Predistortion in satellite signal transmission systems
A signal transmission system for a satellite comprises means ( 31 ) for producing a signal to be transmitted; a first signal channel ( 37 ) which includes a first digital pre-distortion device ( 32 ) for applying pre-distortion to the signal; a second signal channel ( 38 ) for processing an envelope of the signal, which includes a second digital pre-distortion device ( 35 ) for applying pre-distortion to the envelope of the signal; and output means ( 34 ) for transmitting the signal.
1. A signal transmission system for a satellite comprising:
means for producing a signal to be transmitted;
a first signal channel which includes a digital pre-distortion device for applying a first pre-distortion to the signal, and a driver amplifier;
a second signal channel for processing an envelope of the signal, wherein the second channel is connected in parallel to the first channel, which includes: an envelope amplifier whose output is connected to the driver amplifier and which controls the power supply to the driver amplifier by applying a power gain to said envelope of the signal, a second digital pre-distortion device for applying a second pre-distortion to the envelope of the signal to cancel out the non-linearity of the envelope amplifier; and
output means for transmitting the signal.
2. A signal transmission system according to claim 1 , wherein the first channel includes a power amplifier.
3. A signal transmission system according to claim 2 , wherein the power amplifier can be switched off when low power output is required.
4. A signal transmission system according to claim 1 , wherein the output means further comprise an antenna.
5. A signal transmission system according to claim 4 , wherein the means for modulating the output load of the system includes a matching network for modulating a load on the antenna.
6. A signal transmission system according to claim 5 , wherein the matching network comprises one or more varactors.
7. A signal transmission system according to claim 4 , wherein the means for modulating the output load of the system include a matching network for modulating a load on the antenna.
8. A signal transmission system according to claim 1 , further comprising means for modulating the power output by the output means.
9. A signal transmission system according to claim 1 , wherein the output means further comprise an antenna.
10. A method of transmitting a signal comprising:
producing a signal to be transmitted;
applying a first pre-distortion to the signal and amplifying the distorted signal using a driver amplifier;
isolating a band-limited envelope of the signal and applying a second pre-distortion to the envelope to substantially cancel out the non-linearity introduced by an envelope amplifier amplifying the envelope of the signal;
using the distorted envelope signal to control the driver amplifier;
modulating an output load of the system; and
transmitting the modulated output using an antenna.
11. A signal transmission system for a satellite comprising:
means for producing a signal to be transmitted;
a first signal channel which includes a digital pre-distortion device for applying pre-distortion to the signal;
a second signal channel for processing an envelope of the signal, which includes a second digital pre-distortion device for applying pre-distortion to the envelope of the signal and an envelope amplifier whose output is connected to a driver amplifier; said envelope amplifier applying a power gain to said envelope of the signal;
means for modulating the output load of the system; and
output means including an output load for transmitting the modulated output signal.