الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
Many technologies have been devised and extensively used for wireless transmission and reception to satisfy the growing demands of the mobile and personal broadband communications. The performance in wireless communication channels would be degraded due to channel characteristics, such as multi-path fading and background noise and, due to intended interference (jammers). Those impairments could be eliminated through the utilization of diversity, multiple input multiple output (MIMO), adaptive channel equalization, adaptive modulation, channel coding, spread spectrum (SS) etc. However, some different kinds of interfering sources, including the significant structure interference due to their operation as multiple access in the cellular communication systems, referred to as the multiple access interference (MAl), and inevitable jammers appeared in the overlapped frequency band for common utility, are still existing and now become the main difficulties to collapse the reception performance and system capacity.
SS techniques llave been used to combat impairments in rapidly varying radio cbannels and to obtain high spectral efficiencies in cellular systems. Frequency hopping spread spectrum (FHSS) is an effective technique for combating Rayleigh fading, and ’enabling efficient frequency reuse in a multiple access communication system.
Chaotic systems with its interesting property, that it is very sensitive to initial o 0on, had attracted a lot of interest in communication society because it is . . tic, and impossible to be predicted in the long term which guarantees the security die communication transmission.
Chaotic frequency hopping (CFH) has received considerable attention in the field of ;1IId communication, because the initial condition is generally thought to be unable to be from a finite length discrete valued sequence, and moreover, chaotic systems are sensitive to their initial conditions. Long period chaos based on spreading codes to provide high anti-jamming (AJ) capability against the jamming based on replication.
In this thesis, we investigate the effectiveness of CFH against intetference and jamming, presenting the prosperities from generating chaotic code instead of m-sequence and, gold codes. The autocorrelation and crosscorrelation for each is presented.
We propose to generate a frequency hopping (FH) pattern matched to the channel transmission coefficient by using a new technique instead of generating it randomly, which, enhance the petformance of transmission in wireless communication channel.
Results show that the new technique makes a good use of the nature of the communication channel. The used frequency slots are selected to be concentrated in the bands in which the transmission coefficient is relatively high, and, thus, it makes use of the inherent gain of the multi-path channels.