MXPA00006432A - Device and method for detecting pcm upstream digital impairments in a communication network - Google Patents

Abstract

A device an method for detecting digital impairments affecting an upstream pulse code modulation (PCM) channel in a digital communication network (36), involves:receiving, by a digital PCM modem (38) interconnected to the digital communication network (36), a random sequence of digital values selected from a constellation of digital values transmitted over the upstream PCM channel of the digital communication network (36);establishing distributions of the received digital values, each distribution corresponding to one of a plurality of time intervals;and deriving from the distributions the types of robbed bit signaling and digital loss affecting the upstream PCM channel of the digital communication network (36) for each time interval.

Description

DEVICE AND METHOD FOR DETECTING CURRENT DIGITAL DETERIORATION OF PCM IN A NETWORK OF COMMUNICATIONS Related Request This application is a continuation in part of the U.S. Application. Series No. 08 / 999,416, filed on December 29, 1997, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION This invention relates to "a device and method for detecting digital deteriorations upstream of PCM by using the detected impairments in order to estimate the analog channel characteristics and the echo downstream of PCM to improve the current transmission. above PCM.

BACKGROUND OF THE INVENTION Conventional modems, such as V.34 modems, treat the public switched telephone network (PSTN) as a pure analog channel even when the signals are digitized through most of the network. In contrast, pulse code modulation modems (PCMs) take advantage of the fact that most of the network is digital and that typically central site modems, such as those of internet service and service providers online, they connect to the PSTN through digital connections (for example, IT in the United States and IT in Europe). The first generation of PCM modems transmits data only in a downstream PCM mode (ie, from a central site digital modem to an analogue end user modem) and transmits in analog mode, eg, V.34 mode, upstream (that is, from the final modem to the central site modem). The second generation of PCM modems will also transmit data upstream in a PCM mode. With the PCM downstream, the modem Central site PCM transmits on a digital network eight-bit digital words (octets) corresponding to different output levels of the central office code. At the end user's central office, the octets are converted to analog levels that are transmitted over an analog cycle. The PCM modem of the end user then converts the analog levels into equalized digital levels. Equalized digital levels are ideally represented again in the originally transmitted octets and the data that the octets represent. With the PCM upstream, the PCM modem of the end user transmits analog levels over the analog cycle corresponding to the data to be transmitted and the levels are quantified in order to form octets by means of a codee in the central office of the end user. The codeine transmits the octets to the PCM central site modem over the digital network. However, due to the deterioration in the digital network, such as the loss of digital line (in the EU, typically 0, 3 or 6 dB) caused by digital compensation and the signaling of subtracted bits (hereinafter referred to as RBS), originated by the signaling in band of the networks, the octets transmitted in both directions, upstream and downstream, can be corrupted.

If this is not taken into account, high data error rates may be generated in the modems. Many modern digital networks that can contain PCM modem data are constructed as T-bearer systems that use the signaling of subtracted bits. The digital data transmitted on these networks are grouped into octets (eight (8) bits) and the octets are grouped into series of bits (twenty-four (24) octets). Figure 1 shows a series of bits 10 containing twenty-four octets, Oo to 02. The series of bits transmitted over the network are continuous and the only series of 24-bit bits 10 is shown only for descriptive convenience. Certain octets are affected by the RBS. The network uses the least significant bit (LSB) position of the affected octets to contain data that carries out control functions in the network. In this way, for example, the first octet, Oo, can be affected by a type of RBS that forces the LSB of that octet to one, odd RBS, as indicated by the "F" in that octet. (The designation "NC" means "without Change"). Depending on the octet of data contained in that interval, the RBS can change the data of that octet. In particular, if that octet has a zero in its LSB, the RBS alters that octet. However, if octet has a one in its LSB, the RBS would not affect the octet from the perspective of the end user. It has been observed that the RBS has a determinate periodicity with periods of six or twenty-four octets. In this example, the period of the RBS is twenty-four. Since the RBS is recurrent every twenty-four octets, the octets can be observed as they appear in a basic period 12 of twenty-four installments or time slots, 0-23, which may or may not be affected by the RBS. For example, the Oo octet appears in the "0" quota that is affected by the RBS, while the Oi octet, for example, appears in the "i" quota and is not affected by the RBS. It should be noted that due to the nature of the networks, it is possible to have more than one range affected by RBS in the basic twenty-four period, as is evident from the affected octet 06. Methods for detecting and mitigating downstream digital impairments are known. Examples of these methods are described in the following co-pending applications, assigned to the assignee of the present invention: Application of E.U. Series No. 08 / 885,710, entitled System, Device and Method for Detecting and Characterizing Impairments in a Communication Network; filed on 06/30/97; the_ Application of E.U. Series No. 08 / 730,433, entitled System And Device For, And Method Of, Detecting, Characterizing And Mitigating Determinis t ic Distortion In A Communications Network; filed on 10/15/96; the Application of E.U. Series No. 08 / 979,994, entitled System, Device and Method for Detecting Impairments in a Communication Network; filed on 11/26/97; and the Application of E.U. Series No. 08 / 979,196, entitled Apparatus, System and Method for Transmitting and Receiving A Training Sequence Optimized for Detecting Impairments in a Communication Network; filed on 11/26/97. These applications are incorporated herein in their entirety. With the transmission downstream, the points transmitted over the digital network are known and this information is used for the detection of digital deterioration according to the above-mentioned requests. However, with the transmission upstream, before determining the digital deteriorations, the downstream PCM echo and the characteristics of the analog cycle (channel), the points transmitted on the digital channel and the techniques to detect digital deterioration are unknown. in the previous applications, they are not applicable to the upstream transmission. Accordingly, there is a need for a device and method for detecting digital impairments upstream of PCM in order to improve upstream transmission of PCM. This information can also be used to estimate the analog channel characteristics and echo downstream of PCM to further improve the upstream transmission of PCM.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a representation of a series of bits of octets and the manner in which they are affected by the RBS; Figure 2 is a block diagram illustrating the upstream transmission of PCM; Figure 3 is a discrete time block diagram equivalent to the block diagram of Figure 2; Figure 4 is the above-discrete block diagram equivalent to Figure 3, including the echo path originated by the downstream transmission; Figure 5 is an example of an occurrence table according to this invention; Figure 6A is an example of an inverse digital deterioration table (IDT) according to this invention; Figure 6B is another example of an inverse digital deterioration table (IDT) according to this invention; Figure 6C is still another example of an inverse digital deterioration table (IDT) according to this invention; Figure 7 is a flowchart illustrating the detection of current upstream digital deterioration according to this invention; Figure 8 is a flow chart illustrating the detection of RBS2 according to this invention; Figure 9 is a flow chart illustrating the detection of digital loss according to this invention; Figure 10 is a flow chart illustrating the detection of RBS1 according to this invention; Figure 11 is the discrete upstream block diagram equivalent to Figure 3 in the absence of echo downstream of PCM; Figure 12 is a block diagram of an analog channel estimator according to this invention; Figure 13 is a block diagram of an echo estimator downstream of PCM in accordance with this invention; Figure 14 illustrates certain μ-law quantifiers and the manner in which the thresholds are altered in the presence of the RBS; Figure 15 illustrates the altered μ-law quantizing thresholds of Figure 14 and the points of the virtual quantizer according to this invention; Figure 16 is a block diagram of a fully duplex analog channel and an echo estimator downstream of PCM according to this invention; Fig. 17 is a block diagram of a downstream echo estimator of improved PCM according to this invention; and Figure 18 is a block diagram of an error signal generator in accordance with this invention.

DETAILED DESCRIPTION OF A PREFERRED MODE Bi-directional PCM communication is described in the U.S. Application. Series No. 08/724, 491, entitled Hybrid Digital / Analog Communication Device, which is assigned to the assignee of the present invention and which is hereby incorporated in its entirety for reference. Figure 2 shows the block diagram 20, an example of upstream transmission of PCM in such bi-directional PCM communication system. An analog PCM modem 22 is included, which has a precoder 24, a pre-filter 25 and a digital-to-analog converter (D / A) 26, interconnected to the analog channel 28. The precoder 24 receives the digital data u (n) and outputs precoded data x (n). The pre-encoded digital data is provided to a pre-filter 25 which emits a filtered signal z (n). The filtered signal z (n) is converted to an analogous form and transmitted as a signal, z (t), on the analog channel 28, which has a channel characteristic, c (t). The analog channel modifies the transmitted signal z (t) to form the signal y (t) which then finds the downstream PCM echo, echo (t) 30, which is added to y (t), producing the signal r (t) . The signal r (t) is received by quantifier 34 of law-μ (law-A in most countries, not counting the EU) in the central office (CO) 32 and is quantified according to the law-μ . See, International Telecommunications Union, Recommendation G.711, Voice Frequency Pulse Code Modulation (PCM), 1972. Quantized octets (digital values), q (n), are transmitted over digital network 36 at a frequency of 8kHz where they can be affected by various digital impairments, as discussed below. The possibly affected octets, v (n), are received by the digital PCM modem 38, which ideally decodes the octets, v (n), in y (n) and then the original digital data, u (n). Before the data can be transmitted upstream, the clock (fi) of D / A 26 on the analog PCM modem 22 must be synchronized with the clock (f2) of CO 32. This can be achieved by learning the clock of the signal PCM downstream (not shown) and clock synchronization by using the technique proposed in the US Patent No. 5,199,046, entitled Device and Method of Synchronization of the Digital Speed Converter, First and Second, incorporated herein by reference in its entirety. Once the clocks are synchronized, the block diagram upstream of PCM 20, FIG. 2, can be represented as the equivalent discrete time block diagram 20 ', FIG. 3, similar components being represented by the same reference numbers containing a bonus (?) In the block diagram 20 'we assume that f? = F2; however, it should be noted that fi does not have to be equal to f2 while the two clocks are synchronized. When fi is equal to f2, n is the time index for 8kHz samples, since the clock (f2) of CO 32 is set to that frequency. The precoder 24 (24 ') and the prefilter 25 (25') can be implemented as described in the co-pending application entitled Device and Method for Precoding Data Signals for its Impulse Code Modulation Transmission (PSM), USA Series No. 08 / 999,249, filed on December 29, 1997 (CX096044P02), which is assigned to the assignee of the present invention and which is hereby incorporated in its entirety. As explained in this co-pending request, the digital data u (n) can be sent through the transmission of z (n), so that the constellation points and (n) will be one of several points in an equivalence class for u (n). The point y (n) in the equivalence class of u (n) that is selected is usually determined to minimize the transmit power which is the power of x (n). In a co-pending application entitled System, Device and Method for Upstream Transmission of PCM through the Use of an Optimized Transmission Constellation, Application of E.U. Series No. 08 / 997,254, filed December 29, 1997 (CX097028), which is assigned to the assignee of the present invention and which is hereby incorporated in its entirety for reference, shows the manner in which the design of the constellation for y (n) decodes y (n) (and eventually u (n)) from v (n) in the presence of echo, the μ-law quantifier and the digital impairments with a certain minimum probability of error. This application also describes the manner in which the digital PCM modem 38 'decodes u (n) from v (n). The discrete time block diagram 40, FIG. 4, shows the discrete upstream block diagram 20 'equivalent along with the echo path 42 originated by the downstream transmission of the digital PCM modem 38'. The digital PCM modem 38 'transmits octets, s (n), downstream on the digital network 36'. The octets s (n) can be affected by digital impairments, such as the signaling of subtracted bits _ and the digital loss in the digital network 36 ', causing the octets s (n) to be modified. In order to represent all possible combinations of digital impairments in the downstream channel 43 of the digital network 36 ', a first occurrence of RBS is shown, designated RBS1 of DS 44, which occurs before the digital loss, designated digital loss of DS 46, and a second occurrence of RBS, designated RBS2 of DS 48. The octets leaving digital network 36 'are designated p (n). The possible types of RBS1 of DS 44 are not RBS, including RBS (LSB = 0) and odd RBS (LSB = 1). The possible types of RBS2 of DS 48 are not RBS, including RBS, odd RBS and RBS of midpoint reconstruction. As described above in the Background of the Invention, the RBS may vary according to the time quota. In contrast, the digital loss does not vary with time, that is, the digital loss is the same for all time shares. There are several possible digital losses that could affect the downstream channel 43 of the digital network 36 ', such as .5dB, IdB, 1.5dB, 2dB, 3dB, 4dB, 4.5dB, 5dB, 6dB, 7dB or 10.5dB. See International Telecommunications Union, ITU-T, Recommendation G.121, Loudness Ratings (LRs) of National Systems, March 1993). also, the downstream channel 43 of digital network 36 'may not be affected by digital loss, often referred to as loss of OdB. The most common types are the losses of 3dB and 6dB and the null digital loss (OdB). Detection of downstream digital impairments, ie, DS_RBS1 44, digital loss DS 46, RBS2 of DS 48, can be found in the copending patent applications referred to above. The octets, p (n), which leave the digital network 36 'are received by the digital-to-analog converter μ-law (D / A) 50 in CO 32', which outputs the corresponding analog levels (levels of law -μ) that are transmitted to the analog PCM modem 22 '. This portion of the downstream transmission is not illustrated; however, the echo, echo (n) 30 ', produced by the downstream transmission, represented by the echo channel 52 (with channel characteristic h (n)), is shown. The downstream PCM echo, echo (n) 30 ', is added to the output of the analog channel and (n) to form the signal r (n) that is entered in the law quantifier-μ 34' in the central office (CO) 32 '. As described above, the signal r (n) is quantized by the law quantizer-μ 34 'that emits the octets of law-μ, q (n), on the upstream channel 53 of the digital network 36'. In order to represent all possible combinations of digital impairments in the upstream channel 53 of the digital network 36 ', a first occurrence of RBS is shown, designated RBS1 of US 54, which occurs before the digital loss, designated p? digital loss of US 56, and a second occurrence of RBS, designated RBS2 of US 58. Possible types of RBS1 of US 54 are not RBS, including RBS (LSB = 0) and odd RBS (LSB = 1). Possible types of RBS2 of US 58 are not RBS, even RBS, and odd RBS. The RBS reconstruction of the midpoint does not occur in the upstream channel. The possible types of digital loss of US are the same as in the downstream channel. The most common types in the United States are 1! loss of 3dB and 6dB and zero digital loss (OdB) and this invention is described with respect to these losses. However, the principles of the invention can easily be applied to any level of digital loss. Detection of upstream digital impairments, ie, RBS1 of US 54, digital loss of US 56, and RBS2 of US 58, according to this invention, is described first below. Next, the analog channel estimate, c (n), is described in the presence of those detected digital deteriorations and the downstream PCM echo estimate, echo (n), introduced in the upstream PCM transmission, and the variance of echo, se2, according to this invention. The digital upstream impairments, the analog channel estimate, c (n), and the echo variance are transmitted to the analog PCM modem and can be used by that modem to select the appropriate transmission constellation, as described in the USA Co-pending Series No. 08 / 999,254 (CX097028). The upstream digital impairments, the analog channel estimate, c (n), and the echo variance can be used alternatively by the digital PCM modem to improve the decoding performance. Digital deterioration detection Unlike the downstream digital deterioration detection, we do not have the control or knowledge about the precise input, octets q (n), to the digital network 36 ', because the analog channel characteristic is not known initially. , c (n). This invention uses a randomized, reference-directed training sequence, z (n), to detect digital impairments. A random training sequence, z (n), according to this invention, is one that produces signals and (n) with an essentially Gaussian distribution that leaves most of the 256 law-μ points in the law quantifier- μ 34 ', randomly. Due to the loss in the analog channel 28 ', some of the larger μ-law points can not be abandoned. For example, the test tone sequence of the phase 2 line specified in the specification of the ITU V.34 analog modem can be used. The signal r (n) (o and (n) will be quantified in the absence of echo (n) 30 '), q (n), by means of the law quantifier-μ 34'. The octets, q (n), pass through the digital network 36 'and the digital modem 38' receives v (n), the digitally deficient version of q (n). Since digital impairments are unknown, q (n) can not be derived from v (n). The basic idea of detecting upstream digital impairments by the PCM digital modem 38 ', according to this invention, involves observing the distribution of octets received v (n) in each RBS time quota during the training sequence , or after it is completed, to determine the impairments, both of RBS and digital losses, that affect the PCM channel upstream of the digital communications network during each RBS time slot. A preferred technique for detecting digital deteriorations according to this invention is described below. First, a distribution of octets received v (n) is collected for each RBS time quota by, for example, the establishment of an occurrence table 60, figure 5, which keeps a count of the number of times each of the possible octets received 0-127 (the constellation of digital values) has been received in each RBS time slot. There are normally 256 possible octets of law-μ, 0-255, which can be received, half are positive and the other half are negative with the corresponding magnitudes. In the preferred embodiment, the received octets are converted to an inverted byte-by-bit (BIOS) form. That is, each bit of the received octets is inverted and it is assumed that all octets referred to here are in a BIOS form unless otherwise specified. In the form of BIOS, the octets of law-μ 0-127 are positive octets and 128-255 are negative octets. The positive octet, where 1 = 0, 1, ..., 127, and the negative octet i, have the same magnitude, but opposite signs. In the occurrence table 60, a count is kept of the number of times each octet is received, without taking into account its sign, in order to form a distribution of the received octets v (n). Depending on the deterioration condition affecting the digital network, certain μ-octets will not be received. For example, in Table 60, the octets of law-μ 1, 3 ... and 127 have zero occurrences ', which means that the digital modem 38' iio has received these octets of law-μ. The other octets of law-μ shown, that is, 0, 2 ... and 4 have been received Xo, X2, X4 ... times, respectively. When the training sequence is completed, or preferably during the training sequence, the received octet distributions v (n) are analyzed to determine the impairments affecting the PCM channel upstream of the digital communications network. As described above, the most common digital impairments are RBS1 =. { 0, 1, NoRBS} , digital loss =. { OdB, 3dB, 6dB} , and RBS2 =. { 0, 1, NoRBS} and each RBS time quota in a given digital network can be affected by any combination of these impairments. A combination of deterioration can be referred to herein as a condition of deterioration. For each digital deterioration condition, an inverse digital deterioration table (IDT) whose first column contains all possible octets v (n), 0-127, which can be received by the digital modem 38 'and the remaining columns with the possible octets q (n) entered into the digital network 36 'which produces the octets received v (n) under the condition of specific deterioration of the table. Table 70, Figure 6A, is an example of an IDT table for the following deterioration condition: RBSl = No RBS, digital loss = 0dB, RBS2 = 1. In this table, it can be seen that, for example, both octets of law-μ q (n)? and q (n) 2, 0 and 1, entered into a digital network affected by the previous deterioration condition, will be represented in a single octet received v (n), 0. As noted above, due to the condition of deterioration in the network, there are certain octets, v (n), that can not be received, without taking into account the μ-law bytes introduced in the digital network. In this way, there are no entries of q (n) in the IDT table corresponding to these octets, v (n). These non-existent entries q (n) are referred to herein as null point entries or simply null points. In the IDT 70 table, there are null points associated with all the impacted octets, v (n), 1,3 ..., 127 because under the deterioration condition associated with the .IDT 70 table, these octets can not be received. The reason for this is that the odd octets v (n) have a one in their least significant bit position (LSB) (in BIOS form) and since 'RBS2 = 1, the LSB of all octets received is forced into a zero (in BIOS form). This is true for all the IDT tables with RBS2 = 1. Table 80, Figure 6B, is an example of an IDT table for the following deterioration condition: RBS1 = No RBS, digital loss = OdB, RBS2 = No RBS. Since there are no impairments associated with this table, it can be observed that there are no null points and, although not all are shown, all octets q (n) introduced in a digital network without deterioration will produce the same octets in the output of the digital network . Table 90, Figure 6C, is an example of an IDT table for the following deterioration condition: RBS1 = No RBS, digital loss = 6dB, RBS2 = No RBS. With this table, it can be seen that there are several octets received that are produced by two octets of μ-law different q (n)? and q (n) 2. And, although not all are shown, only the null points that are associated with this table are the largest octets received, v (n), such as octets greater than 111. Sometimes, these large μ-octets do not come out during the training sequence, especially when the analog channel has a significant loss. Therefore, if the large μ-law bytes in the 60-occurrence table have not been received, it is not clear whether this is due to the fact that the large μ-law octets did not come out during the training sequence or came out but The associated deterioration condition c-on the IDT table 90 affected the network in such a way that it produced null points for these large μ-law octets. The above-described TDI tables are only exemplary and it will be apparent to a person skilled in the art that an RTD table should be established for all expected deterioration conditions. In tion, it will be apparent to an expert in the field, from the above description, how to construct all the necessary RTD tables. "It should be noted that although the IDT tables shown in Figures 6A-C have at most two possible values of q (n) for one octet received v (n), for certain conditions of deterioration, there may be more than two possible values of q (n) that produce a received octet v (n) In order to simplify the description of the deterioration detection according to this invention, the detection of deterioration will be described by the use of a simplified, hypothetical digital network, which only has the following ten deterioration conditions: RBS1 Digital Loss P.BS2 No RBS OdB None RBS No RBS OdB No RBS 3dB None RBS No RBS 3dB 1 3dB None RBS 1 3dB No RBS 6dB None RBS None RBS 6dB 6dB None RBS 6dB It will be apparent to a person skilled in the art how to expand this example and apply the invention to all the possible deterioration conditions expected for a particular application. The digital deterioration detection according to this invention is illustrated in flow chart 100 of Figure 7. In the preferred embodiment, it is assumed that RBS occurs in a period of 24 octets, as described in the Background of the Invention. Accordingly, RBS1 and RBS2 must be detected for each RBS slot or time slot, 0 to 23. In step 102, the octets transmitted in the random training sequence are received from the digital network.

As described above, the deterioration detection can be carried out during the training sequence or after it has finished. In step 104, a distribution of the octets received is established for each time slot of RBS, for example, by establishing a table of occurrences as illustrated in figure 5 and described above. The digital modem 38 'begins the detection process preferably during the training sequence after a sufficient number of octets has been received. In step 106, RBS2 is detected for each time slot, as described more fully in Figure 8. Flow chart 120 of Figure 8 illustrates the detection of RBS2 according to this invention. In step 122, it is determined whether all received octets, v (n), are odd, that is, it is determined if no even octets v (n) have been received. If it is determined that all octets received, v (n), are odd, then in step 124 it is indicated that RBS2 is "0" or the even RBS for that time slot. In the simplified example described above, RBS2 is never "0" or even RBS; however, the detection of this type of RBS2 is described to generalize the description of the detection of RBS2 according to this invention. If in step 122 it is determined that all received octets, v (n), are not odd, then in step 126 it is determined whether all received octets v (n) are even, ie, it is determined if they have not been received odd octets v (n), as in the IDT table 70, figure 6A. If all received octets, v (n), are even, then in step 128 it is indicated that RBS2 is "1" or odd RBS for that time quota. If in step 126 it is determined that all received octets, v (n), are not even, then in step 130 it is indicated that there is no RBS2 in the digital network for that time slot. Referring again to Figure 7, after RBS2 has been detected for each time slot, in step 108, the digital loss in the network is detected, as will be more fully described in Figure 9. The flow chart 140 of Figure 9 illustrates the detection of digital loss according to this invention. In step 142, the null point patterns (ie, the locations of the null points) of all the IDT tables having at least one null point (except the IDT tables with only larger null points, for example the table 90 of Figure 6C) and that they do not have RBS2 are compared with the occurrence tables associated with the time shares that do not have RBS2. The IDT tables and time quotas without RBS2 are used in order to ensure more reliable digital loss detection. Also, since digital loss does not vary from time share to time share, comparisons are made through the time shares to ensure more accurate digital loss detection. In the simplified example there are only five possible RTD tables without RBS2 that must be compared with the occurrence table. They are the IDT tables that have RBS2 = No RBS and the following (i) RBSl = No RBS, digital loss of OdB; (ii) RBSl = No RBS, digital loss of 3dB; (iii) RBS1 = 1, digital loss of 3dB; (iv) RBSl = No RBS, digital loss of 6dB; and (v) RBS1 = 1, digital loss of 6dB. The IDT tables for (ii), (iii) and (v) have null point entries and will therefore be compared with the occurrence tables. For example, with (v), that is, RBS1 = 1, loss of 6dB, the IDT table (not shown) has null points when v (n) is 9, 11, 13, 15, etc. The IDT tables for (i) and (iv) do not have any null points (except for several octets of law-μ in the case of iv), therefore, these RTD tables are not compared with the occurrence tables. In step 144, it is determined if there is any null point pattern that matches between the IDT tables and the occurrence tables. For example, if an occurrence table for a particular time quota has zero occurrences in each of the null points of the TDI table for the case (v), the digital loss in the network in that time quota will be determined as a digital loss of 6dB, the digital loss for the case (v). In step 144, the null pattern of each of the possible RTD tables is compared to the occurrence tables associated with each of the time quotas that do not have RBS2. In step 146, it is determined which TDI table has the highest concordances and in stage 148 the type of digital loss associated with the TDI table that has the highest concordance is indicated as the type of digital loss present in the network for all the time shares. If in step 144 it is determined that no null point pattern matches between the RTD tables that have null points and the occurrence tables, in step 150, the probability patterns of all the RTD tables that do not have points are compared null with the occurrence tables for each time quota. In the simplified example, there are only two IDT tables that do not have null points, that is, the IDT tables of cases (i) and (iv) (except for the various large μ-octets in the case of iv) ). The probabilities of some entries of v (n) in the IDT tables are determined and compared with the occurrence tables to verify similar probability patterns. The IDT tables 80 of Figure 6B and 90 of Figure 6C are the IDT tables for cases (i) and (iv), respectively. In the IDT table 80, case (i), for example, q (n) = 8 (ie, 13.0 <r (n) < _15.0) is represented for v (n) = 8 and q (n ) = 9 (ie, 15.0 <r (n) <_17.O) is represented for v (n) = 9. Therefore, the probability of having v (n) = 8 is almost the same as v (n) = 9 (15.0-13.0 / 17.0-15.0 = 1.0, that is, one to one). In contrast, in the IDT table 90, case (iv), q (n) = 15 and 16 (ie, 29.0 <r (n) <_35.0) is represented for v (n) = 8, yq (n) = 17 (ie, 35.0 <r (n) <39.0) is represented for v (n) = 9. Therefore, with case (iv), the probability of having v (n) = 8 is approximately 1.5 (35.0-29.0 / 39.0- 35.0 = 6.0 / 4.0) times greater than v (n) = 9, assuming that r ( n) is distributed evenly over 29.0 < r (n) < 39.0. Actually, it is not distributed uniformly, but rather it is a Gaussian distribution with a mean = 0 and a variance = sr. Therefore, the probability can be represented more accurately as: Pr (29.0 <r (n) <35.0) / Pr (35.0 <r (n) <39.0) = (1) Q_fcn (35.0) / sr) -Q_fcn (29.0 / sr) / Q fen (39.0 / sr) -Q fcn (35.0 / sr) For a description of Q_fcn see Shanmugan, K.S. and Breipohl, A.M., "Random Signals: Detection, Estimation, and Data Analysis," John Wiley & Sons, Inc., 1988. It can be determined for each occurrence table which RTD table has a probability pattern that agrees with the occurrence table. That is, for a given occurrence table, by using the previous example, the occurrence ratio of v (n) = 8 av (n) = 9 is calculated and determined to be a one-to-one ratio (table of occurrences). IDT 80, digital loss of OdB) or if the ratio is 1.5 (IDT 90 table, digital loss of 6dB). Other octets v (n) that have similar properties can also be used. In step 152, it is determined which TDI table has the highest concordance through the time quota and in step 154 the digital loss associated with the TDI table having the highest probability pattern matches is that indicated to be the type of digital loss present in the digital network. Referring again to Figure 7, RBS1 is detected in step 110. Once RBS2 and the digital loss have been detected, by using the simplified example, there are only two IDT tables that remain with impairments that may correspond to the condition of deterioration that affects the digital network. It is the tables that have the RBS2 and the digital loss detected and either RBS1 = 1 or No RBS. As shown in flow diagram 160, steps 162-174, FIG. 10, by using these IDT tables, RSB1 can be detected for each time slot in a manner corresponding to the digital loss detection described with respect to the Figure 9. It should be noted that certain conditions of deterioration can be established before carrying out any deterioration detection, as described above. For example, if the octets are large, such as octets of value greater than or equal to 112, then the following deterioration condition may be established: RBS = None, Digital loss = 6dB, and RBS2 = None. As described in Table 90, Figure 6C, this is because octets of this magnitude can not be received with this type of deterioration. Estimation of the Analogue Channel The analog channel, c (n), can be estimated taking into account the determined upstream digital deteriorations. To estimate the analog channel in the presence of digital impairments, the upstream transmission of PCM can be modeled as in Fig. 11. In Fig. 11, the upstream transmission block diagram 20 'of Fig. 3 without current echo is shown. down from PCM. The analog channel, c (n), can be estimated in a half-duplex mode, that is, when the digital modem 38 'does not transmit downstream and therefore there is no echo downstream of PCM in the upstream transmission. 0, the upstream transmission of PCM can be modeled as in Figure 4 and c (n) can be estimated in a full duplex mode. The estimate of c (n) in a half-duplex mode will be described first. The estimate of c (n), together with the estimate of echo (n) in the full-duplex mode, will be described below with respect to Figure 16. The analog channel estimator 200 of Figure 12, according to this invention, is implemented in the digital modem 38 '. The analog channel estimator 200 includes the analog channel estimation block 202 which is implemented as an FIR filter and which receives as inputs the training sequence directed by reference z (n) and an error signal, error (n) , and emit a signal and (n) ', an estimate of y (n). The signal y (n) 'is introduced into a quantization block of law-μ 204, which quantifies the signal y (n)' to form the signal q (n) '. The signal q (n) 'is provided to the RBSl block of US 206, the digital loss block of US 208 and the RBS2 block of US 210, which modify the signal according to the detected digital deteriorations to produce a signal v (n) ', an estimate of the received signal v (n). It should be noted that the types of RBSl and RBS2 may vary according to the time quota and it is assumed that they are not present before being determined. The signal v (n) 'is provided to an octet-to-linear converter 211, which converts the octets, v (n)', to linear values, vl (n) '. The linear values, vl (n) ', are given to the totalizer 212. The received real bytes, v (n), are given to an octet to linear convert 213, which converts the octets v (n) to linear vl values. (n) The linear values vl (n) are also provided to the totalizer 212 where the difference between vl (n) and vl (n) 'is taken and given as the error signal, error (n), to the analog channel estimation block 202. The analog channel estimation block 202, using the training sequence directed by reference z (n), the error signal, error (n), and a mean least squares algorithm (LMS), estimates the channel characteristic analog, cr (n), as follows. The analog channel is represented as c (n) where n = 0, l, ..., Nc-l, and where Nc is the length of the channel, then the coefficients of the channel can be determined for i = 0, l, .. ., Nc as follows: cn (i) = cn-? (i) + Verror (n) z (n-i) (2) where cn (i) represents the estimated channel coefficients at time n and V represents the constant of size of LMS. For information on the LMS algorithm see, for example, B. Widrow and S.D. Sterns, "Adaptive Signal Processing", Prentice Hall, Inc., Englewood Cliffs, NJ 1985. The digital modem 38 'transmits the coefficients of the analog channel, c (n), to the analog modem 22', which uses this information to improve the upstream transmission, as described in the EU Application Copendent Series No. 08 / 999,254 (CX097028). PCM Echo Downstream Estimation The PCM downstream echo, echo (n), can be estimated according to this invention by using the echo estimator 220 of FIG. 13, implemented within the digital modem 38 '. The echo estimator 220 takes into account both downstream and upstream digital impairments, as described below. The downstream echo, echo (n), which is estimated is the echo introduced in the upstream transmission at the input of the μ-law quantizer 34 of FIG. 4. When estimating the downstream echo at that location in the channel, instead of the input to the digital modem, reduces the non-linear effects of digital deterioration and quantification and therefore a better estimate of the echo downstream of PCM is obtained.

The echo estimator 220 includes a reverse virtual quantizer block 222 that receives the signal v (n) and outputs virtual quantizing points, vq (n). The quantifier of law-μ 34 'and the detected upstream digital deteriorations are modeled as a new equivalent quantifier, inverse virtual quantizer 222, when establishing equivalent quantifying thresholds, as required given the deteriorations detected. An example of this is illustrated in Figures 14 and 15. It should be noted that to estimate the echo (n) more precisely, the upstream portion of the echo estimator 220 should be modeled as in Figure 4 with the μ-law quantizer and the upstream deterioration blocks, but since this it is not feasible since q (n) is not known nor v (n) is given, the inverse virtual quantifier 222 is used as the best alternative. Figure 14 shows a portion of the original constellation law-μ 240 that has points 241-244 and thresholds 245-249. What is also shown in Figure 14 is that the same portion of the μ-law constellation with its thresholds is modified to consider RBS1 = 1. Now there are fewer thresholds, 250-252, and because of this there are only two points of law-μ, that is, 241 and 243. With the new thresholds, 250-252, the virtual quantifying points, vq (n) 's , for example, 260 and 261 of Figure 15, can be established as the midpoint between each pair of thresholds. It should be noted that these virtual quantifiers points are no longer linear μ-law levels. Therefore, the inverse virtual quantizer 222 of Figure 13 is constructed to convert the octets of v, v (n), to their corresponding virtual quantifying points t, vq (n), based on the new thresholds and points selected as illustrated in Figures 14 and 15. Referring again to Figure 13, the echo estimator 220 also includes the RBSl block of DS 224, which receives the downstream PCM signal, s (n). This signal also passes through the digital loss block of DS 226 and the RBS2 block of DS 228 which emits a digitally transmitted signal deficient to the byte-to-linear converter 229 which converts the bytes p (n) into linear values of law -μ pl (n) Law-μ pl (n) linear values are provided to the echo channel block 230, which is implemented as an FIR filter. The blocks of digital deterioration are designated according to the digital deteriorations detected by the analogue modem 22 '. The emission of echo channel block 230 is the echo downstream of PCM, echo (n), which is provided to the 232 totalizer. The virtual quantizer points, vq (n), are also provided to the totalizer 232, which takes the difference between vq (n) and echo (n) to form the error signal, error (n), which is fed back to the echo channel block 230 The echo channel block 230, by using the digitally deficient signal, the error signal, error (n), and a least-squares average algorithm, estimates the echo downstream of PCM, echo (n), by the adaptation of h (n) as follows. Assume h (n), where n = 0, 1, ... Nn- 1, and where Nn is the length of the echo channel, then the channel coefficients can be determined for 1 = 0, 1, ..., Nn -l as follows: hn (i) = hn-? (i) + Verror (n) pl (ni (3) where hn (i) represents the estimated channel coefficients in time ny .V represents the LMS stage constant.From echo (n), the variance can be obtained of echo, se2, by the average of the square values of echo (n) over a predetermined period of time, for example, 1000 times of the symbol.The digital modem 38 'then transmits to the analogue modem 22' the echo variance and the Analogue modem uses this information to improve upstream transmission, as described in the EU Application Co-pending Series No. 08 / 999,254 (CX097028). Also, the digital modem 38 'uses the estimate of echo (n) in the decoder, also as described in the EU Co-pending Application Series No. 08/999, 254 (CX097028). Combined Estimation of the Analog Channel and the PCM Echo Downstream In Figure 16, a current echo estimator is illustrated. below and a fully combined analog channel d The analog channel estimator 200a is configured like the analog channel estimator 200 of FIG. 12, except that there is an echo component downstream of PCM, echo (n), estimated by the echo estimator 220a, added at the output of the estimation block of the analog channel 202a. The echo estimator 220a is configured in the same way as the echo estimator 220 of FIG. 13, except that there is no inverse virtual quantizer. Also, the estimators use a common error signal, error (n). Improved Estimation of Downstream PCM Echo The echo downstream of PCM, echo (n), can be estimated even more accurately, according to this invention, by using an improved echo estimator 220 of Figure 17, implemented inside the digital modem 38 '. The echo estimator 220b includes a reverse virtual quantizer block 222b which receives the signal v (n) and outputs virtual quantizing points, vq (n). The quantifier of law-μ 34 'of figure 3 and the detected upstream digital deteriorations are modeled as a new equivalent quantifier, a reverse virtual quantizer 222b, by setting thresholds of the equivalent quantifier, as required given the deteriorations detected, as described above. The enhanced echo estimator 220b also includes a RBSl block of DS 224b, which receives the downstream PCM signal, s (n). This signal also passes through the digital loss block of DS 226b and the RBS2 block of DS 228b, which emits a digitally transmitted signal deficient p (n) to the byte-to-linear converter 229b, which converts the octets p (n) in linear values of law-μ pl (n). Law-μ pl (n) linear values are provided to the echo channel block 230b, which is implemented as an FIR filter. The blocks of digital deterioration are designated according to the "digital deteriorations detected by the analogue modem 22." The emission of the echo channel block 230b is the downstream echo of PCM, echo (n), which is provided to the echo. Totalizer 232b: The virtual quantizing points vq (n) and the points y (n), which the digital modem 38 'decodes from v (n) before determining u (n), are also supplied to the totalizer 232b. total sum 232b vq (n), y (n) and echo (n) (vq (n) is positive ey (n) and echo (n) are negative) to form the error signal, error (n), (analog channel error signal) which is feedbacked to the echo channel block 230b. The error signal, error (n), is also transmitted to the analog PCM modem to adapt a directed response p (n) and the prefilter g (n), as described in the co-pending request, Power of Attorney No. CX096044P03, filed on the same date as this one. The more frequent the error signal that is transmitted to the analog PCM modem, the better the adaptation; however, it will be at the expense of the data transmission speed. It is possible to transmit with each symbol only the sign of the error signal and use it for its adaptation without sacrificing too much of the current data transmission speed downstream. The echo channel block 230b, by using the digitally deficient signal pl (n), the error signal, error (n), and a least squares mean algorithm, estimates the downstream echo of PCM, echo (n ), by adapting h (n) as described above with raspe cto to equation (3). Since h (n) is adapted by using the error signal without corrupting by the upstream signal and (n), the adaptation is faster. Another way of obtaining the error signal, error (n), is by using the error signal generator 240 of FIG. 18. The erroneous signal generator 240 includes an octet to linear converter 242 that converts v (n ) in vl (n), which is provided to the totalizer 244. It also includes a law quantifier-μ 246, which receives the decoder values and (n) affected by the estimated echo, echo (n), and emits octets q (n) '. The octets are then modified by the RBSl block of US 248, the digital loss block of US 250 and the RBS2 block of US 252 to form octets v (n) '. The octets v (n) 'are then provided to an octet-to-linear converter 254, which outputs vl (n)' to the totalizer 244. The totalizer 254 sum vl (n) and vl (n) 'and outputs the signal of error, error (n) oe (n). It should be noted that this invention can be incorporated into software and / or firmware that can be stored in a computer-usable medium, such as a computer disk or a memory chip. The invention may also take the form of a computer data signal incorporated in a carrier wave, such as when the invention is incorporated into software / firmware that is transmitted in an electrical manner, for example, over the Internet. The present invention can be incorporated into other specific forms without departing from the spirit or essential characteristics. The described modalities should be considered in all aspects only as illustrative and not restrictive. Accordingly, the scope of the invention is indicated by the appended claims to the above description. All changes that come within the meaning and range within the equivalence of the claims should be considered within their scope.

Claims (65)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and therefore the property described in the following claims is claimed as property. A method for detecting digital deteriorations affecting a modulation channel by upstream pulse code (PCM) in a digital communications network, characterized in that it comprises: receiving, by means of a digital PCM modem interconnected to the digital communications network, a random sequence of digital values selected from a constellation of digital values transmitted on the PCM channel upstream of the digital communications network; establish distributions of the digital values received. each distribution corresponding to one of a plurality of time intervals; and deriving from the distributions the types of signaling of subtracted bits and the digital loss affecting the PCM channel upstream of the digital communication network for each time slot. s or 2. The method according to the claim 1, characterized in that the establishment step includes establishing occurrence tables for the constellation of digital values of the received random sequence by keeping a count of the number of times each of the digital values in the constellation is received, by the modem of Digital PCM during each time interval. 3. The method according to the claim 2, characterized in that there may be a first occurrence of signaling of subtracted bits before the digital loss and a second occurrence of signaling of bits subtracted after the digital loss. 4. The method according to the claim 3, characterized in that the derivation step includes observing the least significant bits of the digital values received in the distributions in order to determine the type of the second signaling occurrence of bits subtracted in each time slot. 5. The method according to the claim 4, characterized in that the derivation step further includes comparing a plurality of deterioration tables, corresponding to different combinations of the first and second occurrences of signaling of subtracted bits and digital loss, with the occurrence tables in order to determine the type of loss that affects the PCM channel upstream of the digital communications network. 6. The method according to the claim 5, characterized in that the comparison step includes comparing a pattern of each of the deterioration tables with the occurrence tables. 7. The method according to the claim 6, characterized in that the comparison stage also includes determining which deterioration tables have null points and comparing the null point patterns of the deterioration tables that have null points with the occurrence tables and determining if any of the null point patterns match with the occurrence tables indicating that the type of digital loss associated with the concordance deterioration table is the type of digital loss that affects the digital. The method according to claim 7, characterized in that the comparison step also includes comparing, when there is no agreement of null point patterns, the probability patterns of the deterioration tables that do not have null points and determining which probability pattern matches with the occurrence table indicating that the type of digital loss associated with the concordance deterioration table is the type of digital loss that affects the digital network. 9. The method according to the claim 8, characterized in that the derivation step further includes comparing a plurality of deterioration tables, corresponding to different combinations of the first and second occurrences of signaling of subtracted bits and digital loss, with the occurrence tables in order to determine the type of the first occurrence of signaling of subtracted bits that affect the PCM channel upstream of the digital communication network for each time interval. 10. The method according to the claim 9, characterized in that the comparison step includes comparing a pattern of each of the deterioration tables with the occurrence tables. 11. The method according to the claim 10, characterized in that the comparison step also includes determining which deterioration tables have null points and comparing the null point patterns of the deterioration tables that have null points with the occurrence tables and determining if any of the null point patterns match with the occurrence tables, indicating that the type of the first occurrence of signaling of subtracted bits associated with the match deterioration table is the type of the first occurrence of signaling of subtracted bits that affects the digital of each time interval. 12. The method according to the claim 11, characterized in that the comparison step further includes comparing, when no null point pattern matches, the probability patterns of the tables of the occurrence table, indicating that the type of the first occurrence of signaling of subtracted bits associated with the table Deterioration of concordance is the type of the first occurrence of signaling of subtracted bits that affects the main network for each time interval. The method according to claim 1, characterized in that the plurality of time intervals are signaling time intervals of subtracted bits. 14. In a digital pulse code modulation (PCM) modem interconnected to the digital communications network and adapted to receive data transmission from an analog PCM modem interconnected to an analog channel, a method for estimating the coefficients of the analog channel, characterized in that it comprises: receiving, by means of the digital PCM modem, a sequence of octets, v (n), from the PCM channel upstream of the digital communications network, whose octets are produced from a sequence of levels transmitted by the analog PCM modem over the analog channel and quantized; determine from the octets received, the digital deteriorations that affect the PCM channel upstream of the digital communications network; convert the received octets to received linear values, vl (n); receive a sequence directed by reference of the levels transmitted by the analog PCM modem; filtering the directed sequence by reference with analog channel filter having analog channel coefficients to produce a filtered directed reference sequence; quantify the directed sequence by filtered reference to produce a sequence of octets directed by reference; modify the sequence of octets directed by reference according to the digital deteriorations, upstream, determined, to produce an estimated sequence of octets, v (n) ', which is an estimate of the sequence of octets received, v (n); convert the estimated sequence of octets, v (n) ', into estimated linear values, vl (n); generate an error signal by taking the difference between the linear values received, vl (n), and the estimated linear values, vl (n) '; and estimate the analog channel coefficients by using the error signal and the directed sequence by reference of the levels. 15. In a modem modulated by digital pulse code (PCM) interconnected to upstream, determined, in virtual quantifying points, vq (n); modifying the octets transmitted downstream from the digital PCM modem according to the predetermined downstream digital impairments in order to produce the modified downstream octets, p (n); convert the downstream modifier octets to modified downstream linear values, pl (n); filter the modified downstream linear values, pl (n), with a downstream echo channel filter that has echo channel coefficients to produce a downstream echo estimate; generate an error signal by adding the virtual quantifying points, vq (n), the estimated downstream echo and decoding y (n); and update the coefficients of the echo channel by using the error signal and modified downstream linear values, pl (n). 16. A device for detecting digital deterioration affecting a modulation channel by upstream pulse code (PCM) in a digital communications network, characterized in that it comprises: reception logic, by means of a digital PCM modem interconnected to the communications network digital, a random sequence of digital values selected from a constellation of digital values transmitted on the PCM channel upstream of the digital communications network; logic for establishing distributions of received digital values, each distribution corresponding to one of a plurality of time intervals; and logic for deriving from the distributions the types of signaling of subtracted bits and digital loss affecting the PCM channel upstream of the digital communication network for each time slot. The device according to claim 16, characterized in that the establishment logic includes logic for the establishment of tables of occurrence with respect to the constellation of digital values of the random sequence received by keeping a count of the number of times received each one of the digital values in the constellation by the digital PCM-56 modem - the digital communications network and adapted to receive the upstream data transmission from an analog PCM modem interconnected to an analog channel, a method to estimate the downstream echo introduced in the data transmission upstream and (n) in the input of a quantization device, originated by the downstream data transmission, from the digital PCM modem to the analog PCM modem, comprising the method : receive, by means of the digital PCM modem, a sequence of octets, v (n), from the channel of PCM upstream of the digital communications network, whose octets are produced from a sequence of levels transmitted by the analog PCM modem over the analog channel and quantized by the quantization device; determine, from the octets received, the digital deteriorations that affect the PCM channel upstream of the digital communications network; decode the received octets a and (n); convert the octets received, based on the quantification device and the digital deteriorations during each time interval. The device according to claim 17, characterized in that there may be a first occurrence of signaling of subtracted bits before the digital loss and a second occurrence of signaling of bits subtracted after the digital loss. The device according to claim 18, characterized in that the derivation logic includes logic for observing the least significant bits of the digital values received in the distributions to determine the t-ipo of the second occurrence of signaling of subtracted bits in each interval of weather. The device according to claim 19, characterized in that the derivation logic further includes logic for comparing a plurality of deterioration tables, corresponding to different combinations of the first and second occurrences of signaling of subtracted bits and digital loss, with the tables of occurrence to determine the type of digital loss that affects the PCM channel upstream of the digital communications network. The device according to claim 20, characterized in that the comparison logic includes logic to compare a pattern of each of the deterioration tables with the occurrence tables. 22. The device according to claim 21, characterized in that the comparison logic also includes logic to determine which deterioration tables have null points and logic to compare the null point patterns of the deterioration tables that have null points with the occurrence tables and to determine if any of the patterns of The null point matches the occurrence tables, indicating that the type of digital loss associated with the concordance deterioration table is the type of digital loss that affects the digital. 23. The device according to claim 33, characterized in that the comparison logic also includes logic to compare, when there are no null point pattern matches, the probability patterns of the deterioration tables that do not have null points and logic to determine which The probability pattern agrees with the occurrence table, indicating that the type of digital loss associated with the concordance deterioration table is the type of digital loss that affects the digital network. The device according to claim 23, characterized in that the derivation logic further includes logic for comparing a plurality of deterioration tables, corresponding to different combinations of the first and second occurrences of signaling of subtracted bits and digital loss, with the tables of occurrence in order to determine the type of the first occurrence of signaling of subtracted bits that affects the PCM channel upstream of the digital communication network for each time interval. 25. The device according to claim 24, characterized in that the comparison logic includes logic to compare a pattern of each of the deterioration tables with the occurrence tables. The device according to claim 25, characterized in that the comparison logic also includes logic to determine which deterioration tables have null points and logic to compare the null point patterns of the deterioration tables that have null points with the occurrence tables and determining whether any of the null point patterns match the occurrence tables indicating that the type of the first occurrence of signaling of subtracted bits associated with the match deterioration table is the type of the first occurrence of signaling of subtracted bits that affects the digital of each time interval. 27. The device according to the indication 26, characterized in that the comparison logic also includes logic to compare, when there is no agreement of the null point patterns, the probability patterns of the deterioration tables that do not have null points and logic for determine which probability pattern matches the occurrence table, indicating that the type of the first occurrence of signaling of subtracted bits associated with the match deterioration table is the type of the first occurrence of signaling of subtracted bits that affects the digital network for each time interval. The method according to claim 16, characterized in that the plurality of time slots are signaling time intervals of subtracted bits. 29. In a digital pulse code modulation (PCM) modem interconnected to the digital communications network and adapted to receive data transmission from an analog PCM modem interconnected to an analog channel, a device for estimating the coefficients of the analog channel, characterized by the device comprising: logic to receive, by means of the digital PCM modem, a sequence of octets, v (n), from the PCM channel upstream of the digital communications network, whose bytes are they produce from a sequence of levels transmitted by the analog PCM modem over the analog channel and quantified; logic to determine from the received octets, the digital deteriorations that affect the PCM channel upstream of the digital communications network; logic to convert the received octets to received linear values, vl (n); logic to receive a sequence directed by reference of the levels transmitted by the analog PCM modem; logic for filtering the directed sequence - by reference with an analog channel filter having analog channel coefficients to produce a filtered reference directed sequence; logic for quantifying the sequence directed by filtered reference to produce a sequence of octets directed by reference; logic to modify the sequence of octets directed by reference according to the digital deteriorations, upstream, determined, to produce an estimated sequence of octets, v (n) ', which is an estimate of the sequence of octets received, v ( n); logic to convert the estimated sequence of octets, v (n) ', into estimated linear values, vl (n); logic to generate an error signal by taking the difference between the linear values received, vl (n), and the estimated linear values, 1 (n) '; and logic to estimate the analog channel coefficients by using the error signal and the sequence directed by reference levels. 30. In a digital pulse code modulation (PCM) modem interconnected to the digital communications network and adapted to receive upstream data transmission from an analog PCM modem interconnected to an analog channel, a device for estimating the downstream echo introduced in the upstream data transmission and (n) in the input of a quantization device, originated by the downstream data transmission, from the digital PCM modem to the analog PCM modem, comprising the device : logic to receive, through the digital PCM modem, a sequence of octets, v (n), from the PCM channel upstream of the digital communications network, whose bytes are produced from a sequence of levels transmitted by the analog PCM modem over the analog channel .y * quantized by the quantization device; logic to determine, from the octets received, the digital deteriorations that affect the PCM channel upstream of the digital communications network; logic to decode the received octets a and (n); logic for converting the received octets, based on the quantification device and the determined upstream digital impairments, into virtual quantifying points, vq (n); logic for modifying the octets transmitted downstream from the digital PCM modem according to the predetermined downstream digital impairments in order to produce the modified downstream octets, p (n); logic for converting modified downstream octets into modified downstream linear values, pl (n); logic for filtering modified downstream linear values, pl (n), with a downstream echo channel filter having echo channel coefficients to produce a downstream echo estimate; logic to generate an error signal by adding the virtual quantizing points, vq (n), the estimated downstream echo and decoding y (n); and logic to update the echo channel coefficients by using the error signal and modified downstream linear values, pl (n). 31. A computer-usable means having computer readable program code means incorporated therein for detecting digital impairments affecting a modulation channel per upstream pulse code (PCM) in a digital communications network, characterized in that it comprises: of computer-readable program code for reception, by means of a digital PCM modem interconnected to the digital communications network, a random sequence of digital values selected from a constellation of digital values transmitted on the PCM channel upstream of the digital communications network; computer readable program code means for establishing distributions of received digital values, each distribution corresponding to one of a plurality of time slots; and computer readable program code means for deriving from the distributions the types of signaling of subtracted bits and digital loss affecting the PCM channel upstream of the digital communications network for each time slot. 32. The computer-usable medium according to claim 31, characterized in that the computer-readable program code means includes computer readable program code means for the establishment of occurrence tables for the constellation of digital values of the sequence random received by maintaining a count of the number of times each of the digital values in the constellation is received by the digital PCM modem during each time interval. 33. The computer-usable medium according to claim 32, characterized in that there may be a first occurrence of signaling of subtracted bits before the digital loss and a second occurrence of signaling of bits subtracted after the digital loss. 34. The computer-usable medium according to claim 33, characterized in that the computer-readable program code means include computer-readable program code means for observing the least significant bits of the digital values received in the distributions to determine the type of the second occurrence of signaling of subtracted bits in each time interval. 35. The computer-usable medium according to claim 34, characterized in that the derivative computer-readable program code means further includes computer readable program code means for comparing a plurality of deterioration tables, corresponding to different combinations of the first and second occurrences of signaling of subtracted bits and digital loss, with the occurrence tables to determine the type of digital loss that affects the PCM channel upstream of the digital communications network. 36. The computer-usable medium according to claim 35, characterized in that the computer-readable program code means includes computer readable program code means for comparing a pattern of each of the deterioration tables with the tables of idea. 37. The computer-usable medium according to claim 36, characterized in that the comparison computer-readable program code means further includes computer readable program code means for determining which deterioration tables have null points and logic for comparing the dot patterns null of impairment tables that have null points with tables 4 © occurrence and determine if any of the null point patterns match the occurrence tables, indicating that the type of digital loss associated with the concordance deterioration table is the type of digital loss that affects the digital. 38. The computer-usable medium according to claim 37, characterized in that the comparison computer-readable program code means further includes computer readable program code means for comparing, when there are no null point pattern matches, the probability patterns of the deterioration tables having no points. null and computer readable program code means to determine which probability pattern matches the occurrence table, indicating that the type of digital loss associated with the concordance deterioration table is the type of digital loss that affects the digital network. 39. The computer-operable medium according to claim 38, characterized in that the derivative computer-readable program code means further includes computer readable program code means for comparing a plurality of deterioration tables, corresponding to different combinations of the first and second occurrences of signaling of subtracted bits and digital loss, with the occurrence tables in order to determine the type of the first occurrence of signaling of subtracted bits affecting the PCM channel upstream of the digital communication network for each interval of time . 40. The computer-readable medium according to claim 39, characterized in that the computer-readable program code means includes computer readable program code means for comparing a pattern of each of the deterioration tables with the tables of the computer. idea. 41. The computer-usable medium of claim 40, characterized in that the comparison computer-readable program code means further includes computer readable program code means for determining which deterioration tables have null points and comparing the dot patterns. null of deterioration tables that have null points with occurrence tables and computer readable program code means to determine if any of the null point patterns match the occurrence tables indicating that the type of first occurrence of signaling of subtracted bits associated with the match deterioration table is the type of the first occurrence of signaling of subtracted bits that affects the digital of each time interval. 42. The computer-usable medium according to claim 41, characterized in that the comparison computer-readable program code means further includes computer readable program code means for comparison, when there is no agreement of the null point patterns, the probability patterns of impairment tables that do not have null points and program code means "readable by computer to determine which probability pattern matches the occurrence table, indicating that the type of the first occurrence of signaling of subtracted bits associated with the table of deterioration of agreement is the type of the first occurrence of signaling of subtracted bits that affects the digital network for each time interval 43. The computer-usable medium according to claim 31, characterized in that the plurality of time intervals. they are signaling time intervals of subtracted bits. A computer-usable means having computer readable program code means thereon for estimating the coefficients of the analog channel for use in a digital pulse code modulation (PCM) modem interconnected to the digital communications network and adapted for receiving data transmission from an analog PCM modem interconnected to an analog channel, characterized in that it comprises: computer readable program code means for receiving, by means of the digital PCM modem, a sequence of bytes, v (n ), from the PCM channel upstream of the digital communications network, whose octets are produced from a sequence of levels transmitted by the analog PCM modem over the analog channel and quantized; computer readable program code means for determining from the bytes received, the digital impairments affecting the PCM channel upstream of the digital communications network; computer-readable program code means for converting the received octets into received linear values, vl (n); computer readable program code means for receiving a sequence directed by reference of the levels transmitted by the analog PCM modem; computer-readable program code means for filtering the reference-directed sequence with an analog channel filter having analog channel coefficients to produce a filtered reference directed sequence; computer readable program code means for quantifying the directed sequence by filtered reference to produce a sequence of directed bytes by reference; computer readable program code means to modify the sequence of octets directed by reference according to the digital impairments, upstream, determined, to produce an estimated sequence of octets, v (n) ', which is an estimate of the sequence of octets received, v (n); computer readable program code means to convert the estimated sequence of. octets, v (n) ', in estimated linear values, vl (n)'; computer readable program code means to generate an error signal by taking the difference between the received linear values, vl (n), and the estimated linear values, vl (n) '; and computer readable program code means for estimating the analog channel coefficients by using the error signal and the reference directed sequence of the levels 45. A computer-usable medium having computer readable program code means incorporated in it to estimate the downstream echo introduced in the data transmission upstream and (n) in the input of a quantization device, originated by the downstream data transmission, from a digital PCM modem to a data modem. Analogue PCM, for use in a digital pulse code modulation (PCM) modem interconnected to the digital communications network and adapted to receive the upstream transmission of the analog PCM modem interconnected to an analog channel, the method comprising: computer readable program code to receive, through the digital PCM modem, a sequence of octets, v (n), from the PCM channel upstream of the digital communications network, whose octets are produced from a sequence of levels transmitted by the analog PCM modem over the analog channel and quantized by the analogue device. quantification; computer readable program code means for determining, from the octets received, the digital impairments affecting the PCM channel upstream of the digital communications network; computer readable program code means for decoding the received octets a and (n); computer-readable program code means for converting received octets, based on the quantization device and determined upstream digital impairments, into virtual quantifying points, vq (n); computer readable program code means for modifying the octets transmitted downstream from the digital PCM modem according to the predetermined downstream digital impairments in order to produce the modified downstream octets, p (n); computer readable program code means for converting modified downstream octets into modified downstream linear values, pl (n); computer-readable program code means for filtering modified downstream linear values, pl (n), with -7! a downstream echo channel filter that has coefficients "~ of echo channel p" to ra p rOdu c i r a downstream echo estimate; computer readable program code means to generate an error signal by adding the virtual quantizing points, vq (n), the estimated downstream echo and decoding y (n); and computer readable program code means for updating the coefficients of the echo channel by using the error signal and modified downstream linear values, pl (n). 46. A computer data signal incorporated in a carrier wave, wherein computer-readable program code means for detecting digital impairments affecting an upstream pulse code modulation channel are incorporated into the computer data signal. (PCM) in a digital communications network, characterized in that it comprises: computer readable program code means for reception, by means of a digital PCM modem interconnected to the digital communications network, a random sequence of digital values selected from a constellation of digital values transmitted over the PCM channel upstream of the digital communications network; computer readable program code means for establishing distributions of received digital values, each distribution corresponding to one of a plurality of time slots; and computer readable program code means for deriving from the distributions the types of signaling of subtracted bits and digital loss affecting the PCM channel upstream of the digital communications network for each time slot. 47. The computer data signal according to claim 46, characterized in that the computer-readable program code means includes computer readable program code means for the establishment of occurrence tables for the constellation of digital values of the computer. random sequence received by keeping a count of the number of times each of the digital values in the constellation is received by the digital PCM modem or during each time interval. 48. The computer data signal according to claim 47, characterized in that there may be a first occurrence of signaling of subtracted bits before the digital loss and a second occurrence of signaling of subtracted bits after the digital loss. 49. The computer data signal according to claim 48, characterized in that the computer readable program code means include computer readable program code means for observing the least significant bits of the digital values received in the distributions for determine the type of the second occurrence of signaling of subtracted bits in each time interval. 50. The computer data signal according to claim 49, characterized in that the derivative computer-readable program code means further includes computer readable program code means for comparing a plurality of deterioration tables, corresponding to different combinations of the first and second occurrences of signaling of subtracted bits and digital loss, with the occurrence tables to determine the type of digital loss affecting the PCM channel upstream of the digital communications network. 51. The computer data signal according to claim 50, characterized in that the computer-readable program code means includes computer readable program code means for comparing a pattern of each of the impairment tables with the tables. of occurrence 52. The computer data signal according to claim 51, characterized in that the comparison computer-readable program code means further includes computer readable program code means for determining which deterioration tables have null points and code means of computer readable program to cover the null point patterns of the deterioration tables that have null points with the occurrence tables and determine if any of the null point patterns match the occurrence tables, indicating that the type of digital loss associated with the match deterioration table is the type of digital loss that affects the digital. 53. The computer data signal according to claim 52, characterized in that the comparison computer-readable program code means further includes computer readable program code means for comparing, when there are no null point pattern matches, the probability patterns of deterioration tables that do not have null points and computer readable program code means for • determine which probability pattern matches the occurrence table, indicating that the type of digital loss associated with the match deterioration table is the type of digital loss that affects the digital network. 54. The computer data signal according to claim 53, characterized in that the derivative computer-readable program code means further includes computer readable program code means for comparing a plurality of deterioration tables, corresponding to different combinations of the first and second occurrences of signaling of subtracted bits and digital loss, with the occurrence tables in order to determine the type of the first occurrence of signaling of subtracted bits affecting the PCM channel upstream of the digital communication network for each time interval. 55. The computer data signal according to claim 54, characterized in that the computer-readable program code means includes computer readable program code means for comparing a pattern of each of the impairment tables with the tables. of occurrence 56. The computer data signal according to claim 55, characterized in that the comparison computer-readable program code means further includes computer readable program code means to determine which deterioration tables have null points and compare the patterns of null point of the 4-deterioration tables that have null points with the occurrence tables and computer readable program code means to determine if any of the null point patterns match the occurrence tables indicating that the type of the first occurrence of subtracted bit signaling associated with the match deterioration table is the type of the first occurrence of signaling of subtracted bits that affects the digital of each time slot. 57. The computer data signal according to claim 56, characterized in that the comparison computer-readable program code means further includes computer readable program code means for comparison, when there is no agreement of the null point patterns, the probability patterns of the impairment tables that do not have null points and computer readable program code means to determine which probability pattern matches the occurrence table, indicating that the type of the first occurrence of the subtracted bit signaling associated with the match deterioration table is the type of the first occurrence of signaling of subtracted bits that affects the digital network for each time interval. 58. The computer data signal according to claim 46, characterized in that the plurality of time slots are signaling time intervals of subtracted bits. 59. A computer data signal on a carrier wave, wherein computer-readable program code means are incorporated into the computer data signal to estimate the coefficients of the analog channel for use in a pulse code modulation modem digital (PCM) interconnected to the digital communications network and adapted to receive data transmission from an analog PCM modem interconnected to an analog channel, characterized in that it comprises: computer readable program code means to receive, by means of the digital PCM modem, a sequence of octets, v (n), from the PCM channel upstream of the digital communications network, whose octets are produced from a sequence of levels transmitted by the analog PCM modem over the analog and quantified channel; computer readable program code means to determine from the octets received, the digital deteriorations affecting the PCM channel upstream of the digital communications network; computer-readable program code means for converting the received octets into received linear values, vl (n); computer readable program code means for receiving a sequence directed by reference of the levels transmitted by the analog PCM modem; computer-readable program code means for filtering the reference-directed sequence with an analog channel filter having analog channel coefficients to produce a filtered reference directed sequence; computer readable program code means for quantifying the directed sequence by filtered reference to produce a sequence of directed bytes by reference; computer-readable program code means to modify the sequence of octets directed by reference according to the digital impairments, upstream, determined, to produce an estimated sequence of octets, v (n) ', which is an estimate of the sequence of octets received, v (n); computer readable program code means for converting the estimated sequence of octets, v (n) ', into estimated linear values, vl (n)'; computer readable program code means to generate an error signal by taking the difference between the linear values received, vl (n), and the estimated linear values, vl (n) '; and computer readable program code means for estimating the analog channel coefficients by using the error signal and the directed sequence by reference of the levels. 60. A computer data signal incorporated into a carrier wave, wherein computer-readable program code means are incorporated into the computer data signal to estimate the downstream echo introduced in the upstream data transmission and ( n) at the input ie a quantization device, originated by the downstream data transmission, from a digital PCM modem to an analog PCM modem, for use in a digital pulse code modulation (PCM) modem interconnected to the digital communications network and adapted to receive the upstream transmission of the analog PCM modem interconnected to an analog channel, the method comprising: computer readable program code means for receiving, by means of the digital PCM modem, a sequence of octets , v (n), from the PCM channel upstream of the digital communications network, whose octets are produced in from a sequence of levels transmitted by the analog PCM modem over the analog channel and quantized by the quantization device; computer readable program code means for determining, from the octets received, the digital impairments affecting the PCM channel upstream of the digital communications network; computer readable program code means for decoding the received octets a and (n); computer readable program code means for converting received octets, based on the quantization device and determined upstream digital impairments, into virtual quantifying points, vq (n); computer readable program code means for modifying the octets transmitted downstream from the digital PCM modem according to the predetermined downstream digital impairments in order to produce the modified downstream octets, p (n); computer readable program code means for converting modified downstream octets into modified downstream linear values, pl (n); computer-readable program code means for filtering the modified downstream linear values, pl (n), with a downstream echo channel filter having echo channel coefficients to produce a downstream echo estimate; computer readable program code means to generate an error signal by adding the virtual quantizing points, vq (n), the estimated downstream echo and decoding and (n); and computer readable program code means for updating the coefficients of the echo channel by using the error signal and modified downstream linear values, pl (n). 61. The method according to the claim 2, characterized in that the derivation step includes the elimination of certain types of RBS and digital loss since types affecting the digital communications network are possible when there are received digital values that exceed a predetermined value. 62. The device according to claim 17, characterized in that the derivation logic includes logic to eliminate certain types of RBS and digital loss since types affecting the digital communications network are possible when there are received digital values that exceed a predetermined value. 63. The computer-usable medium according to claim 32, characterized in that the computer readable program code means for deriving includes computer readable program code means for eliminating certain types of RBS and digital loss since it is possible types that they affect the digital communications network when there are received digital values that exceed a predetermined value. 64. The computer data signal according to claim 47, characterized in that the computer-readable program code for derivation includes computer readable program code means for eliminating certain types of RBS and digital loss since types affecting the digital communications network when there are received digital values that exceed a predetermined value. 65. In a digital pulse code modulation (PCM) modem interconnected to the digital communications network and adapted to receive the transmission of an analog PCM modem interconnected to an analog channel, a method to estimate the coefficients of the analog channel and for estimating the downstream echo introduced in the upstream data transmission at the input of a quantization device, originated by the downstream data transmission, from the digital PCM modem to the analog PCM modem, characterized in that it comprises: receiving , through the digital PCM modem, a sequence of octets, v (n), from the PCM channel upstream of the digital communications network, whose octets are produced from a sequence of levels transmitted by the analog PCM modem over the analog channel and they are quantified; determine from the octets received the digital deteriorations affecting the PCM channel upstream of the digital communications network; convert the received octets to received linear values, vl (n); receive a sequence directed by reference of the levels transmitted by the analog PCM modem; filtering the directed sequence by reference with an analog channel filter having analog channel coefficients to produce a filtered directed reference sequence; add an estimated downstream echo to the sequence directed by filtered reference; quantify the directed sequence by filtered reference to produce a sequence of octets directed by reference; modify the sequence of octets directed by reference according to the determined upstream digital impairments to produce an estimated sequence of octets, v (n) ', which is an estimate of the sequence of octets "received, v (n); the estimated sequence of octets, v (n) 'in estimated linear values, vl (n)', generating an error signal when taking the difference between the linear values received, vl (n), and the estimated linear values, vl ( n) 'and estimate the coefficients of the analogue channel by using the error signal and the directed sequence by reference of the levels, modifying the octets transmitted downstream from the digital PCM modem according to predetermined downstream digital deteriorations in order to produce modified downstream octets, p (n), convert the modified downstream octets to modified downstream linear values, pl (n), filter the modified downstream octets in val Modified downstream linear ores, pl (n), filter modified downstream linear values, pl (n), with a downstream echo channel filter that has echo channel coefficients to produce an estimated downstream echo; and update the echo channel coefficients by using the error signal and modified downstream linear values, pl (n).