Earticle

The limited battery resource of mobile devices is an endless problem. The conventional solution, improving battery technologies, is insufficient; we need alternative energy sources to enhance mobile lifetimes. One solution is to utilize cars as intermediate nodes in mobile ad hoc networks. However, the high velocities of cars may seriously degrade network quality. To overcome this, we need an efficient routing protocol that can establish stable routes even if moving cars are used as network components. This paper conducts simulations to evaluate the impact of high speed cars and proposes a novel technology that allows routing to consider vehicle velocity. Extensive simulation results are presented to show the efficiency that can be achieved by our proposal.

Currently, the IETF RSerPool WG is standardizing a generic protocol framework for server redundancy and session failover: Reliable Server Pooling (RSerPool). An important property of RSerPool is its lightweight architecture: server pool and session management can be realized with small CPU power and memory requirements. That is, RSerPool-based services can also be managed and provided by embedded systems. Up to now, there has already been some research on the performance of the data structures managing server pools. But a generic, application-independent performance analysis – in particular also including measurements in real system setups – is still missing. The aim of this article is therefore – after giving an outline of the RSerPool framework, an introduction to the pool management procedures and a description of our pool management approach – to first provide a detailed performance evaluation of the pool management structures themselves. Afterwards, the performance of a prototype implementation is analysed in order to evaluate its applicability in a real network setup.

Neighbor attachment is the process of establishing links between nodes that on the physical layer are visible to each other. In ad-hoc and sensor networks many strategies can be followed to connect to adjacent nodes. A simple scenario would be to consider all nodes within the transmission range of a node as its neighbors. More sophisticated scenarios can establish neighborhood relations with a limited number of carefully selected nodes. Different neighbor attachment policies result into different network topologies at the link-layer. In any topology a packet sent from a node to one of its neighbors will experience interference, which is caused by simultaneous communications between other nodes in the network. Obviously, high levels of interference would severely disrupt communications and reduce overall network capacity. In this paper we examine how neighbor attachment policies can change the amount of interference experienced by network nodes. We will also show that Carrier-to- Interference ratio (C/I) is directly affected by neighbor attachment policies. Our study enables us to identify neighbor attachment directives that can reduce interference, or optimize C/I in large multi-hop ad-hoc and sensor networks.

Packet loss in IP networks can be congestive due to IP interrupt queue overflow on the nodes, and non-congestive due to hardware failure, signal-fading or obstacles. Recognition of two types of losses can largely help TCP endpoints in making right decisions. In this paper we apply the Visualized IP-based Network Simulator (VINS) to characterize the key differences between congestive packet losses and that of due to link disruption, which is noncongestive and commonly seen in wireless networks. Based on the analyses, suggested improvements for wireless TCP endpoints are proposed on both kernel and application levels in terms of avoiding useless keep-alive probing and congestion window tuning, but re-routing and re-establishing new connections.

The performance of a mobile network is essentially based on the capacity of its radio access technology. A mobile network is spatially and functionally distributed. Its subsystems are in constant interaction with each other and with their geographic environment. Finding an appropriate approach to evaluate the capacity of a radio access technology with respect to a wide range of parameters (radio signal quality, quality of service, user mobility, and network resources) has become increasingly important in today’s wireless network planning. Traditional mathematical and statistical modeling techniques do not satisfy the requirements of such a complex process where spatial data is of fundamental importance. In this paper, we propose a model-based geo-simulation approach in order to assess the capabilities of the 1xEV-DO radio access technology. Results are expressed in terms of signal quality (C/I and EC/I0) for the requested services and applications.

This study focuses on the gain of using progressive download instead of legacy download for streamable media files for wireless multicasting networks. With progressive download, the media content can be played after some waiting time, while the downloading still continues in the background. We focus on 3GPP’s wireless multimedia broadcast multicast system (MBMS). First we provide a legacy MBMS download system optimized for waiting time to play the media. Then we provide a progressive MBMS download system to compare the gain in waiting time. Reliability is assumed to be provided with a FEC mechanism. We considered Reed Solomon and Raptor FEC and finally provided comparisons of both FEC methods with regards to savings in waiting time for progressive download. The results encourage the usage of progressive ownload instead of legacy download mechanism where the data file is streamable, for improved user experience for 3G wireless multicasting systems.

The emerging Car-to-Car communication (C2C) technology, known as Wireless Access in Vehicular Environments (WAVE), enables vehicles on the roadway to communicate with each other and with the roadside infrastructure. In addition to safety-relevant services, drivers may also need Internet access through C2C communications for infotainment services and car maintenance services, as specified in MobilitY and CollAboRative Work in European Vehicle Emergency NeTworks (MYCAREVENT) project. In this article we propose solutions for providing on-board Internet access service to automotive users through C2C communications. The proposed solutions make use of roadside infrastructure and the novel MYCAREVENT Vehicular Communication Gateway (VCG) device. A management scheme is developed for the opportunistic wireless links between On-Board Units (OBUs) and Road-Side Units (RSUs), as well as between OBUs and VCGs in vehicular communications. Furthermore, we invent a novel MAC queue architecture addressing the drawback of the current WAVE MAC protocol in supporting unicast traffic in highly dynamic vehicular environments. At the end, stochastic simulation results are presented to prove the concepts and validate the proposed solutions.

In our society based on communication, the barrier between the spoken and gestural languages remains a main problem for the deaf-mute. To make this communication possible, we propose developing an interface using mobile phone camera with a module of recognition allowing the recognition and the restitution of the sign language in the form of synthesized words. This module is based on a spectral comparison between the image to recognize and a correlation multidecision segmented filter resulting from images reference coming from a predetermined database: correlation technique. The latter has been used for a long time to recognize a target image. However an adaptation of this technique is necessary to take into account particular characteristics of gestures (for which the target image to recognize evolves in time) and to be able to send it with a high transmission rate. Thus to obtain a reliable decision, the module of recognition must carry out a very large number of correlations, which slows down the translation process. In order to reduce this processing time, we propose implementing our recognition module by using multipost technique “PVM”. This technique is based on the distribution of calculation on various stations in parallel. This technique enables us to distribute the required computing effort on various parallel stations using (PVM) a Parallel Virtual Machine. It showed significant gains in computing time but not sufficiently for a real-time translation (mobile phone communication). To further reduce processing time, we propose adding a Comprehension Pre-selection module to the initial recognition module. The former is based on the division of images (resulting from the gesture target) in various zones, in order to reduce and eliminate all the improbable gestures, according to the positions of hands. Thus, we reduce the needed identification time.

UMTS (Universal Mobile Telecommunications System) can be connected to the data networks. So Internet traffic services such as WWW browsing, email, ftp, SMTP (Simple Mail Transfer Protocol) should be handled by UMTS. Each of the traffic services has some specific properties but all of them obey a basic ON/OFF model. For a specific traffic user there is some unused (OFF) times between transmitted packets which we may use them for other services. In this paper based on the offered traffic services, models and parameters presented in 3GPP (3th Generation Partnership Project) we calculate ON and OFF time durations of the above traffic services in some different data rates, then calculate their corresponding activity factors. Finally we survey their impacts on the UMTS capacity and users. Simulation showed that the number of packet traffic users could be increased in comparison with circuit switch voice traffic users because they have lower Erlang traffic figures.

Nonlinear distortion of power amplifier is one of the major factor that degrades the performance of OFDM systems .Instead of estimating the nonlinearity at transmitter such as ordinary pre-distortion (PD), this paper estimates the nonlinearity of amplifier at the receiver. The problem is that nonlinear and multipath dispersion mix together at receiver end. And their parameters are generally unknown, so conventional method doesn’t work well. In this paper, an algorithm that estimates both the nonlinear parameters of the power amplifier and the impulse response of the wireless channel is proposed. Multi-level PN sequences are transmitted to construct a Vandermonde matrix, which separates the nonlinearity and linearity into different subspaces. The separation makes it easy to estimate the nonlinearity and linearity independently.