MXPA99006695A - Dynamic echo canceller and parameter selection in telephony systems - Google Patents

Abstract

An echo canceller pool configuration (110) is provided that allows a user (102) to predetermine and individualize the echo cancellation parameter settings (Fig. 8) for any echo canceller in the pool, based on prior knowledge of the echo path characteristics of the specific transmission route to be used for an ensuing call. The echo canceller with the individualized parameter settings is then switched into that route for the duration of the call. For example, at call setup, once a trunk route has been identified that will be used to complete the call, a"flag"is retrieved that is associated with that specific route. That"flag"identifies specific echo canceller parameter settings to be used for that route. Those parameter settings are downloaded to the echo canceller device selected from the pool (110), and that device is then switched into the specific trunk involved.

Description

CANCELLED-. DYNAMIC ECO AND SELECTION OF PARAMETERS IN TELEPHONE SYSTEMS BACKGROUND OF THE INVENTION Technical Field of the Invention The present invention relates in general to the field of telecommunications and. in particular, with the dynamic selection of echo cancellers and echo cancellation parameters in telephony systems.

Description of the Related Art The quality of speech has become a highly competitive factor in the erratastica of telephony systems. The echo which is a phenomenon typically caused by imperfect impedance matching of network transmission sections. has a significant impact on the general quality of speech in telephone systems. Specifically, the primary cause of echo in many telephony systems in Xa is impedance matching between connected network transmission sections of two wires and four wires. For example, Figure 1 is a schematic block diagram illustrating how the echo in a Public Switched Telephone Network (PSTN) can occur. How I know - % - shows in a typical arrangement, a PSTN subscriber telephone 1 is connected by a two-wire transmission line to a hybrid interface circuit 1 *. The hybrid circuit (l1) functions to convert from the access line of two telephone wires to the four-wire transmission line of the PSTN (needed for two-way communications). Similarly, a second PSTN subscriber telephone 2 is connected via a two-wire transmission line to a second hybrid 2 'circuit, which also converts two wires to four wires. Since each hybrid is a non-ideal circuit, the mismatch of impedance in each hybrid (! ', 2') occurs between the two-wire lines and the four-wire line, which reflects a portion of the incoming speech energy. from the line of four wires again to each of the respective subscriber telephones (1, 2). This reflected speech energy, or echo, is typically a distorted and delayed replica of the outgoing speech reflected from the other side of the subscriber. In Figure 1, the respective energy reflections (echoes) for subscribers 1 and 2 are illustrated by dotted arrows 1"and 2". In general, as long as the reflected energy transmission delay time is relatively short (eg, 25 ms.), The reflected speech energy is usually not perceived as annoying, however, when the delay it increases beyond 25 ms, the reflected energy is normally perceived as an annoyed "echo speech", the higher the delay time, the more annoying and / or confused the echo is made. graph illustrating the echo attenuation required as a function of transmission delay time As shown, the total echo return loss (ERL) can be plotted as a delay time function to generate an echo tolerance curve, As the delay increases above 25 ms, echo control procedures are required. In summary, the echoes become more annoying as the network transmission path delay times increase. Transmission signals can be entered in a number of ways, such as by propagating speech signals over long distances, or by the process of encoding transmitted speech signals. For example, significant propagation delays occur during satellite communication transmissions for intra- and intercontinental calls. The geostationary satellite (due to its substantial distance from the ground) typically introduces a transmission path delay of an address of approximately 260 ms, or a total (round trip) echo path delay of approximately 520 ms. Figure 3 is a diagram showing link satellite communications &; illustrates how such a system introduces a significant transmission path (echo) delay. Digital cellular communications systems also introduce significant echo path delays. For example, the speech and channel coding used for fault tolerance in cellular digital communications system radio transmissions introduces a transmission path delay of an address of approximately 100 ms, as blocks of speech samples are transmitted. and retransmit through the air interface. Figure 4 is a diagram showing a digital cellular communication system and illustrates said echo path delay. The echo cancellers are electronic devices that are used to suppress the effects of echoes in telephony systems. For example, for connections with long transmission delays between subscribers (eg, Figure 1), two echo cancellers are typically used (one on either side of the transmission path that causes the delay). For long-distance satellite communication systems (see Fig. 3) that link to PSTNs, a canceller d $ fco is typically placed in each of the gate switches or transit nodes (e.g., in international switching centers or ISCs) associated with each local exchange, but "oriented" to the respective PSTN. In a digital cellular communications system (e.g., Figure 4) that is linked to a PSTN, an echo canceller is typically placed in a mobile service switching center (MSC) and also "oriented" to the PSTN. Figure 5 is a simplified schematic block diagram illustrating two echo canceller configurations that can be used in existing telephony systems: (1) echo echo cancellers, and (2) echo cancellers in a pool configuration (ECP) ). In the examples illustrated by Figure 5, three trunk lines (2, 4, 8) are shown, each of which connects a PSTN transmission line (11) to a digital cellular system 12 through a switch 10 group (e.g., part of an MSC) for speech communications between them. The group switch 10 can be a component of a digital switching system, such as, for example, a digital switching system AXE 10 manufactured by Ericsson Telecom AB. An echo canceller device 14 is physically connected to the trunk line 2. The electrical parameter settings for the echo echo canceller 14 are controlled by the echo canceller control circuit 16. An exchange terminal circuit 18 is connected between the trunk echo canceller 14 and the group switch 10. An echo canceller tank 30 is associated with the group switch 10. A plurality of echo cancellers is maintained in the cluster (30) to form a part of the trunk signaling subsystem (TSS) of the digital switching system. A conventional echo canceller cluster 30 may be, for example, an ECP 101 product, which is manufactured by Ericsson Telecom AB. As shown, no echo echo canceller is physically placed in the trunk 8. Instead, when a call is initiated between the PSTN (11) and the digital cellular system (12), the traffic control subsystem (TCS) of the digital switching system selects one of the echo cancellers in the cluster (30) and directs the switch 10 to guide the connection through the selected echo canceller for the duration of the call. In this way, a more efficient use of the echo cancellers is possible and, thus, the total number of echo cancellers needed is reduced, compared to the previous configurations of the backbone echo canceller. Likewise, there is an increased reliability over the previous systems, because there are always some echo cancellers available in the grouping, which can be used in case one or more of the other echo cancellers develop a fault. Even though the use of echo canceller grouping configurations has increased the flexibility and reliability of existing telephony systems, there is still a significant problem with respect to echo cancellation. Specifically, all echo cancellers in each existing grouping are configured with the same cancellation parameters, which significantly limits the flexibility of existing telephony systems.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide individual echo cancellation parameter settings for specific echo cancellers in a cluster. It is also an object of the present invention to provide a dedicated grouping of echo cancellers. echo for certain high priority transmission paths in a telephony system, Another object of the present invention especially to make echo cancellers for specific trunk routes in a telephony system, Still another object of the present invention is to create a free clustering of congestion of echo cancellation devices. A further object of the present invention is to minimize the echo and thus improve the speech quality of telephony systems. In accordance with the present invention, the above and other objects are achieved by a method and apparatus, wherein an echo canceller grouping configuration is provided which allows a user to predetermine and individualize the echo cancellation parameter settings for any echo canceller in the pool, based on prior knowledge of the echo path characteristics of the specific transmission address to be used for an incoming call. The echo canceller with the individualized parameter settings is then switched to that route during the term of the call. For example, at the beginning of the call, once a trunk guide has been identified to be used to complete the call, a traffic control system removes a "flag" from a memory address associated with this specific address. That "flag" identifies specific settings of the echo canceller parameter that will be used for that address. These parameter settings are downloaded to the echo canceller device selected from the pool, and that device is then inserted into the specific trunk involved.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding of the method and apparatus of the present invention can be had by referring to the following detailed description when taken in conjunction with the accompanying drawings, wherein: Figure 1 is a block diagram schematic that illustrates how the echo can occur in a Public Switched Telephone Network; Figure 2 is a graph that 'illustrates the required echo attenuation, necessary as a function of transmission delay time; Figure 3 is a diagram showing a satellite communications link and illustrates how said system introduces a significant transmission path delay (echo); Figure 4 is a diagram showing a digital cellular communications system and illustrating an echo path delay; Figure 5 is a simplified schematic block diagram illustrating two echo canceler configurations that can be used in existing telephony systems; Figure 6 is a schematic block diagram of an exemplary cellular communications system that can be used to dynamically select echo cancellers and echo cancellation parameter settings, of confounding with a preferred embodiment of the present invention; Figure 7 is a flow chart illustrating a method that can be used to implement the dynamic selection of an echo canceller and the individualized echo cancellation parameters for a specific route, in accordance with the preferred embodiment of the present invention; and Figure 8 is a table showing exemplary echo canceller parameters and values that can be established for a trunk route, in accordance with the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS The preferred embodiment of the present invention and its advantages are best understood with reference to Figures 1-8 of the drawings., the similar numbers being used for equal and corresponding parts in the various drawings. Essentially, an echo canceller pool configuration is provided which allows a user to predetermine and individualize the echo cancellation parameter settings for any echo canceller in the pool, based on prior knowledge of the echo path characteristics of the echo canceller. the transmission route specifies that it will be used for an incoming call. The echo canceller with individualized parameter settings is then switched to that route for the duration of the call. For example, at the beginning of the call, once a trunk route has been identified to be used to complete the call, a traffic control system removes a "flag" from a memory address associated with that specific route. That "flag" includes specific settings for the echo canceller parameter for that route. These parameter settings are downloaded to the echo canceller device selected from the pool, and that device is then inserted into the specific trunk involved. Specifically, Figure 6 is a schematic block diagram of an exemplary cellular communications system that can be used to dynamically select the echo cancellers and the echo cancellation parameter settings, in accordance with a preferred embodiment of the present invention. The system 100 may include a plurality of mobile terminals, one or more base station transceivers, and one or more gate MSCs or MSCs associated with the base station transceivers. Each gateway MSC may have a pool of associated echo cancellers. However, since only one address connection between users needs to be shown to adequately describe the invention, the system shown in Figure 6 includes a mobile terminal 102 (eg cell phone), a base station transceiver 104 for communicating with the mobile terminal 102 through the air interface, a gate MSC 106 connected to the base station transceiver 104, and an echo canceller cluster 110 connected to the gate MSC 106, In this embodiment, a subsystem 108 traffic control is associated with the gateway MSC 106 and the non-echo canceler grouping. The traffic control subsystem can be fully implemented in software and contains the traffic management and traffic control functions of the switch involved. The functions of the traffic control subsystem can be implemented under the control of a digital processor (not explicitly shown) associated with the gate MSC. The gate MSC (106) is connected via a transmission line to an exchange terminal circuit 111, and a trunk line to a remote switch 112 (eg, a switch in a PSTN exchange), Co or shown, the gate MSC (106) can connect the base station transceiver (104) and the two echo cancellers in the pool (110) to any of a plurality of trunk lines. Also, although remote, the switch 112 is shown as a PSTN switch, the invention is not intended to be limited in this way. For example, the gate MSC (106) can be counted through one transmission line to another MSC or switch in the system 100 or to a switch in a different cellular system. In operation, and in accordance with the exemplary embodiment shown in Figure 6, a call is made by a cellular subscriber (A) on the mobile telephone 102, which is to be directed to a landline (not explicitly shown) of a subscriber (B) of PSTN. At the beginning of the call, the identification information of the calling party (A) and the called party (B) is received by the base station transceiver 104, as part of a call control message using a message protocol control and conventional air interface call. This information is coupled to the gate MSC 106 and analyzed by the traffic control subsystem 108. Once the called party (B) has been identified, the traffic control subsystem (108) conducts a route analysis and associates the called party with a specific route (eg, from switch to switch) through a trunk line to that location of the part, In this mode, the traffic control subsystem (108) determines that the specific trunk route to be followed by subscriber B is through the trunk line of the. circuit 111 exchange terminal to remote switch 112. Once the specific trunk route has been identified, the traffic control subsystem (108) has access to a database (not shown explicitly) and removes the relevant transmission characteristics (eg, previously defined by a system operator) around that route. Route information includes, as a minimum, a "flag" or data field that contains known echo path characteristics for that route. The traffic control system in this way can predetermine the precise echo path characteristics of the trunk route that will be used to complete the call. Depending on the echo path delay characteristics of the trunk path involved, the trunk signaling subsystem 113 may select an echo canceller device (not explicitly shown) from the echo canceller pool (110) to be inserted into that echo canceller pool (110). trunk, in order to handle that ecq path delay. Notably, in accordance with the present invention, the trunk signaling subsystem also selects the echo cancellation parameters that will be used in the echo canceler device selected for that particular route. The parameters used may be the typical failure values provided for all echo canceller devices in the cluster, or more importantly, they may be individualized parameters designated more precisely for the specific trunk route involved. For this mode, the grouping (110) of echo canceller can be a CP 303/404 product manufactured by Ericsson Telecom AB. The echo canceller device used may be Type C Eco Cancellation, as specified by the International Telecommunications Union (ITU) in ITU-T Recommendation G.165, March 1993, entitled "Echo cancers. "(" Echo Cancellers "). Using the individualized echo cancellation parameter settings for the specific route involved, the traffic control subsystem (108) and the trunk signaling subsystem (113) in this manner function to complete the speech quality connection significantly improved between subscriber to cellular and subscriber B of PSTN, compared to previous systems, Figure 3 is a flow chart illustrating a method that can be used to implement the dynamic selection of a echo canceller and individualized echo cancellation parameters for a specific route, in accordance with the preferred embodiment of this invention Preferably, a predetermined percentage of echo eancers in the cluster is defined (eg, by a system operator) as belonging to a dedicated cluster. The remaining echo cancellers, which are not distributed to the dedicated grouping, are defined as belonging to a main grouping. The use of a dedicated grouping of echo cancellers makes it possible for an operator to allow only high-priority trunk routes the use of echo cancellers from the dedicated pool. Consequently, if all the echo cancellers in the main pool are being used, echo cancellers are still available from the dedicated pool for use on the high priority routes. For this embodiment, assume that the long-distance, specific outgoing trunk (T-PATH) of gate MSC 106 to remote switch 112 has been "flagged" as requiring individually defined parameter settings for an echo canceller to be selected and used of the grouping (110). even when there is a number of echo cancellation parameters that can be selected (eg., an end path delay, non-linear processor mode, tone disablement mode, impulse code modulation encoder law, etc.) for a specific trunk path, the method described herein only illustrates the use of individualized end path delay settings for the specific outgoing trunk route shown in Figure 6. However, it should be understood that the method in Figure 7 can also be applied to any trunk route and any or all of the possible parameters of the gate canceller. echo. Examples of echo canceller parameters and values that can be established for any trunk route are shown in the box in Figure 8. As such, an operator can specify any or all of the echo canceller parameter settings for each route outgoing, and in this way significantly improve the overall speech quality of the telephone system. For this illustrative embodiment, it can be assumed that an operator wishes to set the specific echo cancellation parameter "end path delay" to 128 ms for the particular T-PATH -shown in Figure 6. However, the adjustment of the "End path delay" at 128 ms actually works to set the "length" of a Finite Impulse Response (FIR) filter to 128 s, in the echo canceller that will be selected from the pool (110). Returning to Figure 7, in step 202, a system operator inputs the appropriate commands to specify and store in a memory storage location (e.g., relationship database) the specific cancellation characteristics of necessary echoes for any or all trunk routes (from the gate switch to the next respective switch) in the system. In the preferred embodiment, these commands can be made using, for example, a set of Man-Machine Language (MML) commands. In step 204, an operator defines and stores (eg, on the basis of relationship data) data transcripts for the system trunk signaling subsystem (e.g., TSS 113), a game of individual parameters for the specific echo cancellation characteristics specified in step 202. In step 206, an operator defines and stores data transcripts for the system traffic control subsystem (eg, _ TCS 108) , information that specifies that the specific ROUTE-T involved can use the individual parameter established, defined and stored for that route. In step 208, an operator determines whether sufficient echo cancellers or not are available in the pool (110) to handle the traffic through the specific ROUTE-T involved. In step 210, depending on whether or not sufficient echo cancellers are available in the pool, the operator inputs as data transcripts for the trunk signaling subsystem, the information will be decreased or a dedicated pool already created will be increased. In step 212, the operator inputs as data transcripts for the traffic control subsystem, to the information to allow the specific ROUTE-T involved to use an echo canceller from the dedicated pool. In step 214, at the beginning of a call from subscriber A to subscriber B of PSTN, the traffic control subsystem performs a conventional call setup procedure and route analysis. In step 216, based on the results of the route analysis performed, the traffic control subsystem determines whether an echo canceller pool is needed or not to cancel echo on, the T-ROUTE involved. If not (eg, a backbone echo canceller is already being used), in step 218, the connection can be made between subscriber A and B without using an echo canceller of the pool, and the present method can be terminated ( 220), however, if in step 216, the traffic control subsystem determines that an echo canceller of the pool is needed for the RUTA-T involved, then in step 22, both the traffic control subsystem and the trunk signaling subsystem determine whether the specific T-ROUTE involves whether or not the use of the dedicated grouping is allowed (eg, based on the level of priority provided for that ROUTE-T). If so, as in this illustration, in step 224, the trunk signaling subsystem selects an echo canceller from the dedicated pool, otherwise, if the T-ROUTE involved has not been given a particular priority of use, the trunk signaling subsystem selects an echo canceller from the main pool (226). In step 228, the trunk signaling subsystem determines whether or not the RUTA-T involved has been defined as a user of individual parameter settings. If this is the case (as in this illustration), in step 230, the trunk signaling subsystem downloads the previously defined individual parameters (eg, 128 ms echo path delay) to the selected echo canceller device. from the dedicated or main grouping (step 224 or 226), which may be employed under the control of a digital processor, such as, for example, a Digital Signal Processor (DSP) manufactured by Texas Instruments Incorporated. Otherwise, in step 232, the trunk signaling subsystem downloads the failure parameters to the echo canceller device selected from the pool.

In step 234, the trunk signaling subsystem enables the operation of the echo canceller selected from the dedicated or main pool, together with the individualized echo cancellation parameters, in the specific ROUTE-T involved. In step 236, for the duration of the call, the trunk signaling subsystem mediates the traffic of two addresses between the subscriber a and the subscriber B of PSTN through the specific ROUTE-T involved. When the call is terminated, in step 238, the traffic control subsystem disconnects the call. In step 240, the traffic control subsystem and the trunk signaling subsystem are switched off from the echo canceller device from the involved T-ROUTE, and in step 242, the trunk signaling subsystem returns that device to the signaling subsystem. dedicated or main grouping. The method for dynamically selecting an echo canceller from a dedicated or main pool and operating it with optimal echo cancellation parameter settings made especially for the specific trunk route involved is then completed (244). even when a preferred embodiment of the method and apparatus of the present invention has been illustrated in the accompanying Drawings and described in the above Detailed Description, it will be understood that the invention is not limited to the described embodiment, but is capable of numerous redispositions, modifications and substitutions without abandoning the spirit of the invention as established and defined by the following claims.

Claims (1)

1. CLAIMS: 1. - A method for improving the quality of speech traffic in a telephone system, comprising the steps of: determining an identity of a transmission route to be used to direct the speech traffic in the telephony system; selecting an echo canceller from a plurality of echo cancellers; selecting an echo cancellation parameter from a plurality of echo cancellation parameters, the echo cancellation parameter associated with the transmission path; transferring the echo cancellation parameter to the canceller or, and echo, the echo canceller operating in this manner in response to the echo cancellation parameter; and attach the echo canceller to the transmission route. 2 . - The method of claim 1, wherein the echo canceling parameter comprises an end path delay. 3. The method of claim 1, wherein the echo cancellation parameter comprises a "length" of a Finite Impulse Response Filter, 4, - The method of claim 1, wherein the cancellation parameter of echo comprises a type of PCM encoder law. 5. The method of claim 4, wherein the echo cancellation parameter comprises a law-A PCM encoder, 6. The method of claim 4, wherein the echo cancellation parameter comprises an encoder of PCM-Mu law. 7. The method of claim 1, wherein the echo cancellation parameter comprises a non-linear processor mode of "disconnection", without listening comfort. 8. The method of claim 1. wherein the echo cancellation parameter comprises a "non-linear" non-linear processor mode, without listening comfort. 9. The method of claim 1, wherein the echo cancellation parameter comprises a "non-linear" non-linear processor mode, with ease of listening. 10. The method of claim 1, wherein the echo canceling parameter comprises a "disconnect" tone disablement mode. 11. - The method of claim 1, wherein the echo cancellation parameter comprises a "connection" echo suppressor mode. 12. The method of claim 1, wherein the echo cancellation parameter comprises a "connection" echo canceler mode. 13. The method of claim 1, wherein the transmission path comprises a trunk line. 14. The method of claim 1, wherein the plurality of echo cancellers comprises a main grouping of echo cancellers. 15. The method of claim 1, wherein the plurality of echo cancellers comprises a dedicated grouping of echo cancellers. 16. The method of claim 13, wherein the transmission path comprises a priority transmission path. 17. The method of claim 1, wherein the telephony system comprises a cellular communication system. 18. The method of claim 1, wherein the telephony system comprises a satellite communication system. 19. The method of claim 1, wherein the telephone system includes a Public Switched Telephone Network. 20. An apparatus for use in improving the quality of speech traffic in a telephone system, comprising: an electronic switch to direct the speech traffic through a transmission route in the telephone system; an element coupled to the electronic switch, for selecting an echo canceller from a grouping of echo cancellers; an element for selecting a cancellation parameter of e or from a plurality of echo cancellation parameters associated with the transmission path; an element for transferring the echo cancellation parameter to the echo canceller; and an element associated with the electronic switch, for coupling the echo canceller to the transmission path. 21. The apparatus of claim 20, wherein the echo cancellation parameter comprises an end path delay. 22. The apparatus of claim 20, wherein the echo cancellation parameter comprises a "length" of a Finite Impulse Response Filter. 23. The apparatus of claim 20, wherein the transmission path comprises a trunk line. 24. The apparatus of claim 20, wherein the grouping of echo cancellers comprises a dedicated grouping of echo cancellers. 25. The apparatus of claim 23, wherein the transmission route comprises a transmission route with priority. 26. The apparatus of claim 20, wherein the telephony system comprises a cellular communications system. 27, - The apparatus of claim 20, wherein the telephony system comprises a satellite communication system. 28. The apparatus of claim 20, wherein the telephone system includes a Public Switched Telephone Network.