Excavating
Patent
1994-06-10
1997-03-25
MacDonald, Allen R.
Excavating
395 242, 395 223, 371 491, H04M 1106, H04J 316, H04L 2549
Patent
active
056152973
DESCRIPTION:
BRIEF SUMMARY
FILED OF THE INVENTION
The present invention relates to apparatus for coding voice-band signals into digital form, and to apparatus for decoding such signals. More particularly the object is to provide a coder and decoder able to accommodate both speech signals and modulated data signals.
SUMMARY OF THE INVENTION
Thus the invention provides, in a first aspect, an audio-frequency coding apparatus comprising: a predetermined modulation scheme; dependent on the presence or absence respectively of signals according to the predetermined modulation scheme; and from, in the speech mode, the speech coder, into a common framing structure; and positions within the framing structure to generate parity bits and to insert these in predetermined positions within the framing structure, the sense of the parity bits when in the data mode being the reverse of that in the speech mode.
In another aspect of the invention there is provided an apparatus for decoding signals thus coded comprising: checks thereon to produce a parity pass/fail signal for each frame; apparatus between a data mode and a speech mode; to provide a modulated signal to the output of the apparatus; and received signals to provide a speech signal to the said output.
BRIEF DESCRIPTION OF THE DRAWINGS
Some embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a block diagram of one form of voice-band coding apparatus in accordance with the invention; and
FIG. 2 is a block diagram of a decoding apparatus.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring to FIG. 1, analogue voice-band signals received at an input 100 are sampled and converted to digital form in an analogue-to-digital converter 101, the output of which is supplied to the input of a speech coder 102. The speech coder can be any of various types of redundancy-reducing digital speech coder currently available, for example a multipulse-excited LPC coder. The output of the speech coder is supplied to a formatting unit 103 which formats the data with parity bits and framing information into a frame structure. The formatted data are fed to a modulator 104 to convert the signal to a form suitable for transmission by a radio transmitter 105. The parity bits are produced in a parity generator 106 which produces parity bits for all, or for the most sensitive, groups of speech data being transmitted.
FIG. 2 shows a decoder. Signals are received by a radio receiver 200 and demodulated in a demodulator 201. The digital speech parameters are fed to a speech decoder 202 and also to a parity check unit 203; if more than a predetermined number of parity bits is incorrect, a "parity fail" signal is produced and serves to mute the speech decoder 202. The decoded output is converted to analogue form by a converter 204 and supplied to an output 205.
Returning now to FIG. 1, the bit rate reduction in the speech coder 102 is achieved by exploiting the inherent redundancy of a speech signal. Such coders generally are optimized for the known characteristics of speech signals and consequently perform badly if one attempts to use them to process voice-band data such as modulated signals of the type used for group III facsimile transmission. In order to enable the encoder to handle such data signals, a detector 107 monitors the input 100 to identify signals of this kind. In this embodiment the detector 107 serves to detect the presence of phase-shift-keyed (PSK) modulated signals according to CCITT standard V. 27. In the event of recognition by the detector 107 a V. 27 demodulator 108 is enabled; the demodulated data are forwarded to the formatting unit 103 in place of the data from the speech coder 102, via a changeover switch 109. The data are then formatted, in any desired manner, into the same frame structure, subject however to the constraint that the parity bits are generated from the data bits having the same positions in the frame and occupy the same positions in the frame as before. A modulation codeword indicating the type o
REFERENCES:
patent: 4876696 (1989-10-01), Yoshikawa
Roberge et al, "Fast On-Line Speech/Voiceband-Data Discrimination for Statistical Multiplexing of Data with Telephone Conversations", IEEE Transactions on Communications, vol. COM-34, No. 8, Aug. 1986, (New York, US), pp. 744-751.
Casale et al, "A DSP Implemented Speech/Voiceband Data Discriminator", IEEE Global Telecommunications Conference & Exhibition, Hollywood, Florida, 28 Nov.-1 Dec. 1988, vol. 3, pp. 1419-1427.
Patent Abstracts of Japan, vol. 14, No. 252, (E-934), 30 May 1990 & JP A,02072733 (Fujitsu Ltd) 13 Mar. 1990.
Digital Communication by Edward A. Lee and David G. Messerschmitt, Kluwer, 1988, p. 602, Fig. 16-8.
British Telecommunications public limited company
MacDonald Allen R.
Smits Talivaldis Ivars
LandOfFree
Transmission system for coded speech signals and/or voiceband da does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transmission system for coded speech signals and/or voiceband da, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transmission system for coded speech signals and/or voiceband da will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2210959