This paper proposes a new waveform that follows the practical application requirements, high precision requirements, and low system complexity requirements. However, conventional chirp sequence waveforms suffer from the Doppler ambiguity problem. The chirp sequence waveform has the ability to extract the range and velocity parameters of multiple targets. There are several waveforms which have been developed in the last years. A more practical alternative to discontinuous-phase FSK systems are continuous-phase FSK systems, where a polar binary baseband signal is provided as the input to a voltage-controlled oscillator (VCO): FSK output Frequency modulator Carrier freq PSfrag replacements m(t) fcContinuous waveform (CW) radar is widely used in intelligent transportation systems, vehicle assisted driving, and other fields because of its simple structure, low cost and high integration. Bandwidth of the baseband signal.
However, in the case of multiple targets, there are many errors in combinations of up beat frequencies and down beat frequencies. Frequency shift keying (FSK).CCSDS REPORT CONCERNING BANDWIDTH-EFFICIENT MODULATIONS CCSDS 413.0-G-3 Page iv February 2018 DOCUMENT CONTROL Document Title Date Status CCSDS 413.0-G-1 Bandwidth-Efficient Modulations: Summary of Definition, Implementation, and Performance, Issue 1 April 2003 Original issue, superseded CCSDS 413.0-G-2 Bandwidth-Efficient Modulations:Where B is the frequency modulation bandwidth, T chirp is the frequency modulation period and the distance and speed of the target can be solved by the up beat frequency and the down beat frequency. Theoretical analysis and simulation results verify that the new radar waveform is capable of measuring range and radial velocity simultaneously and unambiguously, with high accuracy and resolution even in multi-target situations.The bandwidth required is two times the highest frequency content including any harmonics for binary pulse modulating signals. According to the sign and numerical relationship of the Doppler frequencies (possibly frequency aliasing), the Doppler frequency ambiguity problem is solved in eight cases. The carrier frequencies are different and there is a frequency shift which is large enough to ensure that the Doppler frequencies for the same moving target are different. Each chirp signal has the same frequency modulation, the same bandwidth and the same chirp duration.
For binary ‘0’ S 2 (t) A cos 2 f L t. For binary ‘1’ S 1 (A) Acos 2 f H t. In FSK, the carrier frequency is switched between 2 extremes. R log 2 2 1.FSK (Frequency Shift Keying): In FSK (Frequency Shift Keying) binary 1 is represented with a high-frequency carrier signal and binary 0 is represented with a low-frequency carrier, i.e. The extended measurement time is an important drawback of this LFM technique.If the modulation signal is a square wave, as in the case of discrete FSK modulation, loop bandwidth should be at least twice the baud rate.
However, when multiple targets are moving at the same speed or when multiple targets are stationary, multiple targets cannot be distinguished by phase information, which is the inherent defect of FSK waveform. The peak phase difference is used to estimate the distance, as shown in Equation (2).Frequency Shift Key (FSK) Modulation is a method of transmitting digital information, in which data is coded in a carrier wave by shifting between discrete.It can be realized easily, which is the advantage of FSK waveform. By maintaining f S t e p very small in comparison to the transmitted signals, the Doppler frequencies extracted from the baseband outputs will be approximately the same. The baseband outputs carry the Doppler frequencies generated by the moving target. The received signal is converted to baseband signal by a homodyne receiver. The frequency step between the two carriers is represented as f S t e p = f 2 − f 1.
The delay of the new improved waveform can be precisely controlled by the system clock. The frequency shift between every two adjacent chirps is changed to delay. It is difficult to maintain high-precision frequency shift. Frequency shift is a key factor in determining the phase difference. Doppler ambiguities can be resolved using the additional phase information introduced by the frequency shift. A modified chirp sequence waveform was developed by adding an additional frequency shift between every two adjacent chirps.
Theoretical analysis and simulation results verify the effectiveness of the new radar waveform．This paper focuses on the research of continuous wave radar waveform design, analyzes the two-dimensional FFT processing method and the Doppler ambiguity problem for chirp sequence. According to the sign and numerical relationship of the Doppler frequency f D 1 , a m b and f D 2 , a m b, the velocity direction of the target can be judged, and the aliasing direction can be further judged. When f D 1 , a m b and f D 2 , a m b satisfy the conditions of f D 1 , a m b − f D 2 , a m b < 2 f D , max or f D 2 , a m b − f D 1 , a m b < 2 f D , max, it indicates that q 2 = q 1 + 1.The velocity direction affects the Doppler frequency aliasing direction. ( a) f D 1 , a m b ≥ 0, f D 2 , a m b ≥ 0, f D 1 , a m b ≤ f D 2 , a m b ( b) f D 1 , a m b ≥ 0, f D 2 , a m b ≥ 0, f D 1 , a m b > f D 2 , a m b ( c) f D 1 , a m b f D , max ( f) f D 1 , a m b ≥ 0, f D 2 , a m b ≤ 0, f D 1 , a m b − f D 2 , a m b f D , max ( h) f D 1 , a m b ≤ 0, f D 2 , a m b ≥ 0, f D 1 , a m b − f D 2 , a m b f D , max ( f D 1 , a m b > 0 , f D 2 , a m b f D , max ( f D 2 , a m b > 0 , f D 1 , a m b < 0 ), it means that the number of Doppler frequency aliasing q 2 ≠ q 1. Moreover, the accuracy of the resolved unambiguous Doppler frequencies is not well guaranteed since phase information is susceptible to noise interference.Therefore, the principle of waveform design for continuous wave radar includes the following points:The Doppler spectrum for 8 typical cases.
The peak positions in the amplitude spectrums corresponding to the same target are in the same or adjacent distance units, and they are in different frequency units due to different carrier frequencies. The carrier frequencies are different and there is a frequency shift which is large enough to ensure that the Doppler frequencies for the same moving target are different. Each chirp signal has the same frequency modulation, the same bandwidth and the same chirp duration.
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