KR100465030B1 - Channel Estimator - Google Patents

Abstract

Channel estimation is performed by breaking the intersymbol interference into components due to the component and the channel due to the transmitting device. Based on the correlation of the synchronization symbol and the local replica, multiple channel estimation is performed and the best channel is selected.

Description

Channel estimator

The present invention relates to an estimator circuit for a digital receiver operable in a digital communication system. In particular, the present invention relates to channel estimator circuitry and associated methods comprising transmitter and receiver filter circuits through which digital communication signals are transmitted and estimating channel characteristics of a transmission channel.

The channel estimator circuit and the method associated with the channel estimation improve the quality of the channel estimation. Since the quality of the channel estimation is improved, recovery of the content of the communication signal information is facilitated. The present circuit and method may be advantageously used in a satellite communication system in which intersymbol interference generated on a communication signal transmitted between a transmitter and a receiver is generated only by the filter circuits of the transmitter and the receiver. The circuits and methods are advantageously used in other communication systems, such as digital cellular communication systems.

The communication system consists of at least a transmitter and a receiver interconnected by a communication signal. The communication system may be operable to transmit a communication signal having information content generated on or applied to a transmitter on at least a communication channel. The receiver may be operable to receive the transmitted communication signal and to recreate the information content of the communication signal.

A wireless communication system is a communication system in which communication channels are formed in one or more frequency bands of the electromagnetic frequency spectrum. A transmitter operable in a wireless communication system generates a communication signal that is characteristic of enabling transmission on a communication channel, and a receiver operable in the wireless communication system may be operable to receive a communication signal transmitted on the communication channel.

Typically, a wireless receiver includes a tuning circuit that is tunable to the frequency of the communication channel over which the communication signal is transmitted, a down-conversion circuit that down-converts a received signal formed from the communication signal from the transmission frequency to a low frequency, or information of the communication signal. It includes baseband, signal, demodulation, and decoder circuitry from which content can be reproduced. Wireless communication systems are advantageous because they do not require a fixed or wired connection to form a communication channel extending between the transmitter and the receiver. Communication may be made between the remotely located transmitter and receiver even if no wiring or other fixed connection is established between the remotely located transmitter and receiver.

Technological advances in communication technology have enabled communication systems to utilize digital communication technology. Some existing communication systems have been transformed to make use of digital communication technology, and as a result of technological advances, other communication systems can be planned or implemented. Using digital communication technology allows information to be transmitted more effectively on a communication channel than when using conventional analog communication technology. In addition, the difficulty of transmitting distortion of the communication signal when the communication signal is transmitted by the transmitter to the receiver can be more easily overcome when digital communication technology is used.

A transmitter operable in such a communication system digitizes an information signal to form a digital signal. When digitized, the digital signal may be modulated by a digital modulation technique such as Gaussian Minimum Shift Keying (GMSK) modulation technique. Once modulated, the digitized signal is transmitted on a communication channel.

A receiver operable to receive a signal transmitted on a communication channel includes circuitry that demodulates the signal received at the receiver and preferably forms a digitized signal that can be converted to another form by a decoding process.

Distortion sometimes occurs in the signal transmitted by the transmitter. For example, distortion may be caused by the filter circuit of the transmitter or the filter circuit or communication channel of the receiver. The filter circuit of the transmitter, the communication channel and the filter circuit of the receiver are sometimes referred to hereinafter as "transmission channels".

One form of distortion that sometimes occurs on a signal is referred to as intersymbol interference. The causes of intersymbol interference and the resulting distortions are well known.

Receivers operable to receive signals in a digital communication system sometimes include circuitry called channel estimator circuitry that estimates the channel characteristics of a transmission channel, ie, channel impulse response. This channel estimator generates an estimate for the channel impulse response of the transmission channel. The channel impulse response estimated by the channel estimator is used by the receiver equalizer circuit to reduce intersymbol interference, thereby allowing the receiver to more accurately reproduce the information content of the communication signal actually formed at the transmitter.

US Pat. No. 5,432,821 discloses a data sequence estimation system based on a maximum likelihood sequence estimator (MLSE). A separate channel estimator is provided for each of the N possible survivors of the received signal. A metric calculation is performed to calculate all transition distances for each survivor for a particular transition time.

EP 0 604 209 discloses a maximum likelihood data detector comprising a channel impulse response estimator. The preamble sequence is autocorrelated, and the channel impulse response estimator may include circuitry to calculate a correlation between the received signal and the preamble sequence.

Since accurate estimation of the channel impulse response is critical to the receiver equalizer's ability to reduce intersymbol interference, the quality of the channel estimation is important and a high quality channel estimator is needed to accurately estimate the channel impulse response.

Therefore, a method of improving the quality of channel estimation helps to facilitate good reproduction of the signal transmitted to the receiver at the receiver.

In light of the above background information relating to digital communication systems and channel estimator circuits operable therein, a significant improvement of the present invention is developed.

1 shows a functional block diagram of a communication system in which embodiments of the present invention may be practiced.

Figure 2 shows a functional block diagram of a digital receiver including channel estimator circuitry in an embodiment of the invention.

FIG. 3 shows a functional block diagram of a digital receiver similar to that shown in FIG. 2 but including the channel estimator circuit of another embodiment of the invention.

4 is a flowchart describing a method of operation of an embodiment of the present invention.

The present invention provides a channel estimator circuit and associated method for obtaining a channel estimate with improved quality. In an embodiment for forming a part of a digital receiver operable in a digital communication system, the accuracy of channel characteristic estimation of a transmission channel transmitting a signal to the receiver is improved, thereby facilitating accurate reproduction of information content of a signal transmitted to the receiver .

The present circuit and method further include a satellite in which intersymbol interference generated in a communication signal transmitted between a transmitter and a receiver operable in a satellite communication system is mainly generated by a filter circuit of a transmitter transmitting a communication signal and a receiver receiving the communication signal. It is advantageously used to form part of the receiver circuitry used in the communication system, which is calculated by the channel estimator circuit when intersymbol interference is not generated on the transmitted signal during transmission to the variable communication channel but rather only at the transmitter and receiver. The parameters that must be reduced reduce the efficiency of the estimate. The uplink of a satellite communication system is an example of a communication system having a communication channel with little intersymbol interference during transmission. In such a system, the intersymbol interference generated on the communication signal is mainly generated by the filter circuit of the transmitter and the receiver. Since the characteristics of the filter circuit of the stationary device are determinable, i.e., inherently known quantities, the advantage of this deterministic amount is made to improve the quality of the channel estimation, which is caused by the intersymbol interference during transmission to the receiver. Continuous operation of the equalizer circuit for correcting distortion is facilitated.

The present circuits and methods are advantageously used in communication systems, such as cellular communication systems, in which intersymbol interference occurs on a communication channel while a communication signal is being transmitted between a transmitter and a receiver. By decomposing the distortion generated on the communication signal into the distortion component parts, the component parts of the distortion generated by the transmitter and receiver filters are again known in nature and thus can be determined. It is an advantage to improve the quality of the channel estimator circuit using the ability to determine intersymbol interference generated on the communication signal by the transmitter and receiver circuits. The present circuit and method is more advantageously used when the component part of the distortion generated by the transmitter filter is inherently known.

In one aspect of the invention, the channel estimator estimates a channel impulse response of a transmission channel through which a communication signal with a synchronization symbol is transmitted by a transmitter. The communication signal is transmitted to the receiver at a communication symbol rate. A symbol sampler is coupled to receive a signal representative of the communication signal received by the receiver. The symbol sampler samples some of the signals corresponding to the synchronization word, for example, the synchronization symbol value of the signal at a sampling rate greater than the communication signal sample rate. As such, each synchronization symbol is at least sampled at a first sampling point and a second sampling point. At least a first sampled signal and a second sampled signal are generated that are values representing synchronization symbols sampled at the first and second sampling points. The correlator circuit is coupled to receive the sampled signal generated by the symbol sampler. The correlator circuit correlates a portion of the sampled signal with the stored data word. The stored data word is a value representing a synchronization symbol that is transformed by the selected distortion level generated on the communication signal by the transmitter and receiver before and after the transmission of the communication signal. In addition, the correlator circuit selects which of the first sampled signal and the second sampled signal is most closely correlated with the stored data word to estimate the channel impulse response.

In another aspect of the invention, the channel estimator estimates a channel impulse response of a transmission channel through which a communication signal with a synchronization symbol is transmitted by a transmitter. The communication signal is transmitted to the receiver at a communication signal symbol rate. The symbol sampler is coupled to receive a signal representative of the communication signal received by the receiver. The symbol sampler samples a synchronization symbol value, such as a portion of the signal corresponding to the synchronization word of the signal, and generates a sampled signal that indicates the sampling. The correlator circuit is coupled to receive the sampled signal generated by the symbol sampler. The correlator circuit correlates a portion of the sampled signal with the stored data word. The stored data word is a value representing a synchronization symbol that is transformed by the selected distortion level generated on the communication signal by the transmitter and receiver before and after the transmission of the communication signal. The distortion level corresponds to different sampling points. The correlator circuit also selects which of the stored data words correlate most closely with the stored data words to estimate the channel impulse response.

In this and other aspects, channel estimators and associated methods for digital receivers are disclosed. The symbol sampler is coupled to receive a signal representative of the communication signal received by the receiver. The communication signal includes a synchronization symbol, and the symbol sampler samples at least the synchronization symbol value of the signal to generate a sampled signal representing it. A distance calculation circuit, such as a correlator circuit, is coupled to receive at least the first sampled signal and the second sampled signal generated by the symbol sampler. The distance calculation circuit calculates a distance between at least the first sampled signal and the portion of the second sampled signal using the stored data word. In response to this distance calculation performed by the distance calculation circuit, for example, the channel impulse response corresponding to the best distance is estimated.

A more complete understanding of the invention and its scope can be found in the accompanying drawings, which are briefly summarized below, in the following detailed description of the presently preferred embodiments, and in the appended claims.

First, referring to FIG. 1, the communication system shown at 10 enables communication of the communication signal transmitted by the transmitter 12 to the receiver 14 via the communication channel 16. The communication system 10 is a digital communication system in which the transmitter 12 forms a digital transmitter and the receiver 14 forms a digital receiver.

Transmitter 12 includes transmitter circuitry 18 operable to digitize information applied to transmitter circuitry 18 using line 22 here. Of course, in other embodiments, an already-digitized signal may instead be applied to circuit 18 on line 22. The transmitter circuit may be operable to modulate a digitized signal in accordance with a digital modulation technique.

The modulated signal is generated by the transmitter circuit on line 24 which is coupled to transmitter filter 26 which is part of a duplexer filter. Transmitter filter 26 filters the modulated signal applied to the transmitter filter to form a transmission signal on line 28. Although not shown separately, the transmission signal is formed by an antenna device that converts the electrical signal into electromagnetic form in a conventional manner.

The transmission signal is transmitted to the receiver 14 using the communication channel 16. The receiver 14 is tunable to the frequency included by the communication channel 16, so that once received by the receiver, it receives a transmission signal referred to as a reception signal. Again, although not shown separately, the receiver includes an antenna device to convert the received signal into electrical form.

Receiver 14 includes a receiver filter 34 that receives a received signal applied to receiver filter 34 via line 32. The receive filter generates a filtered receive signal, which is applied to receiver circuit 38 using line 36.

The receiver circuit 38 includes a demodulator circuit corresponding to the modulation circuit of the transmitter circuit 18. The demodulation circuit can be operative to demodulate the received signal filtered by the receiver filter 34. Receiver circuit 38 also includes an equalizer circuit and a decoder circuit to equalize and decode the received signal demodulated by the demodulator circuit of receiver circuit 38.

As mentioned above, intersymbol interference sometimes occurs in the signal generated by the transmitter circuit 18. In some communication systems, such as satellite communication systems, intersymbol interference does not originally occur while transmitting a transmission signal using the communication channel 16. Instead, intersymbol interference is mainly generated by transmitter filter 26 and receiver filter 34 during each filtering operation of transmitter filter 26 and receiver filter 34. This intersymbol interference distorts the information content of the signal applied to the receiver circuit 38 using the line 36.

Channel estimation circuitry is sometimes included as part of receiver circuitry 38 to estimate the channel impulse response. This estimation is provided to the equalizer circuit which affects the distortion that distorts the information content of the communication signal.

The channel estimator circuit of the embodiment of the present invention is configured to be configured to consist of the filters 26 and 34 and the communication channel 16, using the deterministic nature of the intersymbol interference generated by the transmitter and receiver filters 26 and 34. Simplify the calculations needed to estimate the channel impulse response of channel 40. This estimation allows the distortion generated on the communication signal to be reduced by the equalizer circuit.

In communication systems where intersymbol interference is mainly generated by transmitter and receiver filters, the accuracy is improved by characterizing the quality of the estimate made by the channel estimator, i.e., the transmitter and receiver filters. In a communication system in which intersymbol interference is additionally generated on a transmission signal when transmitted over channel 16, the channel estimator circuit of an embodiment of the present invention operates to estimate a channel impulse response, thereby channel-generating components of intersymbol interference. Decomposition into component parts and filter-derived component parts facilitates equalizer circuitry to reduce the intersymbol interference effects. Since the channel estimator can estimate the distortion caused by the intersymbol interference by using a low parameter calculation, it becomes easy to improve the reproduction of the transmitted signal.

2 illustrates a receiver 14 of an embodiment of the invention. The received signal 44 is detected by the antenna device 46 and converted into electrical form on line 48. Line 48 is coupled to a demodulator 52 that demodulates the signal applied over line 48. Demodulator 52 generates a demodulated signal that is applied to symbol sampler 56 using line 54.

The symbol sampler 56 uses the line 54 to sample the signal applied to this sample 56 at a rate that exceeds the symbol rate of the signal. Here, clock 58 is coupled to symbol sampler 56 via line 62, which, for example, picks up the rising or falling edge of the clock signal generated by clock 58. Each of them is used to sample a symbol of a signal applied to the sampler. In one embodiment, the symbol sampler 56 may be operable to oversample the applied signal at an eight-fold symbol rate.

The symbol sampler 56 generates lines of sampled signals that are applied to the correlators 66-1 through 66-n using lines 64-1 through 64-n. The sampled signal generated on the different lines of line 64 corresponds to the sampling position of each symbol for which the symbol is sampled. For example, the first sampled signal generated on line 64-1 is a value corresponding to the first sampling position of each symbol sampled by symbol sampler 56, and generated on line 64-n. The sampled signal is a sampled signal sampled at the nth symbol sampling position where each symbol is sampled.

Each correlator 66-1 through 66-n correlates a synchronization word that forms part of the sampled signal with a stored synchronization word stored in the memory elements 68-1 through 68-n. The stored synchronization word is a synchronization word value known to be transmitted by a transmitter, such as transmitter 12 shown in FIG. 1, but it does not account for distortion caused by transmitter and receiver filters such as filters 26 and 34 shown in FIG. It is transformed by the value indicated.

Correlators 66-1 through 66-n sample the values of the modified synchronization words stored in memory elements 68-1 through 68-n, correspondingly generated via lines 64-1 through 64-n, respectively. Correlate with the signal. The correlator generates signals applied to the comparator 74 using lines 72-1 through 72-n. In other embodiments, other distance calculation circuits are replaced with correlator circuits.

The comparator 74 compares the correlation level determined by the correlator and maximum correlation with the modified synchronization words applied to the correlators 66-1 through 66-n and stored in the memory elements 68-1 through 68-n. A sampled signal corresponding to the sampled signal representing the relationship is passed using line 76. Line 76 is coupled to equalizer 78 and decoder 80 that are operable in a conventional manner. Decoder 80 is coupled to a converter, here a speaker 82, in a conventional manner.

FIG. 2 further shows a counter 84 coupled to receive a clock signal generated by the clock 58 to reset the comparator 74 at the selected time.

Symbol sampler 56, correlator 68-n, and comparator 74 together form an equalizer circuit.

3 illustrates a receiver 14 of another embodiment of the present invention. Again, the received signal 44 is detected by the antenna device 46 and converted into electrical form on line 48. Line 48 is coupled to demodulator 52 which demodulates the applied signal and generates a demodulated signal using line 54.

Line 54 is coupled to a symbol sampler 56 that samples the applied signal. The symbol sampler 56 is coupled to the clock 58 via line 62 and, for example, in response to the rising or falling clock edge of the clock pulse generated by the clock 58. Sample the demodulated signal applied to. In this embodiment, symbol sampler 56 samples each symbol of the applied signal once. In other words, in contrast to the embodiment illustrated in FIG. 2, the symbol sampler 56 of the embodiment shown in FIG. 3 does not oversample the symbols of the demodulated signal.

The symbol sampler 56 generates a sampled signal via line 64 that is applied to the correlators 66-1 through 66-n. Correlators 66-1 through 66-n are coupled to memory elements, which are memory elements 88-1 through 88-n herein. Memory elements 88-1 through 88-n store different values in contrast to the same values stored in memory elements 68-1 through 68-n of the embodiment shown in FIG.

The correlator generates a signal applied to the comparator 74 via lines 72-1 through 72-n. Comparator 74 may be operable to compare the correlation level determined by the correlator and to pass a signal through line 76 corresponding to the correlation level that is best represented. Line 76 is coupled to decoder 78 and to transducer 82.

Clock 58 is coupled to comparator 74 to reset comparator 74 for a selected time.

The symbol sampler 56, correlators 66-1 through 66-n, comparators 74, and memory elements 68-1 through 68-n together form an equalizer circuit.

The channel impulse response of the signal received by the receiver 14 is represented by the following equation.

Where a is the fading level,

c _k is the value of the impulse response taps generated by the transmit and receive filters.

As discussed above, the distortion generated on the communication signal by the transmitter and receiver filters may be determined. Since the transmitter and receiver filters, such as filters 24 and 36 shown in FIG. 1, are inherently stationary devices with fixed characteristics, the c _k value is an amount known inherently for some sampling point k. It is an advantage that the value of c _k can be determined, whereby only the quantity a of the equation is required for estimation and this estimation can be done by using the available information about c _k .

The embodiment shown and described with respect to FIG. 2 utilizes an oversampling receiver that correlates with a known synchronization word where sampling at multiple sampling locations within a symbol period is passed through a good c _k 's set. In the embodiment of Fig. 2, the sampling position at which the optimum correlation is detected is selected and the corresponding value of a is determined from the correlation.

In the embodiment illustrated in FIG. 3, oversampling is not used. Instead, the received signal is sampled at one sample rate per symbol. In this embodiment, memory elements 88-1 through 88-n store a number of c _k models. The best estimate of the multiple models is selected in response to the correlation performed by the multiple correlator members. The best estimate is selected in response to the correlation performed there. Again, in other embodiments, other distance calculations may be substituted for the correlator's correlation operation.

In other embodiments, conventional correlation operations may be performed using estimates combining a and c _k . The values of a and sampling are then selected to fit the models of a, c _k for different c _k values.

When intersymbol interference occurs on a communication channel, such as communication channel 16, decomposition of the actual transmission channel comprising filters 26 and 34 into communication channel 16 is performed. The channel impulse response of the signal received by the receiver 14 is instead represented by the following synthesis equation.

Wherein the term is as described above. Similar to this decomposition can be performed when the characteristics of the transmitter filter are determinable.

The calculation of the channel impulse response is simplified as the value of c is determinable and does not need to be calculated. For example, contributions due to transmit and receive filters 26 and 34 result in taps c ₀ , c ₁ , and c ₂ , with contributions due to fading channel (a ₀ , a ₁ ). When displayed, the combination is (c ₀ a ₀ , c ₁ a ₀ + c ₀ a ₁ , c ₂ a ₀ + c ₁ a ₁ , c ₂ a because the channel has only two independent taps after generating two taps. ₁ ) becomes. The estimator circuit is only needed to estimate a ₀ and a ₁ , thereby reducing the complexity of the calculations that need to be performed by the channel estimator circuit.

4 illustrates a method 110 describing an embodiment of the present invention. The method 110 illustrates a method of operating the equalizer of the embodiment shown in FIG. The method is to estimate the channel impulse response of the transmission channel through which the communication signal with the synchronization symbol is transmitted by the transmitter. The communication signal is transmitted to the receiver at a communication signal symbol rate. Initially, as shown by block 112, at least the value of the synchronization symbol is sampled. The value is sampled at a sampling rate greater than the communication signal symbol rate, thereby sampling each of the synchronization symbols at at least the first sampling point and the second sampling point.

Thereafter, at least a first sampled signal and a second sampled signal are generated, as shown by block 114. The sampled signal is a value representing a synchronization symbol sampled at at least first and second sampling points.

Thereafter, as shown by block 116, a portion of the sampled signal is correlated with the stored data word. The stored data word represents a synchronization symbol, which is transformed by the selected distortion level generated on the communication signal by the transmitter and receiver.

Then, as shown by block 118, the sampled signal that is most closely correlated with the stored data word is selected to estimate the channel impulse response.

Channel estimator circuitry and its associated method for estimating a channel improves the quality of the channel estimation. Due to this improvement, the information content of the signal transmitted to the receiver including the circuit is reproduced more accurately. The circuits and methods of the present invention are advantageously used in satellite communication systems in which a minimum amount of intersymbol interference occurs on a communication channel over which a communication signal is transmitted. The present invention is also advantageously used in other forms of digital communication systems such as digital cellular communication systems.

The operation of the present invention makes tracking of dynamic channels with varying characteristics easier because they are calculated using fewer parameters. Although larger data sequences are transmitted on the dynamic channel, good equalizer operation is allowed even when equalized due to the improved tracking capabilities provided by the present invention.

The foregoing description is a preferred example of practicing the invention, and the scope of the invention is not necessarily limited by the description. The scope of the invention is defined by the following claims.

Claims (18)

A channel estimator for estimating a channel impulse response of a transmission channel in which a communication signal having a synchronization symbol is transmitted to a receiver at a communication signal symbol rate, A portion of a signal that is coupled to receive a symbol sampler, i.e., a signal indicative of a communication signal received by the receiver, so as to at least correspond to a synchronization symbol of the signal to sample each synchronization symbol at at least a first sampling point and a second sampling point Is a symbol sampler that samples a value of at a sample rate greater than the communication signal sample rate and generates at least a first sampled signal and a second sampled signal of a value representing a synchronization symbol sampled at each of the first and second sampling points. And, A distance calculation circuit, i.e., coupled to receive at least a first sampled signal and a second sampled signal generated by the symbol sampler, respectively, on a communication signal by the transmitter and receiver before and after transmission of the communication signal, respectively. Calculate a distance between the stored data word and at least a portion of the first sampled signal and the second sampled signal, the stored data word being a value representing a synchronization symbol transformed by the selected distortion level generated, and the first sampled to estimate the channel impulse response. And a distance calculating circuit for selecting which of the signal and the second sampled signal most closely corresponds to the stored data word. The method of claim 1, The distance calculation circuitry correlates a portion of the sampled signal with the stored data word and selects at least which of the first sampled signal and the second sampled signal correlate most closely with the stored data word. And a circuit estimator for estimating a channel impulse response of a transmission channel. The method of claim 2, And a sampling rate at which the symbol sampler samples at least the value of the synchronization symbol is at least twice the sampling rate of the communication signal symbol rate. The method of claim 2, And the symbol sampler generates a number of sampled signals corresponding to the number of sampling points at which each synchronization symbol is sampled. The method of claim 4, wherein The correlator circuit correlating a portion of each sampled signal with the stored data word and selecting a sampled signal that is most closely correlated with the stored data word; a channel estimator for estimating a channel impulse response of a transmission channel . The method of claim 2, Wherein said stored data word represents a synchronization symbol that is transformed by a selected distortion level generated on said communication signal by said transmission channel. The method of claim 2, And a memory circuit in which the correlator circuit stores a stored data word that correlates a portion of the sampled signal. The method of claim 2, And the symbol sampler comprises an analog-to-digital converter. A channel estimator for estimating a channel impulse response of a transmission channel in which a communication signal having a synchronization symbol is transmitted to a receiver at a communication signal symbol rate, A symbol sampler, i.e., coupled to receive a signal indicative of a communication signal received by the receiver, sampling at least each synchronization symbol value of the signal at a rate corresponding at least to the communication signal symbol rate, the sampling representing the sampled value A symbol sampler for generating a generated signal, Distance calculation circuitry, ie, coupled to receive a sampled signal generated by the symbol sampler, and modified by a selected distortion level generated on the communication signal by the transmitter and receiver before and after transmission of the communication signal, respectively. Calculating a distance between the stored data word and the sampled signal, the value representing a synchronization symbol, and selecting which of the stored data words corresponds most closely to the sampled signal in response to the distance to estimate a channel impulse response. And a channel estimator for estimating a channel impulse response of the transmission channel. The method of claim 9, The distance calculating circuit comprises a correlator circuit for correlating a portion of the sampled signal with the stored data word and selecting a stored data word that exhibits the best level of correlation among the stored data words. A channel estimator for estimating the channel impulse response of the. The method of claim 9, Wherein the stored data words comprise a plurality of stored data words having different values, wherein the channel impulse response of the transmission channel is estimated. The method of claim 9, And a memory circuit in which the correlator circuit stores a stored data word that correlates a portion of the sampled signal. The method of claim 9, And the symbol sampler comprises an analog-to-digital converter. A method for estimating a channel impulse response of a transmission channel in which a communication signal having a synchronization symbol is transmitted to a receiver at a communication signal symbol rate, the method comprising: Sampling at least a synchronization symbol value of the signal at a sampling rate greater than a communication signal symbol rate to sample each synchronization symbol at at least a first sampling point and a second sampling point; Generating at least a first sampled signal and a second sampled signal that are values representing synchronization symbols sampled at each of at least first and second sampling points during the sampling step; Between the stored data word and the first sampled signal and the second sampled signal, each of which is a value representing a synchronization symbol value transformed by a selected distortion level generated on the communication signal by the transmitter and receiver before and after the transmission of the communication signal, respectively. Calculating distances, Selecting which of at least a first sampled signal and a second sampled signal most closely correspond to the sampled signal to estimate a channel impulse response of the channel impulse response of the transmission channel. Estimation method. The method of claim 14, Calculating the distance comprises correlating a portion of the sampled signal with the stored data word. A method for estimating a channel impulse response of a transmission channel in which a communication signal having a synchronization symbol is transmitted to a receiver at a communication signal symbol rate, the method comprising: Sampling at least each synchronization symbol value of a signal representing the communication signal at a rate corresponding at least to a communication signal symbol rate, Generating a sampled signal indicative of the sampled value during the sampling step; Calculating a distance between the stored data word and a portion of the sampled signal, each value representing a synchronization symbol transformed by a selected distortion level generated on the communication signal by the transmitter and the receiver before and after the transmission of the communication signal; Selecting which of the stored data words most closely corresponds to the sampled signal to estimate a channel impulse response. The method of claim 16, And calculating the distance comprises correlating a portion of the sampled signal with the stored word. The method of claim 17, And wherein said selecting comprises selecting which of said stored data words is most closely correlated.