Communications protocol to facilitate handover in a wireless communications network

• US 20040090935A1
• Filed: 11/07/2002
• Published: 05/13/2004
• Est. Priority Date: 11/07/2002
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Inventors: Courtney, William F.
• Granted Patent: US 7,697,477 B2
• Time in Patent Office: Days
• US Class Current: 370/331
• CPC Class Codes: H04B 7/18541 for handover of resources
• CPC Class Codes: H04W 36/0009 for a plurality of users or terminals, e.g. group communication or moving wireless networks user group management H04W4/08; processing of subscriber group data H04W8/186

Abstract

Handover in a wireless communications system from a first communications platform to a post-handover platform is implemented utilizing low-level synchronization mechanisms to enable at least some of a plurality of terminals to adjust timing and synchronize communications with the post-handover platform. Synchronization with the post-handover platform can be facilitated based on a comparison between an expected time to receive response data and the actual time that such data is received from the post-handover platform.

Claims

1. In a wireless communications network having a plurality of terminals synchronized for network communications via a pre-handover base station, a method to facilitate handing over communications for at least one terminal of the plurality of terminals from the pre-handover base station to a post-handover base station, the method comprising:

transmitting from the one terminal a signal having timing information associated with the one terminal;

estimating an expected time for receiving at the one terminal a response to the transmitted signal;

receiving at the one terminal a response to the transmitted signal at an actual time;

comparing the expected time relative to the actual time the response was received; and

adjusting timing for subsequent signal transmissions from the one terminal based on the comparison to facilitate synchronization with the post-handover base station.

2. The method of claim 1, the estimation of the expected time further comprising estimating the expected time for receiving at the one terminal a response to the transmitted signal from the pre-handover base station and the actual time corresponding to the actual time a response to the transmitted signal is received at the one terminal from the post-handover base station.

3. The method of claim 2, the timing information and the response further comprising data in a data link layer of a communications model employed for the communications network.

4. The method of claim 2, the comparison further comprising computing a difference between the expected time and the actual time the response is received at the one terminal, the timing for the subsequent signal transmissions being adjusted based on the difference.

5. The method of claim 4, the response to the transmitted signal received from the post-handover base station further comprising synchronization information for adjusting the timing for the subsequent signal transmissions so as to facilitate synchronization of at the one terminal with the post-handover base station.

6. The method of claim 5, the synchronization information further comprising information indicative of at least one of position and velocity for the post-handover base station in the communications network.

7. The method of claim 5, the synchronization information further comprising an indication for the at least one terminal to advance or retard timing in performing the timing adjustment.

8. The method of claim 1, further comprising entering a handover mode at the one terminal in response to detecting a handover event based on the comparison.

9. The method of claim 8, further comprising detecting the handover event at the one terminal based on a discrepancy in framing information in a signal received from the post-handover base station.

10. The method of claim 1, each of the pre-handover and post-handover base stations comprising a mobile base station.

11. The method of claim 8, each of the pre-handover and post-handover base stations comprising an airborne or space-borne base station.

12. The method of claim 1, further comprising:

receiving at the one terminal a network message broadcast by the pre-handover base station to a set of plural terminals in the communications network, the network message containing handover information for the set of plural terminals in the communications network; and

entering a handover mode at the one terminal in response to the handover information in the network message.

13. A wireless communications network comprising:

a first base station wirelessly associated with a plurality of communications terminals authorized for communications in the network via the first base station;

at least one terminal of the plurality of terminals being operative to transmit synchronization information in a link layer of a network communications protocol during a handover event in the network;

a second base station operative to transmit a network response to the synchronization information for receipt by the at least one terminal; and

the at least one terminal operative to adjust timing for subsequent transmissions based on the network response, whereby synchronization with the second base station is facilitated during the handover event.

14. The network of claim 13, the at least one terminal further comprising:

a timing estimator operative to estimate an expected time for receiving a response to a transmitted signal from the first base station;

a comparator operative to compare the expected time relative to an actual time that a signal containing the network response to the transmitted signal is received at the at least one terminal from the second base station; and

a timing control operative to adjust frame timing for subsequent signal transmissions based on the comparison to facilitate synchronization with the second base station during the handover event.

15. The network of claim 14, the at least one terminal being operative to compute a difference between the expected time and the actual time the signal containing the network response was received, the timing control of the at least one terminal adjusting the timing for the subsequent signal transmissions based on computed difference.

16. The network of claim 14, the signal containing the network response further comprising synchronization information, the at least one terminal employing the synchronization information to adjust the frame timing for the subsequent signal transmissions so as to facilitate synchronization with the second base station.

17. The network of claim 16, the synchronization information further comprising at least one of position and velocity information for the second base station in the network.

18. The network of claim 16, the synchronization information further comprising an indication for the at least one terminal to advance or retard timing in performing the timing adjustment.

19. The network of claim 14, the at least one terminal being operative to enter a handover mode in response to detecting a discrepancy in framing associated with a signal received from the second base station relative to expected framing associated with a corresponding signal from the first base station.

20. The network of claim 19, the framing further comprising at least one of frame identification information and frame timing.

21. The network of claim 13, each of the first and second base stations comprising a space-borne or airborne mobile base station.

22. The network of claim 13, the first base station being operative to broadcast a network message to a set of at least some of the plurality of terminals that includes the at least one terminal, the network message containing handover information for the set of terminals in the communications network, each of the terminals in the set of terminals entering a handover mode in response to the handover information in the network message so as to enable handover from the first base station to the second base station.

23. The network of claim 22, each of the terminals in the set of terminals being operative in the handover mode to adjust timing for subsequent transmissions in the network based on corresponding frame timing difference between an expected response time for a signal received from the first base station relative to an actual response time for a response signal received from the second base station.

29. The terminal of claim 23, further being operative to enter a handover mode in response to detecting a discrepancy in framing associated with an actual signal received from the second base station relative to predicted framing associated with a corresponding expected signal from the first base station.

24. A terminal for wireless communications in a wireless communication network, the network having at least first and second base stations and being operative to hand communications for the terminal from the first over to the second base station, the terminal comprising:

a timing estimator operative to estimate an expected time for receiving a response to a transmitted signal from the first base station;

a comparator operative to compare the expected time relative to an actual time that a response to the transmitted signal is received at the terminal from the second base station; and

a timing control operative to adjust frame timing for subsequent signal transmissions based on the comparison, whereby synchronization of the terminal with the second base station during the handover event is facilitated.

25. The terminal of claim 24, further being operative to compute a difference between the expected time and the actual time the response was received from the second base station, the timing control of the at least one terminal adjusting the timing for the subsequent signal transmissions based on computed difference.

26. The terminal of claim 24 operative to receive a network response to the transmitted signal, the network response comprising synchronization information, the terminal employing the synchronization information from the second base station to adjust the frame timing for the subsequent signal transmissions so as to facilitate synchronization with the second base station.

27. The terminal of claim 26, the synchronization information in the network response further comprising at least one of position and velocity information for the second base station in the network.

28. The terminal of claim 26, the synchronization information in the network response further comprising an indication for the terminal to advance or retard timing in performing the timing adjustment.

30. A communications system configured to facilitate handing over communications for a set of plural terminals in a wireless communications network from a pre-handover base station to a post-handover base station, each of plural terminals comprising:

means for transmitting a wireless signal in the communications network having timing information;

means for estimating an expected time for receiving a response to the transmitted wireless signal from the pre-handover base station;

means for receiving a response to the transmitted signal at an actual time;

means for comparing the expected time relative to the actual time the response was received; and

means for adjusting frame timing for subsequent signal transmissions based on the comparison to facilitate synchronization with the post-handover base station.