Digital Signal Processing

B. Leelaram Prakash ¹, K. Raja Rajeswari ²

Affiliations
1 Vignnan's Institute of Information Technology, Visakhapatnam, IN
2 A.U. College of Engineering (A), Visakhapatnam, IN

Abstract

Pulse compression achieved with un-weighted linear FM (LFM) suffers from relatively high autocorrelation function (ACF) side-lobes. Since the ACF is the inverse Fourier transform of the power spectrum, the ACF sidelobes could be reduced by shaping the signal according to one of the many sidelobe suppression techniques. The shaping is performed by changing the pulse amplitude along the time axis. In LFM instantaneous frequency is linearly related to time. Indeed, the resulting spectral shaping is very close to the desired spectrum. But it has a serious drawback. In a matched transmitter-receiver pair, it results in variable amplitude of the pulse transmitted. Variable amplitude requires linear power amplifiers which are less efficient than saturated power amplifiers. This problem can be alleviated by performing amplitude weighting only at the receiver. The resulting mismatch causes SNR loss. In linear FM the transmitter spends equal time at each frequency; hence the nearly uniform spectrum will result. Another method for shaping the spectrum is to deviate from the constant rate of frequency change and to spend more time at frequencies that need to be enhanced. This approach is termed as nonlinear FM (NLFM). In this paper an attempt is made to compare the performance of Gaussian NLFM, Rayleigh NLFM and the combination of both these NLFM signals with respect to their ambiguity plots and range resolution plots.

Keywords

Pulse Compression, LFM, NLFM, Ambiguity Plot and Range Resolution Plot.

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Ch. Srinivasu ¹, K. Raja Rajeswari ¹

Affiliations
1 Department of ECE, AUCE (A), Visakhapatnam, IN

Abstract

The performance of ultra wideband (UWB) radar in target detection, resolution and recognition depends on the structure of the radar waveform. So, many types of waveforms are being used in multi target detection in the field of radar. Sinusoidal and non-sinusoidal waveforms can be implemented practically. In this paper performance of non-sinusoidal waveforms are presented. Resolution is the important parameter, which gives the goodness of the waveform.  The ambiguity function is a three dimensional and two variable mathematical tool, which demonstrates the both range and Doppler resolution capability of the waveform. These two resolutions are important parameters to know the goodness of the transmitted waveform. In practical applications of the radar these parameters are essential to resolve the closely moving (or stationary) targets in the space. In this paper mathematical models of ambiguity functions are developed for bi-phase coded non-sinusoidal UWB Gaussian waveforms signal. Ambiguity plots are three dimensional plots, which represent range axis, Doppler axis and magnitude axis. The three dimensional plots are generated for the above UWB coded signals and results are compared with sinusoidal coded waveforms.

Keywords

Ambiguity Function, Barker Codes, Range Resolution.

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