Enhanced higher priority public land mobile network (HPPLMN) search
Embodiments provide an enhanced approach for Higher Priority Public Land Mobile Network (HPPLMN) search. In one embodiment, information acquired during a search (for each detected cell per frequency channel) is saved in a database and persisted in the database based on a validity time. An idle mode-to-connected mode transition by the UE, rather than aborting the search, only suspends the search for it to be resumed at a later time upon a connected mode-to-idle mode transition by the UE. Saved search data that is valid at the time of the transition is maintained and the frequency channel(s) associated with it is not re-searched in the current search. In an embodiment, the search is resumed based on weights that are associated with frequency channels, where a weight indicates a priority for visiting the frequency channel.
1. A method for performing a search over a plurality of frequency channels in a device, comprising:
selecting a frequency channel from the plurality of frequency channels according to an order determined by respective weights associated with the plurality of frequency channels, wherein the respective weight for a frequency channel increases with increasing time that has elapsed since the frequency channel was last searched;
searching the selected frequency channel for detectable cells; and
updating weight associated with the selected frequency channel in response to said searching;
wherein each weight of the respective weights is based on a difference between the increasing time that has elapsed since the corresponding frequency channel was last searched for the detectable cells and a threshold associated with the corresponding frequency channel.
2. The method of claim 1 , wherein the difference corresponding to the selected frequency channel is most negative among the weights associated with the plurality of frequency channels.
3. The method of claim 1 , wherein updating the weight associated with the selected frequency channel comprises updating the time elapsed since the selected frequency channel was last searched and updating the threshold associated with the selected frequency channel.
4. The method of claim 1 , further comprising:
detecting a cell on the selected frequency channel;
decoding a system information block associated with the detected cell to determine one or more Public Land Mobile Networks (PLMNs) associated with the detected cell; and
storing the determined PLMNs associated with the cell in a database.
5. The method of claim 1 , further comprising:
detecting an idle mode-to-connected mode transition with the device; and
suspending the search over the plurality of frequency channels in response to said idle mode-to-connected mode transition.
6. The method of claim 5 , further comprising:
detecting a connected mode-to-idle mode transition within the device; and
resuming the search over the plurality of frequency channels in response to said connected mode-to-idle mode transition.
7. The method of claim 6 , wherein resuming the search comprises:
comparing a first cell with a second cell, the first cell being a cell camped on by the device after the connected mode-to-idle mode transition and the second cell being a cell camped on by the device before the idle mode-to-connected mode transition; and
resuming the search over the plurality of frequency channels without re-searching the selected frequency channel if the first cell and the second cell are the same.
8. The method of claim 6 , further comprising:
updating the weight associated with the selected frequency channel based on a connected mode duration between the idle mode-to-connected mode transition and the connected mode-to-idle mode transition.
9. The method of claim 6 , wherein resuming the search comprises:
comparing a validity time associated with data obtained by searching the selected frequency channel with a current time; and
resuming the search over the plurality of frequency channels without re-searching the selected frequency channel if the validity time is later than the current time.
10. The method of claim 9 , wherein the validity time is based on a mobility state of the device, further comprising:
updating the weight associated with the selected frequency channel based on the mobility state of the device.
11. The method of claim 5 , further comprising:
resuming the search over the plurality of frequency channels in response to a connected mode-to-idle mode transition within the device without re-searching a frequency channel searched before the idle mode-to-connected mode transition within the device.
12. The method of claim 11 , wherein a cell camped on by the device after the connected mode-to-idle mode transition is the same as a cell camped on by the device before the idle mode-to-connected mode transition.
13. The method of claim 11 , wherein a validity time associated with data obtained by searching the selected frequency channel before the idle mode-to-connected mode transition is later than a current time.
14. The method of claim 1 , further comprising:
determining a number of past searches of the selected frequency channel; and
updating a search depth associated with the selected frequency channel based on the number of past searches, wherein the search depth indicates a maximum number of cells to decode from cells detected on the selected frequency channel.
15. The method of claim 14 , further comprising:
increasing the search depth associated with the selected frequency channel if a number of detected cells in a previous search of the selected frequency channel is greater than the search depth currently associated with the selected frequency channel; and
decreasing the search depth associated with the selected frequency channel if the number of detected cells in the previous search of the selected frequency channel is lower than the search depth currently associated with the selected frequency channel.
16. A device, comprising:
non-access stratum (NAS) layer circuitry configured to detect an expiration of a Higher Priority Public Land Mobile Network (HPPLMN) search timer and to send a command to an access stratum (AS) layer in response to the expiration of the HPPLMN search timer;
radio resource control (RRC) circuitry of the AS layer configured to initiate a HPPLMN search in response to the command and to save Public Land Mobile Networks (PLMNs) identified on a searched cell during the HPPLMN search, the RRC circuitry further configured to:
suspend the HPPLMN search upon an idle mode-to-connected mode transition, and
resume the HPPLMN search upon a connected mode-to-idle mode transition without discarding the PLMNs identified on the searched cell when a cell camped on by the device after the connected mode-to-idle mode transition is the same as a cell camped on by the device before the idle mode-to-connected mode transition;
wherein the HPPLMN search comprises searching a selected frequency channel for detectable cells, the selected frequency channel being selected from a plurality of frequency channels according to an order determined by respective weights associated with the plurality of frequency channels,
wherein the respective weights are proportional to respective last visit times of the plurality of frequency channels;
wherein the last visit time of a frequency channel of the plurality of frequency channels is a time elapsed since the corresponding frequency channel was last searched for the detectable cells; and
wherein each weight of the respective weights is based on a difference between the time elapsed since the corresponding frequency channel was last searched for the detectable cells and a threshold associated with the corresponding frequency channel.
17. The device of claim 16 , wherein a validity time associated with the PLMNs identified on the searched cell is later than a current time.
18. The device of claim 17 , wherein the validity time is related to a mobility state of the device.
19. A method for performing a search over a plurality of frequency channels in a device, comprising:
selecting a frequency channel from the plurality of frequency channels according to an order determined by respective weights associated with the plurality of frequency channels, wherein the respective weights are proportional to respective last visit times of the plurality of frequency channels;
searching the selected frequency channel for detectable cells; and
updating the weight associated with the selected frequency channel in response to said searching,
wherein the last visit time of a frequency channel of the plurality of frequency channels is a time elapsed since the corresponding frequency channel was last searched for the detectable cells; and
wherein each weight of the respective weights is based on a difference between the time elapsed since the corresponding frequency channel was last searched for the detectable cells and a threshold associated with the corresponding frequency channel.
20. A method for performing a search over a plurality of frequency channels in a device, comprising:
sequentially searching frequency channels of the plurality of frequency channels according to an order determined by respective weights associated with the plurality of frequency channels, wherein the respective weights are proportional to respective last visit times of the plurality of frequency channels;
detecting an idle mode-to-connected mode transition within the device; and
suspending the search over the plurality of frequency channels in response to the idle mode-to-connected mode transition within the device,
wherein the last visit time of a frequency channel of the plurality of frequency channels is a time elapsed since the corresponding frequency channel was last searched for detectable cells;
wherein each weight of the respective weights is based on a difference between the time elapsed since the corresponding frequency channel was last searched for the detectable cells and a threshold associated with the corresponding frequency channel.