Radio (NR) wideband sync detection
A network sync signal with unknown frequency location is detected by sampling the received signal over a band of interest in frequency, and over the repetition period of the sync signal in time. The signal is converted to the frequency domain. Sub-bands of the frequency-domain signal, corresponding to different possible sync locations and frequency offsets, are extracted and converted to the time domain, where the sync signal is searched over the reception window length using time-domain matched filtering.
1. A method, performed by a radio network device, of synchronizing to a wireless communication network, comprising:
receiving a wideband signal and storing the received wideband signal;
transforming the received wideband signal to the frequency domain to generate a frequency domain signal;
selecting part of, but less than all of, the frequency domain signal;
converting the selected part of the frequency domain signal to the time domain to generate a time domain signal;
filtering the time domain signal with a sync reference; and
applying a criterion to detect a sync signal in the time domain signal.
2. The method of claim 1 wherein transforming the received wideband signal to the frequency domain comprises transforming the received wideband signal using a Fast Fourier Transform.
3. The method of claim 1 wherein the received wideband signal is zero-padded in order to have length of a power-of-2.
4. The method of claim 1 wherein selecting part of, but less than all of, the frequency domain signal comprises selecting a subset of frequency bins in the frequency domain signal, further comprising zero-padding the subset of frequency bins in the frequency domain signal in order to have length of a power-of-2.
5. The method of claim 1 wherein the sync reference is adjusted to suit the resulting sampling frequency of the time domain signal.
6. The method of claim 1 wherein the sync signal is detected by a magnitude of a correlation operation exceeding a threshold value.
7. The method of claim 1 wherein sync signal timing is determined as the filter output value resulting in the highest magnitude value, less the filter delay.
8. The method of claim 1 wherein the selecting, converting, filtering, and applying steps are repeated using different frequency error hypotheses, and selecting the hypothesis resulting in the largest filter output magnitude.
9. A radio network device, comprising:
one or more antennas;
a transceiver; and
processing circuitry operatively connected to the transceiver and operative to receive a wideband signal and storing the received wideband signal;
transform the received wideband signal to the frequency domain to generate a frequency domain signal;
select part of, but less than all of, the frequency domain signal;
convert the selected at least part of the frequency domain signal to the time domain to generate a time domain signal;
filter the time domain signal with a sync reference; and
apply a criterion to detect a sync signal in the time domain signal.
10. The device of claim 9 wherein the processing circuitry is operative to transform the received wideband signal to the frequency domain by transforming the received wideband signal using a Fast Fourier Transform.
11. The device of claim 9 wherein the processing circuitry is further operative to zero-pad the received wideband signal in order to have length of a power-of-2.
12. The device of claim 9 wherein the processing circuitry is operative to select at least part of the frequency domain signal by selecting a subset of frequency bins in the frequency domain signal, and wherein the processing circuitry is further operative to zero-pad the subset of frequency bins in the frequency domain signal in order to have length of a power-of-2.
13. The device of claim 9 wherein the processing circuitry is further operative to adjust the sync reference to suit the resulting sampling frequency of the time domain signal.
14. The device of claim 9 wherein the processing circuitry is further operative to detect the sync signal by a magnitude of a correlation operation exceeding a threshold value.
15. The device of claim 9 wherein the processing circuitry is further operative to determine sync signal timing as the filter output value resulting in the highest magnitude value, less the filter delay.
16. The device of claim 9 wherein the processing circuitry is further operative to repeat the selecting, converting, filtering, and applying steps using different frequency error hypotheses, and to select the hypothesis resulting in the largest filter output magnitude.
17. The device of claim 9 wherein the radio network device is a User Equipment.
18. The device of claim 9 wherein the radio network device is any one of a machine-to-machine M2M device, a machine-type communications MTC device, and a Narrowband Internet of Things NB IoT device.