METHOD FOR INTER-RADIO ACCESS TECHNOLOGY CELL RESELECTION

• US 20090088160A1
• Filed: 06/18/2008
• Published: 04/02/2009
• Est. Priority Date: 06/18/2007
• Status: Active Grant

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Sammour, Mohammed, Pani, Diana, Wang, Jin, Somasundaram, Shankar, Mukherjee, Rajat P.
• Granted Patent: US 8,706,115 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 36/00837 Determination of triggering parameters for hand-off
• CPC Class Codes: H04W 36/0085 Hand-off measurements
• CPC Class Codes: H04W 36/0088 Scheduling hand-off measurements
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 36/14 Reselecting a network or an air interface
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data

Abstract

A method for performing cell reselection first determines a current cell selection quality value. The cell selection quality value is compared to a predetermined threshold. Measurements of neighboring cells are taken if the cell selection quality value is less than or equal to the predetermined threshold. Measurements can be taken of intra-frequency cells, inter-frequency cells, and inter-radio access technology cells. If a neighboring cell is found that is better than the current cell based on the measurements, then the better neighbor cell is reselected to.

Claims

1. A method for performing cell reselection, comprising:

determining a current cell selection quality value;

comparing the cell selection quality value to a predetermined threshold;

taking measurements of neighboring cells if the cell selection quality value is less than or equal to the predetermined threshold; and

if a neighboring cell better than the current cell is found based on the measurements, then reselecting to the better neighbor cell.

2. The method according to claim 1, wherein the cell selection quality value is a difference between a reference symbol received quality and a minimum required quality level in the cell.

3. The method according to claim 1, wherein

the threshold is a threshold for triggering intra-frequency measurements;

and

the measurements taken are of neighboring intra-frequency cells.

4. The method according to claim 1, wherein

the threshold is a threshold for triggering inter-frequency measurements;

and

the measurements taken are of neighboring inter-frequency cells.

5. The method according to claim 1, wherein

the threshold is a threshold for triggering intra-frequency measurements;

and

the measurements taken are of neighboring intra-frequency cells and neighboring inter-frequency cells in parallel.

6. The method according to claim 1, wherein the measurements taken are of neighboring intra-frequency cells and neighboring inter-frequency cells in parallel if the cell selection quality value is less than or equal to a threshold for triggering intra-frequency measurements and is less than or equal to a threshold for triggering inter-frequency measurements.

7. The method according to claim 1, wherein

the threshold is a threshold for triggering inter-radio access technology (RAT) measurements;

and

the measurements taken are of neighboring inter-RAT cells.

8. The method according to claim 7, wherein the inter-RAT measurements are taken only if there are no suitable neighboring intra-frequency cells or neighboring inter-frequency cells.

9. The method according to claim 7, wherein a different inter-RAT triggering threshold is used for each supported RAT.

10. The method according to claim 7, further comprising:

waiting for a predetermined period of time between two consecutive measurements.

11. The method according to claim 10, wherein the predetermined period of time is based on a number of discontinuous reception (DRX) cycles.

12. The method according to claim 11, further comprising:

taking measurements on the inter-RAT cells if the current cell fails a predetermined criteria for a predetermined number of consecutive DRX cycles.

13. The method according to claim 12, wherein the predetermined criteria is an S criteria.

14. The method according to claim 13, wherein the S criteria is defined by the formula:

Srxlev=RSRP−

Qrxlevmin−

max(UE_TXPWR_MAX_RACH−

P_MAX,

     0)

where Srxlev is a cell selection reception level, RSRP is a reference symbol received power, Qrxlevmin is a minimum required reception level in the cell, UE_TXPWR_MAX_RACH is a maximum power level that a wireless transmit/receive unit (WTRU) may use when accessing the cell on a random access channel, and P_MAX is a maximum radio frequency output power of the WTRU.

15. The method according to claim 14, wherein the RSRP value is measured by the WTRU and Qrxlevmin and UE_TXPWR_MAX_RACH are received from a network.

16. The method according to claim 10, wherein the predetermined period of time is received by a wireless transmit/receive unit (WTRU) from the network.

17. The method according to claim 16, wherein multiple predetermined period of time values are received by the WTRU from the network and the WTRU selects a predetermined period of time value based on current channel conditions.

18. The method according to claim 16, further comprising:

receiving a scaling factor, the scaling factor being multiplied by the predetermined period of time value to adjust the measurement interval based on current channel conditions.

19. The method according to claim 7, further comprising searching for an inter-RAT cell.

20. The method according to claim 19, wherein the searching comprises:

measuring cells in at least one RAT;

comparing the measured cells from all RATs against a minimum quality threshold;

selecting the cells that exceed the threshold, regardless of RAT; and

ranking the selected cells based on the measurements.

21. The method according to claim 20, wherein a different minimum quality threshold is used for each RAT.

22. The method according to claim 20, wherein the ranking is repeatedly performed on a predetermined interval.

23. The method according to claim 22, wherein the predetermined interval is based on a number of discontinuous reception (DRX) cycles.

24. The method according to claim 20, further comprising:

reselecting to a strongest cell from among all the RATs.

25. The method according to claim 7, further comprising:

receiving priority information for the RATs, wherein the priority information is used to determine an order for measuring the inter-RAT cells.

26. The method according to claim 25, wherein the priority information includes at least one of:

RAT information, frequency information, and cell information.

27. The method according to claim 1, wherein if the predetermined threshold is not available, then neighboring cells are always measured.