Precoding radar receive signals

1 . An apparatus comprising:

a wireless transceiver configured to:

be coupled to at least three antennas;

transmit a radar transmit signal using at least one antenna of the at least three antennas, the radar transmit signal modulated in frequency across multiple cycles based on one or more different frequency-modulation schemes;

receive at least two radar receive signals using at least two other antennas of the at least three antennas, the at least two radar receive signals comprising versions of the radar transmit signal that are reflected by at least one object, each of the at least two radar receive signals modulated in frequency across the multiple cycles based on the one or more frequency-modulation schemes of the radar transmit signal; and

precode at least two radar receive signals across the multiple cycles to generate precoded radar receive signals that are orthogonal to each other,

wherein the wireless transceiver comprises:

a precoder configured to precode the multiple cycles of the at least two radar receive signals to generate the precoded radar receive signals; and

a combiner configured to generate a composite radar receive signal based on the precoded radar receive signals by combining the precoded radar receive signals; and

interface circuitry configured to:

couple the radio-frequency integrated circuit to a modem; and

pass the composite radar receive signal to the modem,

wherein the interface circuitry comprises at least one communication path coupled between the radio-frequency integrated circuit and the modem; and

a quantity of the at least two radar receive signals is greater than a quantity of paths in the at least one communication path.

2 . The apparatus of claim 1 , wherein a quantity of the multiple cycles is equal to a quantity of the at least two other antennas.

3 . The apparatus of claim 1 , wherein:

the wireless transceiver comprises at least two phase shifters configured to be respectively coupled to the at least two other antennas; and

the at least two phase shifters are configured to precode the multiple cycles of the at least two radar receive signals to generate the precoded radar receive signals.

4 . The apparatus of claim 3 , wherein:

the at least two radar receive signals comprise a first radar receive signal and a second radar receive signal;

the multiple cycles comprise a first cycle and a second cycle; and

the at least two phase shifters comprise:

a first phase shifter configured to apply a first phase shift to the first and second cycles of the first radar receive signal; and

a second phase shifter configured to:

apply the first phase shift to the first cycle of the second radar receive signal; and

apply a second phase shift to the second cycle of the second radar receive signal, the second phase shift being offset from the first phase shift by approximately 180 degrees.

5 . The apparatus of claim 4 , wherein the first phase shifter and the second phase shifter are jointly configured to apply the first phase shift based on a delay relative to transmission of the radar transmit signal.

6 . The apparatus of claim 5 , wherein the delay comprises a software programmable delay.

7 . The apparatus of claim 4 , wherein the first phase shift is approximately zero degrees.

8 . The apparatus of claim 1 , wherein:

the one or more frequency-modulation schemes comprise:

a first frequency-modulation scheme; and

a second frequency-modulation scheme that differs from the first frequency-modulation scheme; and

the multiple cycles comprise:

a first cycle having the first frequency-modulation scheme; and

a second cycle having the second frequency-modulation scheme.

9 . The apparatus of claim 8 , wherein:

the first frequency-modulation scheme increases frequency over time; and

the second frequency-modulation scheme decreases frequency over time.

10 . The apparatus of claim 1 , wherein the one or more frequency-modulation schemes comprise a single frequency-modulation scheme.

11 . The apparatus of claim 10 , wherein the single frequency-modulation scheme increases or decreases frequency over time.

12 . The apparatus of claim 1 , further comprising:

the modem, the modem comprising:

a decoder configured to extract versions of the at least two radar receive signals from the composite radar receive signal; and

a digital beamformer configured to generate a spatial response that indicates an angular position of the at least one object based on the extracted versions of the at least two radar receive signals.

13 . A method comprising:

transmitting a radar transmit signal using at least one antenna, the radar transmit signal modulated in frequency across multiple cycles based on one or more different frequency-modulation schemes;

receiving at least two radar receive signals using at least two other antennas, the at least two radar receive signals comprising versions of the radar transmit signal that are reflected by at least one object, each of the at least two radar receive signals modulated in frequency across the multiple cycles based on the one or more frequency-modulation schemes of the radar transmit signal;

precoding the multiple cycles of the at least two radar receive signals to generate precoded radar receive signals that are orthogonal to each other;

generating a composite radar receive signal based on the precoded radar receive signals by combining the precoded radar receive signals; and

passing the composite radar receive signal to a modem across at least one communication path,

wherein a quantity of the at least two radar receive signals is greater than a quantity of paths in the at least one communication path.

14 . The method of claim 13 , wherein the precoding comprises precoding the multiple cycles of the at least two radar receive signals prior to downconverting versions of the at least two radar receive signals.

15 . The method of claim 13 , wherein:

the at least two radar receive signals comprise a first radar receive signal and a second radar receive signal;

the multiple cycles comprise a first cycle and a second cycle; and

the precoding comprises:

applying a first phase shift to the first and second cycles of the first radar receive signal;

applying the first phase shift to the first cycle of the second radar receive signal; and

applying a second phase shift to the second cycle of the second radar receive signal, the second phase shift being offset from the first phase shift by approximately 180 degrees.

16 . An apparatus comprising:

means for transmitting a radar transmit signal, the radar transmit signal modulated in frequency across multiple cycles based on one or more different frequency-modulation schemes;

means for receiving at least two radar receive signals comprising versions of the radar transmit signal that are reflected by at least one object, each of the at least two radar receive signals modulated in frequency across the multiple cycles based on the one or more frequency-modulation schemes of the radar transmit signal;

means for precoding the at least two radar receive signals across the multiple cycles to generate precoded radar receive signals that are orthogonal to each other;

means for generating a composite radar receive signal based on the precoded radar receive signals by combining the precoded radar receive signals; and

means for passing the composite radar receive signal to a modem across at least one communication path,

wherein a quantity of the at least two radar receive signals is greater than a quantity of paths in the at least one communication path.

17 . The apparatus of claim 16 , wherein the means for precoding comprises means for applying phase shifts to the multiple cycles of the at least two radar receive signals.

18 . A radio-frequency integrated circuit configured to:

be coupled to multiple antennas; and

receive multiple radar receive signals via the multiple antennas, each radar receive signal of the multiple radar receive signals modulated in frequency across multiple cycles based on one or more different frequency-modulation schemes,

the radio-frequency integrated circuit comprising:

multiple phase shifters configured to apply multiple phase shifts across the multiple cycles of the multiple radar receive signals to generate precoded radar receive signals that are orthogonal to each other; and

at least one combiner configured to:

be coupled between the multiple phase shifters and a mixer; and

generate a composite radar receive signal based on the precoded radar receive signals by combining the precoded radar receive signals,

wherein the radio-frequency integrated circuit is configured to be coupled to interface circuitry and to transmit the composite radar receive signal to a modem via the interface circuitry,

wherein a quantity of the multiple radar receive signals is greater than a quantity of paths in at least one communication path of the interface circuitry.

19 . The radio-frequency integrated circuit of claim 18 , wherein a quantity of the multiple cycles is equal to a quantity of the multiple antennas.

20 . The radio-frequency integrated circuit of claim 18 , wherein:

the radio-frequency integrated circuit comprises the mixer; and

the mixer is configured to downconvert the composite radar receive signal.

21 . The radio-frequency integrated circuit of claim 18 , wherein:

the multiple radar receive signals comprise a first radar receive signal and a second radar receive signal;

the multiple cycles comprise a first cycle and a second cycle; and

the multiple phase shifters comprise:

a first phase shifter configured to apply a first phase shift of the multiple phase shifts to the first and second cycles of the first radar receive signal; and

a second phase shifter configured to:

apply the first phase shift to the first cycle of the second radar receive signal; and

apply a second phase shift to the second cycle of the second radar receive signal, the second phase shift being offset from the first phase shift by approximately 180 degrees.

22 . The radio-frequency integrated circuit of claim 21 , wherein the one or more frequency-modulation schemes comprise:

a first frequency-modulation scheme that increases frequency over time; and

a second frequency-modulation scheme that decreases frequency over time.