| 摘要 |
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. |
