Method for inter-radio access technology cell reselection
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.
1. A method for performing cell reselection implemented in a wireless transmit receive unit (WTRU), the method comprising:
receiving priority information in a current cell associated with a current radio access technology (RAT), wherein the priority information is indicative of a cell reselection priority of an inter-RAT cell associated with a candidate RAT relative to the current cell associated with the current RAT;
determining whether the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell associated with the current RAT based on the priority information;
determining a cell selection value of the current cell;
determining to perform quality measurements of the inter-RAT cell associated with the candidate RAT on condition that it is determined that the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell associated with the current RAT, wherein the quality measurements of the inter-RAT cell are performed irrespective of the cell selection value of the current cell based on the inter-RAT cell associated with the candidate RAT has having a higher priority than the current cell associated with the current RAT; and
determining to perform quality measurements of the inter-RAT cell associated with the candidate RAT on condition that it is determined that the inter-RAT cell associated with the candidate RAT does not have a higher priority than the current cell in the current RAT and that the cell selection value of the current cell is less than or equal to a predetermined threshold, wherein the WTRU considers the cell selection value of the current cell when determining whether to perform the quality measurements of the inter-RAT cell based on the inter-RAT cell associated with the candidate RAT not having a higher priority than the current cell associated with the current RAT.
2. The method as in claim 1 , wherein one of the current cell or the inter-RAT cell is a long term evolution (LTE) cell in an evolved universal terrestrial radio access network (E-UTRAN).
3. The method as in claim 1 , wherein one of the current cell or the inter-RAT cell is a wideband code division multiple access (WCDMA) cell.
4. The method as in claim 1 , further comprising:
determining to perform quality measurements of the inter-RAT cell associated with the candidate RAT irrespective of a current state of the WTRU on condition that it is determined that the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell associated with the current RAT.
5. The method as in claim 4 , wherein the current state of the WTRU comprises a mobility state based on a speed of the WTRU.
6. The method as in claim 1 , further comprising reselecting to the inter-RAT cell based on the quality measurement.
7. The method as in claim 6 , further comprising performing a location update upon reselecting to the inter-RAT cell.
8. The method as in claim 1 , wherein the quality measurements are evaluated periodically based on a time value signaled by an evolved universal terrestrial radio access network (E-UTRAN).
9. The method as in claim 1 , wherein the inter RAT priority information includes frequency information for the inter-RAT cell.
10. The method as in claim 1 , further comprising:
reselecting to the inter-RAT cell based on a signal strength measured for the inter-RAT cell being greater than a configured threshold for a predetermined period of time on condition that it is determined that the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell associated with the current RAT.
11. The method as in claim 1 , further comprising:
reselecting to the inter-RAT cell based at least in part on there being no cells in a higher priority RAT that meet cell reselection requirements on condition that it is determined that the inter-RAT cell associated with the candidate RAT does not have a higher priority than the current cell associated with the current RAT.
12. The method as in claim 11 , further comprising:
reselecting to the inter-RAT cell based at least in part on the Inter-RAT cell being higher ranked than the current cell on condition that it is determined that the inter-RAT cell associated with the candidate RAT does not have a higher priority than the current cell associated with the current RAT.
13. The method as in claim 1 , further comprising:
always determining to perform quality measurements of the inter-RAT cell associated with the candidate RAT on condition that it is determined that the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell in the current RAT.
14. A wireless transmit receive unit (WTRU) for performing cell reselection, the WTRU comprising:
a receiver configured to receive priority information in a current cell associated with a current radio access technology (RAT), wherein the priority information is indicative of a cell reselection priority of an inter-RAT cell associated with a candidate RAT relative to the current cell associated with the current RAT; and
a processor configured to:
determine whether the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell associated with the current RAT based on the priority information,
determine a cell selection value of the current cell,
determine to perform quality measurements of the inter-RAT cell associated with the candidate RAT on condition that it is determined that the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell associated with the current RAT, wherein the WTRU is configured to perform the quality measurements of the inter-RAT cell irrespective of the cell selection value of the current cell based on the inter-RAT cell associated with the candidate RAT has having a higher priority than the current cell associated with the current RAT, and
determine to perform quality measurements of the inter-RAT cell associated with the candidate RAT on condition that it is determined that the inter-RAT cell associated with the candidate RAT does not have a higher priority than the current cell associated with the current RAT and that the cell selection value of the current cell is less than or equal to a predetermined threshold, wherein the WTRU is configured to consider the cell selection value of the current cell when determining whether to perform the quality measurements of the inter-RAT cell based on the inter-RAT cell associated with the candidate RAT not having a higher priority than the current cell associated with the current RAT.
15. The WTRU as in claim 14 , wherein one of the current cell or the inter-RAT cell is a long term evolution (LTE) cell in an evolved universal terrestrial radio access network (E-UTRAN).
16. The WTRU as in claim 14 , wherein the processor is configured to determine to perform quality measurements of the inter-RAT cell associated with the candidate RAT irrespective of a current state of the WTRU on condition that it is determined that the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell associated with the current RAT.
17. The WTRU as in claim 16 , wherein the current state of the WTRU comprises a mobility state based on a speed of the WTRU.
18. The WTRU as in claim 14 , wherein the processor is further configured to reselect to the inter-RAT cell based on the quality measurements.
19. The WTRU as in claim 18 , wherein the processor is further configured to perform a location update upon reselecting to the inter-RAT cell.
20. The WTRU as in claim 14 , wherein the processor is configured to evaluate the quality measurements periodically based on a time value signaled by an evolved universal terrestrial radio access network (E-UTRAN).
21. The WTRU as in claim 14 , wherein the priority information includes frequency information for the inter-RAT cell.
22. The WTRU as in claim 14 , wherein the processor is further configured to reselect to the inter-RAT cell based on a signal strength measured for the inter-RAT cell being greater than a configured threshold for a predetermined period of time on condition that it is determined that the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell associated with the current RAT.
23. The WTRU as in claim 14 , wherein the processor is further configured to reselect to the inter-RAT cell based at least in part on there being no cells in a higher priority RAT that meet cell reselection requirements on condition that it is determined that the inter-RAT cell associated with the candidate RAT does not have a higher priority than the current cell associated with the current RAT.
24. The WTRU as in claim 23 , wherein the processor is further configured to reselect to the inter-RAT cell based at least in part on the inter-RAT cell being higher ranked than the current cell on condition that it is determined that the inter-RAT cell associated with the candidate RAT does not have a higher priority than the current cell associated with the current RAT.
25. The WTRU as in claim 14 , wherein the processor is configured to always determine to perform quality measurements on the inter-RAT cell associated with the candidate RAT on condition that it is determined that the inter-RAT cell associated with the candidate RAT has a higher priority than the current cell associated with the current RAT.