ISSN:1124-318X    

DOI:10.1002/ett.4460070602

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

年代:1996

数据来源: WILEY

摘要:

AbstractGeneralized concatenation of inner and outer convolutional codes is studied. The essential problem is the partitioning of the inner code. A construction procedure to obtain a suitable equivalent description for a given code is derived, which gives the best possible distances in the partitioned subcodes. The construction rule is illustrated with two examples. A small code is studied to emphasize the ideas of the construction and a large code, namely the satellite standard code, demonstrates the considerable gains in decoding performance when using generalized concatenation. Furthermore, the possibilities for iterative decoding are pointed out.

ISSN:1124-318X    

DOI:10.1002/ett.4460070603

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

年代:1996

数据来源: WILEY

摘要:

AbstractThis paper presents the variance analysis, and performance comparison, of the least‐squares frequency estimator (LSFE), and a specific version of the nonlinear frequency estimator (NIX). The results are obtained for the case where the received signal contains both phase and frequency errors (ΔΘ and Δfrespectively). It is shown that under rather restrictive conditions, the LSFE is a low signal‐to‐noise ratio approximation to the ML estimate of ΔfAlso considered are the effects on the moments of this estimate, if any of these conditions are violated. The latter part of the paper deals with the various versions of the NFE. The problem of phase ambiguity associated with these nonlinear estimators is investigated, and a resolution technique is

ISSN:1124-318X    

DOI:10.1002/ett.4460070604

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

年代:1996

数据来源: WILEY

摘要:

AbstractThrough the use of band‐spreading techniques electrical power distribution networks become reliable and universal data links. For cost and performance reasons all digital solutions for the. construction of modems are paramount. The use of general purpose digital signal processors (DSP) is neither feasible nor cost‐effective. After a review of appropriate signalling schemes the key components for integration into an ASIC will be outlined. Within the transmitter section of the ASIC a programmable address counter together with a sample memory provides precise and fast signal synthesis. In the receiver section a fast front‐end is needed for correlation operations. Furthermore essential steps towards bit decision are performed. A typical ASIC, representing the heart of a power line modem, finally contains the following functional blocks: An 8 bit correlator with a minimum of four separate accumulators, a squarer with at least two additional accumulators forming the decision logic, and a programmable 10 bit address counter. VHDL‐based ASIC design was performed and fabrication took place in October 1994 within the EUROCHIP project. An ASIC incorporates 5250 gates with a power consumption below 50 mW. Modems have been built with different signalling schemes for data rates up to 2400 bits/s. Measurements revealed typical bit error rates belo

ISSN:1124-318X    

DOI:10.1002/ett.4460070605

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn the Remote Sensing application domain, especially forSAR(Synthetic Aperture Radar) images characterized by notable textural properties, the use of context and the integration of multipolarimetric data appear essential to improving the accuracy of classification. Methods based on the MRF approach have recently yielded good results, as they allow the development of robust processing algorithms. Unfortunately, these methods are not free of drawbacks. For instance, they suffer from high computational complexity. Given these conditions, this paper proposes the Fuzzy Contextual Segmentation (FCS) method, which integrates uncertainty and contextual information in a smgle framework through a fuzzifiedk‐NNapproach. The membership value assigned to every site is updated by taking into account the information related to the steps of model‐matching, propagation of global context, and decision on local context. An application of the method to realSARimages is reported. Two fully polarimetric data sets were utilized to assess the performance of our algorithm. Results and error evaluation is supporting evidence for the practical effectiveness of the met

ISSN:1124-318X    

DOI:10.1002/ett.4460070606

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

年代:1996

数据来源: WILEY

摘要:

AbstractIn this paper, a novel ATM switch with a dynamic multimedia traffic priority control scheme (HQMS: Hybrid combination of Queue Length Threshold and Minimum Laxity Threshold Scheme) is proposed. The ATM switch has the same basic topology as the Knockout switch, but employs a simplerN×Lconcentration scheme, which takes into account cells belonging to different priority levels. The structure of the switch supports two priority mechanisms. The first one is calledpriority discardingand acts as a local congestion control scheme within the switch fabric satisfying different cell loss requirements of different ATM traffic classes. The second one is calledpriority schedulingand uses two priority methods: aspace priority methodused for the control of the buffer space when an overflow condition occurs andor when the expiration of the maximum admissible delay of the delay sensitive cells takes place and theservice priority methodwhich assigns transmission priorities to the buffered cells. A hardware implementation of the two priority mechanisms of the HQMS is presented. The performance of the switch has been studied by simulation, considering three ATM classes (video, data, voice) with different source models. The results have shown that for a large range of traffic load, the proposed HQMS satisfies the loss and delay requirements of the three classes

ISSN:1124-318X    

DOI:10.1002/ett.4460070607

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

年代:1996

数据来源: WILEY

摘要:

AbstractMedium access control protocols based on a dual bus topology, such as the IEEE 802.6 Distributed Queue Dual Bus (DQDB), are usually considered to be highly satisfactory for high speed networks. But the DQDB can only partly support new sophisticated multimedia services, mainly because the increase in the channel bit rate needed to meet the greater bandwidth requirements causes an increase in unfairness in the medium access control of the nodes. In this paper the authors propose a Gigabit/s Metropolitan Area Network (MAN) based on the IEEE 802.6 DQDB protocol and multichannel connectivity on optical fiber, by means of Wavelength Division Multiplexing (WDM). They present a parallel node architecture in whichNDQDB subnodes parallelly accessNWDM channels. Channel access at each node is regulated byNfinite state machines operating independently and sharing a single MAC Convergence Functions (MCF) block for the segmentation and reassembly of user information. On the basis of the MAC architecture proposed, B network management structure is also presented, with particular reference to the Quality of Service monitoring processes. The proposed architecture is more modular than the DQDB standard; it provides greater fairness and better access delay and allows efficient management of service classes with priority.

ISSN:1124-318X    

DOI:10.1002/ett.4460070608

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

年代:1996

数据来源: WILEY

摘要:

AbstractTwo protocols suitable for random multiple access packet broadcast in a multichannel. communication system are proposed and analyzed. Broadcast channels are classified as retrans. mission channels devoted in collision resolution of busy stations and as contention channels for the access of free stations. The proposed protocols differ in the way that a busy station is allocated to a retransmission channel for collision resolution. Analytic Markovian models are developed so as to evaluate the system performance in terms of throughput and delay. The performance of multichannel systems is compared with the single channel system. Numerical results show performance improvement under heavy load.

ISSN:1124-318X    

DOI:10.1002/ett.4460070609

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

年代:1996

数据来源: WILEY

摘要:

AbstractA photonic ATM switching node based on the Fibre Delay Line switching element developed in the framework of the RACE project ATMOS (ATM Optical Switching) is described. The feasibility of this switching element has been proved within the physical limitation of present‐day technology to support up to 16 input and 16 output lines and a buffer capacity of at least 16 cells for each output. In this paper various interconnection options are discussed with the aim of a large, high throughput switch implementation. In particular a Clos architecture is chosen for the design of a 256 × 256 switching fabric operating at 2.5 Gbit/s and its performance is evaluated by means of simulation in a random and bursty traffic environment. It is demonstrated that a multiplane configuration of optical matrices followed by an efficient concentration strategy is capable of meeting the target ATM requirements, that is cell loss probability less than 10−‐9with load up to 0.8. A detailed design of the switch and its complexity evaluation are also

ISSN:1124-318X    

DOI:10.1002/ett.4460070610

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

年代:1996

数据来源: WILEY

摘要:

AbstractAnN × NATM switching element with output queueing is considered. Each inlet of the switch is fed by a bursty on/off source with geometrically distributed on/off‐periods. Cells are routed from the inputs to the outputs of the switch in a uniform but correlated manner. Specifically, for the first cell of each on‐period all the destination addresses are equiprobable. Each subsequent cell of the same on‐period has a probabilityRof being routed to the same destination as the previous cell, and is sent to one of theN‐1 other destinations with probability (1 ‐R)/(N ‐1). Cells belonging to different on‐periods are routed entirely independently. By means of an approximate analytical method, the influence of the degree of burstiness of the sources and the amount of correlation in the routing mechanism on the queueing performance of the switch i

ISSN:1124-318X    

DOI:10.1002/ett.4460070611

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

年代:1996

数据来源: WILEY