Method and apparatus for selectively operating satellites in tundra orbits to reduce receiver buffering requirements for time diversity signals

• US 6,442,385 B1
• Filed: 11/04/1999
• Issued: 08/27/2002
• Est. Priority Date: 11/04/1999
• Status: Expired due to Fees

• Current Assignee: Sirius XM Radio Inc. (Liberty Media Corporation)
• Original Assignee: XM Satellite Radio Incorporated (Liberty Media Corporation)
• Inventors: Marko, Paul D.
• Primary Examiner(s): Hunter, Daniel
• Assistant Examiner(s): Harry, Andrew T
• Application Number:
  US09/433,849
• Time in Patent Office: 1,027 Days
• Field of Search: 455/3.02, 455/12.1, 455/13.2, 455/13.1, 455/427, 455/428, 348/533, 370/464, 375/260, 375/316, 244/158, 244/159
• US Class Current: 455/427
• CPC Class Codes: H04B 7/18534 for enhancing link reliablility, e.g. satellites diversity
• CPC Class Codes: H04B 7/195 Non-synchronous stations

Abstract

A time diversity satellite system provides geosynchronous satellites in tundra orbits in three orbital planes. The satellites traverse a common figure-eight ground track comprising northern and southern loops. Power modes and early and late operating modes of the satellites are selectively switched to select the satellite currently traversing the northern loop be the late satellite delivering a late signal, that is, a delayed early signal, to satellite receivers. A receiver can therefore employ a relatively small buffer for storing the early satellite signal for only the selected channel in a multi-channel TDM content signal without experiencing latency problems when selecting a new channel.

Claims

1. A method for controlling first, second and third geosynchronous satellites in tundra orbits in three orbital planes in a time diversity system, the time diversity system providing both an early satellite signal and a late satellite signal to receivers, the late satellite signal corresponding to a delayed early satellite signal, the satellites each traversing a common ground track having a northern loop, a southern loop, and a crossover point between the northern and southern loops, the southern loop being intersected via the equator, the method comprising the steps of:

powering on a first satellite that is ascending said southern loop from the equator;

operating a second satellite at apogee as a late satellite to provide said late satellite signal to said receivers;

powering down a third satellite after descending the southern loop below the equator, said third satellite having operated as an early satellite to provide said early signal to said receivers prior to reaching an orbital position near the equator;

operating said first satellite as said late satellite when said first satellite reaches said crossover point, said first satellite operating as said late satellite while said first satellite traverses said northern loop; and

switching operation of said second satellite from operation as said late satellite to operation as said early satellite when said second satellite traverses said crossover point to commence its descent of said southern loop.

2. A method as claimed in claim 1, further comprising the steps of receiving and using said late satellite signal to generate an output for a user.

3. A method as claimed in claim 1, further comprising the steps of:

receiving said early satellite signal and said late satellite signal; and

storing only as much as a portion of said early satellite signal corresponding to the duration of time that said late satellite signal is delayed with respect to said early satellite signal.

4. A method as claimed in claim 3, wherein said early satellite signal comprises a plurality of channels, and further comprising the step of selecting one of said plurality of channels from said late satellite signal, said portion of said early satellite signal being stored corresponding to the selected one of said plurality of channels.

5. A method as claimed in claim 1, further comprising the steps of receiving and selectively combining said late satellite signal and at least a portion of said early satellite signal corresponding to the duration of time that said late satellite signal is delayed with respect to said early satellite signal, said portion of said early satellite signal being useful when said late satellite signal is not received.

6. A receiver in a time diversity system comprising first, second and third geosynchronous satellites in tundra orbits, the three orbital planes of the satellites being spaced substantially evenly about the celestial body they orbit, the satellite traversing a common ground track having a northern loop, a southern loop, and a crossover point between the northern and southern loops, the southern loop being intersected by the equator, the receiver comprising:

a receiving device for receiving a late satellite signal and an early satellite signal, said late satellite signal corresponding to said early satellite signal and delayed a selected period of time with respect to said early satellite signal, said late satellite signal being received from whichever one of said satellites that is traversing said northern loop, said early satellite signal being received from whichever one of said satellites that is traversing said southern loop from said crossover point; and

a memory device operable to store only as much as a portion of said early satellite signal corresponding to the duration of time that said late satellite signal is delayed with respect to said early satellite signal, at least one of said late satellite signal and said portion of said early satellite signal being useful to generate an output for a user.

7. A receiver as claimed in claim 6, wherein said early satellite signal comprises a plurality of channels, said receiver further comprising a channel selection device to allow selection of one of said plurality of channels from said late satellite signal, said memory device being operable to store said portion of said early satellite signal corresponding to the selected one of said plurality of channels.

8. A receiver as claimed in claim 7, further comprising a signal combining device to generate said output, said signal combining device receiving as inputs said late satellite signal and said portion of said early satellite signal corresponding to the selected one of said plurality of channels.

9. A satellite command system for use in a time diversity system comprising first, second and third geosynchronous satellites in tundra orbits, the three orbital planes of the satellites being spaced substantially evenly about the celestial body they orbit, the satellite traversing a common ground track having a northern loop, a southern loop, and a crossover point between the northern and southern loops, the southern loop being intersected by the equator, the time diversity system comprising a first uplink device for transmitting an early satellite signal and a second uplink device for transmitting a late satellite signal, the late satellite signal corresponding to the early satellite signal but delayed a selected period of time with respect to the early satellite signal, the satellite command system comprising:

at least one of an input device to receive data indicating the location of said satellites along said common ground path, and a device to determine and generate said data relating to the location of said satellites along said common ground path; and

a processing device for generating commands depending said data, said processing device being programmed to generate a first command to operate said second uplink device to transmit to whichever one of said satellites that is traversing said northern loop, and a second command to operate said first uplink device to transmit said early satellite signal to whichever one of said satellites that is traversing said southern loop from said crossover point.

10. A satellite command system as claimed in claim 9, wherein said processing device is programmed to generate a command to power down whichever one of said satellites is traversing said southern loop below said equator.