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This paper provides a comprehensive performance comparison between a current robust military waveform; namely, MIL-STD-188-110D, Waveform 0, and a filter bank multicarrier spread-spectrum (FBMC-SS) waveform proposed for communications through ionospheric/skywave HF channels. Waveform 0 is effectively a direct sequence spread spectrum waveform that uses Walsh multi-codes to enhance the information transmission rate. It may thus be referred to as Walsh-DSSS. FBMC-SS, on the other hand, makes use of filter banks to provide excellent performance when the received signal is subject to partial band interference. Successful application of FBMC-SS for communications across skywave HF channels has been previously demonstrated, both theoretically and through experimental work. However, very little has been done to contrast FBMC-SS against Walsh-DSSS. The goal of this paper is to first add new features to FBMC-SS to bring it on par with Walsh-DSSS. These features include: (i), introduction of multi-codes that achieve a comparable (or better) data rate to Walsh-DSSS; and (ii), addition of a scrambling step applied to the multi-codes to make the receiver detection robust against widely spread multipaths. With this established, in the second part of the paper, we examine the performance of the developed FBMC-SS against Walsh-DSSS when both are applied for communications across skywave HF channels. The two waveforms are compared both through a theoretical study and through experimental works across several skywave channels ranging from hundreds to thousands of kilometers. [ABSTRACT FROM AUTHOR]

This paper presents techniques that are expected to improve the bit error rate (BER) performance of Unmanned Aerial Vehicles (UAVs) communication systems. The decode-and-forward (DF)-based cooperative multi-hop Rician network using space shift keying (SSK) modulation is employed for this purpose. The SSK modulation and cooperative communication are merged and used together. This enhances the BER performance for multiple-input multiple-output (MIMO) channels, thus accentuating its significance as an important technique for consistently reliable communication methodology while, at the same time, eliminating wastage of energy. The new technique is named as high performance (HP) due to not only BER performance improvement but also increase of the diversity of the communication system. This new model is further used for multi-hop networks and the resulting BER characteristics are assessed for possible enhanced performance in Rician channels. The paper also showcases the generalized-n-hop BER equation for various multi-hop DF-based cooperative communication systems in diverse UAV models. The Monte Carlo simulations further confirm the theoretical results that already exist for transmit-receive antennas. This work also underlines the fact that the number of hops in a communication system has no bearing whatsoever on the BER performance diversity value. [ABSTRACT FROM AUTHOR]

The multi-hop unmanned aerial vehicle (UAV) network can serve as data relays where ground users (GUs) do not have reliable direct connections to the base station (BS). Existing works mainly focus on simple dual-hop system. In this paper, we investigate the packet routing problem in a multi-hop UAV relay network to minimize the data transmission time and enhance the network throughput. However, the dynamic network topology due to UAV mobility makes the packet routing challenging since the limited communication range of each UAV leads to volatile wireless connection. Moreover, the line-of-sight communication links may cause strong interference among UAVs. Towards this end, we propose a novel multi-agent deep reinforcement learning based algorithm, named as multi-agent QMIX (MAQMIX) to: 1) design proper UAVs’ trajectories to serve the moving GUs while maintaining the network connection; 2) allocate frequency resource properly among UAVs to alleviate the impact of interference; and 3) choose a proper next hop UAV for each data packet to reduce the transmission time and probability of network congestion. The proposed MAQMIX has two novel training mechanisms, i.e., intra-UAV and inter-UAV training mechanisms, which can tackle the large action space issue and coordinate the training among UAVs in the multi-hop UAV relay network. Simulation results demonstrate that the MAQMIX outperforms baseline schemes in terms of the network congestion avoidance, throughput, and transmission time. [ABSTRACT FROM AUTHOR]

Until now, multi-hop device-to-device (MD2D) routing in mobile wireless networks has been designed to operate over a single-protocol routing framework. Consequently, to the best of our knowledge, no framework has been developed to enable the dynamic deployment and switching of multiple MD2D routing protocols under one framework. This paper proposes a multi-protocol framework to introduce the idea of clustering a cell and deploying different MD2D routing protocols for each cluster based on the cluster requirements. To this end, four clusters are developed with varying network conditions (i.e., node density, mobility rate, and the number of flows). Then, the performance of our two previously designed multi-hop routing protocols, namely hybrid SDN architecture for wireless distributed networks (HSAW) and source-based virtual ad hoc routing protocol (VARP-S), are investigated in each cluster in terms of energy consumption, end-to-end (E2E) delay, packet loss, and cellular-band overhead. Based on the achieved simulation results, a multiple-criteria decision-making (MCDM) approach based on the analytic hierarchy process (AHP) is developed to choose the most suitable protocol for each cluster to provide the best performance. The simulation results indicate that our proposed multi-protocol framework provides better performance compared to traditional single-protocol architectures. [ABSTRACT FROM AUTHOR]

The problem of disseminating continuous data flow from a given source node to all other network nodes is known as the dynamic broadcast problem, which is also a fundamental problem in multi-hop wireless networks (e.g., wireless ad hoc and sensor networks). Due to link unreliability and node mobility, the topology of a network typically changes with time. Little work has been conducted to address the dynamic broadcast problem in time-varying wireless multi-hop networks, especially under the popular Signal-to-Interference-plus-Noise-Ratio (SINR) interference model. In this paper, we study the dynamic broadcast problem in SINR-based time-varying directed acyclic multi-hop wireless networks formed by point-to-point wireless links. We consider the SINR-based link transmission rate model involved in the slot-based link scheduling. We first prove a tight upper bound for the broadcast capacity of the multi-hop wireless networks under study. We then propose an online max-weight Throughput-Optimal Dynamic Broadcast algorithm (TODB) which performs link weight allocation, link scheduling, and data forwarding for each time slot according to the current network connectivity and data reception rates of nodes. We derive the throughput-optimality of the TODB algorithm by proving that the broadcast throughput of TODB can achieve the aforementioned upper bound of the broadcast capacity. We evaluate the performance of TODB in terms of throughput and latency via simulations and the results validate its effectiveness. [ABSTRACT FROM AUTHOR]

While multi-hop multi-frequency mesh has been extensively studied in the past decades, only several deployable and relatively bulky systems have been developed to support small numbers of hops under stationary settings. This paper presents a new Software-Defined Networking (SDN)-based design of multi-hop multi-frequency mesh. A new lightweight hardware platform is developed to support adaptive routing and frequency selection, by modifying and integrating commercial-off-the-shelf WiFi modules. We also extend the celebrated Dijkstra's algorithm in support of the new multi-hop multi-frequency platform, where non-overlapping frequency bands are selected together with the routing paths by maintaining $N^2$ Dijkstra processes for $N$ frequency bands. These processes interact to recursively select the optimal upstream node and frequency for each downstream frequency of a node. Mininet-WiFi is used to evaluate the routing of the new system under dense network settings. The results indicate that our system improves the end-to-end throughput by taking background WiFi traffic into account and adaptively selecting the routes and frequencies, as compared to the shortest-path-based routing strategy. [ABSTRACT FROM AUTHOR]

Reactive symbol-level jammer has attracted attention due to its low energy cost and high jamming efficiency. With the development of software-defined radio (SDR), the implementation of reactive symbol-level jamming has become more practical and efficient. To combat the reactive jammer, this paper proposes an index modulation based frequency hopping spread spectrum (IM-FHSS) scheme. Specifically, the current available frequencies are determined by multiple orthogonal frequency hopping (FH) patterns, and bit information is transmitted through the index of the active FH pattern. At the receiving side, we design an energy detector to distinguish the active and idle frequencies. With such implementation, IM-FHSS can obtain the improved resistance of reactive symbol-level jammer. Subsequently, we propose the alternative spectral efficiency (SE) mode of IM-FHSS in order to meet the high SE and low-power jamming scenarios. Furthermore, we analyze the BER of this scheme for the reactive symbol-level jamming under the cases of energy correlation, jamming rate, and phase offset. Theoretical analysis and simulation results show that IM-FHSS exhibits enhanced resistance to reactive symbol-level jamming than traditional FH scheme. [ABSTRACT FROM AUTHOR]

Timely and reliable information sharing among autonomous vehicles (AVs) provides a promising approach for reducing traffic congestion and improving traffic efficiency in future intelligent transportation systems. In this paper, we consider millimeter-wave (mmWave) based multi-hop vehicle-to-vehicle (V2V) communications to facilitate ultra-reliable low-latency information sharing among AVs. We propose a novel framework for performance analysis and design of relay selection schemes in mmWave multi-hop V2V communications, while taking into account the mmWave signal propagation characteristics, road topology, and traffic conditions. In particular, considering the minimum tracking distance requirement of road traffic, the headway, i.e., the distance between adjacent AVs, is modeled as shifted-exponential distribution. Moreover, we model the communication path losses using the Manhattan distance metric in the taxicab geometry, which can more accurately capture the characteristics of mmWave signal propagation in urban grid roads than conventional Euclidean distance geometry. Based on the proposed model, we investigate the latency and reliability of mmWave multi-hop V2V communications for three widely adopted relay selection schemes, i.e., random with forward progress (RFP), most forward with fixed radius (MFR), and nearest with forward progress (NFP), respectively. Furthermore, we propose a novel relay selection scheme for joint optimization of the single-hop forward progress (FP) and single-hop latency according to the AVs’ instantaneous locations and an estimate of the residual multi-hop latency. Simulation results show that, by balancing the current single-hop latency and the residual multi-hop latency for the multi-hop V2V network, the proposed relay selection scheme significantly outperforms the MFR, NFP and RFP in both multi-hop transmission latency and reliability of mmWave V2V communications. [ABSTRACT FROM AUTHOR]

Channel gain based path selection has been recently proposed to simplify the network design of a cluster-based cross-layer multihop vehicular communications. In vehicular network systems, end-to-end packet delay increases with the growing number of vehicles associated in that path. In delay-sensitive application, the information exchange must be successfully carried out very quickly to ensure the quality of infotainment services. In the case of excessive packet delay, some important information either are needed to be enqueued before reaching the destination or are lost. The packet loss makes it impractical to deploy the network in practice. In this paper, a new delay-sensitive buffer-aided relay selection is proposed using the channel-based greedy scheduling algorithm (CGSA) to overcome the limitations imposed by processing delay. The proposed scheme significantly minimizes average delay by selecting a set of alternative paths based on individual node buffer status. This scheme has less packet delay than existing Max-link scheme with very close system performances, making it an ideal candidate for delay-sensitive applications. Finally, both analytical and simulation results are provided to demonstrate the performance improvement of the proposed algorithm compared with the existing relaying schemes. [ABSTRACT FROM AUTHOR]

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]

Multi-hop device-to-device (D2D) communications play an important role in expanding D2D coverage. In this paper, we study a relay-based and network-coding-assisted (in particular, XOR coding) multi-hop D2D communication system. In the system, toward jointly considering the impact of interference and network traffic conditions on the quality of D2D communications, various channel fading models and traffic models are investigated, and the packet loss probability of D2D links is meticulously computed using these models. With the packet loss probability of D2D links, the general closed-form expressions of end-to-end packet loss probability (E2EPLP) of the system with the presence (or absence) of XOR coding are subsequently derived. Our experiments reveal that both the number of relays and the mechanism of XOR coding can affect the system performance. Specifically, the increase in the number of relays will lower the overall system performance (e.g., an increase in the E2EPLP and end-to-end completion time, and a decrease of the end-to-end rate may follow as a result). On the other hand, although the presence of XOR coding unfortunately raises the system E2EPLP, it can effectively improve the end-to-end completion time and end-to-end rate. It is our belief that the analytical approach proposed in this paper and the results found in our work can be useful to peer studies in the context of applying network coding in multi-hop D2D networks. [ABSTRACT FROM AUTHOR]

For improving the throughput while simultaneously enhancing the security in aeronautical ad-hoc networking (AANET), a channel quality indicator (CQI)-mapped spatially modulated sparse code multiple access (SM-SCMA) scheme is proposed in this paper. On one hand, we exploit the joint benefits of spatial modulation and SCMA for boosting the data rate. On the other hand, a physical-layer secret key is generated by varying the SM-SCMA mapping patterns based on the instantaneous CQI in the desired link. This guarantees the security of AANETs, since this secret key is not exchanged between the source aeroplane and its destination. Due to the line-of-sight (LoS) propagation in the AANET, other aeroplanes or eavesdroppers may detect the signals delivered in the desired link. However, they are unable to translate the detected signals into the original confidential information, even if multiple copies of the signals are recoined over multiple hops of the AANET, because they have no knowledge of the CQI-based SM-SCMA mapping pattern. The performance of the CQI-mapped SM-SCMA is evaluated in terms of both its bit error rate and its ergodic secrecy rate, which substantiates that the proposed scheme secures the confidential information exchange in the multi-hop AANET. [ABSTRACT FROM AUTHOR]

In this paper, we study the network of unmanned aerial vehicles (UAVs) which acts as a relay between a base station, and remotely deployed Internet of Things devices. UAVs have received much attention for connecting remotely located networks/objects, but there is a lack of study on multi-hop relay transmission schemes over UAV networks. It is particularly challenging because of the their high mobility, and limited resources, to name a few. In this regard, we propose an energy-efficient, cooperative multi-hop relay scheme for UAVs. We formulate the optimal multi-hop transmission scheduling problem to minimizes the power consumption of UAVs without violating the given time constraint. We convert the initial formulation into a low-complex iterative algorithm, making it suitable for an online scheduling. Also, we propose a buffer prediction, and correction scheme to initiate the multi-hop transmission scheduling without having the perfect buffered data information. Evaluation results show that the proposed scheme can energy-efficiently schedule the multi-hop transmissions over dynamic UAVs without violating the time constraints. [ABSTRACT FROM AUTHOR]

Horizontal antenna sectorization has been used within all generations of cellular radio networks to improve both the coverage and capacity of such networks. This paper evaluates the potential coverage and capacity gains of sectorization through extensive simulation and real-world trials of deployments of higher order horizontal sectorization (three, six, nine, 12, and 15 sectors) when applied to a Third-Generation (3G) Evolved High-Speed Packet Access (\mbox3\mboxG/\mboxHSPA+) network. Simulation results are presented for idealized homogeneous networks based upon a standardized 3G Partnership Project HSPA/Long-Term Evolution (LTE) network model to find the theoretical downlink capacity gains and the optimum horizontal antenna beamwidth to maximize capacity without significantly reducing coverage and other cellular-network key performance indicators (KPIs). Further simulations have also been performed to assess the potential gain seen within Telefonica UK's central London \mbox3\mboxG/\mboxHSPA+ network, and these results have also been verified using live network field results from the deployment of six-sector sites into Telefonica UK's network. Finally, trial results from the deployment of what is believed to be the industry's first 15-sector 3G site are presented, showing further gains are possible well beyond the six sectors per site. [ABSTRACT FROM AUTHOR]

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]

Multiple-input multiple-output (MIMO) cooperation in cluster-to-cluster communication has shown improved network quality of services by utilizing less transmission power over the fading environment. This is an enhancement from the traditional cluster-based single-input single-output multi-hop relaying used in vehicular communications. In this paper, we deploy multi-hop MIMO clustering relay into vehicular communication for a two-lane road transportation scenario. We deploy precoder and receiver filter in each MIMO link that is characterized by a narrowband classical three-dimensional time-varying channel. With the aid of the precoder and minimum mean square error receiver filtering algorithm in MIMO communication, we derive the end-to-end network signal-to-noise ratio to find the optimal best path using max-min theory with equal power allocation in precoder matrices that minimizes the network mean square error. A low-cost close-optimal best path selection method is also proposed through mathematical modeling. Computer simulation results demonstrate the validity of the theoretical investigations in this work. [ABSTRACT FROM AUTHOR]

Computation offloading is a promising solution to extend the capacity of robot swarms for computation-intensive applications because it allows robot swarms to benefit from the powerful computing resources of modern data centers. However, the existing computation-offloading approaches still face challenges: 1) multi-hop cooperative computation offloading, 2) joint computation offloading and routing, and 3) task slicing. In this paper, we propose a quality of service (QoS)-aware cooperative computation-offloading scheme for robot swarms using game theory. We analyze the multi-hop cooperative communication model in robot swarms and investigate the computation offloading and routing decision-making problems with the goals of both latency minimization and energy efficiency. We formulate the joint optimization problem as a multi-hop cooperative computation-offloading game and show the existence of a Nash equilibrium (NE) of the game for both unsliceable and sliceable tasks. We further propose a QoS-aware distributed algorithm to attain an NE and provide an upper bound on the price of anarchy in the game. Finally, our simulated results show that our algorithm scales well as the swarm size increases and it has a stable performance gain in various parameter settings. [ABSTRACT FROM AUTHOR]

Batched sparse (BATS) codes are a promising technique for reliable data transmission in multihop wireless networks. A BATS code consists of an outer code and an inner code, the design of which can be separated. In this paper, we investigate the design of the inner code and focus on maximizing the expected batch transfer matrix rank normalized by the total number of packets transmitted by both the source and intermediate nodes. By allowing different recoding decisions at different nodes, the problem is formulated as a nonlinear integer programming (NLIP) problem, which is non-deterministic polynomial (NP)-hard in general. We derive a noniterative formula to simplify the evaluation of the expected batch transfer matrix rank. By considering large finite fields and relaxing the integer constraints, we obtain an upper bound on the optimal value of the original maximization NLIP problem. We also derive a centralized and a decentralized algorithm to find suboptimal solutions of the NLIP problem, with different tradeoffs between complexity and performance. Numerical results show that our proposed inner codes outperform the standard BATS, and achieve very close to the upper bound, which verifies the near optimality of our algorithms. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel routing technique for millimeter wave (mmWave) networks to improve the spectral efficiency. The performance of the proposed nth best relay routing technique is investigated using tools from stochastic geometry. First, we derive the probability density function (PDF) of the distance between the nth best relay and destination. Capitalizing on this result, we derive a closed-form expression of the coverage probability over the log-normal fading channels. Monte Carlo simulations show an accurate match with the analytical results. We further demonstrate that the coverage probability varies according to specific system parameters, such as density of relays, blockage density and the signal-to-noise ratio threshold. Furthermore, we show that the adaptive signal-to-noise ratio threshold plays an important role in improving the spectral efficiency for different relay density, blockage density and the order of best relay (n). These findings provide insights for designing multi-hop mmWave networks with better performance. [ABSTRACT FROM AUTHOR]

The fast proliferation of Internet of Things (IoT) exacerbates the current spectrum shortage. As a promising solution, licensed spectrum sharing has received great attentions recently. However, due to the unpredictable activities of incumbent users, the availability of the shared spectrum is uncertain, making the quality of service (QoS) provisioning based on it a difficult task, especially under multi-hop scenarios. In this paper, considering the energy-efficiency issue, we propose an end-to-end (E2E) QoS guaranteed green traffic off-loading scheme over the uncertain shared spectrums in multi-hop networks. Specifically, we formulate it into a two-step problem, an off-loaded traffic maximization (OTM) problem and an energy-efficiency improvement (EEI) problem. The former one is to determine the admitted sessions. To achieve the E2E QoS guarantee under the uncertain spectrum supply, we develop a concept of equivalent link capacity, and construct a risk-averse joint chance constraint. Since the formulated problem is intractable, we first develop a data-driven conservative transformation to make the joint chance constraint a set of deterministic individual ones. Then, we design a convex-hull-based and a substitution-based linearization approach to make all the constraints tractable. For the second step, the EEI problem with the same constraints as the OTM problem is designed to refine the resource scheduling for the admitted sessions to optimize the energy-efficiency. To deal with the fractional-form energy-efficiency objective, a Dinkelbach method based iterative algorithm is further developed. Numerical results have shown the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper addresses the formulation of power allocation for cluster based multihop vehicular relaying communications in order to improve the network quality-of-services (QoS). The cluster-to-cluster (C2C) channel is completely depend on the power gain of vehicle-to-vehicle (V2V) channel that increases the difficulties of the power allocation problem. To meet this goal, we have derived a global channel obtained by joint V2V and C2C cooperation. The most challenging aspect is however the joint V2V and C2C power allocation of the global channel due to the association of its multi-variables objective function. To solve this problem, we apply an alternative optimization technique to make the global problem into a series of sub-problems. We then apply a semi-definite programming (SDP)-based iterative gradient descent (SDP-IGD) power allocation to assign power in each relay. The SDP-IGD power allocation algorithm has been extended from Lagrange Multiplier (LM) that provides better performance than separate LM technique. The minimum mean-square error (MMSE)-decision feedback equalizer (MMSE-DFE) is designed at the receiver to improve the signal detection capability under exact channel state information (CSI) in all forward-and-backward links. Finally, simulation results confirm that our proposed solution performs significantly superior compared to other solutions found in the literature. [ABSTRACT FROM AUTHOR]

D2D communications are considered as effective means to achieve vehicle-to-vehicle (V2V) communications, which can be used to improve the performance in vehicular ad hoc networks (VANETs). In this paper, we investigate the resource allocation and interference management based on clustering mechanism in the D2D communications under-laying VANETs aiming to optimize resource utilization efficiency. Firstly, given the transmission resources of intra-cluster for D2D communications, we design a vehicle clustering algorithm to improve intra-cluster resource efficiency and nullify the intra-cluster interference. Secondly, by analyzing the wireless service in VANETs, a cooperative communication scheme with optimized resource utilization is proposed to maximize intra-cluster spectral efficiency. Thirdly, when uplink spectrums are shared, an interference neutralization (IN) model is developed to manage inter-cluster interference, while each vehicle is equipped with one antenna and there is no extra antenna for interference cancellation. In accordance with the IN model, a cross-layer optimization frame for multi-hop VANETs is proposed to maximize the end-to-end throughput of multiple coexisting communication sessions. To evaluate the performance, we select the method without cooperative communication and IN as a benchmark and compare it against the method with cooperative communication only and the method with both cooperative communication and IN. The simulation results show that the method that uses cooperative communication and IN can dramatically increase the throughput. Furthermore, the throughput gains increase along with vehicle density growing in VANETs. [ABSTRACT FROM AUTHOR]

Device-to-device (D2D) communication permits direct communication between devices, thereby it provides performance gain for traditional cellular networks. In this paper, we investigate how to improve the performance of D2D communication while satisfying the delay constraint for practical applications. Closed-form expressions are derived for trade-offs among system performance, such as successful transmission probability, transmission capacity, delay constraint, and energy consumption. In addition, two schemes are proposed to improve the performance for D2D communication under a given delay constraint. First, an optimal transmission scheme is proposed in which the transmission of user equipment (UE) can be scheduled adaptively to have the best successful transmission probability, whereas the D2D link satisfies the delay constraint. Second, a delay assignment scheme is proposed in which delay is adaptively assigned for each hop to achieve the maximum capacity when the network employs multihop D2D communication. Simulation results show that the adaptive transmission scheme improves the successful transmission probability (e.g., increased by 13 times when the source density is \text10^-4) compared with the fixed-probability transmission scheme, although it can satisfy the delay constraints for different applications. Furthermore, compared with the fixed delay assignment scheme, the network capacity can be improved up to 50% by the proposed scheme with proper delay assignment for each hop. [ABSTRACT FROM AUTHOR]

With the ever-increasing demands for local area services of popular content sharing, device-to-device (D2D) communication is conceived to be a key component of the next-generation cellular networks. D2D communications consume low energy and provide high capacity via proximity range transmissions, where multihop transmissions are needed for real-time content sharing. Aiming to solve the challenging problem for multihop D2D communication networks, existing studies only consider communication domain information to create long-range links (LLs) to reduce multihop transmission delay. In contrast, in this paper, we propose a novel social-community-aware LLs establishment strategy, which exploits the interplay between social network features and communication domain constraints. We first formulate the LLs establishment strategy as a cost-minimization problem and then propose an efficient greedy algorithm to solve the formulated problem, which is suitable for scenarios of both single-sink and distributed content sharing. To decrease the computational complexity, we model the optimization problem as a coalition graph game and propose a dynamic algorithm based on local best response and a near-optimal algorithm based on switching operation, which both run in the distributed approach. Numerical results demonstrate that our proposed solution decreases the average path length significantly with low computational complexity compared with other state-of-the-art schemes. [ABSTRACT FROM PUBLISHER]

In typical wireless networks, multihop communication is a method used to establish connectivity between distant nodes. Adapting this technique to vehicular networks requires bypassing several challenging constraints imposed by the nature of vehicular environments (e.g., high mobility and speeds and repetitive link disruptions). This paper revolves around establishing a multihop connectivity path between an isolated source vehicle $S$ and a faraway gateway roadside unit (RSU) $D$ through cooperative vehicles serving as intermediate relays. A stochastic model is formulated for the purpose of deriving an expression for the probability of the existence of a connectivity path between $S$ and $D$. Then, the dynamic changes in the network topology are carefully examined to present a tight upper bound for the average end-to-end packet delivery delay. Finally, taking into account the inherent contention-based nature of the employed IEEE 802.11p medium access control (MAC) protocol, together with several other limiting factors such as relay unavailability and hidden terminals, the per-hop and the end-to-end throughput expressions are presented. Extensive simulations are conducted for the purpose of validating the proposed model and examining the system's performance. [ABSTRACT FROM PUBLISHER]

In this paper, we consider random-access wireless multihop networks, with multipacket reception capabilities, where multiple flows are forwarded to the gateways through node disjoint paths. We explore the issue of allocating flow on multiple paths, exhibiting both intra- and interpath interference, in order to maximize average aggregate flow throughput (AAT) and provide bounded packet delay. A distributed flow allocation scheme is proposed where allocation of flow on paths is formulated as an optimization problem. Through an illustrative topology, it is shown that the corresponding problem is nonconvex. Furthermore, a simple but accurate model is employed for the AAT achieved by all flows, which captures both intra- and interpath interference through the signal-to-interference-plus-noise ratio (SINR) model. The proposed scheme is evaluated through Ns2 simulations of several random wireless scenarios. Simulation results reveal that the model employed accurately captures the AAT observed in the simulated scenarios, even when the assumption of saturated queues is removed. Simulation results also show that the proposed scheme achieves significantly higher AAT for the vast majority of the wireless scenarios explored than for the following flow allocation schemes: one that assigns flows on paths on a round-robin fashion, one that optimally utilizes the best path (BP) only, and another one that assigns the maximum possible flow on each path. Finally, a variant of the proposed scheme is explored, where interference for each link is approximated by considering its dominant interfering nodes only. [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]

Radio Frequency jamming attacks constitute a major threat to the availability of the vehicular networks. In particular, if the control channel is under persistent jamming attacks, the victim vehicles may fail to receive the safety related messages from the Road Side Unit, which can possibly cause tremendous economic loss and claim human lives. In this paper, we propose a cooperative relaying scheme to circumvent the control channel jamming problem in the vehicular networks, whereby the vehicles outside of the jamming area serve as relays to help forward the received control channel signal to the victim vehicles through another jamming-free service channel. By combining the signals from all relays using the selection combining or maximum-ratio combining methods, the spatial diversity provided by the relays can be effectively exploited to reduce the outage probability of the victim vehicles. Theoretical models are developed to characterize the performance of this cooperative antijamming relaying scheme, which take into account both the large-scale path loss and small-scale channel fading between relaying and victim vehicles under different jamming scenarios. We also propose a relay selection scheme to optimize the performance of the victim vehicles under the relay number constraint. Simulation results are provided to show the performance of the proposed cooperative relaying scheme and relay selection algorithm under different network settings. [ABSTRACT FROM AUTHOR]

The optimum designs of multihop networks operating in an interference-limited environment are studied in this paper. The objective is to identify the optimum operation parameters that can maximize the end-to-end throughput of a multihop link in the network. The optimum designs are performed with respect to two parameters, the number of hops, and the signal-to-interference ratio (SIR) threshold for successful transmission. Under a fixed total transmission power, more hops means shorter distance for each hop, but also less power per hop and longer delays. A higher SIR threshold can achieve a higher throughput by employing high-order modulations, but at the cost of a higher outage probability. We capture these tradeoff relationships by deriving the throughput, which is expressed as an explicit function of a number of system parameters. It is shown through theoretical analysis that the throughput is quasi-concave in the number of hops or the SIR threshold, and the optimum design parameters that can maximize the throughput are obtained analytically and verified through simulations. [ABSTRACT FROM AUTHOR]

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]

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]

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]

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]

In this paper, we examine the problem of designing and allocating transmission sequences to users in a mobile ad hoc network that has no spatial boundary. A basic tenet of the transmission sequence approach for addressing media access control (MAC) is that under normal operating conditions, there is no feedback-triggered retransmission. This obviously is a major departure from the Slotted-ALOHA or carrier-sense multiple-access (CSMA)-type approaches. While these traditional solutions enjoy excellent throughput performance, a fundamental drawback is that they are based on feedback information. For systems without a naturally defined central controller that can play the role of a base station, the task of providing feedback information could easily become unmanageable. This highlights the advantage of the feedback-free approach. A second advantage is the ability to handle unlimited spatial coverage. We propose in this paper a concept for MAC that is akin to frequency reuse. However, instead of reusing frequency, the new approach allows transmission sequences to be reused. A study of the transmission sequence approach against other approaches is conducted by comparing the minimal frame lengths that can guarantee the existence of conflict-free transmissions. [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]

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]

In cloud radio access networks (C-RANs), the baseband processing of radio units (RUs) is migrated to remote control units (CUs). This is made possible by a network of backhaul links that connect RUs and CUs and that carry compressed baseband signals. While prior work has focused mostly on single-hop backhaul networks, this paper investigates efficient backhaul compression strategies for the uplink of C-RANs with a general multihop backhaul topology. A baseline multiplex-and-forward (MF) scheme is first studied, in which each RU forwards the bit streams received from the connected RUs with no processing. It is observed that this strategy may cause significant performance degradation in the presence of a dense deployment of RUs with a well-connected backhaul network. To obviate this problem, a scheme is proposed in which each RU decompresses the received bit streams and performs linear in-network processing of the decompressed signals. For both the MF and the decompress-process-and-recompress (DPR) backhaul schemes, the optimal design is addressed with the aim of maximizing the sum rate under backhaul capacity constraints. Recognizing the significant demands of the optimal solution of the DPR scheme in terms of channel state information (CSI) at the RUs, decentralized optimization algorithms are proposed under the assumption of limited CSI at the RUs. Numerical results are provided to compare the performance of the MF and DPR schemes, highlighting the potential advantage of in-network processing and the impact of CSI limitations. [ABSTRACT FROM AUTHOR]

Device-to-device (D2D) communications are usually considered to be two user equipment units (UEs) communicating directly without going through the central base station (BS). In fact, they can be further broadened to multihop D2D communications in which a UE may help other UEs communicate with each other or assist other UEs to communicate with the BS. In this paper, we investigate a scenario of multihop D2D communications where one UE may help other two UEs to exchange information with a two-time-slot physical-layer network coding scheme. We analyze the average energy efficiency and spectral efficiency of multihop D2D communications under Rayleigh fading channels and get close analytical approximations based on Taylor series expansion. Comparisons with direct D2D communications and traditional cellular communications through BS are provided. The optimal UE transmission powers of these three different modes to maximize the energy efficiency are also derived. [ABSTRACT FROM PUBLISHER]

Due to the unique physical-layer characteristics associated with multiple-input multiple-output (MIMO) and cognitive radio (CR), the network performance is tightly coupled with mechanisms at the physical, link, network, and transport layers. In this paper, we consider an energy-efficient cross-layer optimization problem in multihop MIMO CR networks (CRNs) and provide a new formulation to balance the weighted network utility and the weighted power consumption of secondary users (SUs), with the minimum transmission rate constraint of primary users (PUs) and the SU power consumption constraint. However, this formulation is highly challenging due to the nonconvexity of the PU rate constraint. We propose a solution that features a linearization-based alternative optimization method and a heuristic primal recovery method. We further develop a distributed algorithm to jointly optimize the covariance matrix of the transmitted signal vector at each SU node, bandwidth allocation at each SU link, rate control at each session source, and multihop/multipath routing. Extensive simulation results demonstrate that the performance of the proposed distributed algorithm is very close to that of the centralized algorithm, and the proposed formulation provides an efficient way to save power consumption significantly, while achieving the network utility very close to that achieved with full power consumption. [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]

In this paper, we first develop an analytical framework for the total energy consumption of an amplify-and-forward (AF) multihop network employing M-ary quadrature amplitude modulation (MQAM) while satisfying an average bit error rate (BER) requirement at the destination over Rayleigh fading channels. Based on this framework, we then establish the conditions under which a dual-hop relay network is always more energy efficient when compared with a reference single-hop network. Moreover, the impact of the relay's location and the energy resource allocation between the relay and the source on the possible energy savings is also analyzed. Since a realistic power consumption model is considered, it is shown that there exists an optimal number of relays for the linear multihop relay network and that the maximum energy efficiency (EE) is obtained through the joint optimization of the number of relays and the constellation size. Considering this fact, we first formulate the optimization problem, and then, this problem is transformed into a convex form by relaxing constraints to be defined over the real numbers (instead of taking only discrete values). The new closed-form optimal solution that involves only elementary functions is derived for this relaxed problem. It is also demonstrated that the optimized multihop network has the potential not only to reduce the total energy consumption but to satisfy the peak-power constraint simultaneously at the expense of more delay as well. Finally, our analysis shows that significant energy savings are possible through joint optimization not only for delay-tolerant networks but for delay-limited networks as well, and up to about 55% energy savings are achievable over the optimized single-hop system. [ABSTRACT FROM PUBLISHER]

Network coding schemes have recently been used for error control when communicating over lossy channels. However, there does not exist congestion control mechanisms in the literature that are specifically tailored for these coding techniques. This paper, for the first time, proposes Trickle, a lightweight and practical congestion control framework that is customized to meet the needs of coding. Trickle is designed based on the principle of back pressure, and maintains a novel triple-node indexed queueing structure at each node. As compared to existing back pressure protocols with perdestination or perlink queues, Trickle uses significantly fewer queues, and is thus more scalable to larger networks. Our experimental results have shown that Trickle achieves much higher throughput than IEEE 802.11b for fountain codes, network coding, as well as noncoded TCP in multihop wireless networks. [ABSTRACT FROM AUTHOR]

Multihop relaying is used for increasing the communication range of cognitive radio networks. To circumvent the implied loss in throughput due to multihop relaying, in this paper, we propose incremental relaying (IR) for cooperative multihop cognitive radio networks (CMHCRNs). Two IR protocols that select a relay from the qualified relays (the relays whose received signal-to-noise-ratio (SNR) values are greater than a predefined threshold) in each hop are proposed to study the performance of the considered CMHCRN. The first protocol is named IR-based highest SNR (IR-HSNR) protocol that selects a relay with best SNR to the destination. Another one, termed IR-based highest transmit power (IR-HTP) protocol, selects a relay with the highest available transmit power. Expressions for the exact outage probability and throughput are derived for both routing protocols by considering both peak–power and peak–interference constraints. Moreover, closed-form expressions for floor values of outage probability and throughput are derived for both the protocols. It is shown through numerical results that throughput of the considered system shows a concave behavior with respect to number of relaying hops for both the proposed protocols. It is further observed that the performance of the IR-HSNR is superior to that of the IR-HTP, whereas the latter has lower implementation complexity. [ABSTRACT FROM AUTHOR]

In this paper, two-stage random-access-based massive Internet-of-things uplink transmission is investigated. In this scheme, aggregator nodes are additionally deployed to relay packets to deal with a massive number of arrivals. A user node determines whether to utilize aggregator nodes according to the received signal strength from base stations and aggregator nodes. If the user node selects and transmits a packet to an aggregator node, the aggregator node stores and forwards the received packet to the base station. The use of aggregator nodes can reduce the per-hop delay as well as the user energy consumption by reducing the transmission distance from user nodes. However, in the two-stage random access protocol, an increase in the number of aggregator nodes incurs collisions in the wireless medium, and hence, increases the queueing delay at the aggregator node. Thus, improved radio resource allocation and network design are required to reduce additional delay in the two-hop uplink system. We, therefore, focus on optimizing the transmission probabilities of transmitting nodes and the aggregator node density to minimize the delay in two-stage random access networks. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the performance of tactical radio networks, particularly for communication scenarios where multihop relaying along with spatial reuse techniques are applied. The tactical scenarios of concern have a diverse range of reliability and/or delay requirements. We first employ cross-layer protocol architecture with integrated time-division-multiple-access-based fast packet forwarding and automatic-repeat-request-based multihop error control to support tactical applications with a diverse range of reliability and/or delay requirements. Then, we develop analytical models to study the link-level and network-wide behaviors of the tactical radio networks. The developed models capture the effects of end-to-end channel memory due to multihop relays, interference due to spatial reuse, uneven interslot delays due to fast packet forwarding, and jamming attack in hostile network environment. It is shown that the protocol architecture with proposed fast packet forwarding and multihop error control mechanisms can significantly improve communication performance and support delay-sensitive applications. In addition, it is demonstrated that cross-layer adaptivity, where different network environments require different logical topologies and radio modes, is needed to achieve best performance tradeoffs among throughput, efficiency, delivery ratio, and transport capacity. [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]