System and method for effecting information transmission and soft handoff between frequency division duplex and time division duplex communications systems

• US 6,611,507 B1
• Filed: 07/30/1999
• Issued: 08/26/2003
• Est. Priority Date: 07/30/1999
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Nokia Corporation
• Inventors: Teittinen, Marko, Sunay, M. Oguz, Hottinen, Ari
• Primary Examiner(s): Maung, Nay
• Assistant Examiner(s): Trinh, Sonny
• Application Number:
  US09/364,523
• Time in Patent Office: 1,488 Days
• Field of Search: 370/280, 370/281, 370/294, 370/295, 370/331, 370/332, 370/328, 370/329, 370/310.2, 455/436, 455/437, 455/438, 455/439, 455/442, 455/422, 455/403, 455/440, 455/444
• US Class Current: 370/331
• CPC Class Codes: H04W 36/0066 of control information between different types of networks in order to establish a new radio link in the target network
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 36/302 due to low signal strength

Abstract

A system and method for controlling information transmission and communication handoff between frequency division multiplexing (FDD) and time division multiplexing (TDD) communication systems using any multiple access scheme is provided. The mobile unit transmits information via a current one of the FDD and TDD communication systems while it moves toward the other, or targeted one of the FDD and TDD communication systems. A pilot search signal is generated by the targeted communication system, where the pilot search signal corresponds to a transmission range of the targeted communication system. A communication handoff is initiated from the current communication system to the targeted communication system when the mobile unit recognizes a predetermined threshold level of the pilot search signal. Concurrent communications are synchronized and temporarily maintained between the mobile unit and both the current and targeted communications systems using an increased data rate for each of the communications links. When the handoff is complete, transmission between the mobile unit and the current communication system is terminated, while communication between the mobile unit and the targeted communication system is maintained when the handoff is complete.

Claims

1. A method for controlling mobile unit communication handoffs between a frequency division duplex (FDD) communication system and a time division duplex (TDD) communication system, the method comprising:

transmitting between the mobile unit and a current one of the FDD and TDD communication systems while moving towards a targeted one of the FDD and TDD communication systems, the current communication system being different from the targeted communication system;

generating a pilot search signal corresponding to a transmission range of the targeted communication system;

monitoring pilot search signals at designated frequencies using one of time division processing and frequency division processing;

initiating the communication handoff from the current communication system to the targeted communication system when the mobile unit recognizes a predetermined threshold level of the pilot search signal;

synchronizing concurrent communications between the mobile unit and both the current and targeted communications systems; and

terminating transmission between the mobile unit and the current communication system and maintaining communication between the mobile unit and the targeted communication system when synchronization is complete.

2. The method as in claim 1, wherein the current communication system is the FDD communication system, and the targeted communication system is the TDD communication system.

3. The method as in claim 1, wherein the current communication system is the TDD communication system, and the targeted communication system is the FDD communication system.

4. The method as in claim 1, wherein initiating the communication handoff comprises requesting a handoff by the mobile unit when the mobile unit recognizes the predetermined threshold level of the pilot search signal.

5. The method as in claim 4, wherein requesting a handoff by the mobile unit comprises notifying the current communication system of the handoff request, and providing the handoff request to the targeted communication system via the current communication system.

6. The method as in claim 5, further comprising determining whether to grant access to the mobile unit at the targeted communication system based on predetermined parameters, and providing an acknowledge signal from the targeted communication system to the mobile unit via the current communication system when warranted by the predetermined parameters.

7. The method as in claim 6, wherein determining whether to grant access to the mobile unit based on predetermined parameters comprises analyzing load control parameters.

8. The method as in claim 1, wherein synchronizing concurrent communications between the mobile unit to both the current and targeted communications systems comprises:

increasing a data rate in an uplink frame between the mobile unit and the current communications system; and

transmitting a synchronizing preamble to the targeted communications system during a remaining portion of the uplink frame made available by the increased data rate.

9. The method as in claim 8, wherein increasing the data rate comprises approximately doubling the data rate between the mobile unit and the current communications system.

10. The method as in claim 8, further comprising acknowledging synchronization to the mobile unit by the targeted communication system.

11. The method as in claim 10, wherein acknowledging synchronization comprises providing an acknowledge signal to the mobile unit via a control channel.

12. The method as in claim 10, further comprising operating in a multirate mode upon the synchronization acknowledgment, wherein the multirate mode comprises transmitting the information to the current communication system at an increased data rate in the uplink frame between the mobile unit and the current communications system, and transmitting the information to the targeted communication system at an increased data rate in a remaining portion of the uplink frame between the mobile unit and the targeted communications system.

13. A method for controlling mobile unit communication handoffs from a frequency division duplex (FDD) communication system to a time division duplex (TDD) communications system, wherein the mobile unit is transmitting information via the FDD communications system, the method comprising:

generating a pilot search signal corresponding to a transmission range of the TDD communication system;

initiating the communication handoff from the FDD communication system to the TDD communication system when the mobile unit recognizes a predetermined threshold level of the pilot search signal;

synchronizing concurrent communications between the mobile unit to both the FDD and TDD communications systems;

transmitting the information in a multirate mode upon acknowledgment of the synchronization by the TDD communication system, including communicating the information with the FDD communication system at an increased FDD data rate in the uplink frame between the mobile unit and the FDD communications system, and communicating the information with the TDD communication system at an increased TDD data rate in a remaining portion of the uplink frame between the mobile unit and the TDD communications system; and

terminating transmission between the mobile unit and the FDD communication system and maintaining communication between the mobile unit and the TDD communication system when the synchronization is complete.

14. The method as in claim 13, wherein synchronizing concurrent communications between the mobile unit to both the FDD and TDD communications systems comprises:

increasing the FDD data rate in an uplink frame between the mobile unit and the FDD communications system; and

transmitting a synchronizing preamble to the TDD communications system during a remaining portion of the uplink frame made available by the increased FDD data rate.

15. The method as in claim 14, wherein increasing the FDD data rate during synchronization comprises approximately doubling the FDD transmit data rate between the mobile unit and the FDD communications system.

16. The method as in claim 14, further comprising acknowledging synchronization to the mobile unit by the TDD communication system.

17. The method as in claim 13, wherein communicating the information to the FDD communication system at an increased FDD data rate comprises transmitting the information at approximately double the FDD transmit data rate.

18. The method as in claim 13, wherein communicating the information to the TDD communication system at an increased TDD data rate comprises transmitting the information at approximately quadruple the FDD transmit data rate.

19. The method as in claim 13, wherein the information is communicated by the mobile unit using CDMA.

20. A method for controlling mobile unit communication handoffs from a time duplex (TDD) communication system to a frequency division duplex (FDD) communications system, wherein the mobile unit is transmitting information via the TDD communications system, the method comprising:

generating a pilot search signal corresponding to a transmission range of the FDD communication system;

initiating the communication handoff from the TDD communication system to the FDD communication system when the mobile unit recognizes a predetermined threshold level of the pilot search signal;

synchronizing concurrent communications between the mobile unit to both the TDD and FDD communications systems;

transmitting the information in a multirate mode upon acknowledgment of the synchronization by the FDD communication system, including communicating the information with the TDD communication system at an increased TDD data rate in the uplink frame between the mobile unit and the TDD communications system, and communicating the information with the FDD communication system at an increased FDD data rate in a remaining portion of the uplink frame between the mobile unit and the FDD communications system; and

terminating transmission between the mobile unit and the TDD communication system and maintaining communication between the mobile unit and the FDD communication system when the synchronization is complete.

21. The method as in claim 20, wherein synchronizing concurrent communications between the mobile unit to both the TDD and FDD communications systems comprises:

increasing the TDD data rate in an uplink frame between the mobile unit and the TDD communications system; and

transmitting a synchronizing preamble to the FDD communications system during a remaining portion of the uplink frame made available by the increased TDD data rate.

22. The method as in claim 20, wherein the information is communicated by the mobile unit using CDMA.

23. A system for managing mobile unit communication handoffs between a frequency division duplex (FDD) communication system and a time division duplex (TDD) communication system, the system comprising:

an FDD base station within the FDD communication system for communicating with the mobile unit in frequency division duplex mode, and for generating a pilot search signal corresponding to a transmission range of the FDD communication system;

a TDD base station within the TDD communication system for communicating with the mobile unit in time division duplex mode, and for generating a pilot search signal corresponding to a transmission range of the TDD communication system;

a mobile unit which is transmitting information via a current one of the FDD and TDD communication systems while moving towards the other, or targeted one of the FDD and TDD communication systems, the mobile unit comprising;

a receiving unit to receive the first and second pilot search signals, and to initiate a handoff from the current communication system to the targeted communication system when the pilot search signal from the targeted communication system has reached a predetermined threshold level; and

a dual-transceiver to synchronize concurrent communications between the mobile unit and the current and targeted communication systems, and to concurrently communicate the information with the current communication system and the targeted communication system upon synchronization, wherein the dual-transceiver comprises a burst mode capable of increasing a data rate between the mobile unit and the current and targeted communication systems during the handoff to concurrently support communication with both the current and targeted communications systems.

24. A method for maintaining a connection between a frequency division duplex (FDD) communication system and a time division duplex (TDD) communication system during handoff of a communication unit from one communication system to the other, the method comprising:

transmitting a first portion of a communication frame to one of the FDD and TDD communication systems;

transmitting a second portion of the communication frame to the other one of the FDD and TDD communication systems;

transmitting at least one of the first and second portions of the communication frame at an increased data rate; and

wherein communication occurs with both the FDD and TDD systems during the transmission of the communication frame, and wherein the communication occurs in a time equivalent to the time required to transmit the communication frame to either of the FDD and TDD systems when no handoff is occurring.

25. The method as in claim 24, wherein:

transmitting the first portion of the communication frame comprises transmitting all of the communication frame to one of the FDD and TDD communication systems;

transmitting the second portion of the communication frame comprises transmitting all of the communication frame to the other one of the FDD and TDD communication systems; and

transmitting at least one of the first and second portions of the communication frame at an increased data rate comprises transmitting both the first and second portions of the communication frame at an increased data rate such that all of the communication frame is transmitted to both the FDD and TDD systems in a time equivalent to the time required to transmit the communication frame to either of the FDD and TDD systems when no handoff is occurring.

26. The method as in claim 25, wherein transmitting both the first and second portions of the communication frame at an increased data rate comprises:

transmitting the first portion of the communication frame to the FDD communication system at a double rate; and

transmitting the second portion of the communication frame to the TDD communication system at a quadruple rate.

27. The method as in claim 24, wherein a first portion of the communication frame is sent only to one, but not the other, of the FDD and TDD systems, and a second portion of the communication frame is sent only to the other of the FDD and TDD systems.

28. The method as in claim 27, wherein the communication frame is received and reconstructed by combining the first and second portions of the communication frames sent to the FDD and TDD systems.

29. The method as in claim 27, wherein:

transmitting the first portion of the communication frame comprises transmitting a first half of the communication frame to one of the FDD and TDD communication systems;

transmitting the second portion of the communication frame comprises transmitting a second half of the communication frame to the other one of the FDD and TDD communication systems; and

transmitting at least one of the first and second portions of the communication frame at an increased data rate comprises transmitting the second half of the communication frame at an increased data rate such that the first half of the communication frame is transmitted to the FDD system at a non-increased data rate, and the second half of the communication frame is transmitted to the TDD system at a double data rate.

30. The method as in claim 27, wherein a first number of subframes of the communication frame is sent only to one, but not the other, of the FDD and TDD systems, and a second number of subframes of the communication frame is sent only to the other of the FDD and TDD systems.

31. The method as in claim 30, wherein at least one of the first number of subframes is transmitted in a different frequency than the other ones of the subframes.

32. The method as in claim 31, wherein the frequency is changed using a predetermined pattern.

33. The method as in claim 24, wherein the FDD and TDD communication systems operate in different frequency bands.

34. The method as in claim 24, wherein the FDD and TDD communication systems are co-located and operate in different frequency bands.

35. The method as in claim 24, wherein the FDD and TDD communication systems operate at least partly in a common frequency band.

36. The method as in claim 24, wherein the handoff is requested by a mobile station in a cellular network.

37. A method for controlling information transmissions between a communications unit and frequency division duplex (FDD) and time division duplex (TDD) communication systems, wherein the communication unit is transmitting information via a first one of the FDD and TDD communication systems, the method comprising:

generating a cell identification signal corresponding to a transmission range of a second one of the FDD and TDD communication systems;

initiating substantially simultaneous communication between the communications unit and both the FDD and TDD communications systems when the communications unit acknowledges the cell identification signal and is thereby in the coverage area of both the FDD and TDD communications systems; and

maintaining the substantially simultaneous communication between the communications unit and each of the FDD and TDD communications systems by simultaneously communicating at least a part of the information with each of the FDD and TDD communications systems.

38. The method of claim 37, wherein simultaneously communicating at least a part of the information with each of the FDD and TDD communications systems comprises operating in a multirate mode such that an information transfer rate during the simultaneous communication of the information with each of the FDD and TDD communications systems is greater than the information transfer rate associated with only FDD information transmissions or only TDD information transmissions.

39. The method of claim 37, wherein simultaneously communicating at least a part of the information with each of the FDD and TDD communications systems comprises simultaneously transmitting different portions of the information via the FDD and TDD communications systems respectively to provide for load sharing.

40. The method of claim 37, wherein simultaneously communicating at least a part of the information with each of the FDD and TDD communications systems comprises simultaneously transmitting data via the TDD communications system while transmitting control signals via the FDD communications system.

41. The method of claim 40, wherein the control signals are selected from the group of transmission rate control signals, power control signals, modulation control signals, and encoding control signals.

42. A method for controlling mobile unit communication handoffs between a frequency division duplex (FDD) communication system and a time division duplex (TDD) communication system, the method comprising:

transmitting between the mobile unit and a current communication system;

generating a pilot search signal corresponding to a transmission range of a targeted communication system, the current communication system being different from the targeted communication system;

monitoring pilot search signals at designated frequencies using one of time division processing and frequency division processing;

initiating a communication handoff from the current communication system to the targeted communication system when the mobile unit recognizes a predetermined threshold level of the pilot search signal;

transmitting a synchronizing preamble to the targeted communication system in a portion of a frame to synchronize concurrent communications between the mobile unit and both the current and targeted communication systems; and

terminating transmission between the mobile unit and the current communication system and maintaining communication between the mobile unit and the targeted communication system when synchronization is complete.

43. The method as in claim 42, wherein the current communication system is the FDD communication system and the targeted communication system is the TDD communication system.

44. The method as in claim 42, wherein the current communication system is the TDD communication system and the targeted communication system is the FDD communication system.

45. A method for controlling mobile unit communication handoffs between a frequency division duplex (FDD) communication system and a time division duplex (TDD) communication system, the method comprising:

transmitting between the mobile unit and the FDD communication system;

generating a pilot search signal corresponding to a transmission range of the TDD communication system;

monitoring pilot search signals at designated frequencies using time division processing;

initiating a communication handoff from the FDD communication system to the TDD communication system when the mobile unit recognizes a predetermined threshold level of the pilot search signal;

synchronizing concurrent communications between the mobile unit and both the FDD and TDD communication systems; and

terminating transmission between the mobile unit and the FDD communication system and maintaining communication between the mobile unit and the TDD communication system when synchronization is complete.

46. A method for controlling mobile unit communication handoffs between a time division duplex (TDD) communication system and a frequency division duplex (FDD) communication system, the method comprising:

transmitting between the mobile unit and the TDD communication system;

generating a pilot search signal corresponding to a transmission range of the FDD communication system;

monitoring pilot search signals at designated frequencies using frequency division processing;

initiating a communication handoff from the TDD communication system to the FDD communication system when the mobile unit recognizes a predetermined threshold level of the pilot search signal;

synchronizing concurrent communications between the mobile unit and both the FDD and TDD communication systems; and

terminating transmission between the mobile unit and the TDD communication system and maintaining communication between the mobile unit and the FDD communication system when synchronization is complete.