However, an OFDM signal can be modulatedeither in phase or frequency for radar applications, which increases power andamplifier efficiency 10. Thus the amplifier operates in the region near tosaturation and fading in multipath also increases.
This will result in poorrange resolution for radar with OFDM. Theprimary drawback of OFDM is that there will be high amplitude variations of themodulated waveform and this produces high peak-to-average power ratio (PAPR) 11.The reduction in peak-to-average power ratio (PAPR) problem associated withradar with modulated waveform mentioned here can be used to enhance theperformance. It is widely used to analyze the variation of the output waveform. When the signal is passed through apre-modulation filter with 0.5 modulation index then it is called as GMSKmodulation 9.
This helps in suppressing high- frequency components. In aradar system, it comprises of a transmitter and a receiver, having a fair SNRby using a GMSK filter with a name as a pre-modulationfilter 9. The reason is that this filter produces better accuracy andincreased efficiency while filtering the signal components. In this paper, the same filterdesign will also use in the receiver section and is equally proportioned in theform of matched filter. Pulse shaping is an important task performed on thetransmitter side and in order to reduce the effective bandwidth duringtransmission suitable Gaussian low pass filter is used 5.
The choice ofbandwidth B and bit-rate T is a compromise between spectrum efficiency and BERperformance 1. Hence smaller BT leads to compact spectrum and more ISI. Hencethese parameters suitably are chosen to reduce ISI while doing this paper.The above mentioned Gaussian filter introduces overlapping of the transmittedsignal, and this causes the degradation and it is small if the 3dB bandwidth bitduration product (BT) is greater than 0.5 value 9. This ISI occurred by the channel can be controlled by filteringthe shaped pulses5. Earlier initially the inputdata is in the form of NRZ data and it is given to a pulse shaping filter(Gaussian filter) before feeding them to the LFM modulator.
Digital phasemodulation system involves sending information through channel either byvarying the physical quantities and it is smoothed by using pulse shapingfilter. The requirement of pulse shaping filter is effective againsteliminating spectral leakage, reducing the channel width and also to eliminatethe ISI 5. This results in a verycompact signal spectrum and better utilization of available bandwidth.
At thereceiving end, the matched filter eliminates the reflected echo to overlap witha subsequent symbol period 11.