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 as compared to a random selection of codes. In the event of imperfect orthogonality, the subtraction of strong already-detected target signals allows for better detecting of weaker signals or moving targets that are rendered non-orthogonal by their Doppler shift.
1 . A radar system comprising:
a plurality of transmitters, each configured to transmit bursts of modulated radio signals, wherein first and second transmitters of the plurality of transmitters are configured to modulate radio signals as defined by first and second selected subsets of a code set, respectively, wherein each subset is a respective sequence of bits chosen from the code set such that the first subset is orthogonal to the second subset;
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 round-trip echo delay with respect to the plurality of receivers; and
a processor configured to correlate the received radio signals with the selected subsets to determine corresponding round-trip echo delays and thus the corresponding distances, wherein selected subsets comprise respective selected sequences of bits that are chosen from the code set such that the respective subsets exhibit lower cross-correlation than a pseudo-random generated selection of codes, 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.
2 . The radar system of claim 1 , wherein the first and second subsets are each inverted according to first and second inversion patterns, respectively, such that the first subset is orthogonal to the second subset.
3 . The radar system of claim 2 , wherein the processor is configured to improve a level of orthogonality between the first and second subsets 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 further configured to correlate the residual of the received radio signals such that additional targets are identified.
4 . The radar system of claim 1 , wherein each transmitter of the plurality of transmitters is configured to digitally modulate the transmitted radio signals.
5 . The radar system of claim 1 , wherein each transmitter is configured to transmit the modulated radio signals for a selected duration for a selected transmit duty cycle.
6 . The radar system of claim 5 , wherein the selected transmit duty cycle is defined by a selected maximum round-trip echo delay of an object of the plurality of objects.
7 . The radar system of claim 5 , wherein the selected transmit duty cycle is defined by a selected maximum distance of an object, and wherein a signal strength of a received radio signal from the object is above a selected threshold value.
8 . The radar system of claim 1 , wherein the lower cross-correlation comprises zero cross-correlation, and wherein the subsets are mutually orthogonal.
9 . The radar system of claim 1 , wherein the processor comprises a Fast Walsh Transform (FWT) engine configured to perform the correlations.
10 . The radar system 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.
11 . The radar system of claim 10 , wherein the plurality of dipole antennas comprises six dipole antennas, and wherein each of the dipole antennas comprises a bow-tie shape.
12 . The radar system of claim 10 further comprising a reflector, wherein the plurality of dipole antennas are arranged as a linear array of antennas, and wherein the reflector is positioned with respect to the linear array of antennas such that a directivity of the linear array of antennas is controlled.
13 . The radar system of claim 1 , 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.
14 . A method for correlating received radio signals in a radar system, the method comprising:
transmitting bursts of modulated radio signals with a plurality of transmitters of the radar system, wherein each respective modulation is defined by a selected subset of a code set, respectively, wherein the subsets are selected for orthogonality between transmitters, and wherein selected subsets comprise respective selected sequences of bits that are chosen from the code set such that the respective subsets exhibit lower cross-correlation than a pseudo-random generated selection of codes;
receiving radio signals with a plurality of receivers of the radar system, wherein the received radio signals were 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 round-trip echo delay with respect to the plurality of receivers; and
correlating with a processor the received radio signals with the selected subsets to determine corresponding round-trip echo delays and thus the corresponding distances, wherein the processor correlates the received radio signals for a selected quantity of range bins during a radar scan, 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, and 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.
15 . The method of claim 14 , wherein first and second transmitters of the plurality of transmitters are configured to modulate radio signals as defined by first and second selected subsets of the code set, respectively, and wherein each subset is a respective sequence of bits chosen from the code set such that the first subset is orthogonal to the second subset.
16 . The method of claim 15 further comprising inverting the first and second subsets according to first and second inversion patterns, respectively, such that the first subset is orthogonal to the second subset.
17 . The method of claim 15 further comprising improving a level of orthogonality between the first and second subsets 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.
18 . The method of claim 17 further comprising correlating the residual of the received radio signals such that additional targets are identified.
19 . The method of claim 14 , wherein each transmitter of the plurality of transmitters is configured to digitally modulate the transmitted radio signals.