Joint sensing and communications using OFDM waveforms
Various embodiments comprise systems, methods, architectures, mechanisms and apparatus providing a dual-function radar communication (DFRC) system a multiple-input multiple-output (MIMO) radar is configured to have only a small number of its antennas active in each channel use. Probing waveforms are of an orthogonal frequency division multiplexing (OFDM) type. OFDM carriers are divided into two groups, one group that is used by the active antennas in a shared fashion, and another group where each subcarrier is assigned to an active antenna in an exclusive fashion (e.g., private subcarriers). Target estimation is carried out based on the received and transmitted symbols. The system communicates information via the transmitted OFDM data symbols and the pattern of active antennas in a generalized spatial modulation (GSM) fashion. A multi-antenna communication receiver can identify the indices of active antennas via sparse signal recovery methods. The private subcarriers may be used to synthesize a virtual array for high angular resolution, and also for improved estimation on the active antenna indices.
1 . A multiple-input multiple-output (MIMO) radar system, comprising:
a uniform linear array (ULA) transmit array having N t active transmit elements, spaced apart by d t ; and
a transmitter processing stage, configured for transmitting Ns symbol-bearing sections via a plurality of active antennas, the transmitter processing stage:
identifying antennas to be active during the channel use iteration, each of the active antennas being associated with each of a first group of subcarriers to be used as shared subcarriers and a respective one private subcarrier;
performing OFDM modulation based on Ns shared subcarriers and one respective private subcarrier on the symbols of each active antenna, wherein the private subcarrier associated with a respective active antenna includes a non-zero symbol only at a symbol location corresponding to an index of the respective active antenna to enable thereby active transmit antenna identification at a receiver using sparse signal recovery;
converting the modulated subcarriers into analog signals; and
upconverting each analog signal in accordance with a carrier frequency for transmission by a respective assigned active antenna.
2 . The multiple-input multiple-output (MIMO) radar system of claim 1 , wherein for each channel use iteration an activation code is provided to indicate the active antennas for the channel use iteration.
3 . The multiple-input multiple-output (MIMO) radar system of claim 1 , wherein the transmitter processing stage comprises a plurality of quadrature amplitude modulation (QAM) modulators configured to generate respective modulated data symbols sequences in response to respective received output data stream sections.
4 . The multiple-input multiple-output (MIMO) radar system of claim 3 , wherein the transmitter processing stage comprises:
a plurality of serial to parallel (S/P) converters configured to convert respective serial input data streams into output data stream sections for use by respective QAM modulators; and
a plurality of parallel to serial (P/S) converters configured to convert respective IDFT/CP processed modulated data symbols sequences to serial data symbol streams; and
a plurality of analog to digital (A/D) converters to convert respective serial data symbol streams into respective analog transmission signals (TX).
5 . The multiple-input multiple-output (MIMO) radar system of claim 1 , further comprising:
a ULA receive array with N r active receive elements, spaced apart by d t ; and
a receiver processing stage, configured for:
downconverting reflected subcarrier signals to retrieve respective samples,
discard a cyclic prefix (CP) from the received samples;
applying an Ns-point discrete Fourier transform (DFT) to the received samples to obtain respective symbols;
estimating target elevation angles based on location of peaks of an Nr-point DFT performed along a receiving array, each Nr-point DFT peak having associated with it a corresponding frequency amplitude;
for each estimated target elevation angle, obtaining a range parameter based on the frequency amplitudes along all subcarriers;
estimating target ranges based on location of peaks of cross-correlations of Ns-point DFTs, each Ns-point DFT peak having associated with it a corresponding range amplitude; and
for each target range estimate, estimating a velocity parameter based on location of peaks of an Np-point DFT of the range amplitudes across Np OFDM symbols.
6 . The multiple-input multiple-output (MIMO) radar system of claim 5 , wherein the receiver processing stage is further configured for:
formulating a virtual array having a larger aperture than the ULA receive array; and
using the virtual array and sparse signal recovery to refine the target elevation angle estimates.
7 . The multiple-input multiple-output (MIMO) radar system of claim 5 , wherein the receiver processing stage is further configured for:
applying sparse signal recovery on at least some of the received subcarriers to determine if a received subcarrier contains only one nonzero element,
wherein each received subcarrier containing only one nonzero element comprises a private subcarrier associated with a respective transmitting antenna, the symbol location of the nonzero element being indicative of the respective transmitting antenna.
8 . A method for use by a multiple-input multiple-output (MIMO) radar system including a uniform linear array (ULA) transmit array having N t active transmit elements, spaced apart by d t and configured for transmitting Ns symbol-bearing sections via a plurality of active antennas, the method comprising:
identifying antennas to be active during the channel use iteration, each of the active antennas being associated with each of a first group of subcarriers to be used as shared subcarriers and a respective one private subcarrier;
performing OFDM modulation based on Ns shared subcarriers and respective one private subcarrier on the symbols of each active antenna, wherein the private subcarrier associated with a respective active antenna includes a non-zero symbol only at a symbol location corresponding to an index of the respective active antenna to enable thereby active transmit antenna identification at a receiver using sparse signal recovery;
converting the modulated subcarriers into analog signals; and
upconverting each analog signal in accordance with a carrier frequency for transmission by a respective assigned active antenna.
9 . The method of claim 8 , wherein for each channel use iteration an activation code is provided to indicate the active antennas for the channel use iteration.
10 . The method of claim 8 , wherein a plurality of quadrature amplitude modulation (QAM) modulators are configured to generate respective modulated data symbols sequences in response to respective received output data stream sections.
11 . The method of claim 8 , wherein:
a plurality of serial to parallel (S/P) converters are configured to convert respective serial input data streams into output data stream sections for use by respective QAM modulators; and
a plurality of parallel to serial (P/S) converters are configured to convert respective IDFT/CP processed modulated data symbols sequences to serial data symbol streams; and
a plurality of analog to digital (A/D) are converters to convert respective serial data symbol streams into respective analog transmission signals (TX).
12 . The method of claim 8 , wherein the MIMO radar system further includes a ULA receive array with N r active receive elements spaced apart by d t , the method further comprising:
downconverting reflected subcarrier signals to retrieve respective samples;
discarding a cyclic prefix (CP) from the received samples;
applying an Ns-point discrete Fourier transform (DFT) to the received samples to obtain respective symbols;
estimating target elevation angles based on location of peaks of an Nr-point DFT performed along a receiving array, each Nr-point DFT peak having associated with it a corresponding frequency amplitude;
for each estimated target elevation angle, obtaining a range parameter based on the frequency amplitudes along all subcarriers;
estimating target ranges based on location of peaks of cross-correlations of Ns-point DFTs, each Ns-point DFT peak having associated with it a corresponding range amplitude; and
for each target range estimate, estimating a velocity parameter based on location of peaks of an Np-point DFT of the range amplitudes across Np OFDM symbols.
13 . The method of claim 12 , further comprising:
applying sparse signal recovery on at least some of the received subcarriers to determine if a received subcarrier contains only one nonzero element,
wherein each received subcarrier containing only one nonzero element comprises a private subcarrier associated with a respective transmitting antenna, the symbol location of the nonzero element being indicative of the respective transmitting antenna.
14 . An apparatus, comprising:
a uniform linear array (ULA) transmit array having N t active transmit elements, spaced apart by d t ; and
a transmitter processing stage, configured for transmitting Ns symbol-bearing sections via a plurality of active antennas, the transmitter processing stage:
identifying antennas to be active during the channel use iteration, each of the active antennas being associated with each of a first group of subcarriers to be used as shared subcarriers and a respective one private subcarrier;
performing OFDM modulation based on Ns shared subcarriers and respective one private subcarrier on the symbols of each active antenna, wherein the private subcarrier associated with a respective active antenna includes a non-zero symbol only at a symbol location corresponding to an index of the respective active antenna to enable thereby active transmit antenna identification at a receiver using sparse signal recovery;
converting the modulated subcarriers into analog signals; and
upconverting each analog signal in accordance with a carrier frequency for transmission by a respective assigned active antenna.
15 . The apparatus of claim 14 , wherein for each channel use iteration an activation code is provided to indicate the active antennas for the channel use iteration.
16 . The apparatus of claim 14 , wherein the transmitter processing stage comprises a plurality of quadrature amplitude modulation (QAM) modulators configured to generate respective modulated data symbols sequences in response to respective received output data stream sections.
17 . The apparatus of claim 16 , wherein the transmitter processing stage comprises:
a plurality of serial to parallel (S/P) converters configured to convert respective serial input data streams into output data stream sections for use by respective QAM modulators; and
a plurality of parallel to serial (P/S) converters configured to convert respective IDFT/CP processed modulated data symbols sequences to serial data symbol streams; and
a plurality of analog to digital (A/D) converters to convert respective serial data symbol streams into respective analog transmission signals (TX).
18 . The apparatus of claim 14 , further comprising:
a ULA receive array with N r active receive elements, spaced apart by d t ; and
a receiver processing stage, configured for:
downconverting reflected subcarrier signals to retrieve respective samples;
discard a cyclic prefix (CP) from the received samples;
applying an Ns-point discrete Fourier transform (DFT) to the received samples to obtain respective symbols;
estimating target elevation angles based on location of peaks of an Nr-point DFT performed along a receiving array, each Nr-point DFT peak having associated with it a corresponding frequency amplitude;
for each estimated target elevation angle, obtaining a range parameter based on the frequency amplitudes along all subcarriers;
estimating target ranges based on location of peaks of cross-correlations of Ns-point DFTs, each Ns-point DFT peak having associated with it a corresponding range amplitude; and
for each target range estimate, estimating a velocity parameter based on location of peaks of an Np-point DFT of the range amplitudes across Np OFDM symbols.
19 . The apparatus of claim 18 , wherein the receiver processing stage is further configured for:
formulating a virtual array having a larger aperture than the ULA receive array; and
using the virtual array and sparse signal recovery to refine the target elevation angle estimates.
20 . The apparatus of claim 18 , wherein the receiver processing stage is further configured for:
applying sparse signal recovery on at least some of the received subcarriers to determine if a received subcarrier contains only one nonzero element,
wherein each received subcarrier containing only one nonzero element comprises a private subcarrier associated with a respective transmitting antenna, the symbol location of the nonzero element being indicative of the respective transmitting antenna.