Method and apparatus for performing fast handover through fast ranging in a broadband wireless communication system

• US 20050192011A1
• Filed: 02/15/2005
• Published: 09/01/2005
• Est. Priority Date: 02/13/2004
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Song, Bong-Gee, Cho, Min-Hee, Ju, Hyeong-Jong, Hong, Seung-Eun, Eom, Kwang-Seop
• Granted Patent: US 7,613,148 B2
• Time in Patent Office: Days
• US Class Current: 455/440
• CPC Class Codes: H04W 36/0061 of neighbour cell information
• CPC Class Codes: H04W 36/0077 of access information of target access point
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A method for performing a handover by a subscriber station (SS) in a broadband wireless communication system including a serving base station (BS) communicating with the SS, and at least one neighbor BS neighboring the serving BS. The SS receives downlink signals from the serving BS and the neighbor BS; measures an arrival time difference between the downlink signal received from the serving BS and the downlink signal received from the neighbor BS; and transmits the measured arrival time difference to the serving BS.

Claims

1. A method for performing a handover by a subscriber station (SS) in a broadband wireless communication system including a serving base station (BS) communicating with the SS, and at least one neighbor BS neighboring the serving BS, the method comprising the steps of:

receiving downlink signals from the serving BS and the neighbor BS;

measuring an arrival time difference between the downlink signal received from the serving BS and the downlink signal received from the neighbor BS; and

transmitting the measured arrival time difference to the serving BS.

2. The method of claim 1, further comprising the step of determining to perform handover to a particular neighbor BS, and receiving fast ranging information from the neighbor BS through a message in which the arrival time difference is reflected.

3. The method of claim 1, wherein the arrival time difference is a value used for compensating for a round trip delay(RTD) caused by signal transmission/reception between the selected BS and the SS located in a distance form the serving BS.

4. The method of claim 3, wherein the round trip delay (RTD_BS2) is estimated using an RTD (RTD_BS1) of the downlink signal from the serving BS and the arrival time difference (DTPA:

Difference Time of downlink frame Preamble Arrival) between the downlink signal from the serving BS and the downlink signal from the neighbor BS in accordance with

RTD_—

BS2=RTD_—

BS1+2DTPA.

5. A method for performing a handover by a subscriber station (SS) from a serving base station (BS) to a target BS selected from a plurality of neighbor BSs in a broadband wireless communication system including the serving BS communicating with the SS, and the plurality of neighbor BSs neighboring the serving BS, the method comprising the steps of:

transmitting a ranging request message to the target BS;

receiving from the target BS in response to the ranging request message a ranging response message including a temporary connection identifier (CID) allocated to the SS; and

receiving an allocated fast ranging information element from the target BS through the temporary CID upon determining handover to the target BS.

6. The method of claim 5, wherein the temporary CID is a CID temporarily used by the SS to perform an initial ranging to the target BS and is comprised of 16 bits.

7. The method of claim 5, wherein the target BS withdraws the temporary CID if there is no traffic connection using the allocated temporary CID until a predetermined time.

8. The method of claim 5, wherein upon receiving the allocated fast ranging information element, the SS performs a fast ranging to the target BS through the allocated fast ranging information element.

9. The method of claim 5, further comprising the steps of:

transmitting upon receiving the ranging response message from the target BS to the serving BS a handover request message for handover to the target BS; and

receiving a handover response message from the serving BS.

10. A method for performing a handover by a subscriber station (SS) from a serving base station (BS) to a target BS selected from a plurality of neighbor BSs in a broadband wireless communication system including the serving BS communicating with the SS, and the plurality of neighbor BSs neighboring the serving BS, the method comprising the steps of:

measuring a arrival time difference of a downlink signal received from the target BS relative to a downlink signal received from the serving BS;

estimating a round trip delay between the SS and the neighbor BS using the measured arrival time difference; and

transmitting to the serving BS a handover request message including the estimated round trip delay.

11. The method of claim 10, further comprising the step of:

receiving from the target BS a fast ranging information element adjusted by the estimated round trip delay; and

performing initial ranging for handover to the target BS upon receiving the fast ranging information element.

12. The method of claim 10, wherein the arrival time delay of the downlink signal received from the target BS relative to the downlink signal received from the serving BS is a value used for compensating for the round trip delay (RTD) caused by signal transmission/reception between the target BS and the SS located in a distance from the serving BS.

13. The method of claim 10, wherein the round trip delay (RTD_BS2) to the target BS is calculated by reflecting the arrival time difference (DTPA:

Difference Time of downlink frame Preamble Arrival) between the serving BS and the target BS in an RTD value (RTD_BS1) between the SS and the serving BS in accordance with

RTD_—

BS2=RTD_—

BS1+2DTPA.

14. The method of claim 13, wherein the RTD to the target BS is used as for time correction reflected by the SS during signal transmission to the target BS, through an initial ranging between the SS and the target BS.

15. The method of claim 10, further comprising the steps of:

receiving a handover response message including a temporary connection identifier (CID) allocated to the SS from the serving BS in response to handover request message after transmitting the handover request message;

receiving a fast ranging information element from the target BS upon determining handover to the target BS; and

performing initial ranging with the target BS through the temporary CID upon receiving the fast ranging information element.

16. The method of claim 15, further comprising the steps of:

recognizing, by the target BS, the SS through a handover notification message transmitted from the serving BS; and

allocating, by the target BS, a corresponding temporary CID to the recognized SS, and transmitting to the serving BS a handover notification response message including the temporary CID,

wherein the serving BS transmits the temporary CID received from the target BS to the SS through the handover response message.

17. The method of claim 15, wherein the temporary CID is a CID temporarily used by the SS to perform an initial ranging to the target BS and is comprised of 16 bits.

18. The method of claim 15, wherein the target BS withdraws the temporary CID if there is no traffic connection using the allocated temporary CID until a predetermined time.

19. A method for performing a handover by a subscriber station (SS) from a serving base station (BS) to a target BS selected from a plurality of neighbor BSs in a broadband wireless communication system including the serving BS communicating with the SS, and the plurality of neighbor BSs neighboring the serving BS, the method comprising the steps of:

measuring a carrier-to-interference and noise ratio (CINR) of a signal transmitted from the serving BS, and comparing the measured result value with a predetermined threshold;

if the measured result value is less than the threshold, scanning for a neighbor BS, detecting a signal transmitted from the neighbor BS, and measuring a CINR of the detected signal and a signal arrival time difference relative to the signal transmitted from the serving BS;

after the scanning for the neighbor BSs, transmitting a handover request message including the measured signal arrival time difference;

upon receiving a handover response message from the serving BS in response to the handover request message, transmitting a handover indication message to the serving BS; and

performing a network re-entry process with a round trip delay(RTD) reflected by the signal arrival time difference for handover to the target BS.

20. The method of claim 19, wherein the signal arrival time difference is a value used for compensating for a round trip delay (RTD) caused by signal transmission/reception between the target BS and the SS located in a distance from the serving BS.

21. The method of claim 19, wherein the RTD value (RTD_BS2) to the target BS is calculated by reflecting the signal arrival time difference (DTPA:

Difference Time of downlink frame Preamble Arrival) between the serving BS and the target BS in an RTD value (RTD_BS1) between the SS and the serving BS in accordance with

RTD_—

BS2=RTD_—

BS1+2DTPA.

22. The method of claim 21, wherein the RTD value to the target BS is used as a time correction value for time correction reflected by the SS during signal transmission to the target BS, wherein the estimated RTD value to the target BS is acquired through initial ranging between the SS and the target BS.

23. The method of claim 19, further comprising the steps of:

receiving a handover response message including a temporary connection identifier (CID) allocated to the SS itself from the serving BS in response to handover request message after transmitting the handover request message;

receiving a fast ranging information element from the target BS upon determining handover to the target BS; and

performing initial ranging with the target BS through the temporary CID upon receiving the fast ranging information element.

24. The method of claim 23, wherein the temporary CID is a CID temporarily used by the SS to perform initial ranging to the target BS and is comprised of 16 bits.

25. A method for supporting handover by a serving base station (BS) in a broadband wireless communication system including the serving BS in data communication with a subscriber station (SS), and at least one neighbor BS neighboring the serving BS, the method comprising the steps of:

receiving from the SS a handover request message including an arrival time difference measured by the SS between the downlink signals from the serving BS and from the neighbor BS of a selected neighbor BS;

estimating a round trip delay (RTD) information through the arrival time difference; and

transmitting the estimated RTD information to the selected neighbor BS.

26. The method of claim 25, wherein the RTD (RTD_BS2) is estimated using a RTD (RTD_BS1) between the SS and the serving BS and the arrival time difference (DTPA:

Difference Time of downlink frame Preamble Arrival) in accordance with

RTD_—

BS2=RTD_—

BS1+2DTPA.

27. A method for supporting handover by a serving base station (BS) in a broadband wireless communication system including the serving BS in data communication with a subscriber station (SS), and at least one neighbor BS neighboring the serving BS, the method comprising the steps of:

receiving from the SS a handover request message including a round trip delay (RTD) information estimated by the SS between the SS and the neighbor BS of a selected neighbor BS; and

transmitting the RTD information to the selected neighbor BS.

28. The method of claim 27, wherein the RTD (RTD_BS2) is estimated using a RTD (RTD_BS1) between the SS and the serving BS and the arrival time difference (DTPA:

Difference Time of downlink frame Preamble Arrival) in accordance with

RTD_—

BS2=RTD_—

BS1+2DTPA.

29. A method for supporting a handover by a serving base station (BS) in a broadband wireless communication system including the serving BS communicating with a subscriber station (SS), and a plurality of neighbor BSs neighboring the serving BS, the method comprising the steps of:

upon receiving a handover request message from a particular SS, generating a handover table using information related to the handover request message;

transmitting a handover notification message including information related to the SS that transmitted the handover request message, to the neighbor BSs;

upon receiving a handover notification response message corresponding to the handover notification message from the neighbor BSs, updating the handover table using information included in the handover notification response message;

setting a target BS that can provide the SS with an appropriate service level by analyzing a temporary connection identifier (CID) included in the handover notification response message, and transmitting to the target BS a handover confirm message indicating that the SS will be handed over to the target BS; and

after transmitting the handover confirm message, transmitting to the SS a handover response message including information on the target BS and the temporary CID.

30. The method of claim 29, further comprising the step of, upon receiving a handover indication message from the SS in response to the handover response message, updating the handover table using final target BS information included in the handover indication message.

31. The method of claim 29, wherein the handover request message includes a signal arrival time difference that the SS considers for handover and information on candidate target BSs.

32. The method of claim 31, wherein the signal arrival time difference is a value used for compensating for a round trip delay (RTD) caused by signal transmission/reception between the SS and the target BS, wherein the serving BS maps the signal arrival time difference to the handover table.

33. The method of claim 32, wherein the RTD value (RTD_BS2) to the target BS is calculated by reflecting the signal arrival time difference (DTPA:

Difference Time of downlink frame Preamble Arrival) value between the serving BS and the target BS in an RTD value (RTD_BS1) between the SS and the serving BS in accordance with RTD_BS2=RTD_BS1+2DTPA.

34. The method of claim 32, wherein the RTD value to the target BS is used as a time correction value for time correction reflected by the SS during signal transmission to the target BS, wherein the estimated RTD value to the target BS is acquired through an initial ranging between the SS and the target BS.

35. The method of claim 29, wherein the temporary CID is a CID temporarily used by the SS to perform initial ranging to the target BS and is comprised of 16 bits.

36. A method for supporting a handover by a target base station (BS) in a broadband wireless communication system including a serving BS communicating with a particular subscriber station (SS), and a plurality of neighbor BSs neighboring the serving BS, the method comprising the steps of:

receiving from the serving BS a handover notification message including a estimated round trip delay between the SS and the target BS;

determining to approve handover requested by a handover requesting SS included in the handover notification message, determining a bandwidth and a service level, which can be provided to the SS;

transmitting to the serving BS the handover notification response message including the determined information in a handover notification response message; and

upon receiving a handover confirm message from the serving BS in response to the handover notification response message, allocating a fast ranging information element reflected by the estimated round trip delay for a fast ranging to the SS.

37. The method of claim 36, further comprising the step of,

determining a temporary connection identifier (CID) to be allocated to the SS;

and

transmitting to the serving BS the handover notification response message including the temporary CID.

38. The method of claim 37, wherein the RTD value is used as a time correction value for time correction reflected by the SS during signal transmission to the target BS, and is acquired through initial ranging between the SS and the target BS.

39. The method of claim 37, wherein the temporary CID is a CID temporarily used by the SS to perform an initial ranging to the target BS and is comprised of 16 bits.

40. The method of claim 36, wherein the target BS withdraws the temporary CID if there is no traffic connection using the allocated temporary CID until a predetermined time.

41. The method of claim 36, wherein the round trip delay (RTD_BS2) between the target BS and the SS is calculated by reflecting a DTPA (Difference Time of downlink frame Preamble Arrival) value between the serving BS and the target BS in an RTD value (RTD_BS1) between the SS and the serving BS in accordance with

RTD_—

BS2=RTD_—

BS1+2DTPA.

42. A method for performing a handover by a subscriber station (SS) from a serving base station (BS) to a target BS selected from a plurality of neighbor BSs in a broadband wireless communication system including the serving BS communicating with the SS, and the plurality of neighbor BSs neighboring the serving BS, the method comprising the steps of:

estimating a round trip delay (RTD) value to the target BS based on an RTD value to the serving BS and a signal arrival time difference between a signal received from the serving BS and a signal received from the target BS;

transmitting the estimated RTD value to the target BS to the serving BS; and

determining to perform a handover to the target BS, and receiving from the target BS a message including an allocated fast ranging information element and the estimated RTD value.

43. The method of claim 42, wherein the RTD value to the target BS is calculated by

RTD_—

BS2=RTD_—

BS1+2DTPA

where RTD_BST denotes an RTD value to the target BS, RTD_BS1 denotes an RTD value to the serving BS, and DPTA denotes an arrival time difference between a signal received from the service BS and a signal received from the target BS.

44. The method of claim 42, wherein the signals received from the serving BS and the target BS, and used to calculate the arrival time difference, are downlink frame preamble (DFP) signals.

45. The method of claim 42, wherein after transmitting the handover request message, the SS receives from the serving BS a handover response message including a temporary connection identifier (CID) allocated by the target BS.

46. The method of claim 45, wherein the SS performs an initial ranging with the target BS using the allocated temporary CID.

47. The method of claim 45, wherein the temporary CID is a CID temporarily used by the SS to perform an initial ranging to the target BS and is comprised of 16 bits.

48. The method of claim 45, wherein the target BS withdraws the temporary CID if there is no traffic connection using the allocated temporary CID until a predetermined time.

49. The method of claim 42, wherein upon receiving the allocated fast ranging information element, the SS performs fast ranging with the target BS through the allocated fast ranging information element.

50. A subscriber station (SS) apparatus for performing a handover from a serving base station (BS) to a target BS selected from a plurality of neighbor BSs in a broadband wireless communication system including the serving BS communicating with the SS, and the plurality of neighbor BSs neighboring the serving BS, the apparatus comprising:

a receiver for calculating an arrival time difference between a signal received from the serving BS and a signal received from the target BS;

a medium access control (MAC) processor for estimating a round trip delay (RTD) value to the target BS based on an RTD value to the serving BS and the arrival time difference calculated by the receiver; and

a transmitter for transmitting the RTD value to the target BS, estimated by the MAC processor, to the serving BS or the target BS.

51. The SS apparatus of claim 50, wherein the receiver comprises:

a reference signal processing module for processing a reference signal periodically received from the serving BS;

a timing generation module for generating its own clock information through the signal periodically received from the reference signal processing module and providing a reference time value; and

a time difference calculation module for calculating a difference value between the reference signal arrival time of the serving BS provided from the time generation module and a reference signal arrival time of the serving BS provided from the reference signal processing module.

52. The SS apparatus of claim 51, wherein the reference signal is a downlink frame preamble (DFP), and the reference signal processing module measures a carrier-to-interference and noise ratio (CINR) of the serving BS, and if the measured CINR drops below a predetermined threshold, notifies the MAC processor of the drop of the measured CINR.

53. The SS apparatus of claim 51, wherein the reference signal processing module notifies the timing generation module of an arrival time of the periodic reference signal.

54. The SS apparatus of claim 51, wherein in response to a scanning request from the MAC processor, the reference signal processing module processes reference signals received from neighbor BSs, notifies the time difference calculation module of a arrival time of the reference signals of the neighbor BSs received through scanning, and delivers data received after the reference signal to a fast Fourier transform unit.

55. The SS apparatus of claim 50, wherein the RTD value is estimated by the time difference calculation module through the signal arrival time difference.

56. The SS apparatus of claim 50, wherein the RTD value to the target BS is calculated by

RTD_—

BS2=RTD_—

BS1+2DTPA

where RTD_BST denotes an RTD value to the target BS, RTD_BS1 denotes an RTD value to the serving BS, and DPTA denotes an arrival time difference between a signal received from the service BS and a signal received from the target BS.

57. The SS apparatus of claim 50, wherein the signals received from the serving BS and the target BS, used to calculate the arrival time difference, are downlink frame preamble (DFP) signals.

58. The SS apparatus of claim 50, wherein the estimated RTD value to the target BS is included in a handover request message transmitted to the serving BS.