Adaptive data rate control for narrowcast networks

Abstract

A system to provide narrowcast communications uses adaptive data rate control to individual subscribers such that the effects of precipitation or other link conditions, which are not common to all subscribers, is mitigated. The invention takes advantage of the fact that the narrowcast data consist of packets which are individually addressed to specific subscribers, or groups of subscribers. The narrowcast data is communicated on a plurality of channels, each of potentially differing data rates. The subscribers are assigned a particular channel, based upon their link quality, to receive packets addressed to them. The lower data rate channel will be less affected by adverse link conditions and are hence assigned to subscribers most likely to incur adverse link conditions.

1 . (canceled) 
     
     
         2 . A hub terminal for communicating with a first subscriber terminal and a second subscriber terminal via a satellite, comprising:
 a data source configured to generate a first data packet comprising a first address for the first subscriber terminal and a second data packet comprising a second address for the second subscriber terminal;   
       a demultiplexer coupled to the data source and configured to switch the first data packet into a first carrier modulation circuit and the second data packet into a second carrier modulation circuit; 
       the first carrier modulation circuit configured to provide modulation and coding for a first carrier signal for transmitting the first data packet to the satellite and the second carrier modulation circuit configured to provide modulation and coding for a second carrier signal for transmitting the second data packet to the satellite; 
       a first gain control circuit coupled to the first carrier modulation circuit and configured to adjust signal level of the first carrier signal and a second gain control circuit coupled to the second carrier modulation circuit and configured to adjust signal level of the second carrier signal; and 
       a first transponder coupled to the first gain control circuit and configured to transmit the first carrier signal to the satellite and a second transponder coupled to the second gain control circuit and configured to transmit the second carrier signal to the satellite. 
     
     
         3 . The hub terminal of  claim 2 , wherein the first gain control circuit is adjusted based on a saturated output power of the first transponder. 
     
     
         4 . The hub terminal of  claim 2 , wherein the first gain control circuit is adjusted based on a gain of the first transponder. 
     
     
         5 . The hub terminal of  claim 2 , wherein the first gain control circuit is adjusted based on an output power backoff of the first transponder. 
     
     
         6 . The hub terminal of  claim 2 , further comprising an uplink power control circuit configured to change power level of the first carrier signal transmitted from the hub terminal to the satellite. 
     
     
         7 . The hub terminal of  claim 6 , wherein the power level of the first carrier signal is determined based on rain fade condition for the first carrier signal between the hub terminal and the satellite. 
     
     
         8 . The hub terminal of  claim 7 , wherein the rain fade condition of the first carrier signal between the hub terminal and the satellite is determined based on monitoring a downlink between the satellite and the hub terminal. 
     
     
         9 . The hub terminal of  claim 2 , wherein the first transponder transmits only the first carrier signal and the second transponder transmits only the second carrier signal. 
     
     
         10 . The hub terminal of  claim 2 , wherein the first carrier signal occupies a first frequency range and the second carrier signal occupies a second frequency range, wherein the first frequency range is different from the second frequency range. 
     
     
         11 . The hub terminal of  claim 2 , wherein the first carrier signal and the second carrier signal are frequency-division multiplexed (FDM) carrier signals. 
     
     
         12 . The hub terminal of  claim 2 , wherein the first carrier signal and the second carrier signal are time-division multiplexed (TDM) carrier signals. 
     
     
         13 . The hub terminal of  claim 2 , wherein the first carrier signal and the second carrier signal are code division multiplexed (CDM) carrier signals. 
     
     
         14 . A method for communicating with a first subscriber terminal and a second subscriber terminal via a satellite, comprising:
 generating a first data packet comprising a first address for the first subscriber terminal and a second data packet comprising a second address for the second subscriber terminal;   assigning the first data packet to a first carrier signal and the second data packet to a second carrier signal;   modulating and coding the first carrier signal according to a first modulation and coding scheme and the second carrier signal according to a second modulation and coding scheme;   adjusting gain of the first carrier signal and the second carrier signal;   transmitting to the satellite, using a first transponder, the first carrier signal; and   transmitting to the satellite, using a second transponder, the second carrier signal.   
     
     
         15 . The method of  claim 14 , wherein the gain for the first carrier signal is adjusted based on a saturated output power of the first transponder. 
     
     
         16 . The method of  claim 14 , wherein the gain for the first carrier signal is adjusted based on a gain of the first transponder. 
     
     
         17 . The method of  claim 14 , wherein the gain for the first carrier signal is adjusted based on an output power backoff of the first transponder. 
     
     
         18 . The method of  claim 14 , further comprising adjusting a power level of the first carrier signal transmitted from the hub terminal to the satellite. 
     
     
         19 . The method of  claim 18 , wherein the power level of the first carrier signal is determined based on rain fade condition for the first carrier signal between the hub terminal and the satellite. 
     
     
         20 . The method of  claim 19 , wherein the rain fade condition of the first carrier signal between the hub terminal and the satellite is determined based on monitoring a downlink between the satellite and the hub terminal. 
     
     
         21 . The method of  claim 14 , wherein the first carrier signal and the second carrier signal are or one or more of frequency-division multiplexed (FDM) carrier signals, time-division multiplexed (TDM) carrier signals or code division multiplexed (CDM) carrier signals.