Systems and methods for wireless network discovery and synchronization using spatial whiteners, matched filters, and adaptive beamformers to identify reference signal waveforms
Physical layer processing methods for network acquisition by remote nodes in wireless communication systems are described herein. New methods for wireless network discovery and synchronization by remote nodes are described herein that utilize spatial (e.g., antenna array) processing algorithms which may achieve enhanced functioning in challenging radio frequency environments, such as those containing interference and multi path distortion effects. These methods may include advantageous use of spatial whiteners and associated pluralities of adaptive beamformers to detect network reference and synchronization signals and estimate their parameters.
1. An antenna-array based receiver comprising:
a plurality of antennas, each antenna of the plurality of antennas configured to receive radio frequency (RF) signals arriving from different signal sources;
downconverters and digitizers connected to the plurality of antennas and configured to generate a set of digitized baseband data streams spanning a same frequency band, wherein the digitized baseband data streams include representations of the RF signals from the different signal sources;
a spatial whitener configured to reduce a variation of received power across the representations of the RF signals from the different signal sources to provide a plurality of whitened data streams;
a spatial matched filter (SW) having an impulse response configured for detection of a reference signal waveform; the SMF configured to receive the plurality of whitened data streams, and generate a plurality of filtered data streams containing indicators of a presence of the reference signal waveform in the plurality of whitened data streams, and, utilizing the filtered data streams, generate an SMF output waveform; and
a synchronous video integrated (SVI) output amplifier configured to sum or average the SMF output waveform to generate an SVI output waveform over multiple time-synchronous snapshots of the SMF output waveform.
2. The receiver of claim 1 , wherein generating the SMF output waveform is based on the spatial matched filter calculating a non-coherent sum or average of the filtered data streams.
3. The receiver of claim 1 , wherein the time-synchronous snapshots are time-aligned at integer multiples of a basic frame-length of a wireless system or signal.
4. The receiver of claim 3 , further comprising a plurality of spatial whiteners, SMRs, and SVIs, each set configured to operate on a sub-frame of the plurality of data streams time-aligned at integer multiples of a frame-length.
5. The receiver of claim 1 , wherein the SMF is further configured to amplitude normalize the SMF output waveform using a finite impulse response (FIR) filter.
6. The receiver of claim 5 , wherein a normalizing FIR filter impulse response is derived from magnitudes of the matched-filter impulse response.
7. The receiver of claim 1 , wherein the reference signal waveform corresponds to a primary synchronization signal (PSS) or sequence within a coarse carrier frequency (CCF) range.
8. The receiver of claim 1 , wherein the spatial whitener is further configured to calculate the plurality of whitened data streams using a linear transformation of the plurality of baseband data streams, such that the plurality of whitened data streams, or their decimated rendering, possesses an identity spatial covariance matrix of dimension K, where K is less than or equal to a number of antennas of the plurality of antennas.
9. The receiver of claim 1 , further comprising:
an adaptive beamformer bank configured to select a time-interval of the baseband data streams containing the reference signal waveform over a selected fine-carrier frequency range, the adaptive beamformer bank further configured to calculate a plurality of beamforming weights for receiving the reference signal waveform for each of a plurality of fine-carrier frequency (FCF) values based on either the data streams over the selected time-interval, or OFDM symbols corresponding to the data streams, to form a respective beamformer for each FCF value of the plurality of FCF values.
10. The receiver of claim 9 , wherein the adaptive beamformer bank is further configured to calculate a respective inverse covariance matrix based on either a time-domain or a frequency-domain (FFT) representation of the baseband data streams, and a cross-correlation vector between the baseband data streams, and each of a plurality of FCF-offset respective time-domain or frequency-domain reference signal waveforms, which each adaptive beamformer of the adaptive beamformer bank uses to produce the beamforming weights and associated detection statistics for each FCF value.
11. The receiver of claim 1 , further comprising:
an adaptive beamformer bank associated with a fine timing offset of the reference signal waveform, wherein the adaptive beamformer bank is configured to select a time-interval of the baseband data streams containing the reference signal waveform, the adaptive beamformer bank further configured to calculate a plurality of beamforming weights based on an inverse covariance matrix calculated from either a time-domain or a frequency-domain (FFT) representation of the baseband data streams, and a cross-correlation vector between such a time-domain or FFT representation of the baseband data streams, and each of a plurality of fine-timing-offset time-domain or frequency-domain reference signal waveforms, to form a respective beamformer and detection statistic for each timing offset of a plurality of fine timing offsets.
12. The receiver of claim 1 , further comprising:
an adaptive beamformer bank associated with a secondary reference signal comprising a set of distinct identification waveforms, wherein the adaptive beamformer bank is configured to select a time-interval of the baseband data streams containing the secondary reference signal, wherein the adaptive beamformer is further configured to time-adjust each stream of the baseband data streams to a selected fine timing offset, wherein the adaptive beamformer is further configured to calculate a plurality of beamforming weights based on an inverse covariance matrix calculated from either a time-domain or a frequency-domain (FFT) representation of the baseband data streams, and a cross-correlation vector between such a time-domain or FFT representation of the baseband data streams, and each of a plurality of time-domain or frequency-domain reference signal waveforms for each respective hypothesis of a multiple hypothesis test (MHT), to form a respective beamformer and detection statistic for each hypothesis of the MHT.
13. The receiver of claim 1 , wherein the receiver is implemented in a processor of a remote node of a wireless network, the processor configured to execute instructions, from a non-transitory computer-readable medium, that implement the spatial whitener and the SMF.