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In this paper, we propose a new adversarial attack on frequency-hopping-based wireless communication between two users, namely Alice and Bob. In this attack, the adversary referred to as Eve, instantaneously modifies the transmitted signal by Alice before forwarding it to Bob within the symbol period. We show that this attack forces Bob to incorporate Eve's signal in the decoding process; otherwise, treating it as noise would further degrade the performance akin to jamming. Through this attack, we show that Eve can convert a slow-fading channel between Alice and Bob to a rapid-fading one by modifying every transmitted symbol independently. As a result, neither pilot-assisted coherent detection techniques nor blind-detection methods are directly applicable as countermeasures. As potential mitigation strategies, we explore the applicability of frequency hopping along with on–off keying (OOK) and binary frequency-shift keying (BFSK) as modulation schemes. In the case of OOK, the attacker attempts to introduce deep fades on the tone carrying the information bit, whereas in the case of BFSK, the attacker pours comparable energy levels on the tones carrying bit-0 and bit-1, thereby degrading the performance. Based on extensive analyses and experimental results, we show that when using OOK, Bob must be equipped with a large number of receive antennas to reliably detect Alice's signal, and when using BFSK, Alice and Bob must agree upon a secret key to randomize the location of the tones carrying the bits, in addition to randomizing the carrier frequency of communication. [ABSTRACT FROM AUTHOR]

The performance analysis of a distributed access wireless network, in which nodes are randomly distributed [namely, a random wireless network (RWN)] over a large area, is challenging. An effective mathematical modeling of these networks can help network designers to predict whether a given set of quality-of-service (QoS) requirements can be satisfied prior to the real network deployment. Previous models for the performance analysis of multihop RWNs fail to give accurate results due to the assumption of a single-hop, limited, and a priori known number of stations; negligence of the hidden terminals; and the use of a Boolean logic collision model. In this paper, we develop an alternative probabilistic modeling approach to analyze the performance of these networks in medium-access-control (MAC) and network layers. Using the proposed modeling approach and obtained metrics, we can identify a set of optimal parameters to maximize the performance of the networks. [ABSTRACT FROM PUBLISHER]

Providing guaranteed quality of service (QoS) for multimedia applications is a challenging topic in wireless mesh networks (WMNs). This paper proposes a distributed resource reservation (RR) mechanism with novel admission control to guarantee QoS performance of real-time sessions (RTSNs) while improving bandwidth utilization in WMNs. The proposed RR mechanism establishes logical clusters (LCs) for identifying interference relationships between nodes and avoids simultaneous transmissions from interfering nodes. Following the established LCs, a cooperative contention and collision-free channel access is achieved in hybrid medium access control (MAC) for multihop data forwarding in WMNs. To efficiently utilize the scarce resources in a contention-free period, soft and hard resources are reserved for RTSNs according to their QoS demands. This is achieved by a novel admission control algorithm. Furthermore, an analytical model is derived for investigating the RR parameters of the proposed mechanism. Simulation results show that the proposed mechanism guarantees the QoS for RTSNs while improving bandwidth utilization. [ABSTRACT FROM PUBLISHER]

Recently, multiple concurrent transmission techniques have been proposed for smartly exploiting interference to improve network throughput. This paper considers zero-forcing (ZF) precoding that allows two interfering links to concurrently transmit under certain situations. This paper focuses on identifying appropriate schedule schemes that efficiently utilize the ZF precoding opportunities to improve network throughput. With this motivation, we define novel link models to formulate our concerned problem. We also develop a distributed scheduling algorithm by using belief propagation. Finally, we conduct extensive simulation experiments to evaluate the efficiency of ZF in improving network throughput in multihop wireless networks. Our simulations confirm that intelligently utilizing ZF in multihop networks is very effective in improving throughput. [ABSTRACT FROM PUBLISHER]

This paper addresses the problem of energy-aware multihop cooperation among the mobile terminals (MTs) that cooperatively download a common content from a wireless network. The base station (BS) unicasts or multicasts the content to selected MTs that, in turn, either unicast or multicast it to other MTs, forming a multihop ad hoc network with a predefined maximum allowed number of hops. This paper presents the optimization formulations whose solution gives the exact optimal set of receiving MTs from the BS, the optimal multihop ad hoc network, and the optimal unicasting and multicasting transmission bit rates that minimize the total energy consumption of the MTs. Second, a simplified multicasting formulation is proposed that has a close-to-optimal performance with notably lower computational complexity. Third, interference avoidance among the transmitting MTs is considered. For each presented formulation, the complexity is identified, and results show that some formulations can be efficiently solved for medium network sizes, while others are more computationally complex. Thus, polynomial-time heuristic solutions are presented that have close-to-optimal performance. Results demonstrate remarkable energy consumption reduction gains and wireless resources savings under various network scenarios. [ABSTRACT FROM PUBLISHER]

In this paper, space-shift keying (SSK) is considered for multihop multiple-input-multiple-output (MIMO) networks. In SSK, only one among ns = \2^{m} available transmit antennas, chosen on the basis of $m$ information bits, is activated during transmission. We consider two different systems of multihop cooperation, where each node has multiple antennas and employs SSK. In system I, a multihop diversity relaying scheme is considered. In system II, a multihop multibranch relaying scheme is considered. In both systems, we adopt decode-and-forward (DF) relaying, where each relay forwards the signal only when it correctly decodes. We analyze the end-to-end bit error rate (BER) and diversity order of both the systems with SSK. For binary SSK (ns = \2), our analytical BER expression is exact, and our numerical results show that the BERs evaluated through the analytical expression overlap with those obtained through Monte Carlo simulations. For nonbinary SSK (ns > \2), we derive an approximate BER expression, where the analytically evaluated BER results closely follow the simulated BER results. We show the comparison of the BERs of SSK and conventional phase-shift keying (PSK) and also show the instances where SSK outperforms PSK. We also present the diversity analyses for SSK in systems I and II, which predict the achievable diversity orders as a function of system parameters. [ABSTRACT FROM PUBLISHER]

Broadcasting is an important operation in wireless networks where control information is usually propagated as broadcasts for the realization of most networking protocols. In traditional ad hoc networks, broadcasts are conducted on a common channel, which is shared by all nodes in the network. However, in cognitive radio (CR) ad hoc networks, unlicensed users may observe heterogeneous spectrum availability, which is unknown to other unlicensed users before the control information was broadcast. Thus, it is extremely challenging that broadcasts can be successfully conducted without knowing the spectrum availability information in advance. In addition, since broadcast collisions (i.e., simultaneous reception of broadcast messages at the same node) often lead to the waste of network resources, they should be efficiently mitigated in multihop scenarios. In this paper, a quality-of-service (QoS)-based broadcast protocol under Blind Information for multihop CR ad hoc networks, i.e., \QB^2\IC, is proposed with the aim of having a high success rate and short broadcast delay. In our design, we do not assume that unlicensed users are aware of the network topology, the spectrum availability information, and time synchronization information. To the best of our knowledge, this is the first paper that investigates the broadcast issue in multihop CR ad hoc networks under blind information. Simulation results show that our proposed \QB^2\IC protocol outperforms other broadcast schemes in terms of a higher success rate and shorter average broadcast delay. [ABSTRACT FROM PUBLISHER]

Multihop propagation of situational information is a promising technique for improving beaconing performance and increasing the degree of situation awareness onboard vehicles. A possible way of achieving this is by piggybacking information on the beacon packets that are periodically sent by each vehicle in the network, as prescribed by the Dedicated Short-Range Communications standards and the European Telecommunications Standards Institute. However, prescribed limitations on beacon size imply that only information on a very small number of surrounding vehicles can be piggybacked in a beacon packet. In most traffic situations, this number is well below the typical number of vehicles within the transmission range, implying that multihop forwarding strategies must be devised to select which neighboring vehicle's information to include in a transmitted beacon. In this paper, we designed different multihop forwarding strategies and assessed their effectiveness in delivering fresh situational information to surrounding vehicles. Effectiveness is estimated in terms of both information age and the probability of experiencing a potentially dangerous situation-awareness blackout. Both metrics are estimated as a function of the hop distance from the transmitting vehicle and in the presence of different levels of radio channel congestion. The investigation is based on extensive simulations whose multihop communication performance is corroborated by real-world measurements. The results show that network-coding-based strategies substantially improve forwarding performance, as compared with a randomized strategy, reducing the average information age by up to 60% and the blackout probability by up to two orders of magnitude. We also consider the effect of multihop propagation of situational information on the reliability of a forward collision warning application and show that network-coding-based propagation yields a factor-3 improvement of reliability with respect to a randomized forwarding strategy and even higher improvements with respect to the case of no propagation. [ABSTRACT FROM PUBLISHER]

This paper considers a multi-hop amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network. In the multi-hop AF MIMO relay network, the performance deteriorates as the number of hops increases because the effect of noise is enhanced. To suppress the effect of noise, this paper proposes the two beamforming schemes using channel state information (CSI) for the transmit beamforming at the source, relay beamforming at the relay, and receive beamforming at the destination. The forward-and-backward-CSI based beamforming and all-CSI based beamforming schemes are designed at each node based on the minimum mean square error criterion under the source and relay transmit power constraint. The forward-and-backward-CSI based beamforming scheme is designed by using the two matrices, forward channel, and backward channel. The two matrices are designed by using the beamforming matrices and channels from the previous nodes. Unlike the forward-and-backward-CSI based beamforming scheme, the all-CSI based beamforming scheme is designed by using all channels and an iterative algorithm. In terms of the complexity, the forward-and-backward-CSI based beamforming scheme is superior to the all-CSI based beamforming scheme. However, the all-CSI based beamforming scheme has advantage over the forward-and-backward-CSI based beamforming scheme in terms of the performance. [ABSTRACT FROM AUTHOR]

In IEEE-802.11-based wireless mesh networks (WMNs), unfair bandwidth sharing may arise, because the carrier sense multiple access with collision avoidance protocol is designed to provide per-station fairness only in one hop. As the hop count from a mobile client to the gateway node increases, the throughput of the node drastically decreases. In this paper, we propose a fair bandwidth allocation scheme for multiradio multichannel WMNs. This scheme provides fair bandwidth sharing among the nodes in a WMN, regardless of their hop distance from the gateway node. To achieve fairness, we first estimate the number of active nodes attached to each router and calculate the effective weights of routers based on the estimation. Then, we differentiate their contention window using their weights. For this method, we derive a multihop packet collision model. The proposed scheme is fully distributed and does not require any global information. Through an extensive simulation study, we show that our scheme ensures per-node fairness without loss of the total aggregate throughput. [ABSTRACT FROM PUBLISHER]

Communications-based train control (CBTC) is a modern signaling system that uses radio communication to transfer train control information between the train and the wayside. A vast majority of CBTC systems worldwide use IEEE 802.11 Wi-Fi as the radio technology mostly due to its cost effectiveness. The trackside networks in these systems are mostly based on the conventional infrastructure Wi-Fi. It means a train has to continuously associate (i.e., perform handshake) with the trackside Wi-Fi access points (AP) as it moves. This is a time-consuming process associated with a certain delay. Additionally, these APs are connected to the wayside infrastructure via optical fiber cables that incurs huge costs. This paper presents a novel design in which trackside nodes function in ad-hoc Wi-Fi mode, which means no association has to be performed with them prior to transmitting. A train simply broadcasts packets to any nodes in its range. A node upon receiving these packets forwards them to the next node and so on, forming a chain of nodes. Following this chain, packets arrive at the destination. To make the design resilient against interference, transmissions are separated on multiple frequencies. Furthermore, redundancy is introduced in the design as a node forwards packets to not only one but two of its neighbors. This paper investigates the performance of the new design from the perspective of resiliency, redundancy, and scalability, and presents the results both from a field experiment carried out using prototype hardware and an extensive simulations study. [ABSTRACT FROM PUBLISHER]

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

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

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

This paper explores the feasibility of designing an outdoor cellular network based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, which was originally developed for wireless local area networks. Specifically, the performance of the 802.11 radio and medium access control (MAC) protocol in outdoor environments is investigated. For channels typical in cellular networks, we study the radio link power budget and the bit error performance of three kinds of receivers. We also propose a new timing structure for the MAC protocol to handle increased signal propagation delay and analyze its throughput performance in the outdoor network. Our analysis shows that the MAC protocol can handle a cell radius of 6 km without violating the 802.11 standard. However, the link budget reveals that the maximum cell radius in an outdoor 802.11 network ranges from 0.4 to 1.2 km, which is about one third that supported by wideband code-division multiple access and enhanced data rates for global system for mobile communications evolution networks. For a root-mean-square delay spread of 1 μs which. is typical for urban-area cells of this size, our simulation results show that the conventional RAKE receiver can yield a satisfactory performance. Combining these results, we conclude that using ordinary equipment, an 802.11-based cellular network with a cell radius up to 1.2 km is feasible. It is possible to further extend the service range by advanced techniques such as smart antennas. [ABSTRACT FROM AUTHOR]

With the increasing demand for high-data mobile traffic and applications, Device-to-Device (D2D) communication has emerged as a promising technique for next generation of cellular networks to increase the network capacity. In this paper, to offload traffic from network backhaul, we investigate the problem of relaying data through multihop nodes, using D2D communication, for a set of transmitter-receiver pairs, by sharing cellular resource blocks. Furthermore, the problem is extended to schedule the transmission links within a maximum time frame to obey a delay constraint. If the transmission path could not be scheduled within the maximum time frame for any D2D communication pair, the communication is redirected through the base station similar to cellular mode. Our problem aims at minimizing the overall D2D transmission power by giving priority to maximizing the number of paths that go through D2D relaying. We mathematically formulate the above problem and find optimal solutions for small networks. We show the NP-hardness of the problem, and owing to its complexity, we propose an algorithmic method for more extensive networks. Through numerical results, the performance of our mathematical optimization model and algorithm is compared and the efficiency of the proposed algorithmic method is shown. [ABSTRACT FROM AUTHOR]

Multihop relaying is a transmission technique that splits the communication link between the source and the destination into several, possibly shorter, hops for extended coverage, improved reliability, and less power consumption. Previous works on multihop communications use the assumption of frequency-flat and quasi-static fading, which can be justified only for narrowband systems resulting from stationary or quasi-static channels. In this paper, we extend multihop relaying into vehicular communication in highways. We deploy a precoded transmission over multihop vehicle-to-vehicle links that is characterized by time- and frequency-selective fading. We propose and investigate a transmission scheme where traveling vehicles are allowed to relay signals via neighboring vehicles to the final destination. With the aid of the precoded transmission and best-relaying vehicular selection, we succeeded to extract the rich diversity gains that are inherent in these types of doubly selective fading channels (i.e., through time and frequency dimensions), and through space dimension using cooperative transmission. We developed a mathematical model and derived a tight upper-bound expression for the pairwise error probability for future studies and analysis. Computer simulations are used to verify the correctness and accuracy of the derived analytical error. [ABSTRACT FROM AUTHOR]

This paper presents a tractable analytical framework for the exact calculation of the probability of node isolation and the minimum node degree distribution when $N$ sensor nodes are independently and uniformly distributed inside a finite square region. The proposed framework can accurately account for the boundary effects by partitioning the square into subregions, based on the transmission range and the node location. We show that for each subregion, the probability that a random node falls inside a disk centered at an arbitrary node located in that subregion can be analytically expressed in closed form. Using the results for the different subregions, we obtain the exact probability of node isolation and minimum node degree distribution that serves as an upper bound for the probability of $k$-connectivity. Our theoretical framework is validated by comparison with the simulation results and shows that the minimum node degree distribution serves as a tight upper bound for the probability of $k$-connectivity. The proposed framework provides a very useful tool to accurately account for the boundary effects in the design of finite wireless networks. [ABSTRACT FROM PUBLISHER]

Satellite high-mobility communications can provide global communication services for mobile terminals, which plays a vital role in today's world of wireless communications. Different from traditional terrestrial-satellite communications, high-mobility terminals impose more challenges on the direct sequence spread spectrum (DSSS) signal acquisition in satellite communications. On the one hand, the spread spectrum sequence used in satellite communication systems is relatively long, which inevitably increases the computational complexity. On the other hand, high Doppler frequency offsets and time-varying Doppler rates caused by high-mobility terminals make satellite DSSS signal acquisition become the bottleneck. To solve such a problem in high-mobility satellite communications, we propose a new acquisition algorithm based on the new factor graph where time-varying Doppler rate is modeled by the random walk model, named the turbo iterative acquisition algorithm. It consists of the constraint-detection loop and the Doppler-estimation loop. By means of soft messages passed between these loops, the negative influence of time-varying Doppler frequency offsets can be eliminated effectively. Simulation results show that, compared with traditional algorithms, the proposed algorithm improves acquisition performance more than 1.3 dB with low computational complexity, which demonstrates the superiority of the proposed algorithm in terms of acquisition performance and complexity. [ABSTRACT FROM AUTHOR]

Wireless sensor network devices commonly use a single antenna for transmission and reception, as well as for relaying packets over multiple hops to a final destination, which is referred to as single-input–single-output (SISO) multihop transmission. Advancements in multiple antenna systems enable reliable broadband wireless communications using multiple-input–multiple-output (MIMO) transmission technology. In addition, through collaboration of several single-antenna-equipped devices, cooperative MIMO communication is possible in the form of virtual MIMO (V-MIMO), virtual multiple-input-single-output (V-MISO), and virtual single-input-multiple-output (V-SIMO), which are collectively called V-MIMO technology. In this paper, a multihop hybrid V-MIMO (HV-MIMO) networking scheme is proposed to configure a minimum energy consuming route (MECR) that provides high end-to-end connectivity while satisfying end-to-end data rate and bit error rate (BER) requirements by using the best cooperative MIMO configuration for each hop. In the proposed scheme, first, the source-to-destination path is divided into long wireless communication hops, and the minimum energy consuming V-MIMO configuration is applied to each hop. Next, the long communication hops are individually evaluated for replacement with two half-length V-MIMO hops, where changes are applied only when a gain in energy consumption is obtainable. If no gain is obtainable for a certain hop, then the hop configuration is not changed, and that hop is no longer compared for replacement. This procedure of testing for possible replacement with two half-length hops is repeated individually for all hops until no further changes are made in the source-to-destination path, which is when the HV-MIMO MECR is complete. For equivalent end-to-end data rate and BER requirements, the proposed HV-MIMO multihop scheme provides a significant energy saving (e.g., 52.32% energy saving at the node density of 0.003 \nodes/m^2) compared with the conventional SISO multihop path's MECR. In addition, the HV-MIMO scheme always results in an energy saving gain and a significantly higher end-to-end multihop MECR connection probability compared with using the same type of cooperative MIMO configuration for each hop (i.e., homogeneous V-MIMO configuration). [ABSTRACT FROM PUBLISHER]

In this paper, we propose a distributed and asynchronous topology control framework for wireless multihop networks, aiming at improving the quality-of-service capabilities of such systems. The proposed mechanisms exploit cross-layer information such as physical-layer signal-to-interference-plus-noise ratio (SINR) values and medium-access-control (MAC)/network-layer connectivity to effectively allocate resources. Based on properly defined utility functions, we cast the transmission power allocation problem as a noncooperative game and then show that it belongs to the class of potential games. We obtain structural properties of the defined game and its variations and demonstrate their effectiveness. Through analysis and simulation, we explore the behavior of the proposed framework and compare it with the most relevant approach in the literature. It is shown that the proposed unifying game-theoretic framework achieves three key goals for multihop ad hoc networks, i.e., reduced transmission power, high-quality links, and connectivity maintenance. [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]

Vehicular networks allow vehicles to exchange information that can be used to improve traffic efficiency and drivers' safety. In addition to these new applications, Internet connectivity is also expected to be available in the cars of the near future, speeding up the global adoption of vehicular communication systems. One of the requirements for connecting vehicles to the Internet is their ability to autoconfigure Internet Protocol (IP) addresses. In this paper, we propose an optimization to Geographically Scoped stateless Address Configuration (GeoSAC), which is an IP address autoconfiguration mechanism for geographically aware location vehicles. The benefits of this optimization are twofold: 1) It can reduce the IP address configuration time, and 2) it can be used to reduce the signaling overhead of GeoSAC. The optimization requires no changes to the GeoSAC operation, being fully compatible with the original solution. We derive an analytical model for the probability of our optimization being effective in realistic scenarios and for the IP address configuration time. We also provide a thorough evaluation of the performance improvements of the optimization, including simulations with a realistic model for wireless technology, real vehicular traces, and experiments with a real prototype, which provide strong support for our analytical model. [ABSTRACT FROM PUBLISHER]

In multihop ad hoc networks over 802.11, the real bandwidth-delay product (BDP) cannot reach a value as large as in wired networks due to contention through wireless shared channels. As a result, conventional congestion-control algorithms cause an overshooting window problem and result in poor throughput in ad hoc networks. In this paper, we split the real round-trip time (RTT) into two parts: 1) congestion RTT and 2) contention RTT. We reveal that the contention RTT has nothing to do with the BDP and that the BDP is determined by only the congestion RTT if a link with the worst contention status does not lead to link breakage. An inadequate use of contention RTT causes a Transmission Control Protocol (TCP) congestion window overshooting problem. We propose a novel mechanism called congestion window adaptation through contention detection, which provides a more accurate method of estimating the contention status. Based on this mechanism, we present a congestion window adaptation method to limit the window size from overshooting. Simulation results show that our proposed mechanism outperforms the conventional TCP and the enhanced mechanisms called TCP with contention control and TCP with a maximum window. [ABSTRACT FROM PUBLISHER]

Although the system throughput of a wireless communication system considering multiple users' geographical distribution on a 2-D plane and various traffic characteristics is an important performance metric, its mathematical analysis is very difficult due to the nonindependent identically distributed distribution of the received signal-to-noise ratio (SNR) of each mobile terminal and the complex dynamics of the traffic patterns. Therefore, complicated system-level simulations have been the only approach to evaluate the system throughput of downlink packet-access systems. In this paper, we propose an efficient analytical approach to estimate the system throughput of downlink packet-access systems by using point mass approximation, which is widely used in physics and mechanics. The proposed analysis framework enables the mathematical analysis of the system throughput performance by considering various positions of mobile terminals and traffic patterns without the complicated and heavy system-level simulations. Although the proposed approach has a tradeoff relation between computation complexity and accuracy, we show that it is possible to obtain an effective accuracy with moderate complexity using the proposed analytical approach. [ABSTRACT FROM PUBLISHER]

In this paper, we develop a performance modeling technique for analyzing the time-varying network layer queuing behavior of multihop wireless networks with constant bit rate (CBR) traffic. Our approach is a hybrid of a time-varying adjacency matrix and a fluid flow queuing network model. The mobile network topology is modeled using a time-varying adjacency matrix, whereas node queues are modeled using fluid-flow-based differential equations that are solved using numerical methods. Numerical and simulation experiments show that this new approach can provide reasonably accurate results. Moreover, when compared with the computation time required in a standard discrete event simulator, the fluid-flow-based model is shown to be a more scalable tool. Finally, an illustrative example of our modeling technique application is given to show its capability of capturing the time-varying network performance as a function of traffic load, node mobility, and wireless link quality. [ABSTRACT FROM PUBLISHER]

In this paper, we propose two cross-layer algorithms, namely, the Power-optimal Scheduling Algorithm (PSA) and the Throughput-optimal Scheduling Algorithm (TSA), to minimize energy consumption and to maximize throughput, respectively, in multihop wireless networks. Our algorithms guarantee a flow-based minimum data rate and jointly integrate congestion control, power allocation, routing, and link rate scheduling. Different from traditional algorithms that assume infinite buffers, the proposed algorithms deterministically upper bound the flow-based packet queue length and thus can be employed in multihop networks with finite buffers. In addition, the algorithms achieve a power expenditure/throughput “\epsilon-close” to the optimal value, with a tradeoff of order O(\1/\epsilon) in buffer size. The average end-to-end delay upper bound can also be derived from the finite buffer property. Finally, numerical results are presented to show the performance of the two algorithms with different system parameters. [ABSTRACT FROM PUBLISHER]

Multicarrier (MC) modulation and code division multiple access (CDMA) schemes have seen much recent attention for the high capacities and flexibility they can provide. A potential difficulty with these systems is their sensitivity to the effects of imperfect frequency up/down conversion due to local oscillator phase noise and frequency offset. In this paper, we provide a general method to upper bound and/or approximate system performance in multitone direct-sequence spread spectrum (MT-DS-SS) signaling in the presence of imperfect synchronization. We model phase noise as a slow random processes with small variance. In particular, we assume coherent detection with binary phase-shift keying (BPSK) modulation and use a phase noise model based upon one for a practical phase-locked loop (PLL). Comparisons between simulations and analysis show excellent agreement, and also show that system degradation is dominated by the common phase noise, and that the intersubcarrier-same-user interference (IS-SUI) contribution is very small. The approach we employ provides an effective analytical/numerical method for performance evaluation for low target error probability values, on the order of 10-6 or lower. In addition, our method can also be easily applied to any multicarrier system with other frequency offset/phase noise models. [ABSTRACT FROM AUTHOR]

Interference alignment (IA) is widely regarded as a promising interference management technique for wireless networks and its potential is most profound in interference-intensive environments. This motivates us to study IA for multicast communications in multihop MIMO networks, which are rich in interference by nature. We develop a set of linear constraints that can characterize a feasible design space of IA for multicast communications. The set of linear constraints constitutes a simple mathematical model of IA that allows us to conduct cross-layer multicast throughput optimization in multihop MIMO networks, but without getting involved into the onerous signal design at the physical layer. Based on the mathematical model of IA, we formulate a multicast throughput maximization problem and develop an approximation solution that can achieve $(1-\varepsilon)$ -optimality. Simulation results show that the use of IA can significantly increase the multicast throughput in multihop MIMO networks and the throughput gain increases with the volume of multicast traffic and the number of antennas. [ABSTRACT FROM AUTHOR]

We consider the problem of link scheduling in multihop wireless networks subject to interference constraints. We consider a graph-based representation of wireless networks where scheduled links adhere to the $K$ -hop link interference model. For this scheduling problem, we develop an asynchronous and distributed greedy heuristic. Furthermore, we show that this distributed heuristic computes the exact same schedule as the well-known centralized greedy link scheduling algorithm. [ABSTRACT FROM AUTHOR]

In a multihop wireless network, the traffic at each node and the channel over each link may fluctuate with time. Thus, traditional optimal resource allocation needs to be computed for each moment with instantaneous information of channel states over all links and the traffic rates at all nodes, leading to huge communication overhead and computation cost. To solve this challenge, in this correspondence, we propose to use robust resource allocation, in which the only needed information is the mean and variance of the wireless channels and the traffic rates. In the formulated problem, there are probabilistic constraints, which are difficult to handle. Effective methods are provided that can transform the probabilistic constraints to convex constraints. As the resource allocation does not need instantaneous channel state information or instantaneous traffic rate information, it is robust to channel and traffic variations, with very little communication and computation overhead. [ABSTRACT FROM AUTHOR]

Network coding aware routing (NCAR) has been emerging as an effective approach to create coding opportunities actively in multihop networks. To the best of our knowledge, most of the existing methods focus on a “static” design that considers coding opportunities based on fixed routes and invariable packet flows. This “static” way results in the optimality of routes suffering from a high sensitive behavior on both network topology and flow dynamic and, hence, reduces the throughput of routes in time-varying networks. To solve this problem, we propose a high-throughput NCAR scheme that supports dynamic multihop network connectivity and achieves throughput optimization, even with multiple variable flows. In the proposed scheme, a back-pressure-based NCAR algorithm is designed to push the flows dynamically into the nodes that have better network coding opportunities with no knowledge of network topology and flow dynamic. As a byproduct, the proposed method also exhibits a significantly improved delay performance relative to the traditional back-pressure algorithm. Simulation results reveal that the proposed scheme improves network capacity and alleviates end-to-end delay in heavy load networks. [ABSTRACT FROM PUBLISHER]