WO2000064204A1

WO2000064204A1 - Method and device for avoiding transmission of redundant information in a digital communication network

Info

Publication number: WO2000064204A1
Application number: PCT/SE2000/000742
Authority: WO
Inventors: Torbjörn SILLÉN
Original assignee: Telia Ab
Priority date: 1999-04-19
Filing date: 2000-04-19
Publication date: 2000-10-26
Also published as: SE9901381D0; SE9901381L

Abstract

A procedure and a device for control of transmission of information in a transmitting subnetwork in a digital time division multiplex mobile communication system is presented. The subnetwork transmits frames containing information from a station (201) in a radio subnetwork to an adaptation unit (213) in the transmitting subnetwork and is characterised in that it includes the steps: reception of information frames from the radio subnetwork, interpretation of at least a fraction of the content in the information frames, at which the interpretation at least determines one type of frame for each of the received information frames, at which the type of frame is one of at least three types of frames, at which a first type of frame is a speech frame that includes sound information, a second type of frame is a silence frame that includes silence information, and a third type of frame is a faulty frame that includes a frame error indicator, transmission of the information in the received information frames, at which the transmission is made depending on the interpretation.

Description

METHOD AND DEVICE FOR AVOIDING TRANSMISSION OF REDUNDANT INFORMAΗON IN A DIGITAL COMMUNICATION NETWORK

TECHNICAL FIELD 5 The present invention relates to procedures and devices for control of transmission of information in a transmitting subnetwork in a time division multiplex mobile communication system_¬

ic. BACKGROUND

Mobile communication systems, such as GSM, can broadly be divided into two different subnetworks. A radio subnetwork and a (packet) transmitting subnetwork consisting of more or less fixed terrestrial connections between the radio 15 subnetwork and public telecommunication networks. In the radio subnetwork, information is exchanged between mobile telephone stations and radio base stations via a radio interface. The radio base stations transmit the information from the radio subnetwork to units in the transmitting 20 subnetwork, which in their turn transmit the information to public telecommunication networks, or back to mobile telephone stations in the radio subnetwork.

Well known to the expert is that the difference in supply, 25 and by that the cost, of transmission resources in the radio subnetwork in comparison with the transmitting subnetwork is great. The radio resources are usually very limited and by that expensive. A general aim at construction and operation of mobile communication systems 30 consequently is that the degree of utilisation of the resources in the radio subnetwork, for instance in form of the time slots in time division multiplex systems such as GSM, shall be as great as possible.

35 One method of increasing the utilisation of resources in a radio subnetwork where the communication is in form of traditional telephone calls, is to utilise the fact that calls between persons to a great extent contains time intervals of silence.

In digital mobile communication systems, the information that is transmitted between the in the system included units is divided into so called frames. Frames are sequences of information bits, the length of which can vary between different types of systems. The physical transmission of these frames is made in time division multiplex systems, such as GSM, in the time slots in one for the expert well-known way.

In order to avoid unnecessary use of radio resources, for instance the time slots in the radio interface between mobile station and radio base station, the mobile telephone station can analyse the sound information that is generated by a user. If the analysis finds that the user is silent, a synthetic silence information is crated in the frames, at which only a fraction of the frames are allowed to be transmitted via the radio interface. The transmission of the frames consequently are made in a broken sequence of frames, which means that the load of the time slots is reduced.

After reception in the radio base station, an unbroken sequence of frames are recreated, which, irrespective of whether they contain sound or silence information, then are transmitted via reserved connections to other units in the transmitting subnetwork.

A plurality of radio base stations are usually connected to a base control station, which results in that a plurality of reserved connections are utilised to transmit silence information with a high level of redundancy. This identifies a problem: How avoid transmission of redundant, and by that unnecessary, information frames in a transmitting subnetwork in a mobile communication system ?

DESCRIPTION OF THE INVENTION

One aim of the invention is to solve the problem: How avoid transmission of redundant, and by that unnecessary, information frames in a transmitting subnetwork in a mobile communication system ?

The invention achieves this aim by interpreting the frame information and transmiting this depending on this interpretation. More exactly, the problem is solved as claimed in patent claim number one, in which is presented a procedure for control of transmission of information in a packet switched subnetwork in a digital time division multiplex mobile communication system. The subnetwork transmits frames containing information from a station in a radio subnetwork to an adaptation unit in the transmitting subnetwork and is characterised in that it includes the steps : reception of information frames from the radio subnetwork; - interpretation of at least a fraction of the content in the information frames, at which the interpretation at least determines one type of frame for each of the received information frames, at which the type of frame is one of at least three types of frames, at which a first type of frame is a speech frame that includes sound information, a second type of frame is a silence frame, which includes silence information, and a third type of frame is a faulty frame, which includes a frame error indicator; - transmission of the information in the received information frames, at which the transmission is made depending on the interpretation.

One advantage of the invention is that it allows a reduction of the utilisation of resources in a transmitting subnetwork, which means higher efficiency, and consequently a lower cost.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows a schematic representation of a digital communication system in which the present invention is intended to be used.

Figure 2 shows a schematic block diagram over a device according to the invention.

Figure 3 illustrates schematically information frames that are transmitted according to the invention.

Figure 4 shows a flow chart over a method according to the invention .

PREFERRED EMBODIMENTS

Figure 1 illustrates in a schematic way a mobile communication system 100 connected with an external telephone network 103 of traditional (PSTN) kind, an external data network 104, which is exemplified by an ISDN network, and a second mobile communication system 105 of a generic (PLMN) type.

For the sake of clarity, a typical GSM-system is used to illustrate the invention. Consequently both terminology and the general network structure are known to the expert in the field. However, the selection of GSM as illustration should not be regarded as a limitation. The invention is applicable in all telecommunication networks in which there is a possibility to sense/read silence in an established speech connection and as a result of the sensing/reading limits the amount of transmitted silence information.

The mobile communication system 100 is divided into two subnetworks, a radio subnetwork 101, and a transmitting subnetwork 102. In the radio subnetwork 101 there is a first 110 and a second 112 mobile terminal in radio contact via respective radio interface 114, 116, with a first 118 and a second radio base station 120. Certainly a real radio subnetwork includes more than two mobile terminals.

Especially should be observed that each of the radio base stations 118, 120 normally manages connections with a number of tens of mobile terminals at a time.

For the sake of clarity, the borderline between the radio subnetwork 101 and the transmitting subnetwork 102 is illustrated by a dashed borderline between them. However, it will by the following detailed description be evident that that certain functions in the radio base stations 118, 120 constitute a part of the transmitting subnetwork 102 in which the invention is realised.

Each of the radio base stations 118, 120 are connected via a first 122 and a second fixed connection 124 to a base control station 126. The base control station 126 has, among other things, as its task to collect transmission traffic of comparatively low transmission speed from the majority of the radio base stations, to transmission traffic with comparatively high transmission speed to a mobile services switching centre 128. As Figure 1 clearly illustrates, at least one more base control station 136, with additional connections 138 to radio base stations, is connected to the mobile services switching centre 128.

A second mobile services switching centre 130 serves as a gate for traffic to the other networks 103,104,105. The mobile communication system 100 also can include more mobile services switching centres, as is indicated by connections 132 at the second mobile services switching centre 130.

As is well known within the field, connections are set up, held, and disconnected between subscribers in the shown networks 100,103,104,105. Even if only mobile terminals 110,112 are shown, it is well known that subscribers can be connected to any of the networks, and be connected with each other in more or less just any combinations.

The Figures 2 and 3 illustrate more in detail a speech connection between a first terminal and a second terminal that is established and controlled according to the invention. As is shown in Figure 2, the first terminal is a mobile terminal 201 in the radio subnetwork (101 in Figure 1), and the second terminal is a telephone 219 in a telephone network 217. The transmission of information that is relevant in this context is the transmission that is directed from the mobile terminal 201 to the telephone 219. In order to increase the clarity, a GSM network structure has been selected for this example.

According to known technology, information, preferably digitised speech generated by a terminal user, is transmitted from the mobile terminal 201 via a radio interface 203 to a radio base station 205. The speech information is digitally represented in speech frames, the content of which is transmitted in physical channels in form of time slots in the radio interface. The information is transmitted via a first gate 207, and a digital network 209, to a base control unit 213, through a second gate 211. The first 207 and the second gate 211 are illustrated as a part of the radio base station 205, respective the base control unit 213. These gates 207, 211, however, can be physically separated units and be in physical connection with other units by known technology.

Further, the information is transmitted according to known technology to the second terminal 219, via a mobile services switching centre 215, the function of which also includes a gate function for connection to the telephone network 217.

The transmission via the radio interface 213 utilises the within GSM well known technology of discontinuous transmission (DTX) . This means that the mobile terminal 201 detects and analyses the sound that the user produces and transmits information frames depending on whether sound or silence is detected. Sound is transmitted in continuous speech frames, but silence is transmitted discontinuously, that is, less frequent than speech frames, in so called silence frames. The transmitted frames include an indicator (SP-indicator) about which type of information they contain, at which an information frame containing speech has an SP-indicator the value of which is other than zero, and silence frames are indicated by a zero. Further, the content of the frames represents the sound the silence that is detected, and for the silence information an indicator, SID-indicator, is used, the value of which is used to categorise the content of the transmitted silence information.

The application of this DTX-technology has, as has already been mentioned, as its aim to reduce unnecessary transmission, on the resource limited radio interface, of frames the contents of which is only silence. After reception in the radio base station 205, the information from the received speech and silence frames are allocated in so called TDMA-frames, which are schematically illustrated in Figure 3.

Figure 3 shows a sequence of TDMA information frames 300, which, according to known technology, are generated in the radio base station (205 in Figure 2) . An appointed frame 301 contains an information field 303, and a signalling field 305. The information field contains speech information, silence information, or data information, from the mobile terminal 201. The signalling field contains signalling information intended for other units in the network. Reception of the TDMA information frames is made in the base control station 213, which in its turn forwards the information to receiving terminal 219 via the mobile services switching centre 215 and the telephone network 217.

According to the main idea of the invention, however, not all silence information is transmitted between the radio base station 205 and the base control unit 213. In the first gate 207, the TDMA information frames 300 are analysed with regard to their contents, as will be described below. The information is rearranged in IP data packets according to well known TCP/IP, alternatively UDP/IP, technology and is transmitted via an IP-network 209 to the second gate 211, in which the TDMA information frames 300 are recreated and forwarded to the base control unit 213.

In order to with greater clarity illustrate the processing of the information at transmission from the radio base station 205 to the base control unit 213, a method according to the invention will be illustrated with reference to Figure 4. The method is, for instance, realised by suitably adapted software existing in the radio base station (205 in Figure 2), and the first gate (207 in Figure 2) and the second gate (211 in Figure 2) and the base control unit (213 in Figure 2) .

In an initial step 401, a TDMA-frame (301 in Figure 3) containing information received from the mobile terminal (201 in Figure 2) is created. As has been described above, the information can include speech information as well as silence information, at which identification of the different types of information is made by the SP-indicator and the SID-indicator, the values of which are also incorporated in the TDMA-frame.

In an interpretation step 403, the SP-indicator and the SID-indicator are interpreted to make possible a decision about transmitting the TDMA-frame further to the base control unit (213 in Figure 2). Certainly are in this interpretation also included other factors that are of importance for decision of transmission. Such a factor is of course whether one from the mobile terminal (201 in Figure 2) received frame is received faulty, that is corrupted, or not. An indicator for this factor is called BFI-indicator .

In a decision step 405, the SP-, SID- and BFI-indicators are utilised according to the following simple logic:

- If SP is zero and SID is the same as a SID from preceding received speech frame; do not transmit the current TDMA-frame.

- If SP is zero and the difference between the contents in the current SID-indicated frame and a preceding received SID-indicated frame; do not transmit the current TDMA-frame. - If the BFI-indicator indicates a corrupt frame received from the mobile terminal (201 in Figure 2); do not transmit the current TDMA-frame.

All other information is transmitted according to the steps below, with start in a step 407 for arranging packets. In the step 407 for arranging packets, the TDMA-frames are arranged in data packets according to the to expert well known IP-standard, that is, IP-packets, at which for instance an IP-address for receiving unit is connected to the IP-packet. The intended addressee is preferably the receiving base control unit, and more exactly its gate (211 in Figure 2) .

In a transmission step 409, the TDMA-frames arranged in IP- packets are transmitted via the IP-network (209 in Figure 2) according to well known and standardised IP-technology.

In a reception step 411, the IP-packets are received, according to well known IP-technology, by the addressee, which in this example consists of the second gate (211 in Figure 2) connected to the base control unit (213 in Figure 2) .

In a recreating step 413, the in the radio base station created TDMA-frames are recreated from the information in the received IP-packets, after which the base control unit (213 in Figure 2) forwards the information according to previously discussed GSM-technology via the mobile services switching centre (215 in Figure 2) to the second terminal (219 in Figure 2) connected to the telecommunication network (217 in Figure 2) . Even if only GSM-systems have been discussed above, it is a matter of course to the expert in the field to apply this invention in other telecommunication systems. It is possible to forestall implementation in all systems in which the equivalence of DTX is utilised.

Claims

PATENT CLAIMS

1. Procedure for control of transmission of information in a transmitting subnetwork (102) in a digital time

5 division multiplex mobile communication system (100), at which the subnetwork (102) transmits frames containing information from a station (110,112,201) in a radio subnetwork (101) to an adaptation unit (126,213) in the transmitting subnetwork (102), c h a r a c t e r i s e d in

K) that it includes the steps:

- reception of information frames from the radio subnetwork (101),

- interpretation of at least a fraction of the content in the information frames, at which the interpretation

15 at least determines one type of frame for each of the received information frames, at which the type of frame is one of at least three types of frames, at which a first type of frame is a speech frame that includes sound information, a second type of frame is a silence frame that

20 includes silence information, and a third type of frame is a faulty frame that includes a frame error indicator; transmission of information in the received information frames, at which the transmission is made depending on the interpretation.

25

2. Procedure as claimed in patent claim 1, at which the second type of frame is determined, further c h a r a c t e r i s e d in that the interpretation includes :

30 - analysis of the silence information, at which a comparison is made between silence information in the latest received silence frame with silence information in a previously received silence frame, at which the comparison results in a measure of concordance, and that the

35 transmission of the information in the latest received silence frame is made depending on the measure of concordance .

3. Procedure as claimed m patent claim 1, at which the 5 third type of frame is determined, further c h a r a c t e r i s e d in that the interpretation includes :

- analyses of the frame error indicator, and that the transmission of the information in the latest received

10 information frame is made depending on the frame error indicator .

4. Procedure as claimed in any of the patent claims 1-3, further c h a r a c t e r i s e d in that the transmission ι. of the information is preceded by the step:

- division of the information into data packets, and that the transmission of the information is made via a packet switched network part to the adaptation unit.

0 5. Procedure as claimed in patent claim 4, further c h a r a c t e r i s e d in that the division of the information and the transmission is made according to the Internet Protocol.

25 6. Device for control of transmission of information in a transmitting subnetwork (102) m a digital time division multiplex mobile communication system (100), at which the subnetwork (102) includes devices for transmission of frames containing information from a station (110,112,201)

30 in a radio subnetwork (101) to an adaptation unit (126,213) in the transmitting subnetwork (102), c h a r a c t e r i s e d in that it includes: devices (118, 205) for reception of information frames from the radio subnetwork (101),

35 - device (207) for interpretation of at least a fraction of the content in the information frames, at which the interpretation at least determines one type of frame for each of the received information frames, at which the type of frame is one of at least three types of frames, at which a first type of frame is a speech frame, which includes sound information, a second type of frame is a silence frame, which includes silence information, and a third type of frame is a faulty frame, which includes a frame error indicator. - device (207) for transmission of information in the received information frames, at which the transmission is made dependent on the interpretation.

7. Device as claimed in patent claim 6, further c h a r a c t e r i s e d in that the devices (207) for the interpretation include:

- device for analysis of the silence information, including devices for comparison between silence information in the latest received silence frame with silence information in a previously received silence frame, at which the comparison results in a measure of _ concordance, and that the devices for the transmission of the information in the latest received silence frame includes device to take the measure of concordance into consideration.

8. Device as claimed in patent claim 6, further c h a r a c t e r i s e d in that the devices (207) for the interpretation include: - device for analysis of the frame error indicator, and that the devices for transmission of the information in the latest received information frame include device to take the frame error indicator into consideration.

9. Device as claimed in any of the patent claims 6-8, further c h a r a c t e r i s e d in that: - devices for division of the information into data packets, and that the devices for the transmission of the information include device for tranmission via a packet switched network part (209) to the adaptation unit (126,213) .

10. Device as claimed in patent claim 9, further c h a r a c t e r i s e d in that the devices for the division of the information, and the devices for the transmission include devices for division and allocation according to the Internet Protocol.