초록 ▼

A two-way satellite communications system includes an Earth station communicating with a plurality of remote terminals using a network access protocol that facilitates low power consumption by the terminals. The earth station generates forward link TDM packet data transmissions on one or-more satell

A two-way satellite communications system includes an Earth station communicating with a plurality of remote terminals using a network access protocol that facilitates low power consumption by the terminals. The earth station generates forward link TDM packet data transmissions on one or-more satellite channels, and detects, despreads and decodes multiple concurrent return link slotted CDMA packet transmissions on one or more satellite channels. It communicates through a wired connection with a packet processing center which ultimately both delivers return link packet data to end-customers and receives forward link packet data from end-customers. The remote terminals receive, process and act upon forward link TDM transmissions on one or more satellite channels, and generate slotted spread spectrum CDMA transmissions on the return link on one or more satellite channels. The remote terminals communicate with a local digital data source and/or sink, digitize one or more local analog sensor signals, enter into a sleep mode to minimize the terminal's power consumption, and access the satellite communications network in accordance with the system network access protocol.

대표청구항 ▼

We claim: 1. A wireless packet data communications system, comprising: a control station, and a plurality of widely dispersed, remote terminals having an active mode during which they are capable of at least one of transmitting and receiving data packets and a sleep mode during which they are inact

We claim: 1. A wireless packet data communications system, comprising: a control station, and a plurality of widely dispersed, remote terminals having an active mode during which they are capable of at least one of transmitting and receiving data packets and a sleep mode during which they are inactive, said control station and each of said remote terminals being capable of engaging in packet data communication over a TDM forward link from said control station to said terminals and a multiple access return link from said terminals to said control station, each said remote terminal having an address and being assigned specific times on the forward link during which it may be addressed by said control station, and each said terminal including a timer operable in said sleep mode to cause said terminal to periodically enter the active mode during its assigned time and listen for incoming data packets from said control station addressed to said terminal, and a means for interpreting packets received over the forward link, and said control station including a storage device for storing information pertaining to the times assigned to the various remote terminals, means for transmitting data packets addressed to specific terminals at their assigned times on the forward link, and means for receiving data packets from the terminals in times on the return link. 2. The wireless packet data communications system of claim 1, wherein each terminal has a unique address. 3. The wireless packet data communications system of claim 2, wherein a subset of terminals is assigned to each time on the forward link, and each time carries a plurality of time division multiplexed data packets, each including an address field that may be individually addressed to any or all of the terminals assigned to that time. 4. The wireless packet data communications system of claim 1, wherein said control station comprises means for transmitting synchronization packets in at least some of said times of said forward link. 5. The wireless packet data communications system of claim 4, wherein the processor in each terminal is responsive during the active mode to packets transmitted on the forward link to resynchronize the terminal. 6. The wireless packet data communications system of claim 1, wherein said forward and return links employ a hierarchical frame structure and said times are subframes forming the lowest order frames therein. 7. The wireless packet data communications system of claim 1, wherein the times in said return link carry packets multiplexed using code division multiple access format. 8. The wireless packet data communications system of claim 1, wherein the time in said return link are offset by a predetermined time relative to the assigned times in the forward link. 9. The wireless packet data communications system of claim 8, wherein said predetermined time is an integral number of said times. 10. The wireless packet data communications system of claim 1, wherein the processor in each said terminal has a local interrupt for placing said terminal in the active mode so that it can transmit data in response to a local request to said control station over said return link using random access. 11. The wireless packet data communications system of claim 1, wherein, in addition to said active mode, each said terminal has a semi-active mode during which said processor is active just long enough to extract synchronization words from incoming signals without extracting all the accompanying data. 12. The wireless packet data communications system of claim 11, wherein said processor forms part of a microcontroller controlling the operation of the terminal. 13. The wireless packet data communications system of claim 12, where said timer periodically wakes up said microcontroller more frequently than said terminal is programmed to enter the active or semi-active mode, and said microcontroller determines whether it is time to place said terminal into the active or semi-active mode in accordance with a program stored in the terminal. 14. The wireless packet data communications system of claim 13, wherein said microcontroller is responsive to commands received over said forward link to change the times when it is in the active mode. 15. The wireless packet data communications system of claim 13, wherein said wake-up mode occurs several times per second. 16. The wireless packet data communications system of claim 1, wherein said forward and return links travel via satellite, and said control station includes an earth station for communicating with said satellite. 17. The wireless packet data communications system of claim 16, wherein said control station also includes a packet processing center for formatting data sent to, and deformatting data received from, the satellite. 18. The wireless packet data communications system of claim 17, wherein said storage device is located at said packet processing center. 19. The wireless packet data communications system of claim 16, wherein said satellite is a multi-beam satellite, and said control station stores data pertaining to the beam in which each terminal is located, whereby said transmitting means sends data to a terminal in its assigned time and on the beam in which it is located. 20. A remote terminal for use in a wireless packet data communications system comprising a control station and a plurality of widely dispersed, remote terminals having an active mode during which they are capable of at least one of transmitting and receiving data packets and a sleep mode during they are inactive, said control station and each of said remote terminals being capable of engaging in packet data communication over a forward TDM link between said control station and said terminals and a multiple access return link between said terminals and said control station, each said remote terminal having an address and being assigned a time during which it may be addressed by said control station, said remote terminal comprising an electronics unit for transmitting and receiving signals to and from said control station over said respective return and forward links, and a timer operable in said sleep mode period to cause said terminal to periodically enter the active mode during said assigned time to listen for incoming data packets from the control station addressed to said terminal. 21. The remote terminal of claim 20, further comprising a processor for interpreting data received during said assigned time and formatting outgoing data for transmission over said return link. 22. The remote terminal of claim 20, further comprising means for resetting said timer in response to packets received over said forward link. 23. The remote terminal of claim 20, further comprising a local oscillator for generating the necessary frequencies within the terminal to transmit and receive packets over said return and forward links, said local oscillator being resynchronized in response to synchronization packets. 24. The remote terminal of claim 20, wherein said processor prepares outgoing packets for transmission in CDMA format on the return link. 25. The remote terminal of claim 20, wherein said processor includes means for placing said terminal in the active mode in response to a local request to transmit data to the control station using random access on the return link. 26. The remote terminal of claim 25, wherein said processor includes a stored program for controlling the operation of said terminal to minimize network traffic by delaying outgoing packets in the event of network congestion. 27. The remote terminal of claim 20, further comprising an antenna unit that includes an L-band microstrip antenna capable of receiving signals at least at 1575.42 MHz and in the range 1525 to 1559 MHz. 28. The remote terminal of claim 20, further comprising a GPS unit connected to said antenna unit to generate data indicative of the location of the terminal for transmission back to the control station over the return link. 29. The remote terminal of claim 20, wherein said processor is responsive to commands received from the control station over the forward link to change the time in which the terminal is placed in the active mode. 30. The remote terminal of claim 20, which has a semi-active mode in addition to said active mode, said processor being active in said semi-active mode just long enough to extract synchronization packets from the incoming signals on the forward link and resynchronize said terminal. 31. The remote terminal of claim 20, wherein said processor is a microcontroller, and said timer wakes up said microcontroller more frequently than said terminal enters the active or semi-active mode in order to for said microcontroller to determine whether it is time to enter the active or semi-active mode. 32. A control station for a wireless packet data communications system comprising said control station and a plurality of widely dispersed, remote terminals having an active mode during which they are capable of at least one of transmitting and receiving data packets and a sleep mode during which they are inactive, said control station and each of said remote terminals being capable of engaging in packet data communication over a TDM forward link between said control station and said terminals and a multiple access return link between said terminals and said control station, said forward and return links being established via satellite, each said remote terminal having an address and being assigned times during which it wakes up to listen for a data packet from said control station, said control station comprising a database for storing the times assigned to the various remote terminals, means for transmitting data packets addressed to specific terminals in their assigned times in TDM format, means for interpreting data packets received in the times on the multiple access return link, and a packet processing center for formatting packets for transmission on the forward TDM link to remote terminals in their assigned times and deformatting packets received on the multiple access return link, said database being located in said packet processing center. 33. The control station of claim 32 further comprising a CDMA processor for receiving data packets in CDMA format from terminals in times on the return link. 34. The control station of claim 32 wherein said packet processing center comprises means for generating data packets to instruct an addressed terminal to change a parameter, such as its assigned times. 35. A wireless packet data communications system, comprising a control station and a plurality of widely dispersed, remote terminals, means for establishing a forward TDM link from said control station to said terminals, and means for establishing a multiple access return link from said terminals to said control station to permit selective packet data communication between said control station and any of said terminals, groups of said terminals being assigned specific times during which they may be addressed by said control station, and said control station assigning said times so as to spread the active periods throughout the day, and means for controlling a delay between the time of reception of a command by a terminal and the time when it transmits its response back to the control station, said data packets transmitted over said forward link having an overflow flag to indicate that additional data is being transmitted in a subsequent time, and said control station further comprising means for spreading the messages addressed to the terminals over two or more subframes and setting said overflow flag to advise said terminals that messages for them may be spread over several subframes in order to relieve congestion in the system. 36. The wireless packet data communications system of claim 35, wherein the times in said multiple access return link carry packets multiplexed using code division multiple access format. 37. The wireless packet data communications system of claim 35, comprising means for imposing return priority or by allocating more return subframes to specific terminals on the multiple access return link to relieve congestion in the return link. 38. A method of establishing communication in a wireless packet data communications system comprising a control station and a plurality of widely dispersed, remote terminals having an active mode during which they are capable of at least one of transmitting and receiving data packets and a sleep mode during which they are inactive, said control station and each of said remote terminals being capable of engaging in packet data communication over a TDM forward link from said control station to said terminals and a multiple access return link from said terminals to said control station, said forward and return links being via satellite, and each said remote terminal having an address and being assigned specific times on the forward link during which it may be addressed by said control station, said method comprising the steps of: periodically waking up said terminals in their assigned times to listen for incoming data packets addressed thereto from the control station; extracting information pertaining to the times assigned to the various remote terminals from a database at the control station; transmitting data packets addressed to specific terminals in their assigned times on the forward link; and receiving data packets from the terminals in times on the return link. 39. The method of claim 38, wherein said terminals also have a semi-active mode in which they are woken up long enough to extract synchronization data from incoming signals. 40. The method of claim 39, wherein CDMA is employed on the return link.