WO2015154789A1 - Plmn scanning - Google Patents

Plmn scanning Download PDF

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Publication number
WO2015154789A1
WO2015154789A1 PCT/EP2014/056905 EP2014056905W WO2015154789A1 WO 2015154789 A1 WO2015154789 A1 WO 2015154789A1 EP 2014056905 W EP2014056905 W EP 2014056905W WO 2015154789 A1 WO2015154789 A1 WO 2015154789A1
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Prior art keywords
plmn
wireless communication
communication device
current
priority
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PCT/EP2014/056905
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French (fr)
Inventor
Srinivasa K SIVARAM
Sajal Kumar Das
Shiva Kumar GUNDAPPA
Tomas HOLMSTRÖM
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Telefonaktiebolaget L M Ericsson (Publ)
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Priority to PCT/EP2014/056905 priority Critical patent/WO2015154789A1/en
Publication of WO2015154789A1 publication Critical patent/WO2015154789A1/en

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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W48/00Access restriction; Network selection; Access point selection
    • H04W48/16Discovering, processing access restriction or access information

Abstract

A wireless communication device is connected to a current public land mobile network, PLMN, and determines whether or not the current PLMN is a home public land mobile network, HPLMN. If the current PLMN is not the HPLMN a scan timer value is set that specifies a time period between attempts by the wireless communication device to connect to a PLMN having a priority that is higher than a priority of the current PLMN. The scan timer value is an increasing function of a geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN.

Description

PLMN SCANNING

TECHNICAL FIELD

The present disclosure relates to public land mobile network (PLMN) scanning and more specifically to a method performed by a wireless communication device, a corresponding wireless communication device and computer program.

BACKGROUND

A PLMN is a network that is established and operated by an administration or by a recognized operating agency (often denoted "operator") for providing land mobile communications services to the public. Each operator providing mobile services has its own PLMN. As defined in third generation partnership project (3GPP) technical specification TS 24.301 , section 9.9.3.12, every PLMN is identified by a 3 digit Mobile Country Code (MCC) and a 3 (or 2) digit Mobile Network Code (MNC).

A wireless communication device can typically operate in a plurality of PLMN's according to an order of priority as selected by a user of the wireless communication device or as selected by the operator. The PLMN that is associated with the highest priority is often referred to as a home PLMN (HPLMN), and information about HPLMN is stored as International Mobile Subscriber Identity (IMSI) information in a Subscriber Identification Module (SIM) or Universal SIM (USIM) in the wireless communication device as illustrated in table 1 , where HNI is an abbreviation of Home Network Identifier and MSIN is an abbreviation of Mobile Subscriber Identification Number. The home HPLMN is the PLMN that belongs to the operator that issues the SIM or USIM.

IMSI

HNI

MCC MNC MSIN

(3 digits) (2-3 digits) (9-10 digits)

Table 1

At any given point in time, a wireless communication device always knows what the MCC and MNC numbers of the HPLMN are. A function of the MCC is to identify the domiciliary country of a wireless communication device or a user of the wireless communication device. MCC indicates the country of the operator that issues the SIM/USIM. The HPLMN is that operator's network. The function of the MNC is to identify the home network, within the country associated with the MCC, of the wireless communication device/user.

The geographical area under any PLMN is divided into different location areas to locate the wireless communication device. Location area code (LAC) is used to identify different location areas. Each location area of any PLMN has its own unique identifier which is known as its location area identity (LAI). This internationally unique identifier is used for updating the location of mobile subscribers. The structure of LAI is shown in table 2. LAI contains LAC, MNC and MCC. The MCC and MNC are same as defined above and LAC is a 16 bit (2 octets) number thereby allowing 65536 location areas within one PLMN (specified in 3GPP TS 24.008 V12.5.0 (2014-03), page 424, sec. 10.5.1.3). The LAI is broadcast regularly from the network through a broadcast control channel (BCCH). A wireless communication device reads the LAI and stores it. Later, when wireless communication device moves to a new area (or after power on) and found the LAC of the current cell is different from its originally stored LAI, then wireless communication device will inform the network of the current location area via a location update procedure. Also, the network uses the LAI for paging the wireless communication device.

Figure imgf000004_0001

Table 2

After a power on, a wireless communication device searches for the last registered PLMN (R-PLMN). The last registered PLMN may be a HPLMN or any other registered PLMN. If the HPLMN is available it shall have the highest priority. If the wireless communication device is unable to find the HPLMN, it shall search the PLMNs with the highest priority according to the user preference and/or the operator preference lists. Once the PLMN with the highest priority available is found, the wireless communication device performs a location registration.

If the wireless communication device fails to find the HPLMN and therefore performs a location registration by selecting a PLMN other than the HPLMN, the wireless communication device considers a location-registered PLMN as a visited PLMN (VPLMN) and, while connected to the VPLMN, periodically searches for a PLMN with a higher priority than the VPLMN. During these searches, if a PLMN with a higher priority than a currently registered VPLMN is found, the wireless communication device performs a location registration with the found PLMN. In some more detail, during a PLMN search, the wireless communication device performs a radio access technology (RAT) and frequency scanning at regular intervals. The time interval between two successive scanning cycles is stored in Elementary Files_Higher Priority PLMN (EFJHPPLMN) in a SIM. When registered in a VPLMN, the wireless communication device searches for the HPLMN using such a scanning cycle.

As defined in 3GPP TS 23.122 section 4.4.3.3, if the wireless communication device is in a VPLMN, the wireless communication device shall periodically attempt to obtain service on (in priority order):

1 ) Its HPLMN (if an equivalent HPLMN (EHPLMN) list is not present or is empty), or 2) one of its EHPLMNs (if the EHPLMN list is present), or

3) a higher priority PLMN/access technology combinations listed in

a) the User Preferred PLMN List, or

b) the Operator Preferred PLMN List,

by scanning for available networks periodically, based on the fixed HPLMN scan timer value as stored in SIM.

As defined in 3GPP TS 3GPP TS 1 1 .1 1 V8.14.0 (2007-06), section 10.3.5, this HPLMN scanning timer value is set to any value from n minutes (minimum) to (16Y+Z)*n minutes (maximum value). Where, n = 6 minutes, Y = 15 and Z =15. That provides maximum value = (16Y+Z)*n = (16*15+15)*6 = 1530 minutes. But, today generally it is set to 6 to 10 minutes. This periodic scanning leads to large power consumption in the wireless communication device.

Furthermore, today users often travel between countries and roams frequently in

VPLMNs, which means that wireless communication devices often stays in VPLMN areas for long periods of time. This is particularly relevant when users travel (with their wireless communication device) to countries which are very far from their native countries (e.g. countries where their HPLMN belongs), or goes to a place far off from the HPLMN area, then there is a very small probability that the user will be reached at his/her HPLMN area very quickly. So, in such scenarios, scanning the HPLMN with very short periodicity is not a good solution, especially when battery power is a major constraint. On top of that, if the wireless communication device is of a type that has two SIMs (dual SIM device) then both the modems in the wireless communication device will be doing the same activities and that will lead to twice the power consumption of such a dual SIM device. The prior art includes "A method for background scanning for HPLMN in overlapping service areas of HPLMNs & VPLMNs", Indian patent number IN255944, where background scans for HPLMN are restricted to only a particular set of LAIs in which the probability of finding the HPLMN is not equal to zero.

SUMMARY

In view of the above, an object of the present disclosure is to at least mitigate some of the drawbacks of the prior art. This object is achieved in a first aspect by a method performed by a wireless communication device that is connected to a current PLMN. The method comprises determining whether or not the current PLMN is a HPLMN of the wireless communication device. If the current PLMN is not the HPLMN, then a scan timer value is set that specifies a time period between attempts by the wireless communication device to connect to a PLMN having a priority that is higher than a priority of the current PLMN, where the scan timer value is an increasing function of a geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN. In another aspect there is provided a wireless communication device comprising radio circuitry, a processor and a memory. The memory contains instructions executable by the processor whereby the wireless communication device is operative to, when being connected to a current public land mobile network, PLMN:

- determine whether or not the current PLMN is a home public land mobile network, HPLMN, of the wireless communication device and if the current PLMN is not the HPLMN:

- set a scan timer value that specifies a time period between attempts by the wireless communication device to connect to a PLMN having a priority that is higher than a priority of the current PLMN, where the scan timer value is an increasing function of a geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN. In other aspects there are provided a computer program and a carrier. These aspects correspond to the method aspect as summarized above.

In other words, for example, if the wireless communication device finds that it is located in a current PLMN that is far from the HPLMN or other higher prioritized PLMNs, the increasing function may make sure that the scan timer is set to a high value in relation to a default, or typical, value. As the skilled person will realize, an increasing function is a function that increases as the input to the function increases.

For example, if the wireless communication device finds itself located in a PLMN in Australia and the HPLMN of the wireless communication device is a PLMN in Sweden, it would take on the order of one day to return to a geographical location that is in Sweden. Consequently, the wireless communication device will have no chance of being successful in attempting to connect to the HPLMN in Sweden until at least several hours, or even days, have passed. In this situation, thanks to that the scan timer value is an increasing function of the geographical distance, the scan timer value would be set to a value that is much larger than the typical scan timer values of minutes, as is the case in the prior art, and by that mitigating drawbacks related to battery consumption in the wireless communication device. Hence, an advantage is that a larger power saving than in the prior art is obtainable in the wireless communication device. If the wireless communication device has dual SIMs, i.e. dual radio modem wireless communication devices, the power saving will be even larger.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates schematically wireless communication devices and PLMN's, figure 2 is a flow chart of a method performed by a wireless communication device, figure 3 is a flow chart of a method performed by a wireless communication device, figure 4 is a flow chart of a method performed by a wireless communication device, figure 5 is a block diagram of a wireless communication device, and

figure 6 is a block diagram of a wireless communication device.

DETAILED DESCRIPTION

Figure 1 illustrates schematically exemplifying PLMNs in the form of a first PLMN 101 , a second PLMN 103 and a HPLMN 105 in relation to which embodiments herein may be implemented. The PLMNs 101 ,103,105 may be PLMNs of any 3GPP wireless communication system, such as a Universal Mobile Telecommunication System (UMTS) Wideband Code Division Multiple Access (WCDMA) network, a Global System for Mobile communication (GSM) or the like. The PLMNs 101 ,103,105 may even be PLMNs in an evolution of any one of the aforementioned systems or a combination thereof. Moreover, it is to be noted that (as will be discussed in detail below) the HPLMN may correspond to any PLMN that has a priority that is higher than a priority of a PLMN in which a wireless communication device is currently located. The first PLMN 101 comprises a first LA 121 and a second LA 123. The second PLMN 103 comprises a third LA 125.

A wireless communication device 102 is located in a radio cell 122 in the first LA 121 in the first PLMN 101 . As will be discussed in more detail below, the wireless

communication device 102 is capable of moving between different locations, and to illustrate this capability the wireless communication device 102 is also indicated as being located in the third LA 125 in the second PLMN 103. It is to be noted that, as used herein, the term "wireless communication device" may refer to a user equipment (UE), a subscriber unit, mobile phone, a cellular phone, a Personal Digital Assistant (PDA), equipped with radio communication capabilities, a smartphone, a laptop or personal computer (PC) equipped with an internal or external mobile broadband modem, a tablet PC with radio communication capabilities, a portable electronic radio communication device or the like. As the skilled person will realize, communication between entities in the PLMNs

101 ,103,105 typically involves a number of nodes. Schematic representations of such nodes are nodes 111 ,113,115,117 with which the wireless communication device 102 can communicate. The nodes 1 1 1 ,1 13,1 15,1 17 may, for example, refer to a Base Station (BS), a Base Transceiver Station (BTS), a Radio Base Station (RBS), a Remote Radio Unit (RRU), an access point, a NodeB in so called Third Generation (3G) networks, evolved Node B (eNodeB or eNB) in Long Term Evolution (LTE) networks, or the like. In UMTS Terrestrial Radio Access Network (UTRAN) networks, the term "radio network node" may also refer to a Radio Network Controller. Furthermore, in Global System for Mobile Communications (GSM) EDGE Radio Access Network (GERAN), where EDGE is short for Enhanced Data rates for GSM Evolution, the term "radio network node" may also refer to a Base Station Controller (BSC). As will be discussed in more detail below, the nodes 1 1 1 ,1 13,1 15,1 17 provide system information to wireless communication devices in the PLMNs, including the wireless communication device 102. The system information comprises information about the PLMN in which the system information is transmitted, such as the LAI that consists of MCC, MNC and LAC.

Needless to say, the PLMN's 101 ,103,105 typically comprise a plurality of nodes, radio cells and LA's. However, for the sake of simplifying the description, most of these are not illustrated in figure 1 .

Turning now to figure 2 and with continued reference to figure 1 , embodiments of methods in the wireless communication device 102 will be discussed. The wireless communication device 102 is connected to a current public land mobile network, here exemplified by the first PLMN 101. Embodiments of methods comprise a number of actions as follows.

Action 201

A determination is made whether or not the current PLMN 101 is a HPLMN 105 of the wireless communication device 102.

Action 203

If the current PLMN 101 is not the HPLMN 105, the method continues in action 207. If the current PLMN 101 is the HPLMN 105, the method ends without further actions as illustrated by a no action 205. For example, if it is found that current PLMN 101 is the HPLMN 105 there is no need to perform HPLMN scan as the wireless communication device 102 is already camped on the HPLMN. Action 207

A scan timer value is set that specifies a time period between attempts by the wireless communication device 102 to connect to a PLMN having a priority that is higher than a priority of the current PLMN (which may be the HPLMN 105), where the scan timer value is an increasing function of a geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN 101 (which may be the determined geographical distance 1 10).

In some embodiments, the geographical distance 1 10 between a current position of the wireless communication device 102 and a position of the PLMN having a priority that is higher than the priority of the current PLMN is represented by a mobile country code, MCC, of the current PLMN 101 and a MCC of the PLMN having a priority that is higher than the priority of the current PLMN 101 .

In some embodiments, the geographical distance 1 10 between a current position of the wireless communication device 102 and a position of the PLMN having a priority that is higher than the priority of the current PLMN is represented by a mobile network code, MNC, of the current PLMN 101 and a MNC of the PLMN having a priority that is higher than the priority of the current PLMN 101 .

In some embodiments, the geographical distance 1 10 between a current position of the wireless communication device 102 and a position of the PLMN having a priority that is higher than the priority of the current PLMN 101 is obtained by reading a lookup table that comprises mapping information that comprises:

- MCC, MNC pairs pertaining to a plurality of PLMNs, and

- a geographical distance between each MCC, MNC pair.

In some embodiments, the lookup table comprises a scan timer value pertaining to each geographical distance, and wherein the setting of the scan timer value comprises reading the scan timer value from the lookup table.

In other words, scan timer values are stored in the lookup table associated with each stored distance pair between MCC, MNC pairs. In these embodiments there is no need to compute the scan timer value based on estimated distance as is the case in other embodiments (as will be discussed below), rather here the scan timer value is

predetermined and stored according to distance. More specifically, the lookup table (or "database") comprises the distance between different MCCs (e.g. countries). If the distance between two MCCs are small (implying neighboring countries) then the possibility for the wireless communication device returning to the home country location from the visited country location within a specified time (T_distance) is possible. In such a case the HPLMN scan timer value will be set to a lower value (Scan_Timer_low). But if it is found that the MCC of the current PLMN 101 (e.g. obtained from the LAI provided by the current PLMN) is far from the MCC of the HPLMN then there is no possibility that within a specified time (T_distance) the user can reach the HPLMN, so, in such case the HPLMN scan timer value is set to a very high value (Scan_Timer_High). The same is true if the user is in national roaming and changes the location area and goes from one LA to another LA in the current PLMN 101. In that case, the MCC will typically remain unchanged but the MNC will be different at the new location. So, similarly from the lookup table, the wireless communication device will find out the possibility of user returning to the HPLMN from the LA in the current PLMN 101 and based on that it will set the scan timer value to a low or high value.

In some embodiments, instead of reading the scan timer value from the lookup table, the setting of the scan timer value comprises evaluating a continuous function having as input at least the geographical distance (for example, as read from the lookup table) between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN 101 .

That is, using the distance between the MCC, MNC pairs as stored in the database the scan timer value is computed dynamically based on equation 1 below. As already established, a larger distance between these pairs corresponds to a lesser the possibility that the user might return to HPLMN quickly from the visited location, i.e. the current PLMN 101 that is not the HPLMN. So, the scan timer value is set as a continuous function of distance and an example of such a function is: PLMN scan timer value = 3*(Distance between the MCC, MNC pair as per stored table database) (Equation 1 )

Here, β is a constant and the value of it can be derived empirically by knowing the distance between two MCC, MNC pairs and actual need of PLMN scan timer value. The scan timer value can vary from 6 minutes to 1 ,530 minutes as explained above. For example, if the distance between the MCC, MNC pairs found to be 1500 km and a timer value to be set for the HPLMN scanning is, e.g., 10 hours or 600 minutes, then the derived β value would be = 600 min / 1500 km = 0.4 min/km.

Then in all other cases, when distance in km is known from the stored table and β is said to be 0.4 min/km, then the HPLMN scan timer can be set according to equation 1 above. Some embodiments comprises prior to the setting of the scan timer value:

- determining whether or not the current PLMN 101 is a highest preferred PLMN, and wherein the setting of the scan timer value is performed only in case the current PLMN 101 is the highest preferred PLMN.

In some embodiments, the determination of whether or not the current PLMN 101 is a highest preferred PLMN comprises analysing at least one list that comprises information that identifies a plurality of PLMN's and corresponding order of preference for each PLMN in the list.

In some embodiments, said list is any of a user preferred PLMN, UPPLMN, list and an operator preferred PLMN, OPPLMN, list. Some embodiments comprises:

- determining the MCC of the current PLMN 101 ,

- determining the MCC of the PLMN's in the list, and wherein the setting of the scan timer value is performed only in case the MCC of the current PLMN 101 is equal to the MCC of the PLMN having the highest order of preference. In some embodiments, the PLMN having a priority that is higher than the priority of the current PLMN 101 is any of the HPLMN and an equivalent home public land mobile network, EHPLMN.

Turning now to figure 3 and with continued reference to figure 1 , embodiments of methods in a wireless communication device 102 will be discussed in some more detail. The wireless communication device 102 is switched on in action 301 and performs connection procedures via node 1 1 1 resulting in that the wireless communication device 102 is camping on the cell 122 in the first PLMN 101 , as indicated by action 303. The specific procedures involved in actions 301 and 303 are known to the skilled person and will therefore not be discussed in more detail here. Actions 305 and 307

The wireless communication device 102 checks in action 305 whether the currently camped PLMN is Home PLMN or not. If it is a home PLMN then there is no need (as indicated by the no-action 307, to perform a scan for HPLMN as the wireless

communication device 102 is already camped on the HPLMN. So, there is no need to set a timer value since no scan timer is to be used.

If it is found by the checking in action 305 that the PLMN currently camped on is not the HPLMN, then that indicates that the wireless communication device 102 is at a location in a visited PLMN. Then the scanning of user preferred or operator preferred PLMNs are performed according to the following actions. Action 309

A check is made whether a user preferred PLMN list in the wireless communication device 102 is empty or not (an empty list means that the user has not selected any preferred PLMN). Actions 311 and 313

In case the user preferred PLMN list in the wireless communication device 102 is found not to be empty, in action 309, then the wireless communication device 102 checks whether the PLMN on which the wireless communication device 102 is camping on is the highest user preferred PLMN. If so, then the PLMN scan timer value is set in a dynamical manner, indicated by action 313, as summarized above and as will be described in more detail below in connection with figure 4.

Action 315

If it is found in action 31 1 that the PLMN on which the wireless communication device 102 is camping on is not the highest user preferred PLMN, then the wireless communication device 102 checks whether or not there are any remaining PLMNs in the user preferred PLMN list. If there are remaining PLMNs in the user preferred PLMN list, the scan timer value is set in a legacy manner in action 317 as will be described below. If there are no remaining PLMNs in the user preferred PLMN list, action 323 takes place as will be described below. Action 319

In case the user preferred PLMN list in the wireless communication device 102 is found, in action 309 or in action 315, to be empty, then a check is made of an operator preferred PLMN list in action 319. Here, if it is found that the operator preferred PLMN list is empty, then it is actually not a valid case and, as indicated by a non-valid action 321 , in such case an option is to set the timer in a legacy manner as described below.

Actions 323 and 327

If it is found in action 319 that the operator PLMN list is not empty, a check is made whether or not the PLMN on which the wireless communication device 102 is camping is the highest operator preferred PLMN. If the wireless communication device 102 is camping on the highest preferred operator PLMN, then the PLMN scan timer value is set in a dynamical manner, indicated by action 327, as summarized above and as will be described in more detail below in connection with figure 4.. Actions 317 and 325

If it is found, in action 323, that the PLMN on which the wireless communication device 102 is camping on is not the highest operator preferred PLMN, or if there are remaining PLMNs in the user preferred PLMN list, as found in action 315, then the scan timer is set according to a legacy manner by which the HPLMN scan timer value is set at a fixed value ranging from 6 minutes to 1 ,530 minutes as discussed above.

In the above mentioned scenario (action 317 and 325), another option to set the scan timer value is to check the possibility of finding High priority user preferred or operator preferred PLMNs in that location areas (LA) based on the wireless communication device developed trained data base from the past history. Also, it can be based on the mobility detection of the wireless communication device. That means, if the device is moving, then there is a possibility of getting higher priority PLMN compared to the presently camped one. Otherwise if the wireless communication device is static, then it is not required to search for any other higher priority PLMNs in this scenario. Therefore, the HPLMN scan timer set shall be set to a fixed value (legacy method). If the wireless communication device is moving, the HPLMN scan timer value shall be set dynamically.

As already specified in 3GPP TS 23.122, the wireless communication device should only attempt to access higher priority PLMNs from the User preferred PLMN (UPPLMN) or Operator Preferred PLMN (OPPLMN) lists if they belong to the same country as the presently registered PLMN (RPLMN). Where, the user preferred PLMN is preferred list of PLMNs selected by the user according to his/her priority and operator preferred PLMN is the preferred list of PLMN selected by the operator according to its priority. Both are stored in the SIM. As long as there are no other higher priority PLMNs in the list that belongs to the same country the dynamic scan timer values (according to the difference in distance between MCC pairs) could be used. The stored database in the wireless communication device will be containing all MCCs of the UPPLMN and OPPLMN lists.

Turning now to figure 4 and with continued reference to figure 1 , a more detailed description will follow of embodiments relating to setting the scan timer value in a dynamical manner by using the lookup table as discussed above. When the wireless communication device 102 has decided that it shall set the HPLMN scan timer value in a dynamical manner, as indicated by actions 313 and 327 in figure 3, the sequence of actions of figure 4 will be performed. Action 401

The wireless communication device 102 receives and reads system information that is broadcast in the cell 122 and thereby obtains the LAI relating to the first PLMN 101.

Action 403

From the obtained LAI the MCC and MNC values of the currently camped on PLMN, i.e. the current PLMN, are derived. Hereinafter, these are denoted MCC_c and MNC_c, respectively. See table 2 above for an illustration of LAI.

Action 405

SIM information is read and from this the HPLMN and high priority PLMNs (lists of user preferred PLMNs and operator preferred PLMNs) are derived, and from this the corresponding MCC and MNC values are derived. Hereinafter, these are denoted as MCC h and MNC h.

Now, the wireless communication device 102 knows MCC_c, MNC_c and MNC_h, MNC_h. Using these combinations, the wireless communication device 102 refers to the stored lookup table as shown in table 3.

Figure imgf000015_0001

Table 3 In table 3, the different possible combinations of (MCC_c, MNC_c) and (MCC_h, MNC_h) values that represent different locations and countries are shown. The lookup table can be pre-stored in the memory or in SIM (operator specific) of the wireless communication device 102. The distance between the different countries (MCCs) and places (MNCs) are known so, from that data it is also known that if the wireless communication device 102 is presently located at a position that corresponds to a particular MCC_c and MNC_c and the HPLMN is at a position that corresponds to MCC_h and MNC_h, then the distance between these locations are known and pre-stored in the lookup table as shown in column D1 in table 3. The distances indicate approximately how far from each other the countries/locations are. For example, if (MCC_c, MNC_c) is (India, Kolkata) and (MCC_h, MNC_h) is (USA, New York), then the distance D1 is preset in the table for this combination, at 12,000 km.

The lookup table can also be developed automatically through training such that whenever the wireless communication device goes to other locations it shall store the MCCs/MNCs corresponding to the new locations and calculates the corresponding distances.

Based on the known distances it is also known approximately how much time it would take to travel from the current PLMN (i.e. a visited PLMN defined by MCC_c, MNC_c) to the home PLMN (i.e. to a PLMN defined by MCC_h, MNC_h). That value indirectly indicates whether there is a possibility that the user can travel back to the home PLMN within a short time or not. A movement possibility indication is marked against each visited PLMN (MCC_c, MNC_c) to Home PLMN (MCC_h, MNC_h) . The wireless communication device may check the database to find out the possibility of movement from current PLMN (MCC_c, MNC_c) to the home PLMN (MCC_h, MNC_h). If the 'movement possibility indication' is 'yes', then wireless communication device may set the HPLMN scan timer value to a lower value. Else, if the 'movement possibility indication' is 'no', then the wireless communication device may set the HPLMN scan timer value to a higher value.

Action 406

As discussed above, the lookup table may comprises a pre-stored HPLMN scan timer value corresponding to each combination of (MCC_c, MNC_c) and (MCC_h, MNC_h) as exemplified by T1 in table 4. Here, the timer values have been obtained from the past history. This means in the past wireless communication device might have visited the (MCC_c, MNC_c) location. During that time wireless communication device estimated the number of times the HPLMN scan has happened during the movement from (MCC_c, MNC_c) to (MCC_h, MNC_h) location. Say, that value is N and during that time the HPLMN scan timer value was set to 10 min. The total time elapsed will then be 10*N minutes. This also means that the wireless communication device would have

unsuccessfully scanned 9 times to obtain the home PLMN. So, the optimum HPLMN scan timer value for this MCC, MNC pair would be 10*N minutes. This value is illustrated in the table 4. In case of further visit to the same MCC_c, MNC_c location, the wireless communication device shall set the PLMN scan timer value to 10*N (as derived from the past history). Table 4 can also be populated manually based on the estimated worst case time needed to move from MCC_c,MNC_c to MCC_h, MNC_h.

The lookup table (i.e. as exemplified by table 4) can be populated and presorted manually based on the different possible combination of countries and locations. Moreover, the timer values may be obtained through training such that whenever the wireless communication device goes to other locations then the wireless communication device calculates timer values that correspond to the MCCs/MNCs and distances.

Needless to say, the skilled person will realize that the lookup table comprising the combinations of (MCC_c, MNC_c) and (MCC_h, MNC_h) and timer values may be much larger than the exemplifying illustration in table 4.

Figure imgf000017_0001

Table 4 Action 409

Using the above actions, once the wireless communication device computes the HPLMN scan timer value, it sets the scan timer to that derived value. Every time the HPLMN scan timer expires, the wireless communication device shall find out the present

MCC_c,MNC_c and compare with the MCC_h,MNC_h to derive HPLMN scan timer value.

Action 407

An alternative to reading the scan timer from the lookup table, as is the case in the embodiments that comprise action 406, the scan timer value can be calculated using a function that has the distance D1 as input. Such embodiments comprise action 407 where the distance D1 , corresponding to the (MCC_c, MNC_c) and (MCC_h, MNC_h) combination that is relevant for the current location of the wireless communication device 102, is read from the lookup table as exemplified in table 3.

Action 408

The distance D1 that has been obtained from the lookup table is used in a function, such as the function defined in equation 1 above, to calculate a scan timer value. The PLMN scan timer value is then set to that derived value as illustrated by action 409.

In order to exemplify power saving in a wireless communication device that performs embodiments as described above, an analysis will be described that compares the power usage of prior art wireless communication devices and a wireless communication device that operates as exemplified above.

Today, at every time a PLMN scan is to be performed, a wireless communication device has to do the following:

The wireless communication device scans all or a set of radio frequency (RF) carriers as defined by information stored in a SIM of the wireless communication device, e.g. carriers in the UTRAN/E-UTRAN/GSM defined bands, according to its capabilities to find available PLMNs. On each RF carrier, the wireless communication device searches for the strongest cell according to the cell search procedure in that RAT and read its system information in order to find out which PLMN the cell belongs to.

For every PLMN scan, the total estimated energy consumption in a Multi-RAT wireless communication device is then: P_avg * time = Vcc*lcc*Time = 3.3 v * 50 mA * 10 sec = 1 .6 Joule (J) where P_avg is the average battery power consumed, Vcc operating voltage of the device, and Ice is the operating current.

Typically 50 mA is the average current consumed in a receiver in a wireless

communication device during the reception and when scanning in GSM. The average current consumed is higher during WCDMA and LTE scanning. Typically, 10 seconds is the total time taken for the all three RATs scanning.

Now, let's consider an observation period for power saving comparison between prior art systems and an approach according to embodiments herein of 1 day (=1440 min). The power consumed for PLMN scanning using a method according to prior art is:

In 1 day time period according to a prior art method there will be total 1 *1440 min /10 minutes = 144 HPLMN scans, where the value 10 minutes is the prior art timer set for HPLMN scans.

So, the total battery energy consumed for 144 times PLMN scanning is = 144 * energy consumed in each time of the HPLMN scan = 144* 1 .6 J = 230 J.

In comparison, the power consumed for PLMN scanning using a method according to embodiments described above can be expressed as follows.

In embodiments described herein, t the wireless communication device has set the HPLMN scan timer to a large value say, 10 hours = 600 minutes. In such a case, the total number of PLMN scans will be: 24*60/600 = 2.4 (that is, rounded to 3 scans).

So, the above number (i.e. 3 scans) is the worst case consumption.

As a result of 3 times HPLMN scans, the total battery energy consumption is = 1.6 J * 3 = 4.8 J

So, the power saving compared to the legacy method = 230 J - 4.8 J ~ 225 J (which is very significant amount of power savings).

The saving ratio will be 230/4 = 57.

This power saving is a considerable amount and can lead to run the battery last long for: 225 J / Pidle_modePower_con = 225 J / (2mA * 3.3V) = 34000 seconds. This means roughly 10 hours of extra idle mode battery power longevity (over a day). Where, Pidle_modePower_con indicates the idle mode power consumption of the wireless communication device, where 2 mA is the idle mode current and 3.3V is the operating voltage. So, in such scenarios, if typically a mobile battery when fully charged runs for, e.g., 2 days. With the use of a method according to embodiments described herein, it will run for almost 3 days. As mentioned above, even further energy gains can be obtained for a wireless communication device that is equipped with two radio modems, i.e. a dual SIM device, as the skilled person will realize. Turning now to figure 5, and with continued reference to figure 1 a wireless

communication device 500 and corresponding computer program 541 will be described in some detail. The wireless communication device 500 comprises radio circuitry 506, a processor 502, a memory 504 and at least one SIM 507 comprising a lookup table that may hold information as exemplified in tables 3 and 4 above. The memory 504 comprises instructions executable by the processor 502 whereby the wireless communication device 500 is operative to, when being connected to a current PLMN, such as the first PLMN 101 in figure 1 :

- determine whether or not the current PLMN 101 is a HPLMN 105 of the wireless communication device 500 and if the current PLMN 101 is not the HPLMN 105:

- set a scan timer value that specifies a time period between attempts by the wireless communication device 500 to connect to a PLMN having a priority that is higher than a priority of the current PLMN, where the scan timer value is an increasing function of a geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN.

The instructions, e.g. stored in the memory 504, that are executable by the processor 502 may be software in the form of a computer program 541. The computer program 541 may be contained in or by a carrier 542, which may provide the computer program 541 to the memory 504 and processor 502. The carrier 542 may be in any suitable form including an electronic signal, an optical signal, a radio signal or a computer readable storage medium. In some embodiments, the wireless communication device 500 is operative such that the geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN is represented by a mobile country code, MCC, of the current PLMN and a MCC of the HPLMN.

In some embodiments, the wireless communication device 500 is operative such that the geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN is represented by a mobile network code, MNC, of the current PLMN and a MNC of the HPLMN.

In some embodiments, the wireless communication device 500 is operative such that the geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN is obtained by reading a lookup table that comprises mapping information that comprises:

- MCC, MNC pairs pertaining to a plurality of PLMNs, and

- a geographical distance between each MCC, MNC pair.

In some embodiments, the wireless communication device 500 is operative to set the scan timer value by comprising reading the scan timer value from a lookup table that comprises a scan timer value pertaining to each geographical distance.

In some embodiments, the wireless communication device 500 is operative to set the scan timer value by comprising evaluating a continuous function having as input at least the geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN.

In some embodiments, the wireless communication device 500 is operative to determine whether or not the current PLMN is a highest preferred PLMN, and setting the scan timer value only in case the current PLMN is the highest preferred PLMN.

In some embodiments, the wireless communication device 500 is operative to determine whether or not the current PLMN is a highest preferred PLMN by comprising analysing at least one list that comprises information that identifies a plurality of PLMN's and corresponding order of preference for each PLMN in the list.

In some embodiments, the wireless communication device 500 is operative to analyze any of a user preferred PLMN, UPPLMN, list and an operator preferred PLMN, OPPLMN, list.

In some embodiments, the wireless communication device 500 is operative to

- determine the MCC of the current PLMN,

- determine the MCC of the PLMN's in the list, and operative to set the scan timer value only in case the MCC of the current PLMN is equal to the MCC of the PLMN having the highest order of preference.

Figure 6 illustrates a wireless communication device 600 that comprises:

- a determination module 602 configured to, when being connected to a current PLMN, such as the first PLMN 101 , determine whether or not the current PLMN 101 is a HPLMN 105 of the wireless communication device 500,

- a setting module 604 configured to set a scan timer value that specifies a time period between attempts by the wireless communication device 500 to connect to a PLMN having a priority that is higher than a priority of the current PLMN, where the scan timer value is an increasing function of a geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN.

Further embodiments of the wireless communication device 600, and the modules that such further embodiments comprise, correspond to embodiments described above in connection with figures 2 to 5.

As used herein, the term "processing module" may refer to a processing circuit, a processing unit, a processor, an Application Specific integrated Circuit (ASIC), a Field- Programmable Gate Array (FPGA) or the like. As an example, a processor, an ASIC, an FPGA or the like may comprise one or more processor kernels. In some examples, the processing module may be embodied by a software module or hardware module. Any such module may be a determining means, estimating means, capturing means, associating means, comparing means, identification means, selecting means, receiving means, transmitting means or the like as disclosed herein. As an example, the expression "means" may be a module, such as a determining module, selecting module, etc. As used herein, the expression "configured to" may mean that a processing circuit is configured to, or adapted to, by means of software configuration and/or hardware configuration, perform one or more of the steps or actions described herein.

As used herein, the term "memory" may refer to a hard disk, a magnetic storage medium, a portable computer diskette or disc, flash memory, random access memory (RAM) or the like. Furthermore, the term "memory" may refer to an internal register memory of a processor or the like.

As used herein, the term "computer readable medium" may be a Universal Serial Bus (USB) memory, a DVD-disc, a Blu-ray disc, a software module that is received as a stream of data, a Flash memory, a hard drive, a memory card, such as a MemoryStick, a Multimedia Card (MMC), etc.

As used herein, the term "computer readable code units" may be text of a computer program, parts of or an entire binary file representing a computer program in a compiled format or anything there between. As used herein, the terms "number", "value" may be any kind of digit, such as binary, real, imaginary or rational number or the like. Moreover, "number", "value" may be one or more characters, such as a letter or a string of letters, "number", "value" may also be represented by a bit string.

As used herein, the expression "in some embodiments" has been used to indicate that the features of the embodiment described may be combined with any other embodiment disclosed herein.

Even though embodiments of the various aspects have been described, many different alterations, modifications and the like thereof will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the present disclosure.

Claims

1 . A method performed by a wireless communication device (1 1 1 , 1 13, 1 15, 1 17, 500, 600), the wireless communication device being connected to a current public land mobile network (101 , 103), PLMN, the method comprising:
- determining (201 ) whether or not the current PLMN is a home public land mobile network, HPLMN, of the wireless communication device and if the current PLMN is not the HPLMN:
- setting (207) a scan timer value that specifies a time period between attempts by the wireless communication device to connect to a PLMN (105) having a priority that is higher than a priority of the current PLMN, where the scan timer value is an increasing function of a geographical distance (1 10, 1 12) between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN.
2. The method of claim 1 , wherein the geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN is represented by a mobile country code, MCC, of the current PLMN and a MCC of the PLMN having a priority that is higher than the priority of the current PLMN.
3. The method of claim 2, wherein the geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN is represented by a mobile network code, MNC, of the current PLMN and a MNC of the PLMN having a priority that is higher than the priority of the current PLMN.
4. The method of claim 3, wherein the geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN is obtained by reading a lookup table that comprises mapping information that comprises:
- MCC, MNC pairs pertaining to a plurality of PLMNs, and
- a geographical distance between each MCC, MNC pair.
5. The method of claim 4, wherein the lookup table comprises a scan timer value pertaining to each geographical distance, and wherein the setting of the scan timer value comprises reading the scan timer value from the lookup table.
6. The method of claim 4, wherein the setting of the scan timer value comprises evaluating a continuous function having as input at least the geographical distance between a current position of the wireless communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN.
5 7. The method of any of claims 1 to 6, comprising, prior to the setting of the scan timer value:
- determining (31 1 , 323) whether or not the current PLMN is a highest preferred PLMN, and
wherein the setting of the scan timer value is performed only in case the current PLMN is 10 the highest preferred PLMN.
8. The method of claim 7, wherein the determination of whether or not the current PLMN is a highest preferred PLMN comprises analysing at least one list that comprises information that identifies a plurality of PLMN's and corresponding order of preference for each PLMN in the list.
15 9. The method of claim 8, wherein said list is any of a user preferred PLMN, UPPLMN, list and an operator preferred PLMN, OPPLMN, list.
10. The method of claim 8 or claim 9, comprising:
- determining the MCC of the current PLMN,
- determining the MCC of the PLMN's in the list, and wherein the setting of the scan 20 timer value is performed only in case the MCC of the current PLMN is equal to the MCC of the PLMN having the highest order of preference.
1 1 . The method of any of claims 1 to 10, wherein the PLMN having a priority that is higher than the priority of the current PLMN is any of the HPLMN and an equivalent home public land mobile network, EHPLMN.
25 12. A wireless communication device (1 1 1 , 1 13, 1 15, 1 17, 500, 600) comprising radio circuitry (506), a processor (502) and a memory (504), said memory comprising instructions executable by said processor whereby said wireless communication device is operative to, when being connected to a current public land mobile network (101 , 103), PLMN:
30 - determine whether or not the current PLMN is a home public land mobile network, HPLMN, of the wireless communication device and if the current PLMN is not the HPLMN: - set a scan timer value that specifies a time period between attempts by the wireless communication device to connect to a PLMN (105) having a priority that is higher than a priority of the current PLMN, where the scan timer value is an increasing function of a geographical distance (1 10, 1 12) between a current position of the wireless
communication device and a position of the PLMN having a priority that is higher than the priority of the current PLMN.
13. A computer program (541 ) comprising instructions which, when executed by at least one processor (502) in a wireless communication device (1 1 1 , 1 13, 1 15, 1 17, 500, 600), cause the wireless communication device to carry out the method of any one of claims 1 to 1 1 .
14. A carrier (542) containing the computer program of claim 13, wherein the carrier is one of an electronic signal, an optical signal, a radio signal or a computer readable storage medium.
PCT/EP2014/056905 2014-04-07 2014-04-07 Plmn scanning WO2015154789A1 (en)

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