MXPA99003975A - Device and method for eliminating channel interference signs from contiguo in modulation / demodulation receivers having a reference sign - Google Patents

Abstract

A modulation / demodulation receiver having a reference signal in a digital communication system. A method for processing a signal and eliminating contiguous channel interference in the receiver includes the steps of processing an input signal so that it is a predetermined multilevel. , feeding the processed signal to an adaptive equalizer, determining the multilevel type from the signal applied to the adaptive equalizer and selecting an operating mode of at least two multilevel operation modes, for the adaptive equalizer and the blocks that are back of the adaptive equalizer, and causing the adaptive equalizer to adaptively adapt the signal in the predetermined multilevel, in the selected operating mode and eliminating contiguous channel interference

Description

DEVICE AND METHOD FOR ELIMINATING CHANNEL INTERFERENCE SIGNS FROM CONTIGUO IN MODULATION / DEMODULATION RECEIVERS THAT HAVE A REFERENCE SIGNAL Background of the Invention 1. Field of the Invention The present invention relates to a digital communication system and in particular, to a modulation / demodulation receiver system having a reference signal. 2. Detailed Art Description There is a digital communication system in which a transmitter transmits a reference signal together with an original signal to a receiver, in such a way that the receiver can eliminate or minimize the problems caused by the interference, multiple paths and the like, in a transmission channel. The objective of transmitting a reference signal, for example, a REF. 30034 pseudoruide sequence (PN), is that the receiver sufficiently reflects the characteristics of the channel. A method for contiguous channel interference processing has been discovered in the Guide for the Use of the Digital Television Standard, in High Definition Television Broadcasting "(Guide to the Use of the Digi tal Tel evi sión Standard for HDTV Transmi ssi on "), Advanced Television System Committee of the United States of America. { Uni ted Sta tes Advanced Tel evi si on System Commi t tee), April 12, 1995, pages 104-107. In the above method, a high definition television (HDTV) signal that goes inside a residual sideband (VSB), is described by way of example. A receiver system suggested in the method is similar to that shown in Figure 1. Figure 1 is a partial block diagram of a conventional receiver (see Figure 1 in U.S. Patent Number 5, 594, 496). To simultaneously broadcast a VSB signal and a broadcast system signal currently used on the same channels, call the Advanced Television System Committee (NTSC), a VSB transmission system implements an operation related to an NTSC Signal Suppression Filter ( NRF). Most of the NTSC signal suppression filter process is the part of using a comb filter 16, to eliminate the NTSC signal carriers in which the energy is concentrated. More specifically, if a high-definition television signal that goes inside a band GA-VSB (Residual Lateral Band of the Great Alliance) and an NTSC signal are present both in the same channel, a relation between them is made, as it is shown in Figures 3A and 3B. Here, Figures 3A and 3B are identical to Figures 4A and 4D of U.S. Patent Number 5,546,132, respectively. Figures 3A and 3B illustrate, respectively, the radiofrequency spectrum of a high definition television signal and an NTSC signal, and Figures 3C and 3D illustrate respectively, the frequency characteristics of a NTSC signal suppression filter and a filter. of NTSC signal extraction. Common methods to eliminate contiguous channel interference include eliminating carriers (eg, image carrier, color carrier, audio carrier) where the energy is concentrated. The band GA-VSB uses comb filters (ie, NTSC signal suppression filters) 14 and 15, having the delays 141 and 151 to delay 12 symbols, and the subtractors 142 and 152, to obtain the difference between a symbol without delay and a delayed symbol, in order to eliminate the interference of adjacent channel. Figure 2 is identical to Figure 3 of U.S. Patent No. 5,546,132 and Figure 10.8 of the aforementioned volume, page 106. Since the NTSC signal carriers are present around the null point, as shown in Figure 3C, yes a received signal passes through the comb filters 14 and 15 of Figure 2, thus eliminating much of the NTSC signal interference. The NTSC signal interference can also be eliminated, using a staging filter, in which the NTSC signal carriers are present around the null point. As described above, conventional receivers include a switching portion (switch 19 of Figure 1 and multiplexer 23 of Figure 2), to select a signal processed by a NTSC signal suppression filter in 15 levels and a signal not processed in 8-level NTSC signal suppression filter, based on the selection of a JSFTSC signal suppression filter block, to eliminate contiguous channel interference and adjusting the blocks to handle the signal suppression filter block NTSC. Accordingly, the input of a channel or adaptive equalizer, to the rear of a NTSC signal suppression filter block, depends on whether it is operated or not, the NTSC signal suppression filter. This means that the equalizer is configured to accommodate both 8-level and 15-level signals. Since the 15-level signal has a number of levels greater than the 8-level signal, due to comb filtering, the equalizer must have an input limit that is in a range of up to 15 levels. Also, even when the equalizer input is in the required range, by reducing the gain of a 15-level signal, certain restrictions on the resolution may be imposed on the input terminal of the equalizer or on the contrary, they may generate bias errors due to rounding.

Brief Compendium of the Invention An object of the present invention is to provide a device and a method for processing a multi-level input of a predetermined type in one or more multilevel operation modes in a modulation / demodulation receiver, within a digital communication system. Another object of the present invention is to provide a receiver having an equalizer, capable of operating in both an 8-level mode and a 15-level mode, to enter 8 levels in a VSB band. A further object of the present invention is to provide a device and a method for eliminating or reducing multiple paths in a modulation / demodulation transmission channel, with a reference signal. Another additional objective of the present invention is to provide a device and method for eliminating contiguous channel interference in a modulation / demodulation channel with a reference signal. Yet, another objective of the present invention is to provide a device and method for implementing NTSC signal suppression filtering, equalization and filtering operations, without having to require any additional components. To achieve the aforementioned objectives, a method is provided for processing the signal and eliminating the adjacent channel interference signal in a modulation / demodulation receiver having a reference signal, in a digital communication system. In the method, an input signal is processed to be in a predetermined multilevel and to be fed to an adaptive equalizer, the multilevel type is determined from the signal applied to the adaptive equalizer, an operation mode is selected from at least two Multilevel operation modes, for the adaptive equalizer and the blocks that are behind the adaptive equalizer and the adaptive equalizer adaptively equalize to the signal that is at a predetermined multilevel in the selected operating mode and eliminates contiguous channel interference.

Brief Description of the Drawings The objects and advantages described above of the present invention will be more apparent in describing the preferred embodiments thereof, upon reference to the accompanying drawings, in which: Figure 1 is a partial block diagram of a conventional receiver; Figure 2 is a block diagram of a general NTSC signal interference detector; Figure 3A is a graph showing the radiofrequency spectrum of a high definition television signal; Figure 3B is a graph showing the radiofrequency spectrum of an NTSC signal; Figure 3C is a graph showing the frequency characteristic of an NTSC signal extraction filter; Figure 3D is a graph showing the frequency characteristic of a NTSC signal subtraction filter; Figure 4 is a block diagram of a receiver in accordance with an embodiment of the present invention; Figure 5 is a block diagram of a mode of an adaptive equalizer, in accordance with the invention; Figure 6 is a block diagram of a mode of an adaptive equalizer, in accordance with the invention; and Figure 7 is a block diagram of a mode of an adaptive equalizer, in accordance with the invention.

Detailed Description of the Preferred Modalities The embodiments of the present invention will be described in detail, with reference to the accompanying drawings. It should be noted that similar reference numerals denote the same components of the drawings and any detailed description of a known function or structure of the present invention will be omitted, if this obscures the related matter of the present invention. The following description is constructed based on a receiver that is in a digital communication system GA-VSB, for a better understanding of the present invention.

Figure 4 is a partial block diagram of a receiver according to an embodiment of the present invention. The difference between Fig. 1 and Fig. 4 is that the comb filter 16, a comparator 36, a comb filter 38 and a timing circuit 44 of Fig. 1, are replaced by a mode selection controller. , in Figure 4. That is, the output of a block 14, which identifies an IF amplifier demodulator and Analog to Digital (A / D) converter, is directly powered up to an adaptive equalizer 22. In the embodiment herein invention, the adaptive equalizer 22 effects a suppression of the interference of the NTSC signal, as well as an equalization, when compared to the conventional comb filters (16 and 38 of Figure 1, and 14 and 15 of Figure 2) dedicated to the suppression of NTSC signal interference. In accordance with the features of the present invention, an adaptive equalizer 22 may be limited to the equalization function in which a multi-level input of a predetermined type is processed in one or more multilevel operation modes. Considering that an adaptive equalizer 22 operates based on an LMS algorithm (minimum mean square), it is preferable that the * 22 host an input to a predetermined multilevel, instead of an entry to a multilevel changed by a comb filter. A conventional adaptive equalizer operates selectively for 8-level and 15-level inputs. Accordingly, the embodiment of the present invention is characterized by an input to a predetermined type, for example, an 8-level signal, and to operate the adaptive equalizer in modes of operation corresponding to one or type (e.g., 8 levels and 15). levels) according to the presence or absence of NTSC signal suppression filter processing. In Figure 4, the mode selection controller 50 determines whether a signal contains contiguous channel interference. Until the occurrence of contiguous channel interference, it provides a signal to operate the adaptive equalizer 22, a phase tracker 24 and a lattice decoder in a 15-level mode. On the other hand, up to the absence of contiguous channel interference, it provides a signal to be operated in an 8-level mode. For this purpose, the mode selection controller 50 compares the mean square errors (MSEs) to the front or back of a NTSC signal suppression filter block, as in US Patent Number 5,546,132, it is obtained to the NTSC signal components. , as in U.S. Patent Number 5,446,132, a synchronization of NTSC signals is detected, or it uses a Reference Signal to Compensate Phantom Images (GCR). Figures 5, 6 and 7 are block diagrams of different embodiments of the adaptive equalizer 22, in accordance with the present invention. Referring to Figure 5, the adaptive equalizer 22 includes a first adaptive filter portion 60 of a Finite Impulse Response (FIR) type, having a first filter 62 and a filter coefficient calculator 64, an error calculator 66 to obtain an error in the output of the adaptive equalizer, and a reference signal generator 68 to generate a reference signal to the error calculator 66. A REFSEL signal is applied to select a reference signal, ~ to the signal generator of reference 68 and a window pulse (NP) indicating a reference signal period is applied to the first adaptive filter portion 60. The error calculator 66 includes a single subtractor and the first filter 62 has a multiplexer (MUX1) 74 to selectively exit a training sequence TS_1 70 as a first reference signal and a training sequence TS_2 72 as a second reference signal, in accordance with the REFSEL signal. It is assumed here that the training sequence TS_1 70 is made for a signal of 8 levels and that the training sequence TS_2 72 is made for a signal of 15 levels, converted from an 8-level signal, due to comb filtering, to eliminate contiguous channel interference. An input signal to the receiver of Figure 4 can be divided into a period of reference signal, such as a pseudo-noise sequence period (PN) or a random data period. The input signal is directly fed from the block 14, to the adaptive equalizer 22, through a tuner 10 and a surface acoustic wave filter (SAW filter) 12, without a comb filtering. Therefore, the signal is fixed in ranges of 8 levels. The signal of 8 levels received in the adaptive equalizer 22, is filtered using a filter coefficient, renewed by an error obtained during the reference signal period and is output as an output signal of the adaptive equalizer. The error calculator 66 receives the adaptive equalizer output signal and a reference signal, selected by the REFSEL signal (the 8-level reference signal TS_1 70 is selected at an initial stage), and calculates the error between the signal selected reference and the output signal of the adaptive equalizer. The filter coefficient calculator 64 applies a renewed filter coefficient, by the error calculated in the first filter 62. That is, the first adaptive filter portion 60 filters the 8-level input signal, using the filter coefficient. A filter coefficient for the random data period is calculated, from a calculated error between an adaptive equalizer output signal corresponding to the random data, and a selected reference signal and thus, the first adaptive filter portion 60 filters to an input signal, using the filter coefficient. In a normal state of absence of a contiguous channel interference signal NTSC, the mode selection controller 50 of Figure 4 causes the 8 level reference signal TS_1 70 to be selected by the signal REFSEL. In a state in which comb filtering is required, the mode selection controller 50 causes the 15-level reference signal TS_2 72 to be selected, until the presence of a contiguous channel interference signal NTSC is found, and then, the first adaptive filter portion 60 transitions from an 8-level mode to a 15-level mode. Accordingly, the contiguous channel interference signal NTSC, contained in a high definition television signal, is eliminated by means of the adaptive equalizer 22 of Figure 5. In a signal including a reference signal, such as a signal high-definition television (HDTV), the reference signal for a 15-level signal, changed from the comb filtering, is fed to the adaptive filter portion 60, which operates in the 15-level mode, without changing the bits in the input terminal of 8 levels, thus avoiding a systematic error, found in the preceding art. An equation expressing the operation of the adaptive equalizer 22, based on an LMS algorithm, will be given for the clearer understanding of an input signal that is set to 8 levels. With the input, output and filter coefficient of the first filter 62, given as Xt (n), z (n) and W (n), the LMS algorithm is expressed as: (Equation 1) - (1) z (ri) = Wt (n - \) Xt (n) (2) e (n) = d (n) - Z (n) (3) W (n) = W ( n - l) + 2μe (n) Xt (n) where, Wt - [w ", > »- ',, ..., w'v ,,] and d (n) is a reference signal value.

The LMS algorithm is performed towards the minimization of E [(e; (n))]. Referring to Equation 1, as long as the input level of the adaptive equalizer 22 is changed (for example / from 8 levels to 15 levels, and vice versa), (n) in both (1), and (3), it must be changed a (x (n) _8) for a signal of 8 levels already (x (n) 15) for a signal of 15 levels. Consequently, the conventional adaptive equalizer 22 selectively receives (x (n) _8) and a (x (n) _15). In this case, the input lines must be prepared for as many bits as required, to operate the adaptive equalizer 22 conventional in both modes and thus, complicating the structure of the conventional adaptive equalizer 22. On the other hand, an input signal is always set to 8 levels a (x (n) _8), regardless of whether an NTSC signal interference or a reference signal is selected by the REFSEL signal, in the mode of this invention. Due to the fixed input level of the adaptive equalizer 22, bit allocation is easy and there is no need to change x (n) in (1) and (3) in Equation 1. Figure 6 illustrates another mode of the adaptive equalizer 22, involving a decision process, generally used in digital communication. This is similar to the structure of Figure 5, but the difference is that a multiplexer (MUX2) 78 is added to select a reference signal and a decision signal using the window impulse (WNP) and a decision portion 76 , for adaptive equalization by means of a decision made by the random data. The decision portion 76 decides an error, as an approximate value to a value of 8 or 15 corresponding levels (for example, for 8 levels, 7, 5, 3, 1, -1, -3, -5 and -7, and for 15 levels, 14, 12, 10, 8, 6, 4, 2, 0, -2, -4, -6, -8, -10, -12 and -14) by means of selectively operating a determinant of 8 levels or a determiner of 15 levels, according to the REFSEL signal. The multiplexer 78 selects a reference signal, selected by the reference signal generator 68, during the reference signal period and a decision signal, generated from the decision portion 76 during the random data period, in accordance with the window impulse WNP. The error calculator 66 calculates the error that exists between the output signal of the multiplexer 78 and the output signal of the adaptive equalizer and feeds its output signal to the filter coefficient calculator 64. Figure 7 illustrates a feedback equalizer of decisions (DFE) most commonly used in digital communications. This equalizer is the same as the equalizer of Figure 6, except for the addition of a second adaptive filter portion 80, of a type of Infinite Impulse Response (IIR), including a second filter 82, to a second computer of filter coefficients 84 and a subtractor 86.

While in the equalizers of Figures 5, 6 and 7, two reference signals are employed, it is to be understood that the number of reference signals may be increased. As described above, the adaptive equalizer of the present invention in various modes, for signals of different multilevel types, without the need to physically operate an input signal and perform a NTSC signal suppression filtering operation. Moreover, the equalizer can be constructed with a reduced number of physical equipment components or hardware or hardware, since there is no need for an NTSC signal suppression filter block, nor its adjustment blocks, used in the prior art. In as much, the present invention has been described in detail, with reference to specific modalities, these are mere exemplary applications. Thus, it should be clearly understood that various variations can be made by any person skilled in the art, who are within the field and the essence of the invention. It is noted that, with regard to this date, the best method known by the requested, to carry out the present invention, is that which is clear from the present, discovering the invention.

Claims (17)

1. A method for eliminating contiguous channel interference, in a modulation / demodulation receiver, having a reference signal, in a digital communication system, characterized in that it comprises the steps of: (1) process an input signal so that it is 10 to a predetermined multilevel and feeding the processed signal to an adaptive equalizer; (2) determine the multilevel type, of the signal applied to the adaptive equalizer and 15 to select an operation mode, of at least two multilevel operation modes, for the adaptive equalizer and the blocks that are behind the adaptive equalizer; Y (3) cause the adaptive equalizer 20 Adapt adaptively to the signal that is at a predetermined multilevel in the selected operating mode and eliminate the adjacent channel interference.
2. The method according to claim 1, Characterized in that a first reference signal for a multilevel signal to the absence of contiguous channel interference and a second reference signal for a multilevel signal, up to the presence of contiguous channel interference are used in step (3).
3. 3. The method according to claim 2, characterized in that the first and second reference signals are predetermined.
4. 4. The method according to claim 3, characterized in that the number of the second reference signals is at least one.
5. 5. A modulation / demodulation receiver, having a reference signal, in a system of 15 digital communication, characterized in that it comprises: a block for processing an input signal to a predetermined multilevel, after subjecting the signal to tuning, processing 20 IF and demodulation; a mode selection controller for selecting a mode of operation of a multilevel signal, with respect to a period of reference signal and a period of random data, 25 depending on whether the adjacent channel interference is present or absent in the multilevel signal; Y an adaptive equalizer for equalizing and eliminating contiguous channel interference of the multilevel signal, using a predetermined reference signal in the operation mode, selected from at least two multilevel operation modes.
6. The receiver in accordance with the claim 10 5, characterized in that the adaptive equalizer comprises: a reference signal generator, for selectively generating a first and a second predetermined reference signals, in accordance 15 with the selection of the selection driver • mode; an error calculator to obtain the difference between the selected reference signal and the equalizer output signal 20 adaptable; Y an adaptive filter portion for receiving the multilevel signal, obtaining a filter coefficient, based on the difference obtained and performing a finite impulse response (FIR) filtering, using the filter coefficient.
7. 7. The receiver according to claim 5, characterized in that the adaptive equalizer comprises: a reference signal generator, for selectively generating a first and a second predetermined reference signals, according to the selection of the selection driver of 10 mode; a portion of decisions to decide the value of an adaptive equalizer output signal, such as a predetermined level value of a multilevel, determined according to the 15 mode selection; a selector to selectively output a signal received from the decision portion and a reference signal, selected in the reference signal generator; 20 an error calculator to obtain the difference between the selected reference signal and the output signal of the adaptive equalizer; Y a filter portion adaptable to receive 25 the multilevel signal, obtaining a filter coefficient, based on the difference obtained and performing a finite impulse response (FIR) filtering, using the filter coefficient.
8. The receiver according to claim 5, characterized in that the adaptive equalizer comprises: r a reference signal generator, to selectively generate a first and a second 10 predetermined reference signals, according to • with the selection of the mode selection controller; a portion of decisions to decide the value of an equalizer output signal 15 adaptive, as a predetermined level value of a multilevel, determined according to the mode selection; a selector to selectively output a signal received from the decision portion and 20 a reference signal, selected in the reference signal generator; an error calculator to obtain the difference between the selected reference signal and the equalizer output signal 25 adaptable; a first adaptive filter portion for receiving the multilevel signal, obtaining a filter coefficient, based on the difference obtained and effecting a finite impulse response (FIR) filtering, using the filter coefficient; Y a second adaptive filter portion to receive the selector output, obtaining a filter coefficient, based on the difference obtained and effecting an infinite impulse response filtering (IIR), using the filter coefficient.
9. 9. The receiver according to claim 6, characterized in that the first reference signal is for a multilevel signal, until the absence of contiguous channel interference and the second reference signal is for a multilevel signal, until the absence of contiguous channel interference .
10. 10. The receiver according to claim 9, characterized in that the first reference signal is for a signal of 8 levels and the second reference signal is for a signal of 15 levels.
11. 11. A method for eliminating contiguous channel interference, in a modulation / demodulation receiver, having a reference signal, in a digital communication system, characterized in that it comprises the steps of: processing an input signal to be at a predetermined multilevel and feeding the processed signal to an adaptive equalizer; determining the multilevel type of the signal applied to the adaptive equalizer and selecting an operation mode, of at least two multilevel operation modes, for the adaptive equalizer and the blocks that are behind the adaptive equalizer; Y cause the adaptive equalizer to adaptively adapt to the signal that is at a predetermined multilevel and that the blocks operate in the selected operating mode.
12. 12. The method according to claim 11, characterized in that the adaptive equalizer uses two reference signals to enter at least two multilevel signals according to the selection mode, when performing an equalization.
13. A modulation / demodulation receiver, having a reference signal in a digital communication system, characterized in that it comprises: a block for processing an input signal to a predetermined multilevel, after subjecting the signal to tuning, IF processing and demodulation; a mode selection controller for selecting a mode of operation of a multilevel signal, with respect to a period of reference signal and a period of random data, depending on whether the adjacent channel interference is present or absent in the signal multilevel; Y an adaptive equalizer for equalizing the multilevel signal, using a predetermined reference signal in the operation mode, selected from at least two multilevel operation modes.
14. The receiver according to claim 13, characterized in that the adaptive equalizer comprises: a reference signal generator, for selectively generating a first and a second predetermined reference signals, in accordance with. the selection of the mode selection controller; an error calculator to obtain the difference between the selected reference signal and the output signal of the adaptive equalizer; Y an adaptive filter portion for receiving the multilevel signal, obtaining a filter coefficient, based on the difference obtained and performing a finite impulse response (FIR) filtering, using the filter coefficient.
15. The receiver according to claim 5, characterized in that the adaptive equalizer comprises: a reference signal generator, for selectively generating a first and a second predetermined reference signals, according to the selection of the mode selection controller; a portion of decisions to decide the value of an adaptive equalizer output signal, such as a predetermined level value of a multilevel, determined according to the mode selection; a selector to selectively output a signal received from the decision portion and a reference signal, selected in the reference signal generator; an error calculator to obtain the difference between the selected reference signal and the output signal of the adaptive equalizer; Y a filter portion adaptable to receive the multilevel signal, obtaining a filter coefficient, based on the difference obtained and performing an infinite impulse response filtering (IIR), using the filter coefficient.
16. The receiver according to claim 5, characterized in that the adaptive equalizer comprises: a reference signal generator, for selectively generating a first and a second predetermined reference signals, according to the selection of the mode selection controller; a portion of decisions to decide the value of an adaptive equalizer output signal, such as a predetermined level value of a multilevel, determined according to the mode selection; a selector to selectively output a signal received from the decision portion and a reference signal, selected in the reference signal generator; 10 an error calculator to obtain the difference between the selected reference signal and the output signal of the adaptive equalizer; a first filter portion adaptable for 15 receive the multilevel signal, obtaining a filter coefficient, based on the difference obtained and performing a finite impulse response (FIR) filtering, using the filter coefficient; and a second adaptive filter portion to receive the selector output, obtaining a filter coefficient, based on the difference obtained and performing an infinite impulse response (IIR) filtering, using the coefficient 25 of filter.
17. 17. The receiver according to claim 9, characterized in that the first reference signal is for a signal of 8 levels and the second reference signal is for a signal of 15 levels.