However, an OFDM signal can be modulated
either in phase or frequency for radar applications, which increases power and
amplifier efficiency 10. Thus the amplifier operates in the region near to
saturation and fading in multipath also increases. This will result in poor
range resolution for radar with OFDM.
primary drawback of OFDM is that there will be high amplitude variations of the
modulated waveform and this produces high peak-to-average power ratio (PAPR) 11.
The reduction in peak-to-average power ratio (PAPR) problem associated with
radar with modulated waveform mentioned here can be used to enhance the
performance. It is widely used to analyze the variation of the output waveform.
When the signal is passed through a
pre-modulation filter with 0.5 modulation index then it is called as GMSK
modulation 9. This helps in suppressing high- frequency components. In a
radar system, it comprises of a transmitter and a receiver, having a fair SNR
by using a GMSK filter with a name as a pre-modulation
filter 9. The reason is that this filter produces better accuracy and
increased efficiency while filtering the signal components.
In this paper, the same filter
design will also use in the receiver section and is equally proportioned in the
form of matched filter. Pulse shaping is an important task performed on the
transmitter side and in order to reduce the effective bandwidth during
transmission suitable Gaussian low pass filter is used 5. The choice of
bandwidth B and bit-rate T is a compromise between spectrum efficiency and BER
performance 1. Hence smaller BT leads to compact spectrum and more ISI. Hence
these parameters suitably are chosen to reduce ISI while doing this paper.
The above mentioned Gaussian filter introduces overlapping of the transmitted
signal, and this causes the degradation and it is small if the 3dB bandwidth bit
duration product (BT) is greater than 0.5 value 9. This ISI occurred by the channel can be controlled by filtering
the shaped pulses5.
Earlier initially the input
data 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 phase
modulation system involves sending information through channel either by
varying the physical quantities and it is smoothed by using pulse shaping
filter. The requirement of pulse shaping filter is effective against
eliminating spectral leakage, reducing the channel width and also to eliminate
the ISI 5. This results in a very
compact signal spectrum and better utilization of available bandwidth. At the
receiving end, the matched filter eliminates the reflected echo to overlap with
a subsequent symbol period 11.