摘要:

AbstractWe present an approach for constructing simple time‐based tariffs for variable bit‐rate (VBR) connections from constant bit‐rate (CBR) prices, using price multipliers that depend on the traffic parameters of the VBR connection and reflect the resource usage of VBR connections relative to CBR connections. Our approach employs an effective bandwidth bound as a proxy for the maximum amount of traffic that conforms to the connection's traffic contract, and thus for the maximum resource usage. We compare the price multipliers computed by our approach with the multipliers published by an actual ATM service provider, and with those computed using a proxy for resource usage that is based on ATM Forum's generic CAC algorithm. Although our approach is presented in the context of ATM VBR services, it can be applied for creating tariffs for service level agreements (SLAs) where the maximum amount of conforming traffic is given by leaky (or token) bucket constraints. Copyright © 20

ISSN:1124-318X    

DOI:10.1002/ett.901

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

年代:2003

数据来源: WILEY

摘要:

AbstractMotivated by the discrete multi‐rate Kaufmann–Roberts recurrence relations, we derive a functional equation (FE), which covers nonintegral states. This FE implies a unique effective step parameterd, which defines an equivalent one‐level recurrence depth, or bit‐rate, at each state under progress. This state‐dependent depth results from the equality requirement of the multi‐rate and the one‐level model in the moment‐generating function transform domain. By this method it is possible to modeldby a few moments of the original multi‐rate statistic. In this case we obtain an explicit FE solution covering the entire (global) state space. Next we verify that the resulting state probability density incorporates iteratively enumerated discrete state probabilities, including the state‐dependent depth. With a system capacityCthe iterations then need time complexities betweenO(C) andO(C2). In contrast to this each FE state, is performed at a time complexityO(1). By the efficient coverage of the whole state space, fast optimizations of multi‐rate networks and multi‐resource systems can be improve

ISSN:1124-318X    

DOI:10.1002/ett.902

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

年代:2003

数据来源: WILEY

摘要:

AbstractOne‐step iterative decoding for bit‐interleaved coded QAM with conventional Gray mapping can give a significant improvement of performance for fading channels. Furthermore, iterative decoding with ideally known feed back bits is easier to analyze theoretically than non‐iterative decoding. In this paper, we derive analytical expressions for the pairwise error probabilities for bit‐interleaved coded QAM with correct feedback bits. They are used to obtain union bounds for the bit error rate. Numerical simulations show that the performance with only one feedback step comes very close to these ideal theoretical curves. They are therefore a reasonable guideline for system design to choose the right code rate and modulation level for bit‐interleaved coded QAM in a fading channel. Copyright

ISSN:1124-318X    

DOI:10.1002/ett.903

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

年代:2003

数据来源: WILEY

摘要:

AbstractThis work presents a semi‐analytic method for the design of orthogonal frequency division multiplexing (OFDM) systems, thereby avoiding the use of intensive simulation runs. In particular, the power of the distortion on each sub‐channel is evaluated analytically for any possible choice of system parameters (namely the number of virtual carriers, the length of the cyclic prefix, the delay spread of the channel, the impulse response of the transmit and receive filters). By this means, we may calculate the values of the above parameters which guarantee a desired system performance. Copyright © 2003

ISSN:1124-318X    

DOI:10.1002/ett.904

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

年代:2003

数据来源: WILEY

摘要:

AbstractIn the absence of channel noise, variable‐length quantizers perform better than fixed‐rate Lloyd–Max quantizers for any source with a non‐uniform density function. However, channel errors can lead to a loss of synchronization resulting in a propagation of error. To avoid having variable rate, one can use a vector quantizer selected as a sub‐set of high probability points in the Cartesian product of a set of scalar quantizers and represent its elements with binary code‐words of the same length (quantizer shaping). We choose these elements from a lattice, resulting in a higher quantization gain in comparison to simply using the Cartesian product of a set of scalar quantizers. We introduce a class of lattices which have a low encoding complexity, and at the same time result in a noticeable quantization gain. We combine the procedure of lattice encoding with that of quantizer shaping using hierarchical dynamic programming. In addition, by devising appropriate partitioning and merging rules, we obtain sub‐optimum schemes of low complexity and small performance degradation. The proposed methods show a substantial improvement in performance and/or a reduction in the complexity with respect to the best known results. Copyrig

ISSN:1124-318X    

DOI:10.1002/ett.905

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

年代:2003

数据来源: WILEY

摘要:

AbstractA robust decoder that performs soft‐decision adaptive decoding of space–time trellis code in mobile wireless channels with impulsive noise is developed. Under the control of an instantaneous impulsive noise detector, the proposed decoder performs clipped adaptive spatial diversity in the trellis search and tracks the time‐varying channel with a variable‐step‐size LMS algorithm. Computer simulation shows that the proposed decoder can enhance system performance remarkably when impulsive noise modeled as ε‐mixture Gaussian is presented. Copyrigh

ISSN:1124-318X    

DOI:10.1002/ett.906

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

年代:2003

数据来源: WILEY

摘要:

AbstractThe diverse nature of Internet applications gives rise to a need for a network architecture that is robust and can support a wide range of quality of service. Differentiated service is one such architecture. Although it has been the subject of much recent research, existing work focuses primarily on wired networks. As wireless networks become more important, it is necessary to examine the performance of differentiated service over these types of networks. In this paper, we analyze the performance of an RIO queue fed with homogeneous On/Off sources over a two‐state Markov wireless channel. The system is used to model the provision of assured forwarding differentiated service over wireless links. A novel stepped‐RIO scheme is used to provide an analytically tractable representation, and simulation results confirm the accuracy of the analytical model. Copyright © 2003

ISSN:1124-318X    

DOI:10.1002/ett.907

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

年代:2003

数据来源: WILEY

摘要:

AbstractHigh‐quality mobile services need to compensate for acoustic echoes that may affect modern cellular phone receivers. To this purpose, adaptive linear filters are generally used since their low complexity allows real‐time implementations. However, they often have to identify an acoustic echo path that may contain significant nonlinearities. Therefore, in such cases, a nonlinear model is required.It is well known that Volterra filters are well suited for modeling a large class of nonlinear systems, but they often require too many computational resources for a real‐time implementation. The purpose of this paper is twofold. First of all, we propose to use a simplified quadratic Volterra filter, derived taking into account the characteristics of the most important nonlinearities that affect cellular receivers. Second, an efficient adaptation algorithm is derived which extends theAffine Projection (AP)algorithm, proposed for linear filters, to quadratic Volterra filters. This adaptation algorithm offers better convergence and tracking capabilities with respect to the standard LMS and NLMS algorithms. The reduced complexity and the fast adaptation rate make the echo cancellers we are proposing attractive for real‐time implementations. Copyright ©

ISSN:1124-318X    

DOI:10.1002/ett.908

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

年代:2003

数据来源: WILEY

摘要:

AbstractThis letter describes a discrete Fourier transform (DFT) for prime transform lengthsN ≥ 3, where the sample values are elements of finite (Galois) fields GF(2m). Aregularanduniformsystem of additions and multiplications is presented which reduces the multiplicative complexity by at least one‐quarter, compared with a brute‐force implementation. The benefits of the algorithm are shown with respect to BCH decoding; in particular, the efficient computation of syndromes will be discussed. Copyright

ISSN:1124-318X    

DOI:10.1002/ett.909

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

年代:2003

数据来源: WILEY

摘要:

AbstractIndoor radio communication systems have challenged scientist's to understand the propagation of radio signals within buildings. A prerequisite to the design of these systems is knowledge of indoor radio propagation characteristics, and the information concerning the building's interior structure that strongly affects the signal propagation. This paper contributes to the modeling of propagation losses, and measurement techniques and methods in modern office buildings, by presenting measurement results at 1.89 GHz (DECT European Frequency). Narrowband propagation measurements were conducted within the Hellenic Telecommunication Organization premises (OTE building) in Athens, Greece. We examine the indoor signal behavior, considering site‐specific information for both single‐floor (including LOS and NLOS scenarios) and multi‐floor cases, extracting the indoor radio channel characteristics. Path‐loss factors ranged from 1.6 to 2.0 for LOS cases and 2.1 to 3.0 for NLOS cases, both for single‐floor topographies. In multi‐floor conditions the decay factor is up to 6.7. The composed prediction for the entire data set gives a mean error and standard deviation of 4.5 and 3.0 dB respectively. Copyr

ISSN:1124-318X    

DOI:10.1002/ett.910

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

年代:2003

数据来源: WILEY