Variable code sequences for radar transmission

1. A system for detecting and estimating a property of an object based on radar, the system comprising:

a signal generator configured to generate a code sequence for a plurality of transmitters configured to emit radar signals over a selected time frame, the code sequence including a plurality of codes, each code of the plurality of codes having a different code length, each code repeated in the code sequence according to a repetition frequency;

each transmitter configured to emit a radar signal based on the code sequence, wherein the plurality of transmitters are configured to simultaneously emit radar signals according to the code sequence, and the code length of a shortest code of the plurality of codes is selected to be greater than or equal to a number of the plurality of transmitters;

a receiver configured to detect return signals from reflections of the emitted radar signals; and

a processing device configured to estimate a property of an object based on the detected return signals.

2. The system of claim 1 , wherein each code includes a series of associated symbols, and the code length is based on a number of the associated symbols.

3. The system of claim 2 , wherein each code is generated by randomly or pseudo-randomly selecting the series of the associated symbols.

4. The system of claim 2 , wherein the number of the associated symbols of the shortest code of the plurality of codes is selected to be greater than or equal to the number of the plurality of transmitters.

5. The system of claim 4 , wherein each pair of adjacent codes have code lengths that do not have a common divider.

6. The system of claim 1 , wherein the processing device is configured to transform the detected return signals and generate a Doppler frequency spectrum.

7. The system of claim 6 , wherein the Doppler frequency spectrum includes ambiguous frequency peaks for each transmitter, the ambiguous frequency peaks being separated due to the code sequence, and estimating the property includes identifying and disregarding the ambiguous frequency peaks.

8. The system of claim 1 , wherein the plurality of transmitters are configured as multi-input-multi-output (MIMO) transmitters.

9. A method of detecting and estimating a property of an object based on radar, the method comprising:

generating, by a signal generator, a code sequence for a plurality of transmitters configured to emit radar signals over a selected time frame, the code sequence including a plurality of codes, each code of the plurality of codes having a different code length, each code repeated in the code sequence according to a repetition frequency;

simultaneously emitting a radar signal from each transmitter based on the code sequence, wherein the code length of a shortest code of the plurality of codes is selected to be greater than or equal to a number of the plurality of transmitters;

detecting, by a receiver, return signals from reflections of the emitted radar signals; and

estimating a property of an object based on the detected return signals.

10. The method of claim 9 , wherein each code includes a series of associated symbols, and the code length is based on a number of the associated symbols.

11. The method of claim 10 , wherein each code is generated by randomly or pseudo-randomly selecting the series of associated symbols.

12. The method of claim 10 , wherein the number of the associated symbols shortest code of the plurality of codes is selected to be greater than or equal to the number of the plurality of transmitters.

13. The method of claim 9 , wherein estimating the property includes transforming the detected return signals and generating a Doppler frequency spectrum.

14. The method of claim 13 , wherein the Doppler frequency spectrum includes ambiguous frequency peaks for each transmitter, the ambiguous frequency peaks being separated due to the code sequence, and estimating the property includes identifying and disregarding the ambiguous frequency peaks.

15. A vehicle system comprising:

a memory having computer readable instructions; and

a processing device for executing the computer readable instructions, the computer readable instructions controlling the processing device to perform:

generating, by a signal generator, a code sequence for a plurality of transmitters configured to emit radar signals over a selected time frame, the code sequence including a plurality of codes, each code of the plurality of codes having a different code length, each code repeated in the code sequence according to a repetition frequency;

simultaneously emitting a radar signal from each transmitter based on the code sequence, wherein the code length of a shortest code of the plurality of codes is selected to be greater than or equal to a number of the plurality of transmitters;

detecting, by a receiver, return signals from reflections of the emitted radar signals; and

estimating a property of an object based on the detected return signals.

16. The vehicle system of claim 15 , wherein each code includes a series of associated symbols, the code length is based on a number of the associated symbols, and the code length is selected to be greater than a number of the plurality of transmitters.

17. The vehicle system of claim 16 , wherein each code is generated by randomly or pseudo-randomly selecting the associated symbols.