Multiplex communications – Wide area network – Packet switching
Patent
1995-05-19
1997-11-25
Tung, Kee M.
Multiplex communications
Wide area network
Packet switching
370336, 370521, 375240, 455 331, 455 561, 455116, 330144, G10L 302
Patent
active
056921055
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a transcoding unit and a transdecoding unit in a digital mobile radio system.
The invention further relates to a method for adjusting the output signal of a transcoding unit and the output signal of a transdecoding unit in a digital mobile radio system.
BACKGROUND OF THE INVENTION
Voice-frequency signals, i.e. speech signals, data signals, and signalling, all encoded into digital bits, are transmitted on the data channel of a Digital Base Station System (DBSS) of a digital mobile radio or radio telephone system. Certain base station system parts processing the data channels can be implemented such that they shape the speech signal. Such shaping may be, e.g., amplification, attenuation, and cutting signal level peaks.
In the prior art systems, speech signals transmitted in the data channel have been amplified in order that the voice formed on the basis of the signal heard by the user of a subscriber station or the subscriber of a telecommunications network will have a sufficient strength. In addition to amplification, the signal typically has to be transcoded, and transdecoded, e.g., by the LTP (Long Term Prediction) or RPE (Regular Pulse Excitation) or LPC (Linear Predictive Coding) method. The GSM system has typically utilized a combination of these, i.e. an RPE-LTP-LPC method, described, e.g., in The GSM System for Mobile Communications, by M. Mouly and M. B. Pautet, 1992, 49 rue Louise Bruneau, Palaiseau F-91120, p. 155-162. A more detailed description of the methods can be found in GSM 06.10, January 1990 , GSM Full Rate Speech Transcoding, ETSI, 93 p. These coding methods handle drastic amplitude variations and instances of exceeding of an allowable amplitude range occurring in the signal to be encoded so that the subscriber receiving the signal and thus hearing the voice experiences distortion and strong interferences in the voice. This is a major problem particularly in the GSM system, where the signal to the subscriber is amplified in order that the transmitted signal heard by the subscriber will have a higher strength.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and a system, by means of which a signal to be transmitted in a telecommunications system can be amplified without causing the signal to be amplified to such an extent that its amplitude exceeds the dynamic range of the equipment used in transmission or coding in the telecommunications system.
The invention thus relates to a transcoding unit in a digital mobile radio system comprising an expander unit for converting companded digital data into a linear signal; a speech encoder for coding a linearized signal into encoded form; and an amplifying means for amplifying the expanded signal.
This new transcoding unit of a digital mobile radio system according to the invention is implemented such that it is characterized in that it further comprises a level-monitoring means for monitoring the amplitude of the linearized signal and for controlling the amplifying means such that the signal produced by the amplifying means is of a desired level.
The invention also relates to a transdecoding unit in a digital mobile radio system, comprising a speech decoder for converting encoded data into linear form; an amplifying means for amplifying the linear data; and a compander unit for companding the amplified linear data. The transdecoding unit of the invention is characterized in that it further comprises a level monitoring means for monitoring the amplitude of the linearized signal and controlling the amplifying means such that the signal produced by the amplifying means is of a desired level.
The invention further relates to a method for adjusting the output signal of a transcoding unit in a digital mobile radio system, where companded digital data is expanded into a linear signal, and the linear signal is encoded. This method is characterized in that it further comprises measuring the amplitude of the linearized signal; and adjusting amplification of the signal
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Mouly et al., The GSM System for Mobile Communications, 1992, pp. 149-184.
Fascicle III.4--Rec. G.711, "7.1 Coding of analogue signals by pulse code modulation", pp. 175-184, 1972.
GSM Full-Rate Speech Transcoding, ETSI/GSM, version 3.2.0, Jul. 5, 1989, pp. 1-93.
Inband Control of Remote Transcoders and Rate Adaptors, ETSI/GSM, Oct. 1994, pp.1-29.
Leppanen Reijo
Vanska Marko
Nokia Telecommunications Oy
Tung Kee M.
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