Smooth Hard Handover Method and Base Station Adapted For The Method

Abstract

A cellular radio communications system, method, mobile station, and base station for a smooth hard handover. Selected base stations prepare radio links for potential communication with a mobile station although only one radio link is actively used for transmission. A handover is then performed from the active radio link to one of the prepared radio links. The smooth hard handover is faster and more secure than a conventional hard handover, while requiring a less complex system architecture than a conventional soft handover.

1 - 26 . (canceled) 
     
     
         27 . A target base station for handover of a mobile station currently being served by a serving base station, the target base station comprising:
 a first interface connecting the target base station to a Radio Network Controller (RNC) or a core network;   a transmitter chain for transmitting radio signals to the mobile station;   a receiver chain for receiving radio signals from the mobile station;   a transceiver controller that controls the transmitter and receiver chains to prepare a radio link for transceiving with the mobile station, wherein the controller causes the transmitter and receiver chains to perform the following steps while the mobile station continues to communicate with the serving base station and without activating the radio link to transceive user data:
 set up a dedicated control channel from the target base station to the mobile station; 
 transmit control data from the target base station to the mobile station on the control channel, enabling the mobile station to synchronize a receiver chain in the mobile station to the target base station; and 
 synchronize a receiver chain in the target base station to mobile station transmissions on the radio link; 
   wherein the target base station immediately begins transceiving user data with the mobile station on the already prepared radio link when the mobile station is handed over to the target base station.   
     
     
         28 . The target base station according to  claim 27 , wherein the transceiver controller controls the transmitter and receiver chains to prepare the radio link in response to receiving a command over the first interface. 
     
     
         29 . The target base station according to  claim 27 , wherein when the mobile station is handed over to the target base station, the transceiver controller controls activation of the prepared radio link by causing the receiver chain to receive user data from the mobile station over the radio link, decode the received user data, and forward the decoded user data to the first interface, and by causing the transmitter chain to transmit user data received over the first interface to the mobile station over the radio link. 
     
     
         30 . A method in a target base station for handover of a mobile station currently being served by a serving base station, wherein the target base station includes a transmitter chain for transmitting radio signals to the mobile station and a receiver chain for receiving radio signals from the mobile station, the method comprising the steps of:
 preparing a radio link for transceiving with the mobile station while the mobile station continues to communicate with the serving base station and without activating the radio link to transceive user data; and   immediately transceiving user data between the target base station and the mobile station on the already prepared radio link when the mobile station is handed over to the target base station.   
     
     
         31 . The method according to  claim 30 , wherein the preparing step includes controlling the transmitter and receiver chains by a transceiver controller to perform the steps of:
 setting up a dedicated control channel from the target base station to the mobile station;   transmitting control data from the target base station to the mobile station on the control channel, enabling the mobile station to synchronize a receiver chain in the mobile station to the target base station; and   synchronizing a receiver chain in the target base station to mobile station transmissions on the radio link.   
     
     
         32 . The method according to  claim 31 , wherein the transceiver controller controls the transmitter and receiver chains to prepare the radio link in response to receiving a command over the first interface. 
     
     
         33 . The method according to  claim 27 , wherein the step of immediately transceiving user data on the already prepared radio link includes activating the prepared radio link by the transceiver controller causing the receiver chain to receive user data from the mobile station over the radio link, decode the received user data, and forward the decoded user data to a Radio Network Controller (RNC) or a core network, and by causing the transmitter chain to transmit user data received from the RNC or core network to the mobile station over the radio link.