Coding for reliable satellite communications

Several error control coding techniques for reliable satellite communications were investigated to find algorithms for fast decoding of Reed-Solomon codes in terms of dual basis. The decoding of the (255,223) Reed-Solomon code, which is used as the outer code in the concatenated TDRSS decoder, was of particular concern

Coding for reliable satellite communications

This research project was set up to study various kinds of coding techniques for error control in satellite and space communications for NASA Goddard Space Flight Center. During the project period, researchers investigated the following areas: (1) decoding of Reed-Solomon codes in terms of dual basis; (2) concatenated and cascaded error control coding schemes for satellite and space communications; (3) use of hybrid coding schemes (error correction and detection incorporated with retransmission) to improve system reliability and throughput in satellite communications; (4) good codes for simultaneous error correction and error detection, and (5) error control techniques for ring and star networks

A concatenated coding scheme for error control

A concatenated coding scheme for error contol in data communications was analyzed. The inner code is used for both error correction and detection, however the outer code is used only for error detection. A retransmission is requested if either the inner code decoder fails to make a successful decoding or the outer code decoder detects the presence of errors after the inner code decoding. Probability of undetected error of the proposed scheme is derived. An efficient method for computing this probability is presented. Throughout efficiency of the proposed error control scheme incorporated with a selective repeat ARQ retransmission strategy is analyzed

Characterization of Network Inaccessibility in IEEE 802.15.4 Wireless Networks

Wireless communications are vulnerable to the presence of errors during the network operation. These errors may be originated from different sources such as external electromagnetic interferences, obstacles in communication path, or even glitches in the communication circuitry. Such origins may lead the medium access control (MAC) layer to deviate from its normal operation (without presence of errors), forcing the execution of additional actions to maintain the network operational. The execution of such actions may imply the occurrence of periods of "communication silence", where the network, although not being failed, is not performing communications. These periods of ``communication silence" are dubbed network inaccessibility, which may induce inaccurate fault detections and deadline misses. Additionally, the occurrence of network inaccessibility may compromise network properties such as predictability, dependability, and timeliness. Thus, this report presents an exhaustive study about network inaccessibility, using the 802.15.4 standard as a case study. All network inaccessibility scenarios are presented, discussing important steps to achieve predictability, dependability, and timeliness in wireless communications.This work was partially supported by EC, through project IST-STREP-288195 (KARYON) and by FCT through the Multiannual Funding and CMU-Portugal Programs and the Individual Doctoral Grant SFRH/BD/45270/2008

Calcolo della Distribuzione dei Pesi nei Codici Ciclici Accorciati

La tesi parte dall'algoritmo sul calcolo della distribuzione dei pesi per codici CRC che si trova nell'articolo di Castagnoli-Bräuer-Hermann dal titolo "Optimization of Cyclic Redundancy-Check Codes with 24 and 32 Parity Bits" pubblicata dalla IEEE Trans. on Communication nel giugno del 1993. Lo scopo della tesi è l'estensione di tale algoritmo ai campi finiti con p^n elementi con p un primo. Per lo sviluppo di tale algoritmo si sono toccati argomenti di algebra di base e sono stati dimostrati risultati sulla scomposizione di quozienti dell'anello dei polinomi sul campo con p^n elementi. La tesi comprende pure una implementazione dell'algoritmo nel caso p=2 e n=1 in linguaggio C++ con la libreria NTL (number theory library)

Réseau de communication à haut niveau d'intégrité pour des systèmes de commande-contrôle critiques intégrant des nappes de microsystèmes

Vu le développement important des micro-systèmes, leur utilisation sous forme de nappes dans les systèmes de commande-contrôle critiques est incontournable. Cela soulève néanmoins des défis, parmi lesquels la définition d'un système de communication à haut niveau d'intégrité. L'étude que nous avons effectuée sur des réseaux standard montre que les protections classiques à base de codes CRC ne permettent pas d'obtenir le niveau d'intégrité visé. Pour l'atteindre, nous avons proposé une solution originale - fonction de contrôle évolutive - qui tire profit du fait que, pour les systèmes de commande-contrôle envisagés (systèmes à dynamique lente), l'intégrité est à considérer sur un lot de messages et non un seul message. La solution proposée a ensuite été validée via des simulations Matlab-Simulink. Le cas d'étude utilisé est celui de systèmes de commande de vol du futur, en vue de pouvoir commander des nappes de milliers de micro-surfaces tels que des micro-spoilers. ABSTRACT : With the wide development of microsystems, it is likely that they will be massively used in critical control systems. This raises many new challenges, among which the definition of a dependable communication network with high integrity level. The study of standard communication networks and their basic commonly used transmission errors detection techniques based on CRC codes shows that they cannott ensure the required integrity level. To reach this integrity level, we propose an original solution - an evolutive error control function - based on the slowly evolution characteristic of the control systems considered, for which the integrity is considered for a set of consecutive messages and not for a single message. The validation of the proposed solution is based on MATLAB simulation models we have developed. The study case is about the integration of thousands of micro-surfaces such as micro-spoilers in future flight control systems