Techniques for rach (random access channel)-less synchronized handover for wireless networks

Abstract

An example technique is provided for receiving, by a target base station (BS) from a source BS, information identifying a source cell or the source BS, and a first time advance value used by the user device to transmit signals to the source BS, receiving a signal by the target BS that was transmitted from the user device based on the first time advance value, determining, by the target BS based upon the first time advance value and the received signal from the user device, a second time advance value to be used by the user device to transmit data to the target BS, sending the second time advance value from the target BS to the source BS, receiving, by the target BS, a handover of the user device from the source BS to the target BS, and receiving data by the target BS from the user device based on the second time advance value.

1 - 47 . (canceled) 
     
     
         48 . An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to:
 determine, by a user device, a first time advance value for the user device for use in transmitting signals from the user device to a source base station (source BS);   determine, by the user device, a first propagation delay from the source BS and the user device;   determine, by the user device, a time difference value as a difference between the first propagation delay and a second propagation delay, the second propagation delay including a propagation delay from a target base station (target BS) and the user device;   determine, by the user device based on the first propagation delay and the time difference value, a second time advance value for use in transmitting signals from the user device to the target BS;   perform, by the user device, a handover from the source BS to the target BS; and   transmit signals from the user device to the target BS based upon the second time advance value.   
     
     
         49 . The apparatus of  claim 48 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to perform a synchronized and random access-free handover from the source BS to the target BS in response to a handover command received from the source BS, the synchronized handover being performed by the user device at a time identified in the handover command. 
     
     
         50 . The apparatus of  claim 48 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:
 send, from the user device to the source BS, a measurement report indicating a handover to the target BS;   receive, by the user device from the source BS, a handover command including at least a handover time field that identifies a time to perform the handover to the target BS;   begin to receive data from the target BS at a time identified by the handover time field; and   send a handover completion message from the user device to the target BS.   
     
     
         51 . The apparatus of  claim 48 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to determine the second time advance value based on the following: 
       TA2=TA1−2*X, wherein TA1 is the first time advance value, TA2 is the second time advance value, and X is the time difference value. 
     
     
         52 . The apparatus of  claim 48 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:
 receive a first signal from the source BS;   receive a second signal from the target BS, wherein the first signal and the second signal are transmitted at the same time; and   determine a difference in arrival time between the first signal and the second signal as received by the user device, wherein the time difference value comprises the difference in arrival time of the first signal and the second signal.   
     
     
         53 . The apparatus of  claim 48 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:
 receive at least one first common reference signal (CRS) from the source BS;   receive at least one second CRS from the target BS, wherein the first CRS and the second CRS are transmitted at the same time; and   determine a difference in an arrival time between the least one first CRS and the least one second CRS as received by the user device, wherein the time difference value comprises the difference in arrival time of the least one first CRS and the at least one second CRS.   
     
     
         54 . An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to:
 receive, by a target base station (target BS) from a source base station (source BS), information identifying a user device that is connected to the source BS, information identifying a source cell or the source BS, and a first time advance value used by the user device to transmit signals to the source BS;   receive a signal by the target BS that was transmitted from the user device based on the first time advance value;   determine, by the target BS based upon the first time advance value and the received signal from the user device, a second time advance value to be used by the user device to transmit data to the target BS;   send the second time advance value from the target BS to the user device;   receive a handover of the user device from the source BS to the target BS; and   receive data by the target BS from the user device based on the second time advance value.   
     
     
         55 . The apparatus of  claim 54 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to receive by the target BS from the source BS a handover request to perform a handover of the user device from the source BS to the target BS, the handover request including a handover time that identifies a time when a synchronized handover for the user device is to be performed from the source BS to the target BS. 
     
     
         56 . The apparatus of  claim 54 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:
 receive, by the target BS from the source BS, a signal configuration information identifying a configuration of a reference signal transmitted by the user device to the source BS using the first time advance value;   receive, by the target BS from the source BS, scheduling information identifying scheduled resources for the user device to transmit the reference signal to the source BS;   wherein the receiving a signal by the target BS from the user device includes the target BS receiving the scheduled reference signal from the user device.   
     
     
         57 . The apparatus of  claim 56  wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to determine, by the target BS, a second time advance value to be used by the user device to transmit data to the target BS based upon the first time advance value and the reference signal received from the user device via the scheduled resources. 
     
     
         58 . The apparatus of  claim 56 , wherein the reference signal comprises a sounding reference signal. 
     
     
         59 . The apparatus of  claim 54 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to receive a synchronized and random access-free handover of the user device from the source BS to the target BS in response, the synchronized handover being performed at a time identified by a handover command. 
     
     
         60 . An apparatus comprising at least one processor and at least one memory including computer instructions, when executed by the at least one processor, cause the apparatus to:
 determine, by a source base station (source BS), a first time advance value for a user device to use in transmitting signals from the user device to the source BS;   send, from the source BS to the user device a request to measure a target base station (target BS) propagation delay of a signal transmitted from a target BS to the user device;   receive the target BS propagation delay from the user device;   determine, by the source BS, a second time advance value for the user device to use in transmitting signals to the target BS;   send a handover command to the user device, the handover command including the second time advance value.   
     
     
         61 . The apparatus of  claim 60 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to determine, by the source BS based on the first time advance value and the target BS propagation delay, the second time advance value for the user device to use in transmitting signals to the target BS. 
     
     
         62 . The apparatus of  claim 60 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to determine, by the source BS based on the following:
 TA2=TA1−2*(T2−T1), where T1 is a source BS propagation delay of a signal transmitted from the source BS to the user device, T2 is the target BS propagation delay, TA1 is the first time advance value for the user device, and TA2 is the second time advance value for the user device.   
     
     
         63 . The apparatus of  claim 60 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to perform a synchronized and random access procedure-free handover of the user device from the source BS to the target BS based on the handover command, the handover of the user device being performed at a time identified in the handover command. 
     
     
         64 . The apparatus of  claim 60 , wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to perform a handover of the user device from the source BS to the target BS, including:
 receive, by the source BS from the user device, a measurement report indicating a handover to the target BS; and   send, by the source BS to the user device, a handover command including at least a handover time field that identifies a time to perform a random access procedure-free and synchronized handover to the target BS.