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George C. Clark

Bio: George C. Clark is an academic researcher from Harris Corporation. The author has contributed to research in topics: Turbo code & Viterbi decoder. The author has an hindex of 2, co-authored 2 publications receiving 1250 citations.

Papers
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Book
30 Jun 1981
TL;DR: This paper presents a meta-modelling architecture for Convolutional Code Structure and Viterbi Decoding, and some of the techniques used in this architecture can be applied to Group Codes and Block Codes.
Abstract: 1. Fundamental Concepts of Coding.- 2. Group Codes.- 3. Simple Nonalgebraic Decoding Techniques for Group Codes.- 4. Soft Decision Decoding of Block Codes.- 5. Algebraic Techniques for Multiple Error Correction.- 6. Convolutional Code Structure and Viterbi Decoding.- 7. Other Convolutional Decoding Techniques.- 8. System Applications.- Appendix A. Code Generators for BCH Codes.- Appendix B. Code Generators for Convolutional Codes.- B.1. Viterbi Decoding.- B.2. Table Look-up Decoding.- B.3. Threshold Decoding.- B.4. Sequential Decoding.- References.

1,208 citations

Patent
19 Jun 1981
TL;DR: In this paper, a message is assembled to contain alternately arranged known and unknown pluralities of data symbols, and the received message is subjected to a prescribed data recovery algorithm containing a transversal filter function and a data estimate refinement scheme.
Abstract: In a communication system for transmitting information over a dispersive link, a transmitted message is assembled to contain alternately arranged known and unknown pluralities of data symbols. At the transmitter, the known data symbols may be produced by a maximal length PN sequence generator, with an identical generator being provided at the receiver for reproducing the known symbol sequences to enable data recovery to be achieved. In the received signal processing equipment, the received message is subjected to a prescribed data recovery algorithm containing a transversal filter function and a data estimate refinement scheme which takes advantage of the a priori knowledge of data symbols of those portions of the transmitted message between which unknown data symbols are located. A transmitted message contains a plurality of successive frame, each frame containing N known data symbols followed by M unknown data symbols. Thus preceding and succeeding each set of M unknown data symbols there are respective sets of N known data symbols that enable the characteristics of the transversal filter function, and thereby the data estimates of the unknown symbols, to be updated and adaptively refined. Synchronization of the local PN sequence generator at the receiver with the PN sequence of which the successive sets of N known data symbols are composed in the transmitted message is achieved through a prescribed tone sequence/initialization scheme, subsequent to which unknown data is transmitted and processed at the receiver in accordance with the data recovery algorithm.

77 citations


Cited by
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Journal ArticleDOI
TL;DR: Using log-likelihood algebra, it is shown that any decoder can be used which accepts soft inputs-including a priori values-and delivers soft outputs that can be split into three terms: the soft channel and aPriori inputs, and the extrinsic value.
Abstract: Iterative decoding of two-dimensional systematic convolutional codes has been termed "turbo" (de)coding. Using log-likelihood algebra, we show that any decoder can be used which accepts soft inputs-including a priori values-and delivers soft outputs that can be split into three terms: the soft channel and a priori inputs, and the extrinsic value. The extrinsic value is used as an a priori value for the next iteration. Decoding algorithms in the log-likelihood domain are given not only for convolutional codes but also for any linear binary systematic block code. The iteration is controlled by a stop criterion derived from cross entropy, which results in a minimal number of iterations. Optimal and suboptimal decoders with reduced complexity are presented. Simulation results show that very simple component codes are sufficient, block codes are appropriate for high rates and convolutional codes for lower rates less than 2/3. Any combination of block and convolutional component codes is possible. Several interleaving techniques are described. At a bit error rate (BER) of 10/sup -4/ the performance is slightly above or around the bounds given by the cutoff rate for reasonably simple block/convolutional component codes, interleaver sizes less than 1000 and for three to six iterations.

2,632 citations

Journal ArticleDOI
TL;DR: A generalization of the convex hull of a finite set of points in the plane leads to a family of straight-line graphs, "alpha -shapes," which seem to capture the intuitive notions of "fine shape" and "crude shape" of point sets.
Abstract: A generalization of the convex hull of a finite set of points in the plane is introduced and analyzed. This generalization leads to a family of straight-line graphs, " \alpha -shapes," which seem to capture the intuitive notions of "fine shape" and "crude shape" of point sets. It is shown that a-shapes are subgraphs of the closest point or furthest point Delaunay triangulation. Relying on this result an optimal O(n \log n) algorithm that constructs \alpha -shapes is developed.

1,648 citations

Journal ArticleDOI
TL;DR: A class of nonlinear estimation algorithms is described to estimate the unknown phase of a carrier which is fully modulated by m -ary PSK modulation, and the effect of quantization and finite read-only-memory implementation of the nonlinearity are determined by computer simulation.
Abstract: Burst transmission of digital data and voice has become commonplace, particularly in satellite communication systems employing time-division multiple-access (TI)MA) and packet demand-assignment multiple-access (DAMA) techniques. In TDMA systems particularly, phase estimation on each successive burst is a requirement, while bit timing and carrier frequency can be accurately tracked between bursts. A class of nonlinear estimation algorithms is described to estimate the unknown phase of a carrier which is fully modulated by m -ary PSK modulation. Performance of the method is determined in closed form and compared to the Cramer-Rao lower bound for the variance of the estimation error in the phase of an unmodulated carrier. Results are also obtained when the carrier frequency is imprecisely known. Finally, the effect of quantization and finite read-only-memory (ROM) implementation of the nonlinearity are determined by computer simulation.

1,116 citations

Patent
25 Apr 2002
TL;DR: In this article, a system and method for wireless communication between a plurality of subscriber units and a base station, the base station communicating information signals from an originating source to a destination subscriber unit over a channel at an assigned one of a plurality OF frequencies using repetitive time frames, each said time frame comprising a sequence of time slots.
Abstract: A system and method for wireless communication between a plurality of subscriber units and a base station, the base station communicating information signals from an originating source to a destination subscriber unit over a channel at an assigned one of a plurality of frequencies using repetitive time frames, each said time frame comprising a sequence of time slots. The channel is defined as having the same one or more time slots from the sequence of time slots in one or more of the time frames. The base station includes a central processing unit capable of assigning a duration of time for the information signals being sent to the destination subscriber unit. The duration equals the duration of one or more time slots in the same frame. The central processing unit maintains a memory of which time slots of each time frame have been assigned and provides the time slot assignment, and therefore channel assignment, by consulting said memory. The system includes a multiplexer for multiplexing the information signals onto the assigned channel; and a transmitter for transmitting the information signals to the destination subscriber unit using the assigned channel.

877 citations