Evaluation of interpolated frequency hopping signals

number: 
988
إنجليزية
Degree: 
Author: 
Firas Mehdi Muhsin Al-Salbi
Supervisor: 
Dr. Jafar W. Abdul-Sada
Dr. Sattar B. SadKan
year: 
1999
Abstract:

Frequency synthesizers are the common devices used for commandable, wideband frequency hopping (FH) communications. Thus, in order to obtain an optimum detection to the received slow FH signals, the problems encountered with the synthesizer part of the FH system are carefully studied. Some problems such as the spectral splatter and the transient mismatch, which are a concern in conventional phase-locked loop (PLLbased) FH systems, are the main cause of the imperfect reception to the incoming FH signal. A new technique called interpolated-frequency hopping (IFH) introduced by Filiol and Riley have been presented and used to . eliminate the phase-locked loop PLL synthesizer problems. In IFH technique, the pseudorandom hopping code is passed through a digital interpolation filter prior to controlling the synthesizer instantaneous frequency input. By filtering the hopping PN code prior to the synthesizer input will make the synthesizer continuously track the input sequence rather than to jump in a discrete manner. Thus, minimizing the transient mismatch effect and resulting in an improved reception to the IF signal at the receiver, which will significantly minimize the spectral splatter problem. While such filtering is commonly used in data pulse shaping to improve the spectral characteristics of the modulated carrier, such filtering has not been reported for IFH codes, where the frequency deviations are changing and can span several MHz. Initial simulation to the FH system including the effects of the synthesizer problems and the use of IFH technique are employed. The IFH technique has been simulated with symmetrical low-pass digital interpolation filter. It has been shown that for the worst case conditions of the tested synthesizer effects, an improvement of 2 dB can be gained in the overall FH system performance (SNR) using digital filter with an interpolation factor of 50% from the number of transmitted bits per hop..