handover

Abstract

A user equipment, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the user equipment at least to perform: obtaining an indication that the user equipment is to perform acquisition of a timing advance relating to a target cell; and based on obtaining the indication, causing transmission of a message to a target network node associated with the target cell during a random access procedure, the message encoding an indication that the user equipment is performing the random access procedure to obtain acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

Description

[0001] HANDOVER

[0002] TECHNOLOGICAL FIELD

[0003] Various example embodiments relate to preparing for handover in a wireless telecommunication network.

[0004] BACKGROUND

[0005] As user equipment (UE) moves through a wireless telecommunication network, it may move through cells that comprise regions of radio coverage that are supported by one or more network access node or base station. As the UE moves from cell to cell, handover may occur between base stations to maintain an ability for the UE to communicate effectively as it moves through regions of radio coverage.

[0006] BRIEF SUMMARY

[0007] The scope of protection sought for various example embodiments of the invention is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0008] According to various, but not necessarily all, example embodiments of the invention there is provided a user equipment, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the user equipment at least to perform: obtaining an indication that the user equipment is to perform acquisition of a timing advance relating to a target cell; and based on obtaining the indication, causing transmission of a message to a target network node associated with the target cell during a random access procedure, the message encoding an indication that the user equipment is performing the random access procedure to obtain acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0009] The acquisition of the timing advance may occur during the random access procedure, prior to handover to the target cell being initiated.

[0010] The message may encode an indication to the target network node instructing nonallocation of grant of uplink resources during the random access procedure for use by the user equipment following handover. The message may encode an indication to the target network node to omit an indication, during the random access procedure in a response message from the target network node to the user equipment, of grant of uplink resources for use by the user equipment following handover.

[0011] The message may encode an indication to the target network node to omit or fail to include an indication of grant of uplink resources during the random access procedure in a response message from the target network node to the user equipment, wherein the uplink resources are for use by the user equipment following handover.

[0012] The message may comprise an uplink scheduled transmission message.

[0013] The message may comprise a msg3 message of a contention-based random access procedure.

[0014] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining a time alignement timer during the random access procedure.

[0015] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining the time alignment timer from the response message.

[0016] The response message may comprise a msg4 message of the contention-based random access procedure.

[0017] The message may precede the response message.

[0018] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining the timing advance during the random access procedure.

[0019] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining the timing advance from a random access message. The random access message may comprise a msg2 message of the contention-based random access procedure.

[0020] The random access message may precede the message.

[0021] The instructions when executed by the at least one processor may cause the user equipment at least to perform: detecting at least one of the following: contention during the random access procedure; or expiry of the time alignment timer; and based on the detection, discarding the timing advance.

[0022] The instructions when executed by the at least one processor may cause the user equipment at least to perform: based on the discarding the timing advance, repeating the acquisition of the timing advance relating to the target cell.

[0023] The target network node may comprise a target distributed unit.

[0024] The instructions when executed by the at least one processor may cause the user equipment at least to perform: causing transmission of a timing advance message to a serving network node associated with a serving cell, the timing advance message encoding an indication of the timing advance associated with the target cell.

[0025] The instructions when executed by the at least one processor may cause the user equipment at least to perform: determining a validity of the timing advance from the time alignment timing.

[0026] The timing advance message may encode an indication of the validity of the timing advance.

[0027] The validity of the timing advance may indicate at least one of the following: when the timing advance was obtained; or how long the timing advance will be valid.

[0028] The timing advance message may comprise at least one of the following: a radio resource control message; or a measurement report.

[0029] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining an indication to execute handover. The instructions when executed by the at least one processor may cause the user equipment at least to perform: using the time alignment timer to determine whether the timing advance is valid based on obtaining the indication to execute handover.

[0030] The instructions when executed by the at least one processor may cause the user equipment at least to perform: based on determining that the timing advance is valid, causing the transmission of the timing advance message to the serving network node.

[0031] The timing advance message may encode an indication instructing the serving network node to initiate a RACH-less handover procedure between the user equipment and the target network node.

[0032] The timing advance message may encode an indication instructing the serving network node to initiate the RACH-less handover procedure between the user equipment and the target network node by indicating that a valid timing advance for the RACH-less handover procedure between the user equipment and the target network node has been obtained by the user equipment.

[0033] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining uplink grant information for useby the user equipment following the RACH-less handover.

[0034] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining the uplink grant information for use by the user equipment following the RACH-less handover from a handover command from the serving network node.

[0035] The instructions when executed by the at least one processor may cause the user equipment at least to perform: initiating RACH-less handover to the target network node in response to the handover command.

[0036] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining an identity of the target cell.

[0037] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining the identity of the target cell from a message encoding the identity of the target cell from the serving network node. The instructions when executed by the at least one processor may cause the user equipment at least to perform: based on obtaining the identity of the target cell, obtaining contention-based random access configuration information relating to the target cell.

[0038] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining the contention-based random access configuration information relating to the target cell from SIB1 of the target cell.

[0039] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining at least one of the following: a random access preamble index; or an SSB index to be used in the contention-based random access procedure from the message encoding the identity of the target cell.

[0040] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining scheduling information for obtaining the timing advance from the random access message.

[0041] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining scheduling information for obtaining the timing advance from the random access message for a plurality of target cells.

[0042] The instructions when executed by the at least one processor may cause the user equipment at least to perform: obtaining information indicating at least one timing advance acquisition triggering event from the message encoding the identity of the target cell.

[0043] The instructions when executed by the at least one processor may cause the user equipment at least to perform: causing transmission of a capability message to the serving network node, the capability message encoding an indication that the user equipment supports the obtaining acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0044] The capability message may encode an indication that the user equipment supports RACH-less handover to the target network node when in possession of a valid timing advance for the target network node. According to various, but not necessarily all, example embodiments of the invention there is provided a user equipment, comprising: means for obtaining an indication that the user equipment is to perform acquisition of a timing advance relating to a target cell; and means for causing transmission of a message to a target network node associated with the target cell during a random access procedure based on obtaining the indication, the message encoding an indication that the user equipment is performing the random access procedure to obtain acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0045] The means may perform the optional features set out in relation to the apparatus mentioned above.

[0046] The processor, memory, and example algorithms, encoded as instructions, program, or code, may be the means for providing or causing the performance of the operation.

[0047] According to various, but not necessarily all, example embodiments of the invention there is provided a user equipment comprising circuitry configured to perform obtaining an indication that the user equipment is to perform acquisition of a timing advance relating to a target cell; and configured to perform causing transmission of a message to a target network node associated with the target cell during a random access procedure based on obtaining the indication, the message encoding an indication that the user equipment is performing the random access procedure to obtain acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0048] The circuitry may be configured perform the optional features set out in relation to the apparatus mentioned above.

[0049] According to various, but not necessarily all, example embodiments of the invention there is provided a method, comprising: obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell; and based on obtaining the indication, causing transmission of a message to a target network node associated with the target cell during a random access procedure, the message encoding an indication that the user equipment is performing the random access procedure to obtain acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover. The acquisition of the timing advance may occur during the random access procedure, prior to handover to the target cell being initiated.

[0050] The message may encode an indication to the target network node instructing nonallocation of grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0051] The message may encode an indication to the target network node to omit an indication, during the random access procedure in a response message from the target network node to the user equipment, of grant of uplink resources for use by the user equipment following handover.

[0052] The message may encode an indication to the target network node to omit or fail to include an indication of grant of uplink resources during the random access procedure in a response message from the target network node to the user equipment, wherein the uplink resources are for use by the user equipment following handover.

[0053] The message may comprise an uplink scheduled transmission message.

[0054] The message may comprise a msg3 message of a contention-based random access procedure.

[0055] The method may comprise obtaining a time alignment timer during the random access procedure.

[0056] The method may comprise obtaining the time alignment timer from the response message.

[0057] The response message may comprise a msg4 message of the contention-based random access procedure.

[0058] The message may precede the response message.

[0059] The method may comprise obtaining the timing advance during the random access procedure. The method may comprise obtaining the timing advance from a random access message.

[0060] The random access message may comprise a msg2 message of the contention-based random access procedure.

[0061] The random access message may precede the message.

[0062] The method may comprise detecting at least one of the following: contention during the random access procedure; or expiry of the time alignment timer; and based on the detection, discarding the timing advance.

[0063] The method may comprise based on the discarding the timing advance, repeating the acquisition of the timing advance relating to the target cell.

[0064] The target network node may comprise a target distributed unit.

[0065] The method may comprise causing transmission of a timing advance message to a serving network node associated with a serving cell, the timing advance message encoding an indication of the timing advance associated with the target cell.

[0066] The method may comprise determining a validity of the timing advance from the time alignment timing.

[0067] The timing advance message may encode an indication of the validity of the timing advance.

[0068] The validity of the timing advance may indicate at least one of the following: when the timing advance was obtained; or how long the timing advance will be valid.

[0069] The timing advance message may comprise at least one of the following: a radio resource control message; or a measurement report.

[0070] The method may comprise obtaining an indication to execute handover.

[0071] The method may comprise using the time alignment timer to determine whether the timing advance is valid based on obtaining the indication to execute handover. The method may comprise based on determining that the timing advance is valid, causing the transmission of the timing advance message to the serving network node.

[0072] The timing advance message may encode an indication instructing the serving network node to initiate a RACH-less handover procedure between the user equipment and the target network node.

[0073] The timing advance message may encode an indication instructing the serving network node to initiate the RACH-less handover procedure between the user equipment and the target network node by indicating that a valid timing advance for the RACH-less handover procedure between the user equipment and the target network node has been obtained by the user equipment.

[0074] The method may comprise obtaining uplink grant information for use by the user equipment following the RACH-less handover.

[0075] The method may comprise obtaining the uplink grant information for use by the user equipment following the RACH-less handover from a handover command from the serving network node.

[0076] The method may comprise initiating RACH-less handover to the target network node in response to the handover command.

[0077] The method may comprise obtaining an identity of the target cell.

[0078] The method may comprise obtaining the identity of the target cell from a message encoding the identity of the target cell from the serving network node.

[0079] The method may comprise based on obtaining the identity of the target cell, obtaining contention-based random access configuration information relating to the target cell.

[0080] The method may comprise obtaining the contention-based random access configuration information relating to the target cell from SIB1 of the target cell.

[0081] The method may comprise obtaining at least one of the following: a random access preamble index; or an SSB index to be used in the contention-based random access procedure from the message encoding the identity of the target cell. The method may comprise obtaining scheduling information for obtaining the timing advance from the random access message.

[0082] The method may comprise obtaining scheduling information for obtaining the timing advance from the random access message for a plurality of target cells.

[0083] The method may comprise obtaining information indicating at least one timing advance acquisition triggering event from the message encoding the identity of the target cell.

[0084] The method may comprise causing transmission of a capability message to the serving network node, the capability message encoding an indication that the user equipment supports the obtaining acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0085] The capability message may encode an indication that the user equipment supports RACH-less handover to the target network node when in possession of a valid timing advance for the target network node.

[0086] According to various, but not necessarily all, example embodiments of the invention there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell; and based on obtaining the indication, causing transmission of a message to a target network node associated with the target cell during a random access procedure, the message encoding an indication that the user equipment is performing the random access procedure to obtain acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0087] The instructions may be for performing the optional features set out in relation to the method mentioned above.

[0088] According to various, but not necessarily all, example embodiments of the invention there is provided a signal with embedded data, the signal being encoded in accordance with an encoding process comprising the method set out above. The signal may be encoded with an encoding process which comprises the optional features set out in relation to the method mentioned above.

[0089] According to various, but not necessarily all, example embodiments of the invention there is provided a target network node, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the target network node at least to perform: obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell supported by the target network node; and based on obtaining the indication, causing transmission of a response message to the user equipment during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0090] The instructions when executed by the at least one processor may cause the target network node at least to perform: based on obtaining the indication, preventing allocation of grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0091] The instructions when executed by the at least one processor may cause the target network node at least to perform: based on obtaining the indication, omitting or failing to include an indication in the response message from the target network node to the user equipment of grant of uplink resources for use by the user equipment following handover.

[0092] The instructions when executed by the at least one processor may cause the target network node at least to perform: obtaining the indication by receiving a message from the user equipment, the message encoding the indication that the user equipment is performing the random access procedure to obtain acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0093] The message may comprise an uplink scheduled transmission message.

[0094] The message may comprise a msg3 message of a contention-based random access procedure. The instructions when executed by the at least one processor may cause the target network node at least to perform: based on obtaining the indication, including an indication in the response message of a time alignment timer.

[0095] The response message may comprise a msg4 message of the contention-based random access procedure.

[0096] The message may precede the response message.

[0097] The instructions when executed by the at least one processor may cause the target network node at least to perform: causing transmission of the timing advance during the random access procedure.

[0098] The instructions when executed by the at least one processor may cause the target network node at least to perform: causing transmission of the timing advance in a random access message during the random access procedure.

[0099] The random access message may comprise a msg2 message of the contention-based random access procedure.

[0100] The random access message may precede the message.

[0101] The target network node may comprise a target distributed unit.

[0102] The instructions when executed by the at least one processor may cause the target network node at least to perform: obtaining an indication that handover is to occur.

[0103] The instructions when executed by the at least one processor may cause the target network node at least to perform: obtaining the indication by receiving a handover request message encoding the indication instructing the target network node to perform a RACH- less handover procedure between the user equipment and the target network node.

[0104] The handover request message may encode an indication that the user equipment has a valid timing advance for handover to the target network node.

[0105] The instructions when executed by the at least one processor may cause the target network node at least to perform: based on receiving the handover request message, providing uplink grant information for use by the user equipment following the RACH-less handover.

[0106] The instructions when executed by the at least one processor may cause the target network node at least to perform: providing uplink grant information for use by the user equipment following the RACH-less handover by transmitting a handover request acknowledgement message encoding the uplink grant information to a source network node.

[0107] According to various, but not necessarily all, example embodiments of the invention there is provided a target network node, comprising: means for obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell supported by the target network node; and means for causing transmission of a response message to the user equipment during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover based on obtaining the indication.

[0108] The means may perform the optional features set out in relation to the apparatus mentioned above.

[0109] The processor, memory, and example algorithms, encoded as instructions, program, or code, may be the means for providing or causing the performance of the operation.

[0110] According to various, but not necessarily all, example embodiments of the invention there is provided a target network node comprising circuitry configured to perform obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell supported by the target network node; and means for causing transmission of a response message to the user equipment during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover based on obtaining the indication.

[0111] The circuitry may be configured perform the optional features set out in relation to the apparatus mentioned above.

[0112] According to various, but not necessarily all, example embodiments of the invention there is provided a method, comprising: obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell supported by a target network node; and based on obtaining the indication, causing transmission of a response message to the user equipment during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0113] The method may comprise based on obtaining the indication, preventing allocation of grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0114] The method may comprise based on obtaining the indication, omitting or failing to include an indication in the response message from the target network node to the user equipment of grant of uplink resources for use by the user equipment following handover.

[0115] The method may comprise obtaining the indication by receiving a message from the user equipment, the message encoding the indication that the user equipment is performing the random access procedure to obtain acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0116] The message may comprise an uplink scheduled transmission message.

[0117] The message may comprise a msg3 message of a contention-based random access procedure.

[0118] The method may comprise based on obtaining the indication, including an indication in the response message of a time alignment timer.

[0119] The response message may comprise a msg4 message of the contention-based random access procedure.

[0120] The message may precede the response message.

[0121] The method may comprise causing transmission of the timing advance during the random access procedure.

[0122] The method may comprise causing transmission of the timing advance in a random access message during the random access procedure. The random access message may comprise a msg2 message of the contention-based random access procedure.

[0123] The random access message may precede the message.

[0124] The target network node may comprise a target distributed unit.

[0125] The method may comprise obtaining an indication that handover is to occur.

[0126] The method may comprise obtaining the indication by receiving a handover request message encoding the indication instructing the target network node to perform a RACH- less handover procedure between the user equipment and the target network node.

[0127] The handover request message may encode an indication that the user equipment has a valid timing advance for handover to the target network node.

[0128] The method may comprise based on receiving the handover request message, providing uplink grant information for use by the user equipment following the RACH-less handover.

[0129] The method may comprise providing uplink grant information for use by the user equipment following the RACH-less handover by transmitting a handover request acknowledgement message encoding the uplink grant information to a source network node.

[0130] According to various, but not necessarily all, example embodiments of the invention there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell supported by a target network node; and based on obtaining the indication, causing transmission of a response message to the user equipment during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0131] The instructions may be for performing the optional features set out in relation to the method mentioned above. According to various, but not necessarily all, example embodiments of the invention there is provided a signal with embedded data, the signal being encoded in accordance with an encoding process comprising the method set out above.

[0132] The signal may be encoded with an encoding process which comprises the optional features set out in relation to the method mentioned above.

[0133] According to various, but not necessarily all, example embodiments of the invention there is provided a source network node, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the target network node at least to perform: obtaining an indication that a user equipment supports obtaining acquisition of a timing advance relating to a target cell supported by a target network node; and based on obtaining the indication, causing transmission of a message to the user equipment encoding an identity of the target cell to be used during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0134] The instructions when executed by the at least one processor may cause the source network node at least to perform: based on obtaining the indication, causing transmission a message encoding the identity of the target cell.

[0135] The instructions when executed by the at least one processor may cause the source network node at least to perform: based on obtaining the indication, causing transmission at least one of the following: a random access preamble index; or an SSB index to be used in the contention-based random access procedure in the message encoding the identity of the target cell.

[0136] The instructions when executed by the at least one processor may cause the source network node at least to perform: causing transmission of the message using at least one of the following: a PDCCH order; or an RRC Reconfiguration message.

[0137] The instructions when executed by the at least one processor may cause the source network node at least to perform: causing transmission of a message encoding said identity of said target cell between a source central unit and a source distributed unit of said source network node to cause the source distributed unit to transmit said message to the user equipment encoding said identity of the target cell to be used during said random access procedure without allocating grant of uplink.

[0138] The instructions when executed by the at least one processor may cause the source network node at least to perform: reception of a timing advance message from the user equipment, the timing advance message encoding an indication of the timing advance associated with the target cell.

[0139] The timing advance message may indicate that the user equipment has a valid timing advance for handover to the target network node.

[0140] The timing advance message may indicate at least one of the following: when the timing advance was obtained; or how long the timing advance will be valid.

[0141] The timing advance message may comprise at least one of the following: an RRC Reconfiguration message; or a measurement report.

[0142] The instructions when executed by the at least one processor may cause the source network node at least to perform: based on reception of the timing advance message, initiating the RACH-less handover with the target network node.

[0143] The instructions when executed by the at least one processor may cause the source network node at least to perform: initiating the RACH-less handover with the target network node by transmitting a handover request message encoding an indication that the user equipment has a valid timing advance for handover to the target network node.

[0144] The instructions when executed by the at least one processor may cause the source network node at least to perform: receiving uplink grant information for use by the user equipment following the RACH-less handover.

[0145] The instructions when executed by the at least one processor may cause the source network node at least to perform: receiving uplink grant information for use by the user equipment following the RACH-less handover.

[0146] The instructions when executed by the at least one processor may cause the source network node at least to perform: providing uplink grant information for use by the user equipment following the RACH-less handover by transmitting a handover command message encoding the uplink grant information to the user equipment.

[0147] The instructions when executed by the at least one processor may cause the source network node at least to perform: receiving a capability message from the user equipment, the capability message encoding an indication that the user equipment supports the obtaining acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0148] The capability message may encode an indication that the user equipment supports RACH-less handover to the target network node when in possession of a valid timing advance for the target network node.

[0149] According to various, but not necessarily all, example embodiments of the invention there is provided a source network node, comprising: means for obtaining an indication that a user equipment supports obtaining acquisition of a timing advance relating to a target cell supported by a target network node; and means for causing transmission of a message to the user equipment encoding an identity of the target cell to be used during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover based on obtaining the indication.

[0150] The means may perform the optional features set out in relation to the apparatus mentioned above.

[0151] The processor, memory, and example algorithms, encoded as instructions, program, or code, may be the means for providing or causing the performance of the operation.

[0152] According to various, but not necessarily all, example embodiments of the invention there is provided a source network node comprising circuitry configured to perform obtaining an indication that a user equipment supports obtaining acquisition of a timing advance relating to a target cell supported by a target network node; and means for causing transmission of a message to the user equipment encoding an identity of the target cell to be used during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover based on obtaining the indication. The circuitry may be configured perform the optional features set out in relation to the apparatus mentioned above.

[0153] According to various, but not necessarily all, example embodiments of the invention there is provided a method, comprising: obtaining an indication that a user equipment supports obtaining acquisition of a timing advance relating to a target cell supported by a target network node; and based on obtaining the indication, causing transmission of a message to the user equipment encoding an identity of the target cell to be used during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0154] The method may comprise based on obtaining the indication, causing transmission a message encoding the identity of the target cell.

[0155] The method may comprise based on obtaining the indication, causing transmission at least one of the following: a random access preamble index; or an SSB index to be used in the contention-based random access procedure in the message encoding the identity of the target cell.

[0156] The method may comprise causing transmission of the message using at least one of the following: a PDCCH order; or an RRC Reconfiguration message.

[0157] The method may comprise causing transmission of a message encoding said identity of said target cell between a source central unit and a source distributed unit of said source network node to cause the source distributed unit to transmit said message to the user equipment encoding said identity of the target cell to be used during said random access procedure without allocating grant of uplink.

[0158] The method may comprise reception of a timing advance message from the user equipment, the timing advance message encoding an indication of the timing advance associated with the target cell.

[0159] The timing advance message may indicate that the user equipment has a valid timing advance for handover to the target network node.

[0160] The timing advance message may indicate at least one of the following: when the timing advance was obtained; or how long the timing advance will be valid. The timing advance message may comprise at least one of the following: an RRC Reconfiguration message; or a measurement report.

[0161] The method may comprise based on receiving the timing advance message, initiating the RACH-less handover with the target network node.

[0162] The method may comprise initiating the RACH-less handover with the target network node by transmitting a handover request message encoding an indication that the user equipment has a valid timing advance for handover to the target network node.

[0163] The method may comprise receiving uplink grant information for use by the user equipment following the RACH-less handover.

[0164] The method may comprise receiving uplink grant information for use by the user equipment following the RACH-less handover.

[0165] The method may comprise providing uplink grant information for use by the user equipment following the RACH-less handover by transmitting a handover command message encoding the uplink grant information to the user equipment.

[0166] The method may comprise receiving a capability message from the user equipment, the capability message encoding an indication that the user equipment supports the obtaining acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0167] The capability message may encode an indication that the user equipment supports RACH-less handover to the target network node when in possession of a valid timing advance for the target network node.

[0168] According to various, but not necessarily all, example embodiments of the invention there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: obtaining an indication that a user equipment supports obtaining acquisition of a timing advance relating to a target cell supported by a target network node; and based on obtaining the indication, causing transmission of a message to the user equipment encoding an identity of the target cell to be used during a random access procedure without allocating grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0169] The instructions may be for performing the optional features set out in relation to the method mentioned above.

[0170] According to various, but not necessarily all, example embodiments of the invention there is provided a signal with embedded data, the signal being encoded in accordance with an encoding process comprising the method set out above.

[0171] The signal may be encoded with an encoding process which comprises the optional features set out in relation to the method mentioned above.

[0172] Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

[0173] Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

[0174] BRIEF DESCRIPTION

[0175] Some example embodiments will now be described with reference to the accompanying drawings in which:

[0176] FIG.1 is an exemplary message sequence chart for PDCCH-ordered early TA acquisition according to one example embodiment;

[0177] FIG.2 is an exemplary message sequence chart for event-trigger early TA acquisition according to one example embodiment;

[0178] FIG. 3 is an exemplary flow chart showing steps according to one example embodiment; and

[0179] FIG. 4 illustrates a set of apparatuses according to certain example embodiments.

[0180] DETAILED DESCRIPTION

[0181] Before discussing the example embodiments in any more detail, first an overview will be provided. Some example embodiments provide a technique whereby a user equipment can indicate to a network that a random access procedure is being used to obtain a timing advance associated with a target cell and that the user equipment does not need to be allocated uplink resources for use during subsequent handover at this stage. Instead, the network can omit to allocate the uplink resources and does not need to indicate an allocation of uplink resources at this stage to the user equipment. Instead, the user equipment stores the timing advance. Should a subsequent handover occur, and the timing advance is still valid, the user equipment can use the stored timing advance for accessing the target. The enables the network to configure a RACH-less handover to the target cell and the uplink resources are allocated at that stage.

[0182] In particular, some example embodiments recognise that, although Contention-Based Random Access (CBRA) can be considered for early Timing Advance (TA) acquisition, the detailed implementation of this approach for early TA acquisition have may lead to potential resource waste. More specifically, after receiving message 3 (msg3) of the CBRA, the target cell replies to the User Equipment (UE) with message 4 (msg4), containing an uplink (UL) grant for subsequent transmission of the UE in the UL of the target. This is useful for the UE in conventional use cases, e.g., in baseline HO at the time of HO execution, where the UE uses the provided UL to transmit the Radio Resource Control (RRC)ReconfigurationComplete message to complete the Handover (HO) and potentially continue with data transmission and reception. But, in the context of early TA acquisition, the provision of the UL grant of the UE is unnecessary, as the UE is not being handed over to the target (at least at this point) and therefore does not use the UL grant. Furthermore, a Physical Downlink Control Channel (PDCCH) order for a random access (RA) preamble transmission to a candidate cell has been specified in Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM), where the source Distributed Unit (DU), which receives L1 measurements from the UE, decides (potentially based on the L1 measurements) to order the UE to perform RA preamble transmission to the candidate. For L3 baseline HO, which is based on L3 measurements (provided by the UE to the Central Unit (CU) in the RRC layer), the DU does not have access to the L3 measurements. Therefore, unlike LTM, the DU cannot know when to issue the PDCCH order to the UE. Also, after the UE has successfully acquired the TA, it may report it to the network, i.e., the DU, using a Medium Access Control Control Element (MAC-CE). This may lead to unnecessary resource consumption. In addition, for L3 mobility, the DU must subsequently inform the CU about the acquisition of the TA, which is the one issuing the HO command.

[0183] Some example embodiments provide a modified random access procedure such as CBRA procedure that is performed between the UE and the target cell for early TA or other configuration acquisition. More specifically, an indication is included in msg3 that the RA procedure is being performed for TA acquisition. This allows the target cell / DU to know that the UE is not going to handover to the target cell immediately and, therefore, to modify its msg4 by not providing an UL grant to the UE (as would be done in conventional CBRA).

[0184] Also, to enable the source DU to know when to issue a PDCCH order, a PDCCH order trigger is sent from the CU to the DU, which includes the target cell ID, to which the RA preamble transmission should be performed. In some example embodiments, the early TA acquisition from a target cell is triggered using an event configured in the UE.

[0185] Regarding reporting by the UE that a TA has been acquired, to avoid the overhead of an additional MAC-CE sent from the UE to the source DU and a subsequent message from the source DU to the CU, an indication that a (valid) TA has been acquired for a target cell is included in the L3 measurement report. This indication may be just one additional bit per target cell.

[0186] Some example embodiments provide for two approaches to triggering the CBRA for early TA acquisition. The first is PDCCH order-based and the second is event-based.

[0187] In either approach, the UE may signal to the network an indication about its capability to support early TA acquisition for Random Access Channel (RACH)-less HO. Accordingly at Step 0 (which precedes Step 1 in the following example embodiments), the UE will send the capability indication to the S-CU / base station. The serving CU / base station is able to receive the capability indication from the and process / order a RACH-less HO with early TA acquisition for UEs which indicated support of this capability. For example, after receiving a L3 measurement report, the S-CU will only decide to send the trigger described in Step 2 of FIG. 1 if the UE has indicated capability of supporting early TA acquisition for RACH-less HO as set out below. Likewise, after receiving a L3 measurement report, the S-CU will only decide to send the event configuration described in Step 2 of FIG. 2 if the UE has indicated capability of supporting early TA acquisition for RACH-less HO as set out below.

[0188] PDCCH-ordered early TA acquisition

[0189] FIG.1 is an exemplary message sequence chart for PDCCH-ordered early TA acquisition according to one example embodiment.

[0190] At Step 1: The UE 10 provides a L3 measurement report to the S-Cll 30. At Step 2: The S-Cll 30 issues a PDCCH order trigger to the S-Dll 20, to trigger the S-Dll 20 to send a PDCCH order to the UE 10. The trigger may contain the ID of the target cell, to which RA preamble transmission should be performed, and the Synchronization Signal Block (SSB) index to be used by the UE in the RA procedure.

[0191] At Step 3: The S-DU 20 issues a PDCCH order to the UE 10, so that the UE 10 performs CBRA to the target cell with ID indicated in Step 2. In a further example embodiment, after reception of the PDCCH order, the UE 10 is triggered to decode System Information Block 1 (SI B 1 ) of the target cell to obtain the CBRA configuration of the target cell. In addition the UE 10 may be provided with scheduling / measurement restriction to receive the Random Access Request (RAR) message 2 (msg2) from the T-DU. Additionally and / or alternatively, the UE 10 may be configured with a priority list indicating which of the transmission / reception signals has higher priority. Also the UE 10 behavior is specified (e.g., reattempt with / without power ramping or sending an indication to S-DU 20 / S-CU 30) in case of some missing RAR due to the other high priority measurements / transmission / receptions.

[0192] At Step 4: The UE 10 sends CBRA RA preamble message 1 (msg1) to the target cell for early TA acquisition.

[0193] At Step 5: The network (in this example T-DU 40) responds with RAR (msg 2) including the TA value for the target cell supported by T-DU 40. Reception of the TA value may trigger the UE 10 to perform additional measurement (and reporting) of the target-cell.

[0194] At Step 6: The UE 10 sends a modified msg3 of the RA procedure to T-DU 40. Msg3 is modified to encode an indication that this procedure is for Early TA acquisition and no UL Grant for subsequent handover is needed.

[0195] At Step 7: The target cell supported by T-DU 40 sends a modified msg4 of the RA procedure to the UE 10. Msg4 is modified to encode an indication the no UL Grant for subsequent handover has been provided to the UE 10. This encoding may be the omission of an indication of the UL Grant. T-DU 40 omits to allocate UL Grant to the UE 10. In one approach, the target cell supported by T-DU 40 includes a configuration of the time alignment timer (TAT) value for the UE 10 to evaluate validity of the obtained TA. If no TAT configuration is provided by the target cell supported by T-DU 40 in msg4, then the UE 10 may use a (typically pre-)configured value it has obtained from the serving cell. At Step 8: The UE 10 switches to the serving gNB (node 1) and continues being served by it. On receiving the TA value, the UE 10 triggers the TAT. Should contention occur during the CBRA procedure, then the UE 10 may stop the TAT and discard the TA received through msg2 and trigger RA again by returning to Step 4.

[0196] Thereafter, two options are possible.

[0197] Option 1 :

[0198] At Step 9: With an RRC signalling message, the UE 10 informs the serving node (node 2) S-CU 30 that it has obtained the TA for the target cell supported by T-DU 40. In this example, the network is responsible for maintaining the TA validity. The UE 10 may inform the network about the timestamp indicating when the TA was obtained or for how long the TA will be valid - this approach requires extra RRC signalling to inform the network about the acquisition of a valid TA value. Therefore, option 2 may be preferred.

[0199] Option 2:

[0200] At Step 10: The measurement event to trigger measurement reporting is triggered. The UE 10 evaluates if the TA that the UE 10 has is for the target cell and if it is valid, typically using the TAT.

[0201] At Step 11: The UE 10 sends a measurement report to the serving node (node 2) S-CU 30 and includes in the measurement report the TA validity information for the target cell supported by T-DU 40. The UE 10 includes TA validity-related information, which indicates to the network whether it has a valid TA, a timestamp of the time the TA was received or for how long the TA will be valid. The measurement report may contain measurements for multiple candidate (target) cells and, therefore, contain multiple TA validity information for those multiple candidate (target) cells.

[0202] Irrespective of whether option 1 or option 2 are pursued, the following steps typically occur.

[0203] At Step 12: The source gNB S-CU 30 sends to the target gNB T-CU 50 a handover request informing the target gNB T-CU 50 that the UE 10 has a valid TA for the cell supported by the target gNB T-CU 50.

[0204] At Step 13: UE context setup request and response occurs between T-CU 50 and T-DU 40. At Step 14: The target gNB T-Cll 50 responds to the source gNB S-Cll 30 with a handover request acknowledgement; optionally the handover request acknowledgement includes a configure grant (CG) for the target cell supported by the target gNB T-Cll 50.

[0205] At Steps 15-18: The source gNB S-Cll 30 provides to the UE 10 the handover command and stops transmission (Tx) / reception (Rx) to / from the UE 10 and starts data forwarding.

[0206] At Steps 19-20: The UE 10 applies the target cell configuration and performs cell change using RACH-less access.

[0207] At Steps 21-25: Data transmission and path switch is performed if needed. UE context release is performed as well.

[0208] Event-triggered early TA acquisition

[0209] FIG.2 is an exemplary message sequence chart for event-trigger early TA acquisition according to one example embodiment.

[0210] At Step 1 : The UE 10 provides a L3 measurement report to the S-CU 30.

[0211] At Step 2: The UE 10 receives an RRC Reconfiguration message with a target cell configuration for an event for early TA acquisition with the CBRA configuration for the UE 10 to obtain the TA from a target cell supported by T-DU 40. This configuration can be part of a HO command for a target cell. The UE 10 responds with an RRC Reconfiguration complete (not in case of HO message).

[0212] At Step 3: The UE 10 applies the RRC configuration that it is provided from the source gNB S-CU 30.

[0213] At Step 4: Once the event for the UE 10 to perform early TA acquisition is triggered, the UE 10 initiates early TA acquisition from the target cell supported by T-DU 40.

[0214] At Step 5: The UE 10 sends CBRA RA preamble message 1 (msg1) to the target cell for early TA acquisition. At Step 6: The network (in this example T-Dll 40) responds with RAR (msg 2) including the TA value for the target cell supported by T-Dll 40. Reception of the TA value may trigger the UE 10 to perform additional measurement (and reporting) of the target-cell.

[0215] At Step 7: The UE 10 sends a modified msg3 of the RA procedure to T-DU 40. Msg3 is modified to encode an indication that this procedure is for Early TA acquisition and no UL Grant for subsequent handover is needed.

[0216] At Step 8: The target cell supported by T-DU 40 sends a modified msg4 of the RA procedure to the UE 10. Msg4 is modified to encode an indication the no UL Grant for subsequent handover has been provided to the UE 10. This encoding may be the omission of an indication of the UL Grant. T-DU 40 omits to allocate UL Grant to the UE 10. In one approach, the target cell supported by T-DU 40 includes a configuration of the time alignment timer (TAT) value for the UE 10 to evaluate validity of the obtained TA. If no TAT configuration is provided by the target cell supported by T-DU 40 in msg4, then the UE 10 may use a (typically pre-)configured value it has obtained from the serving cell.

[0217] At Step 9: The UE 10 switches to the serving gNB (node 1) and continues being served by it. On receiving the TA value, the UE 10 triggers the TAT. Should contention occur during the CBRA procedure, then the UE 10 may stop the TAT and discard the TA received through msg2 and trigger RA again by returning to Step 5.

[0218] Thereafter, two options are possible.

[0219] Option 1 :

[0220] At Step 10: With an RRC signalling message, the UE 10 informs the serving node (node 2) S-CU 30 that it has obtained the TA for the target cell supported by T-DU 40. In this example, the network is responsible for maintaining the TA validity. The UE 10 may inform the network about the timestamp indicating when the TA was obtained or for how long the TA will be valid - this approach requires extra RRC signalling to inform the network about the acquisition of a valid TA value. Therefore, option 2 may be preferred.

[0221] Option 2:

[0222] At Step 11 : The measurement event to trigger measurement reporting is triggered. The UE 10 evaluates if the TA that the UE 10 has is for the target cell and if it is valid, typically using the TAT. At Step 12: The UE 10 sends a measurement report to the serving node (node 2) S-Cll 30 and includes in the measurement report the TA validity information for the target cell supported by T-Dll 40. The UE 10 includes TA validity-related information, which indicates to the network whether it has a valid TA, a timestamp of the time the TA was received or for how long the TA will be valid. The measurement report may contain measurements for multiple candidate (target) cells and, therefore, contain multiple TA validity information for those multiple candidate (target) cells.

[0223] Irrespective of whether option 1 or option 2 are pursued, the following steps typically occur.

[0224] At Step 13: The source gNB S-CU 30 sends to the target gNB T-CU 50 a handover request informing the target gNB T-CU 50 that the UE 10 has a valid TA for the cell supported by the target gNB T-CU 50.

[0225] At Step 14: UE context setup request and response occurs between T-CU 50 and T-DU 40.

[0226] At Step 15: The target gNB T-CU 50 responds to the source gNB S-CU 30 with a handover request acknowledgement; optionally the handover request acknowledgement includes a configure grant (CG) for the target cell supported by the target gNB T-CU 50.

[0227] At Steps 16-19: The source gNB S-CU 30 provides to the UE 10 the handover command and stops transmission (Tx) / reception (Rx) to / from the UE 10 and starts data forwarding.

[0228] At Steps 20-21 : The UE 10 applies the target cell configuration and performs cell change using RACH-less access.

[0229] At Steps 22-26: Data transmission and path switch is performed if needed. UE context release is performed as well.

[0230] Compared with existing RACH-less HO, some example embodiments result in reduced interruption time for baseline L3 HO for all cases, not only when the target TA is equal to 0 or equal to the TA of the source, which is an advantage of early TA acquisition methods. Compared with existing RACH-less HO with early TA acquisition, some example embodiments are CBRA-based, i.e., not requiring the reservation of Contention-free RA (CFRA) resources, which are limited. Also, only one RRC reconfiguration message (HO command) is sent to the UE 10, as in legacy HO. Apart from the reduced signalling overhead, this makes the approach less disruptive and, therefore, easier to be agreed. Furthermore, as explained above, the waste of UL grants in message 4 of the CBRA procedure is avoided. Finally, depending on the specific implementation, some example embodiments have little to no impact on the signalling between the source and the target CU.

[0231] Some example embodiments provide for an improved cell change method for 5G baseline handover where the contention based random access (CBRA) procedure with the target cell is speeded-up by skipping the TA acquisition step. This approach helps to provide a shorter transition from serving to target cell and to reduce the interruption time. Therefore, TA is acquired by UE from target cell before the CU / base station triggers the baseline handover (early TA acquisition) in a more efficient manner regarding: timing to prepare the target cell and UE for cell change (which avoids resource allocation in target cell and UE); random access (RA) procedure and radio resources (improved RA request (msg3) indicating intention for RA is just to obtain TA early, improved RA response (msg4) does not provide UL grant resources to UE); and signalling messages between UE, CU / base station, serving DU / base station, target DU / base station to synchronize (serving CU / base station indicates to serving DU when to trigger early TA acquisition by a UE towards a candidate target cell ID, L3 measurement report from UE to CU / base station comprises an indication that UE has a valid TA for a target cell, indicating which target cells, HO request indicating that UE obtained TA already and that cell change can be executed RACH-less, UE indicates to the serving base station / CU its support of this improved RACH-less HO, serving base station applies the improved RACH-less HO only to Ues which have indicated their support). Optionally a TA preamble value to be used may be provided. An indication may be provided which further indicates the time duration between the indicated CLI measurement resource (or the slot containing the indicated CLI measurement resource) and the reporting resource (or the slot containing the reporting resource),

[0232] The CU may trigger the serving DU to send a PDCCH order to a UE, or the CU may configure a UE when to perform and execute an event based trigger for early TA acquisition.

[0233] In some example embodiments, a serving CU / base station triggers a UE to perform early TA acquisition to a target cell comprising: an indication indicating to perform a random access procedure to the indicated candidate target cell for early TA acquisition; information about target cell identifier, or additionally target cell SSB index to be used; Some example embodiments involve performing by the UE a random access procedure to the indicated candidate target cell to obtain the TA early; sending msg3 by a UE to a target base station / DU indicating RA only for early TA acquisition, no need for UL resources; receiving msg4 by a UE indicating that contention resolution succeeded, assigned TA value is in msg2=RAR; skipping of assigning and sending UL resources in msg4 to the UE at the target base station / DU. Msg3 may optionally indicate need for TA validity period. Msg4 may optionally indicate a validity period of the assigned TA value.

[0234] Some example embodiments involve sending a report by the UE to the base station / CU comprising an indication that: a TA has been obtained for a candidate target cell, indicating when the TA value has been received, indicating the remaining validity period of the obtained TA value. Reporting may be comprised in a RRC signalling message (option 1) or L3 measurement message (option 2). Improved 5G baseline HO may be provided where transition to target cell is executed faster (RACH-less). Allocated resources during HO preparation (early TA acquisition is during HO preparation) in the target cell are reduced because the UL grant resource is not allocated at target cell / DU with msg4 (compared to the existing RA procedure). There may be lower interruption time while switching into the target cell. The CBRA procedure does not require to allocate RA preambles / resource during the HO preparation phase and is therefore less resource demanding.

[0235] FIG. 3 is an exemplary flow chart showing steps according to one example embodiment. At step S10, an indication is obtained that the user equipment is to perform acquisition of a timing advance relating to a target cell. At step S20, based on obtaining the indication, the user equipment causes transmission of a message to a target network node associated with the target cell encoding an indication that the user equipment is performing a random access procedure to obtain acquisition of the timing advance without requiring grant of uplink resources during the random access procedure for use by the user equipment following handover.

[0236] FIG. 4 illustrates a set of apparatuses 100 and 200 according to certain example embodiments. In certain example embodiments, the apparatus 100 may be an element in a communications network or associated with such a network, such as the UE 10 (e.g., anchor UE, target UE, receiving UE, etc.), mobile equipment (ME), mobile station, mobile device, stationary device, loT device, or other device. The user equipment may be any mobile end or terminal device that may be capable of wireless communication. By way of example rather than limitation, user equipment UE may also be referred to as a communication device, a terminal device, a Mobile Station (MS). The user equipment may include, but is not limited to, a mobile phone, a cellular phone, a smart phone, a tablet, a wearable terminal device, a personal digital assistant (PDA) , vehicle-mounted wireless terminal devices, smart devices etc. In some example embodiments, apparatus 100 may include one or more processors 12, one or more computer-readable storage medium 14 (for example, memory, storage, or the like), one or more radio access components 18 (for example, a modem, a transceiver, or the like), and / or a user interface. In some example embodiments, apparatus 100 may be configured to operate using one or more radio access technologies, such as GSM, LTE, LTE-A, NR, 5G, WLAN, WiFi, NB- loT, Bluetooth, NFC, MulteFire, and / or any other radio access technologies. It should be noted that one of ordinary skill in the art would understand that apparatus 100 may include components or features not shown. Apparatus 100 may include or be coupled to the processor 12 for processing information and executing instructions or operations. Processor 12 may be any type of general or specific purpose processor. In fact, processor 12 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples. Processor 12 may perform functions associated with the operation of apparatus 100 including, as some examples, the processing of information set out above. Apparatus 100 may further include or be coupled to a memory 14 (internal or external), which may be coupled to processor 12, for storing information and instructions that may be executed by processor 12. The instructions stored in memory 14 may include program instructions or computer program code that, when executed by processor 12, enable the apparatus 100 to perform tasks as described herein. Apparatus 100 may also include or be coupled to one or more antennas 15 for receiving a downlink signal and for transmitting via an UL from apparatus 100. Apparatus 10 may further include a transceiver 18 configured to transmit and receive information. The transceiver 18 may also include a radio interface (e.g., a modem) coupled to the antenna 15. According to certain example embodiments, apparatus 100 may optionally be configured to communicate with apparatus 200 via a wireless or wired communications link 70 according to any radio access technology, such as NR.

[0237] As illustrated in the example of FIG. 4, apparatus 200 may be a network, core network element, or element in a communications network or associated with such a network, such as the S-DU 20, S-CU 30, T-DU 40, T-CU 50, gNB, BS, cell, NW. Apparatus 20 may include a processor 22, a memory 24, a transceiver 28 and antenna 25 in a similar manner to the apparatus 100 mentioned above. A person of skill in the art would readily recognize that steps of various above-described methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computerexecutable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover computers programmed to perform said steps of the above-described methods. The tern non-transitory as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. RAM vs ROM).

[0238] As used in this application, the term “circuitry” may refer to one or more or all of the following:

[0239] (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and

[0240] (b) combinations of hardware circuits and software, such as (as applicable):

[0241] (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and

[0242] (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

[0243] (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0244] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device. As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0245] The ordering of method steps set out above may not be critical or fixed and the exact ordering of the steps may be varied as appropriate.

[0246] Although example embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

[0247] Features described in the preceding description may be used in combinations other than the combinations explicitly described.

[0248] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0249] Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

[0250] Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

CLAIMS1. A user equipment, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the user equipment at least to perform: obtaining an indication that said user equipment is to perform acquisition of a timing advance relating to a target cell; and based on obtaining said indication, causing transmission of a message to a target network node associated with said target cell during a random access procedure, said message encoding an indication that said user equipment is performing said random access procedure to obtain acquisition of said timing advance without requiring grant of uplink resources during said random access procedure for use by said user equipment following handover.

2. The user equipment of claim 1 , wherein said acquisition of said timing advance occurs during said random access procedure, prior to handover to said target cell being initiated.

3. The user equipment of claim 1 or 2, wherein said message encodes at least one of the following: an indication to said target network node instructing non-allocation of grant of uplink resources during said random access procedure for use by said user equipment following handover; an indication to said target network node to omit an indication, during said random access procedure in a response message from said target network node to said user equipment, of grant of uplink resources for use by said user equipment following handover; or an indication to said target network node to omit or fail to include an indication of grant of uplink resources during said random access procedure in a response message from said target network node to said user equipment, wherein said uplink resources are for use be said user equipment following handover.

4. The user equipment of any preceding claim, wherein said message comprises at least one of the following: an uplink scheduled transmission message; a msg3 message of a contention-based random access procedure.

5. The user equipment of any preceding claim, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform at least one of the following: obtaining a time alignment timer during said random access procedure; or obtaining said time alignment timer from said response message.

6. The user equipment of any preceding claim, wherein at least one of the following: said response message comprises a msg4 message of said contention-based random access procedure; or said message precedes said response message.

7. The user equipment of any preceding claim, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform at least one of the following: obtaining said timing advance during said random access procedure; or obtaining said timing advance from a random access message.

8. The user equipment of claim 7, wherein at least one of the following: said random access message comprises a msg2 message of said contentionbased random access procedure; or said random access message precedes said message.

9. The user equipment of any one of claims 5 to 8, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform: detecting at least one of the following: contention during said random access procedure; or expiry of said time alignment timer; and based on said detection, discarding said timing advance.

10. The user equipment of claim 9, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform: based on said discarding said timing advance, repeating said acquisition of said timing advance relating to said target cell.

11. The user equipment of any preceding claim, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform:causing transmission of a timing advance message to a serving network node associated with a serving cell, said timing advance message encoding an indication of said timing advance associated with said target cell.

12. The user equipment of any one of claims 5 to 11, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform: determining a validity of said timing advance from said time alignment timer.

13. The user equipment of claims 11 or 12, wherein at least one of: said timing advance message encodes an indication of said validity of said timing advance; said validity of said timing advance indicates at least one of the following: when said timing advance was obtained; or how long said timing advance will be valid; or said timing advance message comprises at least one of the following: a radio resource control message; or a measurement report.

14. The user equipment of any preceding claim, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform: obtaining an indication that handover is to occur.

15. The user equipment of any one of claims 5 to 14, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform at least one of the following: using said time alignment timer to determine whether said timing advance is valid based on obtaining said indication that handover is to occur; or based on determining that said timing advance is valid, causing said transmission of said timing advance message to said serving network node.

16. The user equipment of any preceding claim, wherein said timing advance message encodes at least one of the following: an indication instructing said serving network node to initiate a RACH-less handover procedure between said user equipment and said target network node; an indication instructing said serving network node to initiate said RACH-less handover procedure between said user equipment and said target network node by indicating that a valid timing advance for said RACH-less handover procedure betweensaid user equipment and said target network node has been obtained by said user equipment.

17. The user equipment of claim 16, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform at least one of the following: obtaining an identity of said target cell; obtaining said identity of said target cell from a message encoding said identity of said target cell from said serving network node; based on obtaining said identity of said target cell, obtaining contention-based random access configuration information relating to said target cell; obtaining said contention-based random access configuration information relating to said target cell from SIB1 of said target cell; obtaining at least one of the following: a random access preamble; or an SSB index to be used in said contention-based random access procedure from said message encoding said of identity of said target cell, obtaining scheduling information for obtaining said timing advance from said random access message; obtaining scheduling information for obtaining said timing advance from said random access message for a plurality of target cells; or obtaining information indicating at least one handover event from said message encoding said identity of said target cell; obtaining uplink grant information for use by said user equipment following said RACH-less handover; obtaining said uplink grant information for use by said user equipment following said RACH-less handover from a handover command from said serving network node; initiating RACH-less handover to said target network node in response to said handover command.

18. The user equipment of any preceding claim, wherein said instructions when executed by the at least one processor cause the user equipment at least to perform: causing transmission of a capability message to said serving network node, said capability message encoding an indication that said user equipment supports said obtaining acquisition of said timing advance without requiring grant of uplink resources during said random access procedure for use by said user equipment following handover.

19. The user equipment of claim 18, wherein said capability message encodes an indication that said user equipment supports RACH-less handover to said target network node when in possession of a valid timing advance for said target network node.

20. A method, comprising: obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell; and based on obtaining said indication, causing transmission of a message to a target network node associated with said target cell during a random access procedure, said message encoding an indication that said user equipment is performing said random access procedure to obtain acquisition of said timing advance without requiring grant of uplink resources during said random access procedure for use by said user equipment following handover.

21. A target network node, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the target network node at least to perform: obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell supported by said target network node; and based on obtaining said indication, causing transmission of a response message to said user equipment during a random access procedure without allocating grant of uplink resources during said random access procedure for use by said user equipment following handover.

22. A method, comprising: obtaining an indication that a user equipment is to perform acquisition of a timing advance relating to a target cell supported by a target network node; and based on obtaining said indication, causing transmission of a response message to said user equipment during a random access procedure without allocating grant of uplink resources during said random access procedure for use by said user equipment following handover.

23. A source network node, comprising: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the target network node at least to perform: obtaining an indication that a user equipment supports obtaining acquisition of a timing advance relating to a target cell supported by a target network node; and based on obtaining said indication, causing transmission of a message to said user equipment encoding an identity of said target cell to be used during a random access procedure without allocating grant of uplink resources during said random access procedure for use by said user equipment following handover.

24. A method, comprising: obtaining an indication that a user equipment supports obtaining acquisition of a timing advance relating to a target cell supported by a target network node; and based on obtaining said indication, causing transmission of a message to said user equipment encoding an identity of said target cell to be used during a random access procedure without allocating grant of uplink resources during said random access procedure for use by said user equipment following handover.

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