Cell reselection method and apparatus for preventing ping-pong in a mobile communications system

A cell reselection method for preventing ping-pong in a mobile communications system, comprising the steps of:

• acquiring first and second duration thresholds and first and second occurrence number thresholds for controlling a cell reselection procedure, the second duration threshold being shorter than the first duration threshold and the second occurrence number threshold being less than the first occurrence number threshold;
• excluding, if the number of cell reselections of a user equipment (UE) to the same cell during the second duration threshold exceeds the second occurrence number threshold, the number of cell reselections during the second duration threshold or the number of cell reselections to the same cell during the second duration threshold from the number of cell changes during the first duration threshold;
• setting the UE to a non-high-speed state if the number of cell changes during the first duration threshold is equal to or less than the first occurrence number threshold;
• setting the UE to a high-speed state if the number of cell reselections to the same cell during the second duration threshold is equal to or less than the second occurrence number threshold and if the number of cell changes during the first duration threshold exceeds the first occurrence number threshold;
• selectively performing cell reselection according to a predetermined cell reselection time limit in the non-high-speed state;
• and
• selectively performing cell reselection according to a scaled-down value of the predetermined cell reselection time limit in the high-speed state.

A user equipment (UE) apparatus for cell reselection to prevent ping-pong in a mobile communications system, comprising:

• a parameter storage for acquiring and storing first and second duration thresholds and first and second occurrence number thresholds for controlling a cell reselection procedure, the second duration threshold being shorter than the first duration threshold and the second occurrence number threshold being less than the first occurrence number threshold;
• first and second timers set to the first and second duration thresholds, respectively;
• a UE state decider for;
• excluding, if the number of cell reselections to the same cell exceeds the second occurrence number threshold until the second timer expires, the number of cell reselections during the second duration threshold or the number of cell reselections to the same cell during the second duration threshold from the number of cell changes during the first duration threshold;
• setting the UE to a non-high-speed state if the number of cell changes is equal to or less than the first occurrence number threshold until the first timer expires;
• and
• setting the UE to a high-speed state if the number of cell reselections to the same cell is equal to or less than the second occurrence number threshold until the second timer expires and if the number of cell changes exceeds the first occurrence number threshold until the first timer expires;
• and
• a cell reselection controller for selectively performing cell reselection according to a predetermined cell reselection time limit in the non-high-speed state, and performing cell reselection according to a scaled-down value of the predetermined cell reselection time limit in the high-speed state.