Bit synchronization method for a digital radio telephone system

A method of maintaining continuous bit synchronization of digitally encrypted speech transmitted over both landline and radio frequency (RF) data transmission paths between a land station and a remote station through a base station, said bit synchronization in the remote station:

• converting an analog input speech signal into digital speech data to provide an input data stream having a first bit rate;
• encrypting said input data stream to provide an encrypted data stream;
• interleaving a predetermined number of data bits of said encrypted data stream with a plurality of predetermined signalling words to provide a combined data message having a second bit rate;
• encoding said combined data message into a digital format;
• transmitting said encoded data message via said RF transmission path;
• in the base station:
• receiving said transmitted data message from said RF transmission path;
• phase-locking a clock signal to said received data message and clocking said received data message through subsequent steps with said phase-locked clock signal;
• decoding said received data message;
• correlating said signalling words of said received data message with known signalling words to provide a correlation detect signal;
• counting a number of data bits of said received data message occurring after said correlation detect signal until said predetermined number of data bits have been counted;
• separating said counted number of data bits from said received data message to provide a plurality of separated data words having an instantaneous bit rate corresponding to said phase-locked clock signal;
• buffering said separated data words to provide a continuous data stream at said first bit rate;
• adjusting the clock rate of said continuous data stream to meet predetermined data rate tolerance requirements of landline transmission equipment;
• transmitting said adjusted data stream via said landline transmission path;
• in said land station:
• receiving said tansmitted data stream from said landline transmission path;
• decrypting said received data stream and
• converting said decrypted data stream into an analog signal, thereby reconstructing said input speech signal.

A data communications system capable of maintaining continuous bit synchronization of an input data stream to an output data stream over a data transmission path having digital signalling capabilities, said data communications system comprising:

• (a) means for accepting an input data stream at a first bit rate, and accepting at least one predetermined signalling word;
• (b) means for interleaving said signalling word with a predetermined number of data bits of said input data stream to provide a combined data message having a second bit rate;
• (c) means for transmitting said combined data message via said data transmission path;
• (d) means for receiving said transmitted data message;
• (e) means for recovering a clock signal from said received data message;
• (f) means for separating said signalling word from said received data message to provide separated data words having an instantaneous bit rate corresponding to said recovered clock signal;
• (g) means for modifying the number of data bits of said separated data words to approximate said predetermined number of data bits, thereby providing
• (h) means for modifying the clock rate of said modified data words to correspond to said first bit rate, thereby providing an output data stream which is in bit synchronization with said input data stream.

A method of providing continuous bit synchronization of an input data stream to an output data stream, said input data stream having a first bit rate, wherein a predetermined number of data bits of said input data stream are interleaved with at least one predetermined signalling word to form a received data message, said received data message having a second bit rate, said bit synchronization method comprising the steps of:

• (a) recovering a clock signal from said received data message;
• (b) separating said signalling word from said received data message to provide separated data words having an instantaneous bit rate corresponding to said recovered clock signal;
• (c) modifying the number of data bits of said separated data words to correspond to said predetermined number of data bits, thereby providing modified data words;
• and
• (d) modifying the clock rate of said modified data words to correspond to said first bit rate, thereby providing an output data stream which is in bit synchronization with said input data stream.

A data communications receiver capable of maintaining continuous bit synchronization of an input data stream to an output data stream, said input data stream having a first bit rate, wheein a predetermined number of data bits of said input data stream are interleaved with at least one predetermined signalling word to form a transmitted data message, said transmitted data message having a second bit rate, said data communications receiver comprising:

• (a) means for receiving said transmitted data message;
• (b) means for recovering a clock signal from said received data message;
• (c) means for separating said signalling word from said received data message to provide separated data words having an instantaneous bit rate corresponding to said recovered clock signal;
• (d) means for modifying the number of data bits of said separated data words to correspond to said predetermined number of data bits, thereby providing modified data words;
• and
• (e) means for modifying the clock rate of said modified data words to correspond to said first bit rate, thereby providing an output data stream which is in bit synchronization with said input data stream.