Additive stable solutions on perfect cones of cooperative games

Closed kernel systems of the coalition matrix turn out to correspond to cones of games on which the core correspondence is additive and on which the related barycentric solution is additive, stable and continuous. Different perfect cones corresponding to closed kernel systems are described. Received: December 2001/Revised: July 2002 RID="*" ID="*"  This note contains the new results, which were presented by the first author in an invited lecture at the XIV Italian Meeting on Game Theory and Applications in Ischia, July 2001. The lecture was dedicated to Irinel Dragan on the occasion of his seventieth birthday.     

Broadband arrayed waveguide gratings on InP

Broadband arrayed waveguide gratings on InP are presented using a novel S-shape design. This design was utilized to accommodate the large free spectral range required for broadband operation. Four and eight channel AWGs with a wavelength channel spacing of 18 nm are discussed. The output peaks of the AWGs have a wide FWHM of 11 nm which provides insensitive operation to polarization, temperature fluctuations, and chromatic dispersion.     

自由空间基于激光编码调制技术语音通讯机的系统设计

基于自由空间光通讯(FSO)技术和OCDMA编码调制技术实现了自由空间语音异地通讯,具有高速高效、抗干扰能力强、保密性好等优点。系统设计采用双CPU结构,主控CPU单元主要实现语音采集、信号编码、数字调制等功能,辅单片机则为FSO关键技术ATP伺服系统的控制核心,论述了设计要点,并给出了测试结果。     

无线通信领域的“下一个大事件”——认知无线电

认知无线电是在软件无线电基础上发展而来的能够自适应外界环境变化的智能无线通信系统,其核心思想是使无线通信设备具有发现"频谱空穴"并合理利用所发现的"频谱空穴"的能力。认知无线电的提出为从根本上解决日益增长的无线通信需求与有限的无线频谱资源之间的矛盾开辟了一条行之有效的新途径。从认知无线电技术的研究背景入手,综合阐述了认知无线电的定义及其特点、实现认知无线电的关键技术以及超宽带与认知无线电相结合的认知超宽带通信技术。     

A combined optical–wireless indoor communication system

This new combined optical–wireless indoor communication system provides an economic and flexible approach for local area networks mainly in large buildings or in a group of several buildings. The radiation from the radio base stations of mobile networks cannot penetrate into large buildings completely. That problem is more serious at higher frequencies. The present approach offers a good solution to this problem. In this approach the wireless communication serves small picocells which are interconnected by an optical backbone. The performance of the system is enhanced by assigning a specific radio frequency for each picocell which enables the transmission of the wireless channels without altering their modulation formats. This method allows for a simple, and low-cost indoor communication system.     

Mitigating the gateway bottleneck via transparent cooperative caching in wireless mesh networks

Wireless mesh networks (WMNs) have been proposed to provide cheap, easily deployable and robust Internet access. The dominant Internet-access traffic from clients causes a congestion bottleneck around the gateway, which can significantly limit the throughput of the WMN clients in accessing the Internet. In this paper, we present MeshCache, a transparent caching system for WMNs that exploits the locality in client Internet-access traffic to mitigate the bottleneck effect at the gateway, thereby improving client-perceived performance. MeshCache leverages the fact that a WMN typically spans a small geographic area and hence mesh routers are easily over-provisioned with CPU, memory, and disk storage, and extends the individual wireless mesh routers in a WMN with built-in content caching functionality. It then performs cooperative caching among the wireless mesh routers.We explore two architecture designs for MeshCache: (1) caching at every client access mesh router upon file download, and (2) caching at each mesh router along the route the Internet-access traffic travels, which requires breaking a single end-to-end transport connection into multiple single-hop transport connections along the route. We also leverage the abundant research results from cooperative web caching in the Internet in designing cache selection protocols for efficiently locating caches containing data objects for these two architectures. We further compare these two MeshCache designs with caching at the gateway router only.Through extensive simulations and evaluations using a prototype implementation on a testbed, we find that MeshCache can significantly improve the performance of client nodes in WMNs. In particular, our experiments with a Squid-based MeshCache implementation deployed on the MAP mesh network testbed with 15 routers show that compared to caching at the gateway only, the MeshCache architecture with hop-by-hop caching reduces the load at the gateway by 38%, improves the average client throughput by 170%, and increases the number of transfers that achieve a throughput greater than 1 Mbps by a factor of 3.     

Network Synchronization of an Orthogonal CDMA Satellite Communication System

This paper provides the network synchronization of an orthogonal CDMA geostationary satellite system for fixed service communications. It includes the synchronization procedures, the system architecture and the performance evaluation. The main objective is to provide network wide synchronization of all uplink orthogonal CDMA transmissions. This is achieved in steps; first by providing coarse synchronization using the uplink random access channel and then fine sync using innovative tracking control mechanisms. The uplink access channel receiver utilize a parallel/serial search method for rapid code acquisition, while the code tracking of the uplink orthogonal CDMA traffic channel is based on a delay feedback early-late gate in which the sych control resides in the receiver. The proposed system is designed to minimize the onboard complexity and satisfy the performance requirements. As shown in the performance section, the requirement that all uplink transmissions are synchronized to a reference time within 10% of the chip length can be achieved. In addition, the system analysis determines the design parameters values which optimize performance.     

High Altitude Platform Station (HAPS): A Review of New Infrastructure Development for Future Wireless Communications

This paper looks into the relatively new field of high altitude platform stations. HAPS is seen as a ‘middle ground’ between the terrestrial and satellite cases, and aims to exploit of the advantages of both types of system. Since HAPS is such a new field, this paper focuses on the technology behind a HAPS communications system, how this has developed, and compares it to the terrestrial and satellite equivalents. One important area that is being investigated is the applications for which HAPS should be used. This is a critical issue if a significant business case is to be made for HAPS. Worldwide HAPS projects and research issues are also highlighted. Finally, the review concludes with the remarks on the future of HAPS for wireless communications systems.     

Non-coherent UWB Radio for Low-rate WPAN Applications: A Chaotic Approach

The requirements of low cost, low power and longer operation range for low-rate wireless personal area network (LR-WPAN) applications has driven the utilization of non linear communication approach. In this paper, a combined ultra-wideband (UWB) and chaotic communication technologies is proposed to meet these challenging demands. Among the candidates, the differential chaos shift keying (DCSK) modulation appears to be a very promising solution. The DCSK is a family of transmit reference (TR) system where a correlator based receiver is used to demodulate the received signal. However, this is not very well understood in the literature and therefore we will exemplify this issue in terms of noise performance. Furthermore, the feasibility study of the proposed DCSK is presented through the scalability and link budget analysis in two different operation modes. The system performance in both additive white Gaussian noise (AWGN) channel and standardized IEEE 802.15.4a UWB multipath channels are provided in order to further demonstrate the capability of the proposed system.     

Generation, detection and characterization of optical minimum shift keying data format

This paper presents the detailed principle on the generation and detection of optical minimum shift keying (MSK) format for high-speed and high spectral efficiency WDM systems. 10.7 Gb/s optical MSK data is successfully generated by experiment using the proposed scheme. The results show that optical MSK signal exhibits very compact optical spectrum, which is promising for high spectral efficiency WDM applications. Simulation results on dispersion and nonlinear tolerance comparison confirm that MSK signal has better dispersion tolerance and nonlinear tolerance compared with 50% duty cycle return-to-zero differential phase shift keying (RZ-DPSK) and 50% duty cycle RZ on-off-keying (RZ-OOK) formats.