[Technical Field]
[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 10 Generation Partnership Project
(3GPP) standards or equivalents or derivatives thereof, such as the Universal
Terrestrial Radio Access Network (UTRAN, referred to as a 3G network) and the
Long Term Evolution (LTE) of UTRAN (E-UTRAN, referred to as a 4G network),
including LTE-Advanced (LTE-A). The invention also has some but not exclusive
15 relevance to wireless communication systems and devices thereof operating
according to the Global System for Mobile Communications (GSM) standards or
equivalents or derivatives thereof (general ly referred to as 2G) and to Wireless
Local Area Networks (WLAN).
20 [Background Art]
[0002]
LTE networks are packet switched (PS) for voice and data, unlike legacy
3G networks which are a combination of PS for carrying data and Circuit Switched
(CS) for carrying voice. 2G networks also provide CS voice connect ions. To
25 date, many telecommunications network operators continue to use legacy (3G or
2G) networks to route voice calls.
[0003]
For LTE, standards bodies have defin ed standards for voice services which
are provided using only the LTE network, referred to as Voice over LTE (VoLTE).
30 [0004]
VoLTE has various potential advantages, such as high-definition voice
calls. However, problems can occur when VoLTE calls are ini tiated, or ongoing,
when a mobile device is in an area where LTE coverage is limited. Furthermore,
it may be the case that a mobile device is in an area in which the received LTE
3
radio signal is good enough for data communications but not good enough for
VoLTE communications.
[Summary of Invention]
[5 Technical Problem]
[0005]
One example of managing VoLTE calls where LTE coverage is limited is for
an eNB to trigger a Single Radio Voice Call Continuity (SRVCC) handover to a
legacy network (3G/2G). However, if this approach is used, the VoLTE setup may
10 fai l if, for example, the UE does not support SRVCC. As a result, call drop rate is
increased due to call setup fai lure. Also, SRVCC is a complex mechanism which
requires changes at the UE, eNB and MME level.
[0006]
The present invention seeks to provide a communicat ion system and
15 associated apparatus and methods for addressing or at least part ially ameliorating
the above issues.
[Solution to Problem]
[0007]
20 In one aspect of the invention there is provided a communication device for
a long term evolution (LTE) communicat ion system, the communication device
comprising: a control ler and a transceiver, wherein the controller is con figu r ed to
control the communication device to: establish and engage in Voice over LTE
(VoLTE) communicat ion via a communicat ion connection with a base station;
25 obtain information indicating at least one cri terion for determining whether VoLTE
communicat ion via the communication connection with the base stat ion can be
sustained; perform signal measurements for signals received from the base station;
and determine whether VoLTE communication via the communication connection
with the base station can be sustained based on whether or not the signal
30 measurements meet the at least one criterion.
[0008]
In another aspect of the invent ion there is provided a base stat ion for a long
term evolution (LTE) communication system, the base station comprising: a
control ler and a transceiver, wherein the controller is co n figu red to control the
4
base stat ion to: establish and engage in Voice over LTE (VoLTE) communicat ion
via a communication connection with a communicat ion device; and transmit, to the
communicat ion device, information indicating a criterion for determining whether
VoLTE communication via a communication connection with the base station can
5 be sustained.
[0009]
In another aspect of the invention there is provided a communication
device for a long term evolution (LTE) communicat ion system, the communication
device comprising: a control ler and a transceiver, wherein the controller is
10 configured to control the communication device to: establish and engage in Voice
over LTE (VoLTE) communicat ion via a communicat ion connect ion with a base
station; perform signal measurements for signals received from the base station;
provide at least one result of said signal measurements, to the base station, whi le
the communication device is engaged in an at tempt to establish VoLTE
15 communicat ion via the communication connection; receive, from the base station,
responsive to provision of the at least one result of said signal measurements, a
message indicating that the communication connect ion cannot be sustained; and
establish, on receipt of said message indicating that the communication connection
cannot be sustained, a communication connection via a non-LTE radio access
20 technology (RAT) in order to establish or maintain a voice call via that non-LTE
RAT.
[0010]
In another aspect of the invent ion there is provided a base stat ion for a long
term evolution (LTE) communication system, the base station comprising: a
25 control ler and a transceiver, wherein the controller is configured to control the
base stat ion to: establish and engage in Voice over LTE (VoLTE) communicat ion
via a communication connection with a communicat ion device; receive, from the
communicat ion device, while the base stat ion is engaged in an attempt to establish
VoLTE communication via the communicat ion connection, at least one result of
30 signal measurements made by the communication device; determine, based on the
received at least one result of the signal measurements, whether or not the
communicat ion connection can be sustained; and transmit , to the communication
device, when it has been determined that the communication connection cannot be
sustained, a message indicating that the communicat ion connect ion cannot be
5
sustained.
[0011]
In another aspect of the invention there is provided a communication
device for a long term evolution (LTE) communicat ion system, the communication
device comprising: a control ler and a transceiver wherein 5 the control ler is
con figu red to control the communication device to: setup and engage in VoLTE
communicat ion via a communicat ion connection with a base station; receive, when
the communication device is engaged in at least one of: (i) ongoing VoLTE
communicat ion via the communication connection; and (ii) an attempt to establish
10 VoLTE communication via the communicat ion connection, from the base station, a
message indicating that the communication connect ion cannot be sustained,
wherein the message comprises an indication that a cause of the message is voice
call continuity; and establ ish, on receipt of said message indicating that the
communicat ion connection cannot be sustained, a communication connection via a
15 non-LTE radio access technology (RAT) in order to establish or maintain a voice
call via that non-LTE radio access technology (RAT).
[0012]
In another aspect of the invent ion there is provided a base stat ion for a long
term evolution (LTE) communication system, the base station comprising: a
20 control ler and a transceiver wherein the control ler is configured to control the base
station to: establish and engage in VoLTE communicat ion via a communicat ion
connection with a communicat ion device; determine, when the base stat ion is
engaged in at least one of: (i) ongoing VoLTE communication via the
communicat ion connection; and (ii) an attempt to establ ish VoLTE communication
25 via the communication connection, that the communication connection cannot be
sustained; and transmit, to the communicat ion device, when it has been determined
that the communicat ion connection cannot be sustained, a message indicat ing that
the communication connect ion cannot be sustained, wherein the message
comprises an indication that a cause of the message is voice cal l continuity.
30 [0013]
In another aspect of the invention there is provided a core network node of
a long term evolution (LTE) communicat ion system, the core network node
comprising a controller, wherein the controller is configured to control the core
network node to: receive, from a base station, information indicating a
6
communicat ion connection associated with a voice over LTE (VoLTE) voice call
has been released and information indicating a possibility that said voice cal l wi ll
be continued via another radio access technology (RAT); notify an internet
protocol multimedia subsystem (IMS) that the communication connect ion
associated with the VoLTE voice call has been released; and not 5 ify the IMS of the
possibility that said voice call will be cont inued via another RAT.
[0014]
In another aspect of the invention there is provided a communication node
of a Universal Terrestrial Radio Access Network (UTRAN), the communicat ion
10 node comprising a control ler, wherein the control ler is configured to control the
communicat ion node to: receive, from an internet protocol mult imedia subsystem
(IMS), in-formation for support ing continuation of a voice call via a radio access
technology (RAT) of the UTRAN, wherein a voice over LTE (VoLTE) connect ion
over which the voice call was previously being provided has been released, and
15 wherein said in-formation comprises context information associated with the
VoLTE connection.
[0015]
Aspects of the invent ion extend to corresponding systems, methods, and
computer program products such as computer readable storage media having
20 instructions stored thereon which are operable to program a programmable
processor to carry out a method as recited in the claims and/or to program a
suitably adapted computer to provide the apparatus described in the aspects and
possibilities set out above or recited in any of the claims.
[0016]
25 Each feature disclosed in this specification (which term includes the
claims) and/or shown in the drawings may be incorporated in the invention
independently (or in combination with) any other disclosed and/or i llustrated
features. In particular but without limitat ion the features of any of the claims
dependent from a particular independent claim may be introduced into that
30 independent claim in any combination or individually.
[0017]
Example embodiments of the invention wil l now be described by way of
example only with reference to the attached figures in which:
7
[Brief Description of Drawings]
[0018]
[fig.1]
Figure 1 schematical ly illustrates a mobile telecommunicat ion system to
which example embodiments of the invent 5 ion may be applied;
[fig.2]
Figure 2 is a block diagram illustrating the main components of the mobile
telephone forming part of the system shown in Figure 1;
[ fig.3]
10 Figure 3 is a block diagram illustrating the main components of a base
station forming part of the system shown in Figure 1;
[ fig. 4]
Figure 4 shows an example timing diagram illustrating a method performed
by components of the communication system when a voice call is initiated;
15 [fig.5]
Figure 5 shows an example timing diagram illustrating an alternative
method performed by components of the communication system when a voice call
is initiated;
[fig.6]
20 Figure 6 shows an example timing diagram illustrating a further alternat ive
method performed by components of the communication system when a voice call
is initiated; and
[fig.7]
Figure 7 shows an example timing diagram illustrating a method performed
25 by components of the communication system when a voice call is transferred to a
different RAT.
[Description of Embodiments]
[0019]
30 Overview
Figure 1 shows a mobile (cellular) communication network 100 in which
mobile devices 3 (or other such user equipment) can communicate wi th other such
devices and/or other communicat ion entities via an E-UTRAN base stat ion (eNB)
5, operating an associated ( ‘4G’ ) cell , and/or via a UTRAN base station (NodeB) 6,
8
also operat ing an associated ( ‘2G/ 3G’ circuit-switched) cell, and/or via a wireless
local area network (WLAN) termination (WTs) 7 each of which, in this example,
comprises a single access point (AP) but may comprise a plurality of APs.
[0020]
Communication via the eNB 5 is typically routed 5 through a Mobility
Management Enti ty (MME) 9 which is accessed using an E-UTRA radio access
technology (RAT). Communication via the NodeB 6 is typical ly routed through a
Radio Network Controller (RNC) 19 and a core network 21, which are accessed
using a UTRA radio access technology (RAT). Communication via the AP of the
10 WT 7 is typically via an associated access control ler (AC) and the internet .
[0021]
As those skilled in the art wi ll appreciate, whilst two mobile devices 3,
base stations 5 and 6 and WT 7 are shown in Figure 1 for illustration purposes, the
system, when implemented, wi ll typically include other base stations, WTs and
15 mobile devices. Furthermore, only some of the elements of each of the three
exemplary RAT networks have been shown in Figure 1 for simplicity.
[0022]
The eNB 5 is con figu red to co-ordinate wi th the MME 9 via an associated
interface (SI interface) and the mobile devices 3 within the cell to set up radio
20 bearers (e.g. a E-UTRAN Radio Access Bearer, ‘E-RAB’) for communication
between the mobile devices 3 and the MME 9. In the context of VoLTE, the eNB
5 and the MME 9 are col lectively referred to as the Internet Protocol (IP)
Connect ivity Access Network ( IP-CAN) 11. It will be appreciated that , typically,
an IP-CAN 11 will comprise a plurality of eNBs 5.
25 [0023]
In order to provide VoLTE services to the UEs 3, the IP-CAN 11 provides
the mobile devices 3 with connectivity to an IP Multimedia Subsystem or IP
Multimedia Core Network Subsystem ( IMS) 15.
[0024]
30 The IMS 15 manages the delivery of IP multimedia services to the mobile
devices 3, thereby allowing multimedia based sessions between the mobile devices
3. The IMS 15 employs a Session Ini tiat ion Protocol (SIP) for establ ishing,
managing and terminating such sessions on IP networks.
[0025]
9
The core network 21 connected to the NodeB 6 includes a mobile swi tching
centre server (MSC-S) 23 which is responsible for managing cal l setup and
mobility for the mobi le devices 3 served by the NodeB 6. The MSC-S 23 can
communicate with the IMS 15 for conveying SIP signaling between the mobile
devices 5 3 and the IMS 15.
[0026]
As shown in Figure 1, the mobile devices 3-1 and 3-2 are located near the
edge of the cell operated by the eNB 5, where radio signals received by the mobile
devices 3-1 and 3-2 tend to be of low strength. However, both of the mobile
10 devices 3-1 and 3-2 located in areas of good coverage by the cell operated by the
NodeB 6. Furthermore, the mobile device 3-1 also receives good coverage from
the WT 7.
[0027]
Ben efici all y, in this example, when the mobile device 3-1 is about to
15 initiate a voice call, i t first determines whether the LTE signal strength is sufficient
for a VoLTE call by comparing a signal strength measurement with at least one
VoLTE threshold received from the eNB 5. If the LTE signal strength is
sufficient, the mobile device 3-1 initiates a VoLTE call, while if the LTE signal
strength is not sufficient, the mobile device 3-1 selects another RAT (in this
20 example either the 3G RAT of the NobeB 6 or the WLAN RAT of the WT 7) and
initiates a voice call using the alternat ive RAT. In this example, the eNB 5 also
provides the mobile device 3-1 with additional in-formation for use by mobile
device 3-1 to assist with the selection of and/or connection to the alternative RAT
(referred to as ‘ as sist an ce in fo rmation ’ ).
25 [0028]
Furthermore, in this example, when the mobile device 3-1 is connected to
the eNB 5 with an ongoing VoLTE call, the mobile device 3-1 provides
measurement reports to the eNB 5. Ben eficial ly, if the eNB 5 determines that the
LTE signal strength is no longer sufficient for VoLTE, an enhanced RRC
30 Connect ion Release procedure is performed. The enhanced RRC Connection
Release procedure involves sending a message to the mobile device 3-1 to indicate
release of the VoLTE connection. The message b en efici all y includes information
indicating the cause of the release to be for the purposes of ‘v oice call con tinuit y’
(e.g. in a cause information element, ‘ IE ’, with a value set to ‘ voice call
10
cont inuit y’ ) . In this example, the eNB 5 also provides the mobile device 3-1 with
addi tional information for use by mobile device 3-1 to assist wi th the selection of
and/or connection to the alternative RAT (e.g. 2G, 3G, WLAN) for the purposes of
cont inuing the voice call (referred to as ‘ assist an ce informatio n ’) . The assistance
information may include cell system information for the alternative 5 RAT, in order
to allow faster acquisition of system information by the mobile device 3-1, which
in turn allows faster resumpt ion of the voice call , providing a better user
experience.
[0029]
10 It can be seen, therefore, that this process advantageously avoids the
signaling associated with failed VoLTE connection attempts when a VoLTE call
cannot properly be supported (or there is a relatively high likelihood of failure)
because of insufficient radio coverage (even where radio coverage is sufficient for
a 4G data service).
15 [0030]
In this example, the eNB 5 also communicates, directly or indirectly, with
the IMS 15 to notify the IMS that the VoLTE connection of the mobile device 3-1
has been released, but that the mobile device 3-1 may try to continue the voice call
via another RAT (e.g. 2G, 3G, WLAN). When the mobile device 3-1 attempts to
20 cont inue the voice call via a connection to a new RAT, the mobi le device 3-1
indicates that the connection is for voice call continuity. In order to support the
voice call continuity, the context for the VoLTE connection is maintained in the
IMS and can thus be obtained from the IMS by the MSC-S while a connection for
cont inuing the voice call is being established via the new RAT. The context for
25 the VoLTE connection may include information such as calling party, called party
and QoS parameters. Alternatively or additionally, the context may include
subscription parameters such as parameters relating to accounting – for example a
user ’s remaining credit (for ‘p a y as you go ’ users) or a us er‘ s usage limi ts for
voice, video etc. (for pay monthly users).
30 [0031]
It can be seen, therefore, that this process advantageously has the potential
to reduce the incidence of VoLTE call failures arising from degradat ion in radio
coverage by al lowing a VoLTE call to be continued, relatively quickly, as a voice
call via a new RAT (e.g. 2G, 3G, WLAN) even where SRVCC cannot be used (e.g.
11
because SRVCC is not supported).
[0032]
In a benefici al variation of this example, when the mobile device 3-1
attempts to initiate a voice call, the eNB 5 determines whether the LTE signal
strength is sufficient for a VoLTE call by comparing a signal strength 5 measurement
with at least one VoLTE threshold. If the LTE signal strength is sufficient, the
VoLTE call is progressed. However, if the LTE signal strength is not sufficient ,
the VoLTE cal l connection is released/rejected. In this variation, on
release/rejection the eNB 5 may also provide the mobile device 3-1 with addi tional
10 information for use by the mobile device 3-1 to assist with the selection of and/or
connection to an alternative RAT (referred to as ‘assist an ce in fo rmation ’ ). This
assistance information may be provided in a release/rejection message or
separately. The release/rejection message may also include an appropriately set
cause of the release/rejection (this may, for example, be a cause information
15 element, ‘ IE’, with a value set to ‘voice call continuity’ or similar).
[0033]
It can be seen, therefore, that this variat ion also advantageously avoids
much of the signaling associated wi th failed VoLTE connection attempts when a
VoLTE call cannot properly be supported (or there is a relatively high likelihood of
20 fai lure) because of insufficient radio coverage (even where radio coverage is
sufficient for a 4G data service). This variation also has the b en efit of reducing
the complexity at the mobile device side.
[0034]
Mobile Device
25 Figure 2 is a block diagram illustrating the main components of a mobile
device 3 as shown in Figure 1. As shown, the mobile device 3 has a transceiver
circuit 31 that is operable to transmit signals to and to receive signals from an eNB
5 (or NodeB 6 or WT 7) via one or more antenna 33. The operation of the
transceiver circuit 31 is control led by a control ler 37 in accordance with software
30 stored in memory 39. The software includes, among other things, an operating
system 41, a communications control module 43, a radio resource control (RRC)
module 45, a signal measurement module 46, and a voice call module 47.
[0035]
The communications control module 43 controls communication with the
12
base stat ion 5 including, for example, allocation of resources to be used by the
transceiver circuit 31 in its communications with the base station 5.
[0036]
The radio resource control module 45 controls the transition between
various RRC modes and handles associated RRC signaling to/from 5 the base station
5 (via the voice call module 47).
[0037]
The signal measurement module 46 obtains signal strength measurements
(e.g. Reference Signal Received Power ( ‘RSRP’), Reference Signal Received
10 Quality (‘RSRQ’) or Reference Signal Strength Indicator (‘RSSI’)) of signals (e.g.
reference signals) received via the antenna 33. The signal measurement module
46 can send the signal strength measurements to the eNB 5.
[0038]
The voice call module 47 is responsible for ini tiat ing and managing voice
15 calls via LTE (i.e. VoLTE) or via a different RAT. In this example, the voice call
module 47 determines whether a VoLTE call can be ini tiated (e.g. based on one or
more thresholds for the signal strength measurements). It wil l be appreciated,
however, that determination of whether a VoLTE call can be ini tiated may be
performed at the base stat ion 5. The voice call module 47 also manages
20 cont inuation (or attempted continuation) of voice calls, that begin as VoLTE calls
but can no longer be supported (e.g. because of a change in radio condi tions), via
an alternative RAT.
[0039]
The voice call module 47 selects the RAT or initiating or continuing with a
25 voice call (where VoLTE cannot or can no longer be used). The RAT selection
may be based on assistance information provided by the eNB 5 to aid selection of
the RAT.
[0040]
Base Station (eNB)
30 Figure 3 is a block diagram illustrating the main components of a base
station (eNB) 5. The base stat ion 5 is a fixed communication node providing
services to mobi le device 3 within its coverage area. As shown, the base station 5
includes a transceiver circui t 51 which transmits signals to, and receives signals
from, the mobile device 3 via at least one antenna 53. The base stat ion 5 also
13
transmits signals to and receives signals from the MME 9 and other neighbouring
base stat ions 5 via a network interface 55 (for communicating with neighboring
base stat ions 5 and with the MME 9 using the X2 and S1 interfaces, respectively).
[0041]
The operation of the transceiver circuit 51 is control led 5 by a control ler 57
in accordance with software stored in memory 59. The software includes, among
other things, an operating system 61, a communicat ions control module 63, a radio
resource control (RRC) module 65, a measurement configuration module 67, a
VoLTE threshold module 68, and a voice call module 70.
10 [0042]
The communications control module 63 controls communications between
the base station 5 and the mobile devices 3, and the network devices such as the
MME 9.
[0043]
15 The radio resource control module 65 controls the radio communication
resources used between the base station 5 and the mobile devices 3 attached
thereto. In particular, the radio resource control module 65 controls the
establishment of an RRC connection between the base station 5 and the mobile
devices 3 within its cell(s).
20 [0044]
The measurement configuration module 67 is responsible for generating
measurement con figu rat ions for con figu ri n g the mobile device 3-1 to perform
measurements such as signal strength measurements (e.g. Reference Signal
Received Power ( ‘RSRP'), Reference Signal Received Quality ( ‘RSRQ’) or
25 Reference Signal Strength Indicator (‘RSSI’)) for the purposes determining
whether the signal strength is sufficient for VoLTE.
[0045]
The VoLTE threshold module 68 stores one or more signals strength
thresholds for the purposes determining whether the signal strength is sufficient
30 for VoLTE. In this example, the VoLTE threshold module 68 also provides the
mobile device 3 wi th these thresholds. It will be appreciated, however, that if
determination of whether a VoLTE call can be initiated is performed at the base
station 5, then the VoLTE threshold module 68 may carry out the comparison
required for such a determinat ion.
14
[0046]
The voice call module 70 is responsible for the base station's part in
initiating and managing voice calls via LTE (i .e. VoLTE). The voice call module
70 also provides information (e.g. the assistance information) for support ing
selection of alternative RATs in the event that a VoLTE voice call 5 cannot, or can no
longer, be supported by the prevailing radio condi tions. The assistance
information may, for example, inform the mobile device of a priority order for
different RATs (e.g. respective priorit ies for 2G, 3G, WLAN) and/or may include
target cell system information that reduces the burden on the mobile device when
10 setting up / continuing a voice call thereby allowing a new/ongoing call to be
established more quickly. The voice call module 70 also provides continuity
information for supporting continuity of voice calls via alternat ive RATs, to other
network enti ties, such as functions of the IMS 15, for example notifying the IMS
that a mobi le device 3 has been released using an enhanced RRC connection
15 release procedure.
[0047]
In this example the voice call module 70 also determines the priority order
for different RATs, al though it will be appreciated this could be
pre-programmed(for example set by an operator).
20 [0048]
In the above descript ion, the mobile device 3 and the base station 5 are
described for ease of understanding as having a number of discrete modules (such
as the communications control modules and the media access control modules).
Whilst these modules may be provided in this way for certain applications, for
25 example where an existing system has been modified to implement the invention,
in other applications, for example in systems designed with the inventive features
in mind from the outset, these modules may be built into the overall operating
system or code and so these modules may not be discernible as discrete entities.
These modules may also be implemented in software, hardware, firmware or a mix
30 of these.
[0049]
A number of different examples will now be described that il lustrate how
different aspects of the invention can be put into effect using the above mobile
device (UE) 3 and base stat ion (eNB) 5. The examples will be described with
15
reference to the timing diagrams shown in Figures 4 to 7.
[0050]

Figure 4 illustrates, in simp li fied form, the procedure for initiating a voice
call taking into account at least one threshold for ini tiat ing a 5 VoLTE voice call.
[0051]
At step s401, the eNB 5 transmits one or more thresholds associated with
VoLTE to the UE3-1. In this example, the threshold(s) are broadcast by the eNB 5
to any UEs 3 which are present with in the cell operated by eNB 5. In this
10 example the one or more thresholds are included in a system information block
(SIB).
[0052]
In this example, the one or more thresholds for VoLTE comprise at least
one of a reference symbol received power (RSRP) threshold, a received signal
15 strength indicator (RSSI) threshold, and a reference signal received quality
(RSRQ) threshold. Each threshold value transmitted to the UE 3-1 indicates a
respective value below which a VoLTE cal l is considered not to be viable.
[0053]
At step s403, assistance information is transmitted by the eNB 5 to the UE
20 3-1. In this example the assistance information is broadcast by the eNB 5 to any
UEs 3 within its cell in an SIB (ei ther with or separately from the one or more
thresholds). The assistance informat ion includes information for assisting the UE
3-1 to connect to a new cell, and in this example the assistance information
comprises RAT priori ty information. The RAT priority information id ent i fies an
25 order of priority of any RATs which may be part of the overlaid coverage received
by the UE 3-1. In this case, and as can be seen from Figure 1, UE 3-1 is wi thin
the coverage the cell of the 3G NodeB 6 and the WLAN cell of the WT 7. As
shown in Figure4, exemplary assistance informat ion comprises information
specifying that 3G RATs have the highest priority, followed by 2G RATs and then
30 WLAN RATs. A UE receiving this information will therefore attempt to connect
in the first instance to a 3G RAT for a voice call if available, and then to a 2G RAT
where connection cannot be made with the 3G RAT; and in turn to a WLAN RAT if
connection to the 2G RAT is not possible.
[0054]
16
The assistance information may also include configuration information of
the target RATs, and/or of target cel ls. The con figu rat ion information is provided
in order to expedite the process of the UE 3-1 connecting to a new cell or RAT.
The con figu r ati on information may include system information for the target cells.
Where the target RAT is WLAN, the con fig ur ation informat ion 5 may include WLAN
iden ti fiers such as a Basic Service Set ldentifier (BSSID), Access Point ldent i fier
(APID), Service Set Ident i fier (SSID)and/or a Homogeneous Extended Service Set
Identi fier (HESSID).
[0055]
10 The configuration information may also provide assistance in the security
procedure, for example allowing the UE 3-1 to skip WLAN security or allow a
light weight security mechanism for be performed. For example, in the standard for
public-access Wi-Fi referred to as ‘Hotsp ot 2.0 ‘, a UE authorized with an Extensible
Authent ication Protocol Subscriber Identity Module (EAP-SLVI) moving from a
15 3GPP network may not need to be authenticated by the WLAN. Accordingly, the
con figu rati on information may provide information allowing the UE 3-1 to connect
to a WLAN without authenticat ion and using the same credentials as used in the
3GPP network, in order to reduce signaling load.
[0056]
20 It is noted that where the UE 3-1 connects to a 2G or 3G RAT, securi ty keys
associated with the UE 3-1 are transferred by the source RAT(e.g. 4G RAT) to the
target RAT (e.g. 3G RAT), in a simi lar way as performed in SRVCC.
[0057]
At step s405 the UE 3-1 measures the signal strength of reference signals
25 transmitted by the eNB 5. As wil l be appreciated by those skil led in the art, the
signal strength measurement may be performed before or after the UE 3-1 receives
the one or more thresholds and/or the assistance information from the eNB5.
[0058]
At step s407 the UE 3-1 compares the signal strength measurement of the
30 reference signals to the corresponding threshold value for the VoLTE. For example,
if the threshold value received by the UE 3-1 is an RSRP threshold value, the
RSRP signal strength measurement of the reference signal transmitted by the eNB
5 is compared to this RSRP threshold. If the signal strength measurement is less
than the threshold, the UE does not initiate a VoLTE call via the eNB 5, and instead
17
proceeds to step s409 where the UE 3-1 selects an alternative RAT using the
assistance information. As the exemplary assistance informat ion in Figure 4
specifies that a 3G RAT has a higher priority than a WLAN RAT, at step s411 the
UE 3-1 init iates a col lection with the NodeB 6 in order to establ ish a voice call.
5 [0059]
If at step s407 the signal strength measurement is greater than or equal to
the threshold value, the UE 3-1 proceeds to step s413 where an RRC connection is
initiated with the eNB 5 in order to establ ish a VoLTE call. In this example, the
coverage check is performed before a random access (RA) procedure is
10 commenced in pursuance of the RRC connection(i.e. before ‘message 1’ of the RA
procedure). It will be appreciated, however, that the coverage check may be
performed later, for example after a random access (RA) procedure has commenced
but before an RRC connection request (i .e. ‘mess age 3’) is sent.
[0060]
15 Although not illustrated in Figure4, if a voice call cannot be established via
the NodeB 6, then using the assistance information the UE 3-1 may proceed to
attempt to establish a col lection with the WLAN WT 7 in order to place the voice
call.
[0061]
20 Initiating Voice Call based on VoLTE Threshold Comparison at eNB
Figures 5 and 6 illustrates, in simpli fied form, two exemplary procedures
according to an example in which the UE 3-1, in idle mode, ini tiates a VoLTE call
and provides signal strength measurements to the eNB 5 in order to allow the eNB
5 to quickly determine if VoLTE is viable or if the call needs to be transferred to
25 another RAT.
[0062]
At step s501 the UE 3-1 performs signal strength measurement of reference
signals transmitted by the eNB 5. As in the previous example, these signal
strength measurements may comprise at least one of RSRP, RSRQ and RSSI signal
30 strength measurements.
[0063]
At step s503, the first step of initiating a VoLTE call is performed when the
UE 3-1 transmits a random access preamble to the eNB 5. The eNB 5 responds at
step s505 with a random access response. Next, at step s507, the UE 3 sends an
18
RRC connection request to the eNB 5 and at step s509 the eNB 5 responds with an
RRC connection setup message. At step s511, the UE 3-1 sends an RRC
connection complete message to the eNB 5, where the RRC connection complete
message includes a signal strength measurement result on the signal strength
measurement performed at step s501. At step s512, the eNB 5 5 uses the signal
strength measurement resul t transmitted with the RRC connection complete
message to determine whether the signal strength received by the UE 3-1 is
suitable for a VoLTE call by comparing the signal strength measurement with at
least one VoLTE threshold, such as the VoLTE thresholds described above. If the
10 signal strength is considered suitable, the eNB 5 proceeds to step s513 where it
transmits a security mode command to the UE3-1. The UE 3-1 then forms with a
security mode to complete message at step s515, and at step s516 a VoLTE call is
established.
[0064]
15 If, on the other hand, the signal strength is not considered suitable for a
VoLTE call by the eNB 5, the eNB 5 proceeds to step s517 where an RRC
connection release message is transmitted to the UE3-1.
[0065]
The RRC connection release procedure between the eNB 5 and the UE 3-1
20 is an enhanced RRC connection release procedure in which the eNB 5 provides
addi tional information to the UE to aid the voice call continuity. For example,
the RRC connection release messages transmitted at step s517 may include a new
RRC connection release cause value, along with an indication of preferred RAT
and associated assistance information. The enhanced RRC connection release
25 procedure is described in more detail in relation to Figure 7 below.
[0066]
Figure 6 illustrates, in simp li fied form, an alternative procedure in which
the UE 3-1, in idle mode, initiates a VoLTE call and provides signal strength
measurements to the eNB 5 in order to al low the eNB 5 to quickly determine if
30 VoLTE is viable or if the call needs to be transferred to another RAT. The
procedure illustrated in Figure6 is similar to that illustrated in Figure 5 except that
the signal strength measurement result is sent to the eNB 5 at a different point in
the procedure.
[0067]
19
At step s601 the UE 3-1 performs a signal strength measurement in the
same way as described in relation to Figure 5. At step s603 the first step of
initiating a VoLTE call is performed when the UE transmits a random access
preamble to the eNB 5. At step s605, the eNB 5 responds with a random access
response message. At step s607, the UE 3-1 transmits an RRC 5 connection request
to the eNB 5, where the RRC connection request includes a signal strength
measurement result. Next, at step s609, the eNB 5 uses the signal strength
measurement result transmi tted with the RRC connect ion request to determine
whether the signal strength received by the UE 3-1 is sui table for a VoLTE call by
10 comparing the signal strength measurement with at least one VoLTE threshold,
such as the VoLTE thresholds described above. If the signal strength is
considered suitable, the eNB 5 proceeds to step s611 where it transmi ts an RRC
connection setup message to the UE 3-1, at step s613 the UE 3-1 responds with an
RRC connection complete message, and at step s616 a VoLTE call is established.
15 [0068]
However, if the signal strength measurement in considered not suitable for
a VoLTE call, the eNB 5 proceeds to step s617 where an RRC connect ion reject
message is transmitted to the UE 3-1.
[0069]
20 In a similar way as stated above in relation to Figure 5, preferably the RRC
connection reject procedure between the eNB 5 and the UE 3-1 is an enhanced
RRC connection reject procedure. For example, the RRC connection reject
messages transmitted at step s617 may include a new RRC connection reject cause
value, along with an indication of preferred RAT and associated assistance
25 information. The enhanced RRC connection release/reject procedure is described
in more detail in relation to Figure 7 bel low.
[0070]
It can be seen that, in the example of Figure 5, signal strength information
is sent to the eNB 5 by the UE 3-1 in an RRC connection complete message.
30 Contrast ingly, in the example of Figure 6, signal strength information is sent to the
eNB 5 by the UE 3-1 in an RRC connection request message. However, signal
strength information may be provided to the eNB5 at other points in the procedure.
[0071]
For example, the signal strength information may be provided as part of a
20
random access (RA) procedure. However, since space is limi ted in RA message 1
(being designed for preamble transmission), the part itioning of RA resources
between modes A and B (currently used for indicating different coverage levels for
machine type communication devices) may be reused by VoLTE devices.
5 [0072]
In a further example. signal strength information may be provided to the
eNB 5 in a new request/response RRC message before security activation.
Alternatively, the signal strength informat ion may be provided to the eNB 5 after
security activation (although it will be appreciated that this is relatively late in the
10 procedure).
[0073]
In a further example, the UE 3-1 may provide a single bi t (e.g. in any of the
messages described above) rather than a complete set of measurement results. This
bit may represent a trigger to indicate, for example, whether the signal strength is
15 above or below a threshold. The thresholds for such single bit trigger may be
broadcasted or transmitted in dedicated signal ling.
[0074]
Providing a single bit rather than a complete set of measurement resul ts
ben eficiall y reduces signalling, and allows signal strength information to be
20 provided in messages having fixed sizes, such as an RRC Connection request.
Furthermore, where the UE 3-1 is transmit ting signal strength information before
authentication has taken place, sending a single bit poses a security risk than
sending measurement results (for example it is unlikely that the UE location can be
determined from the single bit alone).
25 [0075]
Enhanced RRC Connection Release/Reject Procedure
Figure 7 illustrates, in simp li fied form, a procedure performed by the
communicat ion system 100 as illustrated in Figure 1 which includes an enhanced
RRC connection release procedure in which a dedicated ‘ r elease caus e’ value is
30 used to indicate that an RRC Connection Release is due to voice call continuity
requirements.
[0076]
At step s701 , an active VoLTE RRC connection exists between the UE 3-1
and the eNB 5. At step s703 the UE 3-1 transmits a measurement report to the eNB
21
5, where the measurement report comprises a signal strength measurement of
reference signals transmitted by the eNB 5. At step s704, the eNB 5 uses the signal
strength measurement resul ts transmitted in the measurement report to determine
whether the signal strength received by UE 3-1 is suitable for a VoLTE call. If the
signal strength measurement is considered suitable for a VoLTE 5 call, the eNB 5
proceeds to establish a VoLTE call with the UE 3-1. However, if the signal strength
measurement is not considered suitable for a VoLTE call , the eNB 5 proceeds to
step s705 where it transmits an RRC connection release message to the UE 3-1.
According to the enhanced RRC connection release procedure, the RRC connection
10 release message comprises a RRC connect ion release cause value which indicates
that the release cause is “voi ce call continuity” . Preferably, the RRC connection
release message also includes assistance informat ion; including information
indicating a preferred RAT(s) for voice cal l continuity (e.g. indicating a priority
order for RATs) and further including associated information, such as system
15 information of the preferred RAT(s).
[0077]
It is noted that the assistance information may be included with the RRC
connection release message or may be transmitted separately from the RRC
connection release message.
20 [0078]
As step s706 the eNB 5 informs the IMS, via the MME 9, of the RRC
connection release and noti fies the IMS that the UE 3-1 may attempt to reconnect
via another RAT for voice call continuity. In this example the other RAT may be,
for example. a 3G, 2G or WLAN RAT.
25 [0079]
At step s707, the UE 3-1 maintains the RRC connection release cause value
in its upper layers, for example NAS, IMS or IP.
[0080]
At step s709 the UE 3-1 selects a new RAT with which to attempt to
30 connect for voice cal l continuity, using the assistance informat ion received at step
s705. Then, at step s710, the UE 3-1 establ ishes a connection wi th the chosen RAT,
in this case establishing an RRC connection with the NodeB 6 of the 3G network
(UTRAN).
[0081]
22
At step s711, the MSC-S 23 of the 3G network associated with NodeB 6
obtains the context for the voice call with the mobile device from the IMS 15.
[0082]
Once the MSC-S 23 has obtained the context , the voice cal l can be
cont inued via the 3G network. Preferably, the call will continue 5 seamlessly; in
some systems if the procedure takes less than 20 msec then no packets wil l be lost .
[0083]
In the above description in relat ion to Figure 7, the RRC connection release
procedure is enhanced by including extra information (e.g. a new cause value and
10 assistance information) with an RRC connection release message. However, it will
he appreciated that the RRC connection reject procedure can be enhanced in the
same way by including the extra information with an RRC connection reject
message (for example by including a cause value identifying the cause for
rejecting the RRC connection).
15 [0084]
WLAN Target RAT
In the scenario where the UE 3-1, when in connected mode, at tempts to
establish VoLTE call and the UE 3-1 is transferred to WLAN for the call, it may
take a longer time for an association between the UE 3-1 and the WLAN to be
20 established. This may result in the ongoing voice call being affected.
[0085]
However, if the UE 3-1 has received the RAT priori ty order information as
described above, and the WLAN has a high priority for voice cal l (e.g. higher than
2G/3G), then the mobile device may start association with the WLAN earlier.
25 Furthermore, the eNB may set the one or more thresholds accordingly (e.g. a
higher single strength threshold) to ensure that there is enough time to cater for a
delay arising from WLAN association.
[0086]

30 Detailed example embodiments have been described above. As those skilled
in the art will appreciate, a number of mo di ficatio ns and alternatives can be made
to the above example embodiments whilst still b en efitin g from the inventions
embodied therein. By way of illustration only a number of these alternatives and
modi ficati ons will now be described.
23
[0087]
In the above example embodiments, the mobile devices are cellular
telephones. It will be appreciated that the above example embodiments could be
implemented using devices other than mobile telephones such as, for example,
personal digi tal assistants, laptop computers, web browsers, 5 etc. The above
example embodiments are applicable to non-mobile or generally stat ionary user
equipment as well.
[0088]
In the above example embodiments, a number of software modules were
10 described. As those skilled in the art will appreciate, the software modules may be
provided in compiled or un-compiled form and may be supplied to the mobile
device, eNB or WT as a signal over a computer network, or on a recording medium.
Further, the functionality performed by part or all of this software may be
performed using one or more dedicated hardware circuits.
15 [0089]
The IMS 15 may comprise a number of ent ities or ‘ fu nct ions ’ for delivering
the IP multimedia services to the mobi le devices 3. It will be appreciated that the
functions may be provided as separate communicat ion entities. Al ternatively, some
or all of the functions may be integrated into a single communication entity.
20 [0090]
The IMS 15 may include a Call State Control Function (CSCF), which
comprises a Proxy CSCF (P-CSCF), an interrogating CSCF (I-CSCF) and a Serving
CSCF (S-CSCF). The IMS 15 may also include an Applicat ion Server (AS) and a
Home Subscriber Server (HSS).
25 [0091]
The CSCF, in this example, is a SIP server that implements IMS call
session control functional ity for the mobi le device 3. The CSCF also supports the
DIAMETER protocol for communicating with the HSS.
[0092]
30 The P-CSCF provides connect ivity between the mobile devices 3 and the
IMS 15. The P-CSCF is con figu red to handle all SIP requests and responses
between the mobile devices 3 and the IMS 15. The P-CSCF also manages security
and Quali ty of Service (QoS).
[0093]
24
The I-CSCF acts as a forwarding point for the IMS 15, as remote servers
address SIP packets to the IP address of the I-CSCF. The I-CSCF is also con figur ed
to communicate with the HSS to retrieve the address of the S-CSCF for a SIP
request.
5 [0094]
The S-CSCF is co n fig ur ed to process the location registration of each
mobile device 3, and also to perform user authentication and VoLTE call routing.
[0095]
The AS is responsible for end-to-end communications between (an
10 appropriate application in) the mobile device 3 and a corresponding applicat ion
hosted by the AS (and/or a node connected to i t).
[0096]
The HSS is responsible for storing and managing subscriber data and
provides details of the subscribers to the other entities wi thin the IMS network.
15 [0097]
Although not necessarily shown in Figure 2, the mobile device 3 will of
course have all the usual functionali ty of a conventional mobile device 3 (such as a
user interface 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
20 the memory 39 and/or may be downloaded via the telecommunication network or
from a removable data storage device (RMD), for example.
[0098]
It will be appreciated that whilst it is envisaged that the variation in which
the eNB 5 determines whether the LTE signal strength is s uf fici ent for a VoLTE
25 call represents a possible alternative to the example in which the mobile device 3-1
determines whether the LTE signal strength is suf fici ent for a VoLTE call , it may
be b en efici al for both options to be integrated into a single communication system.
The opt ions may, for example, be part of a single integrated process in which both
the mobile device 3-1 and the eNB 5 check whether the LTE signal strength is
30 sufficient for a VoLTE call .
[0099]
The mobile device 3-1 may compare its signal strength measurement with
the at least one threshold when in connected mode. preferably periodically. and if
it determines that the signal strength is below the associated threshold it transmits
25
a RRC Relocation request to the eNB, specifying that the cause is voice call
cont inuity. In response, an enhanced RRC Connection Release may be performed
as described above.
[0100]
In relat ion to Figure 4, in alternative examples, no assistance 5 information
is transmitted by the eNB 5 to the UE 3-1, and therefore the UE 3-1 selects an
alternative RAT without use of assistance information.
[0101]
The one or more thresholds, and the assistance information, may not be
10 broadcast by the eNB 5, and instead may be sent directly to mobile devices 3 by
the eNB 5. This may allow the eNB 5 to tailor the thresholds and/or the assistance
information for each mobile device 3.
[0102]
It is noted that the broadcast of VoLTE thresholds by an eNB may also
15 implicitly indicate that the eNB supports the use of VoLTE thresholds.
Furthermore, an eNB may broadcast an indication that it supports VoLTE
thresholds, optionally without broadcasting sp eci fic thresholds. In such a case, a
UE may determine thresholds itself, for example based on capabilities of the eNB
and UE.
20 [0103]
It is noted that the VoLTE sp eci fic thresholds may also be used for idle
mode mobility. For example, a UE 3-1 may decide whether to select a 4G cell in
idle mode mobility based on whether measurements of reference signals from the
4G cell are above a VoLTE sp eci fic threshold. It with be appreciated that generally,
25 when a UE is performing idle mode mobi lity, it is not known whether it will
establish a VoLTE connection or a data service connection in the future.
Accordingly, the VoLTE s peci fic thresholds may particularly b eneficiall y be used
for UEs which support VoIP and which do not support a data connection, as such
UEs will only establish VoLTE connections.
30 [0104]
The priority order of the RATs can be decided by the eNB 5, or may be
con figu red by the operator during an operations, administration and maintenance
(OAM) procedure. If decided by the eNB 5, the eNB can determine the coverage
area of the other avai lable RATs, either by performing signal measurements itself,
26
or by instructing the UE to provide measurement reports relating to each of the
RATs. The eNB 5 then decides the priority order of the RATs based on the coverage
areas. Situat ions where the priority order of the RATs is con figu red by the operator
may include the case where, for example, the whole LTE cell of the eNB 5 has
overlaid UMTS cel l coverage. The priority order may also be 5 determined via any
combination of the above options. Furthermore, both UEs and eNBs can use
addi tional information to determine priori ty order, such as minimisation of drive
tests (MDT) informat ion and self-organising network (SON) informat ion.
[0105]
10 In order to know what cells are present, the eNB 5 may ask the UE 3 to
perform location reporting to determine the posit ion of the UE 3. Furthermore, the
UE may report ‘ fin ge rp rints ’ comprising the radio signal level/signal strength of,
for example, up to 6 cells including other RATs. The eNB 5 may use this
fin gerp rint ‘ to decide priority accordingly. The UE location and ‘ fin gerpr int’ can be
15 used in combination with radio quality when a UE 3 is in connected mode.
[0106]
Although it is described above that the MSC server 23 obtains the context
from the IMS, it is noted that an evolved Packet Data Gateway (ePDG) may
addi tionally or alternatively perform this task.
20 [0107]
In examples where the UE provides signal strength information using a
single bit, the UE may separately indicate to the RAT that it has the capability to
provide signal strength information using a single bit. However, the single bit and
the capabil ity indicat ion may be combined together - for example a predefined
25 value of the single bi t may indicate both that the UE has the capabi lity to provide
signal strength information using a single bit and that the signal strength
measurement is below a threshold.
[0108]
Additionally or alternatively, the one or more thresholds may include a
30 power headroom (PH) reporting threshold for VoLTE. This may beneficial if VoLTE
is not viable due to UE power being limited. In this case, the UE 3-1 can provide a
PH report to the eNB 5 based on this new threshold (this is similar to the RSRP,
RSRQ and/or RSSI thresholds described above, but done at Media Access Control
(MAC) layer reporting).
27
[0109]
It wil l he appreciated that whilst much of the above description is based on
an RRC implementation, the procedure could instead be based on a MAC
implementation, for example as in the power headroom (PH) reporting example
5 above.
[0110]
For 2G/3G RATs, the information sent by the eNB 5 to the UE 3-1 may
include thresholds for VoLTE establishment and target RAT cel l information for
2G/3G case. However for WLAN RATs, the information sent by the eNB 5 to the
10 UE 3-1 may include VoLTE thresholds and target WLAN information (e.g. WLAN
AP ID/ Basie Service Set ID (BSSID)/other IDs). Ben eficiall y, therefore, if WLAN
is the highest priority RAT for voice call continuity then the UE 3 is made aware of
this in advance.
[0111]
15 The system information of the preferred RAT(s) may include informat ion
similar to that used for circuit -swi tched fallback, for example the UTRA sp eci fic
system information contained in “ut ra-BCCH-Container-r10”.
[0112]
It is noted that the VoLTE threshold information and/or assistance
20 information can be provided in new SIB or existing SIB. For example, a WLAN
of flo ad indicator in an existing SIB may additionally include VoLTE thresholds.
The “WLAN offload con fig” in SIB 17 (as shown in the version of SIB 17 below,
only the relevant part of which has been illustrated) can be used as reference. It is
noted that additional information may be added to SIBs such as SIB 17, however it
25 is expected that the same or similar information to that in SIB 17 can be used.
28
[0113]
[Table 1]
[0114]
In order to implement voice cal l continuity from 5 VoLTE to another RAT, at
the end of LTE coverage, similar informat ion may be used, in an RRC Connection
Release message, to that used for CS fallback switching (as highlighted in the
-- ASNlSTART
WLAN-OffloadConfig-r12 ::=
threshold RSRP-r12
SEQUENCE {
{
I
Range,
I
Range I {
I
Range,
I
RSRQ-Range I RSRQ-Range,
I
fSRQ-Range
RSRQ-Range,
I
RSRQ-Range I Range,
I
Range
threshold RSRP-Low-r12
thresholdRSRP-High-r12
} OPTIONAL, -- Need OR
threshold RSRQ-r12
thresholdRSRQ-low-r12
thresholdRSRQ-High-r12
} OPTIONAL, -- Need OR
SEQUENCE
RSRPRSRPSEQUENCE
RSRQthresholdRSRQ-
OnAIISymbolsWithWB-r12 SEQUENCE {
thresholdRSRQ-OnAIISymbolsWithWB-low-r12
thresholdRSRQ-OnAIISymbolsWithWB-High-r12
} OPTIONAL1 -- Need OP
threshold RSRQ-OnAIISym bols-r12
thresholdRSRQ-OnAII5ymbolsLow-r12
thresholdRSRQ-OnAIISymbo[sHigh-r12
} OPTIONAL1 --Need OP
threshold RSRQ-WB-r12
thresholdRSRQ-WB-Low-r12
thresholdRSRQ-WB-High-r12
SEQUENCE {
SEQUENCE {
RSRQRSRQI
} OPTIONAL,- Need OP
SIB 17. ASN.1 (truncated and shows relevant part only)
29
truncated version of the RRC Connection Release message shown below, only the
relevant part of which has been illustrated). For example the ‘v oice call co ntinu it y’
release cause for VoLTE may, for example, be implemented as a new
‘Rel eas eCause’ in “s pare 1”.
5 [0115]
Similarly, to shorten the time required to connect to a 2G/3G RAT the
assistance information may comprise target cell system information that is the
same, or similar to the system information broadcast for CS fallback.
[0116]
10 [Table 2]
30
[0117]
It will be appreciated that the determination of whether or not the signal
measurements meet the at least one criterion may be based on a comparison of said
signal measurements with at least one threshold. The at least one threshold may
comprise a signal strength threshold below which VoLTE communication 5 is not
considered sustainable. For example, the at least one threshold may comprise at
least one of a Reference Signal Received Power (RSRP) threshold, a Reference
Signal Received Qual ity (RSRQ) threshold, a Reference Signal Strength Indicator
(RSSI) threshold and a power headroom (PH) threshold.
10 [0118]
It will be appreciated that when the communication device determines
whether VoLTE communication via the communicat ion connect ion with the base
station can be sustained, the communication device may be in idle or connected
mode.
15 [0119]
The controller of the communicat ion device may be further co n figu r ed to
control the communication device to receive assistance information (e.g.
indicating a priority / priori ty order associated with the at least one non-LTE RAT
and/or comprising system information associated with the at least one non-LTE
20 RAT) to assist with the selection of and/or connection to at least one non-LTE
radio access technology (RAT) for establ ishing a voice call . In this case, the
control ler may be further con figu red to control the communicat ion device to select
a non-LTE RAT for the continuation of voice communication, based on the
assistance information. The controller of the communicat ion device may be further
25 configured to control the communication device to connect to non-LTE RAT to
establish a voice call , based on the assistance information.
[0120]
The at least one threshold may comprise a power headroom (PH) threshold
and the controller of the communication device may be further con figu red to
30 control the communication device transmit a PH report to the base station based on
the PH threshold.
[0121]
The controller of base station may be further con figur ed to control the base
station to: transmit , to the communication device, assistance information (e.g.
31
indicating a priority /priority order associated with at least one non-LTE RAT
and/or comprising system information associated with the at least one non-LTE
RAT) to assist with the selection of and/or connection to at least one non-LTE
radio access technology (RAT) for establ ishing a voice call .
5 [0122]
It will be appreciated that the message indicating that the communication
connection cannot be sustained may comprise an indication that a cause of the
message is voice call continuity.
[0123]
10 The communication device may provide the at least one result of the signal
measurements to the base stat ion in a Radio Resource Control (RRC) Connect ion
Complete message; and the message indicating that the communication connection
cannot be sustained may comprise an RRC Connection Release message.
[0124]
15 The communication device may provide the at least one result of the signal
measurements to the base stat ion in a Radio Resource Control (RRC) Connect ion
Request message: and the message indicat ing that the communication connection
cannot be sustained may comprise an RRC Connection Reject message.
[0125]
20 The at least one resul t of the signal measurements may comprise an
indicator (e. g. a one bit indicator) to indicate whether or not the signal
measurements meet at least one pre-determined criterion.
[0126]
The controller of the communicat ion device may be further co n figu r ed to
25 control the communication device to: determine whether or not the signal
measurements meet the at least one pre-determined criterion based on a
comparison of said signal measurements with at least one threshold. In this case,
the at least one threshold may be a signal strength threshold below which VoLTE
communicat ion is not considered sustainable.
30 [0127]
The controller of the communicat ion device may be further configured to
control the communication device to: provide the indication that a cause of the
message is voice call continuity to the non-LTE RAT when the communication
connection via the non-LTE RAT is established.
32
[0128]
The controller of the communicat ion device may be further co n figu r ed to
control the communication device to: receive assistance information (e.g.
indicating a priority / priori ty order associated with the at least one non-LTE RAT
and/or comprising system information associated with the at 5 least one non-LTE
RAT) to assist with selection of and/or connection to the non-LTE RAT for
establishing or maintaining the voice call.
[0129]
The controller of the communicat ion device may be further co n figu r ed to
10 control the communication device to: select the non-LTE RAT for the continuation
of voice communication, based on the assistance information.
[0130]
The controller of the communicat ion device may be further co n figu r ed to
control the communication device to: provide the indication that a cause of the
15 message is voice call continuity to the non-LTE RAT when the communication
connection via the non-LTE RAT is established.
[0131]
The controller of the base stat ion may be further con figu red to control the
base station to: transmit, to the communication device, assistance information (e.g.
20 indicating a priority / priori ty order associated with the at least one non-LTE RAT
and/or comprising system information associated with the at least one non-LTE
RAT) to assist with selection of and/or connection to at least one non-LTE radio
access technology (RAT) for establishing a voice call.
[0132]
25 The controller of the base stat ion may be further configured to control the
base stat ion to: transmit, to a mobility management entity (MME), a further
message indicating that the communication connect ion with the communicat ion
device cannot be sustained.
[0133]
30 The further message indicating that the communicat ion connect ion with the
communicat ion device cannot be sustained may comprise a noti ficat ion that the
communicat ion device may establish a communicat ion connect ion via a non-LTE
RAT in order to establish or maintain a voice call via that non-LTE RAT.
[0134]
33
According to an example, there is provided a method performed by a core
network node of a long term evolution (LTE) communication system, the method
comprising the steps of receiving, from a base stat ion, information indicating a
communicat ion connection associated with a voice over LTE (VoLTE) voice call
has been released and information indicating a possibility that said 5 voice cal l wi ll
be continued via another radio access technology (RAT); notifying an internet
protocol multimedia subsystem (IMS) that the communication connect ion
associated with the VoLTE voice call has been released; and not ifying the IMS of
the possibility that said voice call will be cont inued via another RAT.
10 [0135]
According to another example, there is provided a method performed by a
communicat ion node of a Universal Terrestrial Radio Access Network (UTRAN),
the method comprising the steps of receiving, from an internet protocol multimedia
subsystem (IMS), information for supporting the continuat ion of a voice call via a
15 radio access technology (RAT) of the UTRAN, wherein a voice over LTE (VoLTE)
connection over which the voice call was previously being provided has been
released, and wherein said information comprises context information associated
with the VoLTE connection.
[0136]
20 Various other modifications will be apparent to those skilled in the art and
will not be described in further detail here.
[0137]
While the invention has been particularly shown and described with
reference to example embodiments thereof, the invention not limited to these
25 embodiments. It will be understood by those of ordinary skil l in the art that various
changes in form and details may be made therein without departing from the sprit
and scope of the present invention as d efin ed by the claims.
[0138]
This applicat ion is based upon and claims the benefit of priority from
30 United Kingdom patent application No. 1603509.9, filed on February 29, 2016, the
disclosure of which is incorporated herein in its entirety by reference.
34
WE CLAIM:
[Claim 1]
A communication device for a long term evolution (LTE) communication
system, the communication device 5 comprising:
a controller and a transceiver, wherein the controller is co n figu red to
control the communication device to:
establish and engage in Voice over LTE (VoLTE) communication via a
communicat ion connection with a base station;
10 obtain information indicating at least one cri terion for determining whether
VoLTE communication via the communicat ion connection with the base stat ion can
be sustained;
perform signal measurements for signals received from the base station;
and
15 determine whether VoLTE communication via the communication
connection with the base station can be sustained based on whether or not the
signal measurements meet the at least one cri terion.
[Claim 2]
20 A communication device according to claim 1, wherein the determination
of whether or not the signal measurements meet the at least one criterion is based
on a comparison of said signal measurements with at least one threshold.
[Claim 3]
25 A communication device according to claim 2, wherein the at least one
threshold comprises a signal strength threshold below which VoLTE
communicat ion is not considered sustainable.
[Claim 4]
30 A communication device according to claim 3, wherein the at least one
threshold comprises at least one of a Reference Signal Received Power (RSRP)
threshold, a Reference Signal Received Quality (RSRQ) threshold, a Reference
Signal Strength Indicator (RSSI) threshold and a power headroom (PH) threshold.
35
[Claim 5]
A communication device according to any one of claims 2 to 4, wherein the
control ler is further con figu r ed to control the communication device to receive
assistance information (e.g. indicating a priority / priority order associated with
the at least one non-LTE RAT and/or comprising system information 5 associated
with the at least one non-LTE RAT) to assist with selection of and/or connection to
at least one non-LTE radio access technology (RAT) for establ ishing a voice call .
[Claim 6]
10 A communication device according to claim 5, wherein the controller is
further con figu r ed to control the communication device to select a non-LTE RAT
for the continuation of voice communication, based on the assistance information.
[Claim 7]
15 A communication device according to claim 5 or 6, wherein the controller
is further co n figu r ed to control the communication device to connect to non-LTE
RAT to establish a voice call , based on the assistance information.
[Claim 8]
20 A communication device according to any one of claims 2 to 7, wherein the
at least one threshold comprises a power headroom (PH) threshold and wherein the
control ler is further configured to control the communicat ion device transmit a PH
report to the base station based on the PH threshold.
25 [Claim 9]
A base station for a long term evolution (LTE) communicat ion system, the
base stat ion comprising:
a controller and a transceiver, wherein the controller is co n figu red to
control the base station to:
30 establish and engage in Voice over LTE (VoLTE) communication via a
communicat ion connection with a communication device; and
transmit , to the communication device, informat ion indicating a cri terion
for determining whether VoLTE communication via a communication connection
with the base station can be sustained. (Deleted)
36
[Claim 10]
A base station according to claim 9, wherein the controller is further
con figu red to control the base station to: transmi t, to the communication device,
assistance information (e.g. indicating a priority/ priority order 5 associated wi th at
least one non-LTE RAT and/or comprising system information associated with the
at least one non- LTE RAT) to assist with selection of and/or connection to at least
one non-LTE radio access technology (RAT) for establishing a voice call.
10 [Claim 11]
A communication device for a long term evolution (LTE) communication
system, the communication device comprising:
a controller and a transceiver, wherein the controller is co n figu red to
control the communication device to:
15 establish and engage in Voice over LTE (VoLTE) communication via a
communicat ion connection with a base station;
perform signal measurements for signals received from the base station;
provide at least one result of said signal measurements, to the base station,
while the communication device is engaged in an attempt to establish VoLTE
20 communicat ion via the communication connection;
receive, from the base station, responsive to provision of the at least one
result of said signal measurements, a message indicating that the communication
connection cannot be sustained; and
establish, on receipt of said message indicating that the communication
25 connection cannot be sustained, a communication connection via a non-LTE radio
access technology (RAT) in order to establ ish or maintain a voice call via that
non-LTE RAT. (Deleted)
[Claim 12]
30 A communication device according to claim 11, wherein the message
indicating that the communicat ion connect ion cannot be sustained comprises an
indication that a cause of the message is voice call continuity. (Deleted)
[Claim 13]
37
A communication device according to claim 11 or 12, wherein the at least
one result of said signal measurements are provided to the base station in a Radio
Resource Control (RRC) Connect ion Complete message; and wherein the message
indicating that the communicat ion connect ion cannot be sustained comprises an
RRC Connection Release 5 message. (Deleted)
[Claim 14]
A communication device according to claim 11 or 12, wherein the at least
one result of said signal measurements are provided to the base station in a Radio
10 Resource Control (RRC) Connect ion Request message; and wherein the message
indicating that the communicat ion connect ion cannot be sustained comprises an
RRC Connection Reject message. (Deleted)
[Claim 15]
15 A communication device according to any one of claims 11 to 14, wherein
said at least one result of the signal measurements comprises an indicator (e.g. a
one bit indicator) to indicate whether or not the signal measurements meet at least
one pre-determined criterion. (Deleted)
20 [Claim 16]
A communication device according to any one of claims 11 to 15, wherein
the controller is further con figu r ed to control the communication device to:
determine whether or not the signal measurements meet the at least one
pre-determined criterion based on a comparison of said signal measurements with
25 at least one threshold. (Deleted)
[Claim 17]
A communication device according to claim 16, wherein the at least one
threshold is a signal strength threshold below which VoLTE communicat ion is not
30 considered sustainable. (Deleted)
[Claim 18]
A communication device according to claim 12, wherein the control ler is
further con figu r ed to control the communication device to: provide the indication
38
that a cause of the message is voice call continuity to the non-LTE RAT when the
communicat ion connection via the non-LTE RAT is established. (Deleted)
[Claim 19]
A base station for a long term evolution (LTE) communicat 5 ion system, the
base stat ion comprising:
a controller and a transceiver, wherein the controller is co n figu red to
control the base station to:
establish and engage in Voice over LTE (VoLTE) communication via a
10 communicat ion connection with a communication device;
receive, from the communicat ion device, while the base station is engaged
in an attempt to establish VoLTE communication via the communication
connection, at least one result of signal measurements made by the communication
device;
15 determine, based on the received at least one result of the signal
measurements, whether or not the communication connection can be sustained; and
transmit , to the communication device, when it has been determined that
the communication connect ion cannot be sustained, a message indicating that the
communicat ion connection cannot be sustained. (Deleted)
20
[Claim 20]
A communication device for a long term evolution (LTE) communication
system, the communication device comprising:
a controller and a transceiver wherein the control ler is con figu r ed to control
25 the communication device to:
setup and engage in VoLTE communication via a communication
connection with a base station;
receive, when the communicat ion device is engaged in at least one of: (i)
ongoing VoLTE communication via the communicat ion connect ion; and (ii) an
30 attempt to establish VoLTE communication via the communication connection,
from the base station, a message indicating that the communication connection
cannot be sustained, wherein the message comprises an indication that a cause of
the message is voice call continuity; and
establish, on receipt of said message indicating that the communication
39
connection cannot be sustained, a communication connection via a non- LTE radio
access technology (RAT) in order to establ ish or maintain a voice call via that
non-LTE radio access technology (RAT). (Deleted)
5 [Claim 21]
A communication device according to claim 20, wherein the control ler is
further con figu r ed to control the communication device to: receive assistance
informat ion (e.g. indicating a priority / priority order associated with the at least
one non-LTE RAT and/or comprising system information associated with the at
10 least one non-LTE RAT) to assist with selection of and/or connection to the
non-LTE RAT for establishing or maintaining the voice cal l. (Deleted)
[Claim 22]
A communication device according to claim 21, wherein the control ler is
15 further configured to control the communication device to: select the non-LTE RAT
for continuation of voice communication, based on the assistance information.
[Claim 23]
A communication device according to any one of claims 20 to 22, wherein
20 the controller is further configured to control the communication device to: provide
the indication that a cause of the message is voice call continui ty to the non-LTE
RAT when the communication connect ion via the non-LTE RAT is established.
[Claim 24]
25 A base station fora long term evolution (LTE) communication system, the
base stat ion comprising:
a controller and a transceiver wherein the control ler is con figu r ed to control
the base station to:
establish and engage in VoLTE communication via a communication
30 connection with a communicat ion device;
determine, when the base stat ion is engaged in at least one of: (i) ongoing
VoLTE communication via the communicat ion connection; and (ii) an attempt to
establish VoLTE communication via the communicat ion connect ion, that the
communicat ion connection cannot be sustained; and
40
transmit , to the communication device, when it has been determined that
the communication connect ion cannot be sustained, a message indicating that the
communicat ion connection cannot be sustained, wherein the message comprises an
indication that a cause of the message is voice call continuity.
5
[Claim 25]
A base station according to claim 24, wherein the controller is further
con figu red to control the base station to: transmi t, to the communication device,
assistance information leg. indicating a priority/ priority order associated with the
10 at least one non-LTE RAT and/or comprising system information associated with
the at least one non- LTE RAT) to assist with selection of and/or connection to at
least one non-LTE radio access technology (RAT) for establishing a voice call.
[Claim 26]
15 A base station according to claim 24 or 25, wherein the controller is further
configured to control the base station to: transmit, to a mobility management entity
(MME), a further message indicating that the communication connect ion with the
communicat ion device cannot be sustained.
20 [Claim 27]
A base station according to claim 26, wherein the further message
indicating that the communicat ion connect ion with the communication device
cannot be sustained comprises a n oti ficati o n that the communication device may
establish a communication connection via a non- LTE RAT in order to establish or
25 maintain a voice call via that non- LTE RAT.
[Claim 28]
A method performed by a communicat ion device operable to establish and
engage in Voice over LTE (VoLTE) communication via a communication
30 connection with a base station, the method comprising:
obtaining information indicating at least one criterion for determining
whether VoLTE communication via the communicat ion connect ion with the base
station can be sustained;
performing signal measurements for signals received from the base station;
41
and
determining whether VoLTE communication via the communicat ion
connection with the base station can be sustained based on whether or not the
signal measurements meet the at least one cri terion.