WO2021135819A1

WO2021135819A1 - Cell selection in tracking area

Info

Publication number: WO2021135819A1
Application number: PCT/CN2020/133941
Authority: WO
Inventors: Manish Kumar; Naveen Bodapati
Original assignee: Guangdong Oppo Mobile Telecommunications Corp., Ltd.
Priority date: 2019-12-30
Filing date: 2020-12-04
Publication date: 2021-07-08

Abstract

The present disclosure describes methods, apparatus and devices for registration of a user equipment 102 in a communication network. According to some embodiments, the user equipment 102 performs an attempt to camp on a first preferred cell 108 in a first tracking area 130 by sending a registration request to a control node 200. The control node 200 in response to the first registration request sends a first rejection response comprising a first reject cause. On receiving the first rejection response from the control node 200 when the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN), the user equipment 102 blocks the first preferred cell 108 for further attempts for a preconfigured time and performs an attempt to camp on a second preferred cell 110 in the first tracking 130 area and sends a second registration request to the control node 200.

Description

CELL SELECTION IN TRACKING AREA

TECHNICAL FIELD

The present invention relates generally to registration of a user equipment in a communication network, and more particularly to cell selection for registration of a user equipment in a tracking area in a communication network.

BACKGROUND

A user equipment registers its presence in a registration area, for instance when entering a new area, when it is powered on or periodically. A registration request by a user equipment may face network reject with several different causes.

A communication network includes different tracking areas and several base stations are provided within each tracking area. Each base station has a “cell” -a Radio network object that can be uniquely identified by the user equipment from a (cell) identification that is broadcasted over a geographical area from one Universal Terrestrial Radio Access Network (UTRAN) Access Point.

The new technologies such as 5th Generation (5G) radio access technology (RAT) and Long Term Evolution (LTE) RAT are amongst the more advanced technologies for communication networks. In 5G RAT or LTE RAT, a user equipment would select a cell in a tracking area to initiate registration and such cell selection is based on different considerations.

The user equipment sends a registration request to a base station of the selected cell and In case of the selected cell being a faulty cell, a control node sends a rejection response to the user equipment and the user equipment stores the current tracking area of the selected cell as “FORBIDDEN” and searches for available cells in a different tracking are. If such cells are not found in the different tracking area, the user equipment would switch to a legacy network such as 2G or 3G RAT for Public Land Mobile Network (PLMN) selection.

The 3rd Generation Partnership Project (3GPP) 5G specification 24.501, 5.3.13 provides:

5.3.13 Lists of 5GS forbidden tracking areas

The UE shall store a list of "5GS forbidden tracking areas for roaming" , as well as a list of "5GS forbidden tracking areas for regional provision of service" . Within the 5GS, these lists are managed independently per access type, i.e., 3GPP access or non-3GPP access. These lists shall be erased when

a) the UE is switched off or the UICC containing the USIM is removed or an entry of the "list of subscriber data" with the SNPN identity of the current SNPN is updated; and

b) periodically (with a period in the range 12 to 24 hours) .

Over 3GPP access, when the lists are erased, the UE performs cell selection according to 3GPP TS 38.304 [28] . A tracking area shall be removed from the list of "5GS forbidden tracking areas for roaming" , as well as the list of "5GS forbidden tracking areas for regional provision of service" , if the UE receives the tracking area in the TAI list or the Service area list of "allowed tracking areas" in REGISTRATION ACCEPT message or a CONFIGURATION UPDATE COMMAND message. The UE shall not remove the tracking area from "5GS forbidden tracking areas for roaming" or "5GS forbidden tracking areas for regional provision of service" if the UE is registered for emergency services.

In N1 mode, the UE shall update the suitable list whenever a REGISTRATION REJECT, SERVICE REJECT or DEREGISTRATION REQUEST message is received with the 5GMM cause #12 "tracking area not allowed" , #13 "roaming not allowed in this tracking area" , or #15 "no suitable cells in tracking area" .

Each list shall accommodate 40 or more TAIs. When the list is full and a new entry has to be inserted, the oldest entry shall be deleted.

The 3rd Generation Partnership Project (3GPP) LTE specification 24.301, 5.3.2 provides:

5.3.2 Lists of forbidden tracking areas

The UE shall store a list of "forbidden tracking areas for roaming" , as well as a list of "forbidden tracking areas for regional provision of service" . These lists shall be erased when the UE is switched off or when the UICC containing the USIM is removed, and periodically (with a period in the range 12 to 24 hours) . When the lists are erased, the UE performs cell selection according to 3GPP TS 36.304 [21] . One or more tracking areas is removed from the list of "forbidden tracking areas for roaming" in the UE, as well as the list of "forbidden tracking areas for regional provision of service" if, after a subsequent procedure e.g. attach procedure, tracking area updating procedure and GUTI reallocation procedure, one or more tracking areas in the lists is received from the network. If the UE has only one PDN connection established which is for emergency bearer services, the tracking areas shall not be removed from these lists if one or more tracking areas in the lists are received from the network.

In S1 mode, the UE shall update the suitable list whenever an ATTACH REJECT, TRACKING AREA UPDATE REJECT, SERVICE REJECT or DETACH REQUEST message is received with the EMM cause #12 "tracking area not allowed" , #13 "roaming not allowed in this tracking area" , or #15 "no suitable cells in tracking area" .

A user equipment operating in 5G RAT is required to follow the following sections of 3GPP specification 24.501:

5.5.1.2.5 Initial registration not accepted by the network

If the initial registration request cannot be accepted by the network, the AMF shall send a REGISTRATION REJECT message to the UE including an appropriate 5GMM cause value.

The UE shall take the following actions depending on the 5GMM cause value received in the REGISTRATION REJECT message.

#15 (No suitable cells in tracking area) ;

The UE shall set the 5GS update status to 5U3 ROAMING NOT ALLOWED (and shall store it according to subclause 5.1.3.2.2) and shall delete any 5G-GUTI, last visited registered TAI, TAI list and ngKSI. Additionally, the UE shall reset the registration attempt counter.

The UE shall store the current TAI in the list of "5GS forbidden tracking areas for roaming" and enter the state 5GMM-DEREGISTERED. LIMITED-SERVICE. The UE shall search for a suitable cell in another tracking area according to 3GPP TS 38.304 [28] .

If the message was received via 3GPP access and the UE is operating in single-registration mode, the UE shall handle the EMM parameters EMM state, EPS update status, 4G-GUTI, TAI list, eKSI and attach attempt counter as specified in 3GPP TS 24.301 [15] for the case when the EPS attach request procedure is rejected with the EMM cause with the same value.

5.5.1.3.5 Mobility and periodic registration update not accepted by the network

If the mobility and periodic registration update request cannot be accepted by the network, the AMF shall send a REGISTRATION REJECT message to the UE including an appropriate 5GMM cause value.

#15 (No suitable cells in tracking area) .

The UE shall set the 5GS update status to 5U3 ROAMING NOT ALLOWED (and shall store it according to subclause 5.1.3.2.2) . The UE shall reset the registration attempt counter and shall enter the state 5GMM-REGISTERED. LIMITED-SERVICE. The UE shall search for a suitable cell in another tracking area according to 3GPP TS 38.304 [28] .

The UE shall store the current TAI in the list of "5GS forbidden tracking areas for roaming" and shall remove the current TAI from the stored TAI list, if present.

If the message was received via 3GPP access and the UE is operating in single-registration mode, the UE shall handle the EMM parameters EMM state, EPS update status and tracking area updating attempt counter as specified in 3GPP TS 24.301 [15] for the case when the normal tracking area updating procedure is rejected with the EMM cause with the same value.

A user equipment not operating in NB-S1 or WB-S1 is required to follow the following sections of 3GPP specification 24.301:

5.5.1.2.5 Attach not accepted by the network

If the attach request cannot be accepted by the network, the MME shall send an ATTACH REJECT message to the UE including an appropriate EMM cause value.

#15 (No suitable cells in tracking area) ;

The UE shall set the EPS update status to EU3 ROAMING NOT ALLOWED (and shall store it according to subclause 5.1.3.3) and shall delete any GUTI, last visited registered TAI, TAI list and eKSI. Additionally, the UE shall reset the attach attempt counter.

The UE shall store the current TAI in the list of "forbidden tracking areas for roaming" and enter the state EMM-DEREGISTERED. LIMITED-SERVICE and:

- if the UE is in WB-S1 mode and the Extended EMM cause IE with value "E-UTRAN not allowed" is included in the ATTACH REJECT message, the UE supports "E-UTRA Disabling for EMM cause #15" , and the "E-UTRA Disabling Allowed for EMM cause #15" parameter as specified in 3GPP TS 24.368 [15A] or 3GPP TS 31.102 [17] is present and set to enabled; then the UE shall disable the E-UTRA capability as specified in subclause 4.5 and search for a suitable cell in GERAN, UTRAN or NG-RAN radio access technology;

- if the UE is in NB-S1 mode and the Extended EMM cause IE with value "NB-IoT not allowed" is included in the ATTACH REJECT message, then the UE may disable the NB-IoT capability as specified in subclause 4.9 and search for a suitable cell in E-UTRAN radio access technology;

- otherwise, the UE shall search for a suitable cell in another tracking area or in another location area according to 3GPP TS 36.304 [21] .

In S101 mode, the UE shall store the PLMN identity provided with the indication from the lower layers to prepare for an S101 mode to S1 mode handover in the list of "forbidden PLMNs for attach in S101 mode" and enter the state EMM-DEREGISTERED. NO-CELL-AVAILABLE and if the UE is configured to use timer T3245 (see 3GPP TS 24.368 [15A] or 3GPP TS 31.102 [17] ) then the UE shall start timer T3245 and proceed as described in subclause 5.3.7a.

If A/Gb mode or Iu mode is supported by the UE, the UE shall in addition handle the GMM parameters GMM state, GPRS update status, P-TMSI, P-TMSI signature, RAI, GPRS ciphering key sequence number and GPRS attach attempt counter as specified in 3GPP TS 24.008 [13] for the case when the normal attach procedure is rejected with the GMM cause with the same value.

If the UE is operating in single-registration mode, the UE shall in addition handle the 5GMM parameters except the current TAI as specified in 3GPP TS 24.501 [54] for the case when the initial registration procedure performed over 3GPP access is rejected with the 5GMM cause with the same value.

5.5.1.3.5 Combined attach not accepted by the network

If the attach request can neither be accepted by the network for EPS nor for non-EPS services, the MME shall send an ATTACH REJECT message to the UE including an appropriate EMM cause value.

#15 (No suitable cells in tracking area) ;

The UE shall set the EPS update status to EU3 ROAMING NOT ALLOWED (and shall store it according to subclause 5.1.3.3) and shall delete any GUTI, last visited registered TAI, TAI list and eKSI. Additionally, the UE shall reset the attach attempt counter and enter the state EMM-DEREGISTERED. LIMITED-SERVICE.

The UE shall store the current TAI in the list of "forbidden tracking areas for roaming" and:

- if the UE is in WB-S1 mode and the Extended EMM cause IE with value "E-UTRAN not allowed" is included in the ATTACH REJECT message, the UE supports "E-UTRA Disabling for EMM cause #15" , and the "E-UTRA Disabling Allowed for EMM cause #15" parameter as specified in 3GPP TS 24.368 [15A] or 3GPP TS 31.102 [17] is present and set to enabled, then the UE shall disable the E-UTRA capability as specified in subclause 4.5 and search for a suitable cell in another location area or 5GS tracking area;

If A/Gb mode or Iu mode is supported by the UE, the UE shall in addition handle the MM parameters update status, TMSI, LAI, ciphering key sequence number and location update attempt counter, and the GMM parameters GMM state, GPRS update status, P-TMSI, P-TMSI signature, RAI, GPRS ciphering key sequence number and GPRS attach attempt counter as specified in 3GPP TS 24.008 [13] for the case when the combined attach procedure is rejected with the GMM cause with the same value.

5.5.3.2.5 Normal and periodic tracking area updating procedure not accepted by the network

If the tracking area updating cannot be accepted by the network, the MME sends a TRACKING AREA UPDATE REJECT message to the UE including an appropriate EMM cause value.

#15 (No suitable cells in tracking area) ;

The UE shall set the EPS update status to EU3 ROAMING NOT ALLOWED (and shall store it according to subclause 5.1.3.3) . The UE shall reset the tracking area updating attempt counter and shall enter the state EMM-REGISTERED. LIMITED-SERVICE.

The UE shall store the current TAI in the list of "forbidden tracking areas for roaming" and shall remove the current TAI from the stored TAI list if present and:

- if the UE is in WB-S1 mode and the Extended EMM cause IE with value "E-UTRAN not allowed" is included in the TRACKING AREA UPDATE REJECT message, the UE supports "E-UTRA Disabling for EMM cause #15" , and the "E-UTRA Disabling Allowed for EMM cause #15" parameter as specified in 3GPP TS 24.368 [15A] or 3GPP TS 31.102 [17] is present and set to enabled; then the UE shall disable the E-UTRA capability as specified in subclause 4.5 and search for a suitable cell in another location area or 5GS tracking area;

- if the UE is in NB-S1 mode and the Extended EMM cause IE with value "NB-IoT not allowed" is included in the TRACKING AREA UPDATE REJECT message, then the UE may disable the NB-IoT capability as specified in subclause 4.9 and search for a suitable cell in E-UTRAN radio access technology;

If A/Gb mode or Iu mode is supported by the UE, the UE shall handle the GMM parameters GMM state, GPRS update status and routing area updating attempt counter as specified in 3GPP TS 24.008 [13] for the case when the normal routing area updating procedure is rejected with the GMM cause with the same value.

If the UE is operating in single-registration mode, the UE shall in addition handle the 5GMM parameters except the current TAI as specified in 3GPP TS 24.501 [54] for the case when the registration procedure for mobility and periodic registration update performed over 3GPP access and indicating "mobility registration updating" in the 5GS registration type IE of the REGISTRATION REQUEST message is rejected with the 5GMM cause with the same value.

5.5.3.3.5 Combined tracking area updating procedure not accepted by the network

If the combined tracking area updating cannot be accepted by the network, the MME shall send a TRACKING AREA UPDATE REJECT message to the UE including an appropriate EMM cause value.

#15 (No suitable cells in tracking area) ;

The UE shall indicate the Update type IE "combined TA/LA updating with IMSI attach" when performing the tracking area updating procedure.

If A/Gb mode or Iu mode is supported by the UE, the UE shall handle the MM parameters update status and the location update attempt counter, and the GMM parameters GMM state, GPRS update status and routing area updating attempt counter as specified in 3GPP TS 24.008 [13] for the case when the combined routing area updating procedure is rejected with the GMM cause with the same value.

5.6.1.5 Service request procedure not accepted by the network

If the service request cannot be accepted, the network shall return a SERVICE REJECT message to the UE including an appropriate EMM cause value.

#15 (No suitable cells in tracking area) ;

The UE shall set the EPS update status to EU3 ROAMING NOT ALLOWED (and shall store it according to subclause 5.1.3.3) . The UE shall enter the state EMM-REGISTERED. LIMITED-SERVICE.

The UE shall store the current TAI in the list of "forbidden tracking areas for roaming" and remove the current TAI from the stored TAI list if present.

If the UE initiated service request for mobile originated CS fallback and a CS fallback cancellation request was not received, then the UE shall attempt to select GERAN or UTRAN radio access technology. If the UE finds a suitable GERAN or UTRAN cell, it then proceeds with the appropriate MM and CC specific procedures and the EMM sublayer shall not indicate the abort of the service request procedure to the MM sublayer. Otherwise the EMM sublayer shall indicate the abort of the service request procedure to the MM sublayer.

If the service request was not initiated for mobile originated CS fallback, the UE shall search for a suitable cell in another tracking area or in another location area according to 3GPP TS 36.304 [21] .

If A/Gb mode or Iu mode is supported by the UE, the UE shall handle the GMM parameters GMM state and GPRS update status as specified in 3GPP TS 24.008 [13] for the case when the service request procedure is rejected with the GMM cause with the same value.

If the UE is operating in single-registration mode, the UE shall in addition handle the 5GMM parameters except the current TAI as specified in 3GPP TS 24.501 [54] for the case when the service request procedure performed over 3GPP access is rejected with the 5GMM cause with the same value.

3GPP TS 24.501 V16.2.0 (2019-09) and 3GPP TS 24.301 V16.2.0 (2019-09) are hereby incorporated by reference in their entirety as fully set forth herein.

SUMMARY

The present disclosure describes various embodiments that relate to methods and apparatus for addressing the network reject issues and for performing registration of a user equipment in a communication network.

In a first aspect of the present disclosure, a method of registration performed by a user equipment in a communication network using a radio access technology (RAT) is disclosed, the method may comprise performing an attempt to camp on a first preferred cell in a first tracking area; sending a registration request to a control node of a first public land mobile network; receiving, from the control node, a first rejection response comprising a first reject cause #15 “no suitable cells in tracking area” ; in response to receiving the first rejection response, when the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or an Equivalent Home Public Land Mobile Network (EHPLMN) blocking the first preferred cell for further attempts for a preconfigured time; performing an attempt to camp on a second preferred cell in the first tracking area and sending a second registration request to the control node.

According to an embodiment in conjunction to the first aspect of the present disclosure, the RAT may be a 5th generation (5G) RAT.

According to an embodiment in conjunction to the first aspect of the present disclosure, the RAT may be a Long Term Evolution (LTE) RAT.

According to an embodiment in conjunction to the first aspect of the present disclosure, the registration request may comprise one of an initial registration request or a mobility and periodic registration update request.

According to an embodiment in conjunction to the first aspect of the present disclosure, the registration request may comprise one of an attach request, a combined attach request, a tracking area update request, or a combined tracking area update request.

According to an embodiment in conjunction to the first aspect of the present disclosure, the method may further comprise comparing the first Public Land Mobile Network (PLMN) of the first preferred cell to a database of the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) on a SIM (Subscriber Identity Module) or a USIM (Universal Subscriber Identity Module) to determine if the first preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) .

According to an embodiment in conjunction to the first aspect of the present disclosure, the first reject cause may comprise a 5 ^th Generation Mobility Management (5GMM) cause #15 “no suitable cells in trackingarea” .

According to an embodiment in conjunction to the first aspect of the present disclosure, the first reject cause may comprise an evolved packet service mobility management (EMM) cause #15 “no suitable cells in tracking area” .

According to an embodiment in conjunction to the first aspect of the present disclosure, the method may further comprise receiving a second rejection response comprising a second reject cause “no suitable cells in tracking area” ; in response to receiving the second rejection response, when the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) blocking the second preferred cell for further attempts for a preconfigured time; performing an attempt to camp on a next preferred cell in the first tracking area and sending a next registration request to the control node.

According to an embodiment in conjunction to the first aspect of the present disclosure, in case of receiving a further rejection response, the method may comprise a further reject cause “no suitable cells in tracking area” , in response to receiving the further rejection response, when the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) blocking the next preferred cell for further attempts for a preconfigured time; performing an attempt to camp on a subsequent preferred cell in the first tracking area and sending a next registration request to the control node.

According to an embodiment in conjunction to the first aspect of the present disclosure, the method may further comprise receiving a further rejection response comprising a further reject cause “no suitable cells in tracking area” ; in response to receiving the further rejection response, when the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) blocking the next preferred cell for further attempts for a preconfigured time; performing an attempt to camp on a subsequent preferred cell in the first tracking area and sending a next registration request to the control node, on receiving a subsequent rejection message, on remaining cells in the first tracking area until the registration request of the user equipment is rejected by all available cells in the first tracking area.

According to an embodiment in conjunction to the first aspect of the present disclosure, the method may further comprise fixing a threshold of a maximum number of available cells in the first tracking area on which the user equipment may attempt the registration.

According to an embodiment in conjunction to the first aspect of the present disclosure, when the threshold is reached or all the available cells in the first tracking area have sent the reject response, the first tracking area may be added to a forbidden list and the registration may be initiated on an available cell in a second tracking area.

According to an embodiment in conjunction to the first aspect of the present disclosure, the threshold may be fixed at three cells in the first tracking area.

According to an embodiment in conjunction to the first aspect of the present disclosure, the threshold may be fixed at a total number of the available cells in the first tracking area.

According to an embodiment in conjunction to the first aspect of the present disclosure, the threshold may be fixed at a total number of the available cells in the first tracking area or three cells in the first tracking area, whichever is less.

According to an embodiment in conjunction to the first aspect of the present disclosure, the user equipment may maintain a registration attempt counter of a number of cells on which the registration has been attempted.

According to an embodiment in conjunction to the first aspect of the present disclosure, the method may further comprise fixing a threshold of a maximum number of available cells in the second tracking area on which the user equipment may attempt the registration.

According to an embodiment in conjunction to the first aspect of the present disclosure, when the threshold is reached, the second tracking area may be added to a forbidden list and the user equipment may initiate the registration using a legacy RAT.

According to an embodiment in conjunction to the first aspect of the present disclosure, the legacy RAT may be a 3G or a 2G RAT.

According to an embodiment in conjunction to the first aspect of the present disclosure, the control node may be an Access and Mobility Management function, AMF.

In a second aspect of the present disclosure, a user equipment may comprise a processor; a storage memory; and a transceiver connected to the processor and the storage memory, the transceiver may be configured to use radio access technology (RAT) to communicate with a communication network and the user equipment may be configured to perform an attempt to camp on a first preferred cell in a first tracking area; send a registration request to a control node of a first public land mobile network; receive, from the control node, a first rejection response comprising a first reject cause #15 “no suitable cells in tracking area” ; in response to receiving the first rejection response, when the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or an Equivalent Home Public Land Mobile Network (EHPLMN) block the first preferred cell for further attempts for a preconfigured time; perform an attempt to camp on a second preferred cell in the first tracking area and sending a second registration request to the control node.

According to another embodiment in conjunction to the second aspect of the present disclosure, the transceiver may communicate with the communication network via a 5th generation (5G) RAT.

According to another embodiment in conjunction to the second aspect of the present disclosure, the transceiver may communicate with the communication network via a Long Term Evolution (LTE) RAT.

According to another embodiment in conjunction to the second aspect of the present disclosure, the registration request may comprise one of an initial registration request or a mobility and periodic registration update request.

According to another embodiment in conjunction to the second aspect of the present disclosure, the registration request may comprise one of an attach request, combined attach request, tracking area update request, or combined tracking area update request.

According to another embodiment in conjunction to the second aspect of the present disclosure, the user equipment may be further configured to compare the first Public Land Mobile Network (PLMN) of the first preferred cell to a database of the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) on a SIM (Subscriber Identity Module) or a USIM (Universal Subscriber Identity Module) to determine if the first preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) .

According to another embodiment in conjunction to the second aspect of the present disclosure, the user equipment may be further configured to receive a second rejection response comprising a second reject cause “no suitable cells in tracking area” ; in response to receiving the second rejection response, when the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) block the second preferred cell for further attempts for a preconfigured time; perform an attempt to camp on a next preferred cell in the first tracking area and sending a next registration request to the control node.

According to another embodiment in conjunction to the second aspect of the present disclosure, the user equipment may be further configured to receive a further rejection response comprising a further reject cause “no suitable cells in tracking area” ; in response to receiving the further rejection response, when the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) block the next preferred cell for further attempts for a preconfigured time; perform an attempt to camp on a subsequent preferred cell in the first tracking area and sending a next registration request to the control node.

According to another embodiment in conjunction to the second aspect of the present disclosure, the user equipment may be further configured to receive a further rejection response comprising a further reject cause “no suitable cells in tracking area” ; in response to receiving the further rejection response, when the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) block the next preferred cell for further attempts for a preconfigured time; perform an attempt to camp on a subsequent preferred cell in the first tracking area and sending a next registration request to the control node, on receiving a subsequent rejection message, on remaining cells in the first tracking area until the registration request of the user equipment is rejected by all available cells in the first tracking area.

According to another embodiment in conjunction to the second aspect of the present disclosure, the user equipment may further comprise a registration attempt counter and provided with a threshold of a maximum number of available cells in the first tracking area on which the user equipment may attempt the registration.

According another embodiment in conjunction to the second aspect of the present disclosure, when the registration attempt counter reaches the threshold or all the available cells in the first tracking area have sent the reject response, the user equipment may be configured to add the first tracking area to a forbidden list and the user equipment may initiate registration on an available cell in a second tracking area.

According to another embodiment in conjunction to the second aspect of the present disclosure, the threshold may be fixed at three cells in the first tracking area.

According to another embodiment in conjunction to the second aspect of the present disclosure, the threshold may be fixed at a total number of the available cells in the first tracking area.

According to another embodiment in conjunction to the second aspect of the present disclosure, the threshold may be fixed at a total number of the available cells in the first tracking area or three cells in the first tracking area, whichever is less.

According to another embodiment in conjunction to the second aspect of the present disclosure, the user equipment may further comprise a registration attempt counter and provided with a threshold of a maximum number of available cells in the second tracking area on which the user equipment may attempt the registration.

According to another embodiment in conjunction to the second aspect of the present disclosure, when the threshold is reached, the second tracking area may be added to a forbidden list and the user equipment may initiate the registration using a legacy RAT.

According to another embodiment in conjunction to the second aspect of the present disclosure, the legacy RAT may be 3G or 2G RAT.

In a third aspect of the present disclosure, a method performed at a control node of a first public land mobile network, for registration of a user equipment in a communication network using a radio access technology (RAT) may comprise receiving a registration request from the user equipment when the user equipment attempts to camp on a first preferred cell in a first tracking area; sending a first rejection response comprising a first reject cause #15 “no suitable cells in tracking area” ; and instructions to the UE to block the first preferred cell, if the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) , for further attempts for a preconfigured time and to perform an attempt to camp on a second preferred cell in the first tracking area.

According to another embodiment in conjunction to the third aspect of the present disclosure, the control node may be an Access and Mobility Management function, AMF.

According to another embodiment in conjunction to the third aspect of the present disclosure, the control node may be a Mobility Management Entity, MME.

According to another embodiment in conjunction to the third aspect of the present disclosure, the RAT may be a 5th generation (5G) RAT.

According to another embodiment in conjunction to the third aspect of the present disclosure, the RAT may be a Long Term Evolution (LTE) RAT.

According to another embodiment in conjunction to the third aspect of the present disclosure, the registration request may comprise one of an initial registration request or a mobility and periodic registration update request.

According to another embodiment in conjunction to the third aspect of the present disclosure, the registration request may comprise one of an attach request, a combined attach request, tracking area update request, or a combined tracking area update request.

According to another embodiment in conjunction to the third aspect of the present disclosure, the method may further comprise receiving a second registration request from the user equipment, when the user equipment attempts to camp on a second preferred cell in the first tracking area; sending a second rejection response comprising a second reject cause #15 “no suitable cells in tracking area” ; and instructions to the user equipment to block the second preferred cell, if the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) , for further attempts for a preconfigured time and to perform an attempt to camp on a next preferred cell in the first tracking area.

According to another embodiment in conjunction to the third aspect of the present disclosure, the first reject cause may comprise a 5 ^th Generation Mobility Management (5GMM) cause #15 “no suitable cells in tracking area” .

According to another embodiment in conjunction to the third aspect of the present disclosure, the first reject cause may comprise an evolved packet service mobility management (EMM) cause #15 “no suitable cells in tracking area” .

In a fourth aspect of the present disclosure, a control node of a first public land mobile network (PLMN) , may comprise one or more network ports; and a processing element operably coupled to the one or more network ports; wherein the one or more network ports and the processing element may be configured to receive a registration request from a user equipment using a radio access technology (RAT) , when the user equipment attempts to camp on a first preferred cell in a first tracking area; send a first rejection response comprising a first reject cause #15 “no suitable cells in tracking area” ; and instructions to the user equipment to block the first preferred cell, if the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or an Equivalent Home Public Land Mobile Network (EHPLMN) , for further attempts for a preconfigured time and to perform an attempt to camp on a second preferred cell in the first tracking area.

According to another embodiment in conjunction to the fourth aspect of the present disclosure, the control node may be an Access and Mobility Management function, AMF.

According to another embodiment in conjunction to the fourth aspect of the present disclosure, the control node may be a Mobility Management Entity, MME.

According to another embodiment in conjunction to the fourth aspect of the present disclosure, the registration request may comprise one of an initial registration request or a mobility and periodic registration update request.

According to another embodiment in conjunction to the fourth aspect of the present disclosure, the registration request may comprise one of an attach request, a combined attach request, a tracking area update request, or a combined tracking area update request.

According to another embodiment in conjunction to the fourth aspect of the present disclosure, in the control node the one or more network ports and the processing element may be further configured to receive a second registration request from the user equipment, when the user equipment attempts to camp on a second preferred cell in the first tracking area; send a second rejection response comprising a second reject cause #15 “no suitable cells in tracking area” ; and instructions to the UE to block the second preferred cell, if the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) , for further attempts for a preconfigured time and to perform an attempt to camp on a next preferred cell in the first tracking area.

According to another embodiment in conjunction to the fourth aspect of the present disclosure, the first reject cause may comprise a 5 ^th Generation Mobility Management (5GMM) cause #15 “no suitable cells in tracking area” .

According to another embodiment in conjunction to the fourth aspect of the present disclosure, the first reject cause may comprise an evolved packet service mobility management (EMM) cause #15 “no suitable cells in tracking area” .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included in order to more clearly illustrate the embodiments of the present disclosure and the related art. The drawings included herein provide a further understanding of the disclosure, and are incorporated in and constitute a part of the present disclosure. It is appreciable that the drawings illustrate implementations of the disclosure and, together with the description, serve to explain the principles of the disclosure. It is apparent that the drawings are merely some embodiments of the present disclosure, a person having ordinary skill in this field can obtain other figures according to these figures without paying the premise.

Figure 1 illustrates a user equipment in a communication network with different tracking areas and several cells within such tracking areas.

Figure 2 illustrates a user equipment in communication with a base station and a control node.

Figure 3 illustrates a user equipment and a control node in communication with each other.

Figure 4 illustrates an exemplary block diagram of a control node.

Figure 5 illustrates a flowchart depicting a method of registration of a user equipment in a communication network in accordance with an embodiment of the present invention.

Figure 6 illustrates a flowchart depicting a method of registration of a user equipment in a communication network in accordance with another embodiment of the present invention.

Reference numeral Description

102 User Equipment

104 Radio Access Technology (RAT)

106 Base station

108 First preferred cell in first tracking area

110 Second preferred cell in first tracking area

112 Next preferred cell in first tracking area

114 Subsequent preferred cell in first tracking area

116 Last available cell in first tracking area

118 First preferred cell in second tracking area

120 Second preferred cell in second tracking area

122 Next preferred cell in second tracking area

124 First preferred cell in third tracking area

126 Second preferred cell in third tracking area

128 Second preferred cell in third tracking area

130 First tracking area

132 Second tracking area

134 Third tracking area

200 Control Node

204 Network

302 Registration Request

304 Processor

306 Storage Memory

308 Transceiver

310 Display

312 Registration attempt counter

314 Network port

316 Processing element

318 REGISTRATION REJECT message

402 Memory Management Unit [MMU]

404 Memory

406 ROM

DETAILED DESCRIPTION OF THE DRAWINGS

Detailed embodiments and implementations of the claimed subject matters are disclosed herein in detail with the technical matters, structural features, achieved objects, and effects with reference to the accompanying drawings as follows. It shall be understood that the disclosed embodiments and implementations are merely illustrative of the claimed subject matters which may be embodied in various forms. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments and implementations set forth herein. Rather, these exemplary embodiments and implementations are provided so that description of the present disclosure is thorough and complete and will fully convey the scope of the present disclosure to those skilled in the art. Specifically, the terminologies in the embodiments of the present disclosure are merely for describing the purpose of the certain embodiment, but not to limit the disclosure. In the description below, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments and implementations.

Figure 1 illustrates a user equipment 102 in a communication network with different tracking areas and several cells within such tracking areas.

A user equipment 102 may be any equipment which allows a user access to network services. The user equipment 102 may include a processor and a storage memory. The user equipment 102 may be any of various types of computer system devices which are mobile or portable and which perform wireless communication. The user equipment 102 may be a handheld device, a wireless device, a mobile phone, tablet, computer, laptop, a gaming console, a wearable smart device, an internet-of-things device, a hotspot, a router, PDAs, portable Internet devices, music players, data storage devices, etc., or any other device with wireless communication capabilities. In general, the term user equipment 102 can be broadly defined to encompass any electronic, computing, and/or telecommunications device, or combination of devices which is easily transported by a user and is capable of allowing wireless communication.

A base station 106 may be a wireless communication station installed at a fixed location and used to communicate as part of a wireless communication. The base station 106 may be a base transceiver station or cell site, and may include hardware that enables wireless communication with the user equipment 102. A base station 106 may also enable mobile communication between two portable user equipment 102, and between a portable user equipment 102 and a fixed line. The base station 106 may also be equipped to communicate with a network e.g., a core network of a cellular service provider, a telecommunication network such as a public switched telephone network (PSTN) , and/or the Internet, among various possibilities. Thus, the base station 106 may facilitate communication between the user devices and/or between the user devices and the network. A number of base stations 106 or network access nodes may be included in a wireless communication system, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment 102.

A radio access technology (RAT) 104 is a wireless communication technology, or telecommunication standards. RAT 104 may be defined as the underlying physical connection method for a radio based communication network, such as but not limited to, GSM, UMTS (WCDMA, TD-SCDMA) , LTE, LTE-Advanced (LTE-A) , 3GPP2 CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD) , Wi-Fi, WiMAX, Bluetooth or 5G. The base station 106 and the user equipment 102 may be configured to communicate over the transmission medium using any of various radio access technologies (RATs) .

5 ^th Generation (5G) RAT is one such radio access technology (RAT) which is a standard developed by 3GPP for the 5G mobile network. It designed to be the global standard for the air interface of 5G networks. The base station 106 and the user equipment 102 may be configured to communicate over the transmission medium using 5G RAT.

The Long-Term Evolution (LTE) is also one such standard for high-speed wireless communication for the user equipment 102 and data terminals. It is one of the various radio access technologies (RATs) available and is a standard for 4G wireless broadband technology.

A cell may be defined as the communication area or the coverage area of the base station 106. It may be defined as a geographic area of wireless signal coverage that extends from the base station 106 located within the cell. The base station 106 and the user equipment 102 may be configured to communicate over the transmission medium using any of various radio access technologies (RATs) , also referred to as wireless communication technologies, or telecommunication standards, such as GSM, UMTS (WCDMA, TD-SCDMA) , LTE, LTE-Advanced (LTE-A) , 3GPP2 CDMA2000 (e.g., 1×RTT, 1×EV-DO, HRPD, eHRPD) , Wi-Fi, WiMAX, Bluetooth or 5G etc. Base station 106 operating according to the same or a different cellular communication standards may thus be provided as a network of cells, which may provide continuous or nearly continuous overlapping service to the user equipment 102 over a wide geographic area via one or more cellular communication standards.

A tracking area may be defined as a group of one or more cells which manages and represents the location of the user equipment. Adjacent cells may be combined to form a tracking area, and, when a user equipment enters a tracking area, it may transmit a locating message to the network indicating said tracking area. Thus, the wireless networks determine the location of a user equipment within the network by receiving tracking area updates from the user equipment. In each cell, an identifier indicating the tracking area to which the cell belongs is reported. The tracking area to which a user equipment terminal in idle mode belongs is registered by a location registration. A user equipment terminal stores the identifier indicating the tracking area registered by the location registration. Further, upon being moved, the user equipment terminal receives the reported identifier of the tracking area and determines whether the tracking area is changed.

As shown, a communication network with a first tracking area 130, a second tracking area 132 and a third tracking area 134 has several base stations 106 within each tracking area. Each base station has a “cell” -a Radio network object that can be uniquely identified by the user equipment from a (cell) identification that is broadcasted over a geographical area from one UTRAN Access Point.

As an example, the first tracking area 130 may include

cells

108, 110, 112, 114, 116, the second tracking area 132 may include the

cells

118, 120, 122, and the third tracking area 134 may include the

cells

124, 126, 128.

A user equipment 102 operating in a first tracking area 130 may select a cell based on evaluation of certain parameters. For example, the cell selection may be made based on such as received signal metric, signal code power, signal strength, chip energy or signal quality of the available cells.

The user equipment 102 may give an order of preference to the available cells in the first tracking area 130 and as an example, may list cell 108 as a first preferred cell, cell 110 as a second preferred cell, cell 112 as a next preferred cell, cell 114 as a subsequent preferred cell and cell 116 as the last available cell in the first tracking area 130.

The user equipment 102 using a Radio Access Technology (RAT) 104 may select a first preferred cell 108 and perform an attempt to camp on the first preferred cell 108.

In case of the selected cell being a faulty 5G or LTE cell, as per the current 3GPP specifications, the user equipment 102 may receive a rejection response and set the current tracking area as “FORBIDDEN” and search for available cells in a

different tracking area

132, 134, and if such cells are not found, the user equipment 102 would switch to a legacy network such as 2G or 3G RAT for Public Land Mobile Network (PLMN selection) .

In effect, as per the current scenario, despite having possibly non-faulty other cells in the first tracking area 130, the user equipment 102 may select a cell in another

tracking areas

132, 134 and may also end up switching to a legacy network.

The 5G/LTE cells belonging to an Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) can be categorized as follows:

Faulty cells 108: Available 5G or LTE cells belonging to EPLMN/EHPLMN inside the first tracking area 130 that may reject a registration request with 5GMM Cause #15 or EMM Cause #15 “ “no suitable cells in tracking area” ” . Such cells are considered as faulty cells.

Suitable cells

110, 112, 114, 116: Suitable 5G or LTE cells belonging to EPLMN/EHPLMN inside the first current tracking area 130 that may provide 5G or LTE service to the user equipment 102.

Other

tracking area cells

118, 120, 122, 124, 126, 128: Other 5G or LTE cells belonging to another

tracking areas

132, 134.

In an example of the prior art, the user equipment 102 may be located near the base station 106 of the faulty cell 108 and may select the faulty cell 108 due to high signal strength. The faulty cell 108 may reject the registration request with 5GMM cause #15 or EMM cause #15. The user equipment 102 may store the tracking area as “FORBIDDEN” and may search for a suitable cell in another

tracking areas

132, 134.

In this situation, as per the prior art, the user equipment 102 is not allowed to select another suitable 5G or LTE cell from cells belonging to EPLMN/EHPLMN inside current tracking area 130 that can provide 5G or LTE service to the user equipment 102.

Accordingly, despite having available suitable 5G or LTE cells, the user equipment 102 will have to connect to a cell in another

tracking area

132, 134 which may be much less preferred in the user’s cell selection evaluation otherwise, in comparison to the suitable 5G or

LTE cells

110, 112, 114, 116 in the current tracking area that can provide 5G or LTE service to the user equipment.

Alternatively, if cell selection in

other tracking area

132, 134 also fails, the user equipment may have to switch to a legacy network such as a 2G or a 3G network.

Until the user equipment moves to another tracking area, the user equipment will not be able to perform PLMN selection on 5G or LTE cells and will continue to operate in such legacy network until the forbidden tracking area list is deleted.

A user equipment 102 may communicate with a base station 106 to send a registration request, for example when it enters a new tracking area or when it is powered on. The user equipment 102 may initiate registration and send an initial registration request or a mobility and period registration update in 5G or ATTACH REQUEST/COMBINED ATTACH REQUEST/TRACKING AREA UPDATE REQUEST/COMBINED TRACKING AREA UPDATE REQUEST/SERVICE REQUEST in LTE, to a selected cell in a first tracking area.

The user equipment 102 may use a radio access technology such as 5G RAT or LTE RAT to communicate with the base station 106.

A control node 200 provides functionalities such as mobility, authentication, and bearer management for the user equipment 102 which is served by base stations 106. The control node 200 may receive, as a result of one or more requests sent to user equipment 102, information regarding signal quality between equipment and a number of base stations 106. The control node 200 may determine that a base station 106 is better situated or equipped than the other to communicate with the user equipment 102 based on the signal quality measurements received by the control node 200 or, in the alternative or in addition, based on scheduling factors and other network-side considerations. The control node 200 may be responsible for registering a user equipment 102 which attempt to perform an attach procedure, a tracking area update procedure, and/or any of various other procedures.

The user equipment 102 may be configured to communicate with the base station 106 using any of multiple RATs 104. The base station 106 may be coupled via a network to the control node 200. The user equipment 102 may attempt to obtain access to the network 5G/LTE by sending an initial registration request or a mobility and period registration update in 5G or ATTACH REQUEST/COMBINED ATTACH REQUEST/TRACKING AREA UPDATE REQUEST/COMBINED TRACKING AREA UPDATE REQUEST/SERVICE REQUEST in LTE, to a control node 200. Based on such request the control node 200 determines whether or not the user equipment 102 is permitted 5G/LTE access to the network in a particular tracking area.

The control node 200 may accept or reject the registration request and when it rejects the registration request, it sends a rejection response to the user equipment 102. The rejection response may include a reject cause value indicating the reason for rejection. As per 3GPP specifications, on receiving a rejection response, the user equipment 102 may act according to preconfigured instructions laid down in 3GPP specifications against each cause of rejection.

The user equipment 102 may include a processor 304 which may be any kind of computational or processing device capable of executing program instructions, codes, binary instructions and the like. The processor 304 may be or include a signal processor, digital processor, embedded processor, microprocessor or any variant such as a co-processor (math co-processor, graphic co-processor, communication co-processor or the like) or the like that may directly or indirectly facilitate execution of program code or program instructions stored thereon. In addition, the processor 304 may enable execution of multiple programs, threads, and codes.

The user equipment 102 may also include a storage memory 306. The storage memory 306 may include a random access memory (RAM) or another type of dynamic storage device that may store information and instructions, for example an application, for execution by processor 304, a read-only memory (ROM) device or another type of static storage device.

The user equipment 102 may include a receiver, a transmitter and other components and circuitry for communication with the base station 106 over a wireless network. Alternatively, it may include a transceiver 308. The transceiver is transmitter assembled with a receiver. It is capable of wirelessly transmitting and receiving data over a network. In some embodiments, the processor 304 and the transceiver 308 may be included in an integrated circuit device, while in other embodiments, the processor 304 and the transceiver 308 may be separate.

The user equipment may have a display 310 including a user interface which may be a virtual keypad or any other means through which a user may input information into the user equipment 102. The display 310 may also serve the purpose of providing output to the user. The display 310 may also include, or be integrated with a touch screen or touch-sensitive overlay for receiving touch input from the user.

The user equipment 102 may further include a registration attempt counter 312 for keeping a track of a number of cells on which the registration has been attempted. A registration attempt counter 312 may be implemented in the form of a digital circuitry, for e.g. as a digital counter.

The control node 200 may include a network port 314. The network port 314 may be coupled to and configured to communicate with the base stations 106 and/or the other wireless network, other cellular core network entities and/or other devices.

The control node 200 further includes a processing element 316 which may be coupled operably to the one or more network ports 314, wherein the control node 200 may be configured to implement any of the methods as discussed above. The processing elements 316 include, for example, circuits such as an ASIC (Application Specific Integrated Circuit) , portions or circuits of individual processor cores, entire processor cores, individual processors, programmable hardware devices such as a field programmable gate array (FPGA) , and/or larger portions of systems that include multiple processors.

A Registration request 302 includes an initial registration request or a mobility and period registration update in 5G or ATTACH REQUEST/COMBINED ATTACH REQUEST/TRACKING AREA UPDATE REQUEST/COMBINED TRACKING AREA UPDATE REQUEST/SERVICE REQUEST in LTE.

A REGISTRATION REJECT message 318 includes a 5GMM cause #15 or an ATTACH REJECT/TRACKING AREA UPDATE REJECT/SERVICE REJECT message including an EMM cause #15.

In an embodiment, user equipment 102 having a processor 304, a storage memory 306 and a transceiver 308 connected to the processor 304 and the storage memory 306 is configured to communicate using RAT 104 with a base station 106 in a communication network. The user equipment 102 may perform an attempt to camp on a first preferred cell 108in a first tracking area 130 and send a registration request 302 to a control node 200. The control node 200 of a first public land mobile network (PLMN) may reject the request and transmit a first REGISTRATION REJECT message 318 to the user equipment 102.

Figure 4 illustrates a block diagram of a control node.

As shown, the control node may include processing elements which may execute program instructions for the control node. The processing element 316 may also be coupled to a memory management unit (MMU) for e.g., memory 404 and read only memory (ROM) 406, which may be configured to receive addresses from the processing element 316 and translate those addresses to locations in memory.

The control node 200 may also include a network port 314. The network port 314 may be configured to communicate with base stations 106 and/or other cellular core network entities and/or devices. The processing element 316 may be operably coupled to the one or more network ports 314 wherein the control node is configured to implement any of the methods described above, for e.g. the control node 200 may determine that a base station 106 is better situated or equipped than the other to communicate with the user equipment 102 based on the signal quality measurements received by the control node 200. The processing elements 316 may include, for e.g., circuits such as integrated circuits, portions or circuits of individual processor cores, entire processor cores, individual processors, programmable hardware devices such as a field programmable gate array (FPGA) , and/or larger portions of systems that include multiple processors.

Figure 5 illustrates a flowchart depicting a method of registration of a user equipment 102 in a communication network in accordance with an embodiment of the present invention.

At block 502, a user equipment 102 may perform an attempt to camp on a first preferred cell 108 in a first tracking area 130 and send a registration request 302 to a control node 200 of a first public land mobile network (PLMN) .

At block 504, the registration may be successful or the control node 200 may send a rejection response. Where the rejection response is unsuccessful, it may be determined at block 506 whether the rejection response is a first reject cause #15.

At block 508, in case where the rejection response is a first reject cause #15, the user equipment 102 may determine if the first preferred cell 108 belongs to an Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) .

At block 510, in case where the first preferred cell 108 belongs to an EPLMN or EHPLMN, the user equipment 102 may block the first preferred cell 108 for further registration attempts for a preconfigured time and search for a second preferred cell 110 in first tracking area 130.

At block 512, where the user equipment 102 finds a second preferred cell 110 in the first tracking area 130, it may perform an attempt to camp on the second preferred cell 110 and may restart the same process at block 514 on the second preferred cell 110and send a registration request to the control node 200.

At block 516, where the user equipment 102 does not find any suitable cells in the first tracking area 130 or where the user equipment 102 has received a rejection response from all

available cells

108, 110, 112, 114, 116 in the first tracking area 130, the user equipment 102 may add the first tracking area 130 to a forbidden list and initiate the registration process in a second tracking area 132.

At block 518, where the user equipment 102 finds a suitable cell in the second tracking area, the user equipment 102 may perform an attempt to camp on a first preferred cell 118 in the second tracking area 132 and restart the same process at block 520 on the first preferred cell 118 in the second tracking area 132 and send a registration request to the control node 200.

At block 522, where the user equipment 102 does not find any suitable cells in the second tracking area 132 or where the user equipment 102 has received a rejection response from all

available cells

118, 120, 122 in the second tracking area 130, the user equipment 102 may switch to a legacy RAT such as a 3G or 2G RAT.

In an embodiment of the present invention, a user equipment 102 may attempt to camp on a first preferred cell 108 and send an initial registration request 302 or a mobility and period registration update (302) in 5G or ATTACH REQUEST/COMBINED ATTACH REQUEST/TRACKING AREA UPDATE REQUEST/COMBINED TRACKING AREA UPDATE REQUEST/SERVICE REQUEST (302) in LTE, to the first preferred cell 108 in a first tracking area 130.

In case the user equipment 102 receives a REGISTRATION REJECT message 318 including a 5GMM cause #15 or an ATTACH REJECT/TRACKING AREA UPDATE REJECT/SERVICE REJECT message including an EMM cause #15, the user equipment 102 may check if the selected cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) .

If the selected cell belongs to EPLMN/EHPLMN, the user equipment 102 may store information of the first selected cell and block the first selected cell for registration for a preconfigured time. The user equipment 102 may now select a second preferred cell 110 in the first tracking area 130 for registration. The user equipment 102 may initiate registration on such second preferred cell 110 and may not store the first tracking area 130 as “FORBIDDEN” .

In one of the embodiments, the user equipment 102 may successfully complete registration on the second preferred cell and avails 5G or LTE RAT on the second preferred cell 110 in the first tracking area 130. In this embodiment, the user equipment 102 may benefit from availing 5G or LTE RAT in the first tracking 130 area when registration on the first selected cell 108 in the first tracking area 130 failed with a first reject cause #15. In the prior art, the user equipment 102 would have moved to a second tracking area 132 or a lower legacy RAT.

In a situation where there is no legacy RAT support in a particular tracking area or where the user equipment 102 is a 5G or LTE only device and a faulty 5G or LTE cell rejects one of the above registration/attach/update/service requests of the user equipment 102, the present embodiment would allow the user equipment 102 to avail a 5G or LTE RAT using a second cell 110 in the first tracking area 130. In the prior art, a 5G or LTE only device or a tracking area with 5G or LTE only network would get no service despite having other available working 5G or LTE cells in the first tracking 130 area if the first preferred cell 108 turns out to be a faulty cell or whenever a 5GMM/EMM reject cause #15 is received by the user equipment 102.

In another embodiment, where the user equipment 102 may repeat the same steps of registration on the second preferred cell 110 and in case the user equipment 102 again receives a REGISTRATION REJECT message including a 5GMM cause #15 or an ATTACH REJECT/TRACKING AREA UPDATE REJECT/SERVICE REJECT message including an EMM cause #15, the user equipment 102 shall check if the second preferred cell 110 belongs to an EPLMN/EHPLMN.

If the selected second preferred cell 110 belongs to EPLMN/EHPLMN, the user equipment 102 may block the second selected cell for registration for a preconfigured time. The user equipment 102 shall now select a next preferred cell 112 in the first tracking area 130 for registration. The user equipment 102 may initiate registration on such next preferred cell 112 and may not store the first tracking area as “FORBIDDEN” .

As the number of such faulty cells is foreseen to be low, in another embodiment the steps of next preferred cell selection may continue to be performed on subsequent

available cells

114, 116 until all the available cells in the first tracking area 130 are exhausted.

In another embodiment, when the user equipment 102 receives a REGISTRATION REJECT message 318 including a 5GMM cause #15 or an ATTACH REJECT/TRACKING AREA UPDATE REJECT/SERVICE REJECT message including an EMM cause #15 from all the

available cells

108, 110, 112, 114, 116 in the first tracking area 130, the user equipment 102 may store the first tracking area 130 to a “FORBIDDEN” list and may carry on search for available cells in a second tracking area 132.

In another embodiment, the user equipment 102 may carry out the same steps on all

available cells

118, 120, 122 in the second tracking area 132 and if the user equipment 102 receives REGISTRATION REJECT messages 318 from all

such cells

118, 120, 122, the user equipment 102 may move to legacy RAT such as 2G or 3G RAT.

In another embodiment, the step whether the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) is carried out by comparing Public Land Mobile Network (PLMN) of the first preferred cell to a database of Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) on a SIM (Subscriber Identity Module) or a USIM (Universal Subscriber Identity Module) to determine if the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) .

In another embodiment, a threshold of maximum number of available cells in the first tracking area 130 on which the user equipment 102 may attempt registration is fixed. At block 602, when the user equipment 102 has reached the threshold, the user equipment 102 may store the first tracking area 130 to a “FORBIDDEN” list and may carry on search for available cells in a second tracking area 132.

The fixing of threshold may reduce possible delay in registration in case of large number of faulty cells in a tracking area.

In another embodiment, the threshold is fixed at three cells in the first tracking area 130. In another embodiment, the threshold is fixed at a total number of available cells in the first tracking area 130. In another embodiment, the threshold is fixed at a total number of the available cells in the first tracking area 130 or three cells in the first tracking area, whichever is less.

In another embodiment, the user equipment 102 maintains a registration attempt counter 312 of a number of cells on which the registration has been attempted.

In another embodiment, a threshold of maximum number of available cells in the second tracking area 132 on which the user equipment 102 may attempt registration is fixed. This threshold may be fixed in a similar manner to the threshold for the first tracking 130 such that when the threshold is reached, the second tracking area is added to a forbidden list and the user equipment102 may initiate registration using a legacy RAT.

In another embodiment, the legacy RAT may be a 3G or 2G RAT.

In another embodiment, the user equipment 102 would select a cell based on a predefined cell selection strategy which may include evaluation of several parameters such as received signal metric, signal code power, signal strength, chip energy or signal quality of the available cells.

While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is not to be limited by the foregoing examples, but is to be understood in the broadest sense.

Claims

A method of registration performed by a user equipment in a communication network using a radio access technology (RAT) , comprising:

performing an attempt to camp on a first preferred cell in a first tracking area;

sending a registration request to a control node of a first public land mobile network;

receiving, from the control node, a first rejection response comprising a first reject cause #15 “no suitable cells in tracking area” ;

in response to receiving the first rejection response, when the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or an Equivalent Home Public Land Mobile Network (EHPLMN) :

blocking the first preferred cell for further attempts for a preconfigured time;

performing an attempt to camp on a second preferred cell in the first tracking area and sending a second registration request to the control node.
The method of claim 1, wherein the RAT is a 5th generation (5G) RAT.
The method of claim 1, wherein the RAT is a Long Term Evolution (LTE) RAT.
The method of claim 1 or 2, wherein the registration request comprises one of an initial registration request or a mobility and periodic registration update request.
The method of claim 1 or 3, wherein the registration request comprises one of an attach request, a combined attach request, a tracking area update request, or a combined tracking area update request.
The method of any of the above claims, further comprising:

comparing the first Public Land Mobile Network (PLMN) of the first preferred cell to a database of the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) on a SIM (Subscriber Identity Module) or a USIM (Universal Subscriber Identity Module) to determine if the first preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) .
The method of claim 2, wherein the first reject cause comprises a 5 ^th Generation Mobility Management (5GMM) cause #15 “no suitable cells in tracking area” .
The method of claim 3, wherein the first reject cause comprises an evolved packet service mobility management (EMM) cause #15 “no suitable cells in tracking area” .
The method of claim 1, further comprising:

receiving a second rejection response comprising a second reject cause “no suitable cells in tracking area” ;

in response to receiving the second rejection response, when the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) :

blocking the second preferred cell for further attempts for a preconfigured time;

performing an attempt to camp on a next preferred cell in the first tracking area and sending a next registration request to the control node.
The method of claim 9, further comprising:

receiving a further rejection response comprising a further reject cause “no suitable cells in tracking area” ;

in response to receiving the further rejection response, when the second preferred cell belongs to the Equivalent Public Land Mobile Network (EPLMN) or the Equivalent Home Public Land Mobile Network (EHPLMN) :

blocking the next preferred cell for further attempts for a preconfigured time;

performing an attempt to camp on a subsequent preferred cell in the first tracking area and sending a next registration request to the control node.
The method of claim 10, further comprising:

repeating the steps of claim 10, on receiving a subsequent rejection message, on remaining cells in the first tracking area until the registration request of the user equipment is rejected by all available cells in the first tracking area.
The method of claim 1, further comprising:

fixing a threshold of a maximum number of available cells in the first tracking area on which the user equipment shall attempt the registration.
The method of claim 12, wherein when the threshold is reached or all the available cells in the first tracking area have sent the reject response, the first tracking area is added to a forbidden list and the registration is initiated on an available cell in a second tracking area.
The method of claim 12, wherein the threshold is fixed at three cells in the first tracking area.
The method of claim 12, wherein the threshold is fixed at a total number of the available cells in the first tracking area.
The method of claim 12, wherein the threshold is fixed at a total number of the available cells in the first tracking area or three cells in the first tracking area, whichever is less.
The method of claim 1, wherein the user equipment maintains a registration attempt counter of a number of cells on which the registration has been attempted.
A user equipment comprising:

a processor;

a storage memory; and

a transceiver connected to the processor and the storage memory, the transceiver configured to use a radio access technology (RAT) to communicate with a communication network and the user equipment configured to perform the method of any of claims1-17.
A method performed at a control node of a first public land mobile network, for registration of a user equipment in a communication network using a radio access technology (RAT) , comprising:

receiving a registration request from the user equipment when the user equipment attempts to camp on a first preferred cell in a first tracking area;

sending a first rejection response comprising:

a first reject cause #15 “no suitable cells in tracking area” ; and

instructions to the user equipment to block the first preferred cell, if the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or an Equivalent Home Public Land Mobile Network (EHPLMN) , for further attempts for a preconfigured time and to perform an attempt to camp on a second preferred cell in the first tracking area.
A control node of a first public land mobile network (PLMN) , comprising:

one or more network ports; and

a processing element operably coupled to the one or more network ports; wherein the one or more network ports and the processing element are configured to:

receive a registration request from a user equipment using a radio access technology (RAT) , when the user equipment attempts to camp on a first preferred cell in a first tracking area;

send a first rejection response comprising:

a first reject cause #15 “no suitable cells in tracking area” ; and

instructions to the user equipment to block the first preferred cell, if the first preferred cell belongs to an Equivalent Public Land Mobile Network (EPLMN) or Equivalent Home Public Land Mobile Network (EHPLMN) , for further attempts for a preconfigured time and to perform an attempt to camp on a second preferred cell in the first tracking area.