# US 2013/0156432 A1 · Optical downlink system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2013/0156432 A1 - Document ID: US20130156432A1 - Status: Published application - Kind: A1 - Application number: 13/675,033 - Filed: 2012-11-13 - Published: 2013-06-20 - Earliest claimed: 2011-12-20 - Assignees: RUAG Schweiz AG - Inventors: Felix Andreas Arnold; Thomas Dreischer - Web page: https://patentgrep.com/patent/US20130156432A1 ## CPC - H04B 10/118: specially adapted for satellite communication - H04B 7/185: Space-based or airborne stations; {Stations for satellite systems}(H04B7/204 takes precedence) - H04B: TRANSMISSION ## Abstract Optical downlink system (10) and method of optical data transmission between a remote terminal (20) having a number of n optical communication terminals (OT1-OTn), and a ground terminal (30) comprising a cluster of n optical ground stations (OGS1-OGSn) connected by n optical downlink channels (DL1-DLn) respectively n optical uplink channels (UC1-UCn) characterised by a spatial separation of the optical downlink channels (DL1-DLn) and a temporal separation of the optical uplink channels (UC1-UCn). ## Claims ### Claim 1 Optical downlink system (10) comprising: a remote terminal (20) comprising a number of n optical communication terminals (OT1-OTn), where n is greater than or equal to two; a ground terminal (30) comprising a cluster of n optical ground stations (OGS1-OGSn); each optical communication terminal (OT1-OTn) being connected with a corresponding optical ground station (OGS1-OGSn) with one of n optical downlink channels (DL1-DLn); and each optical ground station (OGS1-OGSn) being connected with a corresponding optical communication terminal (OT1-OTn) with one of n optical uplink channels (UC1-UCn); wherein the optical downlink channels (DL1-DLn) are spatially separated from each other by means of the optical ground stations (OGS1-OGSn) being located a certain distance apart from each other; and wherein the ground terminal (30) is configured such as to synchronise the n optical ground stations (OGS1-OGSn) such that a precise temporal separation is ensured between the n optical uplink channels (UC1-UCn) by a time division multiple access scheme thereby avoiding overlap between the optical uplink channels (UC1-UCn). ### Claim 2 (depends on 1) Optical downlink system (10) according to claim 1, characterised in that the ground terminal (30) comprises a sync unit, preferably as part of one of the n optical ground stations (OGS1-OGSn) being a master ground station, the sync unit being configured to synchronise the n ground stations (OGS1-OGSn) so that at any moment in time, only one ground station (OGS1-OGSn) is transmitting, thus providing for the temporal separation of the n optical uplink channels (UC1-UCn), ensuring that only one of the n optical uplink channels (UC1-UCn) is active at a time. ### Claim 3 (depends on 2) Optical downlink system (10) according to claim 2, characterised in that the n optical uplink channels (UC1-UCn) are pulse position modulated (PPM) signals, wherein the sync unit controls the n optical ground stations (OGS1-OGSn) such that pulses of each of the pulse position modulated PPM signals of any one of the n uplink channels (UC1-UCn) are emitted sequentially during phases of pulse silence (Ps) of the other uplink channels (UC1-UCn), by dividing the period (T) of the pulse position modulated (PPM) signals to the number n of optical uplink channels (UC1-UCn) and assigning each optical ground stations (OGS1-OGSn) a dedicated time slot (Ts) less than or equal to T/n. ### Claim 4 (depends on 3) Optical downlink system (10) according to claim 3, characterised in that the n optical uplink channels (UC1-UCn) comprise n laser beacons directed towards the remote terminal (20) for pointing-acquisition and tracking by the optical communication terminals (OT1-OTn) in order to individually direct the optical communication terminals (OT1-OTn) towards the corresponding optical ground stations (OGS1-OGSn). ### Claim 5 (depends on 4) Optical downlink system (10) according to claim 4, characterised in that one of the n optical communication terminals (OT1-OTn) of the remote terminal (20) is a master optical communication terminal configured to receive the laser beacon of the optical uplink channel (UC1-UCn) from the master ground station and distribute a clock synchronization signal to the other optical communication terminals (OT1-OTn) of the remote terminal (20), thereby initiating a gated viewing of the n optical communication terminal (OT1-OTn), where each optical communication terminals (OT1-OTn) sequentially receives signals from the corresponding optical ground station (OGS1-OGSn). ### Claim 6 (depends on 1) Optical downlink system (10) according to claim 1, characterised in that the n optical communication terminals (OT1-OTn) of the remote terminal (20) are configured to simultaneously transmit payload data to the corresponding optical ground stations (OGS1-OGSn) of the ground terminal (30), and the optical ground stations (OGS1-OGSn) are configured to sequentially transmit control signals to the corresponding optical communication terminals (OT1-OTn), such as automated repeat request ARQ signals for requesting retransmission of lost/erroneously received data packets from the corresponding optical communication terminal (OT1-OTn). ### Claim 7 (depends on 1) Optical downlink system (10) according to claim 1, characterised in that the optical ground stations (OGS1-OGSn) are located a distance (D) apart from each other, said distance (D) being sufficiently high in order to ensure that the optical receive power at any one of the optical ground stations (OGS1-OGSn) from its corresponding optical downlink channel (DL1-DLn) is at least one order of magnitude greater than the optical receive power from interference by any other optical downlink channels (DL1-DLn). ### Claim 8 (depends on 1) Optical downlink system (10) according to claim 1, characterised in that the remote terminal (20) is a communication satellite or a communication platform flying in airspace. ### Claim 9 Method of optical data transmission between a remote terminal (20) having a number of n optical communication terminals (OT1-OTn), where n is greater than or equal to two, and a ground terminal (30) comprising a cluster of n specially separated optical ground stations (OGS1-OGSn) comprising the steps: establishing n optical downlink channels (DL1-DLn) connecting each optical communication terminals (OT1-OTn) with a corresponding optical ground station (OGS1-OGSn); establishing n optical uplink channels (UC1-UCn) connecting each optical ground station (OGS1-OGSn) with a corresponding optical communication terminal (OT1-OTn); transmitting payload data from the remote terminal (20) by the n optical communication terminals (OT1-OTn) to the corresponding optical ground stations (OGS1-OGSn) of the ground terminal (30); sequentially transmitting control data from the n individual optical ground stations (OGS1-OGSn) via the corresponding optical uplink channels (UC1-UCn) to the corresponding optical communication terminals (OT1-OTn) by means of a precise temporal separation by a time division multiple access scheme thereby avoiding overlap between the optical uplink channels (UC1-UCn). ### Claim 10 (depends on 9) Method of optical data transmission according to claim 9, characterised in that it further comprises the following step: a sync unit synchronises the n ground stations (OGS1-OGSn) so that at any moment in time, only one ground station (OGS1-OGSn) is transmitting, thus providing for the temporal separation of the n optical uplink channels (UC1-UCn), ensuring that only one of the n optical uplink channels (UC1-UCn) is active at a time. ### Claim 11 (depends on 10) Method of optical data transmission according to claim 10, characterised in that the n optical ground stations (OGS1-OGSn) modulate the n optical uplink channels (UC1-UCn) according to a pulse position modulated PPM scheme, wherein the sync unit controls the n optical ground stations (OGS1-OGSn) such that pulses of each of the pulse position modulated PPM signals of any one of the n uplink channels (UC1-UCn) are emitted sequentially during phases of pulse silence (Ps) of the other uplink channels (UC1-UCn), by dividing the period (T) of the pulse position modulated PPM signals to the number n of optical uplink channels (UC1-UCn) and assigning each optical ground stations (OGS1-OGSn) a dedicated time slot (Ts) less than or equal to T/n. ### Claim 12 (depends on 11) Method of optical data transmission according to claim 11, characterised in that the n optical uplink channels (UC1-UCn) comprising n laser beacons are directed towards the remote terminal (20), the method further comprising the steps of pointing-acquisition and tracking by the optical communication terminals (OT1-OTn) by means of the laser beacons of the corresponding optical ground stations (OGS1-OGSn) thereby individually directing the optical communication terminals (OT1-OTn) towards the corresponding optical ground stations (OGS1-OGSn). ### Claim 13 (depends on 12) Method of optical data transmission according to claim 12, characterised in that one of the n optical communication terminals (OT1-OTn) of the remote terminal (20) is a master optical communication terminal, the method further comprises the following steps: receive the laser beacon of the optical uplink channel (UC1-UCn) from the master ground station; distribute a clock synchronization signal to the other optical communication terminals (OT1-OTn) of the remote terminal (20), thereby initiating a gated viewing of the n optical communication terminals (OT1-OTn), where each optical communication terminals (OT1-OTn) sequentially receiving signals from the corresponding optical ground station (OGS1-OGSn). ### Claim 14 (depends on 9) Method of optical data transmission according to claim 9, characterised in that: the n optical communication terminals (OT1-OTn) of the remote terminal (20) simultaneously transmit payload data to the corresponding optical ground stations (OGS1-OGSn) of the ground terminal (30); and the optical ground stations (OGS1-OGSn) sequentially transmit control signals to the corresponding optical communication terminals (OT1-OTn), such as automated repeat request ARQ signals for requesting retransmission of lost/erroneously received data packets from the corresponding optical communication terminal (OT1-OTn). ### Claim 15 (depends on 9) Method of optical data transmission according to claim 9, characterised in that the remote terminal (20) re-routes data to be transmitted by any of the n optical communication terminals (OT1-OTn) if the corresponding optical downlink channels (DL1-DLn) is unavailable and/or unreliable, thereby achieving redundancy and greater availability of the optical data transmission.