Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B3/00—Line transmission systems
  • H04B3/02—Details
  • H04B3/04—Control of transmission; Equalising
  • H04B3/14—Control of transmission; Equalising characterised by the equalising network used
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03006—Arrangements for removing intersymbol interference
  • H04L25/03012—Arrangements for removing intersymbol interference operating in the time domain
  • H04L25/03019—Arrangements for removing intersymbol interference operating in the time domain adaptive, i.e. capable of adjustment during data reception
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03006—Arrangements for removing intersymbol interference
  • H04L2025/0335—Arrangements for removing intersymbol interference characterised by the type of transmission
  • H04L2025/03375—Passband transmission
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03006—Arrangements for removing intersymbol interference
  • H04L2025/03433—Arrangements for removing intersymbol interference characterised by equaliser structure
  • H04L2025/03439—Fixed structures
  • H04L2025/03445—Time domain
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03006—Arrangements for removing intersymbol interference
  • H04L2025/03592—Adaptation methods
  • H04L2025/03598—Algorithms
  • H04L2025/03605—Block algorithms
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03006—Arrangements for removing intersymbol interference
  • H04L2025/03592—Adaptation methods
  • H04L2025/03598—Algorithms
  • H04L2025/03611—Iterative algorithms
  • H04L2025/03617—Time recursive algorithms

Definitions

• This invention relates in general to communication systems, and more particularly, to a method and apparatus for providing adaptive equalization using non-linear digital filters.
• channel equalization One signal processing technique that is typically used in digital communication systems is channel equalization.
• the primary goal of equalization is to enhance the performance of a communication system in the presence of channel noise, channel distortion, multipath and multi-user interferences.
• Applications of channel equalization can be found in the consumer electronics, for example, in digital TV and personal communication systems, where various equalizers are used to increase the signal-to-noise ratio of an incoming signal and/or to reduce the bit error rate of the incoming signal.
• the present invention is a method and apparatus for equalizing a signal in a communication system.
• the signal is represented by samples at a time instant, and the samples are filtered using a sign permutation filter.
• An estimate of the signal is determined by a linear combination of the samples with corresponding weights.
• the error of the estimate is then computed.
• the weights are updated by an updating circuit to minimize the error.
• Figure 1 illustrates one embodiment of a communication system which implements the present invention.
• Figure 2 illustrates one embodiment of the adaptive equalizer of Figure 1 , provided in accordance with the principles of the invention.
• Figure 3 illustrates one embodiment of the sign permutation filter 210 of Figure 2 in accordance with the principles of the invention.
• Figure 4 illustrates one embodiment of the estimator 220 of Figure 2, provided in accordance with the principles of the invention.
• Figure 5 illustrates one embodiment of the update factor calculator 230 of Figure 2, provided in accordance with the principles of the invention.
• FIG. 6 illustrates one embodiment of the update circuit 240 of Figure 2, provided in accordance with the principles of the invention.
• Figure 7 illustrates an example of an original signal sequence that is being transmitted.
• Figure 8 illustrates the received signal corresponding to the transmitted signal of Figure 7.
• the present invention is a method and apparatus for equalizing a signal using a new, modular class of nonlinear digital filters denoted as sign permutation filters.
• the present invention provides a systematic way of utilizing sign permutation information embedded in the underlying signal to produce an output signal that provides robust frequency tracking. The resulting output signal is also resistant to interference.
• One example of the observation vector can be given as
• T denotes the matrix transpose.
• n [x 1t x 2l ... , x w ]T
• the sign indicator vector of the rth sample is defined as
• the sign permutation indicator vector of order J is defined as:
• b is an arbitrary vector
• ® represents the Modulo N addition, i.e., a ⁇ b (a + b) Mod N
• the vector p in equation (5) has a length of 2 J , and it effectively discriminates the relative sign permutation of the samples /. * BI . ... . X* B(J - I) among 2 J different sign permutations.
• the location of the 1 in p corresponds to one particular event of the joint sign permutation of the samples x Xm,---, ⁇ i®(j- ⁇
• the sign permutation filter presented here utilizes the sign permutation indicators p defined in equation (5). These form the basis for the ⁇ /2 J long sign permutation vector Xj of order J, defined as:
• ⁇ N is the weight vector described as:
• the output is obtained by a linear combination of the input samples, where the weight assigned to each sample x, is determined by the sign permutation indicator p .
• the sign permutation filter discriminates the joint sign permutation of the samples Xi/Xi ⁇ ⁇ ,-",X @ ( j_i ) by the location of 1 in p which can be noted from its definition given in equation (5).
• / the location of 1 in p , which is associated with the sign permutation of the samples x,,X /® ⁇ , ⁇ ••,* / ⁇ ( . / . ⁇ .) .
• the output of the sign permutation filter given in equation (13) can be expressed as:
• equation (13) the operation behind in equation (13) is to pick up and assign a weight to the sample x, from the weight vector w ; , depending on the sign permutation of the samples x h x m ,... ,x J . ⁇ .
• FIG. 1 A functional structure of the present invention is shown in Figure 1 and described in the following text, where the location parameters /,, / 2 and l w are used to determine which set of weights is applied to the input samples.
• w 2 x2 and w ⁇ 1 are selected and multiplied to the input samples X 2 and X N , respectively.
• the output of the sign permutation filter is a linear combination of the samples in X, which implies that the sign permutation filter is a linear filter with respect to the vector Xj.
• w 1 ( ) represents the /,th element of the sub-weight vector w at the mth iteration.
• the weight vector update in equation (22) only requires the update of N parameters whereas equation (21) requires the update of ⁇ /2 J parameters.
• the adaptation in equation (22) has the same degree of complexity of a linear filter in terms of number of updates at each iteration.
• FIG. 1 illustrates one embodiment of a communication system 100 which implements the present invention.
• the system 100 includes a receiver 110, a demodulator 120, a sampler and quantizer 130, and an adaptive equalizer 140.
• the receiver 110 receives an input signal transmitted from a transmitter (not shown).
• the input signal may originate from a number of sources, such as radio or television stations, for example.
• the input signal may be an audio signal or a video signal.
• the receiver 110 may include a receiver antenna and radio frequency (RF) circuits.
• the demodulator 120 demodulates the received signal and converts the signal into baseband signal.
• the demodulator 120 may also include an appropriate filter to eliminate unwanted frequency components and retain the baseband frequency components which include the signal of interest (SOI).
• SOI signal of interest
• the sampler and quantizer 130 samples the baseband signal according to a suitable sampling frequency and quantizes the sampled signal into digital data with appropriate word length.
• the adaptive equalizer 140 receives the digital data of the input baseband signal samples and performs an adaptive equalization using a sign permutation filter.
• the adaptive equalizer 140 essentially forms a group of non-linear digital filters based on the utilization of sign permutation of the input baseband signal.
• the adaptive equalizer 140 establishes and utilizes the sign permutation information, or, the frequency of zero-crossings embedded in the input baseband signal.
• the non-linearity characteristic of the adaptive equalizer 140 overcomes the drawbacks of the linear equalization for the non-linear characteristics of a communication channel.
• FIG. 2 illustrates one embodiment of the adaptive equalizer 140 of Figure 1 in accordance with the principles of the invention.
• the adaptive equalizer 140 includes a sign permutation filter 210, an estimator 220, an error calculator 230, and an update circuit 240.
• the sign permutation filter 210 performs filtering on the input samples X(n) using a sign permutation indicator.
• the estimator 220 estimates the input sample using a set of weights or coefficients 222 and a linear combination logic 224.
• the error calculator 230 computes the error of the estimated sample produced by the estimator 220.
• the update circuit 240 receives the input samples, the weights, and the error indicator to generate an update to the set of weights 222.
• FIG 3 illustrates one embodiment of the sign permutation filter 210 of Figure 2 in accordance with the principles of the invention.
• the sign permutation filter 210 includes N sign elements 3101 to 310/v and a sign permutation indicator 320.
• the sign elements 310 ⁇ to 310/ ⁇ / process the N input samples to extract the sign values.
• the sign bit can be used as the output of the sign element.
• the sign permutation indicator 320 generates the values h to l/v.
• the sign permutation indicator includes a sign permutation vectorizer to generate a vector having a vector length of 2 ⁇ where J is a positive integer.
• a relative sign permutator is used to determine the relative sign permutation of the samples among 2 ⁇ different sign permutations.
• Figure 4 illustrates one embodiment of the estimator 220 provided in accordance with the principles of the invention.
• the estimator 220 includes a weight storage 222 and a linear combination logic 224.
• the weight storage 222 includes a set of weights 410 ⁇ to 410A/.
• the weights 41 Oi to 410/v represent the weights or coefficients used in estimating the input sample.
• the weights 410 ⁇ to 410/ / are updated by the update circuit 240.
• the weights 410, to 410 W receive the location parameters I, to / N as generated by the sign permutation filter 210 (see Figure 2) to determine which set of weights are to be used.
• each of the weights 410 1 to 410 W is implemented as a storage element (e.g., random access memory) having two write ports, one for the //from the sign permutation filter 210 and one for the updated value uj from the update circuit 240.
• a storage element e.g., random access memory
• the linear combination logic circuit 224 includes multipliers 420 ⁇ to 420 w and a summer 430.
• the summer 430 adds all the products P, to produce the sum d(n).
• the multipliers 420, and 420 w and the summer 430 perform a linear combination on the input samples according to equation (14).
• the linear combination logic 224 produces the estimated sample d(n) .
• FIG. 5 is a diagram illustrating an error calculator 230 according to one embodiment of the invention.
• the error calculator 230 includes a subtractor 510, a multiplier 520, and an optional decision logic 530.
• the subtractor 510 subtracts the estimated sample d(n) from a sample d(n).
• the sample d(n) can be generated in a number of methods.
• a training sample is used.
• a decision process provided by the decision logic 530 may be used.
• the decision logic 530 is a quantizer which quantizes the input to a predetermined discrete signal levels.
• the subtractor 510 generates the error e(n) between the estimated sample d(n) and the expected sample d(n).
• the multiplier 520 multiples the error e(n) and a constant, referred to as a step size.
• the step size ⁇ controls the rate of convergence.
• this constant is 2 ⁇ where ⁇ ⁇ l/ ⁇ max where ⁇ max is the largest eigenvalue of the matrix RJ
• the multiplier 520 generates the update factor h(n).
• FIG. 6 illustrates one embodiment of the updating circuit 240 of Figure 2 provided in accordance with the principles of the invention.
• the update circuit 240 includes multipliers 610, to 610 W and adders 620., to 620 N .
• the update circuit 240 computes the new values of the weights stored in the weights 410 ⁇ to 410/v (see Figure 4) according to the equation (22) which may be expressed as:
• the multipliers 6101 to 61 ON multiply the input samples with the update factor /?(/?) generated by the updating circuit 240 to produce the respective products to r N (n).
• the result of the updating includes a set of updated values u to u N . These updated values are then transferred to the weight storage 222 to replace the old weight values.
• VSB Vestigial Sideband
• the adaptive sign permutation equalizer of the invention for the suppression of inter symbol interference and channel noise, where a finite length of training sequence is implemented with the VSB demodulation system.
• the interference is modeled by the impulse response given by 0.6+0.4 , and the channel noise was generated as a summation of an additive zero-mean Gaussian noise with variance of 1 and 15% impulses.
• the desired signal was given by a random 8-level VSB sequence. A data set of 10,000 samples was generated and the MSE between the original and the corrupted signals is 10.15.
• Figure 7 shows one part of the original sequence and the Figure 8 represents the received signal.
• the present invention thus provides a technique for performing adaptive equalization on a signal using sign permutation filtering.
• the technique efficiently processes signals in non-linear noisy channels, provides robust frequency tracking and is resistant to interference during communications.
• the present invention provides a technique for performing adaptive equalization on a signal using sign permutation filtering.
• the technique l o efficiently processes signals in non-linear noisy channels, provides robust frequency tracking and is resistant to interference during communications.

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• 1999
  • 1999-04-28 US US09/301,021 patent/US6704354B1/en not_active Expired - Fee Related
  • 1999-10-15 CN CNB998121142A patent/CN1193558C/zh not_active Expired - Fee Related
  • 1999-10-15 JP JP2000577809A patent/JP2003523644A/ja active Pending
  • 1999-10-15 MY MYPI99004460A patent/MY119871A/en unknown
  • 1999-10-15 WO PCT/KR1999/000622 patent/WO2000024170A1/en not_active Application Discontinuation
  • 1999-10-15 EP EP99947993A patent/EP1121789A1/en not_active Withdrawn
  • 1999-10-15 KR KR1020017003369A patent/KR100579889B1/ko not_active IP Right Cessation

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