Frequency offset estimating method and frequency offset correcting apparatus utilizing said method
View Patent ↗A frequency offset correcting unit estimates frequency offsets in a preamble period, corrects digital received signals by the estimated initial frequency and further corrects them by residual frequency signals. A receiving weight vector computing unit computes receiving weight vector signals by using LMS algorithm. Based on the error vectors or receiving weight vector signals derived by LMS algorithm, the frequency offsets contained in corrected received signals are also estimated and are outputted as the residual frequency signals. A multiplier weights the corrected received signals with the receiving weight vector signals. An adder sums up outputs of the multiplier so as to output a synthesized signal.
1. A frequency offset correcting apparatus, comprising:
a correcting unit which respectively corrects frequency offsets contained in a plurality of received signals that correspond respectively to a plurality antennas;
a processing unit which applies an adaptive algorithm to the plurality of corrected received signals so as to derive a plurality of weighting factors corresponding respectively to the plurality of corrected received signals and an error derived by the adaptive algorithm; and
an estimating unit which estimates respectively residual components of the frequency offsets contained in the plurality of corrected received signals, based on the plurality of derived weighting factors and the error derived by the adaptive algorithm,
wherein said estimating unit estimates the residual components of frequency offsets by multiplying respectively the error derived by the adaptive algorithm by complex conjugation of the plurality of corrected received signals and by extracting imaginary components from a division result where the multiplication result is divided by the plurality of derived weighting factors, and
wherein said correcting unit corrects the frequency offsets respectively by reflecting the estimated residual components of frequency offsets.
2. A frequency offset correcting apparatus according to claim 1 , further comprising a frequency conversion unit which performs frequency conversion respectively on a plurality of radio frequency signals received respectively by the plurality of antennas, based on a plurality of oscillation signals outputted respectively from a plurality of frequency oscillators and which outputs the frequency-converted signals to said correcting unit as the plurality of received signals.
3. A frequency offset correcting apparatus according to claim 2 , further comprising a weighting unit which weights the plurality of corrected received signals with the plurality of derived weighting factors, respectively.
4. A frequency offset correcting apparatus according to claim 2 , further comprising a frequency-domain conversion unit which converts respectively the plurality of corrected received signals to those in frequency domain and which outputs a plurality of signals in frequency domain for the respective plurality of corrected received signals,
wherein said processing unit derives respectively a plurality of weighting factors and errors, derived by the adaptive algorithm, corresponding respectively to the plurality of signals in frequency domain, by applying the adaptive algorithm to among the plurality of corrected received signals in units of one signal in frequency domain mutually associated thereamong, and
wherein said estimating unit estimates the residual components of frequency offset, based on the plurality of weighting factors and errors, derived by the adaptive algorithm, corresponding respectively to the plurality of signals in frequency domain.
5. A frequency offset correcting apparatus according to claim 4 , wherein said estimating unit estimates the residual components of frequency offset over a unit in which the plurality of corrected received signals are to be converted to those in frequency domain.
6. A frequency offset correcting apparatus according to claim 4 , further comprising a weighting unit which weights the plurality of signals in frequency domain with the plurality of derived weighting factors, respectively.
7. A frequency offset correcting apparatus according to claim 1 , further comprising a weighting unit which weights the plurality of corrected received signals with the plurality of derived weighting factors, respectively.
8. A frequency offset correcting apparatus according to claim 1 , further comprising a frequency-domain conversion unit which converts respectively the plurality of corrected received signals to those in frequency domain and which outputs a plurality of signals in frequency domain for the respective plurality of corrected received signals,
wherein said processing unit derives respectively a plurality of weighting factors and errors, derived by the adaptive algorithm, corresponding respectively to the plurality of signals in frequency domain, by applying the adaptive algorithm to among the plurality of corrected received signals in units of one signal in frequency domain mutually associated thereamong, and
wherein said estimating unit estimates the residual components of frequency offsets, based on the plurality of weighting factors and errors, derived by the adaptive algorithm, corresponding respectively to the plurality of signals in frequency domain.
9. A frequency offset correcting apparatus according to claim 8 , wherein said estimating unit estimates the residual components of frequency offset over a unit in which the plurality of corrected received signals are to be converted to those in frequency domain.
10. A frequency offset correcting apparatus according to claim 8 , further comprising a weighting unit which weights the plurality of signals in frequency domain with the plurality of derived weighting factors, respectively.
11. A frequency offset estimating method characterized in that an adaptive algorithm is applied to a plurality of received signals corresponding respectively to a plurality of antennas so as to respectively derive a plurality of weighting factors corresponding respectively to the plurality of received signals and an error derived by the adaptive algorithm, and then frequency offsets contained in the plurality of received signals are respectively estimated, by multiplying respectively the error derived by the adaptive algorithm by complex conjugation of the plurality of corrected received signals and by extracting imaginary components from a division result where the multiplication result is divided by the plurality of derived weighting factors.
12. A computer readable storage medium having a program causing a computer to perform the steps of:
outputting, from a memory, frequency offsets contained in a plurality of received signals that correspond respectively to a plurality of antennas and correcting respectively the outputted frequency offsets;
applying an adaptive algorithm to the plurality of corrected received signals so as to derive a plurality of weighting factors corresponding respectively to the plurality of corrected received signals and an error derived by the adaptive algorithm; and
estimating respectively residual components of the frequency offsets contained in the plurality of corrected received signals, based on the plurality of derived weighting factors and the error derived by the adaptive algorithm,
wherein said estimating estimates the residual components of frequency offsets by multiplying respectively the error derived by the adaptive algorithm by complex conjugation of the plurality of corrected received signals and by extracting imaginary components from a division result where the multiplication result is divided by the plurality of derived weighting factors, and
wherein said correcting is such that the frequency offsets stored in the memory is updated by the estimated residual components of the frequency offsets.