FORM 2
THE PATENTS ACT, 1970 (39 of 1970) THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
TITLE OF THE INVENTION SYSTEM AND METHOD FOR EPS FALLBACK
APPLICANT
JIO PLATFORMS LIMITED
of Office-101, Saffron, Nr. Centre Point, Panchwati 5 Rasta, Ambawadi, Ahmedabad -
380006, Gujarat, India; Nationality : India
The following specification particularly describes
the invention and the manner in which
it is to be performed

RESERVATION OF RIGHTS
[001] A portion of the disclosure of this patent document contains material
which is subject to intellectual property rights such as, but are not limited to,
copyright, design, trademark, integrated circuit (IC) layout design, and/or trade
5 dress protection, belonging to Jio Platforms Limited (JPL) or its affiliates (herein
after referred as owner). The owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all rights whatsoever. All rights to such intellectual property are fully reserved by the owner. 10
TECHNICAL FIELD
[002] The present disclosure relates to a field of 5G standalone (SA)
cellular technology, and specifically to a system and a method for Evolved Packet System Fallback (EPSFB). 15
BACKGROUND
[003] The following description of related art is intended to provide
background information pertaining to the field of the disclosure. This section may include certain aspects of the art that may be related to various features of the
20 present disclosure. However, it should be appreciated that this section be used only
to enhance the understanding of the reader with respect to the present disclosure, and not as admissions of prior art.
[004] In general, voice over New Radio (NR) with Evolved Packet System
Fallback (EPSFB) may be defined as a mobility procedure where a network triggers
25 the procedure for a User Equipment (UE) to change Radio Access from 5G to 4G.
EPSFB may enable mobile phones to use a 5G Core (5GC) with NR, but a Radio Access Network (RAN) may trigger moving the phone, i.e., Long-Term Evolution (LTE) connected to an Evolved Packet Core (EPC) during call establishment. EPSFB call although initiates on NR but eventually falls back to an LTE layer and
30 succeeds over an EPC core network that is also connected to an Internet Protocol
2

(IP) Multimedia Subsystem (IMS), effectively making it a Voice over Long-Term Evolution (VoLTE) call after the fallback.
[005] Conventionally, a gNodeB (gNB) may configure the UE for B1
measurements and set a wait timer to receive a B1 measurement report, after getting
5 a Packet Data Unit (PDU) session modification request from an Access and
Mobility Management Function (AMF) for Quality of Service (QoS) flow of IMS voice. Due to some uncertainty, if the UE fails to send the B1 measurement before the wait timer expiry, EPSFB procedure via Inter Radio Access Technology (IRAT) handover fails and the UE is not able to make voice call. This issue is also observed
10 when the EPSFB procedure via release with redirection to reported frequency is
enabled. The gNB waits for the B1 measurement report from UE to take decision of release with redirection.
[006] After getting the B1 measurement report from the UE, the gNB may
initiate IRAT handover, but when the UE sends the B1 measurement report for LTE
15 cell, which is not available in the NR to LTE neighbour list, EPSFB procedure fails,
and the UE is not able to make voice call on system. When the gNB initiates IRAT handover procedure after receiving the B1 measurement report from the UE for valid LTE neighbour already available in NR to LTE neighbour list and handover fails in either preparation phase or in execution phase, the EPSFB procedure fails,
20 and the UE is not able to make voice call on system and user faces the bad
experience.
[007] Further, EPS fallback may not be triggered by an Outdoor Small Cell
(ODSC) when it receives an A3 event Measurement Report (MR) for Intra-FA handover to the neighbour cell while it is waiting for B1 MR to start EPSFB. EPSFB
25 may not be triggered, when the UE already sent the A3 event measurement, the
gNB is preparing for Intra-FA handover, and the PDU session modification request is received from the AMF for QOS flow of IMS voice.
[008] There is, therefore, a need in the art to improve state of automatically
allowing the user to make voice call on LTE network when the UE is not capable
30 to make voice call on the 5G SA network via redirection or via handover.
3

DEFINITION
[009] As used in the present disclosure, the following terms are generally
intended to have the meaning as set forth below, except to the extent that the context
in which they are used to indicate otherwise.
5 [0010] The term B1 MR as used herein, refers to B1 measurement report.
B1 is a measurement of the signal quality within a long-term evolution (LTE) system. B1 is measured at the eNodeB (eNB) and indicates the signal quality that a user equipment (UE) would receive from a femtocell if it were connected to that femtocell.
10 [0011] The term IRAT HO as used herein, refers to inter radio access
technology handover. IRAT is mainly used for handover between different RAT. The UE while in one RAT performs neighbour cell measurements and sends measurement report to the network. Based on this measurement report provided by mobile terminal, network can initiate handover from one RAT to the other RAT.
15 [0012] The term EPSFB as used herein, refers to evolved packet system
fallback. The EPSFB call is coordinated between a 5G system and evolved packet
system (EPS), and transition of the call happens from 5G NR to the legacy LTE
network after the negotiation of both UE and network capabilities,
[0013] The term E-UTRA as used herein, refers to evolved UMTS
20 terrestrial radio access. The E-UTRA is the air interface of 3rd generation
partnership project (3GPP) long term evolution (LTE) upgrade path for mobile networks.
[0014] The term EARFCN as used herein, refers to evolved universal
terrestrial radio access (E-UTRA) absolute radio frequency channel number
25 (EARFCN). In LTE, the carrier frequency in the uplink and downlink is designated
by EARFCN. The EARFCN uniquely identify the LTE band and carrier frequency.
OBJECTS OF THE PRESENT DISCLOSURE
[0015] It is an object of the present disclosure to automatically allow a user
30 to make voice call on a Long-Term Evolution (LTE) network when a User
4

Equipment (UE) is not capable to make voice call on a 5G Standalone (SA) network
via redirection or via handover.
[0016] It is an object of the present disclosure to allow the user to release
the 5G SA network and redirect to measured Evolved Universal Terrestrial Radio
5 Access (E-UTRA) Absolute Radio Frequency Channel Number (EARFCN) of LTE
band to proceed an Evolved Packet System Fallback (EPSFB) call successfully, if
there is unprecedented failure during the handover procedure.
[0017] It is an object of the present disclosure to allow the user to redirect
to LTE Radio Access Technology (RAT) on default frequency band configured in
10 gNodeB (gNB) during the emergency voice call or when B1 measurement delayed
or not received, or while the UE is active with other procedure or stuck in race
conditions.
[0018] It is an object of the present disclosure to improvise the network
capabilities.
15 [0019] It is an object of the present disclosure to enhance the user
experience.
[0020] It is an object of the present disclosure to provide seamless network
services to users.
[0021] It is an object of the present discourse to cater all sorts of voice calls.
20
SUMMARY
[0022] In an exemplary embodiment, the present invention discloses a
method for an evolved packet system fallback (EPSFB). The method comprising receiving, by a gNodeB, at least one packet data unit (PDU) session modification
25 request related to a voice call for a user equipment (UE) connected to a first
network. The method comprising determining if the gNodeB is active with the UE on at least one activity after receiving the PDU session modification request. When it is determined that the gNodeB is active with the UE on the at least one activity: aborting, by the gNodeB, the at least one activity; performing, by the gNodeB, a
30 release of the UE from the connection with the first network and redirect the UE on
a predefined configured frequency band of a second network. When it is determined
5

that the gNodeB is not active with the at least one activity: configuring the UE with
a first event measurement, starting a timer having a start time and an end time and
performing, by the gNodeB, a release of the UE from the connection with the first
network and redirect the UE on the predefined configured frequency band of the
5 second network. The method comprising performing, by the gNodeB, a release of
the UE from the connection with the first network and redirect the UE on the predefined configured frequency band of the second network when at least one of the following conditions are met a first measurement report (MR) associated with the one first event measurement is not received between the start time and the end
10 time of the timer, and at least one second MR related to at least one second event
measurement is received from the UE after the UE is configured with the first event measurement.
[0023] In some embodiments, the at least one UE is registered with at least
one radio resource control (RRC) active mode with a downlink (DL) data session
15 and an uplink (UL) data session.
[0024] In some embodiments, the at least one activity includes at least one
inter-radio access technology (RAT) handover procedure.
[0025] In some embodiments, the first MR related to the first event
measurement received from the UE is a B1 measurement report.
20 [0026] In some embodiments, the at least one second event measurement
includes a measurement related to a A3 event and a A5 event.
[0027] In some embodiments, the PDU session modification request is
received from an access & mobility management function (AMF) associated with the first network.
25 [0028] In some embodiments, the predefined configured frequency band of
the second network is associated with an evolved universal terrestrial radio access (E-UTRA) absolute radio frequency channel number (EARFCN).
[0029] In some embodiments, the first network is a 5G network and the
second network is a 4G long-term evolution (LTE) network.
6

[0030] In some embodiments, the EPSFB is triggered through a handover
procedure or a redirection procedure depending upon a plurality of radio frequency (RF) conditions of the UE.
[0031] In some embodiments, the plurality of radio frequency (RF)
5 conditions of the UE depends on a geographical area where the UE is located.
[0032] In some embodiments, the EPSFB is triggered through a handover
procedure or a redirection procedure depending upon the at least one race condition
generated in the first network.
[0033] In some embodiments, the gNodeB performs an emergency release
10 of the UE from the connection with the first network and performs an emergency
redirection of the UE on the predefined configured frequency band of the second network.
[0034] In some embodiments, the gNodeB performs the emergency
redirection of the UE on the predefined configured frequency band of the second
15 network instantly.
[0035] In some embodiments, the predefined configured frequency band is
determined based on at least one of UE capability information message received from the UE, a message from the AMF that comprises an indication regarding a possibility of redirection for the EPSFB, N26 interface availability configuration
20 and the plurality of RF conditions of the UE.
[0036] In an exemplary embodiment, the present invention discloses a
system for an evolved packet system fallback (EPSFB). The system is configured to receive, by a gNodeB, at least one packet data unit (PDU) session modification request related to a voice call for a user equipment (UE) connected to a first
25 network. The system is configured to determine if the gNodeB is active with the
UE on at least one activity after receiving the PDU session modification request. When it is determined that the gNodeB is active with the UE on at least one activity: abort, by the gNodeB, the at least one activity; perform, by the gNodeB, a release of the UE from the connection with the first network and redirect the UE on a
30 predefined configured frequency band of a second network. When it is determined
that the gNodeB is not active with the at least one activity: configure the UE with a
7

first event measurement; start a timer having a start time and an end time, perform,
by the gNodeB, a release of the UE from the connection with the first network and
redirect the UE on the predefined configured frequency band of the second network.
The system is configured to perform, by the gNodeB, a release of the UE from the
5 connection with the first network and redirect the UE on the predefined configured
frequency band of the second network when at least one of the following conditions are met a first measurement report (MR) associated with the one first event measurement is not received between the start time and the end time of the timer, and at least one second MR related to at least one second event measurement is
10 received from the UE after the UE is configured with the first event measurement.
[0037] In some embodiments, the at least one UE is registered with at least
one radio resource control (RRC) active mode with a downlink (DL) data session
and an uplink (UL) data session.
[0038] In some embodiments, the at least one activity includes at least one
15 inter-radio access technology (RAT) handover procedure.
[0039] In some embodiments, the first MR related to the first event
measurement received from the UE is a B1 measurement report.
[0040] In some embodiments, the at least one second event measurement
includes a measurement related to a A3 event and a A5 event.
20 [0041] In some embodiments, the PDU session modification request is
received from an access & mobility management function (AMF) associated with the first network.
[0042] In some embodiments, the predefined configured frequency band of
the second network is associated with an evolved universal terrestrial radio access
25 (E-UTRA) absolute radio frequency channel number (EARFCN).
[0043] In some embodiments, the first network is a 5G network and the
second network is a 4G long-term evolution (LTE) network.
[0044] In some embodiments, the EPSFB is triggered through a handover
procedure or a redirection procedure depending upon a plurality of radio frequency
30 (RF) conditions of the UE.
8

[0045] In some embodiments, the plurality of radio frequency (RF)
conditions of the UE depends on a geographical area where the UE is located.
[0046] In some embodiments, the EPSFB is triggered through a handover
procedure or a redirection procedure depending upon the at least one race condition
5 generated in the first network.
[0047] In some embodiments, the gNodeB performs an emergency release
of the UE from the connection with the first network and performs an emergency redirection of the UE on the predefined configured frequency band of the second network.
10 [0048] In some embodiments, the gNodeB performs the emergency
redirection of the UE on the predefined configured frequency band of the second network instantly.
[0049] In some embodiments, the predefined configured frequency band is
determined based on at least one of UE capability information message received
15 from the UE, a message from the AMF that comprises an indication regarding a
possibility of redirection for the EPSFB, N26 interface availability configuration and the plurality of RF conditions of the UE.
[0050] In an exemplary embodiment, the present invention discloses a
network comprising at least one network element for performing an evolved packet
20 system fallback (EPSFB). The at least one network element is configured to receive,
by a gNodeB, at least one packet data unit (PDU) session modification request related to a voice call for a user equipment (UE) connected to the network. The at least one network element is configured to determine if the gNodeB is active with the UE on at least one activity after receiving the PDU session modification request.
25 The at least one network element is configured to responsive to determining that
the gNodeB is active with the at least one activity: abort, by the gNodeB, the at least one activity, perform, by the gNodeB, a release of the UE from the connection with the network and redirect the UE on a predefined configured frequency band of another network. The at least one network element is configured to responsive to
30 determining that the gNodeB is not active with the at least one activity: configure
the UE with a first event measurement and start a timer having a start time and an
9

end time. The at least one network element is configured to perform, by the
gNodeB, a release of the UE from the connection with the network and redirect the
UE on the predefined configured frequency band of the another network when at
least one of the following conditions are met a first measurement report (MR)
5 associated with the first event measurement is not received between the start time
and the end time of the timer and at least one second MR related to at least one
second event measurement from the UE after the UE is configured with the first
event measurement.
[0051] In an exemplary embodiment, the present invention discloses a user
10 equipment (UE) attached to a network. The network comprising at least one
network element for performing an evolved packet system fallback (EPSFB). The at least one network element is configured to receive, by a gNodeB, at least one packet data unit (PDU) session modification request related to a voice call for the UE. The at least one network element is configured to determine if the gNodeB is
15 active with the UE on at least one activity after receiving the PDU session
modification request. The at least one network element is configured to responsive to determining that the gNodeB is active with the at least one activity: abort, by the gNodeB, the at least one activity, perform, by the gNodeB, a release of the UE from the connection with the network and redirect the UE on a predefined configured
20 frequency band of another network. The at least one network element is configured
to responsive to determining that the gNodeB is not active with the at least one activity: configure the UE with a first event measurement and start a timer having a start time and an end time. The at least one network element is configured to perform, by the gNodeB, a release of the UE from the connection with the network
25 and redirect the UE on the predefined configured frequency band of the another
network when at least one of the following conditions are met a first measurement report (MR) associated with the first event measurement is not received between the start time and the end time of the timer and at least one second MR related to at least one second event measurement from the UE after the UE is configured with
30 the first event measurement.
10

BRIEF DESCRIPTION OF THE DRAWINGS
[0052] In the figures, similar components and/or features may have the
same reference label. Further, various components of the same type may be
distinguished by following the reference label with a second label that distinguishes
5 among the similar components. If only the first reference label is used in the
specification, the description is applicable to any one of the similar components
having the same first reference label irrespective of the second reference label.
[0053] The diagrams are for illustration only, which thus is not a limitation
of the present disclosure, and wherein:
10 [0054] FIG. 1 illustrates an exemplary network architecture (100) in which
or with which embodiments of the present disclosure may be implemented.
[0055] FIG. 2 illustrates an exemplary block diagram (200) of an Evolved
Packet System Fallback (EPSFB) release system, in accordance with an
embodiment of the present disclosure.
15 [0056] FIG. 3 illustrates an exemplary flow mechanism (300) of 5G to 4G
Inter-Radio Access Technology (IRAT) handover, in accordance with an
embodiment of the present disclosure.
[0057] FIG. 4 illustrates an exemplary flow mechanism (400) for
performing 5G to 4G release with redirection, in accordance with an embodiment
20 of the present disclosure.
[0058] FIG. 5 illustrates an exemplary flow mechanism (500) of EPSFB by
emergency redirection, in accordance with an embodiment of the present
disclosure.
[0059] FIG. 6 illustrates an exemplary flow diagram (600) for performing
25 emergency release with redirection on predefined Long-Term Evolution (LTE)
band, in accordance with an embodiment of the present disclosure.
[0060] FIG. 7 illustrates an exemplary computer system (700) in which or
with which embodiments of the present disclosure may be implemented.
30 LIST OF REFERENCE NUMERALS
11

100 - Network architecture
102 - A plurality of users
104, 310, 410, 510 - User equipment (UE)
106 - Network
5 108 - Evolved packet system fallback (EPSFB) release system
200 - Block Diagram
202 - A plurality of processor(s)
204 - Memory
206 - A plurality of interface(s)
10 208 - Processing engine
210 - Configuration engine
212 - Redirection engine
214 - Database
300 - Flow diagram
15 320, 420, 520 - gNodeB
330, 430, 530 - Access and mobility management function (AMF)
340, 440 - Mobile management entity (MME)
350, 450 - eNodeB
400 - Flow diagram
20 500 - Flow diagram
600 - Flow diagram
700 - A computer system
710 - External storage device
12

720 - Bus
730 - Main memory
740 - Read only memory
750 - Mass storage device
5 760 - Communication port(s)
770 - Processor
DETAILED DESCRIPTION
[0061] The following is a detailed description of embodiments of the
disclosure depicted in the accompanying drawings. The embodiments are in such
10 detail as to clearly communicate the disclosure. However, the amount of detail
offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
15 [0062] Generally, Voice over New Radio (NR) with Evolved Packet System
Fallback (EPSFB) may be defined as a mobility procedure where a network triggers the procedure for a User Equipment (UE) to change Radio Access from 5G to 4G. EPSFB may enable phones to use a 5G Core (5GC) with NR, but a Radio Access Network (RAN) may trigger moving the phone Long Term Evolution (LTE)
20 connected to an Evolved Packet Core (EPC) during call establishment. EPSFB call
although initiates on NR but eventually falls back to an LTE layer and succeeds over an EPC core network that is also connected to an Internet Protocol Multimedia Subsystem (IMS), effectively making it Voice over Long-Term Evolution (VoLTE) call after the fallback.
25 [0063] EPSFB call may be coordinated between a 5G System (5GS), and an
Evolved Packet System (EPS) systems and transition of the call happens from 5G NR to a legacy LTE network after the negotiation of both UE and network capabilities. At the stage of UE registration, the 5GS and UE capabilities are
13

negotiated during the initial registration process to conclude if EPSFB or Voice over New Radio (VoNR) may be utilized.
[0064] To maintain the voice service in Next-Generation Radio Access
Network (NG-RAN), the UE provides additional capabilities over a Radio Resource
5 Control (RRC) layer, that may be used to determine accurate NR voice support
options. In UE capability information message in NR RRC layer, UE may convey
capabilities related to the IMS. After voice over IMS is determined, the UE may
start IMS registration and then may make VoNR (or EPSFB) calls.
[0065] At the call initiation, if a request for establishing the QoS flow for
10 IMS voice reaches the NG-RAN, NG-RAN may be configured to support EPS
fallback for IMS voice and decides to trigger fallback to EPS, taking into account UE capabilities, indication from Access and Mobility Management Function (AMF) that "Redirection for EPS fallback for voice is possible", network configuration (e.g. N26 availability configuration) and radio conditions, then the
15 redirection or handover procedure to LTE starts. After the UE camps successfully
on the LTE cell and initiates Tracking Area Update procedure (TAU) or a fresh
attach process (in case of TAU failure or no support for N26), the call continues
normally as VoLTE call.
[0066] The proposed disclosure enhances user experience by increasing the
20 successful attempts of transition from 5G to 4G for UE which are not capable of
VoNR. The proposed disclosure also reduces the delay in transition from 5G to 4G to make a successful voice call. The EPSFB method improves the EPSFB success rate by allowing the user or the UE to take proactive decision to move on to other Radio Access Technology (RAT) when the UE is not capable to make voice call on
25 a 5G Standalone (SA) RAT. The EPSFB method may help the UE to avoid various
race condition generated in the system and blocking the UE to select 4G RAT to make voice call. The method may also help the user and the UE to reduce a transition time from 4G to 5G via Inter Radio Access Technology (IRAT) Handover during the EPSFB. The method may trigger the EPSFB via Handover or via
30 Redirection depending upon the situation and Radio Frequency (RF) conditions on
a geography where the UE is located. The method may allow the gNB to take quick
14

decision of EPSFB Handover based or redirection based, depending on the RF condition of UE, and Race condition of the system.
[0067] FIG. 1 illustrates an exemplary network architecture (100) in which
or with which embodiments of the present disclosure may be implemented.
5 [0068] Referring to FIG. 1, the network architecture (100) may include one
or more user equipments (104-1, 104-2…104-N) associated with one or more users (102-1, 102-2…102-N) in an environment. A person of ordinary skill in the art will understand that one or more users (102-1, 102-2…102-N) may be individually referred to as the user (102) and collectively referred to as the users (102). Similarly,
10 a person of ordinary skill in the art will understand that one or more user equipments
(104-1, 104-2…104-N) may be individually referred to as the user equipment (104) and collectively referred to as the user equipment (104). A person of ordinary skill in the art will appreciate that the terms “computing device(s)” and “user equipment” may be used interchangeably throughout the disclosure. Although three user
15 equipments (104) are depicted in FIG. 1, however any number of the user
equipments (104) may be included without departing from the scope of the ongoing description.
[0069] In an embodiment, the user equipment (104) may include smart
devices operating in a smart environment, for example, an Internet of Things (IoT)
20 system. In such an embodiment, the user equipment (104) may include, but is not
limited to, smart phones, smart watches, smart sensors (e.g., mechanical, thermal, electrical, magnetic, etc.), networked appliances, networked peripheral devices, networked lighting system, communication devices, networked vehicle accessories, networked vehicular devices, smart accessories, tablets, smart television (TV),
25 computers, smart security system, smart home system, other devices for monitoring
or interacting with or for the users (102) and/or entities, or any combination thereof. A person of ordinary skill in the art will appreciate that the user equipment (104) may include, but is not limited to, intelligent, multi-sensing, network-connected devices, that can integrate seamlessly with each other and/or with a central server
30 or a cloud-computing system or any other device that is network-connected.
15

[0070] In an embodiment, the user equipment (104) may include, but is not
limited to, a handheld wireless communication device (e.g., a mobile phone, a smart
phone, a phablet device, and so on), a wearable computer device(e.g., a head-
mounted display computer device, a head-mounted camera device, a wristwatch
5 computer device, and so on), a Global Positioning System (GPS) device, a laptop
computer, a tablet computer, or another type of portable computer, a media playing device, a portable gaming system, and/or any other type of computer device with wireless communication capabilities, and the like. In an embodiment, the user equipment (104) may include, but is not limited to, any electrical, electronic,
10 electro-mechanical, or an equipment, or a combination of one or more of the above
devices such as virtual reality (VR) devices, augmented reality (AR) devices, laptop, a general-purpose computer, desktop, personal digital assistant, tablet computer, mainframe computer, or any other computing device, wherein the user equipment (104) may include one or more in-built or externally coupled accessories
15 including, but not limited to, a visual aid device such as a camera, an audio aid, a
microphone, a keyboard, and input devices for receiving input from the user (102) or the entity such as touch pad, touch enabled screen, electronic pen, and the like. A person of ordinary skill in the art will appreciate that the user equipment (104) may not be restricted to the mentioned devices and various other devices may be
20 used.
[0071] Referring to FIG. 1, the user equipment (104) may communicate
with a system (108), for example, an Evolved Packet System Fallback (EPSFB) release system, through a network (106). In an embodiment, the network (106) may include at least one of a Fifth Generation (5G) network, or the like. The network
25 (106) may enable the user equipment (104) to communicate with other devices in
the network architecture (100) and/or with the system (108). The network (106) may include a wireless card or some other transceiver connection to facilitate this communication. In another embodiment, the network (106) may be implemented as, or include any of a variety of different communication technologies such as a
30 wide area network (WAN), a local area network (LAN), a wireless network, a
16

mobile network, a Virtual Private Network (VPN), the Internet, the Public Switched Telephone Network (PSTN), or the like.
[0072] In accordance with embodiments of the present disclosure, the
system (108) may be designed and configured for automatically allowing the user
5 to make Voice call on LTE network when the UE is not capable to make Voice call
on 5G SA network via redirection or via Handover. Further, the system (108) may allow the user to redirect to LTE RAT on default frequency band configured in gNB during the emergency voice call or when B1 measurement delayed or not received, or while UE is active with other procedure or stuck in race conditions.
10 [0073] Although FIG. 1 shows exemplary components of the network
architecture (100), in other embodiments, the network architecture (100) may include fewer components, different components, differently arranged components, or additional functional components than depicted in FIG. 1. Additionally, or alternatively, one or more components of the network architecture (100) may
15 perform functions described as being performed by one or more other components
of the network architecture (100).
[0074] FIG. 2 illustrates an exemplary block diagram of the EPSFB release
system (200), in accordance with an embodiment of the present disclosure. It may be appreciated that the system (200) may be similar to the system (108) of FIG. 1
20 in its functionality.
[0075] In an embodiment, and as shown in FIG. 2, the system (200) may
include one or more processors (202). The one or more processors (202) may be implemented as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, logic circuitries, and/or any
25 devices that manipulate data based on operational instructions. Among other
capabilities, the one or more processor(s) (202) may be configured to fetch and execute computer-readable instructions stored in a memory (204) of the system (200). The memory (204) may store one or more computer-readable instructions or routines, which may be fetched and executed to create or share the data units over
30 a network service. The memory (204) may comprise any non-transitory storage
device including, for example, volatile memory such as Random-Access Memory
17

(RAM), or non-volatile memory such as Erasable Programmable Read-Only Memory (EPROM), flash memory, and the like.
[0076] In an embodiment, the system (200) may also comprise an
interface(s) (206). The interface(s) (206) may comprise a variety of interfaces, for
5 example, a variety of interfaces, for example, interfaces for data input and output
devices, referred to as I/O devices, storage devices, and the like. The interface(s) (206) may facilitate communication of the system (200) with various devices coupled to it. The interface(s) (206) may also provide a communication pathway for one or more components of the system (200). Examples of such components
10 include, but are not limited to, processing engine(s) (208) and a database (214).
[0077] In an embodiment, the processing engine(s) (208) may be
implemented as a combination of hardware and programming (for example, programmable instructions) to implement one or more functionalities of the processing engine(s) (208). In examples described herein, such combinations of
15 hardware and programming may be implemented in several different ways. For
example, the programming for the processing engine(s) (208) may be processor executable instructions stored on a non-transitory machine-readable storage medium and the hardware for the one or more processors (202) may comprise a processing resource (for example, one or more processors), to execute such
20 instructions. In the present examples, the machine-readable storage medium may
store instructions that, when executed by the processing resource, implement the processing engine(s) (208). In such examples, the system (200) may comprise the machine-readable storage medium storing the instructions and the processing resource to execute the instructions, or the machine-readable storage medium may
25 be separate but accessible to the system (200) and the processing resource. In other
examples, the processing engine(s) (208) may be implemented by electronic circuitry.
[0078] In an embodiment, the database (214) may comprise data that may
be either stored or generated as a result of functionalities implemented by any of
30 the components of the processor(s) (202) or the processing engine(s) (208) or the
18

system (200). In an exemplary embodiment, the processing engine(s) (208) may include a configuration engine (210), and a redirection engine (212).
[0079] In an embodiment, the configuration engine (210) may receive a
Packet Data Unit (PDU) session modification request from an Access and Mobility
5 Management Function (AMF) for voice call. After receiving the PDU modification
request, a gNodeB (gNB) may abort other activities if it is active with other intra 5G system handover procedure, like waiting for A3 or A5 event Measurement Report (MR) from UE or if MR received and preparing for Intra 5G system handover and performs emergency release with redirection on predefined
10 configured LTE Band. If the gNB is not active with other internal procedure while
receiving PDU modification request for 5G Quality of Service (QoS) identifier
(5QI), the configuration engine (210) may configure the UE for B1 measurement
report and start process Timer.
[0080] In an embodiment, the redirection engine (212) may redirect the UE
15 to release with redirection on predefined configured LTE band, if any A3 MR is
received from the UE configured in previous Radio Resource Control (RRC) reconfiguration, even after configuration of B1. The A3 event occurs when a neighbouring cell's signal becomes offset better than the serving cell. It is used in both intra-frequency and inter-frequency handovers. The A5 event occurs when a
20 serving cell becomes worse than threshold-1 and neighbor becomes better than
threshold-2.
[0081] Although FIG. 2 shows an exemplary block diagram (200) of the
EPSFB release system, in other embodiments, the EPSFB release system (200) may include fewer components, different components, differently arranged components,
25 or additional functional components than depicted in FIG. 1. Additionally, or
alternatively, one or more components of the EPSFB release system (200) may
perform functions described as being performed by one or more other components
of the EPSFB release system (200).
[0082] FIG. 3 illustrates an exemplary flow mechanism (300) of 5G to 4G
30 Inter-Radio Access Technology (RAT) handover, in accordance with an
embodiment of the present disclosure.
19

[0083] With respect to FIG. 3, N26 interface between Access and Mobility
Management Function (AMF) (330) and Mobility Management Entity (MME)
(340) may use forward relocation procedure, and session management context and
user plane tunnels in core network are exchanged over from Session Management
5 Function/Unified Performance Management (SMF/UPM) to MME/Serving
Gateway (S-GW).
[0084] The AMF (330) sends a packet data unit (PDU) modification request
for 5QI 1 to gNodeB (320). The gNodeB (320) sends a radio resource control (RRC) reconfiguration for B1 measurement and starts a timer (e.g., 500ms). The UE (310)
10 sends the B1 measurement report to the gNodeB (320). The gNodeB (320) sends a
handover required request to the AMF (330) that further sends a forward relocation request to an MME (340). The MME (340) sends a handover request to the eNodeB (350) of a second network (4G LTE network). The eNodeB (350) acknowledges the handover request and the MME (340) forwards a forward relocation request to
15 the AMF (330) that further sends a handover command to the gNodeB (320). The
gNodeB (320) sends a mobility from NR command and a RRC configuration to the UE (310). The mobility from NR command is a critical component in facilitating smooth handovers and transitions from a universal mobile telecommunications system (UMTS) terrestrial radio access network (UTRAN) to 5G new radio (NR).
20 The command provides the necessary instructions and parameters for the UE (310)
to execute a seamless handover, ensuring continuous and reliable communication within the 5G network. The UE (310) configures a random-access channel (RACH) on target with the eNodeB (350) and completes the RRC configuration. The eNodeB (350) notifies the MME (340) regarding the handover and the MME (340)
25 forwards a relocation complete notification to the AMF (330). The AMF (330)
sends a context release command to the gNodeB (320). The AMF (330) forwards a relocation complete acknowledgement to the MME (340). The gNodeB (320) sends a context release complete notification to the AMF (330). The UE (310) initiates a tracking area update (TAU) procedure by sending a TAU request message to the
30 eNodeB (350). The message includes information about the UE’s current location,
such as the new tracking area (TA) it has entered.
20

[0085] FIG. 4 illustrates an exemplary flow mechanism (400) for
performing 5G to 4G release with redirection, in accordance with an embodiment
of the present disclosure. With respect to FIG. 4, 5G radio connection may be
released with a 5G RRC Release instructing UE (410) to reselect to a 4G cell where
5 a new radio connection may be started for the VoLTE call. In this case the UE
context may be transferred from the AMF (430) to the MME (440) over the N26
interface. The choice of method used for EPSFB may depend on UE capability and
5G Core Network Capability.
[0086] The EPSFB release system (108) may automatically allow the user
10 to make Voice call on LTE network when UE (410) is not capable to make Voice
call on 5G SA network via redirection or via Handover. The EPSFB release system (108) may first prioritize the transition from 5G to 4G during EPSFB via handover, if there is unprecedented failure during the handover procedure it will allow user to release the 5G SA network and redirect to measured Evolved Universal Terrestrial
15 Radio Access (E-UTRA) Absolute Radio Frequency Channel Number (EARFCN)
of LTE band to proceed the EPSFB call successfully.
[0087] The EPSFB release system (108) may allow the user to redirect to
LTE RAT on default frequency band configured in gNB during the emergency voice call or when B1 measurement delayed or not received, or while UE (410) is
20 active with other procedure or stuck in race conditions.
[0088] The AMF (430) sends a packet data unit (PDU) modification request
for 5QI 1 to gNodeB (420). The gNodeB (420) sends a radio resource control (RRC) reconfiguration for B1 measurement to the UE (410) and starts a timer (e.g., 500ms). The UE (410) sends the B1 measurement report to the gNodeB (420). The
25 gNodeB (420) sends a release with direction info command to the AMF (430) that
further sends a UE context release command to the gNodeB (420). The gNodeB (420) sends a UE context release complete command to the AMF (430). The UE (410) initiates a tracking area update (TAU) procedure by sending a TAU request message to the eNodeB (450). The message includes information about the UE’s
30 current location, such as the new tracking area (TA) it has entered.
21

[0089] FIG. 5 illustrates an exemplary flow mechanism (500) of EPSFB by
emergency redirection, in accordance with an embodiment of the present
disclosure. With respect to FIG. 5, after receiving the PDU session modification
request from AMF (530) for 5QI 1 (5G QoS Identifier) QOS flow of IMS voice.
5 ThePDU modification request may get rejected by the gNodeB (520). The gNB
(520) may configure the UE (510) for B1 measurements (RRC reconfiguration) and set a wait timer to receive the B1 measurement report. There are chances of two cases to arise:
[0090] Case 1: When measurement report (MR) for any event other than B1
10 is received from the UE before the RRC reconfiguration gets completes (before the
wait timer expiry), then RRC release with redirection is performed by the gNodeB
(520) to the “default frequency”. The default frequency is the same frequency that
is used in “Default redirection” feature. The UE (510) may fail to send the B1
measurement before the wait timer expiry due to some uncertainty. The gNodeB
15 (520) starts release with redirection process to default frequency configured in the
gNodeB (520). This issue may be also observed when the EPSFB procedure via release with redirection to reported frequency is enabled.
[0091] Case 2: When measurement report (MR) for any event other than B1
is received from the UE (510) after the RRC reconfiguration gets completes (after
20 the wait timer expiry), then RRC release with redirection is performed by the
gNodeB (520) to the “default frequency”.
[0092] In an embodiment, in both the scenario of case 1 and case 2 the UE
context release is transferred from the gNodeB (520) to the AMF (530).
[0093] Further, if the measurement report (MR) is received for any event
25 other than B1 before or after the completion of the RRC reconfiguration, then
whether the MR has E-UTRAN Cell Global Identifier (ECGI) or not is not to be
checked by the gNodeB (520) and “Emergency Redirection” should be triggered.
[0094] The E-UTRAN Cell Global Identifier (ECGI) is a critical element in
LTE (Long-Term Evolution) networks that uniquely identifies each cell in the E-
30 UTRAN. It provides valuable information about the cell's identity, enabling various
functionalities and optimization within the network.
22

[0095] In an embodiment, the gNodeB (520) may wait for the B1
measurement report from the UE (510) to take decision of release with redirection,
when timer expires, the gNB (520) starts release with redirection process to default
frequency configured in the gNB (520).
5 [0096] Further, in the prior art, the EPSFB may not be triggered by an
Outdoor Small Cell (ODSC) when it receives an A3 event Measurement Report (MR) for Intra-FA handover to the neighbour cell while it is waiting for B1 MR to start EPSFB. This may be solved by the present invention emergency redirection process because the action to trigger EPSFB may be taken instantly when the MR
10 for any event other than B1 is received while the UE has initiated a voice call.
[0097] Further, in the prior art, the EPSFB may not be triggered when the
UE (510) already sent the A3 event measurement and the gNB (520) is preparing for Intra-FA handover. This may be solved by the present invention emergency redirection process because the action to trigger the EPSFB may be taken instantly
15 while the UE (510) has initiated the voice call.
[0098] Thus, when a normal process (prior art technique) of waiting for B1
MR is followed, then the UE is likely to face ‘Radio Link Failure’ (RLF) due to poor RF in the handover zone. The RLF occurs when the radio link between the user equipment (UE) and the eNodeB (base station) is lost. This can happen due to
20 various reasons such as interference, coverage issues, handover failures, or
equipment malfunction.
[0099] Thus, the present invention solves the drawbacks present in the prior
art and provides a technique that can automatically allow the user to make voice call on LTE network when UE is not capable to make voice call on 5G standalone
25 (SA) network via redirection or via handover. The present invention, prioritize the
transition from 5G to 4G during EPS fall back (FB) via handover, if there is unprecedented failure during the handover procedure it will allow user to release the 5G SA network and redirect to measured evolved universal terrestrial radio access (E-UTRA) absolute radio frequency channel number (EARFCN) of the LTE
30 band to proceed the EPSFB call successfully.
23

[00100] Thus, the present invention allows user to blindly redirect to LTE
RAT on default frequency band configured in gNodeB during the emergency voice
call or when B1 measurement delayed or not received, or while UE is active with
other procedure or stuck in race conditions.
5 [00101] FIG. 6 illustrates an exemplary flow diagram (600) for performing
emergency release with redirection on predefined Long-Term Evolution (LTE) band, in accordance with an embodiment of the present disclosure. With respect to FIG. 6, at 610, UE may be already registered with Radio Resource Control (RRC) active with Downlink (DL) and Uplink (UL) Data Session.
10 [00102] At 620, Packet Data Unit (PDU) session modification request may
be received from an Access and Mobility Management Function (AMF) for voice call.
[00103] At 630, after receiving the PDU modification request, the gNB may
abort other activities if it is active with other intra 5G system handover procedure,
15 like waiting for A3 or A5 MR from UE or if MR is Received and preparing for intra
5G system handover.
[00104] At 640, the gNB may perform emergency release with redirection on
predefined configured LTE Band.
[00105] At 650, if the gNB is not active with other internal procedure while
20 PDU modification request for 5QI 1 is received, the gNB may configure the UE for
B1 measurement report and start process timer.
[00106] At 660, even after configuration of B1, if any A3 MR is received
from the UE configured in previous RRC reconfiguration, the gNB may redirect the UE to release with redirection on predefined configured LTE band.
25 [00107] At 670, when the UE missed to send the B1 measurement report
within a process timer window, the gNB may redirect the UE to release with redirection on predefined configured LTE band.
[00108] In an embodiment, the emergency redirection may be performed by
the gNB after checking mandatory condition, when the PDU modification request
30 for 5QI 1 is received from the AMF:
24

a. When the UE and the GNB are already active with another inter-RAT
handover procedure.
b. After configuring the UE for B1 measurement if UE the does not send the
measurement report within the predefined time configured by process timer,
5 B1 report Timer.
c. After configuring the UE for B1 measurement if the UE reports
measurement for any event other than B1 (A3 or A5).
[00109] These mandatory conditions may check, enable the UE to explore all
network connection options, prior to emergency handover, and optimize the
10 resource usage for emergency handover procedures of the UEs in the network.
[00110] In an exemplary embodiment, the present invention discloses a
method for an evolved packet system fallback (EPSFB). The method comprising receiving, by a gNodeB, at least one packet data unit (PDU) session modification request related to a voice call for a user equipment (UE) connected to a first
15 network. The method comprising determining if the gNodeB is active with the UE
on at least one activity after receiving the PDU session modification request. When it is determined that the gNodeB is active with the UE on the at least one activity: aborting, by the gNodeB, the at least one activity; performing, by the gNodeB, a release of the UE from the connection with the first network and redirect the UE on
20 a predefined configured frequency band of a second network. When it is determined
that the gNodeB is not active with the at least one activity: configuring the UE with a first event measurement, starting a timer having a start time and an end time and performing, by the gNodeB, a release of the UE from the connection with the first network and redirect the UE on the predefined configured frequency band of the
25 second network. The method comprising performing, by the gNodeB, a release of
the UE from the connection with the first network and redirect the UE on the predefined configured frequency band of the second network when at least one of the following conditions are met a first measurement report (MR) associated with the one first event measurement is not received between the start time and the end
30 time of the timer, and at least one second MR related to at least one second event
25

measurement is received from the UE after the UE is configured with the first event
measurement.
[00111] In some embodiments, the at least one UE is registered with at least
one radio resource control (RRC) active mode with a downlink (DL) data session
5 and an uplink (UL) data session.
[00112] In some embodiments, the at least one activity includes at least one
inter-radio access technology (RAT) handover procedure.
[00113] In some embodiments, the first MR related to the first event
measurement received from the UE is a B1 measurement report.
10 [00114] In some embodiments, the at least one second event measurement
includes a measurement related to a A3 event and a A5 event.
[00115] In some embodiments, the PDU session modification request is
received from an access & mobility management function (AMF) associated with
the first network.
15 [00116] In some embodiments, the predefined configured frequency band of
the second network is associated with an evolved universal terrestrial radio access
(E-UTRA) absolute radio frequency channel number (EARFCN).
[00117] In some embodiments, the first network is a 5G network and the
second network is a 4G long-term evolution (LTE) network.
20 [00118] In some embodiments, the EPSFB is triggered through a handover
procedure or a redirection procedure depending upon a plurality of radio frequency
(RF) conditions of the UE.
[00119] In some embodiments, the plurality of radio frequency (RF)
conditions of the UE depends on a geographical area where the UE is located.
25 [00120] In some embodiments, the EPSFB is triggered through a handover
procedure or a redirection procedure depending upon the at least one race condition
generated in the first network.
[00121] In some embodiments, the gNodeB performs an emergency release
of the UE from the connection with the first network and performs an emergency
30 redirection of the UE on the predefined configured frequency band of the second
network.
26

[00122] In some embodiments, the gNodeB performs the emergency
redirection of the UE on the predefined configured frequency band of the second network instantly.
[00123] In some embodiments, the predefined configured frequency band is
5 determined based on at least one of UE capability information message received
from the UE, a message from the AMF that comprises an indication regarding a
possibility of redirection for the EPSFB, N26 interface availability configuration
and the plurality of RF conditions of the UE.
[00124] In an exemplary embodiment, the present invention discloses a
10 system for an evolved packet system fallback (EPSFB). The system is configured
to receive, by a gNodeB, at least one packet data unit (PDU) session modification request related to a voice call for a user equipment (UE) connected to a first network. The system is configured to determine if the gNodeB is active with the UE on at least one activity after receiving the PDU session modification request.
15 When it is determined that the gNodeB is active with the UE on at least one activity:
abort, by the gNodeB, the at least one activity; perform, by the gNodeB, a release of the UE from the connection with the first network and redirect the UE on a predefined configured frequency band of a second network. When it is determined that the gNodeB is not active with the at least one activity: configure the UE with a
20 first event measurement; start a timer having a start time and an end time, perform,
by the gNodeB, a release of the UE from the connection with the first network and redirect the UE on the predefined configured frequency band of the second network. The system is configured to perform, by the gNodeB, a release of the UE from the connection with the first network and redirect the UE on the predefined configured
25 frequency band of the second network when at least one of the following conditions
are met a first measurement report (MR) associated with the one first event measurement is not received between the start time and the end time of the timer, and at least one second MR related to at least one second event measurement is received from the UE after the UE is configured with the first event measurement.
30 [00125] In an exemplary embodiment, the present invention discloses a
network comprising at least one network element for performing an evolved packet
27

system fallback (EPSFB). The at least one network element is configured to receive,
by a gNodeB, at least one packet data unit (PDU) session modification request
related to a voice call for a user equipment (UE) connected to the network. The at
least one network element is configured to determine if the gNodeB is active with
5 the UE on at least one activity after receiving the PDU session modification request.
The at least one network element is configured to responsive to determining that the gNodeB is active with the at least one activity: abort, by the gNodeB, the at least one activity, perform, by the gNodeB, a release of the UE from the connection with the network and redirect the UE on a predefined configured frequency band of
10 another network. The at least one network element is configured to responsive to
determining that the gNodeB is not active with the at least one activity: configure the UE with a first event measurement and start a timer having a start time and an end time. The at least one network element is configured to perform, by the gNodeB, a release of the UE from the connection with the network and redirect the
15 UE on the predefined configured frequency band of the another network when at
least one of the following conditions are met a first measurement report (MR) associated with the first event measurement is not received between the start time and the end time of the timer and at least one second MR related to at least one second event measurement from the UE after the UE is configured with the first
20 event measurement.
[00126] In an exemplary embodiment, the present invention discloses a user
equipment (UE) attached to a network. The network comprising at least one network element for performing an evolved packet system fallback (EPSFB). The at least one network element is configured to receive, by a gNodeB, at least one
25 packet data unit (PDU) session modification request related to a voice call for the
UE. The at least one network element is configured to determine if the gNodeB is active with the UE on at least one activity after receiving the PDU session modification request. The at least one network element is configured to responsive to determining that the gNodeB is active with the at least one activity: abort, by the
30 gNodeB, the at least one activity, perform, by the gNodeB, a release of the UE from
the connection with the network and redirect the UE on a predefined configured
28

frequency band of another network. The at least one network element is configured
to responsive to determining that the gNodeB is not active with the at least one
activity: configure the UE with a first event measurement and start a timer having
a start time and an end time. The at least one network element is configured to
5 perform, by the gNodeB, a release of the UE from the connection with the network
and redirect the UE on the predefined configured frequency band of the another
network when at least one of the following conditions are met a first measurement
report (MR) associated with the first event measurement is not received between
the start time and the end time of the timer and at least one second MR related to at
10 least one second event measurement from the UE after the UE is configured with
the first event measurement.
[00127] FIG. 7 illustrates an exemplary computer system (700) in which or
with which embodiments of the present disclosure may be implemented. In an
15 implementation, the EPSFB release system 108 may be implanted by the computer
system (700). As shown in FIG. 7, the computer system (700) may include an external storage device (710), a bus (720), a main memory (730), a read only memory (740), a mass storage device (750), a communication port (760), and a processor (770). A person skilled in the art will appreciate that the computer system
20 (700) may include more than one processor (770) and communication ports (760).
Processor (770) may include various modules associated with embodiments of the present disclosure.
[00128] In an embodiment, the communication port (760) may be any of an
RS-232 port for use with a modem-based dialup connection, a 10/100 Ethernet port,
25 a Gigabit or 10 Gigabit port using copper or fiber, a serial port, a parallel port, or
other existing or future ports. The communication port (760) may be chosen
depending on a network, such a Local Area Network (LAN), Wide Area Network
(WAN), or any network to which computer system connects.
[00129] In an embodiment, the memory (730) may be Random Access
30 Memory (RAM), or any other dynamic storage device commonly known in the art.
Read-only memory (740) may be any static storage device(s) e.g., but not limited
29

to, a Programmable Read Only Memory (PROM) chips for storing static information e.g., start-up or Basic Input/Output System (BIOS) instructions for the processor (770).
[00130] In an embodiment, the mass storage (750) may be any current or
5 future mass storage solution, which may be used to store information and/or
instructions. Exemplary mass storage solutions include, but are not limited to, Parallel Advanced Technology Attachment (PATA) or Serial Advanced Technology Attachment (SATA) hard disk drives or solid-state drives (internal or external, e.g., having Universal Serial Bus (USB) and/or Firewire interfaces), one
10 or more optical discs, Redundant Array of Independent Disks (RAID) storage, e.g.,
an array of disks (e.g., SATA arrays).
[00131] In an embodiment, the bus (720) communicatively couples the
processor(s) (770) with the other memory, storage and communication blocks. The bus (720) may be, e.g., a Peripheral Component Interconnect (PCI)/PCI Extended
15 (PCI-X) bus, Small Computer System Interface (SCSI), Universal Serial Bus (USB)
or the like, for connecting expansion cards, drives and other subsystems as well as
other buses, such a front side bus (FSB), which connects the processor (770) to the
computer system (700).
[00132] Optionally, operator and administrative interfaces, e.g., a display,
20 keyboard, joystick, and a cursor control device, may also be coupled to the bus
(720) to support direct operator interaction with the computer system (700). Other operator and administrative interfaces may be provided through network connections connected through the communication port (760). Components described above are meant only to exemplify various possibilities. In no way should
25 the aforementioned exemplary computer system (700) limit the scope of the present
disclosure.
[00133] While the foregoing describes various embodiments of the present
disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof. The scope of the present disclosure
30 is determined by the claims that follow. The present disclosure is not limited to the
described embodiments, versions or examples, which are included to enable a
30

person having ordinary skill in the art to make and use the present disclosure when combined with information and knowledge available to the person having ordinary skill in the art.
[00134] In an aspect, the present disclosure provides a system, and a method
5 that allows a user equipment (UE) to get redirected on default Long-Term Evolution
(LTE) frequency band when the UE stuck in any race condition with other handover
procedure and improves the user experience. In an aspect, the present disclosure.
The present disclosure improves network Key Performance Indicators (KPI) of
EPSFB success rate.
10 [00135] In an aspect, the present disclosure can be implemented within a
communication network with multi-RAT, multi-vendor consisting of different product like macro, micro and small cell.
ADVANTAGES OF THE PRESENT DISCLOSURE
15 [00136] The present disclosure may reduce the delay in Evolved Packet
System Fallback (EPSFB) procedure when a gNodeB (gNB) is automatically taking
decision to start EPSFB with release with redirection.
[00137] The present disclosure may allow User Equipment (UE) to get
redirected on default Long-Term Evolution (LTE) frequency band when the UE
20 stuck in any race condition with other handover procedure and improves the user
experience.
[00138] The present disclosure may allow the UE to release with redirection
to default LTE frequency with emergency fallback, when the UE is active with
some other handover procedure.
25 [00139] The present disclosure may be well suited for any heterogeneous
network with Multi–Radio Access Technology (RAT), multi-vendor consisting of
different product like Macro, Micro and small cell.
[00140] The present disclosure may improve network Key Performance
Indicators (KPI) of EPSFB success rate. 30
31

WE CLAIM:
1. A method for an evolved packet system fallback (EPSFB), the method
comprising:
5 receiving, by a gNodeB (320, 420, 520), at least one packet data unit
(PDU) session modification request related to a voice call for a user equipment (UE) (104, 310, 410, 510) connected to a first network;
determining if the gNodeB (320, 420, 520) is active with the UE
(104, 310, 410, 510) on at least one activity after receiving the PDU session
10 modification request;
responsive to determining that the gNodeB (320, 420, 520) is active with the UE (104, 310, 410, 510) on the at least one activity:
aborting, by the gNodeB (320, 420, 520), the at least one activity;
performing, by the gNodeB (320, 420, 520), a release of the UE (104,
15 310, 410, 510) from the connection with the first network and redirect the
UE (104, 310, 410, 510) on a predefined configured frequency band of a second network;
responsive to determining that the gNodeB (320, 420, 520) is not
active with the at least one activity:
20 configuring the UE (104, 310, 410, 510) with a first event
measurement and starting a timer having a start time and an end time; and
performing, by the gNodeB (320, 420, 520), a release of the UE (104,
310, 410, 510) from the connection with the first network and redirect the
UE (104, 310, 410, 510) on the predefined configured frequency band of the
25 second network when at least one of the following conditions are met:
a first measurement report (MR) associated with the first event measurement is not received between the start time and the end time of the timer; and
at least one second MR related to at least one second event
30 measurement is received from the UE (104, 310, 410, 510) after the
32

UE (104, 310, 410, 510) is configured with the first event measurement.
2. The method as claimed in claim 1, wherein the at least one UE (104, 410,
5 510) is registered with at least one radio resource control (RRC) active mode
with a downlink (DL) data session and an uplink (UL) data session.
3. The method as claimed in claim 1, wherein the at least one activity includes
at least one inter-radio access technology (RAT) handover procedure. 10
4. The method as claimed in claim 1, wherein the first MR related to the first
event measurement received from the UE (104, 310, 410, 510) is a B1 measurement report.
15 5. The method as claimed in claim 1, wherein the at least one second event
measurement includes a measurement related to a A3 event and a A5 event.
6. The method as claimed in claim 1, wherein the PDU session modification
request is received from an access & mobility management function (AMF)
20 (330, 430, 530) associated with the first network.
7. The method as claimed in claim 1, wherein the predefined configured
frequency band of the second network is associated with an evolved
universal terrestrial radio access (E-UTRA) absolute radio frequency
25 channel number (EARFCN).
8. The method as claimed in claim 1, wherein the first network is a 5G network
and the second network is a 4G long-term evolution (LTE) network.
3

9. The method as claimed in claim 1, wherein the EPSFB is triggered through a handover procedure or a redirection procedure depending upon a plurality of radio frequency (RF) conditions of the UE (104, 310, 410, 510).
5 10. The method as claimed in claim 1, wherein the plurality of radio frequency
(RF) conditions of the UE (104, 310, 410, 510) depends on a geographical area where the UE (104, 310, 410, 510) is located.
11. The method as claimed in claim 1, wherein the EPSFB is triggered through
10 a handover procedure or a redirection procedure depending upon the at least
one race condition generated in the first network.
12. The method as claimed in claim 1, wherein the gNodeB (320, 420, 520)
performs an emergency release of the UE (104, 310, 410, 510) from the
15 connection with the first network and performs an emergency redirection of
the UE (104, 310, 410, 510) on the predefined configured frequency band of the second network.
13. The method as claimed in claim 1, wherein the gNodeB (320, 420, 520)
20 performs the emergency redirection of the UE (104, 310, 410, 510) on the
predefined configured frequency band of the second network instantly.
14. The method as claimed in claim 1, wherein the predefined configured
frequency band is determined based on at least one of:
25 UE capability information message received from the UE (104, 310, 410,
510);
a message from the AMF (330, 430, 530) that comprises an indication
regarding a possibility of redirection for the EPSFB;
N26 interface availability configuration; and
30 the plurality of RF conditions of the UE (104, 310, 410, 510).

15. A system for an evolved packet system fallback (EPSFB), the system is configured to:
receive, by a gNodeB (320, 420, 520), at least one packet data unit
(PDU) session modification request related to a voice call for a user
5 equipment (UE) (104, 310, 410, 510) connected to a first network;
determine if the gNodeB (320, 420, 520) is active with the UE (104, 310, 410, 510) on at least one activity after receiving the PDU session modification request;
when it is determined that the gNodeB (320, 420, 520) is active with
10 the at least one activity:
abort, by the gNodeB (320, 420, 520), the at least one activity;
perform, by the gNodeB (320, 420, 520), a release of the UE (104,
310, 410, 510) from the connection with the first network and redirect the
UE (104, 310, 410, 510) on a predefined configured frequency band of a
15 second network;
responsive to determining that the gNodeB (320, 420, 520) is not active with the at least one activity:
configure the UE (104, 310, 410, 510) with a first event
measurement;
20 start a timer having a start time and an end time;
perform, by the gNodeB (320, 420, 520) a release of the UE (104,
310, 410, 510) from the connection with the first network and redirect the
UE (104, 310, 410, 510) on the predefined configured frequency band of the
second network when at least one of the following conditions are met:
25 a first measurement report (MR) associated with the first event
measurement is not received between the start time and the end time of the timer;
and
at least one second MR related to at least one second event
30 measurement is received from the UE (104, 310, 410, 510) after the UE
(104, 310, 410, 510) is configured with the first event measurement.

16. The system as claimed in claim 15, wherein the at least one UE (104, 310,
410, 510) is registered with at least one radio resource control (RRC) active
mode with a downlink (DL) data session and an uplink (UL) data session.
5
17. The system as claimed in claim 15, wherein the at least one activity includes
at least one inter-radio access technology (RAT) handover procedure.
18. The system as claimed in claim 15, wherein the first MR related to the first
10 event measurement received from the UE (104, 310, 410, 510) is a B1
measurement report.
19. The system as claimed in claim 15, wherein the at least one second event
measurement includes a measurement related to a A3 event and a A5 event.
15
20. The system as claimed in claim 15, wherein the PDU session modification
request is received from an access & mobility management function (AMF)
(330, 430, 530) associated with the first network.
20 21. The system as claimed in claim 15, wherein the predefined configured
frequency band of the second network is associated with an evolved universal terrestrial radio access (E-UTRA) absolute radio frequency channel number (EARFCN).
25 22. The system as claimed in claim 15, wherein the first network is a 5G
network and the second network is a 4G long-term evolution (LTE) network.
23. The system as claimed in claim 15, wherein the EPSFB is triggered through
30 a handover procedure or a redirection procedure depending upon a plurality
of radio frequency (RF) conditions of the UE (104, 310, 410, 510).

24. The system as claimed in claim 15, wherein the plurality of radio frequency
(RF) conditions of the UE (104, 310, 410, 510) depends on a geographical
area where the UE (104, 310, 410, 510) is located.
5
25. The system as claimed in claim 15, wherein the EPSFB is triggered through
a handover procedure or a redirection procedure depending upon the at least
one race condition generated in the first network.
10 26. The system as claimed in claim 15, wherein the gNodeB (320, 420, 520)
performs an emergency release of the UE (104, 310, 410, 510) from the connection with the first network and performs an emergency redirection of the UE (104, 310, 410, 510) on the predefined configured frequency band of the second network.
15
27. The system as claimed in claim 15, wherein the gNodeB (320, 420, 520) performs the emergency redirection of the UE (104, 310, 410, 510) on the predefined configured frequency band of the second network instantly.
20 28. The system as claimed in claim 15, wherein the predefined configured
frequency band is determined based on at least one of:
UE capability information message received from the UE (104, 310, 410,
510);
a message from the AMF (330, 430, 530) that comprises an indication
25 regarding a possibility of redirection for the EPSFB;
N26 interface availability configuration; and the plurality of RF conditions of the UE (104, 310, 410, 510).

29. A network comprising at least one network element for performing an evolved packet system fallback (EPSFB), the at least one network element is configured to:
receive, by a gNodeB (320, 420, 520), at least one packet data unit
5 (PDU) session modification request related to a voice call for a user
equipment (UE) (104, 310, 410, 510) connected to the network;
determine if the gNodeB (320, 420, 520) is active with the UE (104,
310, 410, 510) on at least one activity after receiving the PDU session
modification request;
10 responsive to determining that the gNodeB (320, 420, 520) is active
with the at least one activity:
abort, by the gNodeB (320, 420, 520), the at least one activity;
perform, by the gNodeB (320, 420, 520), a release of the UE (104,
310, 410, 510) from the connection with the network and redirect the UE
15 (104, 310, 410, 510) on a predefined configured frequency band of another
network;
responsive to determining that the gNodeB (320, 420, 520) is not active with the at least one activity:
configure the UE (104, 310, 410, 510) with a first event
20 measurement and start a timer having a start time and an end time;
perform, by the gNodeB (320, 420, 520), a release of the UE (104,
310, 410, 510) from the connection with the network and redirect the UE
(104, 310, 410, 510) on the predefined configured frequency band of the
another network when at least one of the following conditions are met:
25 a first measurement report (MR) associated with the first event
measurement is not received between the start time and the end time of the timer; and
at least one second MR related to at least one second event
measurement from the UE (104, 310, 410, 510) after the UE (104, 310, 410,
30 510) is configured with the first event measurement.

30. A user equipment (UE) (104, 310, 410, 510) attached to a
network, wherein the network comprising at least one network element for
performing an evolved packet system fallback (EPSFB), the at least one
network element is configured to:
5 receive, by a gNodeB (320, 420, 520), at least one packet data unit
(PDU) session modification request related to a voice call for the UE (104, 310, 410, 510);
determine if the gNodeB (320, 420, 520) is active with the UE (104,
310, 410, 510) on at least one activity after receiving the PDU session
10 modification request;
responsive to determining that the gNodeB (320, 420, 520) is active with the at least one activity:
abort, by the gNodeB (320, 420, 520), the at least one activity;
perform, by the gNodeB (320, 420, 520), a release of the UE (104,
15 310, 410, 510) from the connection with the network and redirect the UE
(104, 310, 410, 510) on a predefined configured frequency band of another network;
responsive to determining that the gNodeB (320, 420, 520) is not
active with the at least one activity:
20 configure the UE (104, 310, 410, 510) with a first event
measurement and start a timer having a start time and an end time;
perform, by the gNodeB (320, 420, 520), a release of the UE (104,
310, 410, 510) from the connection with the network and redirect the UE
(104, 310, 410, 510) on the predefined configured frequency band of the
25 another network when at least one of the following conditions are met:
a first measurement report (MR) associated with the first event measurement is not received between the start time and the end time of the timer; and
at least one second MR related to at least one second event
30 measurement from the UE (104, 310, 410, 510) after the UE (104, 310, 410,
510) is configured with the first event measurement.
Dated this 06 day of May 2024
~Digitally signed~ Arindam Paul
39REG.NO:IN/PA-174 of De Penning & De Penning
Agent for the Applicants