wireless ATM links

TCP is the most popular and widely used network transmission protocol. All most 90% of the Internet connections make use of TCP for communication. TCP is reliable for wired networks and it considers all packet timeouts in wired networks as due to network congestion and not because of bit errors. However, TCP suffers from performance degradation over error-prone wireless links, as it has no technique to distinguish error deficits from congestion deficits, with networking becoming more divergent, with wired and wireless topologies. It considers all packet deficits are due to congestion and subsequently reduces the packet burst transmission, at the same time decreasing the network throughput. In this paper a new TCP congestion control mechanism is proposed that is suitable and applicable for wireless and also for wired networks and is capable of distinguishing congestion deficits from error deficits. The proposed technique uses the reserved field of the TCP header to indicate whether t...

Internet is expanding rapidly over the entire globe, TCP/IP is inseparable part of Internet. The increased use of wireless links for providing connectivity in remote areas and facilitating mobility in Internet brought out some serious performance issues of TCP, which was designed for wired links. TCP Westwood (TCPW) is a sender-side modification of the TCP congestion control algorithm that improves upon the performance of TCP Reno in wired as well as wireless networks. It continuously measure the bandwidth used by the connection by monitoring the rate of returning ACKs. The estimate is then used to compute congestion window and slow start threshold after a loss episode. This is to avoid over-shrinking cwnd after loss. In this paper the basic algorithm for TCP Westwood and it's characteristics like fairness friendliness are discussed. Also how error rate, RTT, buffer size and other parameters cause the effect on performance measures like throughput, congestion window utilization and ssthresh. Review of modifications done in basic algorithm based on different parameters is included with scope of improvement.

Web is extending quickly over the whole globe, TCP/IP is as one piece of Internet. The expanded utilization of remote connections for giving availability in remote territories and encouraging portability in Internet drew out a few genuine execution issues of TCP, which was intended for wired links. Behaviours of different TCPs have been broke down over wired and wireless connections. How they initialize their congestion window during slow start and congestion avoidance phase and what is the effect in the performance in wired and wireless networks. Here the investigation of TCP rendition called TCP Westwood which alters the congestion window is incorporated. It controls the congestion window by utilizing end-to-end data transfer capacity estimation. TCP Westwood persistently evaluates the end to end accessible transmission capacity on the premise of ACK entry rate that is utilized to reset the window to coordinate the accessibility of data transfer capacity. The algorithm is called bandwidth estimation algorithm. This makes TCP Westwood very powerful to the sporadic losses as a result of remote channel issues. In this paper execution of TCP Westwood has been assessed in the vicinity of more widely used variants of TCP over wired systems utilizing a system test system apparatus, NS-2.35. It is seen from the simulations that TCP Westwood uses the accessible bandwidth in most proficient way.

Web is extending quickly over the whole globe, TCP/IP is as one piece of Internet. The expanded utilization of remote connections for giving availability in remote territories and encouraging portability in Internet drew out a few genuine execution issues of TCP, which was intended for wired links. Behaviours of different TCPs have been broke down over wired and wireless connections. How they initialize their congestion window during slow start and congestion avoidance phase and what is the effect in the performance in wired and wireless networks. Here the investigation of TCP rendition called TCP Westwood which alters the congestion window is incorporated. It controls the congestion window by utilizing end-to-end data transfer capacity estimation. TCP Westwood persistently evaluates the end to end accessible transmission capacity on the premise of ACK entry rate that is utilized to reset the window to coordinate the accessibility of data transfer capacity. The algorithm is called bandwidth estimation algorithm. This makes TCP Westwood very powerful to the sporadic losses as a result of remote channel issues. In this paper execution of TCP Westwood has been assessed in the vicinity of more widely used variants of TCP over wired systems utilizing a system test system apparatus, NS-2.35. It is seen from the simulations that TCP Westwood uses the accessible bandwidth in most proficient way.

Transmission Control Protocol (TCP) is known to suffer from performance degradation in mobile wireless environments, as such environments are prone to packet losses due to high bit error rates and mobility induced disconnections, because TCP is well reliable protocol for wired networks. In wired network packet loss due to congestion. Proposed scheme is a true end-to-end approach, based on the idea of exclusive handover message and is used for alleviating the degrading effect of host mobility on TCP performance. Experiments are performed using the Network Simulator (NS-2). The simulator has been extended to incorporate wireless link characteristics.

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The MAC protocol, known as MASCARA (Mobile Access Scheme based on Contention And Reservation for ATM), is an infrastructure-based. adaptive TDMA scheme, which combines reservation-and contention-based access methods to provide multiple access efficiency and Quality of Service (QoS) guarantees to wireless ATM terminal connections that share a common radio channel. Radio channel sharing is performed by the PRA-DOS (Prioritized Regulated Allocation Delay Oriented Scheduling) algorithm. In this paper we assess the capability of PRADOS to guarantee to voice and data traffic types the QoS they need. The analysis leads to the conclusion that PRADOS cannot avoid the interference between the various types of traffic. A criterion to alleviate this drawback is also outlined at the end of the paper.

DVB-SH is a new broadcasting standard offering a mobile TV service for handheld devices using hybrid satellite/terrestrial-repeaters solution. A new link layer protection algorithm called Multi-Burst Sliding Encoding (MBSE) has been recently adopted to cope with the long fading time introduced by the direct satellite link. This paper presents a method to optimize the MBSE parameters and an analysis of the performance gain. Various sets of parameters are studied and optimized with respect to the link performance. Furthemore, an algorithm was provided to compute the optimum values of the MBSE parameters according to some constraints. we have implemented MBSE in two UDcast DVB-SH equipements and we have validated our optimization method using intensive experiments with typical usage scenarios under a hardware-emulated wireless link.

This paper presents a hardware/software co-design approach where different specification languages can be used in parallel, allowing effective system co-modeling. The proposed methodology introduces a process model that extends the traditional spiral model so as to reflect the design needs of modern embedded systems. The methodology is supported by an advanced toolset that allows co-modeling and co-simulation using SDL, Statecharts and MATRIX X , and interactive hardware/software partitioning. The effectiveness of the proposed approach is exhibited through two application examples: the design of a car window lift mechanism, and the design of a MAC layer protocol for wireless ATM networks.

Multipath routing protocols are distinguished from single-path routing by the fact that they look for and use several routes from a source to destination. Several routing schemes have been proposed in the context of mobile ad hoc networks that uses multiple paths simultaneously by splitting the information among the multitude of paths. However. the effect of route coupling in this environment can severely limit the gain offered by multipath routing strategies. Route coupling is a phenomenon of wireless medium and occurs when multiple routes are located physically close enough to interfere with each other during data communication. In this paper, we investigate the effect of directional antenna on multipath routing. We have shown that the effect of route coupling across multiple paths with directional antenna is much less compared to that with omni-directional antenna. As a result, the routing performance using multiple paths improves substantially with directional antenna compared to that with omni-directional antenna.

We present a transaction commit protocol "Transaction Commit On Timeout (TCOT)" based on a "timeout" approach for Mobile Database Systems (MDS), which can be universally used to reach a final transaction termination decision (e.g., commit, abort, etc.) in any message oriented system. Particularly suited for a wireless environment, a timeout mechanism is the only way to minimize the impact of the slow and unreliable wireless link. We compare TCOT to a modified version of 2PC to show its superiority based on commit time.

Rapid advances in Wireless Sensor Networks (WSNs) indicate that they are becoming increasingly complex. Consequently users and applications are becoming more demanding. Due to unique characteristics of WSNs, like small dimensions and limited resources and capabilities, Quality of Service (QoS) is imposed as one of the key factors of WSNs. In this paper, we surveyed two main approaches for QoS provisioning in WSNs: layered and cross-layer approach. QoS provisioning with layered approach is surveyed in three WSN layers: MAC, network and transport layer. Current developments show that they can be efficiently used for QoS provisioning. However, they consider QoS only as layer specific isolated set of problems and they are highly dependent on the performance of other layers. Cross-layer approach does not have the restrictions as layered approach and hence can dispose with information from all layers of the communication protocol stack. Although it has huge potential to become the most efficient solution for QoS provisioning in WSNs, current development indicate that there are still many issues and challenges that need to be overcome. Since the concept of the QoS is relatively new in WSNs, there are not a large number of patents currently dealing with this issue, however but in coming years a large increase in the number of such patents is expected. Available patents in this domain are described in the paper.

The idea of using multiple access links (so called multihoming) is commonly used to improve the aggregate bandwidth and the overall service availability, which has been employed by large enterprises and data centers as a mechanism to extract good performance and enhance the network reliability from their service providers for a while. However, in the context of network mobility, because of the diversity and unreliability of the wireless links, adaptable multihomed prototype supporting mobile networks should be studied and implemented. This report introduces us the details from the implementation project of a multihoming agent, which is developed on a Linux based platform and allows router to access and switch between multiple access links including WLAN and GPRS. The prototype is capable of dynamically switching users' data traffic from one network interface to another, i.e. Ethernet, WLAN, and GPRS, without breaking transport layer sessions, based on the interfaces' status and policy in use.

Nodes, using CSMA/CA type medium access control (MAC) protocols (e.g. IEEE 802.11e) and omnidirectional antennas, in an ad-hoc network may not be able to transmit packets to each other concurrently due to spatial contention for the shared wireless medium. The maximum network performance depends on the maximum number of possible concurrent transmissions. This can be maximized in a multi-hop ad-hoc network using directional antennas. Neighboring nodes falling outside the transmission region are less vulnerable to co-channel interference. Directional antennas allow increased transmission range by reducing noise, interference and multi-path fading. We emphasize the interference reduction capability of directional antennas in the context of suburban ad-hoc networks (SAHN). We build an analytical model, based on the basic channel access mechanism of IEEE 802.11, to show the effect of interference on network performance along multiple hops using three antenna schemes; multiple fixed directional antennas, omnidirectional antennas with multiple frequency channels and omnidirectional antennas with single frequency channel. We extend our analyses for IEEE 802.11e to accommodate different traffic classes. We also verify our analyses with extensive simulations.

A suburban ad-hoc network (SAHN) interconnects a cooperative group at broadband speed using wireless links. The nodes are stationary. A SAHN involves low installation and service costs for SAHN specific traffic. Some current routing solutions for mobile ad-hoc networks may be used in the SAHN after certain optimizations. Efficiency can be improved by using smart directional antennas. Neighboring nodes falling outside the transmission region of a directional antenna are less vulnerable to co-channel interference. Additionally, increased transmission range can be achieved by reducing noise, interference and multi-path fading. In this paper, we emphasize the interference reduction capability of directional antennas and investigate the routing performances using three antenna schemes; multiple fixed directional, multiple omnidirectional and single omnidirectional antennas. We present an estimate of the achievable performance in a SAHN through extensive simulations. We also discuss the impact of using omnidirectional antennas on routing performance where different networks, using overlapping frequency channels, exist within each other's transmission ranges.

Provision for quality of service (QoS) for real-time traffic in multi-hop ad-hoc wireless networks with shared medium and a contention based media access control (MAC) pro-tocol is very challenging. In our previous work we have explained the challenges in detail and ...

In the past decades Wireless Fidelity, wireless internet(Wi-Fi) networks have enhanced its features and got closer to the home users. Back in the day home users used wired internet connections in their homes. Due to the technical revolution and the vast use of mobile devices it became a must to have a Wi-Fi network in a regular home. There is a down side in every technology, the major down side in Wi-Fi is the integrity of the network password. This research paper is focuses on “How to improve the integrity of the Wi-Fi network password”. There are various security mechanisms currently used to protect the integrity of the Wi-Fi passphrase from intruders, such as Wireless Equivalent Privacy(WEP)/ Wi-Fi Protected Access (WPA)/ Wi-Fi Protected Access 2 Pre shared key (WPA2PSK)/Wi-Fi Protected Setup(WPS). This research is mainly focusing on WPA2 as the base technology and build a solution on top of it. WPA2-PSK stands for “Wi-Fi protected access 2 pre shared key” it is the predecessor o...

ShoeSoleSense is a proof of concept, novel body worn interfacean insole that enables location independent hands-free interaction through the feet. Forgoing hand or finger interaction is especially beneficial when the user is engaged in real world tasks. In virtual environments as moving through safety training applications is often conducted via finger input, which is not very suitable. To enable a more intuitive interaction, alternative control concepts utilize gesture control, which is usually tracked by statically installed cameras in CAVE-like-installations. Since tracking coverage is limited, problems may also occur. The introduced prototype provides a novel control concept for virtual reality as well as real life applications. Demonstrated functions include movement control in a virtual reality installation such as moving straight, turning and jumping. Furthermore the prototype provides additional feedback by heating up the feet and vibrating in dedicated areas on the surface of the insole.

This paper presents a systematic methodology for the optimal design of wireless power transfer (WPT) systems. To design a WPT for a specific application, the values of coil geometric parameters and the number of resonators should be chosen such that an objective function is maximized while satisfying all the design constraints. The conventional methodologies, which are based on cyclic coordinate optimization, are not comprehensive and efficient methods. This paper presents a design methodology based on the genetic algorithm (GA). The optimization method has been applied to designing different WPTs with series and parallel connections of load and different design constraints. Moreover, the number of resonators is considered as the design parameters. In addition, WPTs with parallel and series connections of load are compared from different aspects. The results of calculation, simulation and measurements demonstrate that the 2-coil WPT can be optimized to achieve maximum efficiency com...

Rapidly deployable wireless networks consist of mobile base stations and less powerful mobile hosts. The mobile base stations have t o maintain wireless connectivity while on the move along pre-de ned paths. Physical obstructions and wireless range limitations may prevent a pair of mobile base stations from establishing a wireless link. We study situations of distance-constrained mobility, and fault situations like distance and topology induced mobility deadlocks. We also propose a deadlock avoidance mobility s c heme using repeaters, and derive an upper bound on the number of repeaters. We propose two heuristics, using sleeper nodes, for providing coverage to areas that may lose coverage due to a mobile base station crash.

This paper presents a hardware/software co-design approach where different specification languages can be used in parallel, allowing effective system co-modeling. The proposed methodology introduces a process model that extends the traditional spiral model so as to reflect the design needs of modern embedded systems. The methodology is supported by an advanced toolset that allows co-modeling and co-simulation using SDL, Statecharts and MATRIX X , and interactive hardware/software partitioning. The effectiveness of the proposed approach is exhibited through two application examples: the design of a car window lift mechanism, and the design of a MAC layer protocol for wireless ATM networks.

This paper describes the design and initial results from implementation work carried out in the European GOLLUM project developing an open, extensible, and unified Application Programming Interface (API) for accessing, querying and controlling all types of wireless links. Key features of this API include a general querying mechanism based on database technologies, and methods for setting up asynchronous notifications regarding changes in link conditions, in a technology-independent manner. Detailed design aspects are described here together with information on the various implementations so far. Initial results show that the proposed ULLA design provides an extensible, scalable, platform independent and power efficient framework enabling seamless link access in various types of systems including embedded devices with limited resources.

IEEE 802.11 is being currently considered to develop telecommunications infrastructures in industrial environments. However, in such environments there may exist a high level of Electromagnetic Fields (EMF) contamination, due to the machinery in use. Wireless LANs are sensitive to this type of hazard, and therefore the performance of the protocols may be affected inside the industrial facilities. In this paper we conduct a study of the wireless link performance in these industrial scenarios, using personal computing devices. Such equipments will be likely used by employees rather than conventional computers. Since the results do not characterize the environment itself, but the set of environment and hardware, a proper measurement test-bed must include direct measurements with these devices. Besides, due to limitations in these equipments, a specific protocol to measure pairs of packet error probability and latency is also developed. Results reveal a significant linear dependency between both magnitudes, and a large correlation coefficient in the measurements under high EMF activity at mid-large ranges (distances greater than 5 meters).

TCP Westwood (TCPW) is a sender-side modification of the TCP congestion window algorithm that improves upon the performance of TCP Reno in wired as well as wireless networks. The improvement is most significant in wireless networks with lossy links, since TCP Westwood relies on endto-end bandwidth estimation to discriminate the cause of packet loss (congestion or wireless channel effect) which is a major problem in TCP Reno. An important distinguishing feature of TCP Westwood with respect to previous wireless TCP "extensions" is that it does not require inspection and/or interception of TCP packets at intermediate (proxy) nodes. Rather, it fully complies with the end-to-end TCP design principle. The key innovative idea is to continuously measure at the TCP source the rate of the connection by monitoring the rate of returning ACKs. The estimate is then used to compute congestion window and slow start threshold after a congestion episode, that is, after three duplicate acknowledgments or after a timeout. The rationale of this strategy is simple: in contrast with TCP Reno, which "blindly" halves the congestion window after three duplicate ACKs, TCP Westwood attempts to select a slow start threshold and a congestion window which are consistent with the effective bandwidth used at the time congestion is experienced. We call this mechanism faster recovery. The proposed mechanism is particularly effective over wireless links where sporadic losses due to radio channel problems are often misinterpreted as a symptom of congestion by current TCP schemes and thus lead to an unnecessary window reduction. Experimental studies reveal improvements in throughput performance, as well as in fairness. In addition, friendliness with TCP Reno was observed in a set of experiments showing that TCP Reno connections are not starved by TCPW connections. Most importantly, TCPW is extremely effective in mixed wired and wireless networks where throughput improvements of up to 550% are observed. Finally, TCPW performs almost as well as localized link layer approaches such as the popular Snoop scheme, without incurring the O/H of a specialized link layer protocol.

We use a stochastic model to study the throughput performance of various versions of transport control protocol (TCP) (Tahoe (including its older version that we call OldTahoe), Reno, and NewReno) in the presence of random losses on a wireless link in a local network. We model the cyclic evolution of TCP, each cycle starting at the epoch at which recovery starts from the losses in the previous cycle. TCP throughput is computed as the reward rate in a certain Markov renewal-reward process. Our model allows us to study the performance implications of various protocol features, such as fast retransmit and fast recovery. We show the impact of coarse timeouts. In the local network environment the key issue is to avoid a coarse timeout after a loss occurs. We show the effect of reducing the number of duplicate acknowledgements (ACK's) for triggering a fast retransmit. A large coarse timeout granularity seriously affects the performance of TCP, and the various protocol versions differ in their ability to avoid a coarse timeout when random loss occurs; we quantify these differences. As observed in simulations by other researchers, we show that, for large packet-loss probabilities, TCP-Reno performs no better, or worse, than TCP-Tahoe. TCP-NewReno is a considerable improvement over TCP-Tahoe, and reducing the fast-retransmit threshold from three to one yields a large gain in throughput; this is similar to one of the modifications in the recent TCP-Vegas proposal. We explain some of these observations in terms of the variation of fast-recovery probabilities with packetloss probability. Finally, we show that the results of our analysis compare well with a simulation that uses actual TCP code.

The growing demand of usage of wireless sensors applications in different aspects makes the quality-of-service (QoS) to be one of paramount issues in wireless sensors applications. Quality of service guarantee in wireless sensor networks (WSNs) is difficult and more challenging due to the fact that the resources available of sensors and the various applications running over these networks have different constraints in their nature and requirements. Traditionally quality of service was focused on network level with concern in metrics such as delay, throughput, jitter e.c.t. In this paper we present appropriate metrics of QoS for WSN which involve service, reliability and availability which ultimately facilitating in archiving qualitable service. We discuss the reverse look of QoS and hence present mathematically the three significant quality factors that should currently be taken into account in developing WSNs application quality services namely, availability, reliability and serviceability. We run experiments incorporating these three phenomenons (reliability, availability and serviceability-RAS) to demonstrate how to attain QoS which effectively improve reliability of the overall WSNs.

Distributed classification fusion using error-correcting codes (DCFECC) has recently been proposed for wireless sensor networks operating in a harsh environment. It has been shown to have a considerably better capability against unexpected sensor faults than the optimal likelihood fusion. In this paper, we analyze the performance of a DCFECC code with minimum Hamming distance fusion. No assumption on identical distribution for local observations, as well as common marginal distribution for the additive noises of the wireless links, is made. In addition, sensors are allowed to employ their own local classification rules. Upper bounds on the probability of error that are valid for any finite number of sensors are derived based on large deviations technique. A necessary and sufficient condition under which the minimum Hamming distance fusion error vanishes as the number of sensors tends to infinity is also established. With the necessary and sufficient condition and the upper error bounds, the relation between the fault-tolerance capability of a DCFECC code and its pair-wise Hamming distances is characterized, and can be used together with any code search criterion in finding the code with the desired fault-tolerance capability. Based on the above results, we further propose a code search criterion of much less complexity than the minimum Hamming distance fusion error criterion adopted earlier by the authors. This makes the code construction with acceptable fault-tolerance capability for a network with over a hundred of sensors practical. Simulation results show that the code determined based on the new criterion of much less complexity performs almost identically to the best code that minimizes the minimum Hamming distance fusion error. Also simulated and discussed are the performance trends of the codes Manuscript

Wireless ad hoc networks will be an important component in future communication systems. The performance of wireless ad hoc networks can be improved by link quality-aware applications. Wireless link quality is dynamic in nature, especially in mobile scenarios. Therefore, accurate and fast packet delivery ratio estimation is a prerequisite to good performance in mobile, multi-hop and multi-rate wireless ad hoc networks. In this paper, we propose a novel packet delivery ratio estimation method that improves the accuracy and responsiveness of the packet delivery ratio estimation. The proposed link quality estimation components are implemented in a IEEE 802.11b/g test-bed. The experiment results show that the accuracy of the packet delivery ratio estimation can improve up to 50% in mobile scenarios without introducing overhead. We also show the end-to-end performance impact of this improved estimation on route selection using different routing metrics and configurations. The measurement results show that our packet delivery ratio method leads to better route selection in the form of increased end-to-end throughput compared to traditional methods, which respond slowly to the link dynamics.

Radio frequency (RF) tags have been widely used in inventory tracking, environmental monitoring, battlefield situational awareness, and combat identification due to their low cost, small size, and wireless functionality. This paper explores the application of active RF tags in outdoor environments responding to random noise radar interrogations with predetermined messages. A conceptual system design for communication between radar and RF tags using ultrawideband (UWB) noise waveforms is proposed and analyzed theoretically and via simulations. The tag structure comprises a sensing receiver and active receiver/transmitter. The sensing receiver senses the radar header consisting of a prearranged secret realization of the noise waveform. The active receiver/transmitter modulates the RF tag's message onto the radar interrogation signal through weighted tapped delays and reradiates the tag message back to the radar. System performance is evaluated in terms of symbol error probability ...

Binaural noise reduction, with applications for instance in hearing aids, has been a very significant challenge. This task relates to the optimal utilization of the available microphone signals for the estimation of the ambient noise characteristics and for the optimal filtering algorithm to separate the desired speech from the noise. The additional requirements of low computational complexity and low latency further complicate the design. A particular challenge results from the desired reconstruction of binaural speech input with spatial cue preservation. The latter essentially diminishes the utility of multiple-input/single-output filter-and-sum techniques such as beamforming. In this paper, we propose a comprehensive and effective signal processing configuration with which most of the aforementioned criteria can be met suitably. This relates especially to the requirement of efficient online adaptive processing for noise estimation and optimal filtering while preserving the binaural cues. Regarding noise estimation, we consider three different architectures: interaural (ITF), cross-relation (CR), and principal-component (PCA) target blocking. An objective comparison with two other noise PSD estimation algorithms demonstrates the superiority of the blocking-based noise estimators, especially the CR-based and ITF-based blocking architectures. Moreover, we present a new noise reduction filter based on minimum mean-square error (MMSE), which belongs to the class of common gain filters, hence being rigorous in terms of spatial cue preservation but also efficient and competitive for the acoustic noise reduction task. A formal real-time subjective listening test procedure is also developed in this paper. The proposed listening test enables a real-time assessment of the proposed computationally efficient noise reduction algorithms in a realistic acoustic environment, e.g., considering time-varying room impulse responses and the Lombard effect. The listening test outcome reveals that the signals processed by the blocking-based algorithms are significantly preferred over the noisy signal in terms of instantaneous noise attenuation. Furthermore, the listening test data analysis confirms the conclusions drawn based on the objective evaluation.

Transmission Control Protocol (TCP) is the vastly researched, used and implemented transport protocol from the bouquet of standardized protocols we have. Since its first introduction, TCP has experienced tremendous revolutions specifically regarding the way it should control congestion . Many TCP flavors exist, one can control its sending rate according to link bandwidth estimation like in the Westwood variant , while another tunes its congestion window (cwnd) based on the round-trip time (RTT) evaluation such as TCP Vegas , just to name few examples. However, all of these TCP versions assume a bulk transfer of data and thus they are optimized upon this type of traffic. On the other hand, Air Traffic Management (ATM) data traffic has other characteristics than file transfer. Messages generated from aeronautical services are triggered by events in the aeronautical environment. Further, these messages have bursty inter-arrival times, which can go up to several minutes, relatively small size mostly in the order of few hundreds of bytes and a maximum delay (a maximum of few seconds) that they have to be delivered within. As can be realized, a TCP source may experience some inactive periods due to the burstiness of the traffic. However, in , it is recommended that to control and avoid congestion, TCP should use slow start mechanism when restarting a transmission after a ratherly long idle period. The NEWSKY project recommends to design a transport protocol for avionics which is based on the User Datagram Protocol (UDP) but with reliability measures. Taking these suggestions into account, the Reliable User Datagram Protocol (RUDP) ) is an interesting option. However, it has features from TCP, which are not desirable for the ATM context, like connection initiation and shutdown, congestion control and byte streaming mechanism, which according to the authors of (NEWSKY, 2009) and (Muhammad & Berioli, 2010) reduce the performance of a transport protocol when transferring small files. Therefore, RUDP could be a highly qualified candidate to transport aeronautical traffic in case it is carefully re-designed and adjusted to consider the properties of an ATM traffic over highly asymmetrical links. Furthermore, in the context of checking the validity of TCP to transfer messages of ATM services, questions related to the performance of the protocol will be addressed. For example, the relation between the cwnd of TCP, aeronautical messages and congestion control. The Seamless Aeronautical Networking through integration of Data links, Radios and Antennas (SANDRA) (SANDRA, 2011) concept consists of the integration of complex and disparate communication media into a lean and coherent architecture. SANDRA as a project 4 www.intechopen.com 2 Future Aeronautical Communications is divided into several sub projects (SPs). This work belongs to the one dealing with seamless networking specifically for the transport layer protocols and performance task. Transport layer protocols should be assessed with respect to their suitability for aeronautical communication and their impact on the system availability and reliability. Finally, an optimization for these protocols in order to be used in avionics context should be provided. The work in this chapter is organized as follows. In the next Section, an overview about the aeronautical services is presented. In Section 3, the system architecture design in which the protocol will be operating is discussed. Section 4 explains some properties and illustrates few drawbacks of using TCP in avionics from theoretical and technical perspectives. The RUDP is further investigated in Section 5 where adjustment recommendations are given. In Section 6, detailed analysis of the ATM traffic pattern is shown and suggestions on system design are provided. Finally, a conclusion is drawn in Section 7.

We use a new method based on discrete fuzzy transforms for coding/decoding frames of color videos in which we determine dynamically the GOP sequences. Frames can be differentiated into intraframes, predictive frames, and bidirectional frames, and we consider particular frames, called Δ-frames (resp., R-frames), for coding P-frames (resp., B-frames) by using two similarity measures based on Lukasiewicz -norm; moreover, a preprocessing phase is proposed to determine similarity thresholds for classifying the above types of frame. The proposed method provides acceptable results in terms of quality of the reconstructed videos to a certain extent if compared with classical-based F-transforms method and the standard MPEG-4.

RAPIDware is a collection of software design techniques for constructing adaptive middleware to support collaborative computing. This paper describes an experimental study in the design of adaptive proxy services for resource-limited mobile hosts. The approach is based on detachable Java I/O streams, which enable proxy filters and transcoders to be dynamically inserted, deleted, and reordered on a given data stream. Unlike conventional Java I/O streams, detachable streams can be stopped, disconnected, reconnected, and restarted. As such, they provide the "glue" needed to to support the dynamic composition of proxy services. The operation and implementation of detachable streams are described, followed by a discussion of their use in demanddriven forward error correction services for wireless hosts.

This paper describes an experimental study in the use of a composable proxy framework to improve the quality of interactive audio streams delivered to mobile hosts. Two forward error correction (FEC) proxylets are developed, one using block erasure codes, and the other using the GSM 06.10 encoding algorithm. Separately, each type of FEC improves the ability of the audio stream to tolerate errors in a wireless LAN environment. When composed in a single proxy, however, they cooperate to correct additional types of burst errors. Results are presented from a performance study conducted on a mobile computing testbed.

With data throughput for mobile devices constantly increasing, services such as video broadcast and multicast are becoming feasible. The 3GPP (3rd Generation Partnership Project) committee is currently working on a standard for Mobile Broadcast and Multicast services (MBMS ). MBMS is expected to enable easier deployment of video and multimedia services on 3G networks. W e present an overview of the standard including the proposed architecture and requirements focusing on radio aspects. We discuss the issue of video error resilience in such services that is critical to maintain consistent quality for terminals. The error resilience techniques currently used in video streaming services are not suitable for MBMS services. W e analyze the error resilience techniques that are applicable within the context of MBMS standard and present our early research in this area.

TCP performance over wireless networks is critical as the Internet gradually expands to the wireless territory. Traditional TCP schemes have been proven to be inefficient for the wireless network, as they are designed and optimized for the wired network. Recently, schemes that are aimed to improve TCP performance in wireless networks have been proposed. In particular, TCP-Jersey, a TCP scheme that was designed for heterogeneous network consisting of wired and wireless links, has shown significant improvement over other TCP variants. In this paper, performance of TCP-Jersey over High Speed Downlink Packet Access (HSDPA) in the Universal Mobile Telecommunication System (UMTS) is evaluated and compared with other TCP variants through detailed system modeling and extensive simulations. The result shows that TCP-Jersey produces significant goodput improvement over other TCP variants tested. I.

This paper presents the measurement and statistical analysis of the temporal variations of the radio channel defined by a fixed link at 3.5 GHz in suburban areas. The analysis provides the required information about the temporal stability of the channel, the probability of occurrence and depth of fades, the Doppler spectrum and, in general, the influence of the environment on the signal behaviour. In particular, the effect of fast traffic on a motorway in the neighbourhood of the receiver is investigated, obtaining some general conclusions particularly useful in wireless communication systems design.

Unmanned aerial vehicle (UAV) has been used recently a lot in military applications as well as in civilian. It shows great advantages and importance in the search and rescue, real-time surveillance, reconnaissance operations, traffic monitoring, hazardous site inspection and range extension. Moreover, UAVs are suited for situations that are too dangerous for direct human monitoring. In general, UAVs have the potential to create an ad-hoc network and greatly reduce the hops from source to destination. However, the type of the mission and the capability of the UAV which are determined by its shape and construction causes a lot of networking issues. Most UAVs used in communication networks assumed the use of omni-directional antenna. In this paper, we considered a collection of UAVs that communicate through a wireless link as a mobile ad-hoc network (MANET) using directional antenna. This technique offers tremendous advantages over that of using omni-directional antenna, although it requires an adaptive medium access control (MAC) to adapt the new antenna system as well as the constraint imposed by the UAV. To be more specific, we introduced a new mechanism that is called target information table to work with our new scheme during the switch from omni-directional to directional antenna. We made a comparison between the two techniques using optimized network engineering tool (OPNET). Our results show good improvement for end-to-end delay as well as throughput.

Since TCP cannot distinguish between packet losses due to transmission errors from those due to congestion, TCP tends to perform poorly on wireless links that are prone to transmission errors. Several techniques have previously been proposed to improve TCP performance over wireless links. Existing schemes typically require an intermediate node (typically, a base station) to be TCP-aware. For instance, the Snoop scheme requires the base station to interpret TCP headers and take appropriate actions to help improve TCP performance. This paper proposes an alternative TCP-unaware technique that attempts to mimic the behavior of the Snoop protocol. Performance evaluation shows that the proposed Delayed Dupacks scheme performs quite well.

Ad hoc networks are the solution to the demands of spontaneous network setup. They are characterized by the use of wireless links, dynamically changing topology, multi-hop connectivity and decentralized routing mechanisms and decision-making. AODV and DSR are the two most widely studied on-demand ad hoc routing protocols. Previous studies have shown limitations of these protocols in certain network scenarios. To improve the performance of AODV, we modify AODV to include the source route accumulation feature of DSR. We call this AODV with path accumulation. This protocol optimizes AODV to perform effectively in terms of routing overhead and delay during high load. The performance of the protocol is evaluated by a simulation model under a variety of network conditions. We also compare its performance with that of unmodified AODV and DSR. We demonstrate how a small change to the AODV protocol can lead to significantly improved performance results.

Mobile Ad Hoc Network (MANET) consists of dynamic topology as nodes in the network are mobile, and connected via wireless links. The nodes are grouped in clusters for the purpose of routing. Nodes within the cluster communicate directly. However, nodes communicate outside the cluster through a centralized node that is called a clusterhead. An elected clusterhead is assigned for communication with all other clusters. The centralized clusterhead can become a bottleneck and possibly cause a lower throughput for the clustering system. We propose a mechanism in which communication outside the cluster is distributed through separate clusterheads. We prove that the overall averaged throughput for the clustering system increases considerably, about doubles for our distributed number of clusterheads. We also show that the increase in overall averaged throughput is reduced by the increase in the overall averaged error rate ratio resulting from the added clusterheads. Additionally, the routing reliability to outside the cluster is increased since routes to different clusters use distinct clusterheads.

Smart antenna is recognized as promising technologies for higher user capacity in 3G wireless networks by effectively reducing multipath and co-channel interference. Advent of powerful, low-cost, digital processing components and the development of software-based techniques has made smart antenna systems a practical reality for both base station and mobile station of a cellular communications systems in the next generation. The core of smart antenna is the selection of smart algorithms in adaptive array. Using beam forming algorithms the weight of antenna arrays can be adjusted to form certain amount of adaptive beam to track corresponding users automatically and at the same time to minimize interference arising from other users by introducing nulls in their directions. Thus interferences can be suppressed and the desired signals can be extracted. This research work provides description, comparative analysis and utility of various reference signal based algorithms as well as blind adaptive algorithms. Exhaustive simulation study of beam patterns and learning characteristics have proved the efficacies of the proposed work from application point of view.

The accurate determination of the link quality is critical for ensuring that functionalities such as intelligent routing, load-balancing, power control and frequency selection operate efficiently. There are 4 primary metrics for capturing the quality of a wireless link: RSSI (Received Signal Strength Indication), SINR (Signal-to-Interference-plus-Noise Ratio), PDR (Packet-Delivery Ratio), and BER (Bit-Error Rate). In this paper, we perform a measurement-based study in order to answer the question: which is the appropriate metric to use, and under what conditions? We evaluate the relative accuracy of each metric by conducting experiments with multiple transmission rates and varying levels of interference on a large set of links. We observe that each metric has advantages and projects one or more limitations. Our study suggests that a careful consideration of these limitations is essential, and provides guidelines on the applicability of each metric. 1

In wireless sensor networks (WSNs), a significant amount of packets are lost when transmitted over wireless links, leading to unnecessary energy expenditure. This lossy property of a link can be described by the packet reception ratio (PRR) over it. In the literature, it was shown that the PRR of a link is a non-decreasing function of its signal to interference-plus-noise ratio (SINR), which indicates that the PRR can be improved by either enhancing the received power or reducing the interferenceplus-noise level. On the other hand, a number of topology control algorithms and channel assignment algorithms have been presented for WSNs to reduce interference. However, most of them simply use the number of interfering nodes to describe the level of interference, which is inaccurate thus cannot guarantee high PRR. In this paper, we propose a joint design of topology control and channel assignment for lossy WSNs, aiming at improving the PRR of each link in the network. We first construct a maximum PRR spanning tree, then adjust the transmitting power and channel of sensor nodes to further improve the PRR of links on the tree. This way, packet retransmission due to lossy links is minimized, which leads to performance improvement in terms of network throughput, energy efficiency and end-to-end packet delay. We formulate the joint design into an optimization problem and prove its NP-hardness. We then present heuristic algorithms to give practical solutions for the problem. We have carried out extensive simulations and the results show that network performance can be significantly improved by using the topology generated by our algorithms compared to the topologies generated by other schemes under the same traffic demand.

We demonstrate that, by jointly optimizing video coding and radio-over-fibre transmission, we extend the reach of 60-GHz wireless distribution of high-quality high-definition video satisfying low complexity and low delay constraints, while preserving superb video quality.