System and method for a robust preamble and transmission delimiting in a switched-carrier transceiver

Abstract

A method and system for robust delimiting of messages in switched-carrier operation in which a preamble precedes each message. The preamble comprises symbols transmitted at a rate lower than that of the following data. The lower rate significantly increases the probability that decoding of the preamble symbols will be error-free. Communication line control information can be included in the preamble, thereby ensuring that line control information is reliably transferred over the channel. The preamble's first symbol can be transmitted at the lower symbol rate and at an increased power level, thereby reliably delimiting the beginning of a transmission. The end of the message can be reliably delimited by sending the first symbol which contains only bits from a next cell of information at a lower symbol rate, and including an extra bit in that symbol. The extra bfit can indicate to a receiver when the last cell of information begins.

1 . A method for adapting transmission rate in a communication device over a communication channel by including rate information in a first portion of a communication message, comprising the steps of: 
 transmitting the first portion at a first rate, the first portion operating to frame the message and to delimit the message from silence and including rate information specifying a rate at which data in a second portion of the communication message is transmitted; and    transmitting the data at a second rate specified by the rate information included in the first portion.    
     
     
         2 . The method of  claim 1 , wherein all transmitted messages include the rate information.  
     
     
         3 . The method of  claim 1 , further comprising the step of encoding the first portion into a plurality of symbol indices, each of the symbol indices encoded at a lower bits-per-symbol rate relative to a maximum rate supported by the device over the communication channel.  
     
     
         4 . The method of  claim 3 , further comprising the step increasing the energy of the first symbol index.  
     
     
         5 . The method of  claim 1 , wherein the rate information specifies a bits-per-symbol rate at which the data is encoded.  
     
     
         6 . The method of  claim 1 , wherein the first rate is a fixed value known to the device and to a remote device in communication with the device over the communication channel.  
     
     
         7 . The method of  claim 1 , further comprising the step of indicating, via the first portion, whether the second portion includes data and, if so, the format and type of data.  
     
     
         8 . The method of  claim 1 , further comprising the step of indicating, via the first portion, whether administrative information follows the first portion.  
     
     
         9 . A computer-readable medium containing a program for adapting transmission rate in a communication device over a communication channel by including rate information in a first portion of a communication message, the program comprising the steps of: 
 transmitting the first portion at a first rate, the first portion operating to frame the message and to delimit the message from silence and including rate information specifying a rate at which data in a second portion of the communication message is transmitted; and    transmitting the data at a second rate specified by the rate information included in the first portion.    
     
     
         10 . The computer-readable medium of  claim 9 , wherein all transmitted messages include the rate information.  
     
     
         11 . The computer-readable medium of  claim 9 , the program further comprising the step of encoding the first portion into a plurality of symbol indices, each of the symbol indices encoded at a lower bits-per-symbol rate relative to a maximum rate supported by the device over the communication channel.  
     
     
         12 . The computer-readable medium of  claim 3 , the program further comprising the step increasing the energy of the first symbol index.  
     
     
         13 . The computer-readable medium of  claim 9 , wherein the rate information specifies a bits-per-symbol rate at which the data is encoded.  
     
     
         14 . The computer-readable medium of  claim 9 , wherein the first rate is a fixed value known to the device and to a remote device in communication with the device over the communication channel.  
     
     
         15 . The computer-readable medium of  claim 9 , the program further comprising the step of indicating, via the first portion, whether the second portion includes data and, if so, the format and type of data.  
     
     
         16 . The computer-readable medium of  claim 9 , the program further comprising the step of indicating, via the first portion, whether administrative information follows the first portion.  
     
     
         17 . An apparatus for adapting transmission rate in a communication device over a communication channel by including rate information in a first portion of a communication message, the apparatus comprising: 
 first logic configured to transmit the first portion at a first rate, the first portion operating to frame the message and to delimit the message from silence and including rate information specifying a rate at which data in a second portion of the communication message is transmitted; and    second logic configured to transmit the data at a second rate specified by the rate information included in the first portion.    
     
     
         18 . The apparatus of  claim 17 , wherein all transmitted messages include the rate information.  
     
     
         19 . The apparatus of  claim 17 , wherein the rate information specifies a bits-per-symbol rate at which the data is encoded.  
     
     
         20 . The apparatus of  claim 17 , wherein the first rate is a fixed value known to the device and to a remote device in communication with the device over the communication channel.