Search frequency correction method, positioning method, program, and receiving apparatus
A search frequency correction method includes: obtaining correlation values by correlating between a received signal that is modulated by direct sequence spread spectrum modulation and a replica code of a spread code with respect to I and Q components at a predetermined search frequency, obtaining accumulated correlation values by accumulating the correlation values of each polarity inversion interval with respect to the I and Q components, calculating a plurality of combinations of the accumulated correlation values in both signs, selecting one of the combinations based on the calculation results of the respective combinations, and correcting the search frequency based on a time variation of an IQ phase represented by the accumulated correlation values of the one of the combinations.
1. A search frequency correction method comprising:
(a) obtaining correlation values by correlating a received signal that is modulated with direct sequence spread spectrum modulation and a replica code of a spread code for each of I and Q components within a frequency search range including a search center frequency;
(b) obtaining accumulated correlation values by accumulating the correlation values for each of the I component and the Q component for a time period corresponding to a polarity inversion interval;
(c) obtaining long-term accumulated values for each of the I component and the Q component using the accumulated correlation values for a time period longer than the polarity inversion interval;
(d) determining an error of the search center frequency based on the long-term accumulated values; and
(e) correcting the search center frequency using the error, wherein
the obtaining the long-term accumulated values includes calculating I addition of the accumulated correlation values for the I component, I subtraction of the accumulated correlation values for the I component, Q addition of the accumulated correlation values for the Q component and Q subtraction of the accumulated correlation values for the Q component, and
the determining the error includes
selecting a first combination of the calculated I addition and the calculated Q addition or a second combination of the calculated I subtraction and the calculated Q subtraction based on the calculated I addition, I subtraction, Q addition and Q subtraction, and
determining the error based on the selected combination.
2. The method according to claim 1 , wherein
the selecting the first combination or the second combination includes selecting the first combination or the second combination based on a first addition of a magnitude of the I addition and a magnitude of the Q addition and a second addition of a magnitude of the I subtraction and a magnitude of the Q subtraction.
3. The method according to claim 1 , further comprising:
executing an incoherent process using the accumulated correlation values for a time period longer than the polarity inversion interval;
setting a peak frequency obtained by the incoherent process to the search center frequency when the corrected search center frequency and the peak frequency fail to satisfy a predetermined approximation condition.
4. A positioning method comprising:
executing the search frequency correction method according to claim 1 using the received signal; and
positioning by executing a predetermined positioning calculation using the accumulated correlation values.
5. A receiving apparatus comprising:
a correlation calculation section adapted to obtain correlation values by correlating a received signal that is modulated with direct sequence spread spectrum modulation and a replica code of a spread code for each of I component and Q component within a frequency search range including a search center frequency;
an accumulation section adapted to obtain accumulated correlation values by accumulating the correlation values for each of the I component and the Q component for a time period corresponding to a polarity inversion interval;
a calculation section adapted to obtain long-term accumulated values for each of the I component and the Q component using the accumulated correlation values for a time period longer than the polarity inversion interval;
a determining section adapted to determine an error of the search center frequency based on the long-term accumulated values; and
a correction section adapted to correct the search center frequency using the error,
wherein
the obtaining the long-term accumulated values includes calculating I addition of the accumulated correlation values for the I component, I subtraction of the accumulated correlation values for the I component, Q addition of the accumulated correlation values for the Q component and Q subtraction of the accumulated correlation values for the Q component, and
the determining the error includes
selecting a first combination of the calculated I addition and the calculated Q addition or a second combination of the calculated I subtraction and the calculated Q subtraction based on the calculated I addition, I subtraction, Q addition and Q subtraction, and
determining the error based on the selected combination.