Carrier activation for data communications

Abstract

In a radio frequency communications system, a data carrier activation method is implemented such that the carrier is switched off when no data is available for transmission. If repeated signalling information is required to be transmitted, only a predetermined number of repeats is transmitted before the carrier is switched off. The data input for transmission are compared with an idle sequence with different bit alignments to detect the presence of idle signalling, and the carrier is switched off if a match is found. When more user data is received, the carrier is switched on and frames (SM) are transmitted in synchronization with the timing of frames (SM) transmitted before the carrier deactivation. After carrier reactivation, a constant power preamble (P) may be transmitted to assist in level control in the transmitter ( 27; 40 ).

1 . Communications interface apparatus for connection between a source of data, including both user data and signalling information, and a transmitter, such that said user data is transmitted by said transmitter on a modulated radio frequency carrier, 
 the apparatus being arranged to receive said data, to detect the presence of repeated signalling information and the absence of user data in said data, and to deactivate said carrier if the number of repetitions of said signalling information is equal to or exceeds a predetermined value, such that excess repetitions are not transmitted.    
     
     
         2 . Apparatus as claimed in  claim 1 , wherein said signalling information is an HDLC line control message.  
     
     
         3 . Apparatus as claimed in  claim 1 , wherein said signalling information is a flow control message.  
     
     
         4 . A method of carrier deactivation, comprising: 
 receiving data, including both user data and signalling information, and transmitting said user data on a modulated radio frequency carrier, the method including: 
 detecting the presence of repeated signalling information and the absence of user data in said data, and  
 deactivating said carrier if the number of repetitions of said signalling information is equal to or exceeds a predetermined value, such that said excess repetitions are not transmitted.  
   
     
     
         5 . A method as claimed in  claim 4 , wherein said signalling information is an HDLC line control message.  
     
     
         6 . A method as claimed in  claim 4 , wherein said signalling information is a flow control message.  
     
     
         7 . Satellite communications interface apparatus for connection between a source of data and an earth station transmitter, 
 the apparatus being arranged to format said data as a series of constant length frames and to selectively output said frames to said transmitter such that said output frames are transmitted on a modulated radio frequency carrier in an SCPC format,    the apparatus being further arranged to detect whether at least an initial portion of each of said frames contains no information or only redundant information, to control the transmitter to deactivate the carrier in response to a positive said detection, to reactivate the carrier in response to a subsequent negative said detection, and to transmit frames subsequent to said reactivation with a timing synchronised with that of frames prior to said deactivation.    
     
     
         8 . Apparatus as claimed in  claim 7 , wherein the apparatus is arranged to detect whether the whole of each of said frames contains no information or only redundant information.  
     
     
         9 . A method of satellite carrier activation, comprising: 
 receiving data, formatting said data as a series of constant length frames, and selectively transmitting said frames on a modulated radio frequency carrier in an SCPC format,    the step of selective transmission comprising detecting whether at least an initial portion of each frame contains no information or only redundant information, and deactivating the carrier such that said portion of the frame is not transmitted,    wherein, after the carrier is deactivated, subsequent frames are transmitted with a timing synchronised with that of frames transmitted prior to said deactivation.    
     
     
         10 . A method as claimed in  claim 9 , wherein the detecting step comprises detecting whether the whole of each of said frames contains no information or only redundant information.  
     
     
         11 . A method of transmitting a data burst via satellite to a receiving terminal, comprising: 
 transmitting the data burst in a format comprising one or more frames having a variable power level modulation, preceded by a preamble having a constant power level.    
     
     
         12 . A method as claimed in  claim 11 , wherein the power level of said preamble is approximately equal to the average power level of said one or more frames.  
     
     
         13 . A data burst signal comprising a frequency carrier modulated by a preamble having a constant power level, followed by one or more data frames having a variable power level.  
     
     
         14 . Radio frequency communications apparatus for connection between a source of data and a radio frequency transmitter, the apparatus being arranged to divide said data in sequence into blocks and to compare a series of bits of a predetermined length at the end of a first block with multiple sequential series of bits of said predetermined length comprising a second block, and, if all of said series are equal, inhibiting transmission of said second block.  
     
     
         15 . Apparatus as claimed in  claim 14 , further comprising carrier control means for deactivating or reducing the power level of a carrier transmitted by the radio frequency transmitter for at least approximately a transmission time corresponding to the length of said second block.  
     
     
         16 . Apparatus as claimed in  claim 14 , further arranged to format the blocks into frames for transmission, each of said blocks being of the same length and each of said frames comprising the same, integral number of said blocks.  
     
     
         17 . Apparatus as claimed in  claim 15 , further arranged to format the blocks into frames for transmission, each of said blocks being of the same length and each of said frames comprising the same, integral number of said blocks.  
     
     
         18 . A method of radio frequency communication, comprising: 
 dividing data for transmission into blocks in sequence;    comparing a series of bits of a predetermined length at the end of a first block with multiple sequential series of bits of said predetermined length comprising a second block, and    if all of said series are equal, inhibiting transmission of said second block.    
     
     
         19 . A method as claimed in  claim 17 , further comprising deactivating or reducing the power level of a carrier transmitted by the radio frequency transmitter for at least approximately a transmission time corresponding to the length of said second block.  
     
     
         20 . A method as claimed in  claim 17 , further comprising formatting the blocks into frames prior to transmission, each of the blocks being of the same length and each of said frames comprising the same, integral number of said blocks.  
     
     
         21 . A method as claimed in  claim 18 , further comprising formatting the blocks into frames prior to transmission, each of the blocks being of the same length and each of said frames comprising the same, integral number of said blocks.  
     
     
         22 . A satellite earth station including apparatus as claimed in  claim 1 .  
     
     
         23 . A satellite earth station including apparatus as claimed in  claim 7 .  
     
     
         24 . A satellite earth station including apparatus as claimed in claim  14 .