Digital frequency modulated continuous wave radar using handcrafted constant envelope modulation

• US 10,191,142 B2
• Filed: 04/16/2018
• Issued: 01/29/2019
• Est. Priority Date: 04/25/2016
• Status: Active Grant

• Current Assignee: Uhnder, Inc.
• Original Assignee: Uhnder, Inc.
• Inventors: Eshraghi, Aria, Davis, Curtis, Ali, Murtaza, Dent, Paul
• Primary Examiner(s): Windrich, Marcus E
• Application Number:
  US15/953,826
• Publication Number:
  US 20180259619A1
• Time in Patent Office: 288 Days
• Field of Search: 342 70- 72
• CPC Class Codes: G01S 13/325 using transmission of coded signals, e.g. P.S.K. signals
• CPC Class Codes: G01S 13/87 Combinations of radar systems, e.g. primary radar and secondary radar
• CPC Class Codes: G01S 13/931 of land vehicles
• CPC Class Codes: G01S 2013/9316 combined with communication equipment with other vehicles or with base stations
• CPC Class Codes: G01S 2013/93271 in the front of the vehicles
• CPC Class Codes: G01S 2013/93272 in the back of the vehicles
• CPC Class Codes: G01S 7/282 Transmitters
• CPC Class Codes: G01S 7/352 Receivers
• CPC Class Codes: G01S 7/358 using I/Q processing

Abstract

A method for determining a frequency modulation includes generating a symbol stream that is filtered, with multiple samples per period. Sample values represent samples of the filtered symbols at instants separated by intervals of a fraction of a time period between successive symbols. Samples of I and Q waveforms are calculated from frequency modulating a signal with the sequence of symbols. For each possible set of symbol values on which a waveform depends, an average waveform is produced over all symbol values outside the group; and on which the waveform is not to depend, all waveforms are superimposed within +/−half a period of the center symbol of each group having the same set of values and averaging the superimposed I, Q samples to produce for each group an averaged set of samples and an average waveform. Final I, Q values are stored for subsequent frequency modulation.

Claims

1. A method for determining a frequency modulation of a continuous wave radar for a vehicle, the method comprising:

generating, with a code generator, a symbol stream comprising a time-sequence of modulating symbols, each symbol belonging to a limited set of symbols having unique numerical values;

feeding the symbol stream through one of (i) a shaping and (ii) filtering process to obtain a sequence of shaped or filtered symbols, respectively, comprising multiple sample values per symbol period, wherein the sample values represent samples of the shaped or filtered symbols at instants separated by intervals of a fraction of a time period between successive symbols;

calculating, with a waveform selection module, for the sample instants, (I, Q) samples of I and Q waveforms resulting from frequency modulating a carrier signal with the sequence of modulating symbols, wherein each I value is equal to a cosine of resulting instantaneous carrier phases at the sample instants, and each Q value is equal to a sine of the instantaneous carrier phases at the sample instants;

for each selected set of symbol values for a plurality of successive symbols on which a waveform is to depend, producing an average waveform over all symbol values outside the selected set of symbol values; and

on which the waveform is not to depend, superimposing all waveforms within plus and minus half a symbol period of the center symbol of each selected set of symbols having the same set of values and averaging the superimposed I, Q samples to produce for each selected set of symbols an averaged set of I, Q samples, and an average waveform, wherein each selected set of symbol values for a plurality of successive symbols are corresponding selected patterns of the successive symbols; and

recording, with the waveform selection module, final I, Q values to be stored in a memory for subsequent use in producing the frequency modulation in the frequency modulated continuous wave radar.

2. The method of claim 1 further comprising rotating the phase angle of all the I, Q samples by an amount that brings an eye diagram into a focus that best represents the modulating symbols.

3. The method of claim 1 further comprising, when the average waveform produced by a selected set of symbols exhibits a discontinuity with the average waveform produced by a following set of symbols having the same overlapping symbols as a previous symbol shift, erasing the discontinuity by applying a smoothing function that forces the sample values on either side of the discontinuity to converge while having an effect on sample values that diminishes towards zero further from the discontinuity.

4. The method of claim 1, wherein the time-sequence of modulating symbols is a sequence of binary bits.

5. The method of claim 4, wherein the sequence of binary bits is a maximum length sequence.

6. The method of claim 1 further comprising precoding the symbol stream according to a precoding scheme for an intended receiver to produce a precoded symbol stream, such that the symbol stream is a precoded symbol stream.

7. The method of claim 6, wherein the modulating symbols are binary bits, and wherein the precoding comprising modulo-2 adding each bit with its predecessor to produce the precoded symbol stream.

8. The method of claim 1, wherein the feeding the symbol stream through one of (i) a shaping and (ii) a filtering process to obtain a sequence of shaped or filtered symbols, respectively, comprises feeding the symbol stream through a Gaussian filter.

9. The method of claim 1, wherein said feeding the symbol stream through one of (i) a shaping and (ii) a filtering process to obtain a sequence of shaped or filtered symbols, respectively, comprises multiplying each symbol value by a shaping function to obtain a pulse shaped symbol waveform.

19. The method of claim 1, wherein the selected patterns of successive symbols comprise a selected quantity of successive symbol patterns.

10. A radar system for a vehicle, the radar system comprising:

at least one transmitter configured for installation and use on a vehicle, and configured to transmit a frequency modulated radio signal;

at least one receiver configured for installation and use on the vehicle, and configured to receive radio signals that include the transmitted radio signals transmitted by the transmitters and reflected from objects in an environment;

wherein a first transmitter of the at least one transmitter comprises a modulator comprising a code generator, a waveform selection module, a filter module, and a memory;

wherein the code generator is configured to generate a symbol stream comprising a time-sequence of modulating symbols, each symbol belonging to a limited set of symbols having unique numerical values;

wherein the filter module is configured to filter the generated symbol stream to generate a sequence of filtered symbols comprising multiple sample values per symbol period, wherein the sample values represent samples of the filtered symbols at instants separated by intervals of a fraction of a time period between successive symbols;

wherein the waveform selection module is configured to calculate, for the sample instants, (I,Q) samples of I and Q waveforms resulting from frequency modulating a carrier signal with the sequence of modulating symbols, wherein each I value is equal to a cosine of resulting instantaneous carrier phases at the sample instants, and each Q value is equal to a sine of the instantaneous carrier phases at the sample instants;

wherein the waveform selection module is configured to, for each selected set of symbol values for a plurality of successive symbols on which a waveform is to depend, produce an average waveform over all symbol values outside the selected set of symbol values; and

on which the waveform is not to depend, to superimpose all waveforms within plus and minus half a symbol period of the center symbol of each selected set of symbols having the same set of values and to average the superimposed I, Q samples to produce for each selected set of symbols an averaged set of I, Q samples, and an average waveform, wherein each selected set of symbol values for a plurality of successive symbols are corresponding selected patterns of the successive symbols; and

wherein the waveform selection module is configured to record final I, Q values to the memory for subsequent use by the modulator in producing the frequency modulated continuous wave signal.

11. The radar system of claim 10, wherein the waveform selection module is further configured to rotate the phase angle of all the I,Q samples by an amount that brings an eye diagram into a focus that best represents the modulating symbols.

12. The radar system of claim 10, when the average waveform produced by a selected set of symbols exhibits a discontinuity with the average waveform produced by a following set of symbols having the same overlapping symbols as a previous symbol shift, which erases the discontinuity via the application of a smoothing function that forces the sample values on either side of the discontinuity to converge while having an effect on sample values that diminishes towards zero further from the discontinuity.

13. The radar system of claim 10, wherein the time-sequence of modulating symbols is a sequence of binary bits.

14. The radar system of claim 13, wherein the sequence of binary bits is a maximum length sequence.

15. The radar system of claim 10, wherein the code generator is configured to generate the symbol stream according to a precoding scheme for an intended receiver to produce a precoded symbol stream, such that the symbol stream is a precoded symbol stream.

16. The radar system of claim 15, wherein the modulating symbols are binary bits, and wherein the precoding comprising modulo-2 adding each bit with its predecessor to produce the precoded symbol stream.

17. The radar system of claim 10, wherein the filter module comprises a Gaussian filter.

18. The radar system of claim 10, wherein the filter module is configured to multiply each symbol value by a shaping function to obtain a pulsed shaped symbol waveform.

20. The radar system of claim 10, wherein the selected patterns of successive symbols comprise a selected quantity of successive symbol patterns.