Showing papers presented at "IFIP Wireless Days in 2009"

eOCSA: An algorithm for burst mapping with strict QoS requirements in IEEE 802.16e Mobile WiMAX networks

Abstract: Mobile WiMAX systems based on the IEEE 802.16e standard require all downlink allocations to be mapped to a rectangular region in the two dimensional subcarrier-time map. Many published resource allocation schemes ignore this requirement. It is possible that the allocations when mapped to rectangular regions may exceed the capacity of the downlink frame, and the QoS of some flows may be violated. The rectangle mapping problem is a variation of the bin or strip packing problem, which is known to be NP-complete. In a previous paper, an algorithm called OCSA (One Column Striping with non-increasing Area first mapping) for rectangular mapping was introduced. In this paper, we propose an enhanced version of the algorithm. Similar to OCSA, the enhanced algorithm is also simple and fast to implement; however, eOCSA considers the allocation of an additional resource to ensure the QoS. eOCSA also avoids an enumeration process and so lowers the complexity to O(n2).

Data dissemination strategies in mobile sink Wireless Sensor Networks: A survey

Abstract: Mobile sink Wireless Sensor Network (MSWSN) has recently received a lot of attention from the research community. Its appealing characteristics of providing longer network lifetimes, delay optimizations and the flexibility to adapt dissemination strategies according to applications' requirements have proved to be more efficient. Numerous mobile sink based data dissemination strategies have been proposed. This work presents state of the art literature review on MSWSN data dissemination strategies. Issues and flexibilities that did not exist with static sink WSN have been discussed. A classification of available data dissemination strategies and their pros and cons has been discussed.

Redeploying mobile wireless sensor networks with virtual forces

Abstract: Wireless Sensor Networks should be self-organized to enhance the coverage after an initial random deployment. Virtual Forces Algorithm, VFA, is one of the most efficient algorithms proposed in the literature. Simulation results prove that the use of this algorithm does not achieve full coverage and connectivity in some cases, even when the number of sensors is sufficient. Because of that, our contribution is to propose some improvement to ensure coverage, connectivity and fault-tolerance, while saving energy. Our final proposed version Dth_Lmax_Serialized_V FA achieves the performance criteria previously cited by serializing and limiting nodes moves as well as increasing the robustness degree.

Distributed gradient optimization for epidemic routing: A preliminary evaluation

Abstract: In this paper we address the problem of designing adaptive epidemic-style forwarding mechanisms for message delivery in Delay Tolerant Networks. Our approach is based on a new analytical framework for multi-agent optimization through distributed subgradient methods. We investigate how this framework can be adapted to the considered networking problem and perform a preliminary evaluation, which shows promising results in terms of convergence speed.

Cooperative beamforming in Cognitive Radio networks

Abstract: In this paper, the problem of cooperative beamforming is investigated in a heterogeneous underlay cognitive network. A major difference exists between a conventional cooperative beamforming problem and cooperative beamforming in a CR (Cognitive Radio)network due to the interference constraints imposed by primary network. These constraints can greatly icrease the complexity of the related optimization problem and make it much more challenging. Here, we have assumed a typical CR network where a set of cognitive relay nodes collaboratively assist the secondary transmitter to relay its message signal to the destination in the presence of a primary transmitter-receiver pair. Each relay employs the Amplify-and-Forward (AF) protocol to retransmit the signal. In fact, the relays comprise a distributed beamformer to beamform the signal towards its destination while maintaining the QoS in the primary user. The objective is designing the beamformer in order to maximize the target SINR in the cognitive network subject to the network power limitations and interference constraints on the primary network. First, the cooperative beamforming problem has been solved and the improved performance in terms of target SINR in the secondary network has been investigated by simulations. Secondly, a parameter has been derived to demonstrate the distance between the optimal beamweights in this problem and the beamweights in a conventional beamforming problem. Simulations show that the target SINR can be dramatically increased by using cooperative beamforming. Moreover, they show that there is a great distinction between the optimal solutions in conventional cooperative beamforming and cooperative beamforming in cognitive radios.

Dynamic scheduling of cover-sets in randomly deployed Wireless Video Sensor Networks for surveillance applications

Abstract: A Wireless Video Sensor Network (WVSN) consists of a set of sensor nodes equipped with miniaturized video cameras. Unlike omni-directional sensors, the sensing region of a video node is limited to the field of view of its camera. Power conservation and coverage is an important issue in such wireless video networks, especially in the context of surveillance applications which is the focus of the article. In this paper, we address the area coverage problem of scheduling the activity of randomly deployed nodes to extend the network lifetime. We present a distributed algorithm for area coverage (no known targets). Moreover, we show that our approach reduces inherent ambiguities when it is necessary. Simulation results are also presented to verify the performance of the proposed approach.

Auction based interface selection in heterogeneous wireless networks

Abstract: The widespread use of heterogeneous wireless technologies and their integration with multi-mode terminals enable users get associated to the best available networks according to user preferences and application specific requirements. In this paper we present a user-centric network selection approach where negotiation between users and network operators is carried out using multi-attribute auctioning mechanism. We do not only consider the utility of users but also model the network operators' utility and discuss the truth telling behavior of network operators in terms of offered prices and service quality. Fuzzy logic approach is used to the reduce frequency of handovers. The performance of our approach is compared with Long-term based and RSS based approaches and simulation results are discussed.

Optimal placement of wireless nodes in Underwater Wireless Sensor Networks with shadow zones

Abstract: Shadow zones in Underwater Wireless Sensor Networks (UWSNs) dramatically impact communication system performance. In this paper an adaptive topology reorganization scheme has been proposed that is able to maintain connectivity in multi-hop three-dimensional UWSNs affected by shadow zones. The optimal placement for the sensor nodes to minimize the transmission loss and to maintain the network connectivity has been found using our proposed mathematical model. The theoretical analysis and the numerical evaluations reveal that our proposed scheme reduces the transmission loss under all propagation phenomena for all water depths in UWSNs and improves communication quality.

Spatial query processing in wireless sensor network for disaster management

Abstract: Recently, the world has witnessed the increasing occurrence of disasters, some of natural origin and others caused by man. Intensity of the phenomenas that cause such disasters, the frequency in which they occur, the number of people affected and the material damage caused have been growing. Areas where disasters have occurred offer many dangers to rescue teams and usually the network infrastructure is destroyed. For these reasons, it is important to create a structure to sense environmental data to detect hazards. This structure needs to be independent, easily deployed and adapted to different situations. This paper presents a mechanism for processing spatial queries on WSN to detect dangers in disasters situations. In other works in literature, they only process spatial queries with rectangular regions. Furtheremore, in this work these regions have irregular contours that needs a lot of points to be represented. Therefore the query needs to be created in more than one packet to send all these points. It also proposes a preprocessing stage to reduce the number of packages to transmit one query. Consequently, in the scenarios analysed, the energy consumption of the WSN decreased by about 40%, with an inaccuracy about 13% in information collected, compared to the processing of query that has a spatial query representation in original form.

Assessing the communication performance of wireless sensor networks in rainforests

Abstract: Wireless sensor networks (WSNs) have a great potential to serve as a monitoring tool for several applications. In particular, environmental monitoring is a leading flag for WSNs, which can provide significant environmental data for Ecology applications. More specifically, rainforests face several ecological challenges. In this case, WSNs may be used as a supporting tool for preserving and conserving the flora and fauna of such environments. However, we still need practical experiments that help us understanding how data communication is affected by environmental conditions, such as forest density, high humidity, and extreme temperature variations. In this work, we present a set of experiments that assess the communication performance in rainforests. Results show that we still need technological advances before using WSN platforms for large-scale applications in such environments. Our experiments show that the communication range of a WSN, deployed in a dense forest, is reduced by 78%, compared to other environments.

CHARON: Routing in low-density opportunistic wireless sensor networks

Abstract: Combining wireless sensor networks (WSNs) with delay-tolerant networking (DTN) has the potential to extend their use in a multitude of previously impossible applications. However, and despite numerous proposed solutions, there is still wide debate as to how to best route messages in these networks and, more importantly, how to do it in an energy-efficient way. This paper proposes CHARON (Convergent Hybrid-replication Approach to Routing in Opportunistic Networks), an approach that focuses on maximizing efficiency in addition to delivery statistics. CHARON uses delay as a routing metric, and provides basic QoS mechanisms, with both a quasi-single-copy mode for general traffic and a multi-copy mode for urgent data. It also integrates time synchronization and radio power management mechanisms. Simulation results show that it is able to achieve good delivery statistics with lower overhead than comparable solutions.

Improving WLAN capacity via OFDMA and cyclic prefix adaptation

Abstract: We study capacity improvements in WLAN technology that uses orthogonal frequency division multiplexing (OFDM) and, conventionally, time division multiple access (TDMA) to deliver high quality of service (QoS) traffic. We show that improvements are attainable via the adaptation of the cyclic prefix to the channel conditions w.r.t. the baseline system that uses a fixed value of CP. Furthermore, we compare TDMA with orthogonal frequency division multiple access (OFDMA) and we show that the latter scheme provides large capacity gains w.r.t. TDMA both with and without CP adaptation. To simplify complexity and lower the amount of feedback, we propose to adapat over a finite set of pre-determined CP values. These values are computed using a method that is based on the analysis of the distribution of the capacity-optimal CP. For the numerical results, we have used the widely adopted channel model of the IEEE 802.11 standard, and we have found that a single value of CP for each channel class of this model is sufficient to achieve nearly optimal capacity for a wide range of distances.

DES-SERT: A framework for structured routing protocol implementation

Abstract: Routing is a general task, yet the implementation of routing protocols requires specific operating system related knowledge. The developer has to deal with particular kernel internals that might have severe side effects. This is especially true for reactive and hybrid protocols where routing and forwarding are heavily intermixed. Furthermore, novel routing protocols require features that are not provided by current operating systems or have to be customized. Thus routing protocols for mobile ad-hoc networks and wireless mesh networks are often studied in simulation environments. However, simulations have limitations that can result in conclusions that do not hold in real networks. A framework for the implementation of routing protocols in operating systems is required to enable real world oriented research. We introduce the DES Simple and Extensible Routing-Framework for Testbeds (DES-SERT). The framework supports the implementation and evaluation of routing protocols in a testbed environment. A structured protocol implementation is advocated by transmitting data in extensions attached to packets and by its pipeline based architecture. Several steps are elaborated how to derive an implementation from a routing protocol specification.

Connected partial target coverage and network lifetime in wireless sensor networks

Abstract: Improving the lifetime of sensor networks that are used to monitor a number of targets lying on a field has lately received considerable attention. The most common approach to tackle this problem divides the sensor nodes into cover sets, where the sensors in each set are capable of monitoring all targets in the field. By activating one cover set at a time, the sensor network lifetime can be extended. In this paper, we analyze the problem of connected partial target coverage where cover sets are allowed to monitor a subset of the targets at any point in time, while connectivity with the base station is retained. We propose an algorithm that computes the desired cover sets and we compare its performance, in terms of network lifetime, to that of a full coverage algorithm. Our solution takes into account several characteristics of the problem, such as the specific topology parameters, the coverage status of the sensors as well as their remaining battery life. Extensive experimental results are presented for different sensor and target placement topologies. Results show that monitoring 90% of the targets may yield twice the network lifetime provided by a full coverage approach.

Knowledge-based middleware for future home networks

Abstract: Humans are lazy. They want to get as much support and assistance in their daily life as possible. To provide sophisticated digital butler functionality a system has to monitor the humans and their environment to understand their desires. It has to control all devices to translate the deduced wills into actions. To provide an integrated intelligent environment to the residents it is necessary to overcome the borders of different manufacturers, devices and access technologies. A management and control middleware is needed that shields users as well as high level management services from the technical details of the network of devices by providing a standardized, resilient and secure communication channel. We present a knowledge-based middleware as base for that purpose in this paper. The novel approach is the transparent connection of highly heterogeneous home devices by requiring only very limited functionality per device. Our design allows the desired high autonomicity in a secure and efficient way.

A Cross-layer approach to optimize the performance of Concurrent Multipath Transfer in wireless transmission

Abstract: Along with the rapid progress of the network technologies, as well as the vast cost decreasing of the peripherals, terminals with several interfaces have become increasingly common. Therefore, developing methods for enabling the concurrent use of available interfaces is in great demand. Although the Stream Control Transport Protocol (SCTP) has supported multihoming feature, the simultaneous data transfer over multiple paths is currently not allowed in standard. However, an extension to the SCTP, Concurrent Multipath Transfer (CMT), offers a solution which enable the simultaneous use of multiple interfaces. Besides, wireless network expresses more complicated characters comparing to its counterpart in wired network. For example, the radio link conditions in wireless network are more variable and the paths are instable because of mobility or interference. Therefore, it is worthwhile for us to conduct the research on CMT in wireless networks with a Cross-Layer approach. In this study, two parameters, Frame Error Rate (FER) at the link layer and Round Trip Time (RTT) at the transport layer are used to evaluate the path conditions. Meanwhile, a performance metric, the reordered packet ratio is adopted to represent the problem associated with the reordering in multipath transfer. The simulation results show that the flow distribution algorithm improves the goodput and reduces the reordered packet ratio in multipath transfer. In fact, distinguishing paths by taking the FER into account and sending packets on the fastest path decrease the number of out-of-order packets at the receiver.

Detection of synchronization signals in reuse-1 LTE networks

Abstract: Robust time and frequency synchronization is an essential requirement for a successful cell search in cellular networks like LTE (Long Term Evolution). High level of co-channel interference experienced in spectrally efficient deployments (Frequency reuse-1) can adversely affect reliable detection of synchronization sequences. Different solutions for the detection of LTE Primary Synchronization Signals (P-SS) are proposed and evaluated in this paper. The global approach consisting in a matched filter or decorrelator based detection module, followed by a decisional entity exhibits good performance: very fast convergence and robustness to interference in different channel conditions. Simulations demonstrate satisfactory detection probabilities from 7dB Signal to Interference ratio. In addition, low complexity and capacity to adapt to any propagation conditions are further important advantages of the proposed solution.

Distance vector routing for public transportation vehicular networks: Performance evaluation on a real topology

Abstract: In this last two years an increasing number of scientists has devoted his attention to Vehicular Ad hoc NETworks (VANETs) as a special case of the more generic Mobile Ad hoc NETworks (MANETs). A public transportation network used as a VANET backbone may be a viable solution - under certain circumstances - also thanks to its almost-complete area coverage and the pre-scheduled repetitive paths. The aim of this paper is to compare performances of distance vector (DV) routing strategies when applied to a VANET moving as for a real city topology. Our two main contributions are: firstly, to compare results with similar - more canonical - experiments using a grid, and secondly, to outline differences between various DV metrics. By means of simulations we demonstrate that, in the considered network scenario, a distance vector-based routing algorithm can perform well and more complex - and resources hungry - protocols are no longer strictly needed. Moreover, simulations based on a grid topology reproduce the behavior of a real city in a limited way.

An assisted device registration and service access system for future home networks

Abstract: In today's home networks security features are very rare. Infact, the only service that is usually secured is the access to the wireless network. Services, such as video streaming and audio distribution systems, often use the popular UPnP protocol since it provides dynamic service discovery and is supported by the Digital Living Network Alliance (DLNA). However, UPnP implements no security features which is not only a problem for today's services, but especially for future services in future home networks. Part of the problem is the complexity and the effort that is needed for maintaining a security infrastructure and for the deployment of security mechanisms that are common in administrated enterprise networks. This paper addresses the problem stated above by introducing an assistance system that allows for the easy and almost automatic issuing and distribution of valid X.509 certificates to new devices. We then use these certificates for controlling network access and for the design and implementation of a secure video streaming system based on the Devices Profile for Web Services (DPWS). This system shows that certificates not only help within a home, but are absolutely mandatory when interconnecting multiple homes.

Resilient P2P multimedia exchange in a VANET

Abstract: Multimedia exchange within a Vehicular Ad Hoc Network (VANET) may be facilitated by exploiting the peer-to-peer (P2P) paradigm. Urban VANETs are characterized by restricted vehicle mobility, driver actions, and bunching at obstacles, leading to wireless interference and broken links. Similarly P2P communication relies on distributed sources which are intermittently available. However, routing packets over multiple hops and multiple paths still results in packet losses, resulting in poor quality reconstructed video at a receiver. This paper proposes a slice compensation scheme employing spatial Multiple Description Coding to provide error resilience as a solution to these problems. Results show constant good quality video despite increasing packet loss ratios.

Troubleshooting of 3G LTE mobility parameters using iterative statistical model refinement

Abstract: This paper presents a new troubleshooting methodology for 3G Long Term Evolution (LTE) networks based on a closed-form expression between Radio Resource Management (RRM) and Key Performance Indicator (KPI) parameters, using statistical learning. This methodology aims at locally optimising the RRM parameters of the cells with poor performance in an iterative manner. The optimization engine uses the closed-form relationship to calculate the optimized RRM parameters for these cells. The main advantage of this methodolgy is the small number of iterations required to achieve convergence and the QoS objective. A troubleshooting application scenario involving mobility in LTE networks is considered. Numerical simulations illustrate the benefits of our proposed scheme.

A distributed data storage and retrieval scheme in unattended WSNs using Homomorphic Encryption and secret sharing

Abstract: Many data storage schemes have been proposed in the past for keeping dependable data storage, but they are not designed for Unattended Wireless Sensor Networks (UWSNs). When applying these schemes to UWSNs, most of them have limitations such as high storage requirement, transmission cost, and not resilient to a large number of node compromises. To address the problem of data storage, transmission cost, and resilience of node compromise in UWSNs, we propose a novel Homomorphic Encryption and Homomorphic Secret Sharing based scheme (HEHSS) to accomplish the goals of confidentiality, resilience to node compromises, reliability, and efficiency of storage and transmission. Our scheme exploits the homomorphic secret sharing scheme to enable sensor nodes encode sensed data into several shares, and distribute them to their neighbors. This property allows the mobile sink to reconstruct data even if some of the shares stored in neighbors of a sensor are compromised. Detailed analysis has been conducted to evaluate the scheme in terms of efficiency and reliability.

Quality of experience of voice communication in large-scale mobile ad hoc networks

Abstract: Real-time voice communication is an essential requirement in first responder scenarios. While mobile ad hoc networks (MANET) already prove to be an appropriate communication substrate in small-scale real-world operations, questions regarding scalability limitations remain. In this paper, we identify major factors that affect the quality of experience of voice communication in MANETs. In a series of simulation studies, we show that voice transmission using MANETs is also feasible in large-scale scenarios, if appropriate settings are chosen.

An underwater acoustic channel model using ray tracing in ns-2

Abstract: Underwater Acoustic Sensor Network (UASN) is the enabling technology for real-time underwater monitoring and data collection. The costly underwater trials and unknown underwater acoustic modem infrastructures increase the need and importance of a reliable network simulator for UASNs. The underwater acoustic propagation method used in the channel modeling is the one of the determining factors influences the reliability level of the network simulator for UASNs. However, recent models implemented in popular open-source network simulators prefer to use empirical formulas due to the computational complexity of the propagation method for inclusion. This preference means neglecting the multipath, fading, and shadow zone effects. Disregarding these effects results in unreal communication links between sensor nodes and approximate propagation loss and delay computation. In this paper, we present the design and implementation of our underwater acoustic channel model developed to eliminate the multipath, fading, and shadow zone effects by using ray tracing propagation method in the ns-2 network simulator. We also compare our model with a previously proposed model. The results show that the considerable differences in spreading loss and propagation delay occur due to the approximation.

Study of a key factor for performance evaluation of wireless cellular networks: The f-factor

Abstract: The f-factor, which is roughly the interference to signal power ratio, plays a crucial role in the performance evaluation of wireless cellular networks. The objective of the present paper is to study the properties of the f-factor and establish approximations for it which we compare to previously proposed approximations. We consider the hexagonal network model, where the base stations are placed on a regular hexagonal grid which may be infinite. The propagation loss is assumed to be a power of the distance between the transmitter and the receiver. In this context, we build a reference method to calculate the f-factor to which previously proposed approximations as well as a new one are compared. It is shown that the previous approximations are not always close to the reference. One should choose the approximation carefully since the performance of cellular networks depend strongly on the f-factor. The results in our paper help to make the appropriate choice. This is particularly important for operational needs as for example dimensioning a real network.

Efficient energy consumption and node distribution algorithm of 802.15.4 physical layer for WSN

Abstract: Wireless sensor networks are often power and/or energy limited. Thus it is very important to statically and (whenever possible) dynamically tune the communication protocol parameters for given performance and quality of service requirements. This paper is devoted to energy consumption optimization by tuning the physical layer parameters of the 802.15.4 Zigbee standard, depending on various application scenarios. We propose a mathematical formulation and an algorithm to optimize parameters such as bit error rate, SNR, number of repeater nodes, distance between repeaters, and optimal neighbor selection at different environmental and interference noise levels.

Inter-cell interference mitigation allocation for half-duplex relays based cooperation

Abstract: Inter-cell interference is one of the most limiting problems in high capacity mobile wireless networks. The goal of our work is to limit inter-cell interference in two-hop cooperative communication systems, by exploiting the half-duplex per chunk property of relays. Such relays cannot be interfered on a chunk while they are transmitting on it. Cooperative communications may improve the reliability of transmissions, but can also be prejudicial if relays are strongly interfered. Furthermore, additional inter-cell interference is introduced by cooperative communications. For these reasons we propose novel resource allocation modes for such relays; our modes try to protect relays from inter-cell interference and reduce energy needs. We compare our proposals to modes based on classical design. Simulation results show how our proposed allocation modes permit to outperform classical modes in terms of cooperation effectiveness, power consumption and perceived Quality of Service.

Enhanced relay selection decision for cooperative communication in energy constrained networks

Abstract: Most of current works related to relay selection algorithms in cooperative communications use the Channel State Information (CSI) to decide whether to use one or another neighbor as a relay. Therefore in wireless sensor networks where the energy is the major constraint such algorithms may lead to quick battery drain of the nodes having the best links. In this paper we propose to enhance the relay selection decision process by taking into account the energy metric in addition to CSI. The results show that we can redistribute the consumed energy when we use the energy as a relay selection metric.

Platform and experimentation of secure service location with P2P/Client-Server over ad hoc networks

Abstract: Ad hoc networking is considered as an inexpensive solution for easy and fast wireless network coverage. However, for real service deployment, security and availability in such networks are still under research even though some experimentation has shown its viability. Additionally, peer-to-peer (P2P) networking has emerged as a key technology to enable resource sharing among users. As a result, the load charge on servers can be reduced by using P2P, but this approach presents a drawback related to the services availability; when a peer is not connected, its resources are not reachable. Alternatively, Client-Server architecture provides a centralized approach; but a high demand on client requests might deteriorate service response and capacity. In the case of ad hoc networks, offering services securely is even more challenging since all nodes are anonymous until being authenticated. In this paper, we propose to offer a secure location of services in an ad hoc environment. We focused on the development of a proxy-based solution to combine a P2P-client/server network overlay in order to provide securely the location information of network services (e.g. AAA service, Kerberos) and to set a platform that can include application services (e.g. multimedia content service). More precisely, we deployed a network overlay P2P platform using JXTA; a set of peer to peer protocols, and we developed simple peer nodes and a proxy server for providing and ensuring service access control. Other security services can also be deployed such as Kerberos, PKI, among others. In our platform, the JXTA was combined; through the proxy server, with a distributed Radius AAA server to perform authentication tasks prior to discovering the location of the required services in the ad hoc network. We added encryption and message authentication code mechanisms to provide a complete secured solution. GPS Bluetooth devices were used to obtain nodes location but other location systems are also possible. Finally, a detailed description of the system architecture and platform is provided describing all the modular components as well as numerical results derived from a simple test bed.

AODV performance evaluation and proposal of parameters modification for multimedia traffic on wireless ad hoc networks

Abstract: This paper presents experiments on the performance and the viability of the AODV protocol (Ad hoc On-demand Distance Vector protocol) in multi-hop ad hoc networks, for use with multimedia traffic. This type of traffic presents some particular characteristics which make it difficult for AODV to serve fluently and reliably. After this experimental study of the problems that may arise in this type of communication and its origins, we conclude that better performance is possible with the modification of some of the protocol's parameters, without modifying the protocol algorithm. Applying these changes, experimental tests show an improvement in the performance of the protocol with video streaming.