Pulse or digital communications – Equalizers – Automatic
Reexamination Certificate
2000-10-20
2004-12-21
Chin, Stephen (Department: 2634)
Pulse or digital communications
Equalizers
Automatic
C375S229000
Reexamination Certificate
active
06834079
ABSTRACT:
FIELD OF THE INVENTION
This present invention relates to equalization of telecommunication devices. More specifically, it relates to a system and method for providing channel equalization between communicating modems.
BACKGROUND OF THE INVENTION
Today, modern communication systems can provide higher speed data communications over the same copper wires that traditionally only carried plain old telephone service (“POTS”). Many of these high-speed communication systems utilize a modulation technique known as discrete multitone (“DMT”) modulation. A popular communication system that uses DMT is known as Digital Subscriber Line (“DSL”). DSL communication systems can provide homes and small businesses high-speed communication access to the Internet and other networks using ordinary copper telephone lines. A central office (“CO”) is typically equipped with a CO DSL modem that provides broadband DSL services such as high-speed Internet access, audio, and video services to a subscriber. To receive DSL services from the CO, the customer premises typically includes a DSL modem or more generally a remote transceiver (“RT”) to terminate a communication link with a CO DSL modem providing high-speed communication services.
The DSL modem pair (i.e., the RT and CO DSL modems) transfers data to and from the CO preferably using communication standards set out by the American National Standards Institute (“ANSI”) such as Standard T1.413, the contents of which are incorporated by reference. ANSI T1.413 specifies a standard for ADSL that is widely followed in the telecommunications industry. The RT DSL modem in connection with a DSL modem at the CO may receive data at rates up to 6.144 Mbps for asymmetric DSL (“ADSL”) and even higher data rates for other DSL variants to provide continuous transmission of high bandwidth video and audio data. Because of a DSL communication system's high data rate capability and its ability to operate over ordinary copper telephone lines, DSL installations are expected to greatly increase in homes and small businesses.
A drawback of DSL, however, is that the ordinary copper telephone line or the communication channel exhibits an undesirable characteristic known as frequency dependent propagation. Frequency dependent propagation leads to a dispersive behavior of the channel, resulting in a wider received pulse at the remote transceiver and causing a time sample to spread into the neighboring time slots. Thus, a time sample may not contain only the contribution of the corresponding sent sample, but also portions of neighboring samples, referred to as intersymbol interference (“ISI”).
To reduce the effects of ISI, an equalizer is often utilized at the receiver. However, an equalizer typically estimates the channel response in order to reduce the channel response effects on the sent signal. To estimate the channel response, the equalizer performs many calculations, sometimes in the millions of calculations, and can often become memory storage intensive, which can prohibit their use in embedded systems. Furthermore, noise or interference that may distort the signals passing through the communication channel can have undesirable effects on the estimation of the channel response.
The embodiments described herein provide for a more time and storage efficient equalization of the communication channel.
SUMMARY OF THE INVENTION
The system and method for channel equalization in discrete multitone communication systems is provided. The exemplary embodiments disclose a system and method capable of reducing the memory storage needed for channel equalizer training. Additionally, the equalization signal is processed to reduce the effect of noise on the equalization training and to accommodate over-sampled receivers.
In accordance with one aspect of the present embodiments, at least one set of equalizer filter coefficients are determined by forming a matrix of data from received and transmitted signals. The matrix is formed into an upper triangular system by performing orthogonal transformations on the matrix. The coefficients are then determined by performing a back-substitution on the upper triangular system.
In accordance with another aspect of the present embodiments, the equalizer training signal is processed to further reduce the effect of noise on the calculation of the filter coefficients. Additionally, the signal can be processed to accommodate over-sampled receivers to improve sub-sample symbol boundary estimation.
The present embodiments provide for an efficient and effective time domain equalization system using the least squares method for discrete multitone communication systems. The embodiments include processing the received signal and the reference signal in order to improve the symbol boundary estimate and reduce the effects of noise on the filters coefficient solution. Furthermore, the embodiments provide a method of reducing the condition of the deterministic correlation matrix used in the least squares method. Included in the embodiments, is a method for realizing a storage-efficient solution of the least squares calculation. The present embodiments can be applied to an over-sampled DMT receiver.
The foregoing and other objects, features and advantages of the system and method for will be apparent from the following more particular description of preferred embodiments of the system and the method as illustrated in the accompanying drawings.
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patent: 2003/0002574 (2003-01-01), Yang et al.
Complex Scaled Tangent Rotations(CSTAR) for Fast Space-time Adaptive Equalization for Wireless TDMA. Massimiliano Martone; IEEE Transactions on Communications, vol. 46, No. 12, Dec. 1998, pp. 1587-1590.*
Laakso, et al, “Splitting the Unit Delay”, IEEE Signal Processing Magazine, pp 30-60, Jan. 1996.
R.K. Bock, “Givens Rotation,” website printout (2pages), Sep. 15, 2000.
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Strait Jeffrey C.
Sy Eugene T.
3Com Corporation
Chin Stephen
McDonnell Boehnen & Hulbert & Berghoff LLP
Vartanian Harry
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