Advanced Orbiting Systems Data Generator/Simulator: A Functional Description of the Software (Version 3)

The Advanced Orbiting System (AOS) Data Generator/Simulator is a software implementation of the transmitter (data generation) section of the CCSDS Recommendation 701.0-B-2 for Advanced Orbiting Systems: Networks and Data Links. An object-oriented approach to the simulation of a complex, high-performance communication protocol, it makes full use of the concepts of data-encapsulation and inheritance to ease implementation. The backbone of the software is a general-purpose packet description and generation module that may be used as part of any packet- based simulation software. The user-interface to the program is in the form of a command-language, designed to ease the process of generation of large, multiple data-streams. The output of the program may be configured for interpretation by a graphical user interface (for visual inspection of the data), or as a bit-stream suitable for further processing. This paper consists of three sections. The first two sections provide a brief, yet comprehensive description of the above CCSDS Recommendation. The various kinds and qualities of user-services, data units involved, and data-paths defined by the protocol are discussed. The different qualities of service (in terms or data reliability) available to the user (and the error-control schemes used to provide them) are also discussed. The last section describes the structure and user-interfaces of the AOS Data Generator/Simulator

Advanced Orbiting Systems Data Generator/Simulator: A Functional Description of the Software (Version 3)

The Advanced Orbiting System (AOS) Data Generator/Simulator is a software implementation of the transmitter (data generation) section of the CCSDS Recommendation 701.0-B-2 for Advanced Orbiting Systems: Networks and Data Links. An object-oriented approach to the simulation of a complex, high-performance communication protocol, it makes full use of the concepts of data-encapsulation and inheritance to ease implementation. The backbone of the software is a general-purpose packet description and generation module that may be used as part of any packet- based simulation software. The user-interface to the program is in the form of a command-language, designed to ease the process of generation of large, multiple data-streams. The output of the program may be configured for interpretation by a graphical user interface (for visual inspection of the data), or as a bit-stream suitable for further processing. This paper consists of three sections. The first two sections provide a brief, yet comprehensive description of the above CCSDS Recommendation. The various kinds and qualities of user-services, data units involved, and data-paths defined by the protocol are discussed. The different qualities of service (in terms or data reliability) available to the user (and the error-control schemes used to provide them) are also discussed. The last section describes the structure and user-interfaces of the AOS Data Generator/Simulator

The Reliability of Systems with Two Levels of Fault Tolerance: The Return of the "Birthday Surprise"

This paper considers the reliability of systems that employ fault tolerance at two different hierarchical levels. Specifically, it assumes the system consists of a two-dimensional array of components. Each component is reliable as long as it has been afflicted by no more than t faults; when t + 1 faults occur in a particular component, the component ceases to be reliable. Furthermore, the system remains operative as long no more than one component in any row is unreliable. By generalizing the techniques used to analyze the well-known "birthday surprise" problem of applied probability, we derive an approximation to the average number of faults needed until the systems fails. Applications include random access memory systems with chip-level and board-level coding as well as fault-tolerant systolic arrays

A Hybrid-ARQ System Using Rate-Compatible Trellis Codes Designed for Rayleigh Fading

This paper presents classes of rate-compatible trellis codes designed for channels with flat, slow Rayleigh fading. The codes thus described are ﲭultiple TCM (MTCM) codes as proposed by Divsalar and Simon - i.e., codes in which multiple symbols are associated with each transition through the trellis; by applying appropriate puncturing tables to low-rate MTCM codes, we obtain families of MTCM codes, all of which can be decoded with (essentially) the same decoder.By means of computer search, several such families are designed so that each family member is at least as good as any comparable code in the literature. (ﲇood here is defined in terms of minimum time diversity and minimum squared product distance, the most important parameters for performance over Rayleigh fading channels.) A protocol to implement these rate-compatible trellis codes in a type-II hybrid ARQ format with only a low-rate feedback channel is described. Upper bounds on the resulting bit error rate are developed and the results are used to select the best adaptive code from several possibilities. Simulation results comparing the proposed scheme with fixed-rate codes of the same throughput show substantial coding gain. Finally, a protocol modification limiting the variability of the code rate over a frame is described; this modification eliminates the need for excessive buffering, with a very small effect on performanc

Distributed Decoding of Cyclic Block Codes Using a Generalization of Majority-Logic Decoding

One-step majority-logic decoding is one of the simplest algorithms for decoding cyclic block codes. However, it is an effective decoding scheme for very few codes. This paper presents a generalization based on the "common-symbol decoding problem." Suppose one is given M (possibly different) codes over the same field; suppose further that the codewords share a single symbol in common. The common-symbol decoding problem is that of estimating the symbol in the common position. (This is equivalent to one-step majority logic decoding when each of the "constituent" codes is a simple parity check.) This paper formulates conditions under which this decoding is possible and presents a simple algorithm that accomplishes the same. When applied to decoding cyclic block codes, this technique yields a decoder structure ideal for parallel implementation. Furthermore, this approach frequently results in a decoder capable of correcting more errors than one-step majority-logic decoding. To demonstrate the simplicity of the resulting decoders, an example is presented

The Performance of Focused Error Control Codes

Consider an additive noise channel with inputs and outputs in the field GF (q ) where q > 2; every time a symbol is transmitted over such a channel, there are q - 1 different errors that can occur, corresponding to the q - 1 non-zero elements that the channel can add to the transmitted symbol. In many data communication/ storage systems, there are some errors that occur much more frequently than others; however, traditional error correcting codes- designed with respect to the Hamming metric - treat each of these q - 1 errors the same. Fuja and Heegard have designed a class of codes, called focused error control codes, that offer different levels of protection against "common" and "uncommon" errors; the idea is to define the level of protection in a way based not only on the number of errors, but the kind as well. In this paper, the performance of these codes is analyzed with respect to idealized "skewed" channels as well as realistic non-binary modulation schemes. It is shown that focused codes, used in conjunction with PSK and QAM signaling, can provide more than 1.0 dB of additional coding gain when compared with Reed- Solomon codes for small blocklengths

A Generalized Gilbert-Varshamov Bound Derived via Analysis of a Code-Search Algorithm

This correspondence derives a generalization of the Gilbert- Varshamov bound that is applicable to block codes whose codewords must be drawn from irregular sets; the bound improves by a factor of four a similar result recently published by Kolesnik and Krachkovsky. It is derived by analyzing a code search algorithm we refer to as the "Altruistic Algorithm". This algorithm iteratively deletes potential codewords so that at each iteration the "worst" candidate is removed; the bound is derived by demonstrating that, as the algorithm proceeds, the average volume of a sphere of a given radius approaches the maximum such volume and so a bound previously expressed in terms of the maximum volume can in fact be expressed in terms of the average volume. Examples of applications where the bound is relevant include error-correcting (d, k)- constrained codes and binary codes for code division multiple access

A Communication Channel Modeled on Contagion

We introduce a binary additive communication channel with memory. The noise process of the channel is generated according to the contagion model of George Polya; our motivation is the empirical observation of Stapper et. al. that defects in semiconductor memories are well described by distributions derived from Polya's urn scheme. The resulting channel is stationary but not ergodic, and it has many interesting properties.We First derive a maximum likelihood (ML) decoding algorithm for the channel; it turns out that ML decoding is equivalent to decoding a received vector onto either the closest codeword or the codeword that is farthest away, depending on whether an ﲡpparent epidemic has occurred. We next show that the Poly-contagion channel is an ﲡveraged channel in the sense of Ahlswede (and others) and that its capacity is zero. We then demonstrate that the Poly- contagion channel is a counter-example to the adage, ﲭemory cannot decrease capacity ; the capacity of the Poly-contagion channel is actually less than that of the associated memoryless channel. Finally, we consider a finite-memory version of the Poly-contagion model; this channel is (unlike the original) ergodic with a non-zero capacity that increases with increasing memory

Optical Orthogonal Codes with Unequal Auto- and Cross- Correlation Constraints

An optical orthogonal code (OOC)is collection of binary sequences with good auto-and cross-correlation properties; they were defined by Salehi and others as a means of obtaining code division multiple access on optical networks. Up to now all work on OOC's have assumed that the constraint placed on the auto- correlation and that placed on the cross-correlation are the same. In this paper we consider codes for which the two constraints are not equal. Specifically, we develop bounds on the size of such OOC's and demonstrate construction techniques for building them. The results demonstrate that a significant increase in the code size is possible by letting the auto- correlation constraint exceed the cross-correlation constraint. These results suggest that for a given performance requirement the optimal OOC may be one with unequal constraints.This paper also views OOC's with unequal auto- and cross-correlation constraints as constant-weight unequal error protection (UEP) codes with two levels of protection. The bounds derived are interpreted from this viewpoint and are compared with previous work on UEP codes

Performance Analysis of Coherent TCM Systems with Diversity Reception in Slow Rayleigh Fading

Coherent trellis coded modulation (TCM) systems employing diversity combining are analyzed. Three different kinds of combining are considered: maximal ratio, equal gain, and selection combining. For each combining scheme, the cutoff rate parameter is derived assuming transmission over a fully- interleaved channel with flat, slow, Rayleigh fading; in addition, tight upper bounds on the pairwise error probabilities are derived. These upper bounds are expressed in product form to permit bounding of the BER via the transfer function approach. In each case it is assumed that the diversity branches are independent and that the channel state information (CSI) can be recovered perfectly.Also included is an analysis of maximal ratio combining when the diversity branches are correlated; the cutoff rate and a tight upper bound on the pairwise error probability are derived. It is shown that, with double diversity, a branch correlation coefficient as high as 0.5 results in only slight performance degradation