摘要:

AbstractCircuit switching, suited to providing real‐time services due to the low and fixed switching delay, is not cost effective for building integrated services networks because it is based on static allocation of resources which is not efficient with bursty data traffic. Moreover it cannot handle flows that are not integer multiple of 64 Kb/s, preventing the usage of low bit rate codecs.This work explores the most suitable alternatives to the circuit switching technology (i.e. packet/cell switching) from the efficiency point of view, assuming that a PGPS scheduler is deployed in the network nodes. The paper defines an index to measure the efficiency of packet telephony, i.e. the volume of real‐time traffic withdeterministicallyguaranteed quality plus the amount of data carried related to the amount of network resources used. Furthermore it determines the maximum efficiency obtainable by packet networks, compares different network technologies and explores the problems of the deploying of low bit‐rate codecs. Copyright ©

ISSN:1124-318X    

DOI:10.1002/ett.926

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY

摘要:

AbstractDual‐Banyan (DB) is a buffered banyan asynchronous transfer mode (ATM) switch encompassing multiple input‐queueing (bifurcated queueing) as its buffering strategy. This paper describes a new analytical model for a performance evaluation of the DB switch under arbitrary traffic patterns. The model developed and presented enables the computation of the switch normalized throughput and the average packet delay by iterative calculations. The efficiency of the given model is verified through a comparison with simulation results, too. We compare throughputs of DB switch and input buffer banyan, and show that DB switch has significantly better performance levels. Copyright © 2003

ISSN:1124-318X    

DOI:10.1002/ett.927

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY

摘要:

AbstractIn the last few years, IP has moved towards resource reservation, with the task to guarantee in the future Quality of Service (QoS). This has led to flow admission control algorithms based on the negotiation of standardised traffic parameters. QoS can be guaranteed in any network,a priorifrom the used technology, only if the used admission control algorithm wisely shares the network's resources among the users. Any admission control algorithm on its turn can do so, only if every user respects the negotiated traffic parameters. Since any user could, maliciously or not, send at a higher rate than negotiated, i.e. use a higher share of resources than the negotiated one, in every network in which admission control is performed, a policing algorithm is used. An ideal policer should guarantee to reject no packet of a well‐behaved user and police contract violation as rigidly as possible. All this independently of the characteristics of the monitored stream and of the background traffic. This holds also for Integrated Services (IS) based IP networks. In these networks, every user negotiates a peak and an average rate. In this paper we present the solution to the peak rate policing issue. We adapt the Generic Cell Rate Algorithm (GCRA), well‐known policer used in ATM networks, to police the peak rate of flows of packets with variable length. We intuitively call this modified GCRA Generic Packet Rate Algorithm (GPRA) and dimension its parameters so that independently of the characteristics of the policed flow and of the background traffic, no packets of a well‐behaved user are rejected and that the flows of any misbehaving user are rigidly policed. Copyright © 20

ISSN:1124-318X    

DOI:10.1002/ett.929

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY

摘要:

AbstractIn this paper we investigate the concept of cyclically extended single carrier transmission with frequency domain equalization (SC/FDE). We present a detailed mathematical derivation of fast Fourier transform (FFT) based optimum linear receivers, and we describe the signal processing steps of an efficient FDE implementation structure. With a specific system design, where the parameters have been adapted to the IEEE 802.11a and Hiperlan/2 orthogonal frequency division multiplexing (OFDM) based wireless local area network (WLAN) standards in the 5 GHz band, we demonstrate that SC/FDE is a powerful candidate for high speed wireless future applications. Copyright © 2003 A

ISSN:1124-318X    

DOI:10.1002/ett.923

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY

摘要:

AbstractWoven convolutional codes are a family of error forward correction codes. An important construction within this code family are woven convolutional codes with outer warp. They allow us to provide unequal error protection for the encoded information. The performance of woven convolutional codes with outer warp and unequal error protection is studied in terms of error exponents. Two constructions are considered. The first is shown to allow a small part of the information to be essentially better protected without degrading the performance of the other part. The second construction possesses a two‐level error protection for a given partitioning of the information. The error exponents for both partitions are given and it is shown how the better protected information can be used in the process of decoding to improve the performance of the less‐protected information. Copyright © 2003

ISSN:1124-318X    

DOI:10.1002/ett.930

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY

摘要:

AbstractAdaptive antennas are used in mobile radio systems for improving coverage and increasing capacity. For realistic system design and simulation, channel models are required in order to assess the performance of such systems. We propose the so‐called ‘geometry‐based stochastic channel model’ (GSCM), which is easy to implement and has a low complexity even when the directional dimension of the channel is taken into account. In this model, we prescribe the probability density function (PDF) of the location of the scatterers. From this, the angularly resolved impulse response can be computed by a simple ray tracing. We then present various extensions of the model in urban environments, namely for diffraction losses and wave guiding by street canyons. We also discuss methods for efficiently implementing GSCM. Copyright ©

ISSN:1124-318X    

DOI:10.1002/ett.928

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY

摘要:

AbstractIn this letter, we propose a simple and useful approach based on artificial neural networks (ANNs) to help the determination process of the despreading sequences weighted by exponential chip weighting waveforms in a low processing gain direct sequence‐code division multiple access (DS‐CDMA) system. Numerical results show that the parameter values of the exponential chip weighting waveforms produced by the proposed network are nearly optimal and satisfactory in viewpoint of the achieved bit error rate (BER) performance. Copyright © 2003

ISSN:1124-318X    

DOI:10.1002/ett.921

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY

摘要:

AbstractA diversity reception system with majority decoding and optimal adaptive power loading (ADRM) applied to a Rayleigh fading channel is considered. It is shown that the proposed system has a lower average bit error rate (BER) than optimal diversity reception (ODR) with uniform power distribution for the same redundancy. The performance of the proposed systems is analyzed via computer simulation under the assumption that both forward and backward channels are noisy and with Rayleigh fading. The proposed ADRM can be used in a multicarrier modulation system with multistage encoding/decoding or in OFDM‐A. Copyright © 2003 A

ISSN:1124-318X    

DOI:10.1002/ett.924

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY

摘要:

AbstractThis paper discusses wireless systems using antenna arrays at both the transmitter and receiver. Space‐time coding is used to exploit the parallelism of the radio channels formed. Theoretical results on signal‐to‐noise ratio (SNR) degradation due to imperfect channel estimation are used to determine the optimum ratio of pilot to data symbols to be used in a Rayleigh fading environment. Exact results initially are obtained for the single transmit antenna case. These results are then extended to multiple transmit antennas, using analysis of an upper bound on error probability. The results can be used for any SNR, for any channel Doppler frequency and for any transmitter and receiver array size. Copyright © 20

ISSN:1124-318X    

DOI:10.1002/ett.925

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY

摘要:

AbstractIn this paper, we investigate joint channel estimation and signal detection approaches for a multi‐user CDMA uplink with a base‐station antenna array over asynchronous multipath fading channels. Based on the space alternating generalized expectation‐maximization (SAGE) algorithm, we develop an iterative multi‐user receiver to jointly estimate channel response vectors and bit sequences for all the active users at known fractional time delays, and a BER lower bound is derived. A simplified bit detection method is then proposed for multi‐rate CDMA systems. Simulation results show that the new iterative receiver performs equally well for both high‐ and low‐rate users, and the BER performance is close to that of the BER lower bound. Copyrig

ISSN:1124-318X    

DOI:10.1002/ett.922

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:2003

数据来源: WILEY