WO1997038498A1

WO1997038498A1 - Discontinuous transmission in an analogue mobile system

Info

Publication number: WO1997038498A1
Application number: PCT/FI1997/000216
Authority: WO
Inventors: Markku Vimpari; Kari Reponen; Jaakko Sippola
Original assignee: Nokia Telecommunications Oy
Current assignee: Nokia Oyj
Priority date: 1996-04-10
Filing date: 1997-04-09
Publication date: 1997-10-16
Anticipated expiration: 1998-10-10
Also published as: AU2510697A; FI961568A0; SE9803420L; FI961568A7; SE9803420D0

Abstract

The invention relates to a method of discontinuous transmission in an analogue mobile system. The method is characterized by monitoring the information activity of an uplink transmission from a mobile station; monitoring the information activity of a downlink transmission from a base station; and controlling the transmission from the mobile station on the basis of both said information activities.

Description

DISCONTINUOUS TRANSMISSION IN AN ANALOGUE MOBILE SYSTEM

FIELD OF THE INVENTION

The invention relates to a method of discontinuous transmission in an analogue mobile system. The invention also relates to an analogue mobile station.

BACKGROUND OF THE INVENTION

In various mobile systems, the aim is to make mobile stations as small as possible. On the other hand, as long service life as possible is also one of the key characteristics affecting the usefulness of a mobile station. High requirements are thus set for the batteries of a mobile station: both small size and long life are required. One attempts to achieve the aim, for example, by reducing the power consumption in a mobile station.

Discontinuous Transmission, or DTX, is a method in which transmission from a mobile station to the radio path can be interrupted for the duration of any pauses occurring in the speech. The aim is to reduce the power consumption of a transmitter, which is essential to a mobile station.

Discontinuous transmission is previously known in connection with digital mobile systems. In the GSM, for example, a mobile station monitors the speech activity of a signal transmitted from the mobile station to a base station and interrupts the transmission from the mobile station to the radio path when the signal lacks speech information. When the speech activity is again started, the speech is encoded and transmitted to the base station in the appropriate time slot. In order that a receiving party would not hear the termination of the transmission as unpleasant complete silence, comfort noise parameters are transmitted to the base station at certain intervals. The comfort noise parameters are utilized in generating comfort noise, which simulates background noise, in a speech decoder at the receiving end.

Fig. 1 shows, by way of example, a simplified block diagram of an analogue mobile system NMT (Nordic Mobile Telephone). In Fig. 1 , the fixed mobile network of the system comprises a Mobile Telephone Exchange MTX and Base Stations BS. A Mobile Station MS communicates over the radio path with a base station BS. The direction of transmission from the base station BS to the mobile station MS over the radio path is called downlink, and from the mobile station MS to the base station BS, uplink. A mobile telephone exchange MTX typically controls the operation of a plurality of base stations BS. Base station control is handled by Base Station Signalling Equipment BSE contained in the mobile telephone exchange. The mobile telephone exchange MTX communicates with a Public Switched Telephone Network PSTN and other mobile telephone exchanges. The operation of the NMT system is monitored by an Operation and Maintenance Centre OMC.

In analogue mobile systems, the transmission from a mobile station to the radio path can also be interrupted by the mobile station for the duration of any pauses occurring in the speech. When the transmitter of the mobile station is switched off for the duration of any pauses in the speech, the power consumption of the mobile station is reduced. The problem then, however, is that the components of the mobile station react slowly when uplink speech activity is again started. It takes a few milliseconds to detect that speech activity has started, and after that it takes about 10 milliseconds to switch on the transmitter of the mobile station. Any speech activity passing over the radio path when the switching of the transmission to the radio path is in progress is distorted. Some sounds or even whole words are thus lost at the beginning of the speech.

BRIEF DESCRIPTION OF THE INVENTION

The object of the present invention is to implement discontinuous transmission in an analogue mobile system without impairing transmission of information.

The new type of discontinuous transmission in an analogue mobile system is achieved by a method according to the invention, which is characterized by monitoring the information activity of an uplink transmission from a mobile station; monitoring the information activity of a downlink transmission from a base station; and controlling the transmission from the mobile station on the basis of both the uplink and downlink information activities.

The invention also relates to an analogue mobile station which is characterized by comprising a first information activity detector for monitoring the information activity of an uplink transmission from a mobile station, a second information activity detector for monitoring the information activity of a downlink transmission from a base station, and a DTX unit, responsive to said first and second information activity detectors, for controlling the transmitter in a radio unit of the mobile station. The invention is based on the idea that message transmission on a mobile connection is typically interactive When the information activity in both directions of transmission is monitored, it is possible to predict the start of uplink information activity and to prepare the mobile station for the start of the uplink transmission

An advantage of the discontinuous transmission like this is that the power consumption of an analogue mobile station can be reduced

Another advantage of the discontinuous transmission according to the invention is that it allows an essential reduction in the distortion, caused by the re-start of the transmitter, in the uplink information signal transmitted from the mobile station to the base station

In the invention, the discontinuous transmission is implemented so that the information transmission activities of the uplink and downlink signals are monitored The transmitter of the mobile station MS is switched off and maintained in the off-state when the downlink signal contains information, such as speech or data, and the uplink signal contains nothing but noise The transmitter of the mobile station MS is switched on and maintained in the on- state when the downlink signal contains nothing but noise Further, in the case of dual transmission, when both the uplink signal and the downlink signal contain information simultaneously, the transmitter of the mobile station MS is switched on and maintained in the on-state for as long as the uplink signal contains information

BRIEF DESCRIPTION OF THE FIGURES

In the following the invention will be described in greater detail with reference to the attached drawings, in which

Fig 1 is a simplified block diagram of an NMT mobile system, Fig 2 is a block diagram illustrating a mobile station according to the invention,

Fig 3 is a flow chart illustrating a preferred embodiment of a method according to the invention, and figs 4A - 4H exemplify situations during a speech connection in a mobile system

DETAILED DESCRIPTION OF THE INVENTION

The present invention can be applied in connection with any analogue mobile system In particular, the invention is suitable for use in analogue radio systems in which the system does not directly support the use of discontinuous transmission in a mobile station. In the following, the invention will be described in greater detail, by way of example, in connection with an NMT mobile system. Fig. 1 shows the simplified structure of the NMT network described above.

The functionality of the discontinuous transmission according to the invention is preferably implemented by equipment arranged in connection with the mobile station. Fig. 2 is a block diagram of a mobile station according to preferred embodiment of the invention, showing only those components of the mobile station that are essential to the invention. A microphone 21 converts acoustic sound into an electrical signal, which is supplied to the transmitter of a radio unit 27. The radio unit 27 comprises a transmitter, a receiver and other radio-technical components. The radio unit 27 sends the electrical uplink signal supplied by the microphone 21 as a radio-frequency signal over the radio path to a base station BS. A radio signal sent by the base station BS is received at the radio unit 27, from which the downlink signal is forwarded to a loudspeaker 29. The loudspeaker converts the electrical signal into acoustic sound.

In a first audio-level-measuring unit 23, the audio level of the electrical uplink signal supplied to the radio unit 27 is measured and the signal strength is compared with a predefined threshold value T1 at voice frequencies. If the signal is stronger than or equal to threshold value T1 , the uplink signal is interpreted to contain information, such as speech or data. A signal strength that is below threshold value T1 is interpreted to indicate lack of speech/data activity, i.e. the signal received from the microphone contains nothing but noise or normal background noise. A measuring result M1 indicating whether the strength is above or below threshold value T1 is transmitted to a DTX unit 25. Correspondingly, in a second audio-level- measuring unit 24, the speech/data activity of the downlink signal supplied from the radio unit 27 to the loudspeaker 29 is measured. The audio level of the downlink signal is compared with a threshold value T2, and a measuring result M2 is transmitted to the DTX unit 25, the result indicating the speech/data activity of the downlink signal or lack of same in relation to threshold value T2. Threshold value T2 is preferably equal to threshold value T1 . The DTX unit 25 controls the radio unit 27 to switch on the transmitter / maintain the on-state, or to switch off the transmitter / maintain the off-state, on the basis of the measuring results M1 and M2 obtained from the audio-level-measuring units 23, 24. If measuring result M2 indicates lack of speech/data activity in the downlink signal, the DTX unit 25 controls the radio unit 27 to switch the transmitter on independently of measuring result Ml If the transmitter is already on, the control signal is interpreted in the radio unit 27 as a command to maintain the on-state. If measuring result M2 indicates speech/data activity in the downlink signal and measuring result M1 simultaneously indicates lack of speech/data activity in the uplink signal, the DTX unit 25 controls the radio unit 27 to switch the transmitter off or, if the transmitter is already off, to maintain the off-state. When both the measuring signals M1 and M2 indicate that speech is being transmitted, the DTX unit 25 controls the radio unit 27 to switch the transmitter on / to maintain the on-state. The audio-level measuring units of the above preferred embodiment can be replaced, if necessary, with some other detectors of information activity. Normal background noise is not regarded as information in the present invention.

Fig. 3 is a flow chart illustrating a preferred embodiment of a method of discontinuous transmission according to the invention. In block 31 , it is monitored whether the downlink signal received from the base station BS by the mobile station MS contains information, such as speech. If the downlink signal contains speech, it is monitored whether the uplink signal obtained from the microphone of the mobile station MS contains speech (block 33). If the uplink signal does not contain speech, the transmitter of the mobile station MS is switched off (block 35). If the transmitter is already off, the off-state is maintained. If the uplink signal as well as the downlink signal contains speech, i.e. in a dual speech situation, in which both participants of a conversation speak simultaneously, the transmitter of the mobile station is switched on (block 37). If the transmitter of the mobile station MS is already on, the on- state is maintained. If it is detected in block 31 that the downlink signal does not contain speech, the transmitter of the mobile station is switched on / the on-state is maintained (block 37).

The signal diagrams of Figs. 4A-4H illustrate, by way of example, various situations during a conversation on a mobile call connection. The situations described below are only intended to illustrate the idea of the invention. The use of the invention is thus not limited to the situations discussed. Fig. 4A illustrates a situation in which the downlink signal at first contains speech. As the speech activity of the downlink signal is terminated, the speech activity of the uplink signal is started with a short delay. In the discontinuous transmission according to the invention, the transmitter of the mobile station MS is switched on after the termination of the downlink signal speech activity, even though the uplink signal speech activity has not started yet. When the uplink signal speech activity is started, the transmitter of the mobile station MS is already on, and so the switching on of the transmitter does not cause any loss of sounds at the beginning of the speech message. The situation corresponds to a normal conversation in which the participants take turns to speak; in such a situation, the method of the invention makes it possible to anticipate when the speech activity of a mobile subscriber is started. Fig. 4B illustrates a situation in which the uplink signal at first contains speech. Shortly after the uplink signal speech activity has been terminated, downlink signal speech activity is started. In the invention, the transmitter of the mobile station is not switched off until the downlink signal speech is started, since a mobile subscriber is then assumed to concentrate on listening to the downlink signal. During the speech activity of the downlink signal, the off-state of the transmitter of the mobile station MS is maintained, whereby the power consumption in the mobile station is reduced. If, however, the mobile subscriber starts the speech activity before the downlink signal speech activity has been terminated, the transmitter of the mobile station MS is switched on immediately after detecting uplink signal speech activity, as shown in Fig. 4C. The uplink signal transmission is then distorted for as long as it takes to switch the transmitter on.

Fig. 4D illustrates the termination of a dual speech situation as a mobile subscriber stops speaking. Since the downlink signal still contains speech, the transmitter of the mobile station MS is switched off to save batteries.

Figs. 4E and 4F illustrate situations in which the downlink signal does not contain any speech. The transmitter of the mobile station MS is then continuously maintained in the on-state independently of the speech activity of the uplink signal. In Figs. 4G and 4H, the uplink signal does not contain any speech activity. The transmitter control is then totally dependent on the speech activity of the downlink signal. In Fig. 4G, the downlink signal at first contains nothing but noise and the transmitter of the mobile station MS is maintained in the on- state. As the downlink signal speech activity is started, the transmitter of the mobile station MS is switched off. In Fig. 4H, the transmitter of the mobile station MS is off until the speech activity of the downlink signal is terminated. The transmitter is then switched on to wait for an uplink signal response.

The drawings and the description thereof are only intended to illustrate the idea of the invention. The discontinuous transmission according to the invention may vary in its details within the scope of the claims. Although the invention is described above mainly in connection with speech and/or data transmission, it can also be used in connection with transmission of other kind of information.

Claims

1. A method of discontinuous transmission in an analogue mobile system, characterized by monitoring the information activity of an uplink transmission from a mobile station (MS); monitoring the information activity of a downlink transmission from a base station (BS); and controlling the transmission from the mobile station (MS) on the basis of both said information activities.

2. A method according to claim 1, c h a r a cte rize d in that the steps of monitoring the information activity of the uplink transmission and the downlink transmission comprise the steps of: measuring the audio levels of the downlink and uplink signals, and comparing said audio levels with predefined threshold values.

3. A method according to claim 1 or 2, characterized by switching on a transmitter of the mobile station (MS) and maintaining the on-state when there is no information activity in the downlink transmission or when there is information activity in both the downlink transmission and the uplink transmission, and switching the transmitter of the mobile station (MS) off and maintaining the off-state when there is information activity in the downlink transmission but not in the uplink transmission.

4. An analogue mobile station (MS), characterized in that the mobile station (MS) comprises a first information activity detector (23) for monitoring the information activity of an uplink transmission from a mobile station (MS), a second information activity detector (24) for monitoring the information activity of a downlink transmission from a base station (BS), and a DTX unit (25), responsive to said first and second information activity detectors (23, 24), for controlling the transmitter of a radio unit (27) of the mobile station (MS).

5. An analogue mobile station (MS) according to claim 4, char¬ acterized in that the information activity detectors (23, 24) for monitoring the information activity of the uplink transmission and the downlink transmission are arranged to measure the audio levels of said transmission signals and compare said audio levels with predefined threshold values.