Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-10-16
2001-10-30
Vincent, David R. (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S516000
Reexamination Certificate
active
06310896
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
TECHNICAL FIELD
This invention relates to the field of data communications, and, more particularly, to the field of data signal correlation in the time domain.
BACKGROUND INFORMATION
In data communications, a data signal transmitted from a first modem to a second modem across a channel is often distorted due to the channel. In particular, the channel may cause intersymbol interference and other distortion. To remedy the distortion to a data signal due to the channel, it is often the case that an equalizer is employed in the receive circuitry of modems. In particular an equalizer may operate in the time domain or in the frequency domain.
Many equalizers that operate in the time domain employ digital signal processing techniques. Such time domain equalizers (TEQ's) may feature a digital filter with several coefficients which must be tuned to cancel the effects of a specific channel employed for data communication. The process of tuning these coefficients generally occurs at the startup of data communication.
To explain further, when TEQ training takes place, often times the transmitting modem sends a continuous data signal which comprises a predetermined data sequence that is repeated over and over. The same predetermined sequence is generated in the receiving modem, the sequence being repeated over and over in similar fashion to the signal received from the transmitting modem. The time domain equalizer generally employs various techniques to tune the coefficients of the digital filter applied to the received signal, thereby canceling the channel distortion so that the received signal matches the signal generated in the receiving modem.
In order to tune the coefficients, it is often the case that the received data signal and the generated data signal are first synchronized in time. When the predetermined sequence which is repeated in both the received and generated data signals is particularly long in nature, such as, for example, in discrete multitone (DMT) data communication, significant processing and memory resources are consumed to accomplish the required synchronization. Consequently, there is a need for a system and method of synchronizing a predetermined repeated data sequence contained in a received data signal and the same repeated data sequence contained in a generated data signal in a receiving modem where the predetermined data sequence is particularly long.
BRIEF SUMMARY OF THE INVENTION
The present invention involves a system for synchronizing a first data signal at a first sample rate with a second data signal at a second sample rate in a data communications device where the information relayed by both the first and second data signals comprises the same repeated predetermined data sequence. The system preferably includes a digital signal processor operating pursuant to logic stored on a memory. The logic includes synchronization logic which reduces the first sample rate to a predetermined correlation sample rate using a first decimator, resulting in a first reduced data signal. The synchronization logic also reduces the second sample rate to the same predetermined correlation sample rate using a second decimator, resulting in a second reduced data signal. Finally, the synchronization logic determines a sequence offset between the repeated sequence contained in the first reduced data signal and the same repeated sequence contained in the second reduced data signal using a correlator. This sequence offset is used to determine a time delay that is applied to the second data signal, thereby synchronizing the repeated sequences transmitted in the first and second data signals. Due to the reduced sample rates of the first and second reduced data signals, the sequence offset may be an approximation. The actual accuracy depends upon the predetermined correlation sample rate chosen for a particular application. The present invention provides a significant advantage in that the correlation functions require less memory and calculation time due to the reduction of the sample rates of the first and second data signals to the predetermined correlation sample rate. However, there exists a tradeoff between accuracy on one hand, and the reduction of memory and calculation time on the other. Generally, the inaccuracies generated can be corrected by the tuned time domain equalizer.
The present invention also comprises a method for synchronizing a predetermined data sequence that is repeated over and over in a first data signal at a first sample rate with the same repeated data sequence in a second data signal at a second sample rate in a data communications device. The method begins with the step of reducing the first sample rate of the first data signal to a predetermined correlation sample rate, thereby creating a first reduced data signal. Next, the second sample rate of the second data signal is reduced to the predetermined correlation sample rate, thereby creating a second reduced data signal. Finally, a sequence offset is determined between the repeated data sequences of the first reduced data signal and the second reduced data signal.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein within the scope of the present invention, as defined by the claims.
REFERENCES:
patent: 4652069 (1987-03-01), Smith
patent: 5883929 (1999-03-01), Wang et al.
patent: 6154487 (2000-11-01), Murai et al.
patent: 6212223 (2001-04-01), Okamoto
Langberg Ehud
Liu Wei-min
Liu Xiao
Scholtz William
Globespan, Inc.
Thomas Kayden Horstemeyer & Risley
Vincent David R.
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