[Technical Field]
5 [0001]
The present invention relates to a communication system. The invention has particular
but not exclusive relevance to wireless communication systems and devices thereof
operating according to the 3rd Generation Partnership Project (3GPP) standards or
equivalents or derivatives thereof (including LTE-Advanced and Next Generation or
10 5G networks). The invention has particular, although not necessarily exclusive
relevance to the so-called random access procedure.
[Background Art]
[0002]
Recent developments of the 3GPP standards are referred to as the Long Term
15 Evolution (LTE) of Evolved Packet Core (EPC) network and Evolved UMTS Terrestrial
Radio Access Network (E-UTRAN), also commonly referred as ‘4G’. In addition, the
term ‘5G’ and ‘new radio’ (NR) refer to an evolving communication technology that is
expected to support a variety of applications and services. Various details of 5G
networks are described in, for example, the ‘NGMN 5G White Paper’ V1.0 by the Next
20 Generation Mobile Networks (NGMN) Alliance, which document is available from
https://www.ngmn.org/5g-white-paper.html. 3GPP intends to support 5G by way of the
so-called 3GPP Next Generation (NextGen) radio access network (RAN) and the
3GPP NextGen core network.
[0003]
25 Under the 3GPP standards, a NodeB (or an ‘eNB’ in LTE, ‘gNB’ in 5G) is the base
station via which communication devices (user equipment or ‘UE’) connect to a core
network and communicate to other communication devices or remote servers. For
simplicity, the present application will use the term base station to refer to any such
base stations.
3
For simplicity, the present application will use the term mobile device, user device, or
UE to refer to any communication device that is able to connect to the core network
via one or more base stations.
[0004]
Communication devices might be, for example, mobile communication 5 devices such
as mobile telephones, smartphones, user equipment, personal digital assistants,
laptop/tablet computers, web browsers, e-book readers and/or the like. Such mobile
(or even generally stationary) devices are typically operated by a user. However,
3GPP standards also make it possible to connect so-called ‘Internet of Things’ (IoT)
10 devices (e.g. Narrow-Band IoT (NB-IoT) devices) to the network, which typically
comprise automated equipment, such as various measuring equipment, telemetry
equipment, monitoring systems, tracking and tracing devices, in-vehicle safety
systems, vehicle maintenance systems, road sensors, digital billboards, point of sale
(POS) terminals, remote control systems, and the like. Effectively, the Internet of
15 Things is a network of devices (or "things") equipped with appropriate electronics,
software, sensors, network connectivity, and/or the like, which enables these devices
to collect and exchange data with each other and with other communication devices. It
will be appreciated that IoT devices are sometimes also referred to as Machine-Type
Communication (MTC) communication devices or Machine-to-Machine (M2M)
20 communication devices.
[0005]
For simplicity, the present application often refers to mobile devices in the description
but it will be appreciated that the technology described can be implemented on any
communication devices (mobile and/or generally stationary) that can connect to a
25 communications network for sending/receiving data, regardless of whether such
communication devices are controlled by human input or software instructions stored
in memory.
[0006]
The core network (i.e. the ‘EPC’ in case of LTE and ‘5GC’ in 5G) typically hosts
30 functionality for subscriber management, mobility management, charging, security,
4
and call/session management (amongst others), and provides connection for
communication devices to external networks, such as the Internet.
[0007]
Before a UE can communicate data via a base station, it needs to perform a so-called
(contention-based) random access procedure with the base station 5 serving the cell in
which the UE is located. Currently, in Release 15, the random access procedure is a
four-step procedure. In the first step (referred to as ‘Msg1’), the UE transmits a
Physical Random Access Channel (PRACH) preamble. If the base station detects the
preamble, the base station responds with a random access response (RAR), also
10 known as ‘Msg2’. The RAR includes the detected preamble identifier, a time-advance
command, a temporary C-RNTI (TC-RNTI), and an uplink grant for scheduling a
Physical Uplink Shared Channel (PUSCH) transmission from the UE (referred to as
‘Msg3’). The UE transmits Msg3 as scheduled and includes an identifier for contention
resolution. Upon receiving Msg3, the network transmits a contention resolution
15 message, also known as ‘Msg4’, with the contention resolution identifier. If the UE
successfully receives Msg4, and if it finds its contention resolution identifier, it sends
an acknowledgement on the Physical Uplink Control Channel (PUCCH), which
completes the four-step random access procedure.
[0008]
20 From Release 16 of the 3GPP standards, a two-step random access procedure has
been proposed (in addition to the currently used four-step Random Access
procedure). The two-step random access is mainly intended for supporting (Ultra) Low
Latency Communications, 10ms control plane latency, fast handover, efficient channel
access in unlicensed spectrum, and transmission of small data packets, amongst
25 others.
[0009]
As can be seen, the four-step random access procedure requires two round-trip
cycles between the UE and the base station. The two-step random access procedure
aims to reduce latency and control-signaling overhead by using a single round trip
30 cycle between the UE and the base station. Effectively, this is achieved by combining
5
the UE’s PRACH preamble (Msg1) transmission and the scheduled PUSCH
transmission (Msg3) into a single message (referred to as ‘MsgA’). Similarly, the
random-access response (RAR/Msg2) from the base station to UE and the contention
resolution message (Msg4) are combined in the two-step random access procedure
(and 5 referred to as ‘MsgB’).
[0010]
Regarding power threshold(s) for MsgA of the two-step random access procedure, the
current 3GPP specifications and drafts propose using two different received target
power levels for the PRACH part (msgA-PRACH) and the PUSCH part (msgA10
PUSCH) of the message in order to ensure that both parts can be decoded by the
receiver (base station / gNB).
[0011]
For the PRACH part, the initial random access preamble power is specified via the
‘preambleReceivedTargetPower’ information element.
15 [0012]
[Math. 1]
[0013]
UEs need to choose between two-step random access and legacy four-step random
20 access (i.e. whether to transmit Msg1 or MsgA). Access to two-step random access is
6
limited because it is less robust than the legacy procedure (as the uplink PUSCH
transmission is not synchronised) and it requires relatively bigger (pre-allocated)
PUSCH formats to accommodate UEs with poor channel quality. The resources for
two-step random access are also more likely to be congested than legacy random
access resources because PUSCH resources require more 5 spectrum than preambles
only (i.e. Msg1) and multiple preambles are mapped to a single PUSCH resource unit
(PRU). However, it will be appreciated that the two-step random access procedure
may be used in any cell in Rel-15 NR (regardless of cell size).
[0014]
10 In addition, the RAN2 work group of 3GPP agreed to control two-step random access
load using a Reference Signal Received Power (RSRP) threshold that both limits
access for low channel quality UEs for better robustness and reduces collisions (less
coverage means fewer UEs). This RSRP threshold is given by the ‘msgA-rsrp-
Threshold’ parameter which is broadcast as part of the system information (in
15 ‘SystemInformationType1’ or ‘SIB1’). Effectively, the msgA-rsrp-Threshold parameter
specifies an RSRP threshold for selection between the two-step random access type
and the four-step random access type (when both types of random access resources
are configured).
[Summary of Invention]
20 [0015]
The inventor has realised that since the selection of the appropriate random access
procedure (two-step or four-step) is based on the RSRP threshold, i.e. radio quality, it
mainly depends on UE location and not on UE category/priority, as originally intended.
A UE that can attempt four-step random access can technically also attempt two-step
25 random access (note: coverage can be affected by the msgA-PUSCH power offset
compared to msg3-PUSCH).
Consequently, while RSRP threshold can effectively reduce access load, the network
does not control how many UEs have good/bad channel quality since it is mainly
dependent on the location of the UEs (relative to the base station). Thus, RSRP
30 threshold appears to be an inaccurate (over)load control mechanism. For example,
7
low priority UEs located close to the cell centre (and hence above the applicable
RSRP threshold) may have access to two-step random access and cause collisions
with other random access transmissions (since there is usually a large number of lowpriority
users in a cell). On the other hand, high priority users near the cell-edge (and
hence below the applicable RSRP threshold) may not be allowed 5 to use the two-step
random access procedure at all and they may suffer delays (compared to those users
that can use the two-step procedure).
[0016]
In summary, RSRP threshold does not allow a base station to accurately achieve load
10 control across the entire coverage area of its cell(s). Accordingly, preferred example
embodiments of the present invention aim to provide methods and apparatus which
address or at least partially deal with one or more of the above issues.
[0017]
Although for efficiency of understanding for those of skill in the art, the invention will
15 be described in detail in the context of a 3GPP system (UMTS, LTE, NR), the
principles of the invention can be applied to other systems in which communication
devices or User Equipment (UE) access a core network using a radio access
technology.
[0018]
20 In one example aspect, the present invention provides a method performed by a user
equipment (UE), the method comprising: receiving information identifying a reference
signal received power (RSRP) threshold value for transmitting a random access
message comprising a preamble part and a Physical Uplink Shared Channel
(PUSCH) transmission part; obtaining information identifying at least one respective
25 offset associated with at least one priority level; and determining a type of random
access procedure to be performed based on an RSRP measured by the UE, said
RSRP threshold value, and a priority level associated with the UE.
[0019]
8
In one example aspect, the present invention provides a method performed by a base
station, the method comprising: broadcasting information identifying a reference signal
received power (RSRP) threshold value for transmitting, by a user equipment (UE), a
random access message comprising a preamble part and a Physical Uplink Shared
Channel (PUSCH) transmission part; and carrying out 5 a random access procedure
with said UE based on an RSRP measured by the UE, said RSRP threshold value,
and a priority level associated with the UE.
[0020]
In one example aspect, the present invention provides a user equipment (UE)
10 comprising: means for receiving information identifying a reference signal received
power (RSRP) threshold value for transmitting a random access message comprising
a preamble part and a Physical Uplink Shared Channel (PUSCH) transmission part;
means for obtaining information identifying at least one respective offset associated
with at least one priority level; and means for determining a type of random access
15 procedure to be performed based on an RSRP measured by the UE, said RSRP
threshold value, and a priority level associated with the UE.
[0021]
In one example aspect, the present invention provides a base station comprising:
means for broadcasting information identifying a reference signal received power
20 (RSRP) threshold value for transmitting, by a user equipment (UE), a random access
message comprising a preamble part and a Physical Uplink Shared Channel
(PUSCH) transmission part; and means for carrying out a random access procedure
with said UE based on an RSRP measured by the UE, said RSRP threshold value,
and a priority level associated with the UE.
25 [0022]
In another example aspect, the present invention provides a user equipment (UE)
comprising a controller and a transceiver, wherein the controller is configured to:
control the transceiver to receive information identifying a reference signal received
power (RSRP) threshold value for transmitting a random access message comprising
30 a preamble part and a Physical Uplink Shared Channel (PUSCH) transmission part;
9
obtain information identifying at least one respective offset associated with at least
one priority level; and determine a type of random access procedure to be performed
based on an RSRP measured by the UE, said RSRP threshold value, and a priority
level associated with the UE.
5 [0023]
In yet another example aspect, the present invention provides a base station
comprising a controller and a transceiver, wherein the controller is configured to:
control the transceiver to broadcast information identifying a reference signal received
power (RSRP) threshold value for transmitting, by a user equipment (UE), a random
10 access message comprising a preamble part and a Physical Uplink Shared Channel
(PUSCH) transmission part; and carry out a random access procedure with said UE
based on an RSRP measured by the UE, said RSRP threshold value, and a priority
level associated with the UE.
[0024]
15 Example aspects of the invention extend to corresponding systems, apparatus, and
computer program products such as computer readable storage media having
instructions stored thereon which are operable to program a programmable processor
to carry out a method as described in the example aspects and possibilities set out
above or recited in the claims and/or to program a suitably adapted computer to
20 provide the apparatus recited in any of the claims.
[0025]
Each feature disclosed in this specification (which term includes the claims) and/or
shown in the drawings may be incorporated in the invention independently of (or in
combination with) any other disclosed and/or illustrated features. In particular but
25 without limitation the features of any of the claims dependent from a particular
independent claim may be introduced into that independent claim in any combination
or individually.
[Brief Description of Drawings]
[0026]
10
Example embodiments of the invention will now be described, by way of example, with
reference to the accompanying drawings in which:
[Fig. 1]
Figure 1 illustrates schematically a mobile (cellular or wireless) telecommunication
system to which example embodiments of the invention 5 may be applied;
[Fig. 2]
Figure 2 is a block diagram of a User Equipment (UE) forming part of the system
shown in Figure 1;
[Fig. 3]
10 Figure 3 is a block diagram of a base station forming part of the system shown in
Figure 1;
[Fig. 4]
Figure 4 is a block diagram of a core network node entity forming part of the system
shown in Figure 1; and
15 [Fig. 5]
Figure 5 is a timing diagram of an exemplary way in which a priority level based
random access procedure may be performed in the system of Figure 1.
[Description of Embodiments]
[0027]
20 Overview
Figure 1 schematically illustrates a mobile (cellular or wireless) telecommunication
system 1 to which example embodiments of the present invention are applicable.
[0028]
In this network, users of mobile devices 3 (UEs) can communicate with each other
25 and other users via respective base stations 5 and a core network 7 using an
appropriate 3GPP radio access technology (RAT), for example, an E-UTRA and/or 5G
RAT. It will be appreciated that a number of base stations 5 form a (radio) access
network or (R)AN. As those skilled in the art will appreciate, whilst one mobile device
3 and one base station 5 are shown in Figure 1 for illustration purposes, the system,
11
when implemented, will typically include other base stations and mobile devices
(UEs).
[0029]
Each base station 5 controls one or more associated cells (either directly or via other
nodes such as home base stations, relays, remote radio heads, 5 distributed units,
and/or the like). A base station 5 that supports E-UTRA/4G protocols may be referred
to as an ‘eNB’ and a base station 5 that supports Next Generation/5G protocols may
be referred to as a ‘gNBs’. It will be appreciated that some base stations 5 may be
configured to support both 4G and 5G, and/or any other 3GPP or non-3GPP
10 communication protocols.
[0030]
The mobile device 3 and its serving base station 5 are connected via an appropriate
air interface (for example the so-called ‘Uu’ interface and/or the like). Neighbouring
base stations 5 are connected to each other via an appropriate base station to base
15 station interface (such as the so-called ‘X2’ interface, ‘Xn’ interface and/or the like).
The base station 5 is also connected to the core network nodes via an appropriate
interface (such as the so-called ‘S1’, ‘N1’, ‘N2’, ‘N3’ interface, and/or the like).
[0031]
The core network 7 typically includes logical nodes (or ‘functions’) for supporting
20 communication in the telecommunication system 1. Typically, for example, the core
network 7 of a ‘Next Generation’ / 5G system will include, amongst other functions,
control plane functions (CPFs) 11 and user plane functions (UPFs) 12. It will be
appreciated that the core network 7 may also include, amongst others, an Access and
Mobility Management Function (AMF) 13. From the core network 7, connection to an
25 external IP network 20 (such as the Internet) may also be provided.
[0032]
The system supports both legacy (i.e. four-step) and two-step random access
procedures. However, only those UEs 3 are allowed to use the two-step random
access procedure that meet an associated RSRP threshold.
12
[0033]
Beneficially, in this system, the effective RSRP threshold for using the two-step
random access procedure is based on the priority level associated with the UE.
Specifically, different offsets are applied to the default RSRP threshold (that is
broadcast in SIB1) depending on the UE type and/or its 5 usage type (i.e. UE priority
level) thereby resulting in a different effective RSRP thresholds for different UE priority
levels.
[0034]
This may be realised by specifying appropriate random access parameters (e.g. a UE
10 priority level based offset) based on UE type and/or usage type and communicating
these parameters to the UE 3. In some cases, a default random access offset (per
priority level) may be stored by the UE 3, e.g. for initial access purposes. In this case,
the UE 3 can obtain the default offset from local memory even if the network has not
yet provided an appropriate (e.g. cell specific) offset value.
15 [0035]
Information identifying the UE priority level based offsets may be provided to the UE 3
either via broadcast (e.g. in SIB1) or via unicast (e.g. Radio Resource Control (RRC)).
Alternatively, at least for some priority levels, the applicable offset may be pre-set or
provided in an implicit manner, e.g. specified in the relevant 3GPP standards as a
20 default value.
[0036]
It will be appreciated that (information identifying) the specific offset for a UE priority
level (or a list of offsets for respective UE priority levels) may be included in an
appropriately formatted information element (e.g. ‘MsgA-rsrp-ThresholdOffset’ and/or
25 the like).
[0037]
For example, the ‘msgA-rsrp-Threshold’ IE of the ‘RACH-ConfigCommon’ IE may be
adapted to specify the appropriate random access parameters in a given cell,
including one or more priority level specific offset(s) for the RSRP threshold broadcast
13
via the SIB1. In this case, the various priority level specific offsets are broadcast and
each UE works out its own applicable offset based on its associated UE type and/or
usage type.
[0038]
Alternatively, (information identifying) the applicable RSRP threshold 5 offset may be
provided to a particular UE using dedicated signalling (e.g. RRC signalling). For
example, the RRCSetup message may be configured to include an appropriate
information element that specifies the applicable RSRP threshold offset for MsgA (e.g.
an ‘MsgA-rsrp-ThresholdOffset’ IE and/or the like).
10 [0039]
It will be appreciated that 4 to 8 priority levels may be used (in any case, at least two
priority levels). For example, when four priority levels are used, the following different
offset values may be configured:
・Offset_0 = -∞
15 (effectively, the UE can always attempt two-step random access using this offset)
・Offset_1 = -10dB (for instance)
(in this case, the UE has a relatively higher chance to attempt two-step random
access than without the offset)
・Offset_2 = 0dB (i.e. no offset, or a relatively low offset)
20 (the UE behaves normally and follows the default threshold broadcast in SIB1)
・Offset_3 = +∞
(effectively, the UE can never attempt two-step random access using this offset)
[0040]
In a first option, SIB1 includes an appropriate information element to specify the
25 applicable RSRP threshold offset for MsgA (e.g. ‘MsgA-rsrp-ThresholdOffset’ IE
and/or the like). In a second option (which may be combined with the first option), the
RRCSetup message includes an appropriate (optional) information element to specify
the applicable RSRP threshold offset for MsgA (e.g. ‘MsgA-rsrp-ThresholdOffset’ IE
and/or the like). It will be appreciated that this information element may also be
30 introduced at a later stage e.g. in an ‘RRCReconfiguration’ message and/or the like.
14
[0041]
Regardless which option is used, i.e. how the UE 3 obtains the applicable offset value
(or offset values in case the UE can have different priority levels), the UE 3 stores the
applicable offset value(s) for later use. When selecting which type of random access
to initiate, the stored offset can be added to (summed with) 5 the RSRP threshold for
the given cell. In this case, for example, the effective offset is given by the sum of i)
the threshold value indicated by the msgA-rsrp-Threshold parameter and ii) the offset
value.
[0042]
10 Beneficially, the network (base station 5) allows access to the two-step random
access procedure to UEs depending on their priority level rather than UE location /
RSRP threshold only. The two-step random access procedure can also be made
available at the cell edge (and possibly for out-of-coverage UEs using an existing
PUSCH power offset).
15 [0043]
Mobile device
Figure 2 is a block diagram illustrating the main components of the mobile device 3
shown in Figure 1 (e.g. a mobile telephone or an IoT device). As shown, the mobile
device 3 has a transceiver circuit 31 that is operable to transmit signals to and to
20 receive signals from a base station 5 via one or more antenna 33. The mobile device
3 has a controller 37 to control the operation of the mobile device 3. The controller 37
is associated with a memory 39 and is coupled to the transceiver circuit 31. Although
not necessarily required for its operation, the mobile device 3 might of course have all
the usual functionality of a conventional mobile telephone (such as a user interface
25 35) and this may be provided by any one or any combination of hardware, software
and firmware, as appropriate. Software may be pre-installed in the memory 39 and/or
may be downloaded via the telecommunications network or from a removable data
storage device (RMD), for example.
[0044]
15
The controller 37 is configured to control overall operation of the mobile device 3 by, in
this example, program instructions or software instructions stored within memory 39.
As shown, these software instructions include, among other things, an operating
system 41, a communications control module 43, and a random access module 45.
5 [0045]
The communications control module 43 is operable to control the communication
between the mobile device 3 and its serving base station 5 (and other communication
devices connected to the serving base station 5, such as other user equipment, core
network nodes, etc.).
10 [0046]
The random access module 45 is responsible for carrying out an appropriate random
access procedure with the base station 5. The random access procedure may be
either a 4-step random access procedure or a 2-step random access procedure,
depending on, for example, a priority associated with the mobile device 3.
15 [0047]
Although not shown in Figure 2, the mobile device 3 will also typically include a paging
module, an RRC module, and a NAS module.
[0048]
The paging module is responsible for maintaining a (RAN based) paging area (e.g. in
20 the form of a list of cells) in which the mobile device 3 can be paged, and to control
the transceiver 31 to monitor for paging messages addressed to the mobile device 3.
The paging module is also responsible for notifying other modules, e.g. the random
access module 45, when the mobile device 3 is being paged by the network.
[0049]
25 The RRC module is operable to generate, send and receive signalling messages
formatted according to the RRC standard. For example, such messages are
exchanged between the mobile device 3 and its serving base station 5. The RRC
messages may include, for example, messages relating to performing a random
16
access procedure (in dependence of a priority level associated with the mobile device
3). For example, the RRC messages may include information identifying one or more
priority level specific offset for determining the type random access to perform.
[0050]
The NAS module is operable to generate, send and receive 5 signalling messages
formatted according to the NAS standard. For example, such messages are
exchanged between the mobile device 3 and the AMF 13 (via the serving base station
5, using the RRC module). The NAS messages may include, for example, messages
relating to registering and/or updating a tracking area (or cell) where the mobile device
10 3 is currently located. The NAS messages may also include messages relating to a
priority level associated with the mobile device 3.
[0051]
Base Station
Figure 3 is a block diagram illustrating the main components of a base station 5
15 shown in Figure 1. As shown, the base station 5 has a transceiver circuit 51 for
transmitting signals to and for receiving signals from user equipment (such as the
mobile device 3) via one or more antenna 53, a core network interface 55 (e.g. an S1
interface, NG-C interface, and/or the like) for transmitting signals to and for receiving
signals from the core network 7, and a base station interface 56 (e.g. an X2 interface,
20 Xn interface, and/or the like) for transmitting signals to and for receiving signals from
neighbouring base stations. The base station 5 has a controller 57 to control the
operation of the base station 5 in accordance with software stored in a memory 59.
The software may be pre-installed in the memory 59 and/or may be downloaded via
the telecommunication network 1 or from a removable data storage device (RMD), for
25 example. The software includes, among other things, an operating system 61, at least
a communications control module 63, and a random access module 65.
[0052]
The communications control module 63 is responsible for handling
(generating/sending/ receiving) signalling between the base station 5 and other nodes,
30 such as the UE 3 and the core network nodes. Such signalling may include, for
17
example, control data for managing operation of the mobile device 3 (e.g. NAS, RRC,
paging, system information, and/or the like).
[0053]
The random access module 65 is responsible for carrying out an appropriate random
access procedure with the UEs 3 in its cell(s). The random 5 access procedure may be
either a 4-step random access procedure or a 2-step random access procedure,
depending on, for example, a priority level associated with the UE 3.
[0054]
Although not shown in Figure 3, the base station 5 will also typically include an RRC
10 module, a base station to base station interface module (e.g. X2/Xn module), and an
appropriate core network interface module.
[0055]
The RRC module is operable to generate, send and receive signalling messages
formatted according to the RRC standard. For example, such messages are
15 exchanged between the base station 5 and the mobile device 3 (and other user
equipment within the cell of the base station 5). The RRC messages may include, for
example, messages relating to a priority level associated with the UE and messages
relating to performing a random access procedure (in dependence of the priority
level). For example, the RRC messages may include information identifying one or
20 more priority level specific offset for random access.
[0056]
The base station to base station interface module is operable to generate, send and
receive signalling messages (X2/Xn messages) formatted according to the X2AP (or
XnAP) standard. The X2/Xn messages may include, for example, messages relating
25 to paging a mobile device 3, handover, data forwarding, transferring/fetching of UE
context (and other information relating to the mobile device 3) between neighbouring
base stations. The X2/Xn messages may include, for example, messages relating to a
priority level associated with the UE.
18
[0057]
The core network interface module is operable to generate, send and receive
signalling messages formatted according to the NG-C standard (or the S1AP standard
in LTE). For example, such messages are exchanged between the base station 5 and
the AMF 13 (or the MME in LTE). The NG-C (or S1AP) messages 5 may include, for
example, messages relating to a priority level associated with the UE.
[0058]
Core network node
Figure 4 is a block diagram illustrating the main components of a generic core network
10 node (or function) shown in Figure 1, for example, the AMF 13. As shown, the core
network node includes a transceiver circuit 71 which is operable to transmit signals to
and to receive signals from other nodes (including the UE 3 and the (R)AN node 5) via
a network interface 75. A controller 77 controls the operation of the core network node
in accordance with software stored in a memory 79. The software may be pre-installed
15 in the memory 79 and/or may be downloaded via the telecommunication network 1 or
from a removable data storage device (RMD), for example. The software includes,
among other things, an operating system 81 and at least a communications control
module 83. The communications control module 83 is responsible for handling
(generating/sending/ receiving) signaling between the core network node and other
20 nodes, such as the UE 3, the (R)AN node 5, and other core network nodes.
[0059]
Detailed description
A more detailed description will now be given of some exemplary ways in which a UE
can be mapped to an appropriate priority level. Effectively, by mapping different UEs
25 to different priority levels, the access network (base station) is able to control the
behaviour of the UEs in its cell, including whether a particular UE can use the two-step
random access procedure or the four-step random access procedure (for a particular
random access attempt).
[0060]
19
3GPP provides multiple tools to categorise UEs (even before initial connection). For
example, the following information may be used by the (access) network to determine
which UEs to prioritise over other UEs:
- 3GPP Technical Specification (TS) 22.261 V16.10.0 specifies UE Access
Identities 5 and Categories.
- For NR user-plane (NR-U), 3GPP defines Channel Access Priority Classes
(CAPC) based on logical channel.
- When (re-)establishing (or resuming) an RRC connection, the UE provides an
appropriate RRC Establishment Cause to indicate the reason for requesting the
10 RRC connection.
- Clause 5.3.14 of 3GPP TS 38.331 V15.8.0 specifies the so-called Unified Access
Control procedure. The purpose of this procedure is to perform access barring
check for an access attempt associated with a given Access Category and one or
more Access Identities upon request from upper layers (e.g. the RRC layer). In
15 the Unified Access Control procedure, the ‘UAC-BarringPerCatList’ information
element (IE) provides access control parameters for a list of access categories.
Specifically, for each access category (as defined in 3GPP TS 22.261), the UACBarringPerCatList
IE includes an entry (‘UAC-BarringPerCat’) defining the
relevant access barring rules for that category.
20 [0061]
The above information is known at the UE side before attempting random access.
Beneficially, the UE 3 may be configured to derive an appropriate two-step random
access priority level for that UE (and/or for that random access attempt) based on one
or more of the above information. Thus, the UE may be configured to determine
25 whether to initiate a two-step random access procedure (by sending MsgA) or a fourstep
random access procedure (by sending Msg1) based on at least one of the
following: UE Access Identity, UE Access Category, CAPC, RRC Establishment
Cause, and the applicable access barring rules.
[0062]
20
Implementation Example 1: Overview
In this example, SIB1 includes an appropriate information element to specify the
applicable RSRP threshold offset for MsgA (e.g. ‘MsgA-rsrp-ThresholdOffset’ IE
and/or the like).
5 [0063]
As explained above, the effective threshold for using the two-step random access
procedure may be based on a UE specific priority level (depending on UE type and/or
usage). By applying different offsets to the RSRP threshold broadcast in SIB1,
different effective RSRP thresholds may be achieved for different UE priority levels.
10 [0064]
This may be realised by specifying appropriate random access parameters based on
UE type and/or usage type. For example, the ‘rsrp-ThresholdSSB’ IE of the ‘RACHConfigCommon’
IE may be adapted to specify the appropriate random access
parameters in a given cell, including one or more priority level specific offset(s) for the
15 RSRP threshold broadcast in SIB1.
[Table 1]
21
[0065]
Implementation Example 1: Mapping by User Access Identity
The UE specific priority level and the corresponding RSRP offset may be derived
based on the UE Access Identity associated with the UE (possibly 5 in combination with
other information). Table 2 provides an overview of the UE Access identities defined in
Clause 6.22.2.2 of 3GPP TS 22.261 V16.10.0. In summary, a UE Access identity
comprises 4 bits, it describes the type of UE, and it is hardcoded in the SIM. As can
be seen, identities 3-10 are reserved for future use.
10 [0066]
[Table 2]
22
[0067]
Implementation Example 1: Mapping by User Access Category
The UE specific priority level and the corresponding RSRP offset may be derived
based on the UE Access Category associated with the UE (possibly 5 in combination
with other information). Table 3 provides an overview of the UE Access categories
defined in Clause 6.22.2.3 of 3GPP TS 22.261 V16.10.0. In summary, a UE Access
category comprises 6 bits, it determines how the UE will access the network, changes
according to the use case (e.g. emergency) and the access identity. As can be seen,
10 categories 32-63 are based on operator classification.
[0068]
[Table 3]
23
[0069]
Implementation Example 1: Mapping by RRC establishment cause
The UE specific priority level and the corresponding RSRP offset may also be derived
based on the RRC establishment cause associated with 5 the UE (and/or other
information). 3GPP TS 38.331 V15.8.0 specifies different RRC establishment causes,
which are directly linked to UE Access Categories and can be used to map different
levels of priority. The currently specified establishment cause values are as follows:
emergency, highPriorityAccess, mt-Access, mo-Signalling, mo-Data, mo-VoiceCall,
10 mo-VideoCall, mo-SMS, mps-PriorityAccess, mcs-PriorityAccess, spare6, spare5,
spare4, spare3, spare2, and spare1. The UE 3 is configured to include an appropriate
24
establishment cause when it sends an RRCSetupRequest message to the base
station 5.
[0070]
In order to ensure that relatively high priority communications (e.g. emergency,
highPriorityAccess, mps-PriorityAccess, and mcs-PriorityAccess) 5 are able to use the
two-step random access procedure whenever possible, and hence benefit from lower
latency than legacy random access, these communications may be assigned to
relatively higher priority levels and use the associated RSRP threshold offset when
selecting which type of random access procedure to perform (i.e. whether to transmit
10 Msg1 or MsgA). On the other hand, relatively low priority communications (e.g. mt-
Access, mo-Signalling, mo-Data, mo-VoiceCall, mo-VideoCall, and mo-SMS) may be
assigned to relatively lower priority levels and use the associated RSRP threshold
offset when selecting the type of random access procedure.
[0071]
15 Implementation Example 2: Mapping via RRC information element
In this example (which may be combined with the above described first
implementation example), the RRCSetup message includes an appropriate
information element which specifies the applicable RSRP threshold offset for MsgA
(e.g. an ‘MsgA-rsrp-ThresholdOffset’ IE and/or the like). For example, the MsgA-rsrp-
20 ThresholdOffset IE may be included in the RRCSetup message as follows:
[Table 4]

WE CLAIM:
[Claim 1]
A method performed by a user equipment (UE), the method comprising:
receiving information identifying a reference signal received power (RSRP)
threshold value for transmitting a random access message 5 comprising a preamble
part and a Physical Uplink Shared Channel (PUSCH) transmission part;
obtaining information identifying at least one respective offset associated with at
least one priority level; and
determining a type of random access procedure to be performed based on an
10 RSRP measured by the UE, said RSRP threshold value, and a priority level
associated with the UE.
[Claim 2]
The method according to claim 1, further comprising:
determining a priority level for a connection attempt; and
15 transmitting a first random access message (Msg1/MsgA) for a connection
based on said RSRP measured by the UE, said RSRP threshold value, and the offset
associated with the priority level for said connection attempt.
[Claim 3]
The method according to claim 1 or 2, further comprising:
20 generating and transmitting a first random access message (MsgA) comprising a
preamble part and a PUSCH transmission part when said RSRP measured by the UE
is equal to or larger than a sum of said threshold value and the offset associated with
the priority level associated with the UE.
[Claim 4]
25 The method according to claim 1 or 2, further comprising:
generating and transmitting a first random access message (Msg1) comprising a
preamble part but no PUSCH transmission part when said RSRP measured by the UE
44
is lower than a sum of said threshold value and the offset associated with the priority
level associated with the UE.
[Claim 5]
The method according to any of claims 1 to 4, further comprising:
generating and transmitting a third random access 5 message (Msg3) comprising
a PUSCH transmission part in response to receiving a second random access
message (Msg2) from the network.
[Claim 6]
The method according to any of claims 1 to 5, comprising obtaining said
10 information identifying at least one respective offset associated with at least one
priority level by receiving an information element identifying, for each priority level, a
corresponding offset.
[Claim 7]
The method according to claim 6, wherein said information element is included
15 in at least one of a system information message (e.g. SIB1) and a dedicated message
(e.g. a Radio Resource Control message).
[Claim 8]
The method according to claim 6 or 7, wherein said information element
comprises at least one ‘MsgA-rsrp-ThresholdOffset’ information element.
20 [Claim 9]
The method according to any of claims 1 to 8, wherein said priority level is
based on at least one of: a UE Access Identity associated with the UE, a UE Access
Category associated with the UE; a Channel Access Priority Class (CAPC) associated
with the UE; an RRC establishment cause associated with the UE; and an Access
25 Barring rule associated with the UE.
[Claim 10]
The method according to any of claims 1 to 9, wherein said at least one
respective offset associated with at least one priority level comprises at least one of:
45
an offset that, when applied to said threshold value, results in a relatively high
chance for transmitting a random access message comprising a preamble part and a
Physical Uplink Shared Channel (PUSCH) transmission part;
an offset that, when applied to said threshold value, results in a relatively low
chance for transmitting a random access message comprising a 5 preamble part and a
Physical Uplink Shared Channel (PUSCH) transmission part;
an offset that, when applied to said threshold value, allows the UE to transmit a
random access message comprising a preamble part and a Physical Uplink Shared
Channel (PUSCH) transmission part irrespective of the RSRP measured by the UE;
10 and
an offset that, when applied to said threshold value, prevents the UE from
transmitting a random access message comprising a preamble part and a Physical
Uplink Shared Channel (PUSCH) transmission part.
[Claim 11]
15 A method performed by a base station, the method comprising:
broadcasting information identifying a reference signal received power (RSRP)
threshold value for transmitting, by a user equipment (UE), a random access message
comprising a preamble part and a Physical Uplink Shared Channel (PUSCH)
transmission part; and
20 carrying out a random access procedure with said UE based on an RSRP
measured by the UE, said RSRP threshold value, and a priority level associated with
the UE.
[Claim 12]
The method according to claim 11, further comprising:
25 transmitting, to the UE, information identifying at least one respective offset
associated with at least one priority level.
[Claim 13]
The method according to claim 11 or 12, further comprising:
46
receiving, from said UE, a first random access message (Msg1/MsgA) based on
said RSRP measured by the UE, said RSRP threshold value, and an offset associated
with a priority level for a connection attempt by the UE.
[Claim 14]
A user equipment 5 (UE) comprising:
means for receiving information identifying a reference signal received power
(RSRP) threshold value for transmitting a random access message comprising a
preamble part and a Physical Uplink Shared Channel (PUSCH) transmission part;
means for obtaining information identifying at least one respective offset
10 associated with at least one priority level; and
means for determining a type of random access procedure to be performed
based on an RSRP measured by the UE, said RSRP threshold value, and a priority
level associated with the UE.
[Claim 15]
15 A base station comprising:
means for broadcasting information identifying a reference signal received
power (RSRP) threshold value for transmitting, by a user equipment (UE), a random
access message comprising a preamble part and a Physical Uplink Shared Channel
(PUSCH) transmission part; and
20 means for carrying out a random access procedure with said UE based on an
RSRP measured by the UE, said RSRP threshold value, and a priority level
associated with the UE.