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This paper focuses on a multicarrier direct-sequence code-division multiple-access system using frequency spread coding, which was proposed by Matsutani and Nakagawa in 1999. Although this system is attractive due to its inherent frequency diversity gain without time or frequency redundancy, it is disadvantaged by its exponential complexity in the maximum likelihood sequence decoding (MLSD). To cope with such a bottleneck, this paper proposes a fast MLSD method which consists of a searching process along the eigenvectors of a symmetric matrix and a refining process. The fast MLSD method is compared with the normal MLSD method via theoretical analysis and simulation results. [ABSTRACT FROM PUBLISHER]

This paper analyzes probability of bit-error (Pe) performance of asynchronous bandlimited direct-sequence code-division multiple-access systems with binary phase-shift keying spreading. The two present methods of Pe analysis under bandwidth-efficient pulse shaping: the often-cited standard Gaussian approximation and the characteristic function (CF) method suffer from either a low accuracy in regions of low Pe (< 10-3) or a prohibitively large computational complexity. The paper presents an alternate method of Pe analysis with moderate computational complexity and high accuracy based on a key observation. A sequence of chip decision statistics (whose sum yields a bit statistic) forms a stationary, m-dependent sequence when conditioned on the chip delay and phase offset of each interfering signal. This observation permits the generalization of the improved Gaussian approximation previously derived for the rectangular pulse and the derivation of a numerically efficient approximation based on the CF method. Numerical examples of systems using the square-root raised-cosine and IS-95 pulses illustrate THE P e performance, user capacity and the accuracy of the proposed method [ABSTRACT FROM PUBLISHER]

Slot synchronization is a critical step for fast and reliable cell search in intercell asynchronous direct sequence-code division multiple access systems. To increase reliability, observations over a number of slots may be combined. In this paper, combining schemes of multiple observations are studied for slot synchronization. The optimal combining rule is determined based on detection theory. It is found that two known combining schemes correspond to special cases of the optimal combining. These schemes may not work well in typical environments, since the schemes are optimized for specific environments. To improve slot synchronization performance in typical environments, a new combining scheme is proposed. The performance of the proposed combining scheme as well as other combining schemes is analyzed for Rayleigh fading channels with frequency offset. Numerical analysis shows that the proposed combining scheme significantly outperforms other combining schemes in typical environments [ABSTRACT FROM PUBLISHER]

In a paper by Cavallini et al. (see IEEE Trans. Commun., vol. 45, p.456-63, Apr. 1997), chip-level differential encoding/detection for direct-sequence spread-spectrum signals was proposed to cope with frequency-nonselective fast fading channels. It was shown that, unlike in the additive white Gaussian noise channel, in time-varying fading channels the system performance may be considerably improved, especially when the spreading factor is increased. In this paper, noncoherent sequence detection, recently proposed by the authors, is the starting point for the derivation of receivers with improved performance with respect to that of standard differential detection. For M-ary phase-shift keying signals, a theoretical analysis is performed and the results are confirmed by means of computer simulation. The performance advantage of taking into account a larger phase memory, with respect to the minimum accounted for by differential detection, is demonstrated. In particular, the amount of phase memory is optimized as a function of the Doppler spread for a Rayleigh frequency-nonselective fading channel. The robustness in the presence of phase noise is also investigated by means of computer simulation [ABSTRACT FROM PUBLISHER]

The emerging paradigm for dynamic spectrum sharing is based on allowing secondary users (SUs) to exploit white space frequency that is not occupied by primary users. White space database provides an opportunity for SUs to obtain spectrum availability information by submitting a location-based query. However, this new paradigm can also be exploited by the attackers to significantly enhance their jamming capability due to the available channel information from spectrum queries, which is expected to increasingly block SUs. The challenge is that the unique characteristics (e.g., lack of the wide range frequencies or continuous broadband) make existing anti-jamming techniques (e.g., direct-sequence spread spectrum and frequency hopping spread spectrum) difficult to be applied. In this paper, we present a novel Jammer Inference-based Jamming Defense (jDefender) framework. The main idea of jDefender is inferring the likelihood of a user being a jammer based on the observed jamming events and then utilizing the inferred attack likelihood to enhance the effectiveness of a series of the proposed anti-jamming strategies. Specifically, we first propose the Channel Allocation-based Jammer Inference scheme to infer the likelihood of an SU being a jammer based on the channels occupied by SUs even under the collusion attack performed by multiple jammers. The strength of the anti-jamming strategies (e.g., puzzle difficulties, available spectrum resources) will be correlated with the possibility of an SU being a jammer to achieve the tradeoff between system performance and jamming tolerance. We then implement the proposed scheme on Universal Software Radio Peripheral and PC. Extensive evaluations are performed to validate the effectiveness of the attacks and countermeasures. [ABSTRACT FROM PUBLISHER]

Cooperation has become an essential element in spectrum sharing between the primary and secondary networks. A new trend in cooperation is to allow the primary and secondary networks to cooperate on the node level for data forwarding. This new paradigm allows to pool network resources from both the primary and secondary networks and allows users in each network to access a much richer network infrastructure in a combined network. This paper offers an in-depth study of such node-level cooperation by explaining its optimal throughput curve—the maximum achievable throughput for both the primary and secondary users. We formulate the problem as a multicriteria optimization problem with the goal of maximizing the throughput of both the primary and secondary users. Through a novel approach based on weighted Chebyshev norm, we transform the multicriteria optimization problem into a single criteria optimization problem and find a sequence of Pareto-optimal points iteratively. Based on the Pareto-optimal points, we construct the throughput curve and show that it provides an $\varepsilon $ -approximation to the optimal curve. We prove some important properties of the optimal throughput curve. Through a case study, we show that the throughput region (the area under the throughput curve) under node-level cooperation is substantially larger than that when there is no node-level cooperation. [ABSTRACT FROM PUBLISHER]

This paper proposes a simple but relatively accurate, receive (Rx)-band-noise estimation method for wideband code division multiple access (WCDMA) handset heterojunction bipolar transistor MMIC power amplifier module (PAM) design. The method is based on small-signal and two-tone large-signal simulations, calculating Rx-band noise and helping circuit designers comprehend noise contributions under a large output power operation. Its effectiveness is verified through the simulations and measurements of a WCDMA band 11/21 MMIC PAM featuring an LC trap circuit placed at the base terminal of the first stage. This trap is designed to resonate at the difference frequency between the transmit- and Rx-bands. The PAM accommodating switchable-amplifier chains for triple-power modes—high power mode (HPM), mid-power mode (MPM), and low-power mode (LPM)—is fabricated using our in-house GaAs BiFET process. Measurements conducted under 3.4 V and 1450-MHz-band WCDMA (Third Generation Partnership Project Release 99, 3GPP R99) modulated signals show an Rx-band noise level of less than −136 dBm/Hz and power gain as high as 30 dB at a high output power ( P\mathrm {{out}} ) of 29 dBm. The measured noise level is in good agreement with that of the proposed estimation. The measurements also show that the PAM achieves power-added efficiency (PAE) as high as 41% at the P\mathrm {{out}} of 29 dBm while maintaining the ±5-MHz-offset adjacent channel power ratio (ACLR1) below −40 dBc in the HPM. The PAE values of 22% at P\mathrm {{out}} of 18 dBm and 17% at 7 dBm are obtained in the MPM and LPM, respectively, with the same ACLR1 levels. [ABSTRACT FROM PUBLISHER]

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]

In this paper, we present a cooperative relaying strategy for half-duplex multihop relay networks. This scheme consists of three parts: 1) relay selection to yield a layered relay network; 2) group successive relaying that establishes a relay schedule to efficiently exploit half-duplex relays; and 3) a cooperative relaying scheme named short message noisy network coding with sliding-window decoding (SNNC-SW) that outperforms other state-of-the-art information theoretical schemes with lower decoding complexity and delay. We derive an achievable rate region of the proposed SNNC-SW scheme and attain a closed-form rate expression in the asymptotic case for several network models of interests. We then focus on the first part of our relaying strategy regarding efficient relay selection. We develop interference-harnessing routing that exploits the fact that in SNNC-SW, interference is treated as a useful signal. We show that, due to the efficient treatment of interference, this scheme can outperform routing schemes that deploy store-and-forward, a solution previously proposed for practical wireless multihop networks. Finally, we develop a low-complexity successive decoder of our scheme (implemented by a conventional MIMO decoder), which is a solution that can readily be implemented in practice. It is shown that also this practical scheme provides a significant gain over routing (based on store-and-forward) and the performance gap increases as the network becomes denser. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel buffer-aided link selection scheme based on network coding in the multiple-hop relay network. The proposed scheme significantly increases transmission throughput by applying data buffers at the relays to decrease the outage probability and using network coding to increase the data rate. The closed-form expressions of both average throughput and packet delay are successfully derived. The proposed scheme not only has significantly higher throughput than both the traditional and existing buffer-aided max-link schemes but smaller average packet delay than the max-link scheme as well, making it an attractive scheme in practice. [ABSTRACT FROM PUBLISHER]

To improve the efficiency of wireless data communications, new physical-layer transmission methods based on known-interference cancelation (KIC) have been developed. These methods share the common idea that interference can be canceled when its content is known. Existing work on KIC mainly focuses on single-hop or two-hop networks, with physical-layer network coding and full-duplex communications as typical examples. This paper extends the idea of KIC to general multihop networks and proposes an end-to-end KIC (E2E-KIC) transmission method, together with its medium access control (MAC) design. With E2E-KIC, multiple nodes in a flow passing through a few nodes in an arbitrary topology can simultaneously transmit and receive on the same channel. We first present a theoretical analysis on the effectiveness of E2E-KIC in an idealized case. Then, to support E2E-KIC in multihop networks with an arbitrary topology, we propose an E2E-KIC-supported MAC protocol (E2E-KIC MAC), which is based on an extension of the Request-to-Send/Clear-to-Send mechanism in the IEEE 802.11 MAC. We also analytically analyze the performance of the proposed E2E-KIC MAC in the presence of hidden terminals. Simulation results illustrate that the proposed E2E-KIC MAC can improve network throughput and reduce end-to-end delay. [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]

The multi-hop multi-flow transmission has been proposed as a promising solution to cope with the spectrum scarcity in densely populated user environments. Due to the mutual interference between different flows and different hops of the same flow, the resource allocation for multi-hop multi-flow wireless networks is in general non-convex, and thus cannot be solved by conventional convex optimization techniques. In this paper, we propose an algorithm to effectively solve the resource allocation problem by jointly optimizing the rate control and scheduling. Specifically, we show that the problem can be decomposed into a set of problems that maximizes the weight-sum-flow rate at each slot. Furthermore, to solve the non-convex weighted sum flow rate maximization problem, we exploit its hidden monotonicity and develop a global optimal rate control and scheduling (G-RCS) algorithm based on the theory of monotonic optimization. Our analysis shows that the proposed G-RCS algorithm is guaranteed to converge to an optimal solution in a finite number of iterations. To reduce the complexity, we propose an accelerated algorithm, referred to as the A-G-RCS, based on the inherent symmetry of the optimal solution. Numerical results validate that the proposed algorithms can serve as a performance benchmark for the existing heuristic algorithms. [ABSTRACT FROM PUBLISHER]

This paper presents a novel dual-band base station antenna array using filtering antenna elements for size miniaturization. It consists of two $1 \times 6$ subarrays arranged side by side, which are designed for Digital Cellular System (DCS: 1710–1880 MHz) and Wideband Code Division Multiple Access (WCDMA: 1920–2170 MHz) applications. The two subarrays are composed of filtering antenna elements with high in-band radiation efficiency and out-of-band radiation rejection levels. The radiation of the DCS subarray is suppressed in the WCDMA band and vice versa. Mutual coupling between the two subarrays, therefore, can be suppressed and high isolation can be obtained with reduced subarray spacing. For demonstration, a dual-band filtering antenna array is designed and fabricated. The overall width of the array is only 206 mm, which is much narrower than that of typical industrial products ( $\sim 290$ mm). An isolation of 35 dB is obtained between the two subarrays without any decoupling network. The measured antenna gains are about 14.2 and 14.5 dBi for DCS and WCDMA bands, respectively, and the 3-dB beamwidths of the horizontal radiation patterns are 65° ± 5°. In addition, null filling below the main beam in the vertical radiation patterns is realized by elaborately designing a feed network to manipulate the output magnitude and phase of each array element. The proposed array is suitable for potential base station applications. [ABSTRACT FROM AUTHOR]

In multiradio multichannel (MR-MC) networks with significantly expanded network resource space, many existing scheduling/routing algorithms rely on a link-based network model and apply different heuristics in algorithm design to achieve/approximate throughput optimality. In this paper, using a tuple-based multidimensional conflict graph model, we establish a cross-layer framework, which facilitates systematically studying distributed scheduling and routing in multihop multipath MR-MC networks. In this framework, each tuple link is installed with a routing controller, which feeds controlled amounts of data to the tuple-link output queues for scheduling and transmission. We rigorously prove that, under a set of certain conditions, the network is queue stable in the mean sense under the distributed maximal scheduling policy. Based on Lyapunov optimization, we further propose a distributed delay-aware multipath routing method, which aims at minimizing the end-to-end delay of each commodity flow. Extensive simulation results demonstrate that the proposed joint scheduling/routing algorithm outperforms existing link-based single-path and multipath algorithms and tuple-based cross-layer control algorithm. [ABSTRACT FROM AUTHOR]

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]

Future wireless networks are envisioned to integrate multi-hop multi-operator multi-technology ( \textm^3 ) components in order to meet the increasing traffic demand at an acceptable price for subscribers. The performance of such a network depends on the multitude of parameters defining traffic statistics, network topology/technology, channel characteristics, and business models for multi-operator cooperation. So far, most of these aspects have been separately addressed in the literature. Since the above parameters are mutually dependent and simultaneously present in a network, for a given channel and traffic statistics, a joint optimization of technology and business model parameters is required. In this paper, we present such joint models of complex wireless networks and introduce optimization with parameter clustering to solve the problem in a tractable way for large number of parameters. By parameter clustering, we compress the optimization vector and significantly simplify system implementation, and hence, the algorithm is referred to as the compressed control of wireless networks. Two distinct parameter compression techniques are introduced, namely, parameter absorption and parameter aggregation. Numerical results obtained in this way demonstrate clear maximum in the network utility as a function of the network topology parameters. The results, for a specific network with traffic offloading, show that the cooperation decisions between the multiple operators will be significantly influenced by the traffic dynamics. For typical example scenarios, the optimum offloading price varies by factor 3 for different traffic patterns, which justifies the use of dynamic strategies in the decision process. Besides, if user availability increases by multi-operator cooperation, network capacity can be increased up to 50% and network throughput up to 30%–40%. [ABSTRACT FROM PUBLISHER]

Previous works on multicast capacity mainly focus on deriving asymptotic order results in large-scale wireless networks. While they can explore the general scaling laws of throughput capacity, it is also of great interest for practical concern to predict the exact achievable throughput in networks with an arbitrary finite number of nodes. In this paper, we investigate the nonasymptotic throughput and delay of multihop wireless networks for multicast applications wherein for each source node, $k$ nodes are randomly selected as receivers. It is challenging for the exact performance analysis since multicast transmission has a dynamic nature due to the following factors: 1) random distribution of nodes; 2) bursty traffic arrivals; and 3) different timescales for transient analysis. To tackle the problem, we propose an explicit analytical model and develop a multicast routing scheme, which accounts for these aspects. With our proposed model, we derive lower bound (LB) and upper bound (UB) on nonasymptotic multicast throughput and delay using stochastic network calculus. We show that the performance results hold for all timescales and network sizes and are strongly correlated to data burstiness and the number of receivers. While we investigate from a nonasymptotic point of view, our results can also cover the asymptotic scaling laws. Simulations are conducted to further verify the accuracy of the analytical bounds. [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]

Exploiting mobility improves the energy efficiency of data collection in wireless sensor networks (WSNs) for many applications. As more and more multimedia sensor nodes, equipped with audio and video capture capabilities are employed to characterize a sensing environment, streaming data are becoming increasingly important in WSNs. However, the mobility of MEs poses challenges on how to efficiently provide uninterrupted message delivery for continuous data streams in WSNs. In this paper, we propose a seamless streaming data delivery (SSDD) protocol for multihop cluster-based WSNs with MEs. Different from existing works, we concentrate on the localized mobility support for the delivery of streaming data in hierarchical WSNs. By introducing a cross-cluster handover mechanism and a path redirection scheme, SSDD efficiently maintains the end-to-end connectivity between a source and a ME during data transmission while avoiding most of the overhead in broadcasting the location of the ME as it moves in the sensing field. Extensive evaluation results demonstrate the effectiveness and high scalability of SSDD in terms of both energy efficiency and delivery latency. [ABSTRACT FROM PUBLISHER]

This paper presents the design and analysis of orthogonal, Doppler-tolerant waveforms for waveform agile radar (e.g. multiple-input multiple-output (MIMO) radar) applications. Previous work has given little consideration to the design of radar waveforms that remain orthogonal when they are received. Our research is focused on: 1) developing sets of waveforms that are orthogonal on both transmit and receive, and 2) ensuring that these waveforms are Doppler tolerant when properly processed. Our proposed solution achieves the above-mentioned goals by incorporating direct sequence spread spectrum (DSSS) coding techniques on linear frequency modulated (LFM) signals. We call this spread spectrum coded LFM (SSCL) signaling. Our transmitted LFM waveforms are rendered orthogonal with a unique spread spectrum (SS) code. At the receiver, the echo signal will be decoded using its spreading code. In this manner, transmitted orthogonal waveforms can be match filtered only with the intended received signals. From analytical expressions of the waveforms we have designed and from simulation results, we found that: 1) cross-ambiguity function (CAF) of two LFM SS coded (orthogonal) waveforms is small for all delays and Dopplers (i.e. transmit and receive signals satisfy near orthogonality constraint); 2) the length of the SS code determines the amount of interference suppression (i.e., complete orthogonal or near orthogonal of the received signal); 3) we can process the same received signal in two different ways; one method can provide LFM signal resolution and the other method can provide ultrahigh resolution; 4) biorthogonal codes can be used to reduce bandwidth when code length is large. Our proposed waveforms inherit multiple attributes (e.g. chirp diversity, code diversity, frequency diversity) of diverse waveforms. [ABSTRACT FROM AUTHOR]

Multihop communication is considered to be a useful approach for improving the coverage area with reduced transmit power. In this paper, we consider a path-selection-based multihop decode-and-forward (DF) cooperative system. A simple parallel multihop path-based cooperative communication system is considered. It is assumed that all hops in all cooperative paths are subject to independent Rayleigh fading. The best path, that is, the best multihop link between the source and the destination, is selected based on the max–min selection criterion. The relays in the selected cooperative path use the symbol-wise DF protocol, in which they demodulate the received data from the preceding node in a symbol-wise manner and forward it to the succeeding node. An analytical framework is developed for finding an accurate (almost close to exact) error performance of the considered system. To be more specific, we derive an accurate expression of the average bit error rate of the max–min-criterion-based best-path selection scheme, in terms of convergent power series. The coding gain and the diversity order of the scheme are also analytically obtained. [ABSTRACT FROM AUTHOR]

Cooperative communication (CC) for wireless networks has gained a lot of recent interests. It has been shown that CC has the potential to significantly increase the capacity of wireless networks, with its ability of mitigating fading by exploiting spatial diversity. However, most of the works on CC are limited to single radio wireless network. To demonstrate the benefits of CC in multiradio multihop wireless network, this paper studies a joint problem of multiradio cooperative routing and relay assignment to maximize the minimum rate among a set of concurrent communication sessions. We first model this problem as a mixed-integer programming (MIP) problem and prove it to be NP-hard. Then, we propose a centralized algorithm and a distributed algorithm to solve the problem. The centralized algorithm is designed within a branch-and-bound framework by using the relaxation of the formulated MIP, which can find a global (1+\varepsilon)-optimal solution. Our distributed algorithm includes two subalgorithms: a cooperative route selection subalgorithm and a fairness-aware route adjustment subalgorithm. Our simulation results demonstrate the effectiveness of the proposed algorithms and the significant rate gains that can be achieved by incorporating CC in multiradio multihop networks. [ABSTRACT FROM AUTHOR]

This paper describes a newly developed Si/GaAs hybrid multiband power amplifier module (MB-PAM) that supports major quad wideband code division multiple access (WCDMA) bands (Bands 5, 8, 2, and 1) for handset applications. With four dies (two GaAs-HBT dies, one GaAs-HEMT die, and one CMOS die) and several surface-mount devices, the hybrid MB-PAM accommodates two amplifier chains and two single-pole double-throw HEMT band-select switches on a 5 mm\,\times\, 5.5 mm laminate, covering 824–915 and 1850–1980 MHz. Each amplifier chain has two switchable signal paths corresponding to dual (high and low) power modes [high-power mode (HPM) and low-power mode (LPM)] for saving battery current in practical handset use. One of the main features of this MB-PAM is the integration of driver stages, RF switches, and their bias control circuits on the CMOS die for pursuing cost reduction. Only the two output power stages are fabricated in a GaA-HBT process. Measurements conducted under the condition of a 3.4-V supply voltage and a WCDMA (Third Generation Partnership Project Release 99) modulated signal are as follows. Owing to optimized linear design and broadband output matching design, the hybrid MB-PAM achieves a power-added efficiency (PAE) as high as 39%–40% at 28 dBm of output power ( Pout) over 824–915 MHz in the HPM while maintaining a \pm \5-MHz-offset adjacent channel leakage power ratio (ACLR1) to less than -\39 dBc. In the LPM, PAE of 15% at a Pout of 17 dBm is obtained while ACLR1 of less than -\40 dBc is maintained. For 1850–1980 MHz, the MB-PAM delivers 35% of PAE with ACLR1 of less than -\40 dBc at 28 dBm of Pout in the HPM and 15% PAE at 17.5 dBm of Pout in the LPM. [ABSTRACT FROM PUBLISHER]

Carrier sense multiple access (CSMA) protocol is standardized for vehicular communication to ensure a distributed and efficient communication between vehicles. However, several vehicular applications require efficient multi-hop information dissemination. This paper exploits stochastic geometry to develop a tractable and accurate modeling framework to characterize the multi-hop transmissions for vehicular networks in a multilane highway setup. In particular, we study the tradeoffs between per-hop packet forward progress, per-hop transmission success probability, and spatial frequency reuse (SFR) efficiency imposed by different packet forwarding schemes, namely, most forward with fixed radius (MFR), the nearest with forward progress (NFP), and the random with forward progress (RFP). We also define a new performance metric, denoted as the aggregate packet progress (APP), which is a dimensionless quantity that captures the aforementioned tradeoffs. To this end, the developed model reveals the interplay between the spectrum sensing threshold (\boldsymbol\rho\boldsymbol{th}) of the CSMA protocol and the packet forwarding scheme. Our results show that, contrary to ALOHA networks, which always favor NFP, MFR may achieve the highest APP in CSMA networks if \boldsymbol\rho\boldsymbol{th} is properly chosen. [ABSTRACT FROM PUBLISHER]

Cooperative spectrum sensing in a multihop cognitive radio (CR) network based on multiple antennas using an improved energy detector is studied in this paper. The improved energy detector uses the $p$th power of the absolute value of samples of primary user's (PU's) signals. We replace the conventional energy detector by an improved energy detector to enhance the performance of CR. Analytical expressions of the probability of false alarm and missed detection in each CR are derived. Furthermore, we extend our study to a multihop cooperative diversity system containing multiple multihop secondary transmission paths between the PU and the fusion center. Performance analysis of multihop cooperative diversity is discussed using an improved energy detector. We introduce a framework to derive a closed-form expression of the optimal number of multihop cooperative diversity branches by minimizing the total error rate. An efficient quick spectrum sensing algorithm is proposed, which requires fewer than the total number of cooperative multihop diversity branches. It is shown, through various numerical examples, that by using the optimal number of secondary transmission paths, it is possible to perform quick spectrum sensing while satisfying an upper bound on the total error rate. [ABSTRACT FROM PUBLISHER]

In this paper, we study, analyze, and evaluate a performance-aware cross-layer design approach for wireless multihop networks. Through network utility maximization (NUM) and weighted network graph modeling, a cross-layer algorithm for performing jointly routing, scheduling, and congestion control is introduced. The performance awareness is achieved by both the appropriate definition of the link weights for the corresponding application's requirements and the introduction of a weighted backpressure (BP) routing/scheduling. Contrary to the conventional BP, the proposed algorithm scales the congestion gradients with the appropriately defined per-pair (link, destination) weights. We analytically prove the queue stability achieved by the proposed cross-layer scheme, while its convergence to a close neighborhood of the optimal source rates' values is proven via an \varepsilon-subgradient approach. The issue of the weights' assignment based on various quality-of-service (QoS) metrics is also investigated. Through modeling and simulation, we demonstrate the performance improvements that can be achieved by the proposed approach—when compared against existing methodologies in the literature—for two different examples with diverse application requirements, emphasizing respectively on delay and trustworthiness. [ABSTRACT FROM AUTHOR]

In this paper, we consider secure communications of one source–destination pair in wireless multi-hop decode-and-forward (DF) relay networks. In the presence of an eavesdropper, we derive an optimal power allocation strategy to maximize achievable secrecy rates under an overall transmit power constraint assuming that a single relay is located at each individual hop. We demonstrate that the optimal power allocation is obtained when the overall power constraint and the DF-relaying constraints necessary to guarantee that each DF relay correctly decodes the information signals hold with equality, which rely on channel conditions between the source, relays, and destination. The channel conditions for the eavesdropper are shown to only influence relays that may be inactive for secrecy rate maximization. We also consider multiple cooperative relays at each hop to perform cooperative beamforming in the presence of multiple eavesdroppers. To improve the secrecy rate in multi-hop relay networks, which include more than two hops, we propose an iterative cooperative beamformer design and transmit power allocation scheme with relay selection. Numerical results are presented to investigate the secrecy capacity obtained by the optimal power allocation in multi-hop DF relay networks and to confirm the secrecy rate enhancement of the proposed cooperative beamforming scheme. [ABSTRACT FROM PUBLISHER]

Interference alignment (IA) is a powerful technique to handle interference in wireless networks. Since its inception, IA has become a central research theme in the wireless communications community. Due to its intrinsic nature of being a physical layer technique, IA has been mainly studied for point-to-point or single-hop scenario. There is a lack of research of IA from a networking perspective in the context of multi-hop wireless networks. The goal of this paper is to make such an advance by bringing IA technique to multi-hop MIMO networks. We develop an IA model consisting of a set of constraints at a transmitter and a receiver that can be used to determine IA for a subset of interfering streams. We further prove the feasibility of this IA model by showing that a DoF vector can be supported free of interference at the physical layer as long as it satisfies the constraints in our IA model. Based on the proposed IA model, we develop an IA design space for a multi-hop MIMO network. To study how IA performs in a multi-hop MIMO network, we compare the performance of a network throughput optimization problem based on our developed IA design space against the same problem when IA is not employed. Simulation results show that the use of IA can significantly decrease the DoF consumption for IC, thereby improving network throughput. [ABSTRACT FROM PUBLISHER]

In this paper, we extend the information theoretic framework that was developed in earlier works to multi-hop network settings. For a given network, we construct a novel deterministic model that quantifies the ability of the network in transmitting private and common messages across users. Based on this model, we formulate a linear optimization problem that explores the throughput of a multi-layer network, thereby offering the optimal strategy as to what kind of common messages should be generated in the network to maximize the throughput. With this deterministic model, we also investigate the role of feedback for multi-layer networks, from which we identify a variety of scenarios in which feedback can improve transmission efficiency. Our results provide fundamental guidelines as to how to coordinate cooperation between users to enable efficient information exchanges across them. [ABSTRACT FROM AUTHOR]

This paper addresses optimizations of both power allocation (PA) and relay position (RP), PA-only, and RP-only in multihop relay networks under a generalized model of fading channels. By adopting a parameterized model of fading distributions in the high-signal-to-noise-ratio region, we formulate the optimization problems in a unified framework, which are applicable to most of fading channels and solved with the Lagrange multiplier method. The optimal solutions are derived in explicit forms that facilitate the analysis on the performance of multihop networks. The analysis shows that the diversity order of the end-to-end performance is governed by the hop with the maximum diversity order in the cases of the joint optimization of PA and RP and optimization of RP-only while it is governed by the hop with the minimum diversity order in the case of the optimization of PA-only. Henceforth, the optimization of RP, improving both the diversity order and coding gain, leverages the system performance more significantly than that of PA, improving only the coding gain. By improving the diversity order and coding gain simultaneously, the joint optimization of RP and PA shows the best performance. [ABSTRACT FROM AUTHOR]

Broadcast is a fundamental network operation, widely used in wireless networks to disseminate messages. The energy-efficiency of broadcast is important particularly when devices in the network are energy constrained. To improve the efficiency of broadcast, different approaches have been taken in the literature. One of these approaches is broadcast with energy accumulation. Through simulations, it has been shown in the literature that broadcast with energy accumulation can result in energy saving. The amount of this saving, however, has only been analyzed for linear multi-hop wireless networks. In this paper, we extend this analysis to two-dimensional (2D) multi-hop networks. The analysis of saving in 2D networks is much more challenging than that in linear networks. It is because, unlike in linear networks, in 2D networks, finding minimum-energy broadcasts with or without energy accumulation are both NP-hard problems. Nevertheless, using a novel approach, we prove that this saving is constant when the path loss exponent $\alpha $ is strictly greater than two. Also, we prove that the saving is $\theta (\log n)$ when $\alpha =2$ , where $n$ denotes the number of nodes in the network. [ABSTRACT FROM AUTHOR]

Medical activity requires responsibility not only based on knowledge and clinical skills, but also in managing a vast amount of information related to patient care. It is through the appropriate treatment of information that experts can consistently build a strong policy of welfare. The primary goal of decision support systems (DSSs) is to give information to the experts where and when it is needed. These systems provide knowledge, models, and data processing tools to help the experts make better decisions in several situations. They aim to resolve several problems in health services to help patients and their families manage their health care by providing better access to these services. This paper presents a deep review of the state of the art of smart DSSs. It also elaborates on the latest developments in intelligent systems to support decision-makers in health care. The most promising findings brought in literature are analyzed and summarized according to their taxonomy, application area, year of publication, and the approaches and technologies used. Smart systems can assist decision-makers to improve the effectiveness of their decisions using the integration of data mining techniques and model-based systems. It significantly improves the current approaches, enabling the combination of knowledge from experts and knowledge extracted from data. [ABSTRACT FROM AUTHOR]

Constrained-energy underwater acoustic nodes are typically connected via a multi-hop underwater acoustic network (MHUAN) to cover a broad marine region. Recently, protocols for efficiently connecting such nodes have received considerable attention. In this paper, we show that the time reversal (TR) process plays an important role in the medium access control (MAC) because of its physical capability to exploit the multi-path energy from the richly scattering underwater environment, as well as to focus the signal energy in both spatial and temporal domains. In MHUANs, with severe multi-path propagation at the physical layer, the active TR process spatially focuses the signals to the location of the intended receiver; this significantly diminishes the interference among parallel links. We propose an active TR-based MAC (TRMAC) protocol for MHUANs, with the aim of minimizing collision and maximizing channel utilization simultaneously. Furthermore, by considering the impact of the cross correlation between different links on the TR-based medium access, we derive the threshold of the link cross correlation to resolve collision caused by the high cross correlation between realistic links. We perform simulations using the OPNET and BELLHOP environments, and show that the proposed TRMAC results in significantly improved throughput, decreased delay, and reduced data drop ratio in MHUANs. [ABSTRACT FROM AUTHOR]

In this paper, we study decode-and-forward relaying networks in the presence of direct links, where they are used by the eavesdropper to overhear the confidential message from the source and relay. The secure data transmission can go through from either the direct or the relaying branch, and we focus on the practical communication scenarios, where the main and eavesdropper channels are correlated. Although traditional opportunistic selection techniques can choose one better branch to ensure the secure performance, it needs to continuously know the channel state information (CSI) of both branches and may result in a high branch switching rate. To overcome these limitations, we propose a distributed secure switch-and-stay combining (DSSSC) protocol, where only one between direct and relaying branches is activated to assist the secure data transmission, and the switching occurs when the branch cannot support the secure communication any longer. The DSSSC protocol uses either the instantaneous or the statistics of the eavesdropping CSI. For both cases, we quantify the impact of correlated fading on secure communication by deriving an analytical expression for the secrecy outage probability (SOP) as well as an asymptotic expression for the high main-to-eavesdropper ratio region. From the asymptotic SOP, we can conclude that the DSSSC can achieve the optimal secure performance of opportunistic selection with less implementation complexity, and the channel correlation can further enhance the transmission security. [ABSTRACT FROM AUTHOR]

In this paper, a novel framework for optimizing the caching of popular user content at the level of wireless user equipments (UEs) is proposed. The goal is to improve content offloading over wireless device-to-device (D2D) communication links. In the considered network, users belong to different social communities while their UEs form a single multi-hop D2D network. The proposed framework allows us to exploit the multi-community social context of users for improving the local offloading of cached content in a multi-hop D2D network. To model the collaborative effect of a set of UEs on content offloading, a cooperative game between the UEs is formulated. For this game, it is shown that the Shapley value (SV) of each UE effectively captures the impact of this UE on the overall content offloading process. To capture the presence of multiple social communities that connect the UEs, a hypergraph model is proposed. Two line graphs, an influence-weighted graph, and a connectivity-weighted graph, are developed for analyzing the proposed hypergaph model. Using the developed line graphs along with the SV of the cooperative game, a precise offloading power metric is derived for each UE within a multi-community, multi-hop D2D network. Then, UEs with high offloading power are chosen as the optimal locations for caching the popular content. Simulation results show that, on the average, the proposed cache placement framework achieves 12, 19, and 21 percent improvements in terms of the number of UEs that received offloaded popular content compared to the schemes based on betweenness, degree, and closeness centrality, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the performance of a mixed radio frequency (RF) and multihop free space optical (FSO) system in a fifth-generation cloud radio access network (C-RAN) architecture. To cope with the practical channel characteristics, the RF link is assumed to experience the $ \kappa - \mu $ shadowed fading that has recently been proposed to model the small-scale multipath fading as well as line-of-sight shadowing. For FSO links, we adopt the exponentiated Weibull distribution, which can represent irradiance fluctuations at the finite receiving aperture over a wide range of turbulence conditions. Furthermore, we consider the pointing error between the FSO end devices. We first derive a novel probability density function (PDF) expression for the $ \kappa - \mu $ shadowed fading so that the $ \kappa $, $ m $, and $ \mu $ can be equal to the arbitrary positive real value. Then, we study the outage probability and the average symbol error rate (ASER) of the considered system. Our analysis is based on a decode-and-forward (DF) relaying scheme. We choose M-ary quadrature amplitude modulation (M-QAM) for the RF link and binary pulse position modulation (BPPM) for the FSO links. Finally, to provide more insights, we present the asymptotic approximate expressions in high signal-to-noise ratio regimes. Our research shows that the performance of the mixed RF and multihop FSO system can be improved by the large receiving aperture and the increasing number of hops. [ABSTRACT FROM AUTHOR]

Nowadays, electric motors and frequency converters have a great variety of applications. In motor feedback systems, communication is performed over separate sensor cables, which are notable for their high cost. Power line communication (PLC) over the motor cable is a promising and cost effective alternative. In this paper, a communication concept based on PLC and direct sequence spread spectrum (DSSS) channel access method is presented for motor cable communication. The channel characteristics and noise in the channel of a laboratory test setup are studied. Effect of the frequency converter output and switching frequencies on the channel noise are investigated. Capacitive and inductive signal coupling methods are evaluated and compared first theoretically by measurements and analysis of channel characteristics, and then practically by data transmission tests carried out in the laboratory test setup. Software‐defined radios (SDRs) are used as the data transmission devices for the communication concept evaluation. Concept's performance against variation of a signal‐to‐noise ratio (SNR) and switching frequency of the converter are evaluated. The concept applicability limits and optimal settings are presented. It can be stated that the concept provides a wider application range, than available solutions and can be effective for motor monitoring and speed data transmission. [ABSTRACT FROM AUTHOR]

It has been shown that it is impossible to achieve stringent timely delivery guarantees in a large network without having complete information of all future packet arrivals. In order to maintain desirable performance in the presence of uncertainty of future, a viable approach is to add redundancy by increasing link capacities. This paper studies the amount of capacity needed to provide stringent timely delivery guarantees. We propose a low-complexity online algorithm and prove that it only requires a small amount of redundancy to guarantee the timely delivery of most packets. Furthermore, we show that in large networks with very high timely delivery requirements, the redundancy needed by our policy is at most twice as large as the theoretical lower bound. For practical implementation, we propose a distributed protocol based on this centralized policy. Without adding redundancy, we further propose a low-complexity order-optimal online policy for the network. The simulation results show that our policies achieve much better performance than the other state-of-the-art policies. [ABSTRACT FROM AUTHOR]

ZigBee is a widely used wireless technology in low-power and short-range scenarios such as the Internet of Things, sensor networks, and industrial wireless networks. However, the traditional ZigBee supports only one data rate, 250 Kbps, which thoroughly limits ZigBee’s efficiency in dynamic wireless channels. In this paper, we propose Mrs. Z, a novel physical layer design to enable multi-rate selection in ZigBee with lightweight modification on the legacy ZigBee modules. The key idea is to change the single spectrum spreading length to multiple ones. Correspondingly, to support the rate adaptation to the channel variations, we propose a bit-error-based rate selection scheme, which predicts BER by leveraging the physical properties of ZigBee to calculate the confidence for each symbol in transmission. Then, the receiver selects the rate based on the negative impact on throughput incurred by bit errors and gives feedback to the transceiver. We implement Mrs. Z on USRPs and evaluate its performance in different scenarios. Experiment results demonstrate that Mrs. Z achieves about 1.15, 1.2, and 1.8 $\times$ average throughput compared to the classic smart pilot, softrate, and the traditional ZigBee. [ABSTRACT FROM AUTHOR]

In this paper, the performance of a multihop decode-and-forward (DF) based freespace optical (FSO) network is investigated over a unified exponentiated Weibull distributed atmospheric turbulence channel with pointing error and both types of detection techniques, i.e., heterodyne detection and intensity modulation/direct detection (IM/DD). We consider the aperture averaging receivers at both the intermediate relays and the destination to diminish the disadvantageous impact of atmospheric turbulence. First, we derive the new unified expression of the probability density function of the instantaneous signal-to-noise ratio (SNR). Based on the derived statistics, the unified closed-form expression of the average symbol error rate (SER) for the considered multihop network employing differentially modulated M-ary phase shift keying data, is obtained by utilizing a transition probability matrix. It is shown that increasing the hop count by 1 provides similar performance gain under both detection schemes. Further, a small increase in aperture size results in greater improvement under moderate turbulence rather than strong turbulence. The mutual information of the considered network is obtained with binary differential data, and it is demonstrated through results that, in the low-SNR region, the heterodyne receiver provides less mutual information as compared with the IM/DD receiver. However, beyond a particular SNR value (which depends on the hop count, aperture size, and turbulence strength), the heterodyne receiver attains more mutual information in comparison with the IM/DD receiver. The unified expression of outage probability for the DF-based multihop FSO network is also derived in terms of Meijer's G function. In addition, the asymptotic SER performance is examined in order to get impactful insight of network performance at high SNRs. All analytical results derived are verified through simulations. [ABSTRACT FROM AUTHOR]

Low-power and multihop wireless networking is envisioned as a promising technology to achieve both energy efficiency and easy deployment for many Internet of Things (IoT) applications. Measuring packet-level path is crucial for managing large-scale multihop wireless networks. Packet-level path information encodes the routing path, a packet that takes through a network. The availability of packet-level path information can greatly facilitate many network management tasks. It is challenging to reconstruct packet-level paths using a small overhead, especially for large-scale networks. While there is a long list of existing path reconstruction algorithms, these algorithms focus on specific network scenarios, e.g., periodic monitoring networks or event detection networks. There lacks a unified model for systematically understanding and comparing the performance of these algorithms in different network scenarios. In this paper, we fill this gap by proposing an abstract model. Using this model, it is possible to derive a decision space for selecting the best algorithm for different networks. Furthermore, this model also guides us to devise better path reconstruction algorithms (cPath $_{T}$ , cPath $_{S}$ , and cPath $_{ST}$) with respect to path reconstruction ratio. Extensive experiments demonstrate the prediction power of our model as well as the advantages of our proposed algorithms. The results show that our algorithm (cPath $_{ST}$) improves a path reconstruction ratio from 94.4%, 34.3%, and 30.8% to 98.9%, 99.9%, and 60.1% on average in three network scenarios, respectively, compared with the best state-of-the-art algorithms. [ABSTRACT FROM AUTHOR]

In this paper, we revisit the problem of finding the longest systematic-length k for a linear minimum storage regenerating (MSR) code with optimal repair of only systematic part, for a given per-node storage capacity l and an arbitrary number of parity nodes r. We study the problem by following a geometric analysis of linear subspaces and operators. First, a simple quadratic bound is given, which implies that k = r + 2 is the largest number of systematic nodes in the scalar scenario. Second, an r-based-log bound is derived, which is superior to the upper bound on log-base 2 in the prior work. Finally, an explicit upper bound depending on the value of r 2 /l is introduced, which further extends the corresponding result in the literature. [ABSTRACT FROM AUTHOR]

Secure neighbor discovery is fundamental to mobile ad hoc networks (MANETs) deployed in hostile environments and refers to the process in which two neighboring nodes exchange messages to discover and authenticate each other. It is vulnerable to the jamming attack in which the adversary intentionally transmits radio signals to prevent neighboring nodes from exchanging messages. Anti-jamming communications often rely on spread-spectrum techniques, which depend on a spreading code common to the communicating parties but unknown to the jammer. The spread code, however, is impossible to establish before the communicating parties successfully discover each other. While several elegant approaches have been recently proposed to break this circular dependence, the unique features of neighbor discovery in MANETs make them not directly applicable. In this paper, we propose JR-SND, a jamming-resilient secure neighbor discovery scheme for MANETs based on direct-sequence spread spectrum and random spread-code predistribution. JR-SND enables neighboring nodes to securely discover each other with overwhelming probability despite the presence of omnipresent jammers. Detailed theoretical and simulation results confirm the efficacy and efficiency of JR-SND. [ABSTRACT FROM PUBLISHER]

In this paper we first build an accurate and general transmission distortion model for H.264/AVC video streams to estimate the importance of each packet. Then, a utility-based optimized cross-layer resource allocation, MCS selection, and packet scheduling algorithm for real-time video transmission over HSDPA is studied. The utility here refers to the packet utility which is defined as a function of the packet urgency and the packet importance . Transmitting the packets with greater utility values firstly in each TTI can provide a higher level of video quality for the users. Thus, we formulate an optimization problem with the objective of maximizing the aggregate packet utility over all the users under the HSDPA physical resource constraints . In order to obtain an optimal transmission strategy, a dynamic programming -based cross-layer algorithm (DPCLA) is proposed. In view of its high complexity, we further develop a greedy-based cross-layer algorithm (GCLA) to find a suboptimal solution. Simulation results show that the proposed utility-based optimized cross-layer scheme, including the proposed transmission distortion model and the algorithms of DPCLA and GCLA, can provide higher received video quality than the existing ones for video transmission over HSDPA. [ABSTRACT FROM PUBLISHER]

Multihop underwater acoustic sensor networks (UASNs) suffer from low throughput caused by low channel utilization and unreasonable bandwidth allocation. The existing media access control (MAC) protocols for UASNs mainly aim to improve channel utilization but neglect to optimize bandwidth, so that they cannot achieve high throughput in miltihop networks. We propose the idea of joint bandwidth optimization and MAC in this paper. We first present a system model to optimize bandwidth for miltihop UASNs. Both the complicated interference relations between links and the different transmission demands of nodes are modeled. Thus, it can accurately reflect the characteristics of miltihop UASNs. By analyzing a 1-D linear miltihop network, we find and formulate a maximum hop number which is determined by nodes’ traffic load and channel capacity. The other finding is that an optimal scheduling needs to allocate the bandwidth based on traffic load, and the nodes with more traffic load should be allocated more bandwidth. This finding inspire us to develop a distributed traffic-based scheduling MAC protocol. This protocol can optimize bandwidth allocation by letting the older packet to be transmitted preferentially. To improve channel utilization, multiple packets are allowed to be transmitted in each data transmission round. Simulation results have confirmed that our protocol can achieve excellent performance owing to its core idea of joint bandwidth optimization and MAC. [ABSTRACT FROM PUBLISHER]

In ad hoc networks, selfish nodes deviating from the standard MAC (Medium Access Control) protocol can significantly degrade normal nodes’ performance and are usually difficult to detect. In this paper, we propose detection and defense schemes to identify and defend against MAC-layer selfish misbehavior, respectively, in IEEE 802.11 multi-hop ad hoc networks. Specifically, the non-deterministic nature of the IEEE 802.11 MAC protocol imposes great challenges to distinguishing selfish nodes from well-behaved nodes. Most traditional selfish misbehavior detection approaches are for wireless local area networks (WLANs) only. They either rely on a large amount of historical data to perform statistical detection, or employ throughput or delay models that are only valid in WLANs for detection. In contrast, we propose a realtime selfish misbehavior detection scheme for multi-hop ad hoc networks. It requires only several samples, and hence is more efficient and can adapt to channel dynamics more quickly. Then, based on the proposed detection scheme, we design three selfish misbehavior defense schemes against three typical kinds of smart selfish nodes. We find that the smart selfish nodes cannot degrade normal nodes’ performance much without getting detected. Extensive simulation results are finally presented to validate the proposed detection and defense schemes. [ABSTRACT FROM AUTHOR]

Energy efficient underwater communications systems design is a crucial task, once battery replacement may be barely feasible in this scenario. As acoustic underwater channels are usually harsher than terrestrial wireless channels, decreasing the transmission distance through a multi-hop approach is very appealing. In this sense, in this paper, we analyze how much energy is required to successfully transfer an information bit over a multi-hop underwater acoustic network while considering the optimum number of hops, retransmissions, code rate, and signal-to-noise ratio. We also investigate the impact of delay constraints in the total energy consumption, by allowing limited or unlimited retransmissions. Our results show that great energy savings can be obtained when the above-mentioned parameters are jointly optimized for a given link distance. Moreover, even though the impact of multiple hops is more beneficial, allowing for a small number of retransmissions lead to important energy savings. Finally, we compare the obtained results with a terrestrial wireless communications case, showing that an adequate modeling of the underwater scenario is imperative for an energy efficient design, once the optimal number of hops for terrestrial wireless may considerably differ from that for underwater communications. [ABSTRACT FROM PUBLISHER]

This paper presents an integrated passive self-interference mitigation (SIM) technique for FDD radios. A Four Port Canceller (FPC) serves a dual function as a receiver input matching network, and provides an auxiliary path from the transmitter (TX) to the receiver (RX) to perform leakage cancellation, with minimal penalty on the RX noise figure (NF), and power consumption. An example of this technique is applied to the design of a WCDMA front-end consisting of a low noise amplifier (LNA), the FPC, and an emulated power amplifier (PA) in a 40 nm, 6-metal-layer TSMC CMOS process. With proper tuning of the FPC and the use of an off-chip +30 dBm power amplifier, greater than 20 dB of TX leakage suppression is achieved over a cancellation bandwidth of 5 MHz. [ABSTRACT FROM AUTHOR]

User-cooperation-based multihop wireless communication networks (MH-WCNs) as the key communication technological component of mobile social networks (MSNs) can be exploited to enhance data rates and extend coverage. As one of the most promising and efficient user cooperation techniques, network coding can increase the potential cooperation performance gains among selfishly driven users in MSNs. To take full advantages of network coding in MH-WCNs, a network coding transmission strategy and its corresponding channel estimation technique are studied in this paper. Particularly, a four-hop network coding transmission is presented first, followed by an extension strategy for the arbitrary $2N$-hop scenario $(N\geq 2)$. The linear minimum mean square error (LMMSE) and maximum-likelihood (ML) channel estimation methods are designed to improve the transmission quality in MH-WCNs. Closed-form expressions in terms of the mean square error (MSE) for the LMMSE channel estimation method are derived, which allows the design of the optimal training sequence. Unlike the LMMSE method, it is difficult to obtain closed-form MSE expressions for the nonlinear ML channel estimation method. In order to accomplish optimal training sequence design for the ML method, the Cramér–Rao lower bound is employed. Numerical results are provided to corroborate the proposed analysis, and the results demonstrate that the analysis is accurate and the proposed methods are effective. [ABSTRACT FROM PUBLISHER]