Signal modeling for unambiguous range rate estimation
This document describes interleaving chirps for unambiguous range rate estimation. A signal model quickly and unambiguously estimates range rates for any chirp within one frame. During each frame, a transmission of radar signals is caused by interleaving two different groups of chirps (e.g., up-chirps and down-chirps) in an ordered sequence. This unique pattern of chirps enables the signal model to compute an ambiguity term for each frame (e.g., an ambiguity variable for each group). The ambiguity term is often not zero. With ambiguity considered for the frame, range rate estimates can be provided without ambiguity. When applied to a solution for estimating range rate, the ambiguity term allows quick, and unambiguous results to be obtained for any possible detection. Ambiguity is resolved without having to analyze multiple frames. This increase in accuracy and performance enables wider adoption of radar and may promote safe driving.
1 . A method comprising:
transmitting, from a radar system, radar signals for a frame by interleaving two different groups of chirps, including a first group and a second group, into an ordered sequence of chirps such that each consecutive pair of chirps includes an initial chirp from the first group and a subsequent chirp from the second group, one of the two groups including up-chirps that increase in frequency during transmission and the other of the two groups including down-chirps that decrease in frequency during transmission;
identifying, based on radar returns obtained in response to transmission of the radar signals, initial range and Doppler measurements of peak detections associated with each of the two groups for the frame;
selecting, from among a plurality of ambiguity terms used for unambiguously estimating range rates for detections, a first ambiguity term associated with the first group of chirps and a second ambiguity term associated with the second group of chirps, the first and second ambiguity terms being selected independently, with the first ambiguity term being selected based on the initial range and Doppler measurements of the peak detections only from the first group of chirps and the second ambiguity term being selected based on the initial range and Doppler measurements only from the second group of chirps; and
using, by the radar system, the ambiguity term selected for each of the two groups to estimate an unambiguous range rate for detections associated with each of the two groups.
2 . The method of claim 1 , wherein:
one of the two groups comprises odd chirps and the initial chirp is the up-chirp, and the other of the two groups comprises even chirps and the subsequent chirp is the down-chirp; or
the initial chirp is the down-chirp, and the subsequent chirp is the up-chirp.
3 . The method of claim 1 , wherein the frame comprises an up frame that shifts the ordered sequence of chirps higher in frequency during transmission of the frame.
4 . The method of claim 1 , wherein the frame comprises a down frame that shifts the ordered sequence of chirps lower in frequency during transmission of the frame.
5 . The method of claim 1 , wherein the plurality of ambiguity terms include at least one integer greater than zero or less than zero.
6 . The method of claim 1 , wherein selecting the ambiguity term for the two groups comprises:
computing, based on the initial range and Doppler measurements for the first group, a first ambiguity variable for the first group;
selecting, from among the plurality of ambiguity terms that is nearest in value to the first ambiguity variable, the first ambiguity term for the first group;
computing, based on the initial range and Doppler measurements for the second group, a second ambiguity variable for the second group; and
selecting, from among the plurality of ambiguity terms that is nearest in value to the second ambiguity variable, the second ambiguity term for the second group.
7 . The method of claim 1 , wherein at least one of the first ambiguity term selected or the second ambiguity term selected is not zero.
8 . The method of claim 1 , further comprising:
outputting, from the radar system, and to a component of a vehicle, the unambiguous range rate for at least some of the detections to enable tracking or other radar dependent functions executing on the vehicle.
9 . A non-transitory computer-readable storage media comprising instructions that, when executed, cause a processor to:
transmit, from a radar system, radar signals for a frame by interleaving two different groups of chirps, including a first group and a second group, into an ordered sequence of chirps such that each consecutive pair of chirps includes an initial chirp from the first group and a subsequent chirp from the second group, one of the two groups including up-chirps that that increase in frequency during transmission and the other of the two groups including down-chirps that decrease in frequency during transmission;
identify, based on radar returns obtained in response to transmission of the radar signals, initial range and Doppler measurements of peak detections associated with each of the two groups for the frame;
select, from among a plurality of ambiguity terms used for unambiguously estimating range rates for detections, a first ambiguity term associated with the first group of chirps and a second ambiguity term associated with the second group of chirps, the first and second ambiguity terms being selected independently, with the first ambiguity term being selected based on the initial range and Doppler measurements of the peak detections only from the first group of chirps and the second ambiguity term being selected based on the initial range and Doppler measurements only from the second group of chirps; and
use the ambiguity term selected for each of the two groups to estimate an unambiguous range rate for detections associated with each of the two groups.
10 . A system comprising a processor configured to:
transmit radar signals for a frame by interleaving two different groups of chirps, including a first group and a second group, into an ordered sequence of chirps such that each consecutive pair of chirps includes an initial chirp from the first group and a subsequent chirp from the second group;
identify, based on radar returns obtained in response to transmission of the radar signals, initial range and Doppler measurements of peak detections associated with each of the two groups, one of the two groups including up-chirps that increase in frequency during transmission and the other of the two groups including down-chirps that decrease in frequency during transmission;
select, from among a plurality of ambiguity terms used for unambiguously estimating range rates for detections, a first ambiguity term associated with the first group of chirps and a second ambiguity term associated with the second group of chirps, the first and second ambiguity terms being selected independently, with the first ambiguity term being selected based on the initial range and Doppler measurements of the peak detections only from the first group of chirps and the second ambiguity term being selected based on the initial range and Doppler measurements only from the second group of chirps; and
use the ambiguity term selected for each of the two groups to estimate an unambiguous range rate for detections associated with each of the two groups.
11 . The system of claim 10 , wherein:
the initial chirp is the up-chirp, and the subsequent chirp is the down-chirp; or
the initial chirp is the down-chirp, and the subsequent chirp is the up-chirp.
12 . The system of claim 10 , wherein the processor is further configured to:
compute, based on the initial range and Doppler measurements for the first group, a first ambiguity variable for the first group;
select, from among the plurality of ambiguity terms that is nearest in value to the first ambiguity variable, the first ambiguity term for the first group;
compute, based on the initial range and Doppler measurements for the second group, a second ambiguity variable for the second group; and
select, from among the plurality of ambiguity terms that is nearest in value to the second ambiguity variable, the second ambiguity term for the second group.
13 . The system of claim 10 , wherein at least one of the first ambiguity term selected or the second ambiguity term selected is not zero.
14 . The system of claim 10 , wherein the processor is further configured to:
output, to a component of a vehicle, the unambiguous range rate for at least some of the detections to enable tracking or other radar dependent functions executing on the vehicle.