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IEEE 1588, built on the classical two-way message exchange scheme, is a popular clock synchronization protocol for packet-switched networks. Due to the presence of random queuing delays in a packet-switched network, the joint recovery of the clock skew and offset from the timestamps of the exchanged synchronization packets can be treated as a statistical estimation problem. In this paper, we address the problem of clock skew and offset estimation for IEEE 1588 in the presence of possible unknown asymmetries between the deterministic path delays of the forward master-to-slave path and reverse slave-to-master path, which can result from incorrect modeling or cyber-attacks. First, we develop lower bounds on the mean square estimation error for a clock skew and offset estimation scheme for IEEE 1588 assuming the availability of multiple master-slave communication paths and complete knowledge of the probability density functions (pdf) describing the random queuing delays. Approximating the pdf of the random queuing delays by a mixture of Gaussian random variables, we then present a robust iterative clock skew and offset estimation scheme that employs the space alternating generalized expectation-maximization (SAGE) algorithm for learning all the unknown parameters. Numerical results indicate that the developed robust scheme exhibits a mean square estimation error close to the lower bounds. [ABSTRACT FROM AUTHOR]

A natural basis for the detection of a wireless random reactive jammer (RRJ) is the perceived violation by the detector [typically located at the access point (AP)] of the carrier sensing protocol underpinning many wireless random access protocols (e.g., Wi-Fi). Specifically, when the wireless medium is perceived by a station to be busy, a carrier sensing compliant station will avoid transmission, while an RRJ station will often initiate transmission. However, hidden terminals (HTs), i.e., activity detected by the AP but not by the sensing station, complicate the use of carrier sensing as the basis for RRJ detection since they provide plausible deniability to a station suspected of being an RRJ. The RRJ has the dual objectives of avoiding detection and effectively disrupting communication, but there is an inherent performance tradeoff between these two objectives. In this paper, we capture the behavior of both the RRJ and the compliant stations via a parsimonious Markov chain model and pose the detection problem using the framework of the Markov chain hypothesis testing. Our analysis yields the receiver operating characteristic (ROC) of the detector and the optimized behavior of the RRJ. While there has been extensive work in the literature on jamming detection, our innovation lies in leveraging carrier sensing as a natural and effective basis for detection. [ABSTRACT FROM AUTHOR]

A secret-key agreement for in-band full-duplex (FD) technology can be regarded as a valuable method for establishing security at the physical layer level. In this paper, we study an FD system model in conjunction with a secret-key agreement. The legitimate users interact through two-way channel probing and one-way reconciliation. We first introduce two complementary key generation models for FD and half-duplex (HD) settings, and compare their performances by introducing the key-reconciliation function. Furthermore, we study the impact of probing-reconciliation tradeoff and the role of a strong eavesdropper, and analyze the system performance in the high-signal-to-noise ratio regime. We show that under certain conditions, the FD mode negatively affects the capabilities of the eavesdropper and offers several advantages in terms of secret-key rate over the conventional HD setups. Our analysis reveals that the perfect self-interference cancelation is not necessary to obtain performance gains over the HD mode. [ABSTRACT FROM AUTHOR]

Recent physical-layer designs capable of decoding multi-packet collisions demonstrate great potential for improving the network performance. Current network protocols, however, tailor the traditional physical layer to avoid collisions and thus cannot fully exploit the benefits of concurrent transmission techniques. In this paper, we propose an innovative generic concurrent transmission aware routing design called mShare. The mShare design exploits the benefits of these techniques by scheduling concurrent senders to utilize co-owned receiver(s) in parallel. This design significantly increases the available number of routing choices and thus improves the network performance. To illustrate the versatility of our design, we test mShare in three settings: unicast, opportunistic routing, and data collection (convergecast). The performance of mShare is evaluated with physical testbed experiments running on USRP and simulations. The experimental results show that compared to conventional designs, mShare: 1) improves 277% of the throughput in unicast; 2) saves 78% of transmissions in opportunistic routing; and 3) reduces 70% of the delivery delay in data collection. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) can improve the spectral efficiency by exploiting the power domain and successive interference cancellation, and in order to improve the throughput, it can be applied to random access that plays a crucial role in the Internet of Things to support connectivity for a number of devices with sparse activity. In this paper, we formulate a game when NOMA is applied to ALOHA to decide users’ access or transmission probabilities. We consider a payoff function based on an energy-efficiency metric and drive the mixed strategy Nash equilibrium (NE). Once the NOMA-ALOHA game is successfully formulated, we generalize it to take into account users’ different fading and multiple orthogonal channels, which might be necessary for NOMA-ALOHA to support a number of users in a realistic environment. A distributed algorithm based on gradient play is derived to find the mixed strategy NE (or transmission probabilities) of multichannel NOMA-ALOHA with fading. [ABSTRACT FROM AUTHOR]

We propose a Context-aware Smallworld routing protocol for wireless ad-hoc networks which finds efficient routes to the destination nodes often through a very short chain of intermediate nodes, without using any routing table. This protocol exploits the “small-world” phenomenon of social networks where source-destination pairs typically get connected through few intermediate friends and the individuals can collectively discover such short paths. The key idea behind our routing protocol is that for forwarding an incoming packet to the destination, a node picks the next hop from among the one-hop neighbor from its one-hop neighborhood that is closest to the destination, and multiple randomly selected long-distance neighbor(s), i.e., from outside of its one-hop neighborhood, based on which of these neighbors is closest to the destination. The long-distance neighbors are selected by using their contextual information through a probabilistic mapping. We provide the theoretical foundations behind our protocol. This simple but effective algorithm can meet performance objectives for most scenarios by reducing loss and latency. Simulation results, using synthetic network topologies, have demonstrated that the routing performance of context-aware Smallworld is better than geographical (distance-based) Smallworld and other standard proactive routing protocols (e.g., OLSRv2) when metrics, such as packet losses, end-to-end delays, hop-counts, connectivity drops, and control traffic generated, are used as the key performance indicators. We also show that the proposed protocol is resilient to dynamic topology changes. [ABSTRACT FROM AUTHOR]

In this paper, we consider multichannel ALOHA for a wireless sensor network (WSN), where sensors’ signals are correlated. The impact of the number of channels on the length of information that an access point (AP) can collect is investigated. Under a certain distributed signal source model, in order for the AP to have a sufficiently long length of information, we show that the number of channels is to be larger than the square of the average number of active nodes. Thus, when the number of channels is limited, we need to use re-transmissions. To this end, we propose an adaptive transmission approach that can effectively exploit the correlation between the collected signals at the AP and nodes’ signals using Slepian–Wolf coding to shorten the total transmission time, which results in a more energy efficient WSN. [ABSTRACT FROM AUTHOR]

In this paper, we study simultaneous wireless information and power transfer (SWIPT) in relay interference channels (ICs), where energy-constrained relays harvest energy from sources’ radio-frequency signals and use the harvested energy to forward the information to destinations. We adopt the power splitting (PS) relay protocol and the interference alignment (IA) technique to jointly realize energy transfer and interference management. We propose two novel transmission schemes for the SWIPT in relay IC networks, namely, one-stage PS IA scheme and two-stage PS IA scheme. For both schemes, we investigate the optimal PS ratios that maximize the network sum rate. We obtain the closed-form optimal PS ratios for the two-stage PS IA scheme and develop a distributed and iterative algorithm to derive the optimal PS ratios for the one-stage PS IA scheme. We further study the optimal design of the IA precoding and decoding matrices. Based on the Grassmann manifold approach, we present an algorithm to obtain the optimal IA matrices for both schemes. The optimality of the designs of both the PS ratios and the IA matrices is then verified by simulations. Our results show that the proposed schemes effectively improve the performance of the network and significantly outperform benchmark schemes. [ABSTRACT FROM PUBLISHER]

We consider the secrecy rate for the multiple-input single-output optical wireless scattering communication, where the detected signal can be characterized by discrete photoelectrons. Assuming a legitimate receiver and an eavesdropper, we propose two secure communication protocols, the non-jamming protocol, and the cooperative jamming protocol, where for the former the transmitter does not send jamming signals but for the latter the transmitter sends jamming signals. We formulate the corresponding power and duty cycle optimization problems for both protocols. We also analyze the properties on the optimal solution, and adopt the alternating optimization to obtain a tractable solution. Moreover, we analyze the condition on the positive secrecy rate for the case where all the sub-channels to the receiver are weaker than their counterparts to the eavesdropper, where the secrecy transmission cannot be realized via a non-jamming protocol. The performance of the proposed two protocols is evaluated by numerical results. It is seen that for the iterative optimization solution, two to three iterations suffice for the convergence of the secrecy rate. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) is a promising technique for the fifth generation mobile communication due to its high spectral efficiency. By applying superposition coding and successive interference cancellation techniques at the receiver, multiple users can be multiplexed on the same subchannel in NOMA systems. Previous works focus on subchannel assignment and power allocation to achieve the maximization of sum rate; however, the energy-efficient resource allocation problem has not been well studied for NOMA systems. In this paper, we aim to optimize subchannel assignment and power allocation to maximize the energy efficiency for the downlink NOMA network. Assuming perfect knowledge of the channel state information at base station, we propose a low-complexity suboptimal algorithm, which includes energy-efficient subchannel assignment and power proportional factors determination for subchannel multiplexed users. We also propose a novel power allocation across subchannels to further maximize energy efficiency. Since both optimization problems are non-convex, difference of convex programming is used to transform and approximate the original non-convex problems to convex optimization problems. Solutions to the resulting optimization problems can be obtained by solving the convex sub-problems iteratively. Simulation results show that the NOMA system equipped with the proposed algorithms yields much better sum rate and energy efficiency performance than the conventional orthogonal frequency division multiple access scheme. [ABSTRACT FROM PUBLISHER]

Non-orthogonal multiple access (NOMA) can exploit the power difference between the users to achieve a higher spectral efficiency. Thus, the power allocation plays a crucial role in NOMA. In this paper, we study the power allocation for hybrid automatic repeat request (HARQ) in NOMA with two users. For the power allocation, we consider the error exponents of the outage probabilities in HARQ with incremental redundancy (IR) and derive them based on large deviations. While a closed-form expression for the error exponent (or rate function) without interference is available, there is no closed-form expression for the error exponent with interference. Thus, we focus on the derivation of a lower bound on the error exponent in this paper. Based on the error exponents, we formulate a power allocation problem for HARQ-IR in NOMA to guarantee a certain low outage probability for a given maximum number of retransmissions. From the simulation results, we can confirm that it is possible to guarantee a certain outage probability by the proposed power allocation method. [ABSTRACT FROM AUTHOR]

In this work, various channel coding schemes that can be used in hybrid automatic repeat request (HARQ) transmission protocols are investigated from an energy efficiency point of view. Conventional HARQ, where only one bit is used to inform the transmitter about the decoding success or failure, is compared to adaptive HARQ where the transmitter adapts either the length or the transmit power of the codewords using outdated channel state information (i.e., experienced by the receiver during the past transmissions). Describing the problems within a Markov decision process framework, we find optimal adaptation policies for both persistent (unlimited number of transmission) and truncated HARQ protocols. Numerical examples obtained in a Rayleigh block fading channel show that, in terms of energy efficiency, the adaptation of the codewords length provides notable gains over power adaptation and conventional HARQ. [ABSTRACT FROM AUTHOR]

In this paper, we consider the wireless broadcasting scenario with a source node sending some common information to a group of closely located users, where each link is subject to certain packet erasures. To ensure reliable information reception by all users, the conventional approach generally requires repeated transmission by the source until all the users are able to decode the information, which is inefficient in many practical scenarios. In this paper, by exploiting the close proximity among the users, we propose a novel two-phase wireless broadcasting protocol with user cooperations based on an efficient batched network code, known as batched sparse (BATS) code. In the first phase, the information packets are encoded into batches with BATS encoder and sequentially broadcasted by the source node until certain terminating criterion is met. In the second phase, the users cooperate with each other by exchanging the network-coded information via peer-to-peer (P2P) communications based on their respective received packets. A fully distributed and light-weight scheduling algorithm is proposed to improve the efficiency of the P2P communication in the second phase. The performance of the proposed two-phase protocol is analyzed and the channel rank distribution at the instance of decoding is derived, based on which the optimal BATS code is designed. Simulation results show that the proposed protocol outperforms most existing cooperative packet exchange schemes, especially when the inter-user links are not reliable. Lastly, the performance of the proposed scheme is further verified via testbed experiments. [ABSTRACT FROM PUBLISHER]

Erasure codes, such as LT and Raptor codes, are designed for the purpose of erasure-resilient distribution of data over computer networks. To achieve a small reception overhead, however, LT and Raptor codes must be used with a large design length $k$, making these codes unsuitable for real-time applications. In this paper, we propose a new class of erasure codes based on Reed–Solomon codes that unlike other Reed–Solomon-based erasure codes are rateless and also, unlike other rateless codes, guarantee zero overhead even for small $k$. Moreover, they have a reasonable computational complexity of coding when $k$ is not too large. In fact, a practical implementation of subfield subcodes of Reed-Solomon codes with arbitrarily large block lengths is presented. [ABSTRACT FROM AUTHOR]

This paper proposes an improved spectrum-sharing protocol for multiuser cooperation in cognitive radio (CR) networks. In CR networks, a secondary user (SU) can access the licensed bands of a primary user (PU) as compensation for cooperative transmission. During cooperative transmission, the SU concurrently transmits its own signal and network-coded signal from the PUs. However, detection errors at the SU cause error propagation which degrades the performance of the PU and SU. To address this problem, we develop a cooperative maximal-ratio combining scheme that mitigates the error propagation and achieves diversity gain. To evaluate the combining scheme, we derive a diversity order and closed-form bit error rate (BER) expression for arbitrary $M$-QAM at high SNR. The analysis results show that the diversity order and BER depend on the fraction of the transmit power at the SU. Based on the dependency of the fraction factor, we propose an optimization problem to minimize the BER of the SU while guaranteeing the PU's BER. Further, we apply the BER-constrained optimization problem to the adaptive modulation system. Simulation results show that the proposed cooperation provides full diversity gain to the PU and thus improves its spectral efficiency by using the optimized fraction factor. [ABSTRACT FROM PUBLISHER]

We develop a unified framework for the performance analysis of arbitrary-loaded downlink heterogeneous networks (HetNets) in which interfering sources are inherently spatially-correlated. Considering a randomly-deployed multi-tier cellular network comprised of a diverse set of large-and small-cells, we incorporate the notion of load-awareness and spatial-correlations in characterizing the activities of base stations (BSs) using binary decision variables. A stochastic geometry-based approach is accordingly employed to systematically develop a bounded expression of ergodic rate with different cellular association and load-balancing strategies. Employing the proposed unified framework hence allows for relaxation of several major limitations in the existing state-of-the-art models, in particular the always-transmitting-BSs, uncorrelated interferers, and Rayleigh fading assumptions. We elaborate on the usefulness of adopting this methodology by providing detailed analysis of the aggregate network interference generated by interdependent load-proportional sources over Nakagami-m fading interfering channels. The analytical formulations are validated through Monte-Carlo (MC) simulations for various scenarios and system settings of interest. We observe that the heavily-adopted fully-loaded model as well as the more recent interference-thinning-based approximations are significantly limited in capturing the actual performance curve. The proposed bounded load-aware model and MC trials reveal several important trends and design guidelines for the practical deployment of HetNets. [ABSTRACT FROM PUBLISHER]

Reliable and energy-efficient reading of Radio Frequency IDentification (RFID) tags is of utmost importance, especially in mobile and dense tag settings. We identify tag collisions as a main source of inefficiency in terms of wasting both medium access control (MAC) frame slots and reader's energy. We propose modulation silencing (MS), a reader-tag interaction framework to limit the effect of tag collisions. Utilizing relatively simple circuitry at the tag, MS enhances the performance of existing anti-collision protocols by allowing readers to terminate collision slots once a decoding violation is detected. With shorter collision slots, we revisit the performance metrics and introduce a new generalized time efficiency metric and an optimal frame selection formula that takes into consideration the MS effects. Through analytical solutions and extensive simulations, we show that the use of MS results in significant performance gains under various scenarios. [ABSTRACT FROM PUBLISHER]