US 5,491,719 AGranted

System for handling data errors on a cellular communications system PCM link

AssigneeTelefonaktiebolaget LM Ericsson

InventorsPatrik C. Sellin, Orjan P. S. Fall, Anders K. Molin, Lars J. Wilhelmsson

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Abstract

A digital cellular communications system has a bidirectional pulse code modulation (PCM) link for conveying encoded speech and control data in the form of blocks, a switching unit coupled to a first end of the PCM link, and a base station coupled to a second end of the PCM link. The switching unit includes a speech encoder for encoding speech signals, an error detection code generator for generating an error detection code from the encoded speech signal, and a formatter, coupled to the error detection code generator, for producing a formatted block to be transmitted on the PCM link, the formatted block having a header, the encoded speech dam, and the error detection code. The base station has a PCM link error detector for signalling the existence of an error in a received block in response to the received block containing an error. The base station further includes a downlink error handler coupled to the PCM link error detector, for discarding a received block in response to the signal indicating the existence of an error therein, and for substituting therefor a default control message to be relayed to a mobile station, the default control message having no meaning defined by the digital cellular communications system, whereby the mobile station, in response to receiving the default control message, performs no operation other than a bad frame masking operation. Uplink error detection and handling is also provided.

Claims15

Dependent claims

In a digital cellular communication system including a switching unit coupled to a base station by means of a bidirectional pulse code modulation (PCM) link, the switching unit including a speech codes for coding downlink speech signals and decoding uplink speech signals that are respectively transmitted to and received from the base station by means of the PCM link, the PCM link conveying encoded downlink and uplink speech and control data in respective downlink and uplink blocks, the base station operating to relay an encoded downlink speech signal received from the switching unit to a mobile station by means of transmission on a radio channel and to relay to the switching unit an encoded uplink speech signal received from the mobile station by means of transmission on the PCM link, the base station further operating to send a defined control message to the mobile station by means of transmission on the radio channel when it is desired to send a command to the mobile station, said transmission of the defined control message occurring in place of the transmission to the mobile station of the encoded downlink speech signal, a system for handling errors in a transmitted block, comprising:

in the base station, input means for receiving a signal indicative of existence of an error in a received downlink block;
and
in the base station, downlink error handling means coupled to the input means, for discarding a received downlink block in response to the signal indicating existence of an error therein, and for substituting therefor a default control message to be relayed to the mobile station, the default control message having no meaning defined by the digital cellular communications system, whereby the mobile station, in response to receiving the default control message, performs no operation other than a bad frame masking operation.

A digital cellular communications system comprising:

a bidirectional pulse code modulation (PCM) link for conveying encoded speech and control data in a block format;
a switching unit coupled to a first end of the PCM link, the switching unit including
a speech encoder for encoding speech signals;
means for generating an error detection code from the encoded speech signal;
and
formatting means, coupled to the generating means, for producing a formatted downlink block to be transmitted on the PCM link, the formatted downlink block having a header, the encoded speech data, and the error detection code;
and
a base station coupled to a second end of the PCM link, the base station including
PCM link error detecting means for signalling existence of an error in a received downlink block in response to the received downlink block containing an error;
and
downlink error handling means, coupled to the PCM link error detecting means, for discarding a received downlink block in response to the signal indicating existence of an error therein, and for substituting therefor a default control message to be relayed to a mobile station, the default control message having no meaning defined by the digital cellular communication system, whereby the mobile station, in response to receiving the default control message, performs no operation other than a bad frame masking operation,
wherein when no error is detected in the received downlink block, the base station relays to the mobile station alternatively an encoded downlink speech signal received from the switching unit or a defined control message.

9 more elements

Dependencies are inferred from the claim text.