obtain the reduced state transition matrix, which is further used to derive an analytical expression for the outage probability with reduced computational complexity. The method is general in the sense that it does not require any prior knowledge about the steady-state probability vector and the state transition matrix. Furthermore, we illustrate, in detail, the construction of the reduced state transition matrix and the related steady-state distribution by an example. An analytical expression for the average packet delay is also derived. Both analytical and simulation results are provided to investigate the performance of buffer-aided multi-hop relaying networks. [ABSTRACT FROM AUTHOR]

In maritime wireless communications, unmanned surface vehicles (USVs) can improve coverage and transmission performance due to their agile maneuverability and flexible deployment. This paper considers a USV-enabled maritime wireless network, where a USV is employed to assist the communication between the terrestrial base station and ships. Considering the maritime environment characteristics and earth curvature, we establish the systematic USV kinetics and information transmission models. To guarantee fairness, we aim to maximize the minimum expected throughput overall ships by jointly optimizing the trajectory and communication resource allocation, subject to the constraints of the USV kinetics, safe sailing, breakpoint distances, line-of-sight links, resource allocation, and information-causality. Due to the complexity of the maritime two-ray signal propagation model, we propose a channel approximation method to find an upper bound of the throughput for the original problem. By the problem decomposition, two sub-problems are derived and solved iteratively using successive convex approximation and interior-point methods. Simulation results confirm the effectiveness of the proposed method and show that USV can significantly improve transmission performance in maritime wireless networks. [ABSTRACT FROM AUTHOR]

Operating beyond-5G networks at the millimeter wave (mmWave) band imposes technological challenges while offering great opportunities. The nature of millimeter waves renders the communication quality susceptible due to blockage caused by obstacles. Hence, multi-hop relaying is likely to play a significant role in improving the performance of mmWave networks. In this paper, we investigate the performance of two appropriate routing techniques for mmWave networks, namely minimum hop count (MHC) and nearest LoS relay to the destination with MHC (NLR-MHC). Analytical models are provided to evaluate the performance of the two routing techniques using tools from stochastic geometry. We model the distribution of hop count using phase-type distribution, and then we use this distribution to derive analytical results for the coverage probability and spectral efficiency. Results reveal the significant impact of densities of relays and blockages on the performance of the aforementioned routing techniques in-terms of spectral efficiency, connectivity probability, and average hop count. It is also demonstrated that NLR-MHC achieves a superior coverage probability and spectral efficiency compared to MHC. However, MHC provides better performance in-terms of connectivity probability and average hop count. [ABSTRACT FROM AUTHOR]

Based on the reverse asymmetric time synchronization framework, we have proposed several schemes with a major focus on the energy efficiency and computational complexity of a large number of battery-powered, low-cost sensor nodes in wireless sensor networks (WSNs). To address the cumulative end-to-end synchronization error, we have also introduced an idea of compensating for the processing delays at packet-relaying gateways as an energy-efficient way of multi-hop extension of WSN time synchronization schemes. In this paper, we present a comprehensive analysis of the multi-hop extension of WSN time synchronization schemes based on packet-relaying gateways with the per-hop delay compensation and the results of extensive experiments for the energy-efficient time synchronization schemes based on the reverse asymmetric time synchronization framework together with the flooding time synchronization protocol as a representative of existing schemes. Experimental results based on a real testbed demonstrate that the multi-hop extension based on packet-relaying gateways with the per-hop delay compensation greatly improves the performance of time synchronization of all the schemes considered compared to the multi-hop extension based on the conventional time-translating gateways. [ABSTRACT FROM AUTHOR]

Locally recoverable codes play a crucial role in distributed storage systems. Many studies have only focused on the constructions of optimal locally recoverable codes with regard to the Singleton bound. The aim of this paper is to construct optimal binary locally recoverable codes meeting the alphabet-dependent bound. Using a general framework for linear codes associated to a set, we provide a new approach to constructing binary locally recoverable codes with locality 2. We turn the problem of designing optimal binary locally recoverable codes into constructing a suitable set. Several constructions of optimal binary locally recoverable codes are proposed by this new method. Finally, we propose constructions of optimal binary locally recoverable codes with locality 2 and locality parameters $(\text {r},\delta)$ by Griesmer codes. [ABSTRACT FROM AUTHOR]

Frequency-hopping (FH) MIMO radar is recently introduced as an underlying system for realizing dual-function radar-communication (DFRC), increasing communication symbol rates to multiples of the radar pulse repetition frequency. As a newly conceived DFRC system, many realistic issues, such as channel estimation and synchronization, are not effectively solved yet. In this paper, we develop a multi-antenna receiver-based downlink communication scheme for the FH-MIMO DFRC, addressing the above issues in multi-path channels. By exploring the unique FH-MIMO radar waveform, we suppress both inter-antenna and inter-hop interference, and introduce minimal constraints on the radar waveform to facilitate DFRC. We then develop accurate estimation methods for timing offset and channel parameters. These methods are further employed to design reliable demodulation methods. We also derive performance bounds for the proposed estimation methods and embedded communications. Simulation results validate the efficacy of our receiving scheme, showing that the performance of estimators and data communications approaches analytical bounds. [ABSTRACT FROM AUTHOR]

This paper proposes a new peak-to-average power ratio (PAPR) reduction technique using a polynomial soft clipping function identified through a nonlinear constrained optimization. The power efficiency optimization problem of a linearized power amplifier can be considered as the minimization of the PAPR constrained by meeting the spectral mask requirements of the signal standard. It is demonstrated that the proposed approach can reduce the PAPR from 9.9 to 5.5 dB while meeting the spectral mask of the wideband code-division multiple-access standard. To compare the results with the traditional clipping and filtering method, the 5.5-dB PAPR clipped signal using the clipping and filtering technique was compared with the soft clipped signal. With the same efficiency, the error vector magnitude (EVM) for the soft clipped signal improved from 4.5% to 1.3% using post-compensation. Later, clipping and filtering are combined with the soft clipping technique. It is shown that the combined structure can reduce the PAPR to 3.4 dB while passing the adjacent channel power ratio and EVM requirements. The performance of the proposed method in the presence of additive white Gaussian noise and fading channels has been evaluated for 64QAM modulations using orthogonal frequency-division multiplexing modulated symbols. [ABSTRACT FROM AUTHOR]

In this paper, we consider the problem of joint secure routing and transmit power optimization for a multi-hop ad-hoc network under the existence of randomly distributed eavesdroppers following a Poisson point process. Secrecy messages are delivered from a source to a destination through a multi-hop route connected by multiple legitimate relays in the network. Our goal is to minimize the end-to-end connection outage probability under the constraint of a secrecy outage probability threshold, by optimizing the routing path and the transmit power of each hop jointly. We show that the globally optimal solution could be obtained by a two-step procedure where the optimal transmit power has a closed-form and the optimal routing path can be found by Dijkstra’s algorithm. Then a friendly jammer with multiple antennas is applied to enhance the secrecy performance further, and the optimal transmit power of the jammer and each hop of the selected route is investigated. This problem can be solved optimally via an iterative outer polyblock approximation with 1-D search algorithm. Furthermore, suboptimal transmit powers can be derived using the successive convex approximation method with a lower complexity. Simulation results show the performance improvement of the proposed algorithms for both non-jamming and jamming scenarios, and also reveal a non-trivial tradeoff between the numbers of hops and the transmit power of each hop for secure routing. [ABSTRACT FROM AUTHOR]

Piggybacking is an efficient framework to reduce the repair bandwidth of distributed storage systems, especially, when the systems meet the settings–maximum distance separable (MDS), high code rate, and a small number of substripes. Through an analysis on the repair ratio of a piggybacking construction, this paper reveals that the proportion $p_{p}$ of piggybacking protected stripes is the key to significantly decrease the repair bandwidth. Based on this analysis, this paper proposes a repair efficient coding under piggybacking framework (REPB) by considering various piggybacking protected stripes and MDS only protected stripes. The repair ratio of REPB tends to 0 and is close to theoretical cut-set bound, as the proportion $p_{p}$ is no longer fixed at 1/2. Furthermore, the proposed REPB codes enjoy low computational complexity in repair operation. [ABSTRACT FROM AUTHOR]

A linear block code with dimension $k$ , length $n$ , and minimum distance $d$ is called a locally repairable code (LRC) with locality $r$ , if it can retrieve any coded symbol by at most $r$ other coded symbols. LRCs have been recently proposed and used in practice in distributed storage systems, such as Windows Azure Storage and Facebook HDFS-RAID. Theoretical bounds on the maximum locality of LRCs ( $r$ ) have been established. The average locality of an LRC ( $\overline {r}$ ) directly affects the costly repair bandwidth, disk I/O, and the number of nodes involved in the repair process of a missing data block. There is a gap in the literature studying $\overline {r}$. In this paper, we establish a lower bound on $\overline {r}$ of arbitrary $(n,k,d)$ LRCs. Furthermore, we obtain a tight lower bound on $\overline {r}$ for a practical case where the code rate $(R=({k}/{n}))$ is greater than $(1-({1}/{\sqrt {n}}))^{2}$. Finally, we design three classes of LRCs that achieve the obtained bounds on $\overline {r}$. Comparing with the existing LRCs, our proposed codes improve the average locality without sacrificing such crucial parameters as the code rate or minimum distance. [ABSTRACT FROM AUTHOR]

In this paper, we study the achievable throughput of batched temporal network coding in multi-hop erasure channels, where network coding is applied only within small coding blocks and each communication hop is modeled as a Gilbert–Elliott (GE) packet erasure channel. The GE channel is a 2-state Markov model that is commonly used for channels with memory. While channel memory does not affect the end-to-end capacity of multi-hop erasure channels, we show that it degrades the end-to-end throughput, when batched network coding with finite batch size is applied, due to the higher variance in erasures within one coding block. On the other hand, if the initial channel state information is available, the channel variance can be significantly reduced. We show that this fact can be utilized for improving the efficiency of the recoding operations at the intermediate nodes, and hence improve the end-to-end throughput of batched network coding schemes. Specifically, we propose adaptive recoding operations, where the network coded packets are adaptively generated based on the number of received packets and the initial channel state for each coding block. The simulation results show that the proposed adaptive recoding scheme significantly enhances the end-to-end throughput of batched network coding over multi-hop GE channels. [ABSTRACT FROM PUBLISHER]

Interference neutralization (IN) is regarded as a promising interference management techniques for multi-hop wireless networks. Yet most existing results of IN are limited to two-hop networks such as the relay-aided cellular network. Little progress has been made so far in the exploration of IN in generic multi-hop (more than two hops) networks. This paper aims to bridge this gap by developing an optimization framework for IN in a generic multi-hop network with the objective of maximizing the end-to-end throughput of multiple coexisting communication sessions. We first derive a mathematical model for IN in a special one-hop network to characterize the capability of IN, and then generalize this model to a multi-hop network. Based on the IN model, we develop a cross-layer optimization framework for a multi-hop network with the objective of fully translating the benefits of IN to the end-to-end throughput of the multi-hop sessions. To evaluate the performance of IN in multi-hop networks, we compare its performance against the case where IN is not employed. Simulation results show that the use of IN can significantly (more than 50%) increase the session throughput and, more notably, the throughput gain of IN increases with the node density and traffic intensity in the network. [ABSTRACT FROM PUBLISHER]

Rateless codes have been found to be particularly attractive for decode and forward based relaying strategy in delay tolerant multihop networks. The latency performance of such networks is dependent on the worst links that results in the starvation of subsequent nodes with good channel conditions. The total delay suffered by such networks can be constrained by limiting the number of rateless coded transmissions, especially for applications with critical latency requirements. However, the performance of rateless codes deteriorates in such circumstances due to the lack of sufficient mutual information for successfully recovering the entire source packets. The fraction of source packets that can be recovered will depend on the encoded packets received across the transmission channel. This paper investigates the degradation in the performance of such rateless coded networks by deriving the average packet recovery rate. In order to improve the reliability in such delay constrained networks, a novel spectrally efficient transmission scheme for reliable multihop data transfer is proposed. The proposed scheme exploits the broadcast nature of wireless transmissions, which provides an inherent implicit feedback channel, to ensure the reliable delivery of information packets to the nodes in the network. Rather than allocating dedicated channels to feedback the packet recovery information, the implicit feedback channel determines such information which enhances the spectral efficiency. Further, the optimum number of packets recoverable within the specified delay constraint to reduce the reprocessing of lost packets across hops is analytically analysed in this paper. [ABSTRACT FROM AUTHOR]

For future wireless networks, enormous numbers of interconnections are required, creating a multi-hop topology and leading to a great challenge on data aggregation. Instead of collecting data individually, a more efficient technique, computation over multi-access channels (CoMAC), has emerged to compute functions by exploiting the signal-superposition property of wireless channels. However, it is still an open problem on the implementation of CoMAC in multi-hop wireless networks considering fading channel and resource allocation. In this paper, we propose multi-layer CoMAC (ML-CoMAC) by combining CoMAC and orthogonal communication to compute functions in the multi-hop network. Firstly, to make the multi-hop network more tractable, we reorganize it into a hierarchical network with multiple layers that consists of subgroups and groups. Then, in the hierarchical network, the implementation of ML-CoMAC is given by computing and communicating subgroup and group functions over layers, where CoMAC is applied to compute each subgroup function and orthogonal communication is adopted for each group to obtain the group function. The general computation rate is derived and the performance is further improved through time allocation and power control. The closed-form solutions to optimization problems are obtained, which suggests that orthogonal communication and existing CoMAC schemes are generalized. [ABSTRACT FROM AUTHOR]

Multipath routing can offer various advantages for wireless multihop networks. Among those advantages, in this paper, we focus on an advantage of multipath routing for security using the notion of information-theoretic security. We formulate an optimization problem that maximizes the transmission rate from a source node to a destination node with information-theoretic security constraints to avoid eavesdropping that can be carried out at some nodes within a wireless multihop network. Binary erasure channel (BEC) modeling is employed to model wireless links that suffer from fading and interference. It is shown that the proposed throughput maximization problem is a linear optimization problem and the optimal rate allocation can be found by standard optimization techniques. We also study performance analysis including an asymptotic analysis to see whether or not multipath routing (with equal rate allocation) could be secure in terms of an information-theoretic security point of view. Through performance analysis, we can show that multipath routing can provide not only more secure routing against eavesdropping, but also a higher throughput as more multipaths are available. [ABSTRACT FROM PUBLISHER]

The deployment of unmanned aerial vehicle (UAV) for surveillance and monitoring gives rise to the confidential information leakage challenge in both civilian and military environments. The security and covert communication problems for a pair of terrestrial nodes against UAV surveillance are considered in this paper. To overcome the information leakage and increase the transmission reliability, a multi-hop relaying strategy is deployed. We aim to optimize the throughput by carefully designing the parameters of the multi-hop network, including the coding rates, transmit power, and required number of hops. In the secure transmission scenario, the expressions of the connection probability and secrecy outage probability of an end-to-end path are derived and the closed-form expressions of the optimal transmit power, transmission and secrecy rates under a fixed number of hops are obtained. In the covert communication problem, under the constraints of the detection error rate and aggregate power, the sub-problem of transmit power allocation is a convex problem and can be solved numerically. Simulation shows the impact of network settings on the transmission performance. The trade-off between secrecy/covertness and efficiency of the multi-hop transmission is discussed which leads to the existence of the optimal number of hops. [ABSTRACT FROM AUTHOR]

In this paper, we consider confidential multicasting in multi-hop multi-antenna decode-and-forward (DF) relay networks, where a source sends a secure common message to multiple destinations in the presence of multiple eavesdroppers with the help of a multi-antenna DF relay located at each hop. Under an overall power constraint, we first show that the optimization problem for relay beamformer design and power allocation to maximize the achievable multicast secrecy rate in a two-hop multi-antenna relay network can be solved by using semidefinite relaxation and bisection technique. Further, we also propose a suboptimal iterative sequential update scheme for a multi-hop relay network including more than two hops. At each iteration, the relay beamformer at each hop is updated sequentially by solving an extended generalized eigenvector problem for a multiple-destination multiple-eavesdropper case, and the power allocation is updated by using the bisection technique with the feasibility problem of linear programming. Numerical results are presented to verify the multicast secrecy rates achieved by the proposed schemes in multi-hop multi-antenna DF relay networks. [ABSTRACT FROM PUBLISHER]

To localize the wireless sensor networks nodes, only the hop-based information (i.e., hops’ number, average hop size, and so on) has been, so far, exploited by range-free techniques, with poor-accuracy, however. In this paper, we show that localization accuracy may greatly benefit from joint exploitation, at no cost, of the information already provided by the forwarding nodes (i.e., relays) between each anchor (i.e., position aware) and sensor nodes pair. As such, we develop a novel range-free localization algorithm, derive its average location estimation error (LEE) in closed-form, and compare it in LEE performance with the best representative algorithms in the literature. We show that the proposed algorithm outperforms them in accuracy. In contrast to the latter, we further prove that it is able to achieve an LEE average and variance of about 0 when the number of sensors is large enough, thereby achieving an unprecedented accuracy performance among range-free techniques. [ABSTRACT FROM PUBLISHER]

An (n,k) erasure code that can recover any coded symbol by at most r other coded symbols is called a locally repairable code (LRC) with locality r . LRCs have been recently implemented in distributed storage systems. Coding complexity reduction can be significantly decreased by using binary LRCs (BLRCs) as they eliminate costly multiplication calculation. In this paper, motivated by the recently erasure codes with d=4 used in practice, we propose BLRCs when (r+1)\mid n and , meaning that neither their locality nor their minimum distance can be improved by non-binary codes. For r\geq 4 , our proposed binary codes offer near-optimal code rate, with a rate gap of \mathcal O(\log r/n) compared with optimal non-binary codes. While keeping the bulk of code structure binary, we eliminate this rate gap by using fields with sizes as small as r+2 for only two redundant symbols. These non-binary codes still eliminate the need for costly multiplications in many operations including a single failure repair (a dominant repair scenario). Using the construction of spanning BLRC with $d=4$ as a backbone, we also construct LRCs with minimum distance $d\geq 6$ . Furthermore, we obtain a closed-form equation for the mean-time to data-loss of arbitrary erasure codes. [ABSTRACT FROM AUTHOR]

Networks formed by energy-harvesting devices impose new technological challenges on data transmission due to uncertainty of the amount of energy that can be harvested. This is even more challenging with multihop networks, in which transmission outage occurs when one single device along the relay path cannot harvest enough energy. A virtual multiple-input multiple-output (MIMO) model for multihop, multipath networks has recently been developed to facilitate reliable open-loop end-to-end transmissions, making networks robust to random transmission outages without the necessity of bandwidth-consuming and complicated end-to-end feedback and control. In this paper, a framework based on a virtual MIMO model of multihop, multipath opportunistic networks formed by energy-harvesting devices is developed. We propose rotated-algebraic path-time codes (RA-PTC), by which data are encoded using Givens rotation and cyclic division algebras. Without rate loss, a form of time diversity is exploited by repeatedly transmitting the RA-PTC-coded data. Extensive theoretical analyses are carried out using amount of fading and diversity as metrics. Both the performance enhancement due to the proposed RA-PTC and the performance loss due to energy shortage are quantified. Furthermore, a simple yet effective cyclic power control is proposed to improve transmission reliability. Numerical results demonstrate that RA-PTC and cyclic power control enable efficient and reliable end-to-end transmission in multipath, multihop opportunistic networks formed by energy-harvesting devices. [ABSTRACT FROM AUTHOR]

We investigate the achievable sum degrees of freedom (DoF) in a class of single-antenna multi-user multi-hop relay networks. The networks consist of multiple information sources and destinations, without direct signal propagation link between them, so that multiple layers of relays are deployed to assist in information delivery. We consider the situation that relays are unable to shield their receptions from the harmful self-interference and from the interference generated by other relays. Hence, ideal full-duplex relaying is not applicable. Utilizing half-duplex decode-and-forward relays, a cluster successive relaying (CSR) transmission scheme is adopted to conduct message transmission. The CSR scheme divides each layer of relays into two successively activated relay clusters to compensate the extra channel consumption demanded by the half-duplex operation. We propose two interference alignment strategies to deal with the interference issues. By properly clustering the relays in each layer, we find the asymptotically achievable sum DoF, subject to time-varying and frequency-selective fading, respectively. These results can lead to new lower bounds for the available DoF in the considered class of multi-user multi-hop networks. [ABSTRACT FROM AUTHOR]

This paper presents a new analytical performance analysis of slow frequency-hopped synchronous spread-spectrum multiple-access (FHSS-MA) networks employing nonorthogonal binary frequency-shift keying (BFSK) and having arbitrary spacing between the hopping carriers. Taking into account the crosstalk due to the nonorthogonality of both hopping carriers and BFSK tones, and based on an accurate interference analysis, we derive new expressions for the average probability of error of a reference signal subjected to a number of similar signals in the additive white Gaussian noise Rayleigh-faded channel. These are used to investigate the effect of carrier and tone spacing on the spectral efficiency of an FHSS-MA network. It is shown that the spectral efficiency depends primarily on the shape of the employed pulses, in addition to both carrier and tone spacing. Numerical results show that rectangular pulses give higher spectral efficiency as compared with the half-sine pulses. Furthermore, orthogonal tone spacing is shown to be more efficient in the case of rectangular pulses, whereas half-sine pulses become more efficient with the nonorthogonal signaling. [ABSTRACT FROM AUTHOR]

In this paper, the performance of a multi-hop underlay cognitive radio network (UCRN) is thoroughly assessed. The co-existence of a primary transceiver and co-channel interference (CCI) is considered along with an uplink single-input multiple-output system utilizing selection combining and maximal ratio combining techniques at the receiver nodes. First, the equivalent per-hop signal-to-interference-plus-noise ratio (SINR) for the UCRN is formulated. Second, the exact cumulative distribution function (CDF) and the probability distribution function of the per-hop SINR are derived and discussed. Furthermore, approximate expressions exhibiting reduced complexity for the per hop equivalent CDF are derived to provide more insights. From the resulting CDF, the exact outage performance of the CR network is thoroughly assessed. In addition, mathematical formulas are derived for the average error probability and system ergodic capacity. Finally, the derived analytical expressions are validated by presenting numerical and simulation results for different network parameters. The results show that several factors contribute to the degradation of the system performance, namely, the interference power constraint, the primary transmitter power, and the presence of CCI, especially in the case where the CCI increases linearly with the secondary transmission powers. [ABSTRACT FROM PUBLISHER]

In this paper, we study the problem of secure routing in a multihop wireless ad-hoc network in the presence of randomly distributed eavesdroppers. Specifically, the locations of the eavesdroppers are modeled as a homogeneous Poisson point process (PPP) and the source-destination pair is assisted by intermediate relays using the decode-and-forward (DF) strategy. We analytically characterize the physical layer security performance of any chosen multihop path using the end-to-end secure connection probability (SCP) for both colluding and noncolluding eavesdroppers. To facilitate finding an efficient solution to secure routing, we derive accurate approximations of the SCP. Based on the SCP approximations, we study the secure routing problem, which is defined as finding the multihop path having the highest SCP. A revised Bellman–Ford algorithm is adopted to find the optimal path in a distributed manner. Simulation results demonstrate that the proposed secure routing scheme achieves nearly the same performance as exhaustive search. [ABSTRACT FROM PUBLISHER]

This paper proposes and analyzes cognitive multihop decode-and-forward networks in the presence of interference due to channel estimation errors. To reduce interference on the primary network, a simple yet effective back-off control power method is applied for secondary multihop networks. For a given threshold of interference probability at the primary network, we derive the maximum back-off control power coefficient, which provides the best performance for secondary multihop networks. Moreover, it is shown that the number of hops for secondary network is upper-bounded under the fixed settings of the primary network. For secondary multihop networks, new exact and asymptotic expressions for outage probability (OP), bit error rate (BER) and ergodic capacity over Rayleigh fading channels are derived. Based on the asymptotic OP and BEP, a pivotal conclusion is reached that the secondary multihop network offers the same diversity order as compared with the network without back off. Finally, we verify the performance analysis through various numerical examples which confirm the correctness of our analysis for many channel and system settings and provide new insight into the design and optimization of cognitive multihop networks. [ABSTRACT FROM PUBLISHER]

This paper investigates the ergodic capacity and outage probability performance of multihop relaying networks subject to independent non-identically distributed Nakagami-m fading. Particularly, we exploit a typical amplify-and-forward relaying system with an arbitrary number of cooperative intermediate relays and no direct link between the source and destination nodes. In our analysis, channel state information is assumed to be known only at the receiving nodes and the cooperative links may have distinct fading parameters and distinct average signal-to-noise ratio (SNR) levels. In this context, a tight closed-form upper bound expression for the ergodic capacity is derived. For this, firstly the moment generating function (MGF) of the inverse of the end-to-end SNR is obtained in closed-form. Then, making use of this expression, an upper bound for the ergodic capacity is attained. Thereafter, we investigate the end-to-end outage probability performance of the multihop relaying channels in Nakagami-m fading by making use of the aforementioned MGF expression. Finally, Monte-Carlo simulation results are provided and show the tightness of the proposed bounds. [ABSTRACT FROM PUBLISHER]

For buffer-aided tandem networks consisting of relay nodes and multiple channels per hop, we consider two traffic allocation schemes, namely local allocation and global allocation, and investigate the end-to-end latency of a file transfer. We formulate the problem for generic multi-hop queuing systems and subsequently derive closed-form expressions of the end-to-end latency. We quantify the advantages of the global allocation scheme relative to its local allocation counterpart, and we conduct an asymptotic analysis on the performance gain when the number of channels in each hops increases to infinity. The traffic allocations and the analytical delay performance are validated through simulations. Furthermore, taking a specific two-hop network with millimeter-wave (mm-wave) as an example, we derive lower bounds on the average end-to-end latency, where Nakagami- $m$ fading is considered. Numerical results demonstrate that, compared with the local allocation scheme, the advantage of global allocation grows as the number of relay nodes increases, at the expense of higher complexity that linearly increases with the number of relay nodes. It is also demonstrated that a proper deployment of relay nodes in a linear mm-wave network plays an important role in reducing the average end-to-end latency, and the average latency decays as the mm-wave channels become more deterministic. These findings provide insights for designing multi-hop mm-wave networks with low end-to-end latency. [ABSTRACT FROM AUTHOR]

We consider the joint detection and decoding of m-sequences. The receiver has to decide whether an m-sequence is received and possibly to decode its initial state. To do so, it implements an iterative message-passing decoding algorithm that operates on a parity check matrix, built upon a number of reference parity-check equations satisfied by the m-sequence. This matrix concatenates several elementary parity check matrices which are derived from reference equations. Unlike the conventional decoding case, the detection problem imposes to consider false alarms that may occur when the decoder is only fed with noise. While absorbing sets are known to be responsible for the error floor phenomenon of iterative message-passing decoders, we show that they may have a beneficial effect on the detection performance, in that they may prevent the decoder to produce false alarms. We further compute the number of hybrid cycles of length six and eight in the Tanner graph of the decoder and use the minimization of this number as criterion to derive an algorithm for selecting the reference parity check equations. This algorithm was found to be efficient for minimizing the probability of false alarm and decreases also the probability of wrong detection in the very small SNR region. This has been achieved at the cost of a reduction of the probability of correct detection. [ABSTRACT FROM PUBLISHER]

Due to the limited energy supplies of nodes in many applications such as wireless sensor networks, energy efficiency is crucial for extending the lifetime of these networks. This paper addresses the cooperative transmission for outage-restricted multihop wireless ad hoc networks. The source node wants to transmit messages to a single destination. Other nodes in the network may operate as relay nodes. In this paper, new multihop cooperative protocol is proposed using the space-time codes for the purpose of energy savings, subject to a required outage probability at the destination. We restrict the cooperation to nodes along a chosen route. Two efficient power allocation schemes are derived, which depend only on the statistics of the channels. Furthermore, three efficient cooperative multihop transmissions are proposed when arbitrary distributed space-time codes are used. The proposed cooperative protocols offer different degrees of energy efficiency, spectral efficiency, complexity, and signalling overhead. Compared to non-cooperative multihop routing, an energy saving of up to 72% is achievable in line networks with 3 relays and an outage probability constraint of 10^-3 at the destination. [ABSTRACT FROM AUTHOR]

This work investigates multi-hop serial relaying half-duplex (HD) networks comprising one source, one destination and $K$ decode-and-forward (DF) relays. Buffer-aided (BA) relays are considered where finite size buffers are added to relays. For this setup, we propose a novel BA relaying strategy that selects the node that must transmit over one epoch in a block fading environment. Selecting a node depends on the buffer state information of all relays and on the availability of the hops. Moreover, the proposed relaying scheme is controlled by an adjustable parameter that allows the system to achieve multiple levels of tradeoff between the average packet delay (APD) and the outage probability (OP). A Markov chain model is adopted to evaluate the system’s performance and simple closed-form expressions were derived for the APD and OP based on an asymptotic analysis. The performance analysis proves the ability of the suggested relaying scheme to achieve significant OP and APD gains with small buffer sizes. Two variants of the proposed relaying scheme are particularly appealing. The APD-prioritizing variant achieves the smallest APD of $2K$ without improving the diversity order. The second OP-prioritizing variant reaches the full diversity order of $K+1$ while increasing the asymptotic APD to $K(K+3)$. [ABSTRACT FROM AUTHOR]

We study the theoretical performance of a combined approach to demodulation and decoding of binary continuous-phase modulated signals under repetition-like codes. This technique is motivated by a need to transmit packetized or framed data bursts in high noise regimes where many powerful, short-length codes are ineffective. In channels with strong noise, we mathematically study the asymptotic bit error rates of this combined approach and quantify the performance improvement over performing demodulation and decoding separately as the code rate increases. In this context, we also discuss a simple variant of repetition coding involving pseudorandom code words, based on direct-sequence spread spectrum methods, that preserves the spectral density of the encoded signal in order to maintain resistance to narrowband interference. We describe numerical simulations that demonstrate the advantages of this approach as an inner code which can be used underneath modern coding schemes in high noise environments. [ABSTRACT FROM PUBLISHER]

Different from previous works in cooperative spectrum sensing that assumed the sensing channels independent identically distributed (i.i.d.), we investigate in this paper the independent but not identically distributed (i.n.i.d.) situations. In particular, we derive the false-alarm probability and the detection probability of cooperative spectrum sensing with the scheme of energy fusion over i.n.i.d. Rayleigh, Nakagami, and Rician fading channels. From the selected numerical results, we can see that cooperative spectrum sensing still gives considerably better performance even over i.n.i.d. fading environments. [ABSTRACT FROM PUBLISHER]

The introduction of relay station (RS) nodes is a key feature in next generation wireless networks such as 3GPP's long term evolution advanced (LTE-Advanced), or the forthcoming IEEE 802.16j WiMAX standard. This paper presents, using game theory, a novel approach for the formation of the tree architecture that connects the RSs and their serving base station in the uplink of the next generation wireless multi-hop systems. Unlike existing literature which mainly focused on performance analysis, we propose a distributed algorithm for studying the structure and dynamics of the network. We formulate a network formation game among the RSs whereby each RS aims to maximize a cross-layer utility function that takes into account the benefit from cooperative transmission, in terms of reduced bit error rate, and the costs in terms of the delay due to multi-hop transmission. For forming the tree structure, a distributed myopic algorithm is devised. Using the proposed algorithm, each RS can individually select the path that connects it to the BS through other RSs while optimizing its utility. We show the convergence of the algorithm into a Nash tree network, and we study how the RSs can adapt the network's topology to environmental changes such as mobility or the deployment of new mobile stations. Simulation results show that the proposed algorithm presents significant gains in terms of average utility per mobile station which is at least 17.1% better relatively to the case with no RSs and reaches up to 40.3% improvement compared to a nearest neighbor algorithm (for a network with 10 RSs). The results also show that the average number of hops does not exceed 3 even for a network with up to 25 RSs. [ABSTRACT FROM AUTHOR]

This paper presents a new unified analytical technique for accurate interference analysis of noncoherent M-ary frequency shift keying (MFSK) wireless communication systems in the presence of additive white Gaussian noise (AWGN) and multiple arbitrary interfering signals. New exact bit error rate expressions are derived for nonorthogonal noncoherent binary FSK in the presence of an arbitrary number of interfering signals having arbitrary spectral shapes at arbitrary frequency offsets. Furthermore, tight upper bounds for the symbol and bit error rates are given for noncoherent MFSK with arbitrary tone spacings. These results are extended to include MFSK signals experiencing Rayleigh, Nakagami-m or Rician fading. Some specific interference scenarios are analyzed in details, including jammers with a given Doppler-spread, direct sequence spread spectrum and orthogonal frequency division multiplexing signals, and a Poisson field of arbitrary interferers. [ABSTRACT FROM PUBLISHER]

Bit error rate performance analysis for communications systems with diversity and partial-band interference often yields complicated probability density functions (PDFs) for the decision statistics. The authors calculate these PDFs via a new technique by evaluating the inverse Laplace transform as an integral of a real integrand over a finite range. [ABSTRACT FROM AUTHOR]

Cache-aided wireless device-to-device (D2D) networks have demonstrated more promising performance improvement for video distribution than conventional distribution methods; thus, understanding the fundamental scaling behavior of such networks is highly important. However, the existing scaling laws for multi-hop networks are not optimal even in the case of Zipf popularity distributions (gaps between upper and lower bounds are not constants); furthermore, there are no scaling law results for such networks for the more practical case of a Mandelbrot-Zipf (MZipf) popularity distribution. We thus in this work investigate the throughput-outage performance for cache-aided wireless D2D networks adopting multi-hop communications, with the MZipf popularity distribution for file requests and users distributed according to Poisson point process. We propose an achievable content caching and delivery scheme, and then analyze its performance. We obtain the optimal scaling law by showing that the achievable performance is tight to the proposed outer bound. Since the Zipf distribution is a special case of the MZipf distribution, the optimal scaling law for the networks considering the Zipf popularity distribution is also obtained, which closes the gap in literature. [ABSTRACT FROM AUTHOR]

Age of Information (AoI) has proven to be a useful metric in networked systems where timely information updates are of importance. In the literature, minimizing “average age” has received considerable attention. However, various applications pose stricter age requirements on the updates which demand knowledge of the AoI distribution. Furthermore, the analysis of AoI distribution in a multi-hop setting, which is important for the study of Wireless Networked Control Systems (WNCS), has not been addressed before. Toward this end, we study the distribution of AoI in a WNCS with two hops and devise a problem of minimizing the tail of the AoI distribution with respect to the frequency of generating information updates, i.e., the sampling rate of monitoring a process, under first-come-first-serve (FCFS) queuing discipline. We argue that computing an exact expression for the AoI distribution may not always be feasible; therefore, we opt for computing upper bounds on the tail of the AoI distribution. Using these upper bounds, we formulate Upper Bound Minimization Problems (UBMP), namely, Chernoff-UBMP and $\alpha $ -relaxed Upper Bound Minimization Problem ($\alpha $ -UBMP), where $\alpha > 1$ is an approximation factor, and solve them to obtain “good” heuristic rate solutions for minimizing the tail. We demonstrate the efficacy of our approach by solving the proposed UBMPs for three service distributions: geometric, exponential, and Erlang. Simulation results show that the rate solutions obtained are near optimal for minimizing the tail of the AoI distribution for the considered distributions. [ABSTRACT FROM AUTHOR]

Multi-hop route optimization in large-scale inhomogeneous networks is typically NP-hard, for most problem formulations, requiring the application of heuristics which, despite their relatively low processing complexity, find sub-optimal solutions. Where optimal solutions can be determined by Lagrangian based constrained optimization techniques for example, the processing complexity typically scales like $O(N^{3})$ , $N$ being the number of relays employed. Here, we propose an alternative approach to route optimization by considering the limit of infinite relay node density to develop a continuum model, which yields an optimized equivalent continuous relay path. The model is carefully constructed to maintain a constant connection density even though the node density scales without bound. This leads to a formulation for minimizing the end-to-end outage probability that can be solved using methods from the calculus of variations. With the continuum model, we show that the processing complexity scales linearly with the number of points that sample the continuous path, which can be lower than the number of relay nodes in a large scale network. We demonstrate the effectiveness of this new approach and its potential by considering a network subjected to point sources of interference. [ABSTRACT FROM AUTHOR]

The radio link between a pair of wireless nodes is determined by radio channels, transmission range, node mobility and node-pair distance, which form a set of random factors in multihop wireless networks. The properties of such radio links can be characterized by link lifetime, residual link lifetime and link change rate, which, in fact, have been widely used for network design and performance evaluation. In this paper, we take a new modeling approach that captures the dynamics of radio channels and node movements in small-scale. More specifically, distance transition probability matrix is designed in order to describe the joint effects of dynamic transmission range due to radio channel fading and relative distance of a node-pair resulting from random movements. We find that the PDF of link lifetime can be approximated by an exponential distribution with parameter characterized by the ratio of average node speed \barV to effective transmission range R_e. To further understand the implication of link properties, analytical results are used to investigate the upper bound of network connectivity and the associated network performance is evaluated by extensive simulations. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of time-delay estimation and proposes an effective time-delay estimator for spread-spectrum communications. The main contribution of our work is twofold: first, we define a new objective function that analytically expresses the performance of different estimation criteria. Second, we introduce a new estimator that outperforms the conventional approaches. In particular, we develop a unified approach, deriving the performance trends of several time-delay estimators by one parametric closed form expression. Furthermore, we propose a new estimator that exploits a fast interpolation, running on few samples in the neighborhood of the coarse estimate, i.e. the (abscissa of the) estimated maximum of the ambiguity function. Mathematical expressions for bias and variance of the estimation error are derived and numerically evaluated by reduced Taylor's expansions up to the second order. The theoretical results, substantiated by computer simulations, have evidenced that the devised method is well suited for spread-spectrum satellite communications. [ABSTRACT FROM PUBLISHER]

In this work, we investigate the impact of mobility on video streaming over multi-hop wireless networks by utilizing a class of scheduling schemes. We show that node spatial mobility has the ability to improve video quality and reduce the transmission delay without the help of advanced video coding techniques. To describe a practical mobile scenario, we consider a random walk mobility model in which each node can randomly and independently choose its mobility direction, and all the nodes can identically and uniformly visit the entire network. The contributions of this work are twofold: 1) It studies the optimal node velocity for the mobile video system. In this case, it is possible to achieve almost constant transmission delay and video quality as the number of nodes increases; 2) It derives an achievable quality-delay tradeoff range for different node velocities. Therefore, it is helpful to shed insights on network design and fundamental guidelines on establishing an efficient mobile video transmission system. [ABSTRACT FROM AUTHOR]