Fuzzy based pseudo random number generator used for wireless networks. +CD

number: 
1552
إنجليزية
department: 
Degree: 
Imprint: 
Computer Science
Author: 
Najwan Abed Hassien
Supervisor: 
Dr. Sattar B. Sadkhan
Dr.Sawsan K. Thamer
year: 
2007

Abstract:

Direct sequence spread spectrum uses a carrier that remains fixed to a specific frequency band. The data signal, rather than being transmitted on a narrow band as is done in microwave communications, is spread onto a much larger range of frequencies using a specific encoding scheme. This encoding scheme is known as a Pseudo Noise sequence (PN). The algorithm used by the PN sequence generates a Pseudo Random Number Generator (PRNG) that is then combined, through a binary encoding process, with the binary information from the data stream. The resulting signal is spread over a much larger amount of bandwidth than would normally be used for a data transmission but at a much lower power level. In this project, three conventional types of PRNG were implemented. These are linear feed back shift register, nonlinear feed back shift register and Blum Blum Shub generator. A fuzzy system is studied and Fuzzy based Pseudo Random Number Generator (FPRNG) had been implemented to generate the frequency hopping sequences for spread spectrum communications system. Thirty sample patterns are the input to FPRNG, while the bandwidth is partitioned into number of frequency bins. Each bin used triangular membership function to analyze the input to fuzzy sets, encoding these as fuzzy rules. The input vector matches if-part of a fuzzy rule and fires that rule's output fuzzy set. Center Of Gravity (COG) was used to defuzzy the fuzzy values into crisp value to yields the number in the frequency hopping sequence. The FPRNG output had been compared with the output of the three other methods of PRNG. The fuzzy system had lower values and thus gives a more uniform spread than did the other methods. The fuzzy system was easier to change and harder to intercept.