Advanced handover in phased-shifted and time-sliced networks

• US 7,660,583 B2
• Filed: 03/19/2004
• Issued: 02/09/2010
• Est. Priority Date: 03/19/2004
• Status: Expired due to Fees

• Current Assignee: RPX Corporation
• Original Assignee: Nokia Corporation
• Inventors: Pekonen, Harri, Vesma, Jussi
• Primary Examiner(s): Eng, George
• Assistant Examiner(s): MANOHARAN, MUTHUSWAMY GANAPATHY
• Application Number:
  US10/804,263
• Publication Number:
  US 20050208942A1
• Time in Patent Office: 2,153 Days
• Field of Search: 455/436, 370/331, 370/333, 370/332, 370/328, 370/329, 370/346, 370/252, 370/478, 370/503
• US Class Current: 455/436
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data
• CPC Class Codes: H04W 36/302 due to low signal strength

Abstract

The present invention provides methods and apparatus for a wireless terminal to receive channel bursts in a wireless system while the wireless terminal is performing a handover from one base station to another base station. The wireless terminal determines that a handover may be necessary if a handover criterion is satisfied based upon a measurement of the signal quality associated with the current serving base station. If so, the wireless terminal performs measurements for the candidate cells, which are maintained in a candidate list. The wireless terminal will select one of the candidate cells (corresponding to the new serving base station) if the associated signal quality is sufficiently better than the current serving base station. After determining that a handover is necessary and before completing the handover to the new serving base station, the wireless terminal receives a last channel burst from the current serving base station.

Claims

1. A method comprising:

(A) receiving a first channel burst broadcasted from a first base station of a unidirectional broadcast network on a wireless channel, wherein the first base station serves a first cell, wherein the first channel burst supports a data service, and wherein the first channel burst comprises timing information identifying a time period of a subsequent channel burst to be transmitted by the first base station;

(B) determining whether a serving signal quality associated with the first cell satisfies a handover criterion;

(C) in response to (B), obtaining measurements associated with a list of candidate cells, wherein the list comprises at least one candidate cell and wherein each measurement gauges a corresponding signal quality that is provided by a corresponding candidate cell, wherein (C) further comprises;

if, based on the timing information, the measurements cannot be completed before receiving the subsequent channel burst;

(i) suspending the obtaining of the measurements;

(ii) receiving the subsequent channel burst from the first base station; and

(iii) in response to (ii), resuming the obtaining of the measurements;

(D) if a selected signal quality is acceptable, deciding to perform a handover to a selected candidate cell, wherein the selected candidate cell is a member of the list and wherein the selected signal quality corresponds to the selected candidate cell;

(E) after performing (D), receiving a final channel burst from the first base station; and

(F) in response to (E), performing the handover to the selected candidate cell and receiving a new channel burst from a selected candidate base station of the unidirectional broadcast network such that the handover occurs between the final channel burst and the new channel burst, wherein the selected candidate base station is serving the selected candidate cell.

2. The method of claim 1, wherein (C) comprises:

setting an interrupt flag if the obtaining of the measurements cannot be completed before receiving the subsequent channel burst from the first base station, and

resetting the interrupt flag upon reception of the subsequent channel burst.

3. The method of claim 1, wherein the serving signal quality is determined from the first channel burst.

4. The method of claim 1, wherein the serving signal quality is selected from a group of indicators consisting of a received signal strength indicator (RSSI) value, a bit error rate (BER), a packet error rate (PER), and a frame error rate (FER).

5. The method of claim 1, wherein (D) comprises:

(i) adjusting the selected signal quality by a hysteresis value.

6. The method of claim 1, farther comprising:

(G) determining the list of candidate cells.

7. The method of claim 6, wherein (G) comprises:

(i) receiving handover information from the first base station, wherein the handover information comprises candidate information indicative of the list of candidate cells.

8. The method of claim 1, further comprising:

(G) determining a phase shift offset that is associated with the selected candidate cell.

9. The method of claim 8, wherein (G) comprises:

(i) receiving handover information from the first base station, wherein the handover information comprises the phase shift offset that is associated with the selected candidate cell.

10. The method of claim 8, further comprising:

(H) in response to (E), suspending reception on the wireless channel until performing (F).

11. The method of claim 10, wherein (H) comprises:

(i) instructing a module of a wireless terminal to reduce power consumption.

12. The method of claim 1, further comprising:

(G) if a candidate signal quality is not acceptable, removing the associated candidate from the list of candidate cells.

13. The method of claim 1, wherein (F) comprises:

(i) receiving the new channel burst associated with a different frequency.

14. The method of claim 1, wherein (F) comprises:

(i) receiving the new channel burst associated with a different channelization code.

15. A computer-readable medium having computer-executable instructions that, when executed, cause a processor to perform the method recited in claim 1.

16. A computer-readable medium having computer-executable instructions that, when executed, cause a processor to perform the method recited in claim 10.

17. The method of claim 1, further comprising serving a digital broadband broadcasting area and the data service is associated with a digital broadband broadcasting service.

18. The method of claim 1, further comprising accessing a lookup table to determine a phase shift offset associated with the selected base station.

19. The method of claim 1, farther comprising:

(G) in response to (E), determining that the serving signal quality is not indicative of a handover; and

(H) in response to (G), canceling the handover to the selected candidate cell.

20. An apparatus comprising:

a storage buffer;

a timing module; and

a radio module configured to communicate with a wireless system over a wireless channel;

a processor configured to receive an indication from the timing module that a current first channel burst is being transmitted, wherein the current first channel burst contains a first group of data packets, and configured to store the first group of data packets into the storage buffer, the processor configured to perform;

(A) receiving a first channel burst broadcasted from a first base station of a unidirectional broadcast network on a wireless channel, wherein the first base station serves a first cell and wherein the first channel burst supports a data service, the first channel burst comprising timing information identifying a time period of a subsequent channel burst to be transmitted by first base station;

(B) determining whether a serving signal quality associated with the first cell satisfies a handover criterion;

(C) obtaining measurements associated with a list of candidate cells, wherein the list comprises at least one candidate cell and wherein each measurement gauges a corresponding signal quality that is provided by a corresponding candidate cell, wherein (C) further comprises;

if, based on the timing information, the obtaining of the measurements cannot be completed before receiving the subsequent channel burst;

(i) suspending the obtaining of the measurements;

(ii) receiving the subsequent channel burst from the first base station; and

(iii) in response to (ii), resuming the obtaining of the measurements;

(D) if a selected signal quality is acceptable, deciding to perform a handover to a selected candidate cell, wherein the selected candidate cell is a member of the list and wherein the selected signal quality corresponds to the selected candidate cell;

(E) after performing (D), receiving a final channel burst from the first base station; and

(F) in response to (E), performing the handover to the selected candidate cell and receiving a new channel burst from a selected candidate base station of the unidirectional broadcast network such that the handover occurs between the final channel burst and the new channel burst, wherein the selected candidate base station is serving the selected candidate cell.

21. The apparatus of claim 20, wherein the processor is configured to perform:

(G) adjusting the selected signal quality by a hysteresis value.

22. The apparatus of claim 20, wherein the processor is configured to perform:

(G) determining a phase shift offset that is associated with the selected candidate cell.

23. The apparatus of claim 20, wherein the processor is configured to perform:

(G) determining a phase shift offset that is associated with the selected candidate cell;

(H) in response to (E), suspending reception on the wireless channel until performing

(F); and

(I) in response to (H), instructing a module of a wireless terminal to reduce power consumption.

24. The apparatus of claim 20, wherein the processor is configured to perform:

(G) if a candidate signal quality is not acceptable, removing the associated candidate from the candidate list.

25. An apparatus comprising:

a communications module configured to receive a plurality of channel bursts broadcasted from a first base station of a unidirectional broadcast network before a handover and a new channel burst from a selected base station and configured to controllably tune to one of a plurality of base stations, wherein the plurality of channel bursts and the new channel burst support a data service on a wireless channel, and wherein at least one of the plurality of channel burst comprises timing information identifying a time period of a subsequent channel burst to be transmitted by the first base station;

a measurement module configured to obtain signal quality information from the communications module, the signal quality information being indicative of the first base station and the selected base station, the selected base station being a member of the plurality of base stations; and

a handover analysis module;

configured to instruct the communications module to tune to said one of the plurality of base stations and to instruct the measurement module to obtain corresponding signal quality information corresponding to said one of the plurality of base station;

configured to process the signal quality information to determine whether handover to the selected base station;

configured to determine if, based on the timing information, the obtaining of the signal quality information cannot be completed before receiving the subsequent channel burst, to instruct the measurement module to suspend the obtaining of the signal quality information to permit the communications module to receive the subsequent channel burst, and to instruct the measurement module to resume the obtaining of the signal quality information in response to the subsequent channel burst being received;

configured to instruct the communications module to receive a last channel burst from the first base station in response to determining to perform the handover; and

configured to instruct the communications module to tune to the selected base station of the unidirectional broadcast network and to receive the new channel burst from the selected base station such that the handover occurs between the final channel burst and the new channel burst.

26. The apparatus of claim 25, further comprising:

a power control module configured to reduce electrical power to the communications module if provided an instruction by the handover analysis module, wherein the handover analysis module is configured to generate the instruction between a time interval between the last channel burst and the new channel burst, and wherein the communications module is configured to suspend reception on the wireless channel.

27. A method comprising:

(A) receiving a first channel burst broadcasted from a first base station of a unidirectional broadcast network on a wireless channel, wherein the first base station serves a first cell, wherein the first channel burst supports a multicast service, and wherein the first channel burst comprises timing information identifying a time period of a subsequent channel burst to be transmitted by the first base station;

(B) determining a list of candidate cells, wherein the list comprises at least one candidate cell;

(C) determining whether a serving signal quality associated with the first cell satisfies a handover criterion;

(D) obtaining measurements associated with the list of candidate cells, wherein each measurement gauges a corresponding signal quality that is provided by a corresponding candidate cell, wherein (D) further comprises;

if, based on the timing information, the obtaining of the measurements cannot be completed before receiving the subsequent channel burst;

(i) suspending the obtaining of the measurements;

(ii) receiving the subsequent channel burst; and

(iii) in response to (ii), resuming the obtaining of the measurements;

(E) adjusting a selected signal quality by a hysteresis value;

(F) if a candidate signal quality is not acceptable, removing an associated candidate from the candidate list;

(G) if the selected signal quality is acceptable, deciding to perform a handover to a selected candidate cell, wherein the selected candidate cell is a member of the list and wherein the selected signal quality corresponds to the selected candidate cell;

(H) after performing (G), receiving a final channel burst from the first base station; and

(I) in response to (H), performing the handover to the selected candidate cell and receiving a new channel burst from a selected candidate base station of the unidirectional broadcast network such that the handover occurs between the final channel burst and the new channel burst, wherein the selected candidate base station is serving the selected candidate cell and wherein the new channel burst supports the multicast service.