Pulse or digital communications – Receivers – Interference or noise reduction
Reexamination Certificate
1999-04-23
2003-04-01
Chin, Stephen (Department: 2634)
Pulse or digital communications
Receivers
Interference or noise reduction
C375S285000, C375S316000
Reexamination Certificate
active
06542560
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of wireless communication, and more particularly, a method of channel estimation and compensation based thereon.
2. Description of Related Art
In recent decades, many new technologies, such as multi-carrier transmission and smart antenna algorithms, have been proposed to increase the capacity of multi-user wireless communication systems. However, the performance improvement promised by such new technologies is usually limited by the accuracy of channel estimation. Channel estimation is the estimate of the distortion between the transmitter and the receiver of a signal introduced by the physical channel or medium through which the signal was transmitted. Using an estimate of this distortion (i.e., channel estimate), the receiver can remove some of this distortion and improve the accuracy of the received signal. Even a small improvement in channel estimation may introduce significant benefit to, for example, multi-user technologies.
Conventional channel estimation techniques usually assume the physical channel, and therefor the distortion therein, is time-invariant over a finite length sampling window. Channel estimates are assigned by taking the mean value of some observed parameter over the sampling window, and then applying the mean value to eliminate distortion in the received signal. Examples of such conventional techniques include recursive least squares (RLS), least mean squares (LMS), and moving average filtering.
These techniques, however, fail to adapt and produce desirable results in a fast varying environment such as a wireless mobile communication system including moving mobile stations; wherein the physical channel can vary rapidly. Moreover, in code-division multiple access (CDMA) systems, where a low signal-to-noise ratio (SNR) is desired to maximize capacity, high noise further complicates the channel estimation problem because the channel estimation technique must satisfy the conflicting requirements of small window size for time-invariance and long window size for noise immunity.
SUMMARY OF THE INVENTION
The method of channel estimation according to the present invention assumes that the channel changes linearly with time. By performing linear regression on the samples within a sampling window of a first signal component in a received signal, a channel estimate, which varies with a rapidly varying environment, is obtained.
The computational complexity of the linear regression is simplified by determining the linear regression coefficients for blocks of samples. On a block-by-block basis, new samples of a received signal are obtained, and the linear regression coefficients therefor are derived. Using the determined linear regression coefficients for the new block and the stored linear regression coefficients for previous blocks, linear regression coefficients for the entire window are determined.
By applying the complex conjugate of the channel estimate to a second signal component in the received signal, the channel distortion in the second signal component can be significantly reduced.
Furthermore, by estimating the distortion caused by frequency offset (frequency mismatch between the modulator of the transmitter and the demodulator of the receiver) and compensating for the frequency offset prior to performing channel estimation, a much larger sampling window is used to perform the channel estimation. This translates into greater noise immunity.
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Buehrer R. Michael
Liu Shang-Chieh
Nicoloso Steven P.
Uptegrove Dirck
Chin Stephen
Fan Chieh M.
Harness & Dickey & Pierce P.L.C.
Lucent Technologies - Inc.
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