Method of cell selection in heirarchical cell structure based on cell quality
A cell selection method where, if a hierarchical cell structure (HCS) is used, a first ranking procedure is performed if the UE has low mobility, and a second ranking procedure is performed if the UE has high mobility. When the UE has low mobility, the first ranking procedure is performed for all measured cells that have a highest HCS priority among those cells that fulfill a criterion S and a criterion H≧0, or the ranking procedure is performed for all measured cells regardless of HCS priorities if no cell fulfills the criterion S and the criterion H≧0. When the UE has high mobility, the second ranking procedure is performed for all measured cells, and if there are cells with lower HCS priority than the serving cell that fulfills the criterion S and the criterion H≧0, the ranking procedure is performed for all cells that have the highest HCS priority.
1. A method of cell reselection for a user equipment (UE) in a network, the method comprising:
performing, by the UE, a measurement of cells;
determining, by the UE, whether a hierarchical cell structure (HCS) is used in a serving cell;
if the HCS is not used in the serving cell, performing ranking of the measured cells satisfying a first criterion, wherein the first criterion is a cell selection criterion S that is used to select measured cells satisfying a minimum quality condition;
if the HCS is used in the serving cell, performing ranking of the measured cells satisfying both the first criterion and a second criterion, wherein the second criterion is a quality level threshold criterion H that is used to determine whether a prioritized ranking according to hierarchical cell reselection rules apply; and
performing, by the UE, cell reselection to a best cell in ranking of the measured cells satisfying both the first criterion and the second criterion,
wherein the first criterion is considered prior to the second criterion when performing ranking of the measured cells.
2. The method of claim 1 , wherein the HCS defines a number of overlapping cells of different sizes that form multiple cell layers.
3. The method of claim 1 , wherein the second criterion is not considered if the HCS is not used in the serving cell.
4. The method of claim 1 , the UE is considered to have low mobility or a high mobility based on a number of cell reselections during a certain time period or based on RRC (radio resource control) signaling from the network.
5. The method of claim 1 , wherein the measured cells are determined by performing signal measurement procedures with a base station in all searchable frequency bands, and then a cell having a strongest signal characteristics value is selected among cells that satisfy certain cell selection conditions and an access to the selected cell is performed.
6. The method of claim 5 , wherein at least one of CPICH RSCP (Common Pilot Channel Received Signal Code Power), CPHIC Ec/N 0 (carrier to noise ratio) and Carrier RSSI (Received Signal Strength Indicator) is used in the signal measurement procedures.
7. The method of claim 1 , wherein the second criterion is calculated based on information sent in system information and on measurements from a CPICH/P-CPCCH (Common Pilot Channel/Primary-Common Control Physical Channel) of the candidate cell.