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02 RN20082EN12GLN1 Idle Mode Operation

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02 RN20082EN12GLN1 Idle Mode Operation
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Template for NTC Training documents written with Word 97 Training Document BSSPAR 12: Chapter 02 Version3 © Nokia Siemens Networks 1 (29)
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Template for NTC Training documents written with Word 97

Training DocumentBSSPAR 12: Chapter 02

Version3 © Nokia Siemens Networks 1 (24)

Idle Mode Operation

The information in this document is subject to change without notice and describes only the product defined in the introduction of this documentation. This document is intended for the use of Nokia Networks' customers only for the purposes of the agreement under which the document is submitted, and no part of it may be reproduced or transmitted in any form or means without the prior written permission of Nokia Networks. The document has been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using it. Nokia Networks welcomes customer comments as part of the process of continuous development and improvement of the documentation.

The information or statements given in this document concerning the suitability, capacity, or performance of the mentioned hardware or software products cannot be considered binding but shall be defined in the agreement made between Nokia Networks and the customer. However, Nokia Networks has made all reasonable efforts to ensure that the instructions contained in the document are adequate and free of material errors and omissions. Nokia Networks will, if necessary, explain issues which may not be covered by the document.

Nokia Networks' liability for any errors in the document is limited to the documentary correction of errors. Nokia Networks WILL NOT BE RESPONSIBLE IN ANY EVENT FOR ERRORS IN THIS DOCUMENT OR FOR ANY DAMAGES, INCIDENTAL OR CONSEQUENTIAL (INCLUDING MONETARY LOSSES), that might arise from the use of this document or the information in it.

This document and the product it describes are considered protected by copyright according to the applicable laws.

NOKIA logo is a registered trademark of Nokia Corporation.

Other product names mentioned in this document may be trademarks of their respective companies, and they are mentioned for identification purposes only.

Copyright © Nokia Networks Oy 2012. All rights reserved.

2 (24) © Nokia Siemens Networks

Idle Mode Operation

Contents

2 Idle Mode Operation.....................................................42.1 Module Objectives..........................................................42.2 Introduction.....................................................................42.3 PLMN Selection..............................................................72.4 States and State Transition in the RRC Idle Mode.........92.5 Pathloss Criterion C1 for Cell Selection and Reselection122.6 Cell Reselection Based on Pathloss Criterion C2.........152.7 Cell Reselection Events................................................182.8 Downlink Signalling Failure...........................................202.9 Location Updates..........................................................21

© Nokia Siemens Networks 3 (24)

Idle Mode Operation

2 Idle Mode Operation

3.2 Module Objectives

At the end of the module the participant will be able to:

List the functions of the MS during the idle mode

Explain the parameters used for PLMN and cell selection

State the purpose of location updates and the associated parameters

3.3 Introduction

Because of the limited radio spectrum that is available, each MS cannot be allocated a dedicated traffic channel (TCH) at all times. Traffic channels are only allocated to the user when it is needed. This leads to the distinction between two states that the mobile can take, namely Idle Mode and Dedicated Mode.

In the idle mode, an MS does not have a dedicated traffic channel (TCH). It listens to paging and broadcast channel. Whenever the MS requests resources it is in idle mode. Once the resources are allocated for full duplex point-to-point communication, the mobile moves from idle mode to dedicated mode.

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Idle Mode Operation

• When the MS is switched ON• When there is no dedicated connection

When?

• To camp on the best suitable cell

Why?

• For MS to receive system info from the NW on DL• For MS to be able to initiate a call whenever needed• For the NW to be able to locate the MS when there is a MT call/SMS

Why to camp on a specific cell?

• PLMN selection• Cell selection & re-selection• Location updates

Idle Mode Tasks

Figure 2-1. Idle mode operation

In idle mode the MS has to perform a number of functions:

(a) During Power On it has to check if it can access a PLMN and cell.

(b) It has to stay in contact with the BTS by decoding the BSIC and listening to System Information.

(c) It listens to paging

(d) It monitors the status of radio links from various BTS and chooses the most appropriate BTS.

(e) It listens to cell broadcast short messages (if supported and if MS is subscribed).

© Nokia Siemens Networks 5 (24)

Idle Mode Operation

locationAreaId

• ncc (Network Colour Code) 0 … 7• bcc (BTS Colour Code) 0 … 7

bsIdentityCode

cell-ID 0 … 65535

Parameter Value

trainingSequenceCode 0 … 7

• mcc (Mobile Country Code) 0 … 999• mnc (Mobile Network Code) 0 … 99• lac (Location Area Code) 0 … 65535

Cell Global Identity MCC + MNC + LAC + CI

Figure 2-2. IDs and ID codes

Four different reasons for camping on a cell in idle mode were identified in the specifications:

The MS is capable to read the system information, which is broadcasted on the BCCH (GPRS option: PBCCH). Hereby, the MS gains also information of the serving PLMN.

If the access to the current cell is not barred, then the MS can use the cell to initiate an interaction with the network. The access network is accessed by common control channels RACH (GPRS option: PRACH) to access the network. Initial access is done to register the MS at the network. Other reasons for accessing the network is to request transmission resources for user data transfer.

If the MS is registered, and there is a mobile terminated call, the serving core network elements know (in most cases) the location area resp. routing area, in which the MS is camping. Paging is done with the common control channel PCH (GPRS option: PPCH). The MS receives the paging message, because is monitors all paging occasions on the paging resources of its paging class within the cell.

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Idle Mode Operation

The MS can receive cell broadcast service messages. In the ETSI specification TS 23.122, the idle mode tasks were subdivided into four processes:

PLMN selection and reselection;

Cell selection and reselection;

Location registration; and

CTS fixed part selection. (CTS stand for Cordless Telephony System, which is not covered in this course documentation.)

Figure 2-3. Camping on a cell

3.4 PLMN Selection

Operators have observed, that 95% to 98% of their subscribers are served in their home PLMN (HPLMN). Roaming, i.e. the use of another operator‘s network infrastructure is allowed to many subscribers. This becomes for instance necessary, if the mobile phone leaves the supply area of the home operator. For PLMN selection, two modes of operations were specified:

Automatic mode At switch-on or recovery from lack of coverage, the MS attempts to select again the PLMN, where it is already registered. Hereby it attempts all its available radio access technologies (e.g. GSM and UMTS).

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Idle Mode Operation

Equivalent PLMNs are treated with the same priority as the registered PLMN. If the MS fails to find the registered PLMN or equivalent PLMNs, it attempts to register at another PLMN in an order, which can be seen in the figure on the right hand side.

Manual mode In this mode, the mobile phone scans the radio interface, and indicates to the user to available PLMNs. The mobile phone attempts to register with the network, the subscriber manually selects. If the subscriber does not select a (suitable) network, then the UE only offers limited services, i.e. emergency calls.

A PLMN identifier and an access technology are always listed on the SIM in a priority order. For the PLMN identifier, three bytes memory are required, while for the access technology, two bytes are necessary. At least one PLMN and associated access technology must be listed.

If there is a PLMN identifier allowing more than one access technology, it is up to the mobile phone implementation to determine the preferred access technology.

Not only international roaming is possible, but also national roaming. In many countries, the regulation authority enforced national roaming of UMTS subscribers in existing GSM networks in order to grant a higher coverage to UMTS subscribers. If national roaming is allowed, the UMTS operator wants to avoid unnecessary roaming fees. In this case the UE must periodically search for the HPLMN (or home country network of higher priority). The value “T” timer is used, and it may be stored on the SIM-card. Its values range between 6 and 480 minutes with a step size of 6 minutes. Its default value is 60 minutes, which is used, when the “T” timer was not set. This timer can be also set in such a way, that no periodic search attempts are conducted.The timer „T“can be also used, when the subscriber is roaming in a foreign country to find a PLMN of higher priority. The search is based on the „user controlled PLMN selector“ and „operator controlled PLMN selector“ on the SIM-card.

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Idle Mode Operation

Figure 2-4. PLMN Selection

3.5 States and State Transition in the RRC Idle Mode

When the mobile phone listens to the system information, which is broadcasted on the BCCH, it receives a wide range of PLMN and cell relevant information. If initial registration was done successfully, it can also receive paging information on the paging channel resources or initiate a mobile originated call. If the MS enters a new location area after a cell reselection, it starts the location update procedure.

The cell re-selection may be based on different methods in GSM and GPRS.

When a MS camps normally on a cell, all network services are available to the phone. The MS is responsible to perform a cell reselection to determine, if there is a better cell to camp on. The cell re-selection is based on received level measurements and system information.

The MS moves in the cell reselection state when cell re-selection is required. It attempts to make a cell re-selection. If it is successful, it ends up again in the state „Camped Normally“. It can also happen that the UE does not find a suitable cell (any more). This is the case, when the subscriber is leaving the mobile communication supply area. The MS then enters the state „Normal Cell Selection“.

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Idle Mode Operation

The „Normal Cell Selection“ state is also often called initial cell selection state. In this state, the MS has no information about the availability of cells or networks on the SIM. Consequently, it has to scan all RF carriers to find BCCH carrying carriers. It tries to find the BCH channels on the RF carrier with the highest received level. If the MS was not successful, the MS will continue its work with the next strongest RF carrier, and so on. If it has found a suitable cell, it will move to the state „camped normally“, otherwise to the state „Any Cell Selection“.

The MS may hold valid BCCH information. If the selects a PLMN, it tries to use this information to allow a fast cell search. Mobile phones are often switched on and off in the same geographical area. Therefore, the MS tries to find the „old “cell again, based on the information it still holds on the SIM. If no suitable cell is to be found, then the mobile station moves into the „Normal Cell Selection “state.

If there is no suitable cell available, then the MS is in the state „Any Cell Selection“. It tries to find any cell to camp on. If such a cell has been found, the MS is then in the state „Camp on any cell“. Only one service can be activated in this state: the emergency call. There is a set of reasons, why a MS is not allowed to camp normally on the cell of one PLMN: There exists no roaming agreement between the home PLMN operator and the visited PLMN operator, i.e. the PLMN is not allowed. If the IMSI is unknown, know successful authentication can be performed. A special case of an unknown IMSI is given, when there is no SIM in the mobile phone. Yet another reason is a mobile equipment the subscriber is not allowed in the network. (For instance, when its IMEI was found in the black list of the EIR.)

In the states „Any Cell Selection“, „Any Cell Reselection“, and „Camp on Any Cell“, cell selection and camping on a cell is done irrespective of the PLMN identity.

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Idle Mode Operation

Figure 2-5. States and State Transition for Cell Selection

Figure 2-6. States and State Transition for Cell Selection (continued)

© Nokia Siemens Networks 11 (24)

Idle Mode Operation

©NOKIA BSSPAR / 11.2006. V3

Normal Cell SelectionSearch all the RF channels, take samples during 3-5 s and calculate averages. And put them in ascending order with respect to signal level.

Then tune to the strongest RF channel.

Search for the frequency correction burst in that carrier in order to verify if it is a BCCH carrier

Camp on the cell

Try to synchronize to the carrier and read the BCCH data

Is it a BCCH carrier?

Is it a correct PLMN ?

Is the cell barred?

Is C1>0

Tune to the next highest RF channel which is not

tried before

No

No

NoNo

Yes

Yes

Yes

Yes

IdleMode

Operation

Figure 2-7. Normal Cell Selection (back-up slide)

Figure 2-7 describes in more details normal cell selection procedure.

3.6 Pathloss Criterion C1 for Cell Selection and Reselection

Is a cell suitable to camp on it? This question can be answered with the pathloss criterion C1:

C1 = A – max (B, 0) =

RLA_C – RXLEV_ACCESS_MIN–max (MS_TXPWR_MAX_CCH – P, 0)for a suitable cell C1 has to be bigger than 0 (C1 > 0).

•The MS must be capable to reliably decode downlink data. This is guaranteed with the termA = RLA_C – RXLEV_ACCESS_MIN > 0. RLA_C is the averaged received RF signal level of the BCCH carrying RF channel, while RXLEV_ACCESS_MIN is an operator set parameter, which determines the received minimum RF signal level at the MS. The parameter RXLEV_ACCESS_MIN defines the cell size for idle mode.

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Idle Mode Operation

•The probability must be high, that communications on the uplink is possible. The condition A > 0 only guarantees, that the MS receives downlink data well. But when the MS transmits on the uplink, are its received signals at the BTS strong enough that the BTS can reliably decode them? The term max(B,0) = max(MS_TXPWR_MAX_CCH – P , 0) is a „power compensation term“: With the parameter MS_TXPWR_MAX_CCH, the operator determines the maximum transmit power level a mobile station can use when accessing the system. Consequently, MS_TXPWR_MAX_CCH represents another cell size defining parameter. If the MS accesses the BTS with MS_TXPWR_MAX_CCH, the probability is high, that the BTS can decode the received RF signals. The parameter P represents the MS‘s maximum RF output power. If the MS‘s maximum output power is smaller than MS_TXPWR_MAX_CCH, than it must be closer to the BTS, before is can start to access it, i.e. the cell‘s RLA_C must be larger.

The pathloss criterion C1 definition of the preceding page is applied for all GSM MSs except for class 3 DCS 1800 MSs. For class 3 DCS 1800 MSs, following – slightly modified – C1 criterion is in use:

C1 = A – max (B,0) = RLA_C – RXLEV_ACCESS_MIN –

max(MS_TXPWR_MAX_CCH + Power Offset – P , 0)

© Nokia Siemens Networks 13 (24)

Idle Mode Operation

An additional power offset is used in the „power compensation term“ max(B,0). The requirements for a well received RF level at the class 3 DCS 1800 MSs had been increased in comparison to all other DCS mobile phones. The Power Offset is transmitted in a 2 bits field:- 00: 0 dB power offset,- 01: 2 dB power offset,

- 10: 4 dB power offset, and- 11: 6 dB power offset.

Figure 2-8. Pathloss Criterion C1 for Cell Selection and Reselection

In case the neighbouring cells belong to different Location Areas, a hysteresis will be applied to avoid the ping-pong phenomena between the cells. The hysteresis is set with a parameter cellReselectHysteresis (0…14dB) which defines the margin how much better signal has to be received from the cell which will be re-selected. See the picture below.

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Idle Mode Operation

Cell Selection with C1IdleMode

Operation

Cell1

LA1

RX Level Cell1

RX Level Cell2

A B C

A= 4 dB

B= 6 dB

C= 8 dB

Cell2

LA2

In case the neighbouringcells belong to different Location Areas a hysteresis is applied with C1 criteria• minimizing ping-pong• cellReselectHysteresis (0…14 dB)

Figure 2-9. Cell re-selection based on C1 on Location Area border

3.7 Cell Reselection Based on Pathloss Criterion C2

The pathloss criterion C1 is always used for (initial or stored list based) cell selection. It is also used for cell reselection if the pathloss criterion C2 is not supported. Otherwise, the criterion C2 is used for the cell reselection evaluation process:

C1 + CELL_RESELECT_OFFSET – TEMPORARY OFFSET * H(PENALTY_TIME - T)for PENALTY_TIME ¹ 640 s

C1 - CELL_RESELECT_OFFSET for PENALTY_TIME = 640 s

0 for x < 0

1 for x ³ 0

For the serving cell: H(x) = 0.

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Idle Mode Operation

The serving cell and and the 6 strongest non-serving cells are evaluated with the C2 criterion. A CELL_RESELECT_OFFSET is applied for the serving cell and the 6 strongest non-serving cell. The offset can be used to priories cells. TEMPORARY OFFSET is a negative offset, which is in use for each of the 6 strongest neighbouring cells for the period of PENALTY_TIME. For each candidate of the list of strongest non-serving cells, there is a timer T implemented. When a new candidate is added to the list of strongest neighbouring cells, then the timer T is set to zero. Adding a cell to the list of strongest neighbours means, that the new cell has become a candidate for cell reselection. For the period of PENALTY_TIME, the new cell‘s evaluation (or ranking) is reduced by TEMPORARY OFFSET, making it less likely that it will be selected soon as a the new serving cell. There is one exception: If the cell, which was added to the list of strongest neighbouring cells, has previously been the serving cell, then the timer T is set to PENALTY_TIME, i.e. the TEMPORARY OFFSET is not applied. If the optional parameters CELL_RESELECT_OFFSET, TEMPORARY OFFSET, and PENALTY_TIME are not broadcasted, then C2 = C1.

Figure 2-10. Pathloss Criterion C2

There are two cases on how to perform cell reselection based on the pathloss criterion C2:

For a period of 5 seconds, a neighbouring cell has a higher C2 value as the cell, the MS is camping on. In addition to that, the neighbouring and current cell belong to the same registration area (e.g. location area). Then the Ms selects the neighbouring cell as new cell to camp on.

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Idle Mode Operation

For a period of 5 seconds, a neighbouring cell‘s C2 value exceeds the current cell‘s C2 value by the value CELL_RESELECT_HYSTERESIS (HRY). In addition to that, the neighbouring belongs to a different registration area (e.g. location area) than the current cell, or even to a different, but equivalent PLMN. Then the Ms selects the neighbouring cell as new cell to camp on. The CELL_RESELECT_Hysteresis value ranges from 0 to 14 dB, step size 2 dB. The hysteresis was introduced to reduce repeatedly location update procedures, when moving in the border area of two registration areas (so-called ping-pong effect). This also reduces the risk of missed paging messages.A similar principle applies for MSs in the (GPRS) Idle, (GPRS) Ready state (A/Gb-mode), and RRC-Cell_Shared state (Iu-mode).

If a MS a selected a new cell within the previous 15 seconds, then cell reselection to a neighbouring cell is only possible, if the C2 value of the neighbouring cell is at least 5dB higher than the C2 value of the current cell. Also this condition must be fulfilled for a period of 5 seconds.

Figure 2-11. Cell Reselection based on Pathloss Criterion C2

Another illustration of C2 procedure with exemplary figures is given below.

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Idle Mode Operation

IdleMode

Operation

Cell Reselection with C2

Cell "A" Cell "B" Cell "C" Cell "D"

cellReselectOffset 0 dB 20 dB 0 dB 0 dB

temporaryOffset 0 dB 30 dB 0 dB 30 dB

penaltyTime 20 s 20 s 20 s 40 s

Micro 900 "D"

Macro 1800 "B"

Macro 900 "A"

Macro 900 "C"Road

Mobile Location

Parameters

=30 Cell "A" (Serving Cell)

=25 Cell "B"

=5 Cell "C"

=50 Cell "D"

=30 + 0 (H(x)=0, serving cell) Cell "A"

=25 + 20 - 30*H(20 - T) Cell "B"

=5 + 0 - 0*H(20 - T) Cell "C"

=50 + 0 - 30*H(40 - T) Cell "D"

C1

C2 = C1 +cellReselectOffset -temporaryOffset*H(penaltyTime-T)

C2

Time T: (0 - 19 s)C2 =30 Cell "A"

C2 =15 Cell "B"

C2 =5 Cell "C"

C2 =20 Cell "D"

Time T: (20 - 39 s)C2 =30 Cell "A"

C2 =45 Cell "B"

C2 =5 Cell "C"

C2 =20 Cell "D"

Time T: (> 40 s)C2 =30 Cell "A"

C2 =45 Cell "B"

C2 =5 Cell "C"

C2 =50 Cell "D"

Figure 2-12. A typical cell reselection case with C2

3.8 Cell Reselection Events

The MS is in the idle mode. It has selected a PLMN, it has performed a successful location registration, and it was accepted by the PLMN. Currently, it is camping on the cell with the highest C2 value. The question is: Which conditions have to be fulfilled, that the MS selects a new cell?

Pathloss criterion C1: The pathloss of the serving cell has become to high, C1 has fallen below zero for the period of 5 seconds.

Pathloss Criterion C2: see previous pages.

DSC criterion: A downlink signalling failure is indicated with DSC £ 0.

RACH criterion: The random access to the current cell failed. Hereby, the MS tried to access the cell MAX RETRANS + 1 times. The parameter MAX RETRANS is part of the system information. Its value is either 1, 2, 4 or 7.

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Idle Mode Operation

The MS camps on a cell, which has become barred. A cell is barred, if the parameter CELL_BAR_ACCESS is set to 1. Can the cell barring be overwritten? This is indicated by the parameter CELL_BAR_QUALIFY (CBQ).

Authentication failed. This information is made available by upper layers and triggers a cell reselection.

All cell reselection events except for the pathloss criterions C1 and C2 trigger immediately the cell reselection process. If the MS has found a suitable cell to camp on, it is not allowed to return to the previous cell within a period of 5 seconds.

But what happens, if the MS does not find any suitable cell?If this is the case for a period of 10 seconds, the MS starts the (stored list, then the initial) cell selection process.

Figure 2-13. Cell Reselection Events

3.9 Downlink Signalling Failure

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Idle Mode Operation

The MS is not listening permanently to the paging channels. Discontinuous Reception (DRX) was introduced as a battery saving feature. Based on information, broadcasted as system information on the BCCH and its IMSI, the mobile phone is capable to determine when exactly it may be paged. It then decodes the signalling block on „its“ subchannel. Interference may degrade the communications. The quality of downlink transmission is monitored by the MS success to decode signalling blocks of its paging subchannel. The success rate is used to determine whether the cell is suitable to camp on.

One of the parameters, which is transmitted as part of the system information, is BS_PA_MFRMS, which informs the mobile phone about the number of 51-multiframes between the transmission of paging messages. The MS uses this parameter to determine the initial integer value for the Downlink Signalling failure Counter DSC: round( 90/BS_PA_MFRMS ).

While the mobile station camps on a cell, it tries to decode the paging messages on its subchannel.

•If it does not successfully decode a signalling message, the DSC counter is decreased by 4.

•If it successfully decodes a signalling message and the current value of the DSC counter is smaller than its initial value, than the DSC counter is increased by one.If it successfully decodes a signalling message and the current value of the DSC counter is equal to its initial value, than the DSC counter remains unchanged. In other words, the Downlink Signalling failure Counter never becomes larger than its initial value.

A downlink signalling failure has been detected, when DSC £ 0. In the idle mode, this triggers a cell reselection

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Idle Mode Operation

Figure 2-14. Downlink Signalling Failures

3.10 Location Updates

A subscriber keeps moving from one place to another and the network must be able to locate it for incoming calls. The transaction that enables the network to keep track of the subscriber is called a Location Update. The mobile phone constantly receives information sent by the network. This information includes the VLR area in which the mobile is currently located. In order to keep track of its location, the mobile stores the ID of the area in which it is currently registered. Every time the network broadcasts the ID of the area, the mobile compares this information to the area ID stored in its memory. When the two IDs are no longer the same, the mobile sends the network a request, i.e. a registration inquiry to the area it has just entered. The network receives the request and registers the mobile in the new VLR area. Simultaneously, the subscriber’s HLR is informed about the new VLR location and the data concerning the subscriber is cleared from the previous VLR as shown below.

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Idle Mode Operation

Figure 2-15 Location update procedures

The VLR area is commonly referred to as a location area. As defined in GSM specifications, it is the smallest area, into which a terminating call towards a mobile subscriber will be paged. Also a location area is the area in which a mobile needs not to update its location with its home location register.

Location update is performed in idle mode when the mobile is roaming into a cell having a different location area code (LAC). In connected mode, the mobile will update its location with the network as soon as it becomes idle again, i.e. after call completion.

While handover boundaries affect only mobiles that are in “connected mode”, location area boundaries affect all mobiles in the network, including the (many) idle mobiles.

Location updating causes signalling and processing load across the entire network hierarchy up to the mobile’s HLR. In case of foreign roaming mobiles (tourists), this is often even international signalling traffic. Therefore planning of location area boundaries should be considered with some thought, such as to avoid “oscillating” location updates along a heavily frequented road.

Furthermore, different MSCs can not use the same LAC, otherwise the BSC will not know to which MSC the mobile belongs.

In a location area, there is a trade-off between paging traffic and location updating traffic. This means that concatenating e.g. a large city into a single location area will avoid any location updating traffic, but on the other hand causes a maximum in paging traffic, since every single terminating call within the area is broadcast to every single cell in the area. (Even several times per call attempt, depending on network parameters). This can cause significant traffic loads within the network.

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BSS MSC VLR HLR

REQUEST SUBSCRIBER INFO

ALL OK - HLR UPDATE

MS

LOCATION UPDATE REQUEST

SEND SUBSCRIBER ID

REQUEST SUBSCRIBER ID

SEND SUBSCRIBER INFO

AUTHENTICATION

AUTHENTICATION RESPONSE

Idle Mode Operation

Paging LocUp

# of cells in Loc. area

signallingtraffic

optimum numberof cells in Loc. area

function of user density,cell size, call arrival rate ...function of

user mobility

Figure 2-16. Trade-off between location update and paging traffic

Location updates are carried out every time a Mobile changes its location area under one MSC, or between two different MSCs. When the location area changes between two MSCs, the HLR is updated.

There are two types of location updates: automatic (random) location update and periodic location update.

An automatic location update occurs when the Mobile is switched on if IMSIAttachDetach (ATT)(BTS) parameter is used.

The IMSIAttachDetach (ATT)(BTS)(Yes/No) parameter is used to decrease signalling load. The Mobile Station sends a message to the MSC notifying that it is switching on or off. When the MSC knows that the Mobile Station is switched off it does not try to page it, and useless paging is avoided.

Periodic location updates carried out by the Mobile Station and is used to check that the location information in MSC/VLR is correct, because by error in the MSC/VLR, the location information of Mobile Station can disappear. Periodic location update is controlled by the timerPeriodicUpdateMS (PER)(BTS)(0.0..25.5 hours) parameter.

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Idle Mode Operation

timerPeriodicUpdateMS 0.0 ... 25.5 hrs 'PER' (BTS) see note in dictionary!allowIMSIAttachDetach Yes/No 'ATT' (BTS)

Parameter Value

• MS => MSC / VLR

• Mobile Station switched ON

• IMSI Attach / Detach

• Same Location Area => No Location Update

• Different Location Area => Location Update

• Change of the Location Area

• Location Area under the same MSC / VLR

• Location Area under another MSC / VLR => HLR will be updated

• Service is rejected (MS unknown in VLR)

• Time-Periodic LU (MS -> MSC/VLR)

Figure 2-17. Location Updates

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