Performance analysis of geography‐limited broadcasting in multihop wireless networks

In multihop wireless networks, delivering a packet to all nodes within a specified geographic distance from the source is a packet forwarding primitive (geography‐limited broadcasting), which has a wide range of applications including disaster recovery, environment monitoring, intelligent transportation, battlefield communications, and location‐based services. Geography‐limited broadcasting, however, relies on all nodes having continuous access to precise location information, which may not be always achievable. In this paper, we consider achieving geography‐limited broadcasting by means of the time‐to‐live (TTL) forwarding, which limits the propagation of a packet within a specified number of hops from the source. Because TTL operation does not require location information, it can be used universally under all conditions. Our analytical results, which are validated by simulations, confirm that TTL‐based forwarding can match the performance of the traditional location‐based geography‐limited broadcasting in terms of the area coverage as well as the broadcasting overhead. It is shown that the TTL‐based approach provides a practical trade‐off between geographic coverage and broadcast overhead. By not delivering the packet to a tiny fraction of the total node population, all of which are located near the boundary of the target area, TTL‐based approach reduces the broadcast overhead significantly. This coverage‐overhead trade‐off is useful if the significance of packet delivery reduces proportionally to the distance from the source. Copyright © 2011 John Wiley & Sons, Ltd.     

New modeling approach to the frequency assignment problem in broadcasting

This paper presents an original algorithm that uses a new modeling approach of the interference constraints and uses a probabilistic taboo search algorithm to solve the frequency assignment problem in the field of broadcasting. The results obtained by our algorithm are compared to the operating solutions in the field of FM broadcasting in France and the best known results obtained by hybrid genetic algorithm (Idoumghar et al. 2002) that uses a classical modeling of the interference constraints. By analyzing the results obtained by our approach we can observe that we efficiently enhance the quality of the solutions.     

Travelling wave expansion: a model fitting approach to the inverse problem of elasticity reconstruction

In this paper, a novel approach to the problem of elasticity reconstruction is introduced. In this approach, the solution of the wave equation is expanded as a sum of waves travelling in different directions sharing a common wave number. In particular, the solutions for the scalar and vector potentials which are related to the dilatational and shear components of the displacement respectively are expanded as sums of travelling waves. This solution is then used as a model and fitted to the measured displacements. The value of the shear wave number which yields the best fit is then used to find the elasticity at each spatial point. The main advantage of this method over direct inversion methods is that, instead of taking the derivatives of noisy measurement data, the derivatives are taken on the analytical model. This improves the results of the inversion. The dilatational and shear components of the displacement can also be computed as a byproduct of the method, without taking any derivatives. Experimental results show the effectiveness of this technique in magnetic resonance elastography. Comparisons are made with other state-of-the-art techniques.     

加强广电台站管理构建和谐电波秩序

近年来，随着广播电视事业的发展，广播电视系统的无线电台大量增加，极大丰富了人民群众的精神文化生活，但广播电视系统无线电管理存在的一些问题也暴露出来，其中，调频广播电台对民用航空无线电专用频率的干扰就是亟需解决的问题之一。     

A general approach for all-to-all routing in multihop WDM optical networks

WDM optical networks provide unprecedented high speed and reliability for message transfer among the nodes. All-to-all routing is a fundamental routing problem in such networks and has been well studied on single hop WDM networks. However, the number of wavelengths to realize all-to-all routing on the single hop model typically is very large. One way to reduce the number of wavelengths is to use k-hop routing, in which each routing path consists of k segments and each segment is assigned a different wavelength, where k usually is a small constant. Because of the complexity of design and analysis for such a routing problem, only few papers discussed and proposed all-to-all routing by k/spl ges/2 hops. However, the proposed algorithms are usually exceeding complicated even for ring topologies. Often, an ad hoc approach is employed to deal with each individual topology. In this paper we propose a generic method for all-to-all routing in multi-hop WDM networks, which aims to minimize the number of wavelengths. We illustrate the approach for several optical networks of commonly used topology, including lines, rings, tori, meshes, and complete binary trees. For each case an upper bound on the number of wavelengths is obtained. The results show that this approach produces clear routing paths, requires less wavelengths, and can easily incorporate load balancing. For simple topologies such as lines and rings, this approach easily produces the same bounds on the number of wavelengths that were hard-obtained previously. Moreover, this general approach provides a unified routing algorithm for any d-dimensional torus, which seems impossible to obtain by the previous approach.     

基于网络编码的无线网络广播重传方法

提出了一种适用于无线广播的基于网络编码的重传方法--NCWBR,通过网络编码组合不同的丢失包进行重传.理论分析表明,该方法能保证接收节点的编码可解性,同时重传次数较原方法更优;模拟测试结果表明,与逐个重传的方法相比,NCWBR有效地减少了信息包的平均传输次数,提高了传输效率.     

Capacity and power control in spread spectrum macrodiversity radionetworks

What is the capacity of the uplink of a radio network of receivers? We consider a spread spectrum model in which each user is decoded by all the receivers in the network (macrodiversity). We use a carrier-to-interference performance criterion that we derive from Shannon theory; each user must find the right transmitter power level to satisfy its carrier-to interference constraint. Satisfying this requirement for all users is equivalent to solving a fixed point problem. We use this power control problem to derive the network capacity region and find that the feasibility of a configuration of users is independent of their positions in the network; each user can be assigned a bandwidth that is independent of the user's position in the network. Our capacity region is an upper bound over all schemes that treat the interference of other users as pure noise. To show that the capacity can be realized in practice, we propose a decentralized power adaptation algorithm and prove global convergence to the fixed point via a monotonicity argument     

A multiagent system for frequency assignment in cellular radionetworks

We present a multiagent algorithm for the frequency assignment problem in cellular radio networks. The algorithm, that has been successfully applied to GSM networks, efficiently assigns frequencies to each radio cell satisfying the constraints given by a compatibility matrix     

COMPLEX RAY EXPANSION OF PLANE WAVE

Based on the high frequency approximation theory, the complex ray expansion of plane wave is derived. The results obtained may be regarded as the basis of the numerical expansion of plane wave, which has been used successfully in some problems.     

Adaptive forwarding in frequency-hop spread-spectrum packet radionetworks with partial-band jamming

Adaptive protocols that specify the ways in which a radio is permitted to modify its normal forwarding procedures based on information obtained locally in the network are considered. A computer program has been developed to simulate a frequency-hop (FH) packet radio network with partial-band jamming and interference due to other FH and narrowband radios. The radios in the network use time-slotted, receiver-directed, FH spread-spectrum signaling. Results on throughput, delay, and end-to-end probability of success are presented, and comparisons between different forwarding protocols are given for a static network topology with both static and mobile network jamming     

Low-cost approach for steerable flat-plate antenna design withapplication to reception of broadcasting from satellite

A novel design approach for circularly polarised flat-plate antennas has been developed. The proposed antenna is of multilayer construction, rotatable about its normal axis, and comprises a polarisation convertor, an array of elements and a beamforming network. In one potentially large application, the reception of satellite broadcast signals in the 12 GHz band, it can be mounted flat on the most suitable wall of an arbitrarily orientated house and be readily aligned     

A Bayesian approach to image expansion for improved definition

Accurate image expansion is important in many areas of image analysis. Common methods of expansion, such as linear and spline techniques, tend to smooth the image data at edge regions. This paper introduces a method for nonlinear image expansion which preserves the discontinuities of the original image, producing an expanded image with improved definition. The maximum a posteriori (MAP) estimation techniques that are proposed for noise-free and noisy images result in the optimization of convex functionals. The expanded images produced from these methods will be shown to be aesthetically and quantitatively superior to images expanded by the standard methods of replication, linear interpolation, and cubic B-spline expansion.     

Delay and throughput for three transmission schemes in packet radionetworks

The results of a simulation of a fully connect packet communication network are presented. The network employs the slotted ALOHA channel access protocol, and Reed-Solomon coding is used to correct errors and erasures in the received packets. The network has a fixed number of channels available for packet transmissions. In two of the transmission schemes considered, a given packet transmission occurs on a single channel only. One of these employs fixed assignment of terminals to the channels, and the other employs random assignment. A third method permits each transmitter to hop randomly over the set of channels during the transmission of a packet. The terminal transmits on one channel at a time, and it transmits a fixed number of symbols during each dwell interval. Delay and throughput are evaluated for all three transmission methods. The effects of code rate on the performance of the channel-hopping scheme are explored, and the improvement that can be obtained for the channel-hopping scheme by use of incremental-redundancy transmission is examined     

Alternative approach to design of wave digital filters

The purpose of the letter is to outline an approach for designing wave digital filters that is based on a suitable interpretation of the scattering parameters of a network. The approach can be used for simulating analogue, doubly terminated, lossless ladder filters.     

The expansion wave concept. II. A new way to model mutual couplingin microstrip arrays

For pt.I see ibid., vol.46, no.3, p.397-406 (1998). A new expansion scheme is introduced to solve the integral equations describing the mutual coupling in microstrip arrays. The scheme is based on the fact that at larger distances the Green's functions in the stratified dielectric medium of the antenna structure can be approximated using analytical expressions. This allows one to describe the waves propagating between the elements thus causing mutual coupling with a small number of parameters. Since only these parameters have to be determined, the resulting number of unknowns is much smaller than with conventional rigorous techniques. The accuracy of the scheme is illustrated by a comparison of measured and calculated data for both a two-element and a linear eight-element microstrip array antenna     

Real-time support in multihop wireless networks

Personal communications and mobile computing will require a wireless network infrastructure which is fast deployable, possibly multihop, and capable of multimedia service support. The first infrastructure of this type was the Packet Radio Network (PRNET), developed in the 70's to address the battlefield and disaster recovery communication requirements. PRNET was totally asynchronous and was based on a completely distributed architecture. It handled datagram traffic reasonably well, but did not offer efficient multimedia support. Recently, under the WAMIS (Wireless Adaptive Mobile Information Systems) and Glomo ARPA programs several mobile, multimedia, multihop (M³) wireless network architectures have been developed, which assume some form of synchronous, time division infrastructure. The synchronous time frame leads to efficient multimedia support implementations. However, it introduces more complexity and is less robust in the face of mobility and channel fading. In this paper, we examine the impact of synchronization on wireless M³ network performance. First, we introduce MACA/PR, an asynchronous network based on the collision avoidance MAC scheme employed in the IEEE 802.11 standard. Then, we evaluate and compare several wireless packet networks ranging from the totally asynchronous PRNET to the synchronized cluster TDMA network. We examine the tradeoffs between time synchronization and performance in various traffic and mobility environments.     

The strongly connecting problem on multihop packet radio networks

The problem of strongly connecting a multihop packet radio network by using a minimal total amount of transmission power is investigated. This problem is shown to be NP-complete. An approximation algorithm with the same computational complexity as that of finding a minimum spanning tree is given. It is also shown that the approximation algorithm can find a solution no greater than twice that of the optimal solution. Experimental results show that the approximation solution may be close to the optimal solution     

A wave approach to hollow cylindrical electron cyclotron masers

A wave method has been applied to analyze and derive the dispersion equation for hollow cylindrical ECM's, which features in simpler mathematics and clearer physical interpretation. Besides, the effects of space charge Columb field have been taken into account. For the time being, the result is more likely suitable for fundamental mode interaction.     

The restricted shortest-path-based topology control algorithm in wireless multihop networks

In this paper, we present an energy-efficient topology control algorithm named RLSP. The algorithm first tries to preserve the minimum-energy paths. However, when a node finds it needs a large transmission power to cover some of its logical neighbors, it uses two-hop paths to reach them instead of using single links. Simulation results show that RLSP can effectively decrease the transmission power and reduce the energy consumption when transmitting.