摘要:

AbstractThe paper concerns the covering polynomial method of decoding cyclic codes. This is an easily‐implementable, robust, and low‐complexity decoding algorithm. The determination of the exact complexity of the algorithm is a difficult open problem. In this paper several methods for constructing minimal sets of covering polynomials are proposed for the caseR<2/τ, where τ is the number of errors to be corrected. Complete closed form specifications of the minimal set are given for the case where τ is even, and a computationally efficient procedure presented for general τ is shown to be optimal in many cases (and conjectured to be globally optimal). These results are sufficient to determine the exact minimal number of covering monomials for all binary cyclic codes of length up to 127 with τ<9. Closed form specifications are available for the covering polynomial set for all su

ISSN:1124-318X    

DOI:10.1002/ett.4460050602

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper describes suboptimal decoding methods for multilevel block‐encoded modulation schemes. These decoding methods can achieve large coding gains with relatively low decoding complexity, and operate, in part, by decoding a supercode of the code to be decoded. By decomposing the multilevel codes in various ways, a wide range of performance/complexity tradeoff points can be obtained. Introducing syndrome checking can further reduce the average decoding complexity with no degradation in performance. Both analysis and extensive simulation results confirm that a given coding gain can be achieved with significantly smaller decoding complexity than Viterbi decodin

ISSN:1124-318X    

DOI:10.1002/ett.4460050603

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe probability of co‐channel interference (PCI) in cellular radio systems is analyzed assuming that the desired signal and the co‐channel interferers are correlated in a log‐normal shadowing environment. The correlation between the signals in a log‐normal shadowing environment reduces the PCI and hence allows operation with shorter frequency reuse distances and smaller cluster sizes. Compared with omnidirectional systems, the cells employing directional antennas can operate with shorter frequency reuse distances and hence provide better usage of the frequency s

ISSN:1124-318X    

DOI:10.1002/ett.4460050604

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

年代:1994

数据来源: WILEY

摘要:

AbstractDirect digital synthesis and sigma‐delta techniques have been proposed in recent years to realize sinewave generators and modulators for data communication. This paper explains the basic principles behind these techniques and presents schemes which implement popular modulation methods such as frequency shift keying, phase shift keying and amplitude modulation. The schemes are mostly implemented with digital circuits. They ensure a high degree of flexibility and are fully compatible with VLSI integration technologies. Experimental results obtained on integrated semicustom devices have demonstrated the validity of this approac

ISSN:1124-318X    

DOI:10.1002/ett.4460050605

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

年代:1994

数据来源: WILEY

摘要:

AbstractSpace‐earth atmospheric attenuation in absence of rain can be estimated from atmospheric physical parameters, which are, in turn, obtainable from radiometric measurements of the sky brightness temperature. In this paper the radiometric inversion coefficients needed to retrieve the total vapour and liquid water content of the atmosphere from radiometric measurements are computed making use of a statistically significant data‐ base of radiosonde vertical profiles. Linear regression is applied to data collected over ten years at five Italian sites to derive the inversion coefficients under various operational hypotheses. Site‐to‐site and seasonal variabilities are analysed as well as the influence of both the instrumental characteristics and the criterium for detecting cloud liquid. A first set of values valid for the Italian territory is presented for system design

ISSN:1124-318X    

DOI:10.1002/ett.4460050606

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe development of very low bit rate image compression algorithms renders the transmission of moving and still video with associated speech in a variety of existing and future narrowband telecommunication networks. Existing analog, narrowband (mobile) networks represent a potential field for the introduction of digital bearer services under utilization of the underlying system resources in a compatible manner. A broader variety of services in coexistence with existing analog services may be provided without new network planning. This paper presents corresponding techniques for video and speech transmission in the existing Nonpublic Land Mobile Network under application of commercially available radio telephones and an additional, external digital signal processing unit. Special attention is given to the choice of a digital modulation method under consideration of network constraints such as adjacent channel interference and linear distortions due to nonideal analog IF filters. In this context a modified maximum likelihood detector based on an equivalent linear model of the baseband transmission link is presented. For robust low bit rate video transmission a combined source‐channel coding scheme with unequal error protection matched to the source and channel characteristics in case of the target mobile narrowband network is propose

ISSN:1124-318X    

DOI:10.1002/ett.4460050607

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

年代:1994

数据来源: WILEY

摘要:

AbstractA code division multiple access detector that employs a combination of a decorrelator and a multidimensional interference canceler is considered. The weights of the canceler are adaptively controlled using a steepest descent algorithm. The probability of error is evaluated and compared to those of the decorrelating detector and a similar, fixed‐weights scheme that requires an estimation of received signal energies. It is shown that the proposed two‐stage detector provides substantial improvement over the decorrelating detector, particularly in the presence of strong interfering signals. This is especially noticeable in the high bandwidth efficiency cases. It is also observed that in the presence of weak interferers, the proposed scheme performs better than its fixed‐weights counte

ISSN:1124-318X    

DOI:10.1002/ett.4460050608

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper deals with the modeling and performance evaluation of different Code Division Multiple Access schemes suitable for applications in terrestrial and satellite mobile communication networks. The use of particular propagation channel models and the relative sensitivity of different demodulation schemes to their parameters are the subject the paper is focused on. In particular, an extension to the case of wideband communications of Lutz's satellite channel model is presented. The main goal is to analyze how the increased interference level, typical of a multipath environment, can influence different demodulator architectures in different propagation conditions. Perfectly coherent and differential modulation methods are employed with conventional and RAKE receivers to derive the error rate performance by computer simulations. Some issues concerning the characterization of the propagation channel models in the case of the RAKE receiver are also investigated and discussed.

ISSN:1124-318X    

DOI:10.1002/ett.4460050609

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn this paper we will describe an algorithm, based on the Simulated Annealing technique, for solving the problem of multipulse excitation computation for speech coding applications. Multipulse excitation modeling is described by two set of parameters: pulse locations and amplitudes. The search for optimal pulse locations is the most burdensome task, since there is no closed form solution. Therefore, suboptimal approaches are used in order to maintain a good effectiveness in the parameter estimation while keeping the computational load within reasonable bounds. As compared to the one described in [2], the proposed algorithm achieves an effective improvement in objective performances of more than 1.5 dB. The price that must be paid for this performance improvement is the higher computational cost that this algorithm requires. The objective results of the proposed algorithm will be compared with the results of the algorithm described in [2], and the computational complexity will be analyzed.

ISSN:1124-318X    

DOI:10.1002/ett.4460050610

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

年代:1994

数据来源: WILEY

摘要:

AbstractA hierarchical control structure is proposed to ensure performance requirements and to maintain load balancing among different traffic classes at an ATM node. A two‐level control hierarchy is defined, where one level performs fixed class‐selective call admission control strategies that are periodically dynamically coordinated by a higher level bandwidth allocation controller. The call admission control rules are designed to maintain a certain grade of service, in terms of cell loss probability, given the buffer space and bandwidth (percentage of cells) assigned to each class. The assignment of buffers is performed off‐line, whereas bandwidth shares are periodically recomputed on‐line by the allocation controller, that attempts to minimize a cost function, accounting for overall cell loss and refused traffic. The bandwidth assignments obtained are passed to the call admission controllers, where they are used as parameters affecting the admission rules until the next intervention. The control structure, the strategies and the optimization algorithm used are described in detail, as well as the assumptions underlying the choices that have been made. Simulation results are reported and di

ISSN:1124-318X    

DOI:10.1002/ett.4460050611

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

年代:1994

数据来源: WILEY