Distributed Wireless Networks Research Articles

A Preamble Pattern Identification based Synchronization System for UWB-based Wireless Networks

In this paper, we address a preamble pattern identification based synchronization system for UWB-based distributed wireless networks. A correlation based preamble pattern identification method is introduced. A network domain division and nodes tree setting approach according to the principle of Voronoi diagram is proposed and discussed. Therefore, synchronization concluding not only synchronization between transmitter and receiver, but also clock drift synchronization for an entire distributed wireless networks is available. Simulation results demonstrate the relationship between preamble patterns and correlation outcomes. Meanwhile, a model nodes tree is simulated for UWB-based distributed wireless networks.

Carrier sense multiple access with improvised collision avoidance and short-term fairness

In this paper, we present a simple method to simultaneously enhance collision avoidance efficiency and short-term fairness of a most popular contention based medium access control protocol, carrier sense multiple access with collision avoidance. The key idea here is to adaptively tune the shape of contention slot selection distribution over the temporal contention window during ongoing collision resolution process which, in the legacy scheme, used to be flat throughout. The tuning mechanism is such designed that it not only maximizes the selection likelihood of relatively less collision prone contention slots over the contention window but also compensates the idle delay that the contending stations have suffered in their recent access attempt. Through rigorous numerical and simulation based analysis, the proposed scheme is shown to enhance the performance of a IEEE 802.11 based distributed wireless network in terms of network throughput efficiency and packet transmission delay while allowing individual stations to share the channel fairly even in short time scale.

Link-Stability and Energy Aware Routing Protocol in Distributed Wireless Networks

Energy awareness for computation and protocol management is becoming a crucial factor in the design of protocols and algorithms. On the other hand, in order to support node mobility, scalable routing strategies have been designed and these protocols try to consider the path duration in order to respect some QoS constraints and to reduce the route discovery procedures. Often energy saving and path duration and stability can be two contrasting efforts and trying to satisfy both of them can be very difficult. In this paper, a novel routing strategy is proposed. This proposed approach tries to account for link stability and for minimum drain rate energy consumption. In order to verify the correctness of the proposed solution a biobjective optimization formulation has been designed and a novel routing protocol called Link-stAbility and Energy aware Routing protocols (LAER) is proposed. This novel routing scheme has been compared with other three protocols: PERRA, GPSR, and E-GPSR. The protocol performance has been evaluated in terms of Data Packet Delivery Ratio, Normalized Control Overhead, Link duration, Nodes lifetime, and Average energy consumption.

On the Delay-Throughput Tradeoff in Distributed Wireless Networks

This paper deals with the delay-throughput analysis of a single-hop wireless network with $n$ transmitter/receiver pairs. All channels are assumed to be block Rayleigh fading with shadowing, described by parameters $(\alpha,\varpi)$, where $\alpha$ denotes the probability of shadowing and $\varpi$ represents the average cross-link gains. The analysis relies on the distributed on-off power allocation strategy (i.e., links with a direct channel gain above a certain threshold transmit at full power and the rest remain silent) for the deterministic and stochastic packet arrival processes. It is also assumed that each transmitter has a buffer size of one packet and dropping occurs once a packet arrives in the buffer while the previous packet has not been served. In the first part of the paper, we define a new notion of performance in the network, called effective throughput, which captures the effect of arrival process in the network throughput, and maximize it for different cases of packet arrival process. It is proved that the effective throughput of the network asymptotically scales as $\frac{\log n}{\hat{\alpha}}$, with $\hat{\alpha} \triangleq \alpha \varpi$, regardless of the packet arrival process. In the second part of the paper, we present the delay characteristics of the underlying network in terms of the packet dropping probability. We derive the sufficient conditions in the asymptotic case of $n \to \infty$ such that the packet dropping probability tend to zero, while achieving the maximum effective throughput of the network. Finally, we study the trade-off between the effective throughput, delay, and packet dropping probability of the network for different packet arrival processes.

Cooperative MIMO multicell networks

Recently, the pressing desire to provide cost-effective solutions aimed at supporting high-throughput broadband wireless access with large-scale coverage has significantly changed the notion of the traditional cellular systems. Physical layer cooperation serves as an enabling technology for such a change. In latest cellular networks, neighboring infrastructure stations, such as base stations (BSs) or relay stations (RSs), share their communication resources to create virtual multiple-input multiple-output (MIMO) systems by means of distributed transmission and signal processing. Cooperative processing at the BSs promises to exceed the limits on spectral efficiency imposed by inter-cell interference, thereby allowing ever more aggressive frequency reuse patterns. On the other hand, cooperation between BSs and RSs, as well as among RSs, is expected to extend coverage and capacity of point-to-multipoint links between BSs and mobile stations in a highly economical fashion. However, to achieve such benefits in practice, numerous research challenges have to be still tackled. This special issue has come up with the intention of collecting cutting-edge research achievements in cooperative MIMO multicell systems. For this special issue, we have received 35 manuscript submissions altogether. After a careful review process, 10 manuscripts have been accepted for publication, which cover the following topics for cooperative MIMO multicell networks: channel modeling, power control and scheduling, interference management, protocol design and performance analysis, cost deployment, simulation tools and testbeds. A brief introduction of all the accepted manuscripts is reported in the following. In the manuscript “A Geometrical Three-Ring-Based Model for MIMO Mobile-to-Mobile Fading Channels in Cooperative Networks” by Talha and Patzold [1], a stochastic narrowband MIMO mobile-to-mobile reference channel model is derived in relay-based cooperative networks and exact closed-form expressions for different correlation functions are provided, under isotropic as well as non-isotropic scattering conditions. A stochastic simulation model is drawn from the reference model. It is shown that the cross-correlation functions of the simulation model closely approximate the corresponding ones of the reference model. In the article “Adaptive Coordinated Reception for Multicell MIMO Uplink” by Lu et al. [2], power control and receive beamforming are jointly optimized with adaptive selection of multiple BSs to minimize the total transmit power, under individual signal-to-interferenceplus-noise ratio constraint per mobile station. To reduce the complexity in the large-scale cellular network, a suboptimal algorithm is derived, which exhibits a good trade-off between performance and complexity if the number of the pre-selected BSs is carefully chosen. In the article “Virtual Cooperation for Throughput Maximization in Distributed Large-Scale Wireless Networks” by Abouei et al. [3], a distributed wireless network with K links is con-sidered, where the links are partitioned into M clusters each operating in a subchannel with bandwidth W/M. The power allocation and number of clusters of such a network are optimized for maximization of the throughput as the number of links approaches infinity. In the article “Distributed Cooperative Precoding with Power Control for Cellular Systems with Correlated Antennas at the Receiver” by Vinosh Babu James et al. [4], the authors consider an analytical model for a multicell and multiuser system with receiver-side correlation. A distributed protocol for cooperation amongst the BSs is also proposed. System performance gains measured in terms of mean and cell-edge spectral efficiency values are reported. In the article “Multimode Transmission in Network MIMO Downlink with Incomplete CSI” by Seifi et al. [5], a two-step scheduling algorithm for a cooperative multicell MIMO downlink is proposed: in the first step, joint user and mode selection is performed, whereas, in the second step, feedback and precoder design is carried out by only considering the users selected in the first step. The metric used to perform user and mode * Correspondence: f.verde@unina.it Department of Biomedical, Electronic and Telecommunication Engineering (DIBET), University of Naples Federico II, Naples, Italy Full list of author information is available at the end of the article Verde et al. EURASIP Journal on Advances in Signal Processing 2012, 2012:41 http://asp.eurasipjournals.com/content/2012/1/41

Optimal distributed interference avoidance: potential game and learning

ABSTRACTThis article studies the problem of distributed interference avoidance (IA) through channel selection for distributed wireless networks, where mutual interference only occurs among nearby users. First, an interference graph is used to characterise the limited range of interference, and then the distributed IA problem is formulated as a graph colouring problem. Because solving the graph colouring problem is non‐deterministic polynomial hard even in a centralised manner, the task of obtaining the optimal channel selection profile distributively is challenging. We formulate this problem as a channel selection game, which is proved to be an exact potential game with the weighted aggregate interference serving as the potential function. On the basis of this, a distributed learning algorithm is proposed to achieve the optimal channel selection profile that constitutes an optimal Nash equilibrium point of the channel selection game. The proposed learning algorithm is fully distributed because it needs information about neither the network topology nor the actions and the experienced interference of others. Simulation results show that the proposed potential game theoretic IA algorithm outperforms the existing algorithm because it minimises the aggregate weighted interference and achieves higher network rate. Copyright © 2012 John Wiley & Sons, Ltd.

Access Control Scheme Adapted to Topology Changes for Multi-hop Distributed Wireless Networks

A multi-hop distributed wireless network can provide a rapidly deployable, mobile communication infrastructure that is suitable for many scenarios of topology changes. In this paper, a new access control scheme which is composed of the coordinated distributed scheduling and multi-path routing protocol is proposed for distributed wireless networks. In which, cross-layer design and some metrics such as priority and staying time are introduced in order to meet different QoS demands and maintain scheduling fairness, and then the optimal and sub-optimal routes are selected in term of the minimum SNR and delay. The simulation results show that the proposed scheme can improve the throughput, reduce the transmission delay, guarantee the system fairness and adapt to topology changes.

Preemptive emergency medium access for wireless sensor networks: performance under realistic network conditions

The proliferation of Wireless Sensor Network (WSN) deployment in threat monitoring applications requires support for emergency–class services with tight Quality–of–Service (QoS) bounds. The CP–EDCA protocol was designed to achieve deterministic delay bounds for emergency–class traffic during distributed wireless network operation. The CP–EDCA scheme could be an ideal choice for prioritised channel access in WSNs, if the performance is demonstrated to be effective under WSN conditions. Here, we evaluate the effectiveness of CP–EDCA protocol under erroneous channel conditions and multi–hop data flow scenarios, which are distinctive features of WSNs. Mathematical and simulation analysis depicts that under typical WSN conditions, distributed preemptions accomplish deterministic delay bounds for emergency traffic even with heavy network loads. Under severe packet losses, CP–EDCA depicted perceivable improvements, relative to IEEE 802.11e standards. Analysis in multi–hop scenarios validates that the channel access preemptions have a significant impact on the end–to–end data flow performance.

Stochastic Modeling of Hello Flooding in Slotted CSMA/CA Wireless Sensor Networks

Broadcasting a request or challenge is a classic method of collecting local information in distributed wireless networks. Neighbor discovery is known to be a fundamental element in ad hoc and sensor networks topology formation, which takes advantage of such methods. Most of the current neighbor discovery protocols rely on a challenge or request broadcast by the discovering node called “Hello.” Hello flooding attack was specifically designed to exploit the broadcasting nature of these protocols in order to convince a large group of nodes that the sender is their neighbor by using very high transmission power. Several studies have been done to mitigate the effectiveness of the flooding threats but little effort has been made in modeling and analyzing this problem. Arguing that random channel access protocols must be inevitably employed in neighbor discovery, we propose an analytical approach for stochastic modeling of the challenge-broadcasting scenarios in networks using slotted carrier sense multiple access with collision avoidance (CSMA/CA) protocols. We model the nonstationary channel right after issuance of the request by a recursive method and then put forward an approach to find the broadcaster's approximate payoff. The model also supports the cases where the broadcaster is a malicious node with an abnormally high transmission and reception range, which is found in severe flooding attacks. We investigate the applications of the model in finding the optimal attack range for the flooding adversaries and deriving a flood-resilient medium access control (MAC) protocol design framework to increase the security of challenge-response protocols. The latter one is especially relevant to mobile networks as it provides a low-cost solution. This paper describes the detailed analysis of the proposed theoretical framework as well as the comprehensive evaluations that have been carried out via simulations.

Distributed Frequency-Locked Loops for Wireless Networks

The establishment of a common frequency reference in a distributed wireless network is a critical factor in enabling any degree of node cooperation in communication and sensing functions. In this paper we introduce Distributed Frequency-Locked Loops (D-FLL's) to control the carrier frequencies of autonomous nodes with wireless communication capabilities. A novel frequency difference detector (FDD) is introduced allowing each node to estimate the frequency difference with respect to the ensemble of its neighbors. D-FLL's are characterized in terms of stability and tracking accuracy when the synchronization network has a peer-to-peer (mutually coupled - MC) or hierarchical (master slave - MS) topology. In particular, synchronization error accumulates in MS architectures as the distance from the reference node increases. MC architectures, instead, trade slower convergence times for a smoother error distribution. Overall, D-FLL's prove to be a robust and accurate technique for carrier frequency synchronization purposes that can be readily employed with any network architecture.

A game‐theoretic approach for relay assignment over distributed wireless networks

ABSTRACTFor full cooperative diversity gains to be achieved while still maintaining spectral and energy efficiency, relay assignment schemes for cooperative communications have been extensively studied in recent research. These schemes select only the best relay from multiple relaying candidates to cooperate with a communication link. However, it is challenging to find the optimal relay in distributed wireless networks because of the dynamic nature of such networks. In this paper, we first formulate the problem of relay assignment as a noncooperative, mixed‐strategy, repeated game, where relaying candidates are modeled as rational players. We then propose a game‐theory‐based relay assignment scheme GTRA, in which each player plays against all the other players and determines whether to cooperate with a communication link on a packet‐by‐packet basis in a distributed manner. To adapt to dynamic environments, players utilized an adaptive learning algorithm, that is, modified‐regret‐matching algorithm, to learn optimal strategies of relay assignment, as well as to orient the game to converge to a set of correlated equilibriums, which is often more system efficient than a Nash equilibrium. To evaluate the performance of GTRA, we compare it with BR, a fictitious two‐player game‐based approach. Simulation results have shown that GTRA outperforms BR in terms of network throughput, especially in environments where the channel fading becomes severe. It is also shown that GTRA can converge to a correlated equilibrium in a short period that enables the GTRA to work well in dynamic environments. Copyright © 2011 John Wiley & Sons, Ltd.

무선 환경의 네트워크에서 랜덤 선형 네트워크 코딩 적용 성능 분석

최근 무선 환경에서 네트워크 효율성 증대를 위하여 네트워크 코딩에 대한 연구들이 많이 진행되고 있다. 본 논문에서는 무선 환경에서 RLNC를 적용하기 위한 고려사항들을 분석해 본다. 우선 기존의 멀티캐스트에서 사용하는 방식으로 우선 분산 환경에 RLNC에 적용 가능한지 살펴보았다. 시뮬레이션 결과 멀티캐스트에서 사용하는 방식대로 적용한 RLNC에서는 디코딩 실패가 발생하였고, X 구조에서 인코딩과 디코딩을 모두 수행하여 디코딩 실패를 제거한 RLNC는 전송 이득이 많지 않았다. 또한 본 논문에서는 hidden 노드 문제, 코딩 기회 분석, RLNC 오버헤드 등의 무선 환경에서 실제적인 고려사항을 분석해 보았다. Recently, studies for the network coding in the wireless network to achieve improvement of the network capacity are conducted. In this paper, we analysis considerations to apply RLNC in the wireless network. First of all, we verify whether the RLNC method in multicast is applied to distributed wireless network. In simulation results, the decoding failure can occur in the original manner of multicast. In RLNC which conducts encoding and decoding in X topology to gets rid of the decoding failure, the RLNC gain is insignificant. In this paper we also discuss considerations such as the hidden node problem, the occurrence of coding opportunity, and the RLNC overhead which are practical issues in the wireless network.

Multi-Robot Control System Based on Wireless Network

A designed network control system of multi mobile robot is presented. It is based on wireless distribution system. One or more mobile robot and some other devices are connected via wireless network to form a network control system. More than one wireless node is provided in order to realize distribution wireless network and extend the coverage range. The hierarchy control structure is used in the robot control system. It is optimized by the features of the network control system especially in time delay. By testing the time delay in different network environment, the performance of the whole control system can be proved.

Coordinating Interfering Transmissions in Cooperative Wireless LANs

In this paper we present a cooperative medium access control (MAC) protocol that is designed for a physical layer that can decode interfering transmissions in distributed wireless networks. The proposed protocol pro-actively enforces two independent packet transmissions to interfere in a controlled and cooperative manner. The protocol ensures that when a node desires to transmit a unicast packet, regardless of the destination, it coordinates with minimal overhead with relay nodes in order to concurrently transmit over the wireless channel with a third node. The relay is responsible for allowing packets from the two selected nodes to interfere only when the desired packets can be decoded at the appropriate destinations and increase the sum-rate of the cooperative transmission. In case this is not feasible, classic cooperative or direct transmission is adopted. To enable distributed, uncoordinated, and adaptive operation of the protocol, a relay selection mechanism is introduced so that the optimal relay is selected dynamically and depending on the channel conditions. The most important advantage of the protocol is that interfering transmissions can originate from completely independent unicast transmissions from two senders. We present simulation results that validate the efficacy of our proposed scheme in terms of throughput and delay.

Cross-Layer Cooperative MAC Protocol in Distributed Wireless Networks

In this paper, we study medium access control (MAC) protocol design for distributed cooperative wireless networks. We focus on beneficial node cooperation by addressing two fundamental issues of cooperative communications, namely when to cooperate and whom to cooperate with, from a cross-layer protocol design perspective. In the protocol design, taking account of protocol overhead we explore a concept of cooperation region, whereby beneficial cooperative transmissions can be identified. We show that a rate allocation in the cooperation region provides higher link utilization than in a non-cooperation region. To increase network throughput, we propose an optimal grouping strategy for efficient helper node selection, and devise a greedy algorithm for MAC protocol refinement. Analysis of a successful transmission probability with cooperative or direct transmission is presented. Simulation results show that the proposed approach can effectively exploit beneficial cooperation, thereby improving system performance. Further, analytical and simulation results shed some light on the tradeoff between multi-user diversity gain at the physical layer and the helper contention overhead at the MAC layer.

Improving the Performance of Wireless Ad Hoc Networks Through MAC Layer Design

In this paper, the performance of the ALOHA and CSMA MAC protocols are analyzed in spatially distributed wireless networks. The main system objective is correct reception of packets, and thus the analysis is performed in terms of outage probability. In our network model, packets belonging to specific transmitters arrive randomly in space and time according to a 3-D Poisson point process, and are then transmitted to their intended destinations using a fully-distributed MAC protocol. A packet transmission is considered successful if the received SINR is above a predefined threshold for the duration of the packet. Accurate bounds on the outage probabilities are derived as a function of the transmitter density, the number of backoffs and retransmissions, and in the case of CSMA, also the sensing threshold. The analytical expressions are validated with simulation results. For continuous-time transmissions, CSMA with receiver sensing (which involves adding a feedback channel to the conventional CSMA protocol) is shown to yield the best performance. Moreover, the sensing threshold of CSMA is optimized. It is shown that introducing sensing for lower densities (i.e., in sparse networks) is not beneficial, while for higher densities (i.e., in dense networks), using an optimized sensing threshold provides significant gain.

WEB2.0 TECHNOLOGY FOR AN EMBEDDED WEB-BASED GATEWAY PLATFORM FOR SPATIALLY DISTRIBUTED WIRELESS NETWORKS

A novel communication platform is presented, which helps in the monitoring and deployment of distributed wireless networks. Its major part is based on distributed embedded web servers connected to RF-communication heads. The web servers act as distributed communication hubs and exchange data via XML-feeds with web2.0-capable clients. The first implementations are concentrating on the monitoring direction, as this approach eases supervision of spatially distributed wireless networks, and also allows seamless remote monitoring. But it is also capable to feed data frames into the wireless network. The platform already supports protocols like Wireless M-Bus and EnOcean Radio Protocol (ERP), but is flexible to integrate arbitrary protocols. In addition, this is - to the very best knowledge of the authors - the very first AJAX implementation on a very lean embedded web server.

Virtual Cooperation for Throughput Maximization in Distributed Large-Scale Wireless Networks

A distributed wireless network with links is considered, where the links are partitioned into clusters each operating in a subchannel with bandwidth . The subchannels are assumed to be orthogonal to each other. A general shadow-fading model described by the probability of shadowing and the average cross-link gains is considered. The main goal is to find the maximum network throughput in the asymptotic regime of , which is achieved by: (i) proposing a distributed power allocation strategy, where the objective of each user is to maximize its best estimate (based on its local information) of the average network throughput and (ii) choosing the optimum value for . In the first part, the network throughput is defined as the average sum-rate of the network, which is shown to scale as . It is proved that the optimum power allocation strategy for each user for large is a threshold-based on-off scheme. In the second part, the network throughput is defined as the guaranteed sum-rate, when the outage probability approaches zero. It is demonstrated that the on-off power scheme maximizes the throughput, which scales as . Moreover, the optimum spectrum sharing for maximizing the average sum-rate and the guaranteed sum-rate is achieved at .

Cooperative Protocol for Analog Network Coding in Distributed Wireless Networks

The concept of analog network coding (ANC) considers the concurrent transmission of signals over the wireless medium so that they intentionally interfere. Higher network throughput can be achieved with ANC when an intended transmission that a receiver desires to receive is made to interfere with a concurrent transmission of a signal known a priori at the receiver. In this paper, we present a cooperative protocol that exploits ANC. We consider a system with cooperative relaying of overlapped transmissions from two independent users. More specifically, we explore the case that network nodes may allow the transmitted signals to interfere both at the final destination node, and also at an intermediate node that acts subsequently as a relay. The relay employs a cooperative and multicast amplify-and-forward protocol so that the two destinations can use the interfered signals in order to recover the desired packet. We analyze this protocol in terms of the achieved rate and present an algorithm to recover signals from the overlapped transmissions. We study the impact of overlapping in signal transmissions on the throughput of the system. We show that even with considerable overlapping, the throughput under the proposed protocol is better in comparison to an orthogonal amplify-and-forward protocol.

Distributed Reinforcement Learning Frameworks for Cooperative Retransmission in Wireless Networks

We address the problem of cooperative retransmission in the media access control (MAC) layer of a distributed wireless network with spatial reuse, where there can be multiple concurrent transmissions from the source and relay nodes. We propose a novel Markov decision process (MDP) framework for adjusting the transmission powers and transmission probabilities in the source and relay nodes to achieve the highest network throughput per unit of consumed energy. We also propose distributed methods that avoid solving a centralized MDP model with a large number of states by employing model-free reinforcement learning (RL) algorithms. We show the convergence to a local solution and compute a lower bound for the performance of the proposed RL algorithms. We further empirically confirm that the proposed learning schemes are robust to collisions and are scalable with regard to the network size and can provide significant cooperative diversity while enjoying low complexity and fast convergence.