The technology employs a state-based power control loop (PCL) architecture to maintain tracking and communication signal-to-noise ratios at suitable levels for optimal tracking performance and data throughput in a free-space optical communication system. Power for a link is adjustable to stay within a functional range of receiving sensors in order to provide continuous service to users. This avoids oversaturation and possible damage to the equipment. The approach can include decreasing or increasing the power to counteract a surge or drop while maintaining a near constant received power at a remote communication device. The system may receive power adjustment feedback from another communication terminal and perform state-based power control according to the received feedback. This can include re-initializing and reacquiring a link with the other communication terminal automatically after loss of power, without human intervention. There may be a default state and discrete states including rain, fade, surge and unstable states.

Embodiments of the present invention comprise a signal processing method and apparatus for use in a satellite payload in which an input RF signal received at a receiver antenna is modulated by using a single optical carrier at the input of an optical modulator. The optical domain signal is processed and is subsequently combined with a single unmodulated optical LO tone to provide an output RF signal for radiation by a transmitter antenna or for further digital processing by an on-board processor. This results in a clean generation of the frequency-converted RF signal at the output of the opto-electrical conversion stage.

Embodiments of the present invention comprise a signal processing method and apparatus for use in a satellite payload in which an input RF signal received at a receiver antenna is modulated by using a single optical carrier at the input of an optical modulator. The optical domain signal is processed and is subsequently combined with a single unmodulated optical LO tone to provide an output RF signal for radiation by a transmitter antenna or for further digital processing by an on-board processor. This results in a clean generation of the frequency-converted RF signal at the output of the opto-electrical conversion stage.

A system and method for high speed communication are provided. The system comprises a laser-based system for communication, the system comprising: an acquisition module configured to acquire and characterize a plurality of laser beams; a tracking module configured to track the acquired laser beams, the tracking module comprising: a beaconing feedback and beam divergence mechanism configured to control a beam and detect a beam; an adaptive learning unit configured to implement an adaptive learning detection algorithm to identify and track a unique optical signature from at least one of the acquired laser beams; and a pointing module configured to point at least one laser beam towards a target based on the acquired laser beams.

A system and method for high speed communication are provided. The system comprises a laser-based system for communication, the system comprising: an acquisition module configured to acquire and characterize a plurality of laser beams; a tracking module configured to track the acquired laser beams, the tracking module comprising: a beaconing feedback and beam divergence mechanism configured to control a beam and detect a beam; an adaptive learning unit configured to implement an adaptive learning detection algorithm to identify and track a unique optical signature from at least one of the acquired laser beams; and a pointing module configured to point at least one laser beam towards a target based on the acquired laser beams.

Methods and systems are described for providing end-to-end beamforming. For example, end-to-end beamforming systems include end-to-end relays and ground networks to provide communications to user terminals located in user beam coverage areas. The ground segment can include geographically distributed access nodes and a central processing system. Return uplink signals, transmitted from the user terminals, have multipath induced by a plurality of receive/transmit signal paths in the end to end relay and are relayed to the ground network. The ground network, using beamformers, recovers user data streams transmitted by the user terminals from return downlink signals. The ground network, using beamformers generates forward uplink signals from appropriately weighted combinations of user data streams that, after relay by the end-end-end relay, produce forward downlink signals that combine to form user beams.

Methods and systems are described for providing end-to-end beamforming. For example, end-to-end beamforming systems include end-to-end relays and ground networks to provide communications to user terminals located in user beam coverage areas. The ground segment can include geographically distributed access nodes and a central processing system. Return uplink signals, transmitted from the user terminals, have multipath induced by a plurality of receive/transmit signal paths in the end to end relay and are relayed to the ground network. The ground network, using beamformers, recovers user data streams transmitted by the user terminals from return downlink signals. The ground network, using beamformers generates forward uplink signals from appropriately weighted combinations of user data streams that, after relay by the end-end-end relay, produce forward downlink signals that combine to form user beams.

A laser communication system for an aircraft has optical head units, separate laser transmitting unit, laser receiving unit, optical fiber for each optical head unit, optical switching device for coupling an optical head unit and a separate laser transmitting unit, and a central control unit, the optical head units connected to the optical switching device through the optical fiber, the optical head units having an optical axis, parallel to which light is emitted or received, and an optical pointing mechanism for adjusting the respective optical axis. The separate laser transmitting unit has a laser. The control unit connects to the optical switching device, laser transmitting unit, laser receiving unit and optical head unit to control a laser based data communication through coupling an optical head unit, which is in a free line of sight to a target outside the aircraft, to the laser transmitting unit and to modulate operation of the laser transmitting unit for emitting a signal.

A method and an apparatus for satellite laser broadband demodulation are provided. The method includes: setting a residual carrier to a carrier acquisition range of a receiver, pulling the residual carrier to an MHz level by adjusting a frequency of a local oscillator laser, and obtaining a precise carrier frequency according to an accurate frequency acquisition, such that the residual carrier enters a fast acquisition band of a carrier tracking phase-locked loop. After carrier acquisition is achieved, carrier tracking and data recovery processing are performed. According to the present disclosure, signal equalization of an ultra-high bandwidth/ultra-high bit rate can be implemented, and carrier acquisition, tracking, and demodulation are quickly achieved for a modulation signal in a high dynamic range.

Methods, apparatus, and systems are provided for performing a quantum key distribution (QKD) protocol between a first device, a second device, and an intermediary device. The intermediary device transmitting: a first secret symbol string over a first quantum channel to the first device; a first basis set over a first communication channel to the first device. The intermediary device; a second secret symbol string over a second quantum channel to the second device; a second basis set over a second communication channel to the second device. The intermediary device generating a third symbol string based on combining the first and second secret symbol strings and transmitting to the second device, via the second communication channel, data representative of the third symbol string. The first device and second device perform a quantum key exchange and sifting based on the corresponding received first and second secret symbol strings and first and second basis sets, and a fourth set of symbols generated by the second device generates a fourth set of symbols based on combining the second received secret symbols with the received third symbol string.