Method and system for base station change of packet switched communications in a mobile communications system

A method in a mobile station (MS) for base station handover from a source cell of a source base station to a target cell of a target base station in a cellular radio network, wherein the base stations transfer packet switched communications between the mobile station and the network, the method comprising the steps of:

• while the MS is still in the source cell:
• receiving from the network, a handover command message ordering the MS to connect to the target cell;
• and
• receiving from the network, information regarding a next expected uplink packet for a packet flow subject to lossless packet switched handover;
• and
• upon arrival of the MS in the target cell, transmitting an uplink sequence number status message to the target base station providing a downlink sequence number status for the packet flow subject to lossless packet switched handover, and starting uplink data transmission to the target base station beginning with the next expected uplink packet.

A mobile station (MS) configured to be handed over from a source cell of a source base station to a target cell of a target base station in a cellular radio network, wherein the base stations transfer packet switched communications between the mobile station and the network, the mobile station comprising:

• a receiver configured to:
• receive, while the MS is still in the source cell, a handover command message from the network ordering the MS to connect to the target cell:
• and
• receive, while the MS is still in the source cell, information regarding a next expected uplink packet for a packet flow subject to lossless packet switched handover;
• and
• a transmitter configured to:
• transmit an uplink message to the target base station when the mobile station arrives in the target cell, the uplink message providing a downlink sequence number status for the packet flow subject to lossless packet switched handover;
• and
• start uplink data transmission to the target base station beginning with the next expected uplink packet.