US-12627545-B2 - Synchronization detection apparatus, synchronization detection method, and non-transitory computer readable medium

Abstract

Provided are a synchronization detection apparatus, a synchronization detection method, and a synchronization detection program that make it possible to follow, in a short time, a frequency deviation of an intermediate frequency after a radio frequency is down-converted. A synchronization detection apparatus according to the present invention includes: a band limitation unit in which, for an externally received signal, each of a plurality of filters each having a different center frequency limits a band of the received signal to output a plurality of band-limited signals; a detection and demodulation unit that detects and demodulates each of the plurality of band-limited signals to output a plurality of detected signals; and a synchronization detection unit that performs synchronization detection of each of the plurality of detected signals to output a plurality of correlation values.

Inventors

• Masayuki Tsuchida

Assignees

• JVCKENWOOD CORPORATION

Dates

Publication Date

20260512

Application Date

20241205

Priority Date

20220627

Claims (4)

1. 1 . A synchronization detection apparatus comprising: a band limitation unit in which, for an externally received signal, each of a plurality of filters each having a different center frequency limits a band of the received signal to output a plurality of band-limited signals; a detection and demodulation unit that detects and demodulates each of the plurality of band-limited signals to output a plurality of detected signals; a synchronization detection unit that performs synchronization detection of each of the plurality of detected signals to output a plurality of correlation values; and a synchronization evaluation unit that selects a predetermined filter from among the plurality of filters based on the plurality of correlation values, wherein the synchronization evaluation unit includes a frequency tracking unit and a filter coefficient setting unit that set the center frequency of the filter based on the correlation values, the synchronization evaluation unit selects the highest correlation value among the plurality of correlation values as a first correlation value, and when the predetermined filter corresponding to the first correlation value is selected from among the plurality of filters, the frequency tracking unit detects a frequency deviation value of the selected predetermined filter, and the filter coefficient setting unit updates the center frequency of the predetermined filter based on the frequency deviation value, and the band limitation unit outputs a predetermined band-limited signal using the updated predetermined filter.
2. 2 . The synchronization detection apparatus according to claim 1 , wherein the band limitation unit, the detection and demodulation unit, the synchronization detection unit, and the synchronization evaluation unit make a transition to a standby state in which the synchronization detection is repeated when all of the plurality of correlation values are less than a predetermined threshold, and make a transition to a symbol-detected state in which the predetermined filter is selected when any of the plurality of correlation values is equal to or greater than the predetermined threshold.
3. 3 . A synchronization detection method comprising: for an externally received signal, each of a plurality of filters each having a different center frequency limiting a band of the received signal to output a plurality of band-limited signals; detecting and demodulating each of the plurality of band-limited signals to output a plurality of detected signals; performing synchronization detection of each of the plurality of detected signals to output a plurality of correlation values; selecting a predetermined filter from among the plurality of filters based on the plurality of correlation values; setting the center frequency of the filter based on the correlation values; selecting the highest correlation value among the plurality of correlation values as a first correlation value, and when the predetermined filter corresponding to the first correlation value is selected from among the plurality of filters, detecting a frequency deviation value of the selected predetermined filter, and updating the center frequency of the predetermined filter based on the frequency deviation value; and outputting a predetermined band-limited signal using the updated predetermined filter.
4. 4 . A non-transitory computer readable medium storing a synchronization detection program causing a computer to execute: for an externally received signal, each of a plurality of filters each having a different center frequency limiting a band of the received signal to output a plurality of band-limited signals; detecting and demodulating each of the plurality of band-limited signals to output a plurality of detected signals; performing synchronization detection of each of the plurality of detected signals to output a plurality of correlation values; selecting a predetermined filter from among the plurality of filters based on the plurality of correlation values; setting the center frequency of the filter based on the correlation values; selecting the highest correlation value among the plurality of correlation values as a first correlation value, and when the predetermined filter corresponding to the first correlation value is selected from among the plurality of filters, detecting a frequency deviation value of the selected predetermined filter, and updating the center frequency of the predetermined filter based on the frequency deviation value; and outputting a predetermined band-limited signal using the updated predetermined filter.

Description

CROSS REFERENCE TO RELATED APPLICATION This application is based upon and claims the benefit of priority from International Patent Application No. PCT/JP2023/019367, filed on May 24, 2023, which is based on Japanese Patent Application No. 2022-102550, filed on Jun. 27, 2022, the disclosure of which is incorporated herein in its entirety by reference. BACKGROUND The present invention relates to a synchronization detection apparatus, a synchronization detection method, and a synchronization detection program, and in particular to a synchronization detection apparatus, a synchronization detection method, and a synchronization detection program that make it possible to follow, in a short time, a frequency deviation of an intermediate frequency (IF) after a radio frequency is down-converted. Auto frequency control (AFC) in receiving land mobile radio (LMR) operates to, when converting the frequency of a received signal received by a reception unit (RX) to an intermediate frequency (IF) using a frequency mixer, vary the local (LO) frequency to follow a frequency deviation of the received signal, thereby aligning the output IF signal with the center frequency of the filter. This has been done to obtain an IF signal that is as unaffected as possible from band limitation due to the filter. However, there has been a problem that it takes time to set the local frequency and it takes time to pull the intermediate frequency determined by the receiving frequency and the local frequency into the frequency band of the filter. In addition, since the receiving frequency differs for each terminal that is a communication counterpart, the local frequency must be varied for each terminal accordingly, which also causes a problem that it takes time to set the frequency. Note that the receiving frequency may be referred to as a carrier frequency. Patent Literature 1 describes that a repeater or a base station detects error information of a signal frequency arriving in the uplink from a radio communication apparatus and transmits the error information in the downlink to the corresponding radio communication apparatus, and the radio communication apparatus corrects its own oscillator frequency based on the error information. Since the technique described in Patent Literature 1 determines frequency error information in the uplink and notifies it in the downlink, it takes time to follow the frequency. Patent Literature 2 describes that “A DAC applies digital conversion to an IF signal including an FM-modulated video signal, and an orthogonal modulation unit applies orthogonal modulation to produce components orthogonal to each other and to perform down-conversion to a baseband (BB). A phase calculation unit and a phase difference detection unit are used to carry out FM demodulation processing in this BB. Since digital processing is used, an NCO (numerical control oscillator) can be used as a local oscillator in the orthogonal modulation unit, the adjustment and the setting are facilitated, subcarrier setting in an FM demodulation unit for an audio signal is also facilitated, and filters for subcarrier extraction are easily modified by only varying the filter coefficients.” The technique described in Patent Literature 2 is a system that demodulates a video signal and an audio signal (subcarrier signals) in parallel, and does not disclose that a plurality of IF signals having frequencies slightly shifted from each other are detected and demodulated in parallel. [Patent Literature 1] Japanese Unexamined Patent Application Publication No. 2008-35132[Patent Literature 2] Japanese Unexamined Patent Application Publication No. 2007-110269 SUMMARY As described above, there has been a problem that it takes time to pull the intermediate frequency determined by the receiving frequency and the local frequency into the frequency band of the filter. Therefore, this embodiment provides a synchronization detection apparatus including: a band limitation unit in which, for an externally received signal, each of a plurality of filters each having a different center frequency limits a band of the received signal to output a plurality of band-limited signals;a detection and demodulation unit that detects and demodulates each of the plurality of band-limited signals to output a plurality of detected signals;a synchronization detection unit that performs synchronization detection of each of the plurality of detected signals to output a plurality of correlation values; anda synchronization evaluation unit that selects a predetermined filter from among the plurality of filters based on the plurality of correlation values. In addition, this embodiment provides a synchronization detection method including: for an externally received signal, each of a plurality of filters each having a different center frequency limiting a band of the received signal to output a plurality of band-limited signals;detecting and demodulating each of the plurality of band-limited sig