Pulse digital mimo radar system
A chip-implementation of a millimeter wave MIMO radar comprises transmitters for transmitting short bursts of digitally modulated radar carrier signals and receivers for receiving delayed echoes of those signals. Various signal formats defined by the number of bits per transmit burst, the transmit burst duration, the receive period duration, the bitrate, the number of range bins, and the number of bursts per scan, facilitate the choice of modulating bit patterns such that when correlating for target echoes over an entire scan, the correlation codes for different ranges and different transmitters are mutually orthogonal or nearly so. In the event of imperfect orthogonality, simple orthogonalization schemes are revealed, such as subtraction of strong already-detected target signals for better detecting weaker signals or moving targets that are rendered non-orthogonal by their Doppler shift.
1. A multiple input, multiple output (MIMO) radar arranged on an integrated circuit chip, comprising:
a plurality of transmitters, each configured to transmit bursts of modulated radio signals, wherein each respective modulation is defined by a selected sequence of bits chosen from a corresponding code set of bits, wherein each selected sequence of bits represents a subset of the code set;
a plurality of receivers, each configured to receive the radio signals transmitted by the transmitters and reflected from a plurality of objects in an environment, wherein each object of the plurality of objects comprises a corresponding distance and commensurate round-trip echo delay; and
a processor configured to correlate the received radio signals with the selected sequences of bits to determine corresponding round-trip echo delays and thus the corresponding distances, wherein each respective sequence of bits is chosen from the corresponding code set such that the respective sequences of bits exhibit lower cross-correlation than a pseudo-random generated selection of bits.
2. The MIMO radar of claim 1 , wherein each transmitter of the plurality of transmitters is configured to digitally modulate the transmitted radio signals, and wherein each transmitter is configured to transmit the modulated radio signals for a selected duration for a selected transmit duty cycle.
3. The MIMO radar of claim 1 , wherein the lower cross-correlation comprises zero cross-correlation, and wherein the subsets are mutually orthogonal.
4. The MIMO radar of claim 1 , wherein the lower cross-correlation comprises a cross-correlation of +/−1/M, and wherein M is the length of the code subset and the subsets are different shifts of an M-sequence.
5. The MIMO radar of claim 1 , wherein the processor comprises a Fast Walsh Transform (FWT) engine for performing the correlations.
6. The MIMO radar of claim 1 , wherein the processor is configured to improve a level of orthogonality between a first subset and a second subset by removing signal values from the received radio signals that are associated with already identified targets to produce a residual of the received radio signals, and wherein the processor is configured to correlate the residual of the received radio signals such that additional targets are identified.
7. The MIMO radar of claim 1 comprising a semiconductor chip, wherein the plurality of transmitters, the plurality of receivers, and the processor are arranged on the semiconductor chip, and wherein the semiconductor chip comprises a metal layer comprising a plurality of dipole antennas, and wherein each of the plurality of dipole antennas is coupled to a respective one of either the plurality of transmitters and the plurality of receivers, such that each of the transmitters and receivers is coupled to a respective dipole antenna of the plurality of dipole antennas.
8. The MIMO radar of claim 7 , wherein the plurality of dipole antennas comprises six dipole antennas, and wherein each of the dipole antennas comprises a bow-tie shape.
9. The MIMO radar of claim 7 further comprising a reflector, wherein the plurality of dipole antennas are arranged as a linear array of antennas, and wherein the reflector is position with respect to the linear array of antennas such that a directivity of the linear array of antennas is controlled.
10. The MIMO radar of claim 1 , wherein the processor is configured to correlate the received radio signals for a selected quantity of range bins during a radar scan, wherein the product of the quantity of range bins with the quantity of transmitters of the plurality of transmitters is less than a quantity of transmission bursts per radar scan, and wherein at least one of the quantity of range bins, the quantity of transmitters, and the quantity of transmission bursts per radar scan is selected such that each selected subset is orthogonal to every other selected subset.
11. The MIMO radar of claim 1 , wherein the plurality of transmitters comprises a first transmitter and a second transmitter, wherein a first subset selected for the first transmitter is inverted according to a first inversion pattern, and wherein a second subset selected for the second transmitter is inverted according to a second inversion pattern such that the first subset is orthogonal to the second subset.
12. A method for improving correlation of received radio signals in a radar system, the method comprising:
providing a radar system comprising (i) a plurality of transmitters configured to transmit bursts of modulated radio signals, wherein each respective modulation is defined by a selected sequence of bits chosen from a corresponding code set of bits, (ii) a plurality of receivers configured to receive the radio signals transmitted by the transmitters and reflected from a plurality of objects in an environment, wherein each selected sequence of bits represents a subset of the code set, wherein each object of the plurality of objects comprises a corresponding distance and commensurate round-trip echo delay; and
correlating the received radio signals with the selected sequences of bits to determine corresponding round-trip echo delays and thus the corresponding distances, wherein each respective sequence of bits is chosen from the corresponding code set such that the respective sequences of bits exhibit lower cross-correlation than a pseudo-random generated selection of bits.
13. The method of claim 12 , wherein each transmitter of the plurality of transmitters digitally modulates the transmitted radio signals, and wherein each transmitter transmits the modulated radio signals for a selected duration for a selected transmit duty cycle.
14. The method of claim 12 , wherein the lower cross-correlation comprises zero cross-correlation, and wherein the subsets are mutually orthogonal.
15. The method of claim 12 , wherein the plurality of transmitters comprises a first transmitter and a second transmitter, wherein a first subset selected for the first transmitter is inverted according to a first inversion pattern, and wherein a second subset selected for the second transmitter is inverted according to a second inversion pattern such that the first subset is orthogonal to the second subset.
16. The method of claim 12 , wherein correlating the received radio signals comprises correlating the received radio signals with a Fast Walsh Transform (FWT) algorithm.
17. The method of claim 12 , and and wherein the method further comprises improving a level of orthogonality between a first subset and a second subset by (i) removing signal values from the received radio signals that are associated with already identified targets to produce a residual of the received radio signals, and (ii) correlating the residual of the received radio signals such that additional targets are identified.
18. The method of claim 12 , wherein the method further comprises (i) correlating the received radio signals for a selected quantity of range bins during a radar scan, wherein the product of the quantity of range bins with the quantity of transmitters of the plurality of transmitters is less than a quantity of transmission bursts per radar scan, and (ii) selecting at least one of the quantity of range bins, the quantity of transmitters, and the quantity of transmission bursts per radar scan such that each selected subset is orthogonal or nearly orthogonal to every other selected subset.