Enhanced access burst for random access channels in TDMA mobile satellite system

• US 5,875,182 A
• Filed: 01/16/1997
• Issued: 02/23/1999
• Est. Priority Date: 01/16/1997
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Hatzipapafotiou, Dimitrios
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): YAO, KWANG BIN
• Application Number:
  US08/784,873
• Time in Patent Office: 768 Days
• Field of Search: 370/316, 370/319, 370/321, 370/322, 370/323, 370/324, 370/326, 370/328, 370/336, 370/337, 370/339, 370/345, 370/347, 370/348, 370/349, 370/350, 455/427, 455/428, 455/430, 455/431
• US Class Current: 370/321
• CPC Class Codes: H04B 7/212 Time-division multiple access [TDMA]

Abstract

A spacecraft (12) cellular TDMA communications system (10) includes many user terminals (16), some of which may be movable. The spacecraft repeats transmissions by way of spot beams (20). A user initiates communication by synchronizing to the TDMA slots (210, 212), and transmits an access request signal. The access request signal is transmitted in at least two slots. The first slot contains time and frequency PN synch information, and the second slot contains one of (a) the user terminal'"'"'s ID code and (b) a code representing the desired type of access. After this message is transmitted and received, the user terminal may transmit the PN synch information on a third slot, followed by the other one of the user terminal'"'"'s ID code and the access-representative code.

Claims

1. A spacecraft TDMA cellular communications system, for communicating traffic signals between disparate terrestrial locations by way of successive temporally-interleaved signal bursts, said system comprising:

a spacecraft including transmitting and receiving means, and an antenna arrangement coupled to said transmitting and receiving means, for forming a plurality of spot beams, each of which defines a footprint, which footprints of said spot beams may partially overlap;

at least one network control center located in one of said footprints, for transmitting electromagnetic control signals to said spacecraft, and for receiving electromagnetic control signals from said spacecraft, for controlling the timing of said temporal bursts;

at least one gateway terrestrial terminal located in one of said footprints, each one of said at least one gateway terrestrial terminal being coupled to a terrestrial communications system, for coupling said terrestrial communications system with said spacecraft communications system, said gateway terrestrial terminal being for transmitting electromagnetic traffic signals to said spacecraft, and for receiving electromagnetic traffic signals from said spacecraft;

a plurality of user terrestrial terminals, at least some of said user terrestrial terminals being located in said footprints, each of said user terrestrial terminals being for transmitting electromagnetic signals to said spacecraft, and for receiving electromagnetic signals from said spacecraft, each of said user terrestrial terminals including access request signal generating means for generating access request signals at the inception of a communication by said user terrestrial terminal, and for transmitting said access request signals by way of said electromagnetic signals to a selected a least one of said network control center each of said access request signals including time and frequency synchronization components and also including information components, said synchronization component of said access request signals being transmitted on a first burst of said TDMA, and said information component of said access request signals being transmitted on at least a second burst of said TDMA, later in time than said first burst.

2. A system according to claim 1, wherein said information components of said access request signals include at least one of a user terminal identification component and a requested function component.

3. A system according to claim 2, wherein said requested function component of said information components of said access request signals includes a telephone number to be which communication is desired from said user terrestrial terminal.

4. A system according to claim 1, wherein said second burst transmitted from said user terrestrial terminal is separated from said first burst transmitted from said user terrestrial terminal by a time equal to an integer multiple, including the integer zero, of TDMA slots.

5. A system according to claim 4, wherein said integer multiple is zero.

6. A system according to claim 1, wherein said time and frequency synchronization components comprise a pseudorandom sequence.

7. A system according to claim 1, wherein said information component of said access request signal include error correction coding.

8. A method for operating a spacecraft TDMA communications system which provides communication of traffic signals between and among disparate terrestrial locations by successive interleaved temporally-interleaved bursts, said method comprising the steps of:

at a user terrestrial terminal, transmitting electromagnetic signals to said spacecraft within slots of said TDMA, and receiving electromagnetic signals within slots of said TDMA from said spacecraft, by way of a spot beam;

at said spacecraft, repeating at least the information content of said electromagnetic signals in the form of transmissions toward other terrestrial terminals;

at said user terrestrial terminal, at a synchronization time occurring near the time of inception of each transmission, including time and frequency components of access request signals within a first one of a succession of time-separated slots of said TDMA within said electromagnetic signals transmitted to said spacecraft;

at said user terrestrial terminal, at a time later than said synchronization time, including information components of said access request signals within a later one of said succession of time-separated slots of said TDMA within said electromagnetic signals transmitted to said spacecraft, whereby said spacecraft repeats said information toward other ones of said terrestrial terminal;

at a network control center terrestrial terminal, receiving said synchronizing components of said access request signals from said spacecraft on said first one of said slots, and using said synchronizing components to perform time and frequency synchronization for reception of said access request signals, and receiving said information components of said access request signals using at least said frequency synchronization derived from said first one of said slots.

9. A method according to claim 8, wherein said user terrestrial terminal transmits within said information component one of (a) an identification code unique to said user terrestrial terminal, and (b) a code representing a request for a particular communication.

10. A method according to claim 9, wherein said code representing a request for a particular communication is in the form of a telephone number to be accessed;

and

said network control center interprets said code as a request for communication between said user terrestrial terminal and the specified telephone number, determines which one of a plurality of gateway terrestrial terminals should route the desired communication, and hands off control of said user terrestrial terminal to the selected one of said gateway terrestrial terminals.