Method and apparatus for transmitting messages in a telecommunication system

• US 6,208,715 B1
• Filed: 08/25/1998
• Issued: 03/27/2001
• Est. Priority Date: 11/02/1995
• Status: Expired due to Term

• Current Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Original Assignee: Nokia Telecommunications Oy (Nokia Corporation)
• Inventors: Haavisto, Petri
• Primary Examiner(s): Tsang, Fan
• Assistant Examiner(s): Hoosain, Allan
• Application Number:
  US09/068,161
• Time in Patent Office: 945 Days
• Field of Search: 379/67.1, 379/88-7-, 379/88.17, 379/93-1-, 379/100-5-1, 369/94, 704/201-224, 711/4-5, 711/11-114, 370/389, 370/351-401, 712/35-36
• US Class Current: 379/88.07
• CPC Class Codes: H04J 3/1688 the demands of the users being taken into account after redundancy removal, e.g. by predictive coding, by variable sampling reducing bandwidth of signals in general H04B1/66; in PCM-systems H04B14/046; removal of redundancy in telegraph communication H03M7/30
• CPC Class Codes: H04J 3/17 in which the transmission channel allotted to a first user may be taken away and re-allotted to a second user if the first user becomes inactive, e.g. TASI speech analysis or identification G10L
• CPC Class Codes: H04L 1/004 by using forward error control H04L1/0618 takes precedence; coding, decoding or code conversion, for error detection or correction H03M13/00
• CPC Class Codes: H04M 1/724 User interfaces specially adapted for cordless or mobile telephones

Abstract

A method and an apparatus for implementing the method, which allow a transmitter (100) of a digital telecommunication system transmitting speech to transmit predetermined messages to a receiver (102) over a speech channel (108). Messages (114) are transmitted from the transmitter (100) to the receiver (102) on the speech channel (108) in such a way that they are encoded in some of the speech coding bits, whereby the speech coding bits selected for message transmission have been selected in such a way that they affect the quality of speech as little as possible. Most preferably, the speech coding bits used for transmitting messages are protected by channel coding (702, 704). Speech coding bits are “stolen” for message transmission only for very short periods at a time and only for exactly the time it takes to transmit the messages (114); at other times, the entire speech channel (108) is used normally for speech transmission.

Claims

1. A method for transmitting messages simultaneously with speech in a digital telecommunication system;

said method comprising coding speech to speech frames which consist of bits and which are positioned in a transmission signal; and

transmitting each message by making at least one change in said transmission signal;

wherein

the messages are transmitted in short sequences relative to the speech information in a speech frame;

for each possible message, a corresponding predetermined bit group is defined;

said at least one change in said transmission signal comprises replacing less than all of the bits of the corresponding speech frame with said predetermined bit group corresponding to the message; and

said at least one change in said transmission signal is restricted in time to the transmission moment of the speech frame corresponding to said message such that no other indication of the presence of the message is required.

2. A method according to claim 1, characterized in that said replacing the bits of speech frames with a predetermined bit group comprises:

setting parameters corresponding to the intensity of the sound of the speech frame to be transmitted in such a way that the amplitude of the received speech frame is minimized; and

positioning the bit group corresponding to the message in a part of the speech frame which is protected in the system against transmission errors.

3. A method according to claim 2, characterized in that the method is used in connection with full-rate speech coding of a GSM-type system and:

the amplitude of the speech frame is minimised by setting the block amplitude parameters of the speech frame to be transmitted substantially as zero; and

the bit group corresponding to the message is positioned in the bits corresponding to the RPE parameters of the speech frame.

4. A method according to claim 1, wherein the number of possible messages is 20 or less and the bit groups corresponding to the messages are selected such that the Hamming distance between them is as great as possible.

5. A method according to claim 1, further comprising:

monitoring any DTMF signals that may occur in the speech; and

in response to the detection of a DTMF signal in the speech, generating a message corresponding to said DTMF signal.

6. A method according to claim 5, further comprising preventing the propagation of a DTMF signal as a DTMF sound to the signal of the transmission channel.

7. A method for receiving a message of short duration in a digital telecommunication system, said method comprising receiving speech frames, some of which contain a message, wherein:

a corresponding predetermined bit group is defined per each possible message; and

identification of speech frames containing messages is based only on examination of the contents of the speech frames; and

identification of a speech frame as a message requires at least that said speech frame contains a bit group which corresponds to one of said messages, wherein the speech frames are interpreted as messages when the speech frame contains a bit group which differs from a predetermined bit group associated with a message by no more than a predetermined threshold value the bit group including less than all bits of the speech frame.

8. A method according to claim 7, wherein the predetermined threshold value is five bits.

9. A method according to claim 8, wherein identification of a speech frame as a message further requires that the parameters corresponding to the intensity of the sound of a speech frame are below a second predetermined threshold to make the speech signal inaudible.

10. A method according to claim 7, wherein at least some messages correspond to different DTMF sounds, and if a speech frame is interpreted as a message corresponding to a DTMF sound, the DTMF sound corresponding to the message is generated.

11. A method according to claim 7, wherein the speech frames that are concluded to contain messages are processed as messages and as normal speech frames.

12. A method according to claim 7, wherein the speech frames that are concluded to contain messages are processed as messages and as bad speech frames.

13. A transmitter of a digital telecommunication system, comprising a speech encoder for encoding speech to speech frames consisting of bits, and a message encoder for encoding messages to a signal of a transmission channel common to the speech and messages;

said transmitter being arranged to make at least one change in the signal of the transmission channel in order to transmit each message simultaneously with speech;

wherein the transmitter is further arranged to;

transmit messages for short periods at a time relative to the time associated with a speech frame;

code each message to a corresponding predetermined bit group;

restrict said change in the signal of the transmission channel in time to the transmission moment of the speech frame corresponding to said message; and

replace less than all of the bits of the speech frame corresponding to said message with the corresponding predetermined bit group associated with said message;

whereby no other indication of the transmission moment of the message is required.

14. A transmitter according to claim 13, wherein the speech encoder is implemented as a state machine to which a feedback signal is further supplied from the message encoder whereby the speech encoder is arranged to change state during transmission of messages such that the effect of the transmission of message on the quality of speech is minimized.

15. A transmitter according to claim 13, wherein the transmitter is arranged to:

set the parameters corresponding to the intensity of the sound of the speech frame to be transmitted in such a way that the amplitude of the received speech frame is minimized; and

position the bit group corresponding to the message in the part of the speech frame which is best protected against transmission errors.

16. A transmitter according to claim 15, wherein the transmitter is part of a GSM system, and the transmitter is arranged to:

minimize the amplitude of the received speech frame by setting the block amplitude parameters of the speech frame to be transmitted below a predetermined threshold to make the speech signal inaudible; and

position the bit group corresponding to the message in the bits corresponding to the RPE parameters of the speech frame.

17. A transmitter according to claim 13, further comprising:

a DTMF detector for detecting DTMF signals occurring in a speech signal and for informing the message encoder of such a detection; and

the message encoder is arranged to generate a message corresponding to said DTMF signal in response to the detection of the DTMF signal.

18. A transmitter according to claim 17, wherein the DTMF detector or the message encoder are further arranged to substantially prevent the propagation of a DTMF signal as a DTMF sound to the transmission channel.

19. A receiver of a digital telecommunication system, comprising a speech decoder for generating speech from speech frames, and a message decoder for decoding messages wherein a corresponding predetermined bit group is defined per each possible message;

and the receiver is arranged to;

receive a signal comprising speech frames, some of which contain a message;

identify the speech frames containing messages only on the basis of the contents of the speech frames; and

monitor at least whether a speech frame contains a bit group which corresponds to one of said messages, and when it does, to interpret said speech frame as a message, the bit group including less than all bits of the speech frame.

20. A receiver according to claim 19, wherein the message decode is arranged to supply messages from the speech frames that are concluded to contain messages to the speech decoder.

21. A receiver according to claim 19, wherein the message decoder is arranged to supply the speech frames containing messages to the speech decoder through a bad parameter replacement block.

22. A receiver according to claim 19, wherein at least some messages correspond to different DTMF sounds, and the receiver is arranged, in response to a speech frame being interpreted as a message corresponding to a DTMF sound, to generate the DTMF sound corresponding to the message.

23. A transmitter according to claim 19, wherein the number of messages is less than 20, and the bit groups corresponding to the messages are selected such that the Hamming distance between them is as great as possible.

24. A signal of a speech channel in a digital telecommunication system, wherein the speech to be transmitted is coded as speech frames, some of which contain a message, wherein the changes to be made in the signal of the speech channel in order to transmit a message are restricted in time to the transmission moment of the message, and that less than all of the bits of the said speech frame are replaced with a predetermined bit group corresponding to said message.

25. A signal of a speech channel according to claim 24, wherein said changing further comprises that the parameters corresponding to the intensity of the sound of the speech frames corresponding to the transmission moment are below a predetermined threshold to make the speech signal inaudible.

26. A signal of a speech channel according to claim 25, wherein the signal is used in connection with full-rate speech coding of a GSM system, and in order to improve the immunity to disturbance, the block amplitude parameters of the speech frame are below a predetermined threshold to make the speech signal inaudible, and the RPE parameters are bit groups other than zero in such a manner that a different bit group corresponds to each different message and the Hamming distance between the bit groups is as great as possible.