Frequency correction circuit, radio receiving apparatus, and frequency correction method

Abstract

A frequency correction circuit used in a radio receiving apparatus that receives a preamble signal through one frequency band and also detects a periodic symbol timing in a receiving period of a part of a symbol that composes the preamble signal, the frequency correction circuit includes a generating unit that generates a detection window of a predetermined time width including each of a first symbol timing and a second symbol timing in the receiving period of a remaining symbol that composes the preamble signal, the first and the second symbol timing being previously determined among periodic symbol timings, a detecting unit that sequentially receives a correlation value between the preamble signal and a reference signal and detects a maximum value from the correlation value input during a period when the detection window is opened, and a correction unit that corrects a frequency deviation of the one frequency band.

What is claimed is: 
     
         1 . A frequency correction circuit used in a radio receiving apparatus that receives a preamble signal through one frequency band and further detects a periodic symbol timing in a receiving period of a part of a symbol that composes the preamble signal, the frequency correction circuit comprising:
 a generating unit that generates a detection window of a predetermined time width including each of a first symbol timing and a second symbol timing in the receiving period of a remaining symbol that composes the preamble signal, the first symbol timing and the second symbol timing being previously determined among periodic symbol timings;   a detecting unit that sequentially receives a correlation value between the preamble signal and a reference signal, and detects a maximum value from the correlation value input during a period when the detection window is opened; and   a correction unit that corrects a frequency deviation of the one frequency band based on the maximum value.   
     
     
         2 . The frequency correction circuit according to  claim 1 , wherein, when the radio receiving apparatus receives the preamble signal through the one frequency band and another frequency band in accordance with a predetermined hopping sequence:
 the generating unit determines the first symbol timing and the second symbol timing for each frequency band and generates the detection window; and   the correction unit corrects the frequency deviation of each frequency band based on the maximum value detected for each frequency band.   
     
     
         3 . The frequency correction circuit according to  claim 1 , wherein the generating unit uses as the first symbol timing and the second symbol timing, a symbol timing that comes after the receiving period of a predetermined number of signals has elapsed since the receiving period of the remaining symbol started. 
     
     
         4 . The frequency correction circuit according to  claim 1 , wherein the generating unit:
 sets the time width depending on a period length in which a delay wave could exist in a radio transmission line; and   opens the detection window before a time that is obtained by multiplying the time width by a coefficient α(0<α<1) from each of the first symbol timing and the second symbol timing.   
     
     
         5 . The frequency correction circuit according to  claim 1 , wherein the generating unit uses an adjacent symbol timing on a time axis as the first and the second symbol timing. 
     
     
         6 . A radio receiving apparatus, comprising:
 the frequency correction circuit according to  claim 1 ;   a circuit that receives the preamble signal;   a circuit that obtains the correlation value from the preamble signal and the reference signal and outputs the correlation value to the frequency correction circuit; and   a circuit that detects the symbol timing using the correlation value and outputs the symbol timing to the frequency correction circuit.   
     
     
         7 . A frequency correction method in a radio receiving apparatus that receives a preamble signal through one frequency band and also detects a periodic symbol timing in a receiving period of a part of a symbol that composes the preamble signal, the frequency correction method comprising:
 detecting a maximum value from a correlation value between the preamble signal and a reference signal obtained within a predetermined time including each of a first symbol timing and a second symbol timing in the receiving period of a remaining symbol that composes the preamble signal, the first symbol timing and the second symbol timing being previously determined among periodic symbol timings; and   correcting a frequency deviation of the one frequency band based on the maximum value.   
     
     
         8 . The frequency correction method according to  claim 7 , wherein, when the preamble signal is received through the one frequency band and another frequency band in accordance with a predetermined hopping sequence,
 wherein the first symbol timing and the second symbol timing are determined for each frequency band and a detection window is generated, and   wherein the frequency deviation of each frequency band is corrected based on the maximum value detected for each frequency band.   
     
     
         9 . The frequency correction method according to  claim 7 , wherein a symbol timing that comes after the receiving period of a predetermined number of symbols has elapsed since the receiving period of the remaining symbol started is used as the first and the second symbol timing. 
     
     
         10 . The frequency correction method according to  claim 7 , wherein a time width is set depending on a period length in which a delayed wave could exist in a radio transmission line, and
 wherein the detection window is opened before a time obtained by multiplying the time width by a coefficient α(0<α<1) from each of the first and the second symbol timing.   
     
     
         11 . The frequency correction method according to  claim 7 , wherein an adjacent symbol timing on a time axis is used as the first symbol timing and the second symbol timing.