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As one of the main data transport protocols of delay/disruption-tolerant networking (DTN), Licklider transmission protocol (LTP) is designed to provide reliable data delivery in an interplanetary Internet environment characterized by frequent and lengthy link disruptions and extremely long signal propagation delays. Some studies have been done on the performance of LTP in cislunar and Mars communications. However, to date the effect of link disruption on LTP for Mars communications has received little attention. In this paper, an analytical framework is presented for the effect of link disruption on reliable data delivery and performance of LTP in Mars communications. The analysis focuses on how various link disruptions affect the number of transmission attempts, the consequent round-trip time (RTT) of data exchange, and the resulting goodput performance of LTP for reliable data block delivery in Mars communications. The analytical framework is validated by means of realistic data block transmission experiments using a PC-based experimental infrastructure, and it can be used to predict the performance of LTP over a deep-space vehicle communication channel in presence of link disruption. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the performance of non-orthogonal multiple access (NOMA)-based overlay cognitive integrated satellite-terrestrial relay network with secondary network selection, where the selected secondary network accesses the licensed spectrum by assisting the communication of primary network with amplify-and-forward protocol. Besides, NOMA techniques are used to improve the spectrum efficiency. Specifically, the closed-form expressions of outage probability (OP) for both primary network and secondary network are obtained. To get inherent insights, the asymptotic analysis of OP is further derived at high signal-to-noise ratios. Moreover, the diversity orders of the both networks are further provided. Finally, Monte Carlo simulations are given to valuate our analysis, and the effects of key parameters on system performance are revealed. Through the comparison between orthogonal multiple access (OMA) scheme and NOMA scheme, the superiority of our proposed scheme is proved. [ABSTRACT FROM AUTHOR]

With the increasing connectivity between the Electronic Control Units (ECUs) and the outside world, safety and security have become stringent problems. The Controller Area Network (CAN) bus is the most commonly used in-vehicle network protocol, which lacks security mechanisms by design, so it is vulnerable to various attacks. In this paper, we propose a novel intrusion detection model called CNN-LSTM with Attention model (CLAM) for the in-vehicle network, especially CAN. The CLAM model uses one-dimensional convolution (Conv1D) to extract the abstract features of the signal values at each time step and feeds it into the Bidirectional Long Short Term Memory (Bi-LSTM) to extract the time dependence. By combining the attention mechanisms, we calculate the weight of each hidden state output by Bi-LSTM and perform a weighted summation, so that the model focuses only on locally important time steps, which can improve the convergence speed of the model and prediction accuracy. The proposed model uses the bit flip rate to extract continuous signal boundaries in the 64-bit CAN data, so it does not need to parse the CAN communication matrix and is suitable for different vehicles. The extensive evaluation results demonstrate that our proposed CLAM model can effectively detect CAN attacks, with an average F1-score of 0.951 and an error rate of 2.16%. Compared with the work in related research fields, the accuracy of attack detection is improved by 2.5%. [ABSTRACT FROM AUTHOR]

Wireless blockchain network is proposed to enable a decentralized and safe wireless networks for various blockchain applications. To achieve blockchain consensus in wireless network, one of the important steps is to broadcast new block using wireless channel. Under wireless network protocols, the block transmitting will be affected significantly. In this work, we focus on the consensus process in blockchain-based wireless local area network (B-WLAN) by investigating the impact of the media access control (MAC) protocol, CSMA/CA. With the randomness of the backoff counter in CSMA/CA, it is possible for latter blocks to catch up or outpace the earlier one, which complicates blockchain forking problem. In view of this, we propose mining strategies to pause mining for reducing the forking probability, and a discard strategy to remove the forking blocks that already exist in CSMA/CA backoff procedure. Based on the proposed strategies, we design Block Access Control (BAC) approaches to effectively schedule block mining and transmitting for improving the performance of B-WLAN. Then, Markov chain models are presented to conduct performance analysis in B-WLAN. The results show that BAC approaches can help the network to achieve a high transaction throughput while improving block utilization and saving computational power. Meanwhile, the trade-off between transaction throughput and block utilization is demonstrated, which can act as a guidance for practical deployment of blockchain. [ABSTRACT FROM AUTHOR]

Backscatter radio is an intriguing technology for Internet of Things applications, which enables ultra-low-power devices to communicate with each other. Most of the existing works on the combination of the backscatter communications and the “harvest-then-transfer” (HTT) protocol focus on the throughput maximization, yet the study on the energy efficiency (EE) maximization is still lacking. Driven by this observation, this paper studies the EE maximization for an RF-powered backscatter network with the HTT protocol. Multiple hybrid devices (HDs) can either use the backscatter mode by backscattering energy signals from the power beacon (PB) to the reader or use the HTT protocol to first harvest energy from the PB, and then to transmit data to the reader. The proposed scheme aims to optimize multiple parameters including PB's transmit power and time, HDs’ transmit power and time allocation between the backscatter mode and the HTT mode for maximizing the EE of all the HDs. An iterative algorithm is developed to find the optimal solution for the proposed resource allocation scheme. Simulation results demonstrate the superiority of the proposed scheme in terms of EE of all the HDs. [ABSTRACT FROM AUTHOR]

In this paper, we study the optimal power allocation for a radio frequency (RF)-powered cooperative network and propose energy-saving time switching relaying (ES-TSR) and energy-saving power splitting relaying (ES-PSR) protocols with an iterative energy-saving (ES) algorithm. In particular, we develop the analytical expressions of the channel capacity and the total energy consumption for the considered cooperative network. We formulate the system energy efficiency maximization problems and then provide the corresponding solutions by deriving the source's optimal transmit power in terms of energy fraction consumed with time switching (TS) factor and power splitting (PS) factor for the proposed ES-TSR and ES-PSR protocols, respectively, in each transmission block. From the past approaches, the optimal power allocation to maximize the system energy efficiency of the RF-powered cooperative networks has been studied under the assumption that the relay must utilize all of its harvested power in each transmission block. This work considers optimal power allocation to maximize the system energy efficiency for the case when the relay node can save energy for the next transmission block. Our simulation results show that the proposed ES-TSR and ES-PSR protocols outperformed the existing TS-based and PS-based relaying protocols with $\text{14.22}\%$ and $\text{8.4}\% $ , respectively, in paticular when the number of transmission blocks $\boldsymbol{L} = 10$. [ABSTRACT FROM AUTHOR]

A number of methods have been proposed for the response-time analysis (RTA) of controller area networks (CANs), which are the industry standard for in-vehicle network protocols. However, most of these methods are unsuitable for analyzing nonperiodically transmitted messages because they assume a constant transmission period for each message. Moreover, the calculated evaluation criteria are limited and comprise many over-pessimistic estimations, such as the worst-case response time (WCRT). To tackle these problems, this paper proposes an RTA method for CANs with randomly occurring messages, which replaces the constant transmission period with the average number of transmission instances per unit time. This approach finds the approximate probability distribution of the response time to any message in a CAN, providing a more general measure than the WCRT. To this end, a mathematical model based on M/G/1 queueing theory is developed. The model accurately emulates the behavior of nonperiodic CAN messages and enables RTA with minimal pessimistic estimations. When tested against the benchmarks, the proposed method accurately obtained response time distributions within several seconds to several tens of seconds. [ABSTRACT FROM AUTHOR]

In this paper, the performance of the cooperative cognitive radio network with the amplify-and-forward protocol is studied when the relay uses a nonlinear power amplifier (NLPA). Furthermore, taking the pulse shaping filter for the data signal into account, the power of the adjacent channel interference (ACI) to the primary users (PUs) caused by the spectral regrowth of the relay output signal is analytically calculated. Moreover, two compensation techniques are proposed which are implemented at the destination receiver to deal with the in-band nonlinear interference. The first technique is based on the calculation of the distorted signal constellation to enhance the performance of the demodulator. The second technique is feedforward compensation at the receiver. The bit error rate (BER) expressions for both techniques are presented. The ACI resulting from the spectral regrowth due to the relay NLPA is investigated by the simulation and numerical studies, and then, the BER performance degradation at the destination node and the performance improvement resulting from the proposed compensation methods are evaluated. Since the ACI confines the transmit power due to the interference power constraint of the PU, the achievable BER of the secondary user (SU) is studied. The simulation results show that the feedforward compensation technique has better BER performance than the modified constellation based approach. [ABSTRACT FROM AUTHOR]

Coherent communications aim to support higher data rates and extended connectivity at lower power consumption compared with traditional point-to-point transmissions. The typical setting of coherent communication schemes is based on a single data stream with multiple transmitters and a single receiver. This paper studies the case of multiple concurrent data streams, each with multiple transmitters and multiple receivers, in self-organizing wireless networks. A distributed optimization solution based on joint network formation and beamforming is developed for coherent group communications in a network of nodes that need to communicate over long distances. This solution significantly improves the power gain for a single data stream and the signal-to-interference-ratio for multiple data streams compared to point-to-point communications. These gains are in turn translated to improvements in communication range, power efficiency, reliability, and throughput. In this multi-layer network optimization solution, nodes coordinate with each other in a distributed manner to form transmitter and receiver groups, and communicate with each other coherently over long distances. The coherent beamforming protocol is optimized for given transmitter and receiver groups, whereas the network formation protocol is optimized to determine these groups. By using single-antenna communication nodes, the proposed optimization solution provides a major gain in network communications and outperforms other benchmark combinations of beamforming and network formation protocols. [ABSTRACT FROM AUTHOR]

Controller area network (CAN) is the most widely adopted network protocol in vehicle communication systems. The intermittent connection (IC) fault, a random cable connectivity problem with short durations, occurring in the CAN network may result in system performance degradation and system level failures in severe cases. Therefore, the health management of CAN-based networked systems demands effective detection and accurate localization of the IC fault. However, the diagnosis of IC fault in CAN network has not been fully exploited. This paper proposes a novel tree-based IC fault diagnosis method to identify the various IC fault locations in the CAN network. First, the error event pairs for network nodes are defined by analyzing the data-link layer information upon each error. Then, the domains of error event pairs and the information cost of IC faults included in the domains are derived. Finally, a tree-based minimal cost diagnosis algorithm is proposed to find the locations of the IC faults. Laboratory testbed is constructed and the case studies are conducted to demonstrate the performance of the proposed method. The results show that IC fault identified by the proposed method agree well with the case study setups. [ABSTRACT FROM AUTHOR]

This paper proposes an analytical model to investigate the performance of periodical broadcast of safety messages in vehicular ad hoc networks (VANETs), regarding a hybrid medium access control (MAC) protocol, called NC-PNC MAC. We first examine the percent of vehicles involved in subcarrier collisions during a random orthogonal frequency-division multiple access scheme, and then theoretically analyze the total number of transmissions and the packet delivery ratio (PDR) during one dissemination period. Based upon the analysis, this paper not only reveals how the subcarrier collision probability influences the PDR performance, but mathematically obtains the maximum PDR. To confirm the results, by adjusting a pivotal parameter of the MAC protocol, the PDR performance for basic safety message broadcast in VANETs can be enhanced by 10% to 30% under the constraint of the delivery latency. [ABSTRACT FROM AUTHOR]

With the development of vehicle networks, the information transmission between vehicles is becoming increasingly important. Many applications, particularly regarding security, are based on communication between vehicles. These applications have strict requirements for factors such as the quality of communication between vehicles and the time delay. Many theoretical communication protocols ignore the presence of buildings or other obstacles that are present during practical use, especially in urban areas. These obstacles can cause a signal to fade or even block direct communication. Many vehicles are often parked at the roadside. Because of their location, these parked vehicles can be used as relays to effectively reduce the shadowing effect caused by obstacles and even solve communication problems. In this paper, we study the problem of parked-vehicle-assistant relay routing communication in vehicle ad hoc networks. We propose an efficient parked vehicle assistant relay routing algorithm that is composed of four parts: a periodic Hello packet exchange mechanism, candidate relay list update, communication link quality evaluation, and candidate relay list selection. Simulation results reveal obvious advantages for indexes such as the quality of communication, success rate, and time delay. [ABSTRACT FROM AUTHOR]

The design of an efficient medium access control (MAC) protocol for multichannel ad hoc cognitive radio networks is an important problem and has been the topic of extensive recent research. In this paper, we present the design and performance evaluation of a protocol, group MAC (GMAC), which is customized for a situation that commonly arises in ad hoc networks: The network consists of multiple groups of nodes such that a large fraction of the traffic of each node needs to be sent to other nodes of its own group. Some examples are 1) units (e.g., platoons) in a military ad hoc network; 2) divisions in an emergency or disaster relief network; and 3) departments in a corporate or university network. Our protocol requires each secondary node to have only one narrowband transceiver, does not rely on a control channel, and incorporates a novel technique for dynamically balancing the traffic load of secondary nodes across the set of free channels. We formulate the problem of partitioning the network nodes into groups based on the volumes of data traffic to be sent between different pairs of nodes, which we call the group formation problem (GFP). We show that the GFP is NP-complete and propose a greedy algorithm to solve it. We analyze the stability region of the GMAC protocol using a queuing theoretic framework. Our extensive simulations show that a large fraction of the bandwidth unoccupied by primary users is utilized by the GMAC protocol for data transmissions. [ABSTRACT FROM AUTHOR]

The portfolio of models offered by car manufacturing groups often includes many variants (i.e., different car models and their versions). With such diversity in car models, variant management becomes a formidable task. Thus, there is an effort to keep the variants as close as possible. This simple requirement forms a big challenge in the area of communication protocols. When several vehicle variants use the same signal, it is often required to simultaneously schedule such a signal in all vehicle variants. Furthermore, new vehicle variants are designed incrementally in such a way as to maintain backward compatibility with the older vehicles. Backward compatibility of time-triggered schedules reduces expenses relating to testing and fine-tuning of the components that interact with physical environment (e.g., electromagnetic compatibility issues). As this requirement provides for using the same platform, it simplifies signal traceability and diagnostics, across different vehicle variants, besides simplifying the reuse of components and tools. This paper proposes an efficient and robust heuristic algorithm, which creates the schedules for internal communication of new vehicle variants. The algorithm provides for variant management by ensuring compatibility among the new variants, besides preserving backward compatibility with the preceding vehicle variants. The proposed method can save about 20% of the bandwidth with respect to the schedule common to all variants. Based on the results of the proposed algorithm, the impact of maintaining compatibility among new variants and of preserving backward compatibility with the preceding variants on the scheduling procedure is examined and discussed. Thanks to the execution time of the algorithm, which is less than one second, the network parameters like the frame length and cycle duration are explored to find their best choice concerning the schedule feasibility. Finally, the algorithm is tested on benchmark sets. [ABSTRACT FROM AUTHOR]

Content caching on the edge of 5G networks is an emerging and critical feature to quench the thirst for content of future connected cars. However, the tight packaging of 5G cells, the finite storage capacity at the edge, and the need for content availability while driving motivate the need to develop smart edge caching strategies adapted to the mobility characteristics of connected cars. In this paper, we propose a scheme called RoadsIde CacHe (RICH), which optimally caches content at edge nodes where connected vehicles require it most. In particular, our scheme is designed to ensure in-order delivery of content chunks to end users. Unlike blind popularity decisions, the probabilistic caching used by RICH accounts for the user mobility information that the system can realistically acquire. Furthermore, we provide a complete system architecture and define the protocols through which the different system entities can interact. We assess the performance of our approach against state-of-the-art solutions, under realistic mobility datasets and system scenarios. Our RICH edge caching scheme improves significantly the content availability at the caches and reduces the required backhaul bandwidth, with beneficial effects for both the end users and the network operators. [ABSTRACT FROM AUTHOR]

We propose a vehicle-to-roadside communication protocol based on distributed clustering where a coalitional game approach is used to stimulate the vehicles to join a cluster, and a fuzzy logic algorithm is employed to generate stable clusters by considering multiple metrics of vehicle velocity, moving pattern, and signal qualities between vehicles. A reinforcement learning algorithm with game theory based reward allocation is employed to guide each vehicle to select the route that can maximize the whole network performance. The protocol is integrated with a multi-hop data delivery virtualization scheme that works on the top of the transport layer and provides high performance for multi-hop end-to-end data transmissions. We conduct realistic computer simulations to show the performance advantage of the protocol over other approaches. [ABSTRACT FROM AUTHOR]

We consider a binary hypothesis testing problem in a wireless sensor network, where a fusion center (FC) makes a final decision about the underlying hypothesis. We assume under hypothesis ${\mathcal H}_0$ , sensors’ observations are uncorrelated and identically distributed Gaussian, however, under ${\mathcal H}_1$ they are correlated and nonidentically distributed Gaussian and sensors are unaware of this correlation when making decisions. Sensors send their local binary decisions over power constrained fading channels. We consider both parallel access channel (PAC) and multiple access channel (MAC) models. To obtain the detection statistic in PAC, we assume that the FC utilizes a linear fusion rule, which linearly combines the signals received from all sensors, while in MAC, the signal received at the FC is naturally the coherent sum of the transmitted signals. For both PAC and MAC, we derive modified deflection coefficient (MDC) of the detection statistic at the FC with coherent reception. Choosing MDC as the detection performance metric, we formulate several constrained transmit power optimization problems. In these problems, MDC is the objective function to be maximized and there are three different sets of transmit power constraints: total power constraint, individual and total power constraints, and individual power constraints only. We refer to the solutions of these constrained optimization problems as MDC-based transmit power allocation. When analytical solutions to these constrained optimization problems are elusive, we discuss how these problems can be converted to convex ones. Our results show that, compared with equal power allocation, detection performance improvement provided by our proposed MDC-based power allocation is more significant in MAC. We quantify the improvement in terms of several factors, including the degree of correlation among sensors’ observations, reliability of local decisions (local detection performance indices), communication channel properties, and the type of transmit power constraint. We also study how the power allocation among sensors varies as these factors change. [ABSTRACT FROM AUTHOR]

In this paper, a relay based network is considered where the source transmits confidential message to the destination via a nonregenerative relay. Due to the fact that the relay is unidentified, and thus may wiretap the relayed message from source to destination. In this regard, two new half-duplex nonorthogonal amplify-and-forward (NAF) secure communication protocols are proposed, with different assumptions on the transmission ability of the destination, i.e., NAF-I for destination without transmission ability and NAF-II for destination with transmission ability. We separately derive the sufficient and necessary conditions to yield positive secrecy rate for these protocols under fixed source/destination transmission power, and discuss their joint power allocation that maximizes the system secrecy rate. Despite the nonconvexity of the considered power allocation problems, alternative optimization approach is proved useful in dealing with these problems, and the corresponding algorithms are proposed. We further prove the convergence of the proposed algorithms and analyze their complexity. The discussion is also extended to the orthogonal amplify-and-forward (OAF) based protocols, i.e., OAF-I or OAF-II, for comparison purpose. Our numerical results demonstrate the gain of the secrecy rate performance of the proposed NAF protocols over existing transmission protocols, and also verify the effectiveness of the designed alternative optimization algorithms. [ABSTRACT FROM AUTHOR]

This paper considers a wireless powered communication network, where a multiantenna power beacon (PB) is employed to assist an energy constrained source to establish secure communications with a destination in the presence of multiple eavesdroppers. We propose a two-phase communication protocol termed as accumulate then transmit to enhance network secrecy. In the energy harvesting phase, the PB transfers radio frequency energy to charge the source; then in the information transmission phase, the PB acts as a friendly jammer to protect the source transmission against eavesdropping. We study the dynamic energy state transitions at the source using an energy discretization method and a finite-state Markov chain. Closed-form expressions are derived for connection outage probability, secrecy outage probability, and effective secrecy throughput, with the aim to evaluate both reliability and security of the proposed protocol. Furthermore, numerical results reveal the impacts of various system parameters on the secrecy performance and demonstrate the superior performance of our proposed protocol over an existing scheme. [ABSTRACT FROM AUTHOR]

Dynamic spectrum access (DSA) allows the spectrum to be utilized efficiently through opportunistic access. Cognitive radio (CR) is a technology used to enable DSA. Unlike a wireless local area network (WLAN) that operates in unlicensed band, cognitive WLAN allows CRs to identify spectrum holes in licensed bands and opportunistically use it. DSA makes the design of the medium access control (MAC) layer in the cognitive WLAN challenging. In this paper, we design and carry out performance analysis of IEEE 802.11 DCF based MAC protocol for multichannel cognitive WLAN. Our main contributions are as follows: 1) A Markov chain model for CRs and 2) another Markov chain to model the joint usage of the channel by the licensed users and CRs. These coupled Markov chain models are then solved for stationary probability distribution. Using the above models, we derive throughput and delay of the CRs and study their variation against the number of CRs, the number of channels, and spectrum availability. Theoretical results are validated using simulation and compared with results from existing literature. [ABSTRACT FROM AUTHOR]

A cooperative wireless-powered communication network protocol is proposed, in which user far away from a hybrid access point (H-AP) is capable of harvesting wireless powers by overhearing the uplink signals of users that are relatively nearer to the H-AP, in addition to downlink signal broadcast by the H-AP. In this setting, time allocations for the downlink transmission of the H-AP and the uplink transmission for the users are jointly optimized for two different purposes. First, the weighted sum-rate maximization problem is solved for a given total transmission time. Then, the total transmission time is minimized under a minimum rate constraint, and an efficient algorithm is also presented to solve the optimal solution by a line search strategy. Numerical results demonstrate that the proposed schemes significantly increase the far user's rate, which in turn improves user fairness and transmission delay. [ABSTRACT FROM PUBLISHER]

Efficient and scalable media access control (MAC) protocol design is crucial to guarantee the reliable broadcast of safety messages in vehicular ad hoc networks. To devise a MAC for safety message broadcasting with reliability and minimum delay, in this paper, we propose a novel time slot-sharing MAC, referred to as SS-MAC, which can support diverse periodical broadcasting rates. In specific, we first introduce a circular recording queue to online perceive time slot occupying status. We then design a distributed time slot sharing (DTSS) algorithm and random index first fit (RIFF) algorithm, to efficiently share the time slot and make the online vehicle-slot matching, respectively. We prove theoretically the efficacy of DTSS algorithm, and evaluate the efficiency of RIFF algorithm by using MATLAB simulations. Finally, we conduct extensive simulations considering various driving scenarios and resource conditions to demonstrate the SS-MAC performance. [ABSTRACT FROM PUBLISHER]

This paper is concerned with the performance analysis of a dual-hop random access network, where a single gateway is employed to connect a random number of independent users which are hidden from their destination(s). The gateway is an amplify-and-forward (AF) relay and is the only mean to connect users to their destinations. We develop accurate mathematical models for the multiple access interference, which take into account, in addition to the distribution of the number of active users and their random locations, the effects of fading and thermal noise at both the relay and destinations. A new unified mathematical method is developed, which leads to the derivation of new analytical expressions for the overall spectral efficiency of the dual-hop random access network over Rayleigh- and Nakagami- m fading channels. The accuracy of the new mathematical results is confirmed by Monte Carlo simulation. The results of this paper can be used to estimate the aggregate throughput of a dual-hop system employing the slotted-Aloha-type protocols. [ABSTRACT FROM AUTHOR]

Along with the ongoing evolution of multiple antenna communication systems, new physical layer security techniques are continuing to achieve higher levels of secrecy. Most physical layer approaches, however, concern time division duplex (TDD) channels which rely on using the channel reciprocity feature as a shared randomness and tend to be associated with a large computational burden. In this paper, we propose a new physical layer method which utilizes private random precoding for exchanging the secret key bits in multiple-input–multiple-output (MIMO) systems. The principle of this method is to exploit the precoding matrix index in a manner that produces low correlation at the adversary. A robust key exchange between the transmitter and the receiver is established by uniquely relating the secret key bits to the channel precoding matrix using a private version of the universal codebooks. What is more is that the proposed method is applicable in both frequency division duplex (FDD) and TDD channels. The results demonstrate that the proposed method can offer superior performance in terms of the key agreement, secrecy level, and computational load. [ABSTRACT FROM AUTHOR]

We investigate the fading cognitive multiple-access wiretap channel (CMAC-WT), in which two secondary-user transmitters (STs) send secure messages to a secondary-user receiver (SR) in the presence of an eavesdropper and subject to interference threshold constraints at multiple primary-user receivers (PRs). We design linear precoders to maximize the average secrecy sum rate for a multiple-input–multiple-output (MIMO) fading CMAC-WT under finite-alphabet inputs and statistical channel state information at STs. For this nondeterministic polynomial-time NP-hard problem, we utilize an accurate approximation of the average secrecy sum rate to reduce the computational complexity and then present a two-layer algorithm by embedding the convex–concave procedure into an outer-approximation framework. The idea behind this algorithm is to reformulate the approximated average secrecy sum rate as a difference of convex functions and then generate a sequence of simpler relaxed sets to approach the nonconvex feasible set. Subsequently, we maximize the approximated average secrecy sum rate over the sequence of relaxed sets by using the convex–concave procedure. Numerical results indicate that our proposed precoding algorithm is superior to the conventional Gaussian precoding method in the medium and high signal-to-noise ratio (SNR) regimes. [ABSTRACT FROM AUTHOR]

This paper investigates distributed linear constellation precoding (DLCP) for two-way relaying communication systems in conjunction with the techniques of bit-interleaved coded modulation (BICM) and BICM with iterative decoding (BICM-ID). First, a decoding strategy for the relay node that is based on quaternary code representation is developed. Then, the union bounds (for the case of BICM) and error-free feedback bounds (for the case of BICM-ID) on the quaternary digit error probability and bit error probability under network coding in the multiple-access (MA) phase are obtained. Based on the obtained bounds, the impact of DLCP on the error performance is analyzed by considering three error types in the MA phase. It is shown that type-3 errors need to be carefully taken into account in the design of a DLCP scheme. By developing a performance metric related to type-3 errors, the design parameter of DLCP is optimized when BICM is used, whereas it is shown that DLCP is not needed when BICM-ID is used. Extensive simulation results are provided to corroborate the analysis and demonstrate the performance superiority of the proposed decoding strategy over the one that directly decodes the exclusive-OR (xor) code. For the case of BICM, the performance advantage achieved by properly designing DLCP is also illustrated. [ABSTRACT FROM AUTHOR]

This paper investigates collaborative spectrum sharing (CSS) for which a cognitive secondary transmitter acts as a decode-and-forward (DF) relay for two primary users (PUs) occupying an interfering multiple-access channel. PUs are assumed to send their signals simultaneously; hence, interference between the primary signals exists due to the multiple-access nature. The secondary user (SU) selects and forwards one of the PU's signals to a desired destination, and at the same time, the SU also transmits its own signal only if it is not harmful to PUs. The selection of a primary signal to relay is investigated, depending on SU's knowledge of two primary source–destination channels, for which closed-form outage probabilities for PUs and SU are provided accordingly. With the help of the closed-form PU's outage probability, an optimal selection strategy between the primary signals and an optimal power allocation between the primary and secondary signals are also obtained in closed form, which minimizes SU's outage probability while keeping the PU's outage performance at an SU-free level. Numerical investigation is used to verify and illustrate the analysis given in this paper. Numerical results also show that the SU's performance can vary significantly according to the amount of channel knowledge that the SU can have. [ABSTRACT FROM PUBLISHER]

Geocast, which consists of delivering messages to a specific location, has become an important technique with the accelerated development of the location-based services in mobile networks. Geocast in the automotive domain is of particular interest, enabling many promising applications, such as geographic advertising, location-based traffic alerts, etc. Different from the conventional geocast algorithms focusing on the distance-based approaches, in this paper, we propose a node mobility-aware and node contact-aware geocast algorithm (GeoMobCon) for urban vehicular ad hoc networks from the delay-tolerant network perspective to better deal with the high mobility and transient connectivity issues. Different levels and aspects of vehicle mobility information and self-maintained contact information are employed, making GeoMobCon simple, scalable, and communication and computation effective. Practical issues are well considered by introducing real-world trace analysis, trace-driven simulation, and efficient buffer management. Extensive performance comparisons with other protocols have been conducted to show the advantages of GeoMobCon. [ABSTRACT FROM AUTHOR]

In the near future, wireless networks will be one of the key technologies for road traffic management in smart cities. Vehicles and dedicated roadside units should be interconnected through wireless technologies such as IEEE 802.11p (WAVE). Traffic lights and road signs may also take their place in this architecture, forming a large-scale network of small devices that report measurements, take orders from a control center, and are able to take decisions autonomously based on their local perception. Such a network shares many similarities with classical wireless sensor and actuator networks, starting with its distributed organization and with the role of the control center. However, its topology, and, subsequently, the appropriate selection of protocols and algorithms, will be strongly influenced by each city's characteristics. In this paper, we characterize and discuss probable topologies of these networks. The aim of this work is to provide network models that can be used to evaluate protocols and algorithms using realistic scenarios in place of generic random graphs. We deploy such networks over 52 city maps extracted from OpenStreetMap and characterize the resulting graphs, with particular focus on the connectivity aspects (degree distribution and connected components). The tools, the complete data sets, and OMNeT++ network models are freely available online. [ABSTRACT FROM AUTHOR]

This paper considers the wiretap channel in which a source node communicates with a destination node with the aid of a single helper and in the presence of an eavesdropper. The helper can apply either amplify-and-forward (AF) relaying or jamming. The secrecy capacity and respective optimal power allocation schemes at the source and the helper are investigated under both individual and joint power constraints. Given that the links among the nodes might not always be available for transmission (e.g., due to heavy shadowing), several network topologies are considered for relaying. To deal with the related nonconcave optimization problems in solving the optimal power allocation schemes, we first propose an analytical approach based on Descartes' rule of signs. Using this approach, optimal power allocation strategies are derived for some relay topologies and for the jamming system. Insights into the proposed schemes for different transmission power ranges and comparisons to the optimal information rate power allocations are also discussed. Simulation results are finally provided to quantify the optimality of the proposed schemes. [ABSTRACT FROM AUTHOR]

Vehicular ad hoc networks (VANETs) have recently received significant attention in improving traffic safety and efficiency. However, communication trust and user privacy still present practical concerns to the deployment of VANETs, as many existing authentication protocols for VANETs either suffer from the heavy workload of downloading the latest revocation list from a remote authority or cannot allow drivers on the road to decide the trustworthiness of a message when the authentication on messages is anonymous. In this paper, to cope with these challenging concerns, we propose a new authentication protocol for VANETs in a decentralized group model by using a new group signature scheme. With the assistance of the new group signature scheme, the proposed authentication protocol is featured with threshold authentication, efficient revocation, unforgeability, anonymity, and traceability. In addition, the assisting group signature scheme may also be of independent interest, as it is characterized by efficient traceability and message linkability at the same time. Extensive analyses indicate that our proposed threshold anonymous authentication protocol is secure, and the verification of messages among vehicles can be accelerated by using batch message processing techniques. [ABSTRACT FROM AUTHOR]

The convergence of wireless access networks significantly changes the way we live and work, bringing us closer to the goal of computing anywhere at any time. Security, privacy, accountability, and efficiency issues are of most concern in the deployment of such networks. Despite the need and importance, little research has been conducted on designing accountable and privacy-preserving authentication schemes for wireless access networks, not to mention schemes that can simultaneously and efficiently provide accountability and privacy protection without involving any trusted third party. This motivates us to develop a novel authentication framework, namely APEA, that integrates a new key management protocol, i.e., an adapted construction of short group signature (SGS) and batch verification, as an effective approach to simultaneously achieve the four goals without involving any trusted third party. Experiments using our implementation on laptop PCs demonstrate that APEA is feasible in practice. [ABSTRACT FROM PUBLISHER]

Energy harvesting technique is a potential way for relay node energy supply in cooperative networks with respect to deployment flexibility and maintenance charge reduction. However, unlike traditional power source, it is intuitive that the fluctuation of harvested energy flow can degrade the benefit resulted from relay-aided cooperative transmission. To this end, this paper focuses on the performance analysis of an energy harvesting relay-aided cooperative network under slow fading channel from a perspective of outage behavior and attempts deriving the closed-form expression of outage probability of the proposed cooperative protocol. Compared with simple direct transmission protocol, it is proved that a multiplicative gain for improving system performance in terms of minimizing outage probability can be obtained by energy harvesting relay-aided cooperative transmission. In particular, if there are multiple available relay nodes around the environment or the energy-exhausted probability of relay node is small, it is very profitable to employ relay-aided cooperative transmission protocol. [ABSTRACT FROM PUBLISHER]

X-by-wire applications have extremely demanding reliability requirements that are increasingly being addressed through the adoption of distributed and fault-tolerant architectures. The development of these applications is facilitated by the availability of high-level services such as agreement or reliable broadcast (RB). Some dependable communication buses, e.g., TTP-C, already provide these services, whereas FlexRay does not. In this paper, we present an approach to evaluate the reliability of a family of RB protocols implemented both on top of FlexRay and on top of ordinary time-division multiple access (TDMA). In particular, we evaluate the impact of the acknowledgment policy on the reliability of these protocols. We express the reliability as the probability of violation of the agreement and validity properties of the protocol during a mission. For that, we develop an analytical model based on discrete-time Markov chains, which considers a comprehensive set of faults (permanent, transient, omissive, and asymmetric) affecting both nodes and channels, and their effects on the protocol execution. The structure of the model is quite flexible and easily adaptable to other TDMA-based protocols. To assess the sensitivity of the protocol to both internal and external factors, we carried out a large number of experiments considering several network configurations and fault rates. The results show that for FlexRay, the negative-acknowledgment policy provides the same reliability as the positive-acknowledgment policy. However, for TDMA-based protocols that lack FlexRay's ability to distinguish silence from the loss of a message, the negative-acknowledgment policy leads to lower reliability, and its fitness for safety-critical applications depends on the system configuration and environment conditions. [ABSTRACT FROM PUBLISHER]

In this paper, we study the higher layer performance as well as the “throughput, delay, energy consumption” tradeoff problem for multirelay-assisted cooperative automatic repeat request (C-ARQ) protocols. We study a practical scenario where only the average channel state information (CSI) is available at the source and relays. We consider four multirelay C-ARQ protocols and derive closed-form expressions for the transmission delay distribution, the energy consumption, and the higher layer queuing performance. Furthermore, we analyze the quality of service (QoS)-constrained energy efficiency performances of the protocols. Our analysis is validated by simulations. In addition, we evaluate the system performance under these C-ARQ protocols and for different topologies. We conclude several guidelines for the design of efficient C-ARQ protocols. Finally, a simple extension of the studied C-ARQ protocols is proposed, which improves the QoS-constrained energy efficiency by 4%. [ABSTRACT FROM PUBLISHER]

In-vehicle communications are emerging to play an important role in the continued development of reliable and efficient X-by-Wire applications in new vehicles. Since vehicle devices, sensors, and the electronic control unit (ECU) are already connected to power wires, the advancement of power line communications (PLCs) can provide a very low cost and virtually free platform for in-vehicle communications. In this paper, we propose a medium access control (MAC) protocol for vehicular PLC systems, where multiple nodes are competing for transmission over the direct current (dc) power line. The proposed protocol uses a combination of time and frequency multiplexing and consists of two key features: 1) a distributed channel selection policy to arbitrate packet transmission across different channels and provide robustness against interference and noise and 2) a distributed collision resolution algorithm to allow efficient nodes completion over selected channels. Specifically, the collision resolution algorithm is optimized with respect to the channel policy such that the success probability of transmission in each channel is maximized. Numerical results are also supplemented to validate the performance of the proposed protocol and provide useful guidelines for developing a robust contention-based MAC protocol for vehicular PLC systems. [ABSTRACT FROM PUBLISHER]

Node clustering is a potential approach to improve the scalability of networking protocols in vehicular ad hoc networks (VANETs). High relative vehicle mobility and frequent network topology changes inflict new challenges on maintaining stable clusters. As a result, cluster stability is a crucial measure of the efficiency of clustering algorithms for VANETs. This paper presents a stochastic analysis of the vehicle mobility impact on single-hop cluster stability. A stochastic mobility model is adopted to capture the time variations of intervehicle distances (distance headways). First, we propose a discrete-time lumped Markov chain to model the time variations of a system of distance headways. Second, the first passage time analysis is used to derive probability distributions of the time periods of the invariant cluster-overlap state and cluster membership as measures of cluster stability. Third, queueing theory is utilized to model the limiting behaviors of the numbers of common and unclustered nodes between neighboring clusters. Numerical results are presented to evaluate the proposed models, which demonstrate a close agreement between analytical and simulation results. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate a three-node two-way relaying network over fading channels. The stability of this system is first discussed. Three protocols are then investigated in this work in terms of throughput, including the opportunistic digital network coding (ODNC) scheduling protocol, the physical network coding (PNC) protocol, and the cooperation protocol of DNC with direct link (CDNC-DL). For the first two protocols, we assume that the direct link is not available. For the third protocol, the direct link is available and can support data rates. The problems of maximizing the long-term totally fair optimal throughput with the three protocols, with respect to the stability constraints, are formulated and solved by allocating power resources with respect to channel fluctuations. To complement this work, optimal time resource allocation for each phase of the three protocols as well as the associated end-to-end throughput are investigated. In the end, it is shown in simulation that ODNC performs better than the conventional DNC and that CDNC-DL outperforms the other two proposed protocols as long as the direct link is in relatively good condition. [ABSTRACT FROM PUBLISHER]

Wireless Access in Vehicular Environment (WAVE) dictates primitives for intelligent transportation system (ITS) applications and services. The medium access control (MAC) layer in WAVE facilitates service differentiation. This offers quality of service (QoS) by prioritizing traffic through different access categories (ACs), which are based on application-requested priorities. However, it is oblivious to network load, to delay requirements for ITS safety applications, and to the “severity” of vehicles. In this paper, we propose a novel opportunistic service differentiation (OSD) scheme as an enhancement to WAVE. We define a fuzzy inference system (FIS) to deduce a context severity metric (CSM) that relates the driving behavior of a vehicle to its environment. Our OSD traffic distribution heuristic prioritizes vehicle traffic, with respect to CSM, and accounts for network load and link layer bounds. Furthermore, the OSD scheme guarantees that ACs do not exceed maximum allowable delay for ITS applications. Our methodology entails defining and designing a linear programming (LP) model for verification and validation of the OSD scheme. We perform a comparative study of OSD-enhanced WAVE and classical WAVE analytically and in a vehicular ad hoc network (VANET) simulator. We show that both simulation and analytical results substantiate our claim of improvement in performance of OSD-enhanced WAVE over classical WAVE. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a multihop broadcast protocol for dissemination of time-critical emergency messages (EMs) in vehicular ad hoc networks (VANETs), where the IEEE 802.11p technology is used for communication among the nodes. The proposed trinary partitioned black-burst-based broadcast protocol (3P3B) consists of two primary mechanisms. First, a mini distributed interframe space (DIFS) in a medium access control (MAC) sublayer is introduced to give the time-critical EMs a higher access priority to the communication channel compared with other messages. Second, a trinary partitioning is designed to iteratively partition the communication range into small sectors. The trinary partitioning mechanism allows the farthest possible vehicle in the farthest sector from the sender node to perform forwarding to increase the dissemination speed by reducing the number of forwarding hops. In addition, 3P3B reduces the contention period jitter, which is independent of the density of vehicles, resulting in a more stable contention period. Analytical models are proposed for performance evaluation in conjunction with simulation-based performance analysis. The results demonstrate that 3P3B outperforms benchmarks of the existing broadcast protocols in VANETs in terms of the average message dissemination speed, message progress, communication delay, and packet delivery ratio. [ABSTRACT FROM PUBLISHER]

As portable devices are gaining more popularity, maintaining Internet connectivity anytime and anywhere becomes critical, particularly for mobile and vehicular networks. Network mobility (NEMO) and Internet Protocol mobility are gaining more and more importance. In this paper, we develop a Session Initiation Protocol (SIP)-based mobile network architecture to support NEMO for vehicular applications. We propose to form a mobile ad hoc network (MANET) by the mobile hosts (MHs) inside a vehicle or a cluster of vehicles. The MANET is connected to the outside world via a SIP-based Mobile Network Gateway (SIP-MNG), which is equipped with one or multiple external wireless interfaces and some internal IEEE 802.11 interfaces. The external interfaces of the SIP-MNG support Internet connectivity by aggregating user traffic to and from the Internet. In addition, exploiting the session information carried by SIP signaling, the SIP-MNG supports resource management and call admission control for the MHs. However, wireless access incurs charges, power consumption, and overhead of mobility management. So, it is desirable to allow the SIP-MNG to disconnect its external interfaces when necessary. To guarantee that users inside the mobile network will not lose any incoming request, we propose a push mechanism through short message service to wake up these wireless interfaces in an on-demand manner. We show the detailed signaling to support such a mechanism. The proposed system is fully compatible with existing SIP standards. Our real prototyping experience and some experimental results are also reported. Index Terms--Mobile ad hoc network (MANET), mobile computing, network mobility (NEMO), push mechanism, Session Initiation Protocol (SIP), wireless network.

Wireless-communication technology can be used to improve road safety and to provide Internet access inside vehicles. This paper proposes a cross-layer protocol called coordinated external peer communication (CEPEC) for Internet-access services and peer communications for vehicular networks. We assume that IEEE 802.16 base stations (BS) are installed along highways and that the same air interface is equipped in vehicles. Certain vehicles locating outside of the limited coverage of their nearest BSs can still get access to the Internet via a multihop route to their BSs. For Internet-access services, the objective of CEPEC is to increase the end-to-end throughput while providing a fairness guarantee in bandwidth usage among road segments. To achieve this goal, the road is logically partitioned into segments of equal length. A relaying head is selected in each segment that performs both local-packet collecting and aggregated packets relaying. The simulation results have shown that the proposed CEPEC protocol provides higher throughput with guaranteed fairness in multihop data delivery in vehicular networks when compared with the purely IEEE 802.16-based protocol. Index Terms--External peer communication (EPC), IEEE 802.16, multihop, scheduling algorithm, vehicle-to-roadside communication (VRC), vehicular networks.

IEEE 802.11 is currently the de facto medium access control (MAC) standard for mobile ad hoc networks (MANETs). However, in a multihop MANET, 802.11 power management may completely fail if stations are out of synchronization. To fix this problem, several papers have proposed various cyclic quorum-based power management (CQPM) protocols, which, however, may also fail if stations have different schedule repetition intervals (SRIs). Hence, adaptive CQPM protocols, namely, adaptive quorum-based energy conserving (AQEC) and hyper quorum system (HQS), were proposed to overcome this drawback. However, the duty cycles of AQEC and HQS are far from optimal. In this paper, we propose the optimal fully adaptive and asynchronous (OFAA) power management protocol for a multihop MANET, which has the following attractive features: 1) By means of factor-hereditary quorum space, the OFAA protocol guarantees that two neighboring stations can discover each other in bounded time, regardless of their clock difference and individual SRIs; 2) given the length of SRI, the duty cycle of a station reaches the theoretical minimum; 3) the number of tunable SRIs of every station reaches the theoretical maximum; 4) the time complexity of OFAA neighbor maintenance is O(\1) ; 5) a cross-layer SRI adjustment scheme is proposed such that a station can adaptively tune the values of SRI to maximize energy conservation according to flow timeliness requirements. Both theoretical analysis and simulation results demonstrate that the OFAA protocol is much more energy efficient than AQEC and HQS protocols. [ABSTRACT FROM AUTHOR]

This paper presents a class of routing protocols for vehicular ad hoc networks (VANETs) called the Intersection-based Geographical Routing Protocol (IGRP), which outperforms existing routing schemes in city environments. IGRP is based on an effective selection of road intersections through which a packet must pass to reach the gateway to the Internet. The selection is made in a way that guarantees, with high probability, network connectivity among the road intersections while satisfying quality-of-service (QoS) constraints on tolerable delay, bandwidth usage, and error rate. Geographical forwarding is used to transfer packets between any two intersections on the path, reducing the path's sensitivity to individual node movements. To achieve this, we mathematically formulate the QoS routing problem as a constrained optimization problem. Specifically, analytical expressions for the connectivity probability, end-to-end delay, hop count, and bit error rate (BER) of a route in a two-way road scenario are derived. Then, we propose a genetic algorithm to solve the optimization problem. Numerical and simulation results show that the proposed approach gives optimal or near-optimal solutions and significantly improves VANET performance when compared with several prominent routing protocols, such as greedy perimeter stateless routing (GPSR), greedy perimeter coordinator routing (GPCR), and optimized link-state routing (OLSR). [ABSTRACT FROM PUBLISHER]

In this paper, a two-user cooperative multiple access (CMA) system is considered. Using the superposition modulation scheme, we propose a low-complexity suboptimal detector at the destination to achieve the performance close to that of the optimal maximum-likelihood sequence detector (MLSD). For independent and non-identically distributed (i.n.d.) Rayleigh-faded channels, we derive error decision regions and present the exact bit-error rate (BER) expression in an integral form, which is validated by simulation results. We also approximate the decision regions and obtain the BER bound in closed form. Another efficient transmission scheme, i.e., the time-division broadcast (TDBC) protocol operating in three time slots, is also considered and analyzed. BER results show that the superposition modulation outperforms the others and can achieve both full diversity order and high coding gain. [ABSTRACT FROM PUBLISHER]

Coding-aware routing is an effective approach for incorporating network coding into practical network protocols. The main challenge in exploiting the network coding is how coding opportunities can accurately be identified and utilized. In this paper, we formally establish coding conditions for a very general scenario: Multiple coding nodes may exist along a path, and multiple flows may intersect at one node. Specifically, we systematically analyze possible coding scenarios and develop generalized coding conditions to ensure the decoding ability at the destinations. In particular, we develop an extended coding graph to make the conditions implementable. With the help of the extended coding graph, we examine the coding relationship between flows. Our coding conditions also include a coding flow selection procedure to guarantee the coding capability of each coding node, in which not only a native packet, but an encoded packet as well, could be involved. Furthermore we propose a novel coding-aware routing metric, the free-ride-oriented routing metric (FORM), with the objective of exploiting the coding opportunities so that a new flow can free ride on the existing traffic and can be supported with a smaller number of transmissions. NS-2 simulations are conducted to demonstrate the advantage of FORM and the proposed coding conditions over well-known COPE scheme in terms of throughput. [ABSTRACT FROM PUBLISHER]

In the IEEE 802.11 distributed coordination function (DCF), the basic service set (BSS) suffers from two unfairness issues: 1) performance anomaly and 2) uplink/downlink unfairness. In this paper, to solve these issues, we propose a window control scheme in the Transmission Control Protocol (TCP) for the IEEE 802.11 DCF mode. The proposed scheme is called channel occupancy time based rate control for TCP (COTRC--TCP). COTRC--TCP controls the maximum window size based on the throughput estimated at the TCP layer so that each station can use the wireless channel for equal duration. The throughput estimation is based on the number of active stations and the channel occupancy period used by each station in the BSS, which are monitored at the Medium Access Control (MAC) layer. The proposed scheme forms a cross-layer approach that involves both MAC and transport layers. The performance of COTRC--TCP over multirate IEEE 802.11 DCF is evaluated and compared with that of previous works through extensive simulations. Simulation results show that COTRC--TCP exhibits fairness in terms of channel-occupancy time among the competing stations, which accordingly remedies the unfairness problems. The proposed scheme also improves the transmission efficiency. [ABSTRACT FROM AUTHOR]

In this paper, we propose a simple protocol for the cognitive multiaccess relay channel (MARC) with no transmit channel-state information and analyze the resulting stable throughputs of the primary and cognitive nodes. We propose allowing the cognitive node (common relay in the MARC topology) to simultaneously relay data for both primary nodes and transmit its own data (cognitive data) using a multilevel modulation (MLM) scheme. This modulation scheme provides unequal protection for the primary and cognitive data, which increases the throughput of the primary nodes by relaying their messages, in turn increasing the transmission opportunities of the cognitive nodes. The proposed scheme is studied from a networking perspective, and the stable throughput for the primary and secondary nodes as a function of the modulation levels and channel statistics is derived using queueing theory. [ABSTRACT FROM AUTHOR]

This paper presents an irregular distributed space-time (Ir-DST) coding scheme designed for near-capacity cooperative communications where the system's effective throughput is also maximized with the aid of a joint source-and-relay mode design procedure. At the source node, a serially concatenated scheme comprising an IRregular Convolutional Code (IRCC), a recursive unity-rate code (URC), and a space-time block code (STBC) was designed for the sake of approaching the corresponding source-to-relay link capacity, where the IRCC was optimized with the aid of EXtrinsic Information Transfer (EXIT) charts. At the relay node, another IRCC is serially concatenated with an identical STBC. Before transmitting the relayed information, the relay's IRCC is reoptimized based on EXIT chart analysis for the sake of approaching the relay channel's capacity and to maximize the relay's coding rate, which results in a maximized effective throughput. We will demonstrate that the topology of the Ir-DST system coincides with that of a distributed turbo code (DTC). At the destination node, a novel three-stage iterative decoding scheme is constructed to achieve decoding convergence to an infinitesimally low bit-error ratio (BER). Finally, our numerical results show the proficiency of our joint source-and-relay mode design procedure, demonstrating that the proposed Ir-DST coding scheme is capable of near-capacity cooperative communications and of maximizing the effective throughput. [ABSTRACT FROM AUTHOR]