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• A study on the possibility of avoiding the HEVC intra-frame drift effect. • Theoretically computing a mask multiplicative matrix cancelling the intra-frame drift effect. • Experimental illustrations and benchmarking over state-of-the-art methods. • Future work on the applicative integration under the watermarking framework. • Paving the way towards studying the intra-drift for the HEVC extensions. This paper investigates the possibility of avoiding the HEVC intra-frame drift effect induced by additive modifications of the luma DCT/DST coefficients. The main novelty consists in solving the intra-drift problem in its general form: starting from the equations defining the 35 intra-prediction modes and the DCT/DST computation, a mask multiplicative matrix cancelling the intra-frame drift effect is computed. The relevance of the advanced method with respect to the state of the art studies is illustrated, discussed and quantitatively assessed. [ABSTRACT FROM AUTHOR]

In this paper, we address the problem of action detection in unconstrained video clips. Our approach starts from action detection on object proposals at each frame, then aggregates the frame-level detection results belonging to the same actor across the whole video via linking, associating, and tracking to generate action tubes that are spatially compact and temporally continuous. To achieve the target, a novel action detection model with two-stream architecture is firstly proposed, which utilizes the fused feature from both appearance and motion cues and can be trained end-to-end. Then, the association of the action paths is formulated as a maximum set coverage problem with the results of action detection as a priori. We utilize an incremental search algorithm to obtain all the action proposals at one-pass operation with great efficiency, especially while dealing with the video of long duration or with multiple action instances. Finally, a tracking-by-detection scheme is designed to further refine the generated action paths. Extensive experiments on three validation datasets, UCF-Sports, UCF-101 and J-HMDB, show that the proposed approach advances state-of-the-art action detection performance in terms of both accuracy and proposal quality. [ABSTRACT FROM AUTHOR]

Abstract Packet delivery delay minimization is a critical issue in Wireless Sensor Networks. In mission-critical applications, the sensed information is highly delay-sensitive, and should be transmitted to the sink within a required delay. In this paper, we propose a new mixed integer linear programming model (MILP) to address the problem of end-to-end delay minimization of data transmission in delay-sensitive applications such as healthcare monitoring. The proposed model simultaneously guarantees (1) timely delivery data packets, (2) network reliability, (3) connectivity, and (4) flow preservation. We verify by computational experiments that the developed mixed integer linear model, using Cplex, is able to provide an optimal solution for timely data packet delivery of all our small and medium size problems. [ABSTRACT FROM AUTHOR]

The tremendous proliferation of smart phones and other smart devices has spurred the explosive growth of delay-sensitive high-rate multimedia services, which significantly increases energy consumption in wireless cellular networks. Therefore, it is an important yet challenging issue to carry out resource allocation for cellular networks to meet the quality of service requirement in terms of high data rate and, at the same time, achieve high energy efficiency. In this paper, two resource allocation approaches are proposed, where user selection and power allocation are jointly considered, to maximize effective capacity (EC) and effective energy efficiency (EEE), respectively, for a relay-assisted downlink of cellular networks. Channel estimation errors are taken into account to make the proposed approaches more practical. Moreover, to solve the EC maximization problem efficiently, we develop an optimal algorithm based on Lagrange method and Karush–Kuhn–Tucker conditions, and derive closed-form optimal solutions for user selection and power allocation at both the base station and relays. For the EEE maximization problem, an iterative algorithm based on the Dinkelbach method is developed to find the optimal solutions. Theoretical analysis and simulation results are presented to demonstrate the performance of the proposed approaches in terms of EC, EEE, and delay bound violation probability. [ABSTRACT FROM PUBLISHER]

Terminal relaying is expected to offer an effective means for realizing machine-type communications (MTC) in wireless cellular networks. In the absence of channel quality indicators, the effective utilization of relaying terminals (RTs) requires a mechanism by which RTs can autonomously assign available resource blocks (RBs) to potentially large numbers of uncoordinated MTC devices with minimal conflicts. Unlike random RB assignments, which do not offer performance guarantees, using prescribed RB assignment sequences provides an opportunity for obtaining performance gains. However, realizing these gains requires optimizing RB assignments over a large set of lengthy sequences. One technique for selecting assignment sequences is based on an exhaustive search of exponential complexity over sequences generated by multiplicative cyclic groups. This technique restricts the number of RBs to be prime minus one and does not consider sequences generated using other group operations. In this paper, we use group isomorphism to eliminate the constraint on the number of RBs and to show that the optimal assignment sequences generated by a specific cyclic group are globally optimal over the set of all cyclically generated sequences. We develop a greedy algorithm with polynomial complexity for the sequential selection of RB assignment sequences in systems with large numbers of RTs and arbitrary device distributions. This algorithm is further simplified by invoking the graphical representation of cyclic groups. The resulting algorithm is more efficient and thus suitable for generating assignment sequences for relay-assisted massive multiple access Internet-of-Things systems. Numerical results show that the performance of the sequences generated by the greedy algorithms is comparable to that of those generated by exhaustive search, but with much less computational cost. [ABSTRACT FROM PUBLISHER]

In this paper we extend the notion of approximate dual to fusion frames and present some approaches to obtain alternate dual and approximate alternate dual fusion frames. We also study the stability of alternate dual and approximate alternate dual fusion frames. [ABSTRACT FROM AUTHOR]

Frequency synchronization of a distributed measurement system requires the transfer of an accurate frequency reference to all nodes. The use of a general-purpose packet-based network for this aim is analyzed in this paper, where oversampling is considered as a means to counter the effects of packet delay variation on time accuracy. A comprehensive analysis that includes the stability of the local clock is presented and shows that frequency transfer through a packet network of this kind is feasible, with an accuracy level that can be of interest to a number of distributed measurement applications. [ABSTRACT FROM PUBLISHER]

Cellular wireless systems rely on frame-based transmissions. The frame design is conventionally based on heuristics, consisting of a frame header and a data part. The frame header contains control information that provides pointers to the messages within the data part. In this paper, we revisit the principles of frame design and show the impact of the new design in scenarios that feature short data packets, which are central to various 5G and Internet of Things applications. We treat framing for downlink transmission in an AWGN broadcast channel with $K$ users, where the sizes of the messages to the users are random variables. Using approximations from finite blocklength information theory, we establish a framework in which a message to a given user is not necessarily encoded as a single packet, but may be grouped with messages to other users and benefit from the improved efficiency of longer codes. This requires changes in the way control information is sent, and it requires that the users need to spend power decoding other messages, thereby increasing the average power consumption. We show that the common heuristic design is only one point on a curve that represents the tradeoff between latency and power consumption. [ABSTRACT FROM PUBLISHER]

In this paper, we perform a system-level feasibility analysis of full-duplex (FD) relay-aided cellular networks that are equipped with multiple antennas at the base stations (BSs) and the relay nodes (RNs). The aim is to understand whether FD relaying is capable of enhancing the rate of cellular networks. With the aid of tools from stochastic geometry, we develop a tractable approach for computing the percentile rate, which allows us to gain insights on the impact of FD relaying for both the cell-edge and the cell-median mobile terminals subject to network interference. Contrary to previous works that do not consider the network interference, the framework reveals that even in the absence of self-interference at the FD RNs, a network with half-duplex (HD) RNs can outperform its FD counterpart for a moderate number of antennas at the BSs and RNs. On the other hand, the FD-based network can substantially outperform both the HD-based one and the one without RNs for a sufficiently large number of antennas at the BSs and RNs and substantially small self-interference power effect at the RNs. Finally, the aforementioned analytical insights are validated by means of Monte Carlo simulations. [ABSTRACT FROM PUBLISHER]

This paper reports an outdoor experiment to optimize the timeout of wireless network coding (WNC) and frame aggregation (FA), which are implemented to carrier sense multiple access with collision avoidance (CSMA/CA)-based wireless two-hop relay prototype. The system throughput is improved. In the prototype, FA is implemented at the terminal nodes. Timeout function for WNC is available at the relay node and that for FA is available at the terminal nodes. Our outdoor experiment shows that optimizing the timeout values of WNC and FA can improve system throughput by 2.04-fold compared to the conventional relay without WNC or FA. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

This paper addresses the area of heterogeneous wireless relaying vehicular clouds. We devise an advanced vehicular relaying technique for enhanced connectivity in densely populated urban areas. We investigate the performance of a transmission scheme over a Long-Term Evolution-Advanced (LTE-A) network where vehicles act as relaying cooperating terminals for a downlink session between a base station and an end-user. The abundance of moving vehicles, operating in an ad hoc fashion, can eliminate the need for establishing a dedicated relaying infrastructure. However, the associated wireless links in vehicular clouds are characterized by a doubly selective fading channel; this causes performance degradation in terms of increased error probability. Hence, we propose a precoded cooperative transmission technique to extract the underlying rich multipath–Doppler-spatial diversity, which is a relay selection scheme to take advantage of the potentially large number of available relaying vehicles. We further contribute by the derivation of a closed-form error rate expression, diversity gain, and outage expressions and introduce our derived performance unconditional expressions as a benchmark to assess our analysis and future research studies of such an approach. Our analytical and simulation results indicate that significant diversity gains and reduced error rates are achievable. In addition, there is a noticeable reduction in the required transmitting power compared with traditional transmission schemes, as well as an increase in distance coverage. [ABSTRACT FROM PUBLISHER]

In this paper, we design and evaluate the proposed geographic-based spray-and-relay (GSaR) routing scheme in delay/disruption-tolerant networks. To the best of our knowledge, GSaR is the first spray-based geographic routing scheme using historical geographic information for making a routing decision. Here, the term spray means that only a limited number of message copies are allowed for replication in the network. By estimating a movement range of destination via the historical geographic information, GSaR expedites the message being sprayed toward this range, meanwhile prevents that away from and postpones that out of this range. As such, the combination of them intends to fast and efficiently spray the limited number of message copies toward this range and effectively spray them within range, to reduce the delivery delay and increase the delivery ratio. Furthermore, GSaR exploits delegation forwarding to enhance the reliability of the routing decision and handle the local maximum problem, which is considered to be the challenges for applying the geographic routing scheme in sparse networks. We evaluate GSaR under three city scenarios abstracted from real world, with other routing schemes for comparison. Results show that GSaR is reliable for delivering messages before the expiration deadline and efficient for achieving low routing overhead ratio. Further observation indicates that GSaR is also efficient in terms of a low and fair energy consumption over the nodes in the network. [ABSTRACT FROM PUBLISHER]

In noise-limited cooperative wireless networks, the diversity order of selection combining (SC) is the same as the diversity order of maximal ratio combining (MRC). The contribution of this paper is to report that the diversity order of SC and MRC may be different in the presence of randomly distributed interferers at the destination. More specifically, an amplify-and-forward (AF) dual-branch dual-hop cooperative relaying protocol in the presence of Nakagami- $m$ fading, additive Gaussian noise at the relay, and additive Gaussian noise and symmetric alpha-stable interference at the destination is investigated. By contrasting the diversity order of SC against recent results on the diversity of MRC, it is shown that both combining schemes provide the same diversity order if the distribution of the interference is unknown to the destination (interference-oblivious design) . They may achieve a different diversity order, on the other hand, if the interference can be estimated at the destination (interference-aware design) . Moreover, it is shown that the achievable diversity order depends on the interference in the broadcast and relaying phases being spatially correlated or independent. [ABSTRACT FROM PUBLISHER]

Many studies have presented the order sense results of information transmission capacity and packet delivery delay in mobile ad hoc networks (MANETs). To achieve the fundamental understanding of MANETs, we focus on deriving the closed-form expressions of the network capacity and end-to-end delay. A MANET with the generalized correlated mobility model is considered in this paper, where the mobility of nodes clustered in one group is confined within a specified area, and multiple groups move uniformly across the network. We also leverage limited packet redundancy to speed up the packet transmission, i.e., each source node is allowed to distribute at most f copies of each packet in its delivery process. Specifically, we first propose an effective multi-hop scheduling-routing scheme under the correlated mobility model, and then develop the closed-form expressions of both per node throughput capacity and expected end-to-end delay. We further explore the tradeoff between throughput capacity and packet delay by using packet redundancy f. The simulation studies validate our theoretical results. [ABSTRACT FROM AUTHOR]

H.264 takes rate distortion optimisation (RDO) technique to perform intra and inter mode decision and achieves higher coding efficiency, but the objective distortion metric such as mean square error (MSE) is employed in traditional RDO framework, which cannot acquire optimal subjective quality. In this paper, structural similarity (SSIM)-based subjective distortion is applied to RDO-based intra mode decision in H.264 I frame video coding, and a linear SSIM distortion model is firstly proposed and SSIM-based rate distortion cost function for intra mode decision is defined. Furthermore, a content adaptive frame layer Lagrange multiplier adjustment scheme is proposed to balance the tradeoff between rate and SSIM distortion better. Experimental results show that, the proposed method encodes image structural information more effectively and thus acquires better perceptual quality and subjective RDO performance compared with objective distortion-based RDO method. Under the same perceptual quality, our scheme achieves about 8·03% I frame bit rate reduction on average for various sequences over MSE-based RDO employed in JM reference software. [ABSTRACT FROM AUTHOR]

In recent years, object detection and tracking has been a dynamic research area. Rapid development of the multimedia and the associated technologies urge the processing of a huge database of video clips. The processing efficiency lies on the search methodologies utilised in the video processing system. Usage of unsuitable search methodologies may make the processing system ineffective. Hence, effective object detection and tracking system is an essential criterion for searching relevant videos from a huge collection of videos. This paper proposes a unique object detection and tracking system where video segmentation, feature extraction, object detection and tracking are combined perfectly using various features. Initially, the database video clips are segmented into different shots before performing the feature extraction process. The proposed system consists of two stages, namely, feature extraction and tracking of object in the video clips. In the feature extraction stage, firstly, colour feature is extracted based on colour quantisation. Next, edge density feature is extracted for the objects present in the query video. Then, the texture feature is extracted based on LGXP technique. Finally, based on these feature extracted, the object will be detected and the detected objects will be tracked by utilising both forward and backward tracking technique. The proposed methodology proved to be more effective and accurate in object detection and tracking. [ABSTRACT FROM AUTHOR]

SUMMARY In this paper, we derive another exact average error rate expression for the Nth best decode-and-forward relay systems over Rayleigh fading channels. On the basis of error-events at relay nodes, the Nth best relay's selection probability is expressed as a more tractable form in which the number of summations and the length of each summation are specified. Then, exact average error performance metrics are obtained as two well-known forms. The first is expressed with a moment generating function, and the other is presented as a closed form. Simulation results are finally presented to validate that the derived analytical expression can be a general frame work covering all Rayleigh fading channel conditions. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Highlights: [•] An intra-refresh line within a video frame acts as a form of error resilience. [•] The intra-refresh line’s position in each frame defines three H.264/AVC slices. [•] Two prioritization schemes are possible based on the slice’s position. [•] The improved packet-based scheme can achieve video quality gains of up to 4dB. [•] Prioritization is demonstrated in a wireless home network. [ABSTRACT FROM AUTHOR]

Abstract: This article presents an interactive software application to analyze and validate the operation of distance relays and its application for educational use. The design stages and theoretical fundamentals of distance relays are described and the proposed application has been structured to evaluate various design alternatives that include signal processing and different tripping characteristics. The software allows for the evaluation and analysis of distance relay operation with real time or simulated events in several commercial and academic electrical programs. Several examples are presented to illustrate the capabilities of this graphical software tool. [Copyright &y& Elsevier]

This paper presents an analytical investigation on the outage performance of dual-hop multiple antenna amplify-and-forward relaying systems in the presence of interference. For both the fixed-gain and variable-gain relaying schemes, exact analytical expressions for the outage probability of the systems are derived. Moreover, simple outage probability approximations at the high signal-to-noise-ratio regime are provided, and the diversity order achieved by the systems are characterized. Our results suggest that variable-gain relaying systems always outperform the corresponding fixed-gain relaying systems. In addition, the fixed-gain relaying schemes only achieve diversity order of one, while the achievable diversity order of the variable-gain relaying scheme depends on the location of the multiple antennas. [ABSTRACT FROM PUBLISHER]

The performance of opportunistic relaying in a dual-hop amplify-and-forward relay network where the relaying nodes are distributed according to a homogeneous two-dimensional Poisson point process with fixed density is analyzed. Largely ignored in the literature, this assumption leads to more realistic results, as in a typical practical scenario neither the number of relays nor their distances from the source and destination are known. An exact expression for the outage probability of this cooperative system for general fading environments and different types of relaying is derived. The expression is then simplified under an assumption that the radius of the relay deployment region is sufficiently large, and specialized to additive white Gaussian noise (no fading), Rayleigh fading and severe (half-Gaussian) fading environments. Simple and tight upper and lower bounds on the outage probability are also derived. Simulation results validate the theoretical analyses and verify the accuracies of the proposed bounds. [ABSTRACT FROM PUBLISHER]

In cooperative orthogonal frequency division multiplexing (OFDM) systems, accurate frequency synchronization is critical to achieving any potential gains brought by the cooperative operation. The carrier frequency offsets (CFOs) present among multiple nodes (source, relays and destination) are more difficult to tackle than the single CFO problem in point-to-point systems. Multiple CFOs cause phase drift, inter-carrier interference (ICI) and inter-block interference (IBI) in the received signal. This paper deals with the CFO induced interference mitigation problem in distributed space time block coded (STBC) amplify-and-forward (AF) cooperative OFDM systems. We propose a two step approach to recover the phase distortion and suppress the ICI and IBI using low complexity methods to achieve high performance. The first step is time domain (TD) compensation and the second step is frequency domain (FD) decoding. Two TD compensation schemes are proposed, i.e., IBI-removal and ICI-removal. The IBI-removal scheme decouples the two blocks of one STBC codeword completely and then decodes the ICI degraded blocks individually. The ICI-removal scheme removes ICI first and the subsequent decoding requires joint decoding of the two blocks. Simulation results show that the IBI-removal scheme which is of lower complexity performs well with small CFO. For large CFO, the ICI-removal with modified iterative joint maximum likelihood decoding (MIJMLD) outperforms other schemes. [ABSTRACT FROM AUTHOR]

Presents the table of contents for this issue of the periodical. [ABSTRACT FROM AUTHOR]

In a communication system in which K nodes communicate with a central sink node, the following problem of selection often occurs. Each node maintains a preference number called a metric, which is not known to other nodes. The sink node must find the `best' node with the largest metric. The local nature of the metrics requires the selection process to be distributed. Further, the selection needs to be fast in order to increase the fraction of time available for data transmission using the selected node and to handle time-varying environments. While several selection schemes have been proposed in the literature, each has its own shortcomings. We propose a novel, distributed selection scheme that generalizes the best features of the timer scheme, which requires minimal feedback but does not guarantee successful selection, and the splitting scheme, which requires more feedback but guarantees successful selection. The proposed scheme introduces several new ideas into the design of the timer and splitting schemes. It explicitly accounts for feedback overheads and guarantees selection of the best node. We analyze and optimize the performance of the scheme and show that it is scalable, reliable, and fast. We also present new insights about the optimal timer scheme. [ABSTRACT FROM AUTHOR]

Large-scale propagation effect plays an important role in multiple-input multiple-output (MIMO) relay systems. In particular, the position of the relay (between the source and destination) determines the path-loss effects of adjacent hops, which will further affect the performance of each hop and thus the relay system. In this paper, by minimizing the outage probability of a decode-and-forward (DF) MIMO relay system with orthogonal space-time block coding, we show that relay position optimization improves the finite-SNR (signal-to-noise ratio) diversity gain of a relay system whose adjacent hops have different diversity orders (unbalanced system). Specifically, with relay position optimization, the diversity gain is no longer bounded by that of the weaker hop, i.e., the hop with a lower diversity order, but approaches the diversity order of the stronger hop. This diversity improvement provides a dramatic improvement for the end-to-end outage probability. It will also be shown that although power allocation has no effects on the achievable diversity order, it provides some SNR gains. [ABSTRACT FROM AUTHOR]

Delay-optimal data delivery in Vehicular Intermittently Connected Networks (VICNs) is challenging since vehicular traffic is affected by numerous recurring and completely random events. Some of these events cause breakdowns and jams while others subserve traffic stability. Researchers observed that mobile vehicles might be wisely exploited to connect two isolated, Stationary Roadside Units (SRUs). In this context, the design of effective delay-minimal data relaying strategies is receiving significant attention. However, many existing such schemes either do not adequately model vehicular traffic behaviours or adapt typical Internet packet-like forwarding protocols to VICNs. In contrast, this manuscript presents a concise, yet comprehensive study of vehicular traffic states based on which a "comme-il-faut" vehicular traffic model is established. This model captures the fundamental traffic characteristics and enables the selection of appropriate distributions for vehicular flow and speeds that parallel the realistic measurements made by traffic theorists. These distributions constitute the basis of a novel Probabilistic Bundle Release Scheme with Bulk Bundle Release (PBRS-BBR) that is proposed with the objective to minimize the average bundle delivery delay. An analytical queueing model is formulated to assess the performance of PBRS-BBR under medium-to-light vehicular traffic. Extensive simulations are conducted to prove the model's validity and accuracy. [ABSTRACT FROM AUTHOR]

In this paper, we present a video streaming system for wireless networks that employs utility optimization of pre-compressed video at the application layer, together with a novel cooperative wireless physical layer (PHY) that allows interfering transmissions. Our system model considers multiple and independent unicast or multicast transmissions between network nodes while a number of them serve as relays. For this new PHY the average transmission rate that each sender-destination pair can achieve is estimated first. Next, we show that the utility optimization problem can be simplified due to the features of the proposed PHY. Subsequently, we devise a utility optimization algorithm that is executed independently at each sender and it derives the optimal video packets that should be sent in the wireless link given the calculated rate constraint. Simulation results demonstrate that for unicast video streaming scenarios and with the utility optimization framework, allowing packets to interfere is a better choice than employing a typical cooperative PHY. For the case of multicast video delivery the performance of the proposed scheme is significantly improved for good channel conditions while the improvement is minimized in the low channel SNR regime when compared to the unicast scenario. [ABSTRACT FROM AUTHOR]

For cooperative amplify-and-forward (AF) relaying in spectrum-sharing wireless systems, secondary users share spectrum resources originally licensed to primary users to communicate with each other and, thus, the transmit power of secondary transmitters is strictly limited by the tolerable interference powers at primary receivers. Furthermore, the received signals at a relay and at a secondary receiver are inevitably interfered by the signals from primary transmitters. These co-channel interferences (CCIs) from concurrent primary transmission can significantly degrade the performance of secondary transmission. This paper studies the effect of CCIs on outage probability of the secondary link in a spectrum-sharing environment. In particular, in order to compensate the performance loss due to CCIs, the transmit powers of a secondary transmitter and its relaying node are respectively optimized with respect to both the tolerable interference powers at the primary receivers and the CCIs from the primary transmitters. Moreover, when multiple relays are available, the technique of opportunistic relay selection is exploited to further improve system performance with low implementation complexity. By analyzing lower and upper bounds on the outage probability of the secondary system, this study reveals that it is the tolerable interference powers at primary receivers that dominate the system performance, rather than the CCIs from primary transmitters. System designers will benefit from this result in planning and designing next-generation broadband spectrum-sharing systems. [ABSTRACT FROM AUTHOR]

We consider communication protocols for N-way all-cast relay networks, which comprise N source terminals such that each source terminal demands messages from all other source terminals with the help of a relay. The derived protocols are characterized by the fact that physical layer network coding is employed at the relay, where each source has side information about the signals it has sent. Amplify-and-forward (AF) and decode-and-forward (DF) protocols are applied to the N-way relay network setting, where the achievable rate regions for those protocols are derived and compared with outer capacity bounds. We propose several practical space-time coding schemes for AF and DF, and introduce two new protocols denoted as denoise-and-forward (DNF) and estimate-and-forward (EF). Further, for AF and DF the fundamental diversity-multiplexing trade-off is characterized. [ABSTRACT FROM AUTHOR]

In a dynamic wireless network where a source terminal communicates with a destination, in presence of other users in the network, it is worthwhile to consider oblivious relaying strategies of a relay in close proximity to the source transmitter. The source-relay channel is assumed to be a fixed gain additive white Gaussian noise (AWGN) channel due to source-relay colocation. The source-destination and the relay-destination transmissions are subject to block flat fading dynamics. A perfect channel state information (CSI) at the respective receivers only is assumed. With the expected throughput as a performance measure, we incorporate a two-layer broadcast approach into a cooperative strategy based on the decode-and-forward scheme - Sequential Decode-and Forward (SDF). The broadcast approach splits the transmitted rate into superimposed layers, corresponding to a "bad" and a "good" channel states, allowing better adaptation to the actual channel conditions. The achievable rate expressions for the SDF strategy are derived under the broadcast approach for multiple settings including single user, multiple-input single-output (MISO) and the general relay setting using successive decoding technique, both numerically and analytically. Continuous broadcasting lower bounds are derived for the MISO and for the oblivious cooperation scenarios. [ABSTRACT FROM AUTHOR]

This paper compares the partial-decode-forward and the complete-decode-forward coding strategies for the half-duplex Gaussian single-relay channel. We analytically show that the rate achievable by partial-decode-forward outperforms that of the more straightforward complete-decode-forward by at most 12.5%. Furthermore, in the following asymptotic cases, the gap between the partial-decode-forward and the complete-decode-forward rates diminishes: (i) when the relay is close to the source, (ii) when the relay is close to the destination, and (iii) when the SNR is low. In addition, when the SNR increases, this gap, when normalized to the complete-decode-forward rate, also diminishes. Consequently, significant performance improvements are not achieved by optimizing the fraction of data the relay should decode and forward, over simply decoding the entire source message. [ABSTRACT FROM AUTHOR]

In this paper, we present a channel estimation scheme for Amplify-and-Forward (AF) relaying systems, using measurements at the destination only. A Least-Squares (LS) based channel estimation algorithm is developed, that provides the destination with full knowledge of all channel responses involved in the transmission. To investigate the algorithm performance, the Cramer-Rao lower bound (CRB) is analytically computed and compared with the asymptotic covariance of the proposed estimator. Since the existing estimator does not reach the CRB, we also propose and analyze an improved algorithm by taking into account the noise characteristics via weighted LS (WLS). The improved algorithm is asymptotically efficient, since it attains the CRB as the SNR tends to infinity. [ABSTRACT FROM AUTHOR]

This paper proposes a low complexity protocol that preserves full diversity in multiuser amplify-and-forward relay networks with NS antennas at the source, NR antennas at the relay, and ND antennas at each of the K destinations. In the proposed protocol, a two-fold diversity is guaranteed: 1) multi-antenna diversity via transmit antenna selection with maximal-ratio combining (TAS/MRC), and 2) multiuser diversity via opportunistic scheduling. Under perfect feedback with precise channel state information (CSI), we derive new exact and asymptotic symbol error rate (SER) expressions in closed-form for the general case of Nakagami-m fading. We prove that the full diversity order of NSNDKmX+ min{NSNRmY,NRNDKmZ} is guaranteed, where mX, mY, and mZ denote the fading parameters of the source-destination, source-relay, and relay-destination links, respectively. To examine the impact of delayed feedback, we next derive new exact and asymptotic SER expressions in closed-form. We prove that in the presence of delayed feedback, outdated CSI degrades the diversity order to NDmX+ min{NRmY,NDmZ}. In addition, based on our asymptotic expressions, we determine the optimal power allocation between the source and the relay such that the SER is minimized. We show that optimal power allocation offers superior performance over uniform power allocation; highlighting a pivotal design choice for maximizing network performance without investing additional resources. [ABSTRACT FROM AUTHOR]

We consider the symmetric discrete memoryless relay channel with orthogonal receiver components and show that polar codes are suitable for decode-and-forward and compress-and-forward relaying. In the first case we prove that polar codes are capacity achieving for the physically degraded relay channel; for stochastically degraded relay channels our construction provides an achievable rate. In the second case we construct sequences of polar codes that achieve the compress-and-forward rate by nesting polar codes for source compression into polar codes for channel coding. In both cases our constructions inherit most of the properties of polar codes. In particular, the encoding and decoding algorithms and the bound on the block error probability O(2^{-N^β}) which holds for any 0<β<\frac{1}{2}. [ABSTRACT FROM AUTHOR]

In cognitive radio networks, cognitive secondary users (CSUs) can interfere with the primary users (PUs) when they falsely occupy the PU's licensed spectrum. If CSUs in transmission temporarily form a cooperative relaying network, the interference from CSUs to PU can be reduced due to the cooperative diversity. In this paper, the outage performance as well as the achievable diversity order of opportunistic relaying used for cooperative CSUs is investigated. The cooperative relaying network of CSUs is referred to opportunistically relayed cognitive secondary network (ORCSN). Exact outage probabilities and then the diversity order by high SNR approximation are provided under Rayleigh and Nakagami-m fading channels, respectively. It is shown that a spectrum-sensing method used by the CSUs plays an important role in determining the diversity order in ORCSN. Under Rayleigh fading channels, a cooperative sensing enables ORCSN to achieve the full diversity order but a distributed sensing provides the diversity order smaller than one. Under Nakagami-m fading channels, the achievable diversity order is restricted by the Nakagami channel parameters between the PU and the CSUs and also depends on the sensing method. Moreover, the full diversity order can be achieved by a proper selection of the threshold used for spectrum sensing. Numerical investigation is also provided and used to verify the analysis. [ABSTRACT FROM PUBLISHER]

In this paper, we address the problem of joint optimal threshold-based relaying and maximum likelihood (ML) detection in network-coded cooperative systems. The purpose of using threshold-based relaying is to circumvent the impact of error propagation, which could lead to degrading the system diversity. For simplicity, we consider a simple network comprising two source nodes and one relay node. The relay operates in the decode-and-forward (DF) mode and employs binary network coding. The communication between the two source nodes is bidirectional, resulting in a two-way relay channel. We assume binary phase shift keying (BPSK) signaling. For a given log-likelihood ratio (LLR)-based threshold used at the relay, we derive the ML detector at the destination assuming that the destination has full knowledge of the locations of the blocked bits at the relay. We then derive an expression for the corresponding end-to-end (E2E) bit error rate (BER) performance, which is used to find the optimal threshold. We also derive two practical discontinuous transmission detectors at the destination for the purpose of identifying whether the relay is forwarding or not. The performance of one of the detectors is similar to that when the destination knows the locations of the blocked bits, whereas the performance of the other detector suffers some performance degradation. We present several numerical examples that illustrate the efficacy of the proposed scheme as compared to existing schemes. [ABSTRACT FROM PUBLISHER]

In a two-hop system with multiple amplify-and-forward (AF) relays, the instantaneous channel state information (CSI) is usually required at the relays to achieve a coherent combining at the destination. In this paper, we investigate the design of non-coherent relaying systems, where no CSI is available at the relays. It will be shown that non-coherent relaying can achieve the optimal diversity and multiplexing tradeoff (DMT) of coherent relaying systems with no penalty in the coding length, but incurs a loss of combining gain. To illustrate the practicality of non-coherent relaying, we propose a simple spreading-based non-coherent relaying scheme which achieves the optimal diversity gain. However, the spreading scheme demonstrates a unique non-coherent penalty, namely, the inclusion of one non-coherent relay may introduce "negative" contribution to the receive SNR. To handle this penalty, a distributed relay selection scheme, which can achieve a better outage performance with less energy, is proposed. [ABSTRACT FROM PUBLISHER]

The interference channel with a relay (ICR) is the fundamental building block of cooperation in wireless networks where there are multiple communicating pairs interfering with each other. This paper considers ICRs in which the links are subject to i.i.d. fading, and each node has channel state information (CSI) only on its incoming links (receive CSI). Two channel models are considered: phase fading and Rayleigh fading. Strong interference conditions are derived for the case where the links from the sources to the relay are good in the sense that the achievable region for decoding both messages at the relay contains the maximal achievable region at the destinations. This leads to the characterization of the capacity region for such scenarios. This is the first time the capacity region of the ICR is characterized for a nondegraded, noncognitive scenario, with a causal relay when all links are active. [ABSTRACT FROM PUBLISHER]

The smallest network model that captures relaying in the presence of multiple communicating pairs causing interference to each other is the interference channel with a relay. In this paper, an achievable rate region for the interference channel with a relay is derived. Special cases of strong interference under which this region is the capacity region are presented. The results obtained demonstrate the benefits of interference forwarding at a relay. By forwarding interfering messages, the relay can improve their reception at unintended receivers and, thus, facilitate interference cancellation. We show that intentionally forwarding interfering messages can improve the achievable rates. The achievable rates and interference forwarding gains are also illustrated by numerical results in Gaussian channels. Finally, a sum-rate outer bound to the capacity region of the Gaussian interference channel with a relay is derived and compared with the achievable rate region. The cut-set bound for this channel is also derived and shown to be much looser than the new sum-rate outer bound. [ABSTRACT FROM PUBLISHER]

In multihop wireless networks, the rational packet droppers may not relay the others' packets because packet relay consumes their resources without benefits, and the irrational packet droppers intentionally drop packets to disrupt the packet transmission process, which may make multihop communication fail. Cooperation stimulation mechanisms can motivate the rational packet droppers to relay packets, but they cannot identify the irrational packet droppers. In this paper, we develop a novel mechanism that can thwart the rational and irrational packet dropping attacks by adopting stimulation and punishment strategies (TRIPO). TRIPO uses micropayment to stimulate the rational packet droppers to relay the others' packets and enforce fairness and uses reputation system (RS) to identify and evict the irrational packet droppers. We propose a novel monitoring technique to measure the nodes' frequency of dropping packets based on processing the payment receipts instead of using the medium overhearing technique. The receipts can be processed to extract financial information to reward the cooperative nodes that relay packets, as well as contextual information, such as broken links, to build up the RS. Extensive analytical and simulation results demonstrate that TRIPO can secure the payment and precisely identify the irrational packet droppers with almost no false-positive nodes, which can improve the network performance in terms of packet delivery ratio. [ABSTRACT FROM PUBLISHER]

Error propagation from the relay to the destination is a major drawback of digital relaying protocols that substantially diminishes the cooperative diversity gain of the system. Appropriately designed selection relaying schemes can effectively mitigate this phenomenon and improve the diversity order, especially when the source-relay channel state information (CSI) is not available at the destination. In this study, the authors investigate the SNR-based selection relaying scheme in a multi-relay cooperative network (with R potential relay nodes) and examine the impact of the error propagation on the end-to-end performance of the system. The authors derive closed-form expressions for the end-to-end symbol error probability (SEP) of the system for both identically distributed and non-identically distributed Rayleigh fading environments. In the analysis, the authors consider M-ary phase shift keying (M-PSK), M-ary pulse amplitude modulation (M-PAM) and M-ary quadrature amplitude modulation (M-QAM) schemes. They also propose a class of geometry-independent thresholds that effectively mitigate the error propagation and provide full diversity of order R+1. Furthermore, for the special case of single-relay network, the authors derive closed-form expressions for the optimal thresholds that minimise the end-to-end SEPs. [ABSTRACT FROM AUTHOR]

In this study, the performances analysis of cooperative-diversity networks using adaptive decode-and-forward (DF) relaying over independent non-identical flat Nakagami-m fading channels is investigated. The authors derive exact and approximate closed-form expressions for the error probability, outage probability and average channel capacity, and analyse their dependence on the channel parameters. In adaptive DF relaying, among M relays that can participate, only C relays (C≤M), with good channels to the source, DF (retransmit) the source information to the destination. Then, the destination combines the direct and the indirect signals using maximum ratio combining technique. The authors derive a closed-form expression for the the moment generating function of the total signal-to-noise ratio (SNR) at the destination node. Then, the authors find an exact closed-form expression for the probability density function (PDF) of the total SNR at the destination. This PDF is used to derive the exact closed-form expressions of the performance metrics. Such closed-form solutions are highly desirable because they allow for rapid and efficient evaluation of system performance. Since exact expressions are complicated, the authors have introduced simple approximate expressions for the error and outage probabilities where these expressions explicitly show the diversity order. Computer simulations are used to validate our analytical results. Results show the significant performance improvement because of the use of the adaptive DF cooperative diversity. Also, results indicate that increasing the number of relays will not always decrease the outage probability. [ABSTRACT FROM AUTHOR]

In this study, the authors investigate the error rate performance of amplify-and-forward relaying over N*Nakagami fading channels. This is a recently introduced channel model that involves the product of N Nakagami-m-distributed random variables. Employing the moment generating function approach, the authors derive symbol error rate expressions for a single-relay system under instantaneous power scaling (IPS) and average power scaling (APS) factors at the relay node, that is, variable and fixed gains. The results achieved by the authors demonstrate that the achievable diversity order is a function of Nakagami fading parameter (m) and degree of cascading (N). An identical diversity order is obtained under both scaling factors when the relay is close to the destination. When the relay is close to the source, IPS becomes advantageous over APS. Monte-Carlo simulations are further provided to confirm the analytical results. [ABSTRACT FROM AUTHOR]

The system performance of the opportunistic relaying technique in amplify-and-forward cooperative systems with adaptive transmission over Rayleigh fading channels is analysed. Two rate-adaptive modulation techniques, continuous-rate and discrete-rate adaptive techniques, are considered. Closed-form expressions are derived for the average spectral efficiency, outage probability and the average bit error rate for two cases: independent and identically distributed (i.i.d.) fading links and independent and non-identically distributed (i.ni.d.) links. Using numerical evaluations, the performances of different cases are compared showing the advantages of each adaptive modulation technique in conjunction with the opportunistic relaying in a cooperative communication over both i.i.d. and i.ni.d. fading links. [ABSTRACT FROM AUTHOR]

We present in this paper channel model simulation to analyze the performance of one of the most widely deployed Wireless Local Area Networks (WLANs) based on IEEE 802.11a standard. IEEE 802.11a uses the basic communication strategy of Orthogonal Frequency Division Multiplexing (OFDM) which is the base technology for next-generation communication systems. The results obtained with varying channel conditions represented by typical models are indicative of the performance of OFDM in different environments. The channel adaptation process essentially captures the propagation characteristics of a typical WLAN-enabled office ranging from a small room to a medium-sized shop floor. MATLAB and Simulink® has been chosen as the modeling tool because of its flexibility and mathematical simulation capabilities. The results show that certain channels are better than others and will help in evolving a signal power benchmark for effective communication. [ABSTRACT FROM AUTHOR]

Despite their attractive features, free-space optical (FSO) communications suffer from several challenges in practical deployment; the major of them is fading or scintillation. To overcome such limitations, multiple input multiple output (MIMO) and cooperative techniques have been proposed. Although the promising effects of cooperative transmissions in radio frequency (RF) communications have greatly been investigated, there have not been remarkable researches on cooperative transmissions in FSO communications. In this study, the authors consider a relay-assisted FSO communication and investigate the outage performance of two well-known cooperative protocols, namely amplify-and-forward (AF) and decode-and-forward (DF), for this communication system. By a new definition of the order of diversity, the authors derive an analytical expression for the performance comparison of different cooperative and non-cooperative protocols. The authors also evaluate the performance of a FSO communication with two transmitter telescopes (MIMO systems) and compare its outage probability with those of cooperation strategies. The authors investigate the best place for the relay for both the AF and DF strategies and show that relay-assisted techniques can be used for FSO communication to achieve spatial diversity. Their performance can surpass that of the two-transmitter case by properly choosing the location of the relay. [ABSTRACT FROM AUTHOR]