Range in FMCW Radar

 

1	Continuously transmit a chirp signal with linearly varying frequency.
2	A frequency difference appears between the transmitted signal and the received echo from the target.
3	Measure this frequency difference(beat frequency) via Range FFT and convert it to distance.

 

 

 

 

 

 

 

 

1. Signal Flow and Processing

 

 

 

 

 

 

one target

 

 

multi-target

 

 

 

 

 

2. Range Formula

Range Measurement (Range FFT) can be performed with a single chirp.

Distance is calculated from the beat frequency between the transmitted and received chirp

 

Range		f_b  Measured Value kr peak BIN index, Nr FFT size, Fs ADC Sampling rate c Speed of light B_RF Chirp Bandwidth Tc Chirp Time S Chirp Slope
Resolution		Chirp bandwidth limit the resolution between 2 objects. c Speed of light B_RF Chirp Bandwidth
Max Range Limit		Baseband signal bandwidth limits the measurable max range. B_BB ADC input baseband signal bandwidth S Chirp Slope

 

 

 

 

 

3. Example Report of Radar Sensor SoC

The data output is MSB first and the Range FFT data type is signed integer.

구분	필드명	Dword	Bit Range	설명
Header	Fixed Pattern	Dword 0	[31:24]	1010 1010
Header	Reserved	Dword 0	[23]	0
Header	Fixed Pattern	Dword 0	[22:20]	11
Header	FFT_chirp_index	Dword 0	[19:11]	Frame 내 chirp 순번 (0부터 시작)
Header	CFG_FFT_TX_MAX	Dword 0	[10:0]	FFT 출력 포인트 수 m + 1
Data	FFT_real_data[0]	Dword 1	[31:16]	Range FFT real part (signed)
Data	FFT_imag_data[0]	Dword 1	[15:0]	Range FFT imaginary part (signed)
Data	FFT_real_data[1]	Dword 2	[31:16]	Range FFT real part (signed)
Data	FFT_imag_data[1]	Dword 2	[15:0]	Range FFT imaginary part (signed)
Data	FFT_real_data[n]	Dword …	[31:16]	Range FFT real part (signed)
Data	FFT_imag_data[n]	Dword …	[15:0]	Range FFT imaginary part (signed)
Data	FFT_real_data[m-1]	Dword m	[31:16]	Range FFT real part (signed)
Data	FFT_imag_data[m-1]	Dword m	[15:0]	Range FFT imaginary part (signed)
Tail	Check_sum	Dword m+1	[31:16]	해당 chirp의 데이터 합 (low 16bit sum 결과)
Tail	FFT_FRAME_INDEX	Dword m+1	[15:12]	Frame counter (0부터 시작)
Tail	Reserved	Dword m+1	[11:10]	0
Tail	CFG_MSG	Dword m+1	[9:8]	User defined bits
Tail	Fixed Pattern	Dword m+1	[7:0]	0101 0101