EP2436174A1

EP2436174A1 - Method for correcting telephone signal degradation caused by the length of the analog line via the receiver

Info

Publication number: EP2436174A1
Application number: EP10724043A
Authority: EP
Inventors: Gilles Bourgoin
Original assignee: Sagemcom Broadband SAS
Current assignee: Sagemcom Broadband SAS
Priority date: 2009-05-29
Filing date: 2010-05-27
Publication date: 2012-04-04
Also published as: US20120063588A1; FR2946213A1; BRPI1012840A2; CN102439958B; CN102439958A; WO2010136518A1; US9363364B2; FR2946213B1

Abstract

The present invention relates to the field of telephony and specifically to a method for correcting the degradation of telephone signal quality caused by analog lines. The invention describes managing, via the receiver, a specific correction of telephone signal degradation caused by the length of the analog line between the parties. Said line length between the receiver and the telephone switchboard to which said receiver is connected is stored in the receiver. Advantageously, the line lengths between the receiver of the called party and the corresponding switchboard are stored, for example in the directory of the apparatus. During a call, said line length is taken into account by a specific correction means for said correction inside the receiver.

Description

Method for correcting the degradation of the telephone signal caused by the analog line length by the handset

The present invention relates to the field of telephony and more particularly to a method for correcting deteriorations in the quality of the telephone signal generated by the analogue lines. Unlike digital telephones such as mobile phones or Internet Protocol (IP) telephones, analog telephones are connected to a switchboard via an analog line that can vary in length from a few meters to several kilometers. The telephone signal carrying the voice of the interlocutor is transmitted analogically on this line. This analog transmission generates a degradation of the telephone signal. This degradation results in a reduction and a change of timbre of the voice. It is dependent on the total length of analog line between the two interlocutors whether on the side of the caller or the recipient of the call.

Today, in the phones of the state of the art, this degradation is not corrected specifically. Some phones include an equalizer in the handset to generate a gain curve depending on the frequency for signals recorded by the microphone or emitted by the speaker. This equalizer is used to correct distortions of the telephone signal due to the physical properties of the handset in which the microphone and loudspeaker are inserted. Some handsets offer the user the ability to adjust this equalizer to suit their tastes. This setting is then applied to all calls, it does not take into account the lengths of analog line between the interlocutors.

The invention aims to solve the above problems by the management by the handset of a specific correction of the degradation of the telephone signal due to the length of analog line between the interlocutors. This line length between the handset and the switchboard to which it is connected is stored on the handset. Advantageously, the line lengths between the receiver's handset and its switchboard are stored, for example in the directory of the device. During a call, this line length is taken into account by means of specific correction of this correction within the handset. A telephone handset includes means for storing an analog line length between the subscriber and the receiver of a call and means for specifically correcting the degradation of the telephone signal caused by the analog line length.

According to a particular embodiment of the invention, the means for storing the analog line length comprise means for storing a local analog line length between the subscriber and the telephone network and means for storing a remote analog line length. between the telephone network and the recipient of the call. Means for specifically correcting the degradation of the telephone signal driven by the remote analog line length include means for correcting the local and remote analog line length.

According to a particular embodiment of the invention, the handset comprises means for selecting an operating mode from the following modes:

- a declutched mode of correction where no correction of the degradation of the telephone signal driven by the length of analog line is carried out;

a local correction mode in which only the degradation of the telephone signal caused by the local analog line length is performed;

a remote correction mode in which only the degradation of the telephone signal driven by the remote analog line length is performed; - A total correction mode where the degradation of the telephone signal driven by the local and distant analog line length is performed.

According to a particular embodiment of the invention, the correction means comprise a digital equalizer programmed by a continuous gain function as a function of the analog line distance to be corrected and the frequency of the telephone signal.

According to a particular embodiment of the invention, the correction means comprise means for applying gain stages as a function of the analog line distance to be corrected and the frequency of the telephone signal. According to a particular embodiment of the invention, the means for applying the gain stages consist of analog filters.

The invention also relates to a method for correcting the degradation of the telephone signal caused by the analog line length between the interlocutors, which comprises a step of obtaining the analog line length to be corrected and a programming step of the correction means. function of said analog line length obtained.

The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of an exemplary embodiment, said description being given in relation to the attached drawings, among which:

Fig. 1 illustrates the overall architecture of the telephone network,

Fig. 2 illustrates the connection of an analogue handset to the telephone network,

Fig. 3 illustrates the impairments affecting the telephone signal transmitted by an analog line, FIG. 4 illustrates the architecture of an exemplary embodiment of the invention,

Fig. 5 illustrates the correction bearings used in a particular embodiment of the invention.

Today's modern telephone network is made up of multiple networks that connect different handsets with different technologies. This is schematically illustrated in FIG. 1. The conventional telephone network, called the PSTN network for Switched Telephone Network 1.1, allows you to connect analog 1.5 and 1.8 handsets. During the development of mobile telephony, the network RTC has been connected to this mobile network 1.2, called GSM network (Global System for Mobile Communications in English). From this In fact, mobile handsets 1.4 and 1.7 can communicate with each other, but also with analog handsets 1.5 and 1.8. At the same time, the global Internet 1.3 data transfer network has developed connecting various information processing devices. On this network, digital voice transfer technologies have been developed, paving the way for the emergence of IP-based digital telephony known as VoIP (Vox over IP), which now allows the connection of handsets. based on these technologies. These handsets, integrating the computers, allow to establish telephone communications between them and also to analog handsets of the PSTN network and mobile handsets of the GSM network. The name GSM network covers here all mobile networks, regardless of the protocol actually used, such as GPRS, UMTS or protocols grouped under the name of 3G protocols.

This is called telephone handset any electronic device for making a phone call. This definition includes, in particular, analogue telephony terminals including DECT (Digital Enhanced Cordless Telephone) type handsets, mobile telephony terminals, computers equipped with telephony software, certain personal assistants, certain GPS terminals embedded in vehicles or others. Apart from the analog handsets connected to the PSTN network, most of these handsets are digital. An analog handset is a handset transmitting the voice signal transmitting the voice analogically, typically on an analog line. This category includes cordless or cordless telephones, typically DECT or Cat-IQ (Cordless Advanced Technology), where the base is connected in analog to the telephone exchange while communicating digitally with handsets. strictly speaking according to a radio transmission technology. In the latter case, the concept of handset is extended to the base, the invention can be implemented within the handsets or in the base. A digital handset is a handset where the voice-transmitting telephone signal is digitally converted on the handset and the handset transmits a digital telephone signal to transmit the voice to the network.

Fig. 2 illustrates the operation of the transmission of the telephone signal between an analogue handset and the telephony network. Handset 2.1 is connected by an analogue line to the telephony central office 2.2. The central office is itself connected by a digital communication network to the telephony network 2.3. When the terminal 2.1 establishes a communication with an interlocutor, its voice is transformed into an analog telephone signal by the microphone of the handset. This telephone signal is then transmitted on the analog line to the central office 2.2. This analog telephone signal is then converted into digital by the central office. It is then a digital telephone signal carrying the voice that is transmitted via the telephony network 2.3 to the recipient.

When this recipient is also equipped with an analog handset, the reverse operation is performed. The telephone signal arrives digitally to the recipient's telephone exchange. It is then converted to analog by this central and then transmitted analog to the handset via the analog line connecting the central to the handset to be restored by the speaker of the handset. The recipient's voice follows an identical transmission pattern in the opposite direction. When this receiver is equipped with a digital handset, the digital telephone signal is transmitted to the handset and is converted into analog in the handset to power the speaker. Here too, the recipient's voice follows an identical path in the opposite direction. In this case, the line length is zero on the recipient side. Fig. Figure 3 illustrates the degradation of the telephone signal as a function of frequency for different line lengths. It can be seen that the telephone signal is overall attenuated. This attenuation varies from the order of 6 dB in the 300 Hz frequency range between a zero distance and a distance of 3.5 km. At this latter distance, it is also noted that the attenuation is 8 dB higher for a 1300 Hz frequency compared to a 300 Hz frequency. During a communication involving at least one analog handset, the voice signal of the transmitted voice is therefore degraded. This degradation is non-uniform depending on the frequency and depends on the total analog line length traversed by the telephone signal between the interlocutors. It is possible to correct this degradation by applying a suitable equalization of the telephone signal. This correction makes it possible to correct the relatively greater attenuation of the high frequencies compared to the low frequencies.

It can, for example, be made by applying the following formula:

C = L ≡ 20

7 Qog _Λ (F) - 2> where F is the frequency expressed in Hz, L is the length of line to be corrected in km and which gives the correction C for this frequency in the form of a gain in dB to be applied to the telephone signal.

Fig. 4 illustrates an exemplary embodiment of the invention. In this example, the invention is implemented in the handset of a DECT 4.1 home wireless telephone system. In this system, the telephone signal is received numerically 4.6 from the DECT base itself connected in analog to the central office. The telephone signal is then decoded by the coding 4.4. It then undergoes equalization processing done by the equalizer 4.5 before being converted to analog by an analog digital converter or Can to be emitted by the speaker 4.8. The voice picked up by the microphone 4.7 is converted to digital by a Can before being subjected to equalization processing by the equalizer 4.5 before being encoded by the codec 4.4 to be sent to the network by the digital wireless interface 4.6. The handset operates under the control of a 4.2 processor. This processor runs a set of control software housed in a memory space 4.3. It controls in particular the decoding coding module 4.4 and the digital equalizer 4.5. This equalizer is typically used to correct the deformations of the sound generated by the particular implementation of the transducers within the handset. According to the invention, the memory 4.3 also constitutes a means for storing the analog line length between the subscriber and the telephone network called local analog line length. Typically, this memory also contains the telephone directory of the subscriber. Advantageously, this directory also contains for each recipient in the directory information on the analog line length between the recipient's handset and the telephone network called remote analog line length. This line length is set to zero in the case of a mobile or IP-based handset.

The presence in the information storage means 4.3 of these analog line lengths, both local and remote, allows the call management software to program the equalizer 4.5 to specifically correct the degradation of the telephone signal caused by the length. analog line. This digital equalizer can be programmed using the function described in the equation above which then constitutes a continuous gain function as a function of the analog line distance to be corrected and the frequency of the telephone signal. This software with the line length information present in the storage means of the memory 4.3 and the equalizer 4.5 is then a means of specific correction of the degradation of the telephone signal caused by the analog line length between the two parties during a call.

Advantageously, the same correction is applied to the telephone signal received from the recipient of the call and to the telephone signal sent to the recipient of the call.

This correction means then comprises means for calculating the total length of analog line associated with a given call, means for programming the equalizer to correct the degradation of the telephone signal caused by this analog line length. It then performs a method of correcting the degradation of the telephone signal driven by the analog line length which comprises a step of obtaining the analog line length to be corrected and a programming step of the correction means according to said length of line. analog line obtained.

Advantageously, the correction can be made according to several modes. In a first mode, called total mode, the equalizer is programmed to correct the degradations caused by the entire length of analog line, local and remote, between the subscribers. In a second mode, called local mode, only the local analog line length is corrected and not the remote analog line length. In a third mode, called remote mode, only the remote analog line length is corrected and not the local analog line length. Finally a fourth mode, said mode disengaged, no correction is made. Advantageously, these different modes can be selected by the user during a call. This makes it possible, among other things, to be able to manage a call between two devices having the invention and to avoid a double correction that would be made by the two devices and which would both correct all of the local and remote degradation. In this embodiment, the correction is therefore performed continuously as a function of frequency.

The invention can be implemented by an analog telephone handset as described in the exemplary embodiment. But it can also be implemented by a digital telephone handset. In this case, the local analog line length is zero, only one can be corrected, if necessary, the degradation of the telephone signal driven by the remote analog line length.

The correction can be entrusted to an equalizer present in the handset for other corrections or to a specific equalizer dedicated to this correction as appropriate. Alternatively, the correction can be carried out not continuously, but by applying incremental gains as a function of frequency and distance. This embodiment can be advantageous on low cost handsets. Fig. 5 illustrates an example of the steps applicable in this embodiment. In this table, the low frequencies are the frequencies between 300 Hz and 1 kHz, while the high frequencies are the frequencies between 1 kHz and 3 kHz. It indicates for each distance the gain values to be programmed to correct the degradation of the telephone signal caused by the analog line length.

Alternatively, for example in a fully analog handset where the telephone signal is not converted to digital, the correction can be performed by applying analog filters. Advantageously, the method then uses bearings, for example those of FIG. 5, to select the right filters according to the distance and frequency of the telephone signal.

Claims

1 / Telephone handset, characterized in that it comprises: - means (4.3) for storing a local analog line length between the subscriber and the telephone network;

means (4.3) for storing a remote analog line length between the telephone network and the recipient of the call;

means for specifically correcting the degradation of the telephone signal driven by the remote analog line length and means for correcting the local analog line length.

2 / handset according to claim 1, characterized in that it comprises means for selecting an operating mode from the following modes:

a local correction mode in which only the degradation of the telephone signal caused by the local analog line length is performed; a remote correction mode in which only the degradation of the telephone signal driven by the remote analog line length is performed;

- A total correction mode where the degradation of the telephone signal driven by the local and distant analog line length is performed.

3 / telephone handset according to one of claims 1 to 2, characterized in that the correction means comprise a digital equalizer programmed by a continuous gain function according to the analog line distance to be corrected and the frequency of the telephone signal .

4 / telephone handset according to one of claims 1 to 2, characterized in that the correction means comprises means for applying gain stages depending on the analog line distance to correct and the frequency of the telephone signal. 5 / handset according to claim 4, characterized in that the means for applying the gain stages consist of analog filters.

6 / A method for correcting the degradation of the telephone signal caused by the analog line length between the interlocutors, characterized in that it comprises:

a step of obtaining the local analog line length to be corrected;

a step of obtaining the remote analog line length to be corrected, and

a step of programming the correction means as a function of said obtained analog line length.