Handover during carrier aggregation operation in wireless communication network
Methods for performing handovers and addition of carriers during carrier aggregation operation are described. A mobile station can indicate failure to perform downlink synchronization to some but not all cells of a target eNB, in response to a handover command. The mobile station can activate carriers based on various combinations of transmission of random access preambles, reception of random access response messages and transmission of handover complete messages. A base station can activate carriers based on various combinations of reception of random access preambles, transmission of random access response messages and reception of handover complete messages.
1. A method in a target base station for handover of a mobile station from a source base station to the target base station, the target base station supporting a plurality of cells, each cell of the plurality of cells operating on a different component carrier frequency, the method comprising:
generating, by the target base station, a handover command indicating a first set of cells of the target base station to be configured for communication, wherein the first set of cells comprises more than one cell;
receiving at the target base station a message from the mobile station indicating a partial completion of handover, wherein partial completion of handover indicates that the mobile station was able to perform downlink synchronization with at least one, and less than all, of the first set of cells; and
transmitting, by the target base station, an activation message indicating a second set of cells of the target base station to be activated.
2. The method according to claim 1 wherein the message indicating a partial completion of handover includes a message identifying at least one cell of the target base station to which the mobile station failed to perform downlink synchronization.
3. The method according to claim 1 wherein the message indicating a partial completion of handover includes a message identifying a subset of cells of the target base station, the subset of cells being a subset of the first set of cells, and the subset of cells not including all of the first set of cells.
4. The method according to claim 1 wherein the first set of cells comprises the set of cells of the target base station operating on carrier frequencies to be configured by the mobile station.
5. The method according to claim 1 wherein the first set of cells comprises the set of cells of the target base station operating on carrier frequencies to be considered for activation by the mobile station.