Pulse or digital communications – Equalizers – Automatic
Reexamination Certificate
1999-04-12
2002-06-11
Pham, Chi (Department: 2631)
Pulse or digital communications
Equalizers
Automatic
C708S323000
Reexamination Certificate
active
06404810
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to the field of digital signal processing in digital communication. More particularly, the invention relates to a data transceiver and an initial activation of adaptive equalization method used in a data transceiver.
2. Description of Related Art
An adaptive equalization method is often-used in a data transceiver to compensate for the amplitude and phase distortions introduced by a transmission channel. Generally, an equalizer is a discrete time filter for compensating amplitude and phase distortions. A channel is a time-varying channel with a typically long time constant compared to the symbol period. The channel may be viewed as quasi-static, with a relatively constant impulse response. Equalizers are also used to recover timing so that the local receiver clock and the remote transmitter clock are synchronous. Usually, the local receiver clock and the remote transmitter clock are asynchronous. If the timing is not recovered, the transmitted signal can be lost or additional incorrect signals can be added. If the receiver clock is slower than the transmitter clock, after a long enough period of time, one sample of the received signal will be lost. On the other hand, if the local receiver clock is faster than the remote transmitter clock, after a long enough period of time, an extra sample of the receiver signal will be obtained. Accordingly, equalizers have been implemented to recover received data and timing in many data transceivers. Often used equalizers include linear equalizers (LE), zero-forcing (ZF) equalizers, mean-square error (MSE) equalizers, etc.
The equalizers also have to be adaptive to compensate continuously for non-idealities of the channel. A data transceiver often uses an adaptive algorithm to correct errors such as inter symbol interference (ISI), noise, etc., that occur in subsequent information bits. Generally, minimizing the inter symbol interference (ISI) enhances noise. Accordingly, different adaptive equalizations are designed to meet different criteria for the noise and ISI.
When using blind equalization in a data transceiver, a key system requirement is to initially recover received timing in the data transceiver. When using a minimum mean square error (MSE) update method, adaptive algorithms can be optimized to provide an optimal tradeoff between noise and ISI. However, the minimum MSE adaptation is slower than a zero-forcing (ZF) adaptation which takes into account only ISI.
Therefore, there is a need for an improved adaptive equalization method in a data transceiver which provides a mechanism to quickly and reliably recover initial timing, while still providing optimal performance in the presence of noise.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention provides a mechanism to quickly and reliably recover initial timing, while still providing optimal performance in the presence of noise.
The present invention discloses an activation method for adaptive equalization in a data transceiver. In the initial stages of activation, the adaptive equalization uses a zero forcing (ZF) adaptation. This allows the data transceiver to converge reliably and quickly. Thus, the system can achieve good signal-noise-ratio (SNR) and lock the received timing. After initialization, the adaptive equalization is changed to a minimum mean square error (MSE) adaptation, such that better performance of recovering signals can be achieved in the presence of noise.
In one embodiment of the present invention, an activation method for adaptive equalization in a data transceiver including a plurality of adaptive filters, includes adapting an adaptive filter with a zero forcing (ZF) adaptation to obtain initial convergence during activation of the data transceiver; and adapting the adaptive filter with a minimum mean square error (MSE) adaptation to optimize performance of recovering signals in the presence of noise. One or more of the adaptive filters in the data transceiver may utilize this activation method.
In another embodiment of the present invention, an activation method for adaptive equalization in a data transceiver including a plurality of adaptive filters, includes adapting an adaptive filter with a first type of adaptation to obtain initial convergence during activation of the data transceiver; and adapting the adaptive filter with a second type of adaptation to optimize performance of recovering signals in the presence of noise. One or more of the adaptive filters in the data transceiver may utilize this activation method.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.
REFERENCES:
patent: 4502077 (1985-02-01), Morotomi et al.
patent: 4757319 (1988-07-01), Lankl
patent: 5513209 (1996-04-01), Holm
patent: 5914983 (1999-06-01), Bowser et al.
Girardeau, Jr. James Ward
Ling Stanley K.
Corrielus Jean
Level One Communications Inc.
Merchant & Gould P,C,
Pham Chi
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