Automatic frequency correction method and receiver for time division duplex modes of 3G wireless communications
First Claim
1. A receiver for use in a wireless communication system, said receiver including a voltage controlled oscillator and estimating means for obtaining a frequency estimate to adjust said voltage controlled oscillator, said estimating means comprising:
- receiving means for receiving a communication signal including time slots containing data symbols and a midamble;
correlating means for performing a given number N of block correlations of the received signal samples with a known midamble reference;
forming means for forming a conjugate product of the N block correlations to form N−
1 conjugate products;
summing means for forming a sum of the N−
1 conjugate products;
accumulating means for accumulating a given number of sums of said N−
1 conjugate products obtained from said summing means;
determining means for determining the magnitude of each accumulated summed value;
searching means for searching for a given number of largest summed values;
detection means for performing a threshold detection of the given number of largest summed values other than the largest summed value, employing a threshold which is a function of the largest summed value;
combining means for combining the largest summed value with the given number of the largest summed values other than the largest summed value and which are greater than the threshold;
computing means for computing the magnitude of the sum obtained by said combining means;
normalizing means for normalizing the complex value obtained by said combining means employing the magnitude obtained by said computing means; and
generating means for generating an argument of the normalized value obtained by said normalizing means for a frequency estimate.
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Abstract
A receiver for use in a wireless communication system includes a voltage controlled oscillator and estimating means for obtaining a frequency estimate to adjust the voltage controlled oscillator, thereby correcting an oscillator frequency error. The estimating means performs a number of block correlations on a received signal with a known midamble reference. The output of the block correlators are conjugately multiplied and summed to produce a low-variance estimate of the phase change between correlators. A number of the largest summed values are located, and the located values that exceed a detection threshold are summed to provide a single complex number whose angle is an estimate of the phase change between the correlators.
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Citations
28 Claims
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1. A receiver for use in a wireless communication system, said receiver including a voltage controlled oscillator and estimating means for obtaining a frequency estimate to adjust said voltage controlled oscillator, said estimating means comprising:
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receiving means for receiving a communication signal including time slots containing data symbols and a midamble; correlating means for performing a given number N of block correlations of the received signal samples with a known midamble reference; forming means for forming a conjugate product of the N block correlations to form N−
1 conjugate products;summing means for forming a sum of the N−
1 conjugate products;accumulating means for accumulating a given number of sums of said N−
1 conjugate products obtained from said summing means;determining means for determining the magnitude of each accumulated summed value; searching means for searching for a given number of largest summed values; detection means for performing a threshold detection of the given number of largest summed values other than the largest summed value, employing a threshold which is a function of the largest summed value; combining means for combining the largest summed value with the given number of the largest summed values other than the largest summed value and which are greater than the threshold; computing means for computing the magnitude of the sum obtained by said combining means; normalizing means for normalizing the complex value obtained by said combining means employing the magnitude obtained by said computing means; and generating means for generating an argument of the normalized value obtained by said normalizing means for a frequency estimate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for obtaining a frequency estimate to adjust a voltage controlled oscillator, comprising the steps of:
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(a) receiving a signal containing data frames and a midamble; (b) converting the signal to baseband by the voltage controlled oscillator; (c) for each of N frames, iteratively performing the following steps; (1) block correlating the received signal with the midamble at X block correlators; (2) calculating the conjugate product of the output of each block correlator, to form X-1 conjugate products; (3) adding the X-1 conjugate products into a summed value; (4) storing the summed value; (d) searching for the largest summed value and Y of the next largest summed values; (e) calculating the magnitude of each of the summed values; (f) applying a threshold to the Y summed values, wherein the Y summed values will be used only if they exceed the threshold; (g) adding the largest summed value and the summed values from step (f) to obtain a second sum; (h) normalizing the second sum; and (i) outputting the second sum as the frequency estimate. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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Specification