CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority under 35 U.S.C. § 119 of European Patent application no. 19158065.3, filed on 19 Feb. 2019, the contents of which are incorporated by reference herein.

FIELD

This disclosure relates to receiver units and receiver systems for use in multiple-input-multiple output, MIMO, radar systems. It further relates to methods for designing filters for use in such receiver units and receiver systems.

BACKGROUND

Recent years have seen a significant increase in interest in the topic of multiple-input-multiple-output (MIMO) radar systems for commercial applications. Whereas MIMO radar systems have been known and used for many years in high-cost high-performance applications, these have typically been limited to military or scientific applications, in which the associated costs are justifiable. However, the recent drive towards autonomous and semi-autonomous driving, in particular, has resulted in pressure to develop radar systems which are increasingly advanced, and yet affordable enough to be used in consumer applications.

As a result, MIMO digitally modulated radar is being developed for use primarily in automobile applications. Automobile radar applications provide significant challenges, in particular to the signal processing of reflected radar signals, since the application environment generally includes multiple targets, and targets with very different cross sections—in which the strength of the reflected signals from different targets may differ by between 20 and 30 dB, or more. Furthermore, for applications such as autonomous driving, the signal processing to yield target acquisition and target tracking must be performed rapidly, and within the constraints of the processing capability on-board the vehicle. This presents challenges to the design of the MIMO receivers, and in particular the signal processing therein.

Whereas, hereinafter in this disclosure, autonomous and quasi-autonomous driving will be used as an example application, the skilled person will appreciate that the disclosure is not limited thereto, but may be equally relevant to other applications in which multiple targets and targets with varying cross sections must be acquired and tracked at affordable cost and relatively quickly. These include but are not limited to commercial and consumer drone applications, commercial and consumer maritime applications, and other applications requiring navigation in a non-empty environment.

SUMMARY

According to a first aspect of the present disclosure, there is provided a receiver unit for use in a multiple-input-multiple output, MIMO, radar system having a plurality of transmitters each for transmitting one of a group of orthogonal digital-transmitter-signals on a carrier wave, the receiver unit configured and adapted to receive a raw-analog-signal on the carrier wave reflected from one or more target objects, the receiver unit comprising: a down-converter configured to extract the raw-analog-signal from the carrier wave; an analog-to-digital converter configured to derive a raw-digital-signal from the raw-analog-signal; a plurality of filter units; each filter unit associated with a different one of the digital-transmitter-signals, operable on the raw-digital-signal and configured to identify reflection-event sequences in the raw-digital-signal; and a time-frequency transform sub-unit, configured to identify a frequency associated with a reflection-event sequence; wherein each filter unit comprises a mismatch filter having predetermined filter coefficients and designed to reduce the magnitude of side-lobes associated with a reflection-event-sequence in the raw-digital-signal.

In one or more embodiments, each filter unit further comprises a match filter configured to cross-correlate the raw-digital-signal with the respective transmitter-signal. The match filter may cross-correlate the raw-digital-signal with the respective transmitter-signal by comparing sections of the raw-digital-signal with the unit-sequence of the respective digital-transmitter-signal.

In one or more other embodiments, the mismatch filter is further designed to maximise the signal-to-noise-ratio, SNR, for the reflection event, thereby providing a correlation function between the raw-digital-signal and the respective transmitter-signal. The match filter may thus be redundant and not required.

In one or more embodiments the receiver unit further comprises a coherent adder operable on the raw-analog-signal. The coherent adder operates on the multiple sequences of the raw-analog-signal, and may improve a signal-to-noise ratio of the raw-analog-signal.

In one or more embodiments the time-frequency transform sub-unit is configured to perform fast Fourier transforms, FFT. Other embodiments may be configured to use other discrete transforms.

According to another aspect of the present disclosure there is provided a receiver system comprising a plurality of receiver-units as described above and further comprising an angle-calculation-unit configured to perform a FFT on an output of the time-frequency transform sub-unit and to determine an angle between a target object and a reference direction. The receiver system may further comprise a target-detection unit, configured to localise targets from the angle, an output of the time-frequency transform sub-unit, and a reflection-event sequence. The receiving system may comprise r receiver units and may be operable with a group of up to M transmitters, wherein each receiver unit comprises at least M filter units, each associated with a different one of the group of transmitters and having predetermined filter coefficients derived for the respective digital-transmitter-signal.

According to a yet further aspect of the present disclosure, there is provided an integrated circuit comprising a receiver system as described above, and a respective transmitter circuit for use in each of the plurality of transmitters.

According to another aspect of the present invention there is provided a method of designing a mismatch filter having n filter coefficients hi, where i equals 1 to n, for use in a receiver unit as claimed in any of claims1to6or a receiver system as claimed in claims7to11, the mismatch filter having filter coefficients h, the method comprising: generating M vectors Xi of size n; calculating a Toeplitz matrix M(i) for each vector Xi; initialising a sidelobe weighting vector v={1/N1, 1/N . . . , 1/N} of length k, wherein k>=M; initialising a matrix B with 0 in all elements; and iteratively calculating the filter coefficients h, from {M(i)} and v.

The vectors Xi may correspond to an expected output of respective match filter for each transmitter channel. In one or more other embodiments, the vectors Xi correspond to the unit sequences for each transmitter channel. A least squares method may be used to iteratively calculate the filter coefficients.

There may be provided a computer program, which when run on a computer, causes the computer to configure any apparatus, including a circuit, controller, sensor, filter, or device disclosed herein or perform any method disclosed herein. The computer program may be a software implementation, and the computer may be considered as any appropriate hardware, including a digital signal processor, a microcontroller, and an implementation in read only memory (ROM), erasable programmable read only memory (EPROM) or electronically erasable programmable read only memory (EEPROM), as non-limiting examples. The software implementation may be an assembly program.

The computer program may be provided on a computer readable medium, which may be a physical computer readable medium, such as a disc or a memory device, or may be embodied as any other non-transient signal.

These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter.

