基于IEEE802．15．4实现无线语音通信

提出一种基于IEEE802.15.4的无线语音通信技术方案,该方案采用TI公司的CC2430芯片进行设计,充分利用CC2430 SoC的性能特点,使用的外围器件很少,很好地实现了短距离无线语音传输,具有成本低,音质较好的优点.     

A mobile virtual-distributed system architecture for supporting wireless mobile computing and communications

This paper describes a novel mobile virtual-distrubuted system architecture for supporting global mobile computing and communications. the principal contribution of this paper is to innovatively apply virtual memory concepts to mobile systems by deploying mobile-floating agents to de-couple services and resources from the underlying network and allow them to move around following their mobile users. The mobile-floating agents maintain data structures associated with a mobile user. By combining the mobile-floating agent functions with a predictive mobility management algorithm and location-aware caching and prefetching, services and user data structure are pre-connected and pre-assigned at the locations to which the user is moving. Thus, the users can maintain their data structures or immediately receive service with virtually the same efficiency as at the previous location.     

Challenges for nomadic computing: Mobility management and wireless communications

In this paper, we present several challenges and innovative approaches to support nomadic computing. The nomadic computing environment is characterized by mobile users that may be connected to the network via wired or wireless means, many of whom will maintain only intermittent connectivity with the network. Furthermore, those accessing the network via wireless links will contend with limitations of the wireless media. We consider three general techniques for addressing these challenges: (1) asymmetric design of applications and protocols, (2) the use of network-based proxies which perform complex functions on behalf of mobile users, and (3) the use of pre-fetching and caching of critical data. We examine how these techniques have been applied to several systems, and present results in an attempt to quantify their relative effectiveness.     

A class of mobile motion prediction algorithms for wireless mobile computing and communications

This paper describes a class of novel mobile motion prediction algorithms for supporting global mobile data accessing. Traditionally, mobility and routing management includes functions to passively keep track of the location of the users/terminals and to maintain connections to the terminals belonging to the system. To maintain uninterrupted high-quality service for distributed applications, it is important that a mobile system be more intelligent and can anticipate the change of the location of its user. We propose an aggressive mobility and routing management scheme, called predictive mobility management. A class of mobile motion prediction algorithms predicts the future location of a mobile user according to the user's movement history, i.e., previous movement patterns. By combining this scheme with mobility agent functions, the service and user routing data are actually pre-connected and pre-assigned at the locations to which the user is moving. Thus, the user can immediately receive service or data with virtually the same efficiency as at the previous location, i.e., without encountering a large data structure handover delay before service or data is available.     

Performance study of the minimax robust phased array for wireless communications

In this paper, new robust M-estimation techniques are developed for combating impulsive noise and multiple-access interference in communication systems. Power functions of the proposed robust estimators are obtained by minimizing a nonquadratic residual function derived from the Huber's minimax robust estimation theory. Maximum peaks of these power functions are used for estimation of communication signals as well as direction of arrival. A strong advantage of the proposed robust M-estimation algorithms is a decreased sensitivity of the estimates with respect to an actual unknown distribution of random noises and interferences. Simulation results demonstrate that the proposed robust algorithms, the robust median, and robust Huber estimators, offer significant performance gain over the conventional and minimum-variance distortionless-response estimators, with the best results given by the robust Huber estimator.     

Proposal of a voice activity detector for noise reduction

In some noise reduction techniques, the learning of noise characteristics is required and a voice activity detector (VAD) must be used to determine noise sequences. The VAD proposed is derived from the coherence function computed from two microphones. It is combined with a noise reduction technique and its influence evaluated     

A low-power-consuming SOM for wireless communications

This paper presents theoretical and experimental results of a low-power-consuming hybrid push-pull self-oscillating mixer (SOM) circuit at the UHF frequency band. The frequency-stable SOM circuit is designed and fabricated using matched-pair Si bipolar junction transistors and high-Q resonators, where measured phase noise of this free-running voltage-controlled oscillator is -101.2 dBc/Hz at 100-kHz offset. A 20-dB up-conversion gain, a compression dynamic range (CDR) of 65 dB·MHz, and a spurious-free dynamic range of 50 dB·MHz ^2/3 are also measured for the mixer portion of this SOM. Moreover, a down-conversion gain of ≈-2 dB with a CDR of 100 dB·MHz is also measured     

Performance evaluation of a triangular pyramidal fly-eye diversity detector for optical wireless communications

Background noise and multipath propagation are the major impairments in indoor optical wireless links. They can introduce heavy distortion in the received optical signal and can degrade the system performance. An investigation into the optical wireless system performance has been carried out for two configurations: a hybrid system, and a diffuse system with a single detector and a triangular pyramidal fly-eye diversity receiver (PFDR). Original results for both systems that employ a PFDR antenna, under different fields of view (FOVs), are presented. The design goal is to reduce the effect of signal spread and improve the signal-to-noise ratio when the system operates under the constraints of background noise and multipath dispersion. It is demonstrated that through PFDR FOV optimization the directional background interference can be reduced and the received pulse shape improved.     

An integrated CDMA code assignment model for voice and data traffic in wireless communications

Wireless personal communication requires a provision of integrated services of multimedia traffic, such as voice and data, over the radio link. The multiple access protocols of code-division multiple-access (CDMA) techniques have been widely investigated in the recent literature. This paper presents an innovative multiple access protocol for CDMA-based wireless communication systems by fully utilizing the characteristics of voice and data traffic. In other words, a voice terminal can reserve a spreading code to transmit packets in multiple talk spurts, while a data terminal can transmit packets by either using the unassigned codes or borrowing the codes from the voice terminals during their silent periods. We build mathematical models for voice and data subsystems, respectively. Two performance parameters, the average dropping probability for voice packets and the average transmission delay for data packets, are derived based on the equilibrium point analysis. The effects of the two performance parameters on the system performance are discussed by varying the code reservation intervals of the voice terminals.     

Turbo-MIMO for wireless communications

This article reviews an important class of MIMO wireless communications, known collectively as turbo-MIMO systems. A distinctive property of turbo-MIMO wireless communication systems is that they can attain a channel capacity close to the Shannon limit and do so in a computationally manageable manner. The article focuses attention on a subclass of turbo-MIMO systems that use space-time coding based on bit-inter-leaved coded modulation. Different computationally manageable decoding (detection) strategies are briefly discussed. The article also includes computer experiments that are intended to improve the understanding of specific issues involved in the design of turbo-MIMO systems.     

A new multistage detector for synchronous CDMA communications

In this paper, we develop a new multistage detector to approach the optimal solution of the detection problem in a synchronous code division multiple access (CDMA) system. The transformation modifies the diagonal elements of the Hessian matrix of the quadratic likelihood function and brings the continuous minimum of the transformed function as close to the optimal solution as possible. The computational complexity is essentially linear with the number of users, except that a few computations of a quadratic function are needed     

A voice over IP service architecture for integrated communications

The convergence of the traditional telecommunications world and the Internet has sparked the rapid evolution of Internet telephony, which has also introduced new implementation paradigms. As a result, the creation of a large variety of new and sophisticated communication services has become possible. This article addresses the problem of integrating IP-based telephony with the legacy circuit-switched intelligent network and proposes a novel service architecture for their seamless integration     

An algorithmic solution for computing circle intersection areas and its applications to wireless communications

A novel iterative algorithm for the efficient computation of the intersection areas of an arbitrary number of circles is presented. The algorithm, on the basis of a trellis structure, hinges on two geometric results, which allow the existence check and the computation of the area of the intersection regions generated by more than three circles by simple algebraic manipulations of the intersection areas of a smaller number of circles. The presented algorithm is a powerful tool for the performance analysis of wireless networks and finds many applications, ranging from sensor to cellular networks. As an example of practical application, an insightful study of the uplink outage probability in a wireless network with cooperative access points as a function of the transmission power and access point density is presented. Copyright © 2012 John Wiley & Sons, Ltd.     

A high-speed transmission method for wireless personal communications

The next-generation wireless personal communications systems are expected to support a wide range of high-quality services that require high data rates. Communicating at high transmission rates over the harsh wireless environment, however, creates many difficult and challenging problems. In this paper, we describe a technique for the high-speed transmission of data in wireless personal communications which we denote as multicode modulation. In this technique, the high-rate bit transmitted data is serial to parallel converted into low-rate bit streams in a similar fashion to multicarrier or multitone modulation. However, in contrast to the multicarrier method, here we propose to modulate each low-rate bit stream using direct-sequence spread-spectrum on a single carrier. It is demonstrated that by selecting the processing gain properly the total required bandwidth will be of the same order as the original high-rate data stream; thereby, gaining the inherent benefit of multipath rejection without expanding the bandwidth of the original high-rate stream. To demonstrate the potential and merits of the proposed method as an alternative technique for high-speed transmission for wireless personal communications, various simulation results over a multipath Rayleigh fading link are presented.Supported in part by the Hong Kong Research Grant Council, Project No. HKUST562/94E and the Hong Kong Telecom Institute of Information Technology, Project No. HKTIIT94/95.EG03.     

Integrated receivers for wireless communications: A review

A review is presented that addresses the circuit-design aspects of integrated receiver front ends with their CMOS realization in mind. Performance data on specific front ends and their individual units are given with emphasis on low-noise amplifiers, mixers, and voltage-controlled local oscillators. Promising lines of research and development are identified.     

A simple transmit diversity technique for wireless communications

This paper presents a simple two-branch transmit diversity scheme. Using two transmit antennas and one receive antenna the scheme provides the same diversity order as maximal-ratio receiver combining (MRRC) with one transmit antenna, and two receive antennas. It is also shown that the scheme may easily be generalized to two transmit antennas and M receive antennas to provide a diversity order of 2M. The new scheme does not require any bandwidth expansion or any feedback from the receiver to the transmitter and its computation complexity is similar to MRRC     

A robust adaptive weighted constant modulus algorithm for blind equalization of wireless communications systems under impulsive noise environment

A robust adaptive weighted constant modulus algorithm is proposed for blind equalization of wireless communication systems under impulsive noise environment. The influence of the impulsive noise is analyzed based on numerical analysis method. Then an adaptive weighted constant modulus algorithm is constructed to adaptively suppress impulsive noise. Theoretical analysis is provided to illustrate that the proposed algorithm has a robust equalization performance since the impulsive noise is adaptively suppressed. Moreover, the proposed algorithm has stable and quick convergence due to avoidance of large misadjuntment and adoption of large step size. Simulation results are presented to show the robust equalization performance and the fast convergence speed of the proposed algorithm under both impulsive noise and Gaussian noise environments.     

Network issues for wireless communications

This article specifically focuses on wireless personal communications, i.e., wireless access, that provides either terminal or personal mobility. In particular, we discuss some important issues in networking, traffic, and performance. Although within radio and networking aspects there are significant commonalities between traditional cellular mobile communications and wireless personal communications, there exist distinct differences due to radio propagation and fading effects, interference environment, smaller cell sizes, type and pattern of mobility, and call delivery. Indeed, with respect to networking issues, a large set of system choices, characteristics of traffic to be carried, and important parameters have to be considered. These include the problems involved in selecting an appropriate multiaccess technology to efficiently handle the required subscriber service profile across a multiplicity of systems to complete a call. To present a meaningful discussion of these issues, we address in some detail radio resource assignment, mobility management, call control, and traffic aspect, which have significant impact on the network performance