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US 5,687,184 AGranted
Method and circuit arrangement for speech signal transmission
AssigneeU.S. Philips Corporation
InventorsDietmar Lorenz, Karl Hellwig
Life of this patent
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AssigneeU.S. Philips Corporation
InventorsDietmar Lorenz, Karl Hellwig
Estimating the term…
When speech data are transmitted via radio in the European mobile radio telephone system according to the GSM standard, always 20 ms speech data are transmitted as source-coded code words between the mobile stations and the fixed stations. The fixed stations are again connected to a central station via a connection having a smaller bandwidth, in which central station the speech decoders are arranged. Since transmission errors which cannot be corrected by the channel decoder in prior-art system are masked in the channel decoder in the central station, only a very simple error masking option is provided. According to the invention, the channel decoder which is arranged in the mobile and fixed stations close to the receiver, more signals are derived which feature the reliability of the received data and, in dependence on these additional data, extensive different error masking measures are carried out on the received code words. This does not only take place in the mobile station, but also in the fixed station. This fixed station then applies only already modified error-free code words to the central station which need not be modified because of this, but in which only the available simple error masking possibilities are not utilized. This may considerably improve the speech quality in disturbed transmission, without intervening in the GSM standard especially during transmission between the base stations and the central station.
A system comprising a first station and at least a second station, for transmitting speech signals between the stations, in which each station comprises a transmitting section for converting the speech signals of a time slot of given length to a plurality of bit code word groups having different connotations and for converting the bits to channel bits of a channel code and for transmitting the channel bits as a bit block, and also comprises a receiver which includes a receiving section for receiving and demodulating transmitted bit blocks to produce channel bits and which receiver includes a channel decoder for producing code word groups which have different connotations from the channel bits on a channel output and for producing error detection signals on at least one error output, at least one station comprising an error masking circuit coupled to the channel output, which error masking circuit includes a memory for code word groups of a previous bit block to produce modified code word groups in response to error detection signals, and a speech decoder for producing speech signals from the modified code word groups, wherein the channel decoder of at least several stations in the system is arranged for supplying on at least one error output error signals which indicate the extent of the fault in the received bit block and the error masking circuit is arranged to store in the memory only several of the code words of a previous bit block and, in dependence on error signals, to modify at least several of the code words of the received bit block in a different manner.
A receiver for receiving bit blocks of which each bit block is formed by speech signals of a time slot of a given duration, in that the speech signals are converted to a plurality of code word groups consisting of bits and having different connotations and the bits of these code word groups are converted to channel bits of a channel code, which receiver comprises a receiving section for receiving and demodulating transmitted bit blocks to produce channel bits, a channel decoder for producing code words having different connotations from the channel bits on a channel output and for producing error indication signals on at least one error output of an error masking circuit coupled to the channel output, which error masking circuit includes a memory for code word groups of a previous bit block, to produce modified code word groups in dependence on error indication signals, and includes a speech decoder for producing speech signals from the modified code word groups, wherein the channel decoder is arranged for producing on at least one error output error signals which indicate the extent of the fault in the received bit block and the error masking circuit is arranged for storing in the memory only several of the code words of a previous bit block and, in dependence on the error signals, modifying at least several of the code words of the received bit block in a different manner.
A method of transmitting speech signals between a first station and at least a second station, said method comprising the steps of:
Dependencies are inferred from the claim text.