06) GSM Radio Parameters.ppt

8/10/2019 06) GSM Radio Parameters.ppt

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GB_0505_E1 ZXG10 RADIOPARAMETERS


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TOPICS FOR DISCUSSION

NETWORK IDENTIFICATION PARAMETERSCGI , BSIC, BCC/ NCC

CELL SELECTION PARAMETERSC1 and C2

SYSTEM CONTROL PARAMETERS

RLT, CBA, CBQ and etc.

NETWORK FUNCTIONAL PARAMETERSINTAVE, LIMITn


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MCC LAC

Cell Global Identi ty

MNC

3 Digi t s 2-3 Digits Max 16 Bits

CI

Max 16 bits

LAI

CELL GLOBAL IDENTITY (CGI)

Cell Global Identity (CGI) It is used for identifying individual cells within an LA


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ROLES OF CGI

The CGI information is sent along the system broadcastinginformation in every cell.

When the MS receives the system information, it will extract theCGI information from it and determines whether to camp on the

cell according to the MCC and MNC specified by the CGI.

It judges whether the current location area is changed, thendetermines whether to take the location updating process. Duringthe location updating process, the MS will report the LAI

information to the network so that the network is fully aware of thecell where the MS is currently located.


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SETTING OF CGI

MCC Mobile Country Code : consists of 3 decimaldigits, and the value range is the decimal 000 999.

MNC Mobile Network Code : consists of 3 decimal

digits, and the value range is the decimal 00 999. LAC Location Area Code : The range is 1-

65535.

CI Cell Identity : The range is 0-65535.


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SETTING OF CGI

MCC resource is allocated and managed by ITU. TheMCC of China is 460 decimal).

MNC is usually allocated by the relevanttelecommunication administration department of acountry.

The LAC encoding mode is specified correspondinglyby every country. Usually, the location area should be

as large as possible.Two or more cells in the same location area are not

allowed to share the same CI.


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NCC BCC

3 Bi ts 3 Bi ts

BSIC

NCC Network/ National Color Code Value Range: 0~7

BCC Base Station Color Code Value Range: 0~7

BASE STATION IDENTITY CODE (BSIC)

Base Station Identity Code (BSIC) It enables MSs to distinguish between neighboring base

stations


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NCC and BCC ROLES

NCC: In the connection mode (during conversation), the MSmust measure the signals in the adjacent cells and report theresult to the network. As each measurement report sent by the MScan only contain the contents of six cells, so it is necessary to

control the MS so as to only report the information of cellsfactually related to the cell concerned. The high 3 bits (i.e. NCC) inthe BSIC serve this purpose.

BCC: The BCC is used to identify different BS using the sameBCCH in the same GSMPLMN.


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CBA

FED

BSIC CONFIGURATION PRINCIPLE

In general, it is required that Cells A, B, C, D, E and Fuse different BSIC. When the BSIC resources are notenough, the cells close to each other may take thepriority to use different BSIC.


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ROLES OF BSIC

1. Inform the MS the TSC used by the common signalingchannel of the cell.

2. As the BSIC takes part in the decoding process of the randomaccess channel (RACH), it can be used to prevent the BS from mis-

decoding the RACH, sent by the MS to an adjacent cell, as theaccess channel of this cell.

3. When the MS is in the connection mode (during conversation),it must measure the BCCH level of adjacent cells broadcasting by

BCCH and report the results to the BS. In the uplink measurementreport, MS must show BSIC of this carrier it has measured to everyfrequency point.


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BA LIST (BCCH ADJACENT LIST)

When a MS is turned on, it will scan from the BA(Adjacent cell BCCH table) it remembered when turnedoff last time. The MS will first search carriers from thistable and if none is found it will turns to find any of 30carriers with highest levels, then try to decode BCCHcarriers one by one according to their level sequences.


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CELL SELECTION C1

When the MS is turned on, it will try to contact apublic GSM PLMN, so the MS will select a proper celland extract from the cell the control channelparameters and prerequisite system messages. Thisselection process is called cell selection. The quality ofradio channels is an important factor in cell selection.The GSM Specifications defines the path loss rule C1.

For the so-called proper cell, C1>0 must be ensured.


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C1 = RXLEV - RXLEV_ACCESS_MIN- Max(MS_TXPWR_MAX_CCH - P ,0)

CELL SELECTION C1

where:

RXLEV_ACCESS_MIN is the minimum received level the MS isallowed to access the network

MS_TXPWR_MAX_CCH is the maximum power level of thecontrol channel (when MS sending on RACH);

RXLEV is average received level; P is the maximum TX power of MS;

MAX X, Y X; if X Y.MAX X, Y Y; if Y X.


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C1 PATHLOSS CRITERION

All the candidate cells for MS must meet the path losscriterion, i.e. C1>0. MS will select the cell with themaximal C1 to access and will camp on this cell unlesssome key conditions has changed greatly.


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RXLEV_ACCESS_MIN

In order to avoid providing unsatisfactory communicationquality and avoid the unnecessary waste of radio resources if theMS accesses to the system (the communication quality after theaccess often cannot ensure the normal communication process) at

the very low received level, the GSM system regulates that, when aMS is to access to a network, its receiving signal level must belarger than a threshold level, i.e. the minimum receiving level theMS is allowed to access to RXLEV_ACCESS_MIN).

Default value is 0 (-110dBm).


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CELL RESELECTION C2

Cell Reselection (C2) is a process when MS change its servicecell in idle mode.

When the MS selects a cell it will begin to measure the signallevels of the BCCH TRX of its adjacent cells, record 6 adjacent

cells whose signal levels are the strongest and extract from themvarious types of system messages and control messages of eachadjacent cell.

When given conditions are met, the MS will move from the

current cell into another one. This process is called cell selection.


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CELL RESELECTION C2

When C2 Parameter Indicator (PI) indicates YES the MS will getparameters (CRO, TO and PT) , from BCCH, to be used to calculateC2(channel quality criterion), which serves as cell reselectionnorm. The equation is as follows:

C2 C1 CRO H PT T TO, when PT 31 C2 C1 CRO, when PT= 31

Where T is a timer. When a cell is recorded by MS as one of thesix strongest cells, timer starts counting, otherwise, T is reset tozero.


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PARAMETER INDICATOR (PI)

PI is used to notify the MS whether to use C2 as thecell reselect parameter and whether the parameterscalculating C2 exist.

PI consists of 1 bit. 1means the MS should extractparameters from the system message broadcasting inthe cell to calculate the C2 value, and use the C2 value

as the standard for cell reselect; 0 means the MSshould use parameter C1 as the standard for cellreselect (equivalent to C2 C1 .


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CRO, PT AND TO

The cell reselection initiated by the radio channelquality regards C2 as the standard. C2 is a parameterbased on C1 plus some artificial offset parameters. Theartificial influence is to encourage the MS to take the

priority in accessing to some cells or prevent it fromaccessing to others. These methods are often used tobalance the traffic in the network.

In addition to C1, there are three other factorsinfluencing C2, namely: CELL_RESELECT_OFFSET(CRO), TEMPORARY_OFFSET (TO) andPENALTY_TIME (PT).


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C2 TYPICAL APPLICATIONS

In general, its not expected that MS access the cellswhere the traffic is very heavy or the channel quality isvery low. In this case , the PT may be set 31, makingTO invalid, so C2=C1-CRO. Because the C2 is lowereddeliberately, the possibility that the cell will bereselected by MS is lowered greatly. The greater theCRO, the less possibility that the cell will be reselected,

and vice versa.


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C2 TYPICAL APPLICATIONS

Its expected that MS stay as much as possible in cells wherethe system utilization are very low and the traffic load is light. Inthis case, its recommended that CRO be ranged from 0 to 20dB.The greater the CRO, the more possible the cells will be

reselected ,and vice versa. Its also suggested that TO is equal or alittle higher than CRO. PT, whose main role is to avoid frequentcell reselection by MS, is generally recommended to be set at 20seconds or 40 seconds.

For cells where the traffic is moderate, the recommended valuefor CRO is zero and PT=31, thus causing C2=C1, i. e. no artificialimpact will be imposed.


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CELL SELECTION HYSTERESIS (2)

To minimize the influence of this issue, the GSMspecifications put forward a parameter called cellreselection hysteresis (CRH), which requires that thesignal level of adjacent cell (in a different location area)

be larger than the local cell signal level, and theirdifference be larger than the value specified by the cellselection hysteresis. In this case, the MS will start thecell reselection.

The cell reselection hysteresis is represented indecimal numerals, its unit is dB, its range is 0 14, itsstep length is 2dB, and its default value is 4.


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CELL RESELECTION PRINCIPLE

If the MS calculates that the C2 value of an adjacent cell (Samelocation area) surpasses the C2 value of the serving cell andmaintains for 5s or longer, the MS will start cell reselection andaccess to the adjacent cell.

If the MS detects a cell that is not in the same location area withthe current cell, the calculated C2 value surpasses the sum of theC2 value of the current cell and the cell reselection hysteresis(CRH) parameter and if it remains for 5s or longer, the MS will

start the cell reselection and access to the new cell. Note that the cell reselection caused by the parameter C2

should be originated at least at the interval of 15s so as to avoidthe frequent cell reselection by MS.


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CELL BAR ACCESS (CBA)

In the system message broadcasting in each cell, there is a bitinformation indicating whether to allow the MS to access to it, which iscalled cell bar access (CBA). The parameter CBA is to indicate whetherthe cell bar access is set in a cell.

The parameter is represented in character string. Its value range is:

YES: the cell is barred for accessNO: the cell is not barred for access

The CBA bit is a parameter for the network operator to set. Usually allthe cells are allowed to be accessed by MS , so the bit is set NO. However,in special cases, the telecom operator may want to assign a certain cellsfor handover service only, then the bit can be set YES.


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Area A

BTS A

BTS B

BTS C

CELL BAR ACCESS (CBA)


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CELL BAR QUALIFY (CBQ)

In areas where the cells overlay with each other anddiffer in capacity, traffic and functions, the telecomoperator often hopes that the MS can have priority inselecting some cells, that is, the setting of cell priority.This function is set by way of the parameter "Cell BarQualify" (CBQ).

YES: The cell has high priority

NO: The cell has low priority


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CBQ CBA Cell SelectionPriority Cell ReselectionState

No No Normal Normal

No Yes Barred Barred

Yes No Low Normal

Yes Yes Low Normal

CELL BAR QUALIFY (CBQ) 2

C1 and C2 States with CBA and CBQ Configurations


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B

EXAMPLE OF CBQ SETTING

For some reasons, the traffic of Cells A and B is apparently higher thanthat of other adjacent cells. To balance the traffic in the whole area, youcan set the priority of Cells A and B as low, and set the priority of the rest

cells as normal so that the traffic in the shade area will be absorbed byadjacent cells. It must be noted that the result of this setting is that theactual coverage of Cell A and Cell B is narrowed. However, this is differentfrom reducing the transmitting power of Cell A and Cell B, the latter maycause blind areas of the network coverage and the reduction ofcommunication quality.


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RANDOM ACCESS

Random access is the process that messages beingtransmitted on RACH when a MS turns from idle tospecialized mode. The main parameters includes:

MAXRETRANSACRE (Re-establishment Enable)


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MAX RETRANS

The MAX RETRANS is often set in the following ways: For areas (suburbs or rural areas) where the cell radius is more

than 3km and the traffic is smaller, the MAX RETRANS can be set11 (i.e. the MAX RETRANS is 7).

For areas (not bustling city blocks) where the cell radius is lessthan 3km and the traffic is moderate, the MAX RETRANS can beset 10 i.e. the MAX RETRANS is 4).

For microcellular, its recommend that the MAX RETRANS beset 01 i.e. the MAX RETRANS is 2).

For microcellular areas with very high traffic and cells withapparent congestion, its recommend that the MAX RETRANS beset 00 i.e. the MAX RETRANS is 1).


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ACCESS CONTROL AC

The access levels are distributed as follows:C 0 C9: ordinary subscribers;C11: used for PLMN management;C12: used by the security department;

C13: public utilities e.g. water, gas ;C14: emergency service;C15: PLMN staff.


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SETTING OF AC

In the BS installation and commissioning process or in theprocess of maintaining or testing some cells, the operator can setC0 C9 as 0 to forcedly forbid the access of ordinary subscribersso as to reduce the unnecessary effects on the installation or

maintenance work.

In some cells with very high traffic, the congestion will occur inbusy hours. For example, the RACH conflict happens frequently,

the AGCH is overloaded and the Abis interface flow is overloaded.The network operator can set proper access control parameters C0 C15 to control the traffic of some cells.


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RE-ESTABLISHMENT ENABLE (RE)

For the drop calls caused by the radio link fault, the MS can startthe call reestablishment process to resume the conversation, butthe network is entitled to determine whether the callreestablishment is allowed or not. 0=Yes, 1=No.

In some special circumstances, the drop call may occur whenthe MS goes through a blind area during the conversation. If thecall reestablishment is allowed, the mean drop call rate will bereduced. However, the call reestablishment process will occupy alonger period of time, most of the subscribers have hung up

before the reestablishment process is over, as a result, the callreestablishment failed to achieve its purpose and wasted manyradio resources. We recommend that the call reestablishment benot allowed in the network except for some individual cells.


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LIMITn

According to GSM Specification 05.08, the BTS must measurethe interference levels of the upward links of all the free channelsfor the purpose of providing basis for managing and allocatingradio resources.

Moreover, the BTS should analyze its measured results, dividethe interference levels into 5 grades and report them to the BSC.The division of the 5 interference grades (i.e. the so-calledinterference bands) is set by the operator through the man-

machine interface. The parameter "Interference band border(LIMITn) determines the borders of the 5 interference bands.


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Value Range Specified dBm Level0


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IMSI ATTACH/ DETACH (ATT)

An ATT mark should be set as YES so that the network will no longerprocess the paging process for the called MS after the MS shuts down,thus saving the processing time of the network entities and saving lots ofnetwork resources.

Please note that the ATT in different cells but in the same location areashould be set the same. Because the shutdown of the MS in cells wherethe ATT is YES will start the IMSI detach process, and the network willrecord the fact that the MS is in the non-working state and reject all theconnection requests when using MS as the called. When the MS restartsand is in the same location area (so the location update process is not

started) as when it shuts down but is in a different cell and the ATT of thecells is set as NO, so the MS will not start the IMSI attach process, either.In this case, the MS cannot become the called party until it starts thelocation updating process.


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IMSI ATTACH/ DETACH (ATT)

The IMSI detach process is that: the MS notifies the network that it ismoving from the working state to the non-working state, or the process ofthe SIM card being taken from the MS.

When receiving the notification from the MS, the network will indicatethe IMSI subscriber to be in the non-working state, so the connectionrequest ending the subscriber as the called party will be rejected. Thecorresponding IMSI attach process is that the MS notifies the networkthat it has been in the working state , or the SIM card is re-inserted intothe MS.

When the MS re-enters the working state, it will detect whether thecurrent LAI is the same as the LAI finally recorded in the MS. If they are

the same, the MS will start the IMSI attach process, otherwise the MS willstart the location updating process (instead of the IMSI attach process).When receiving the location updating or IMSI attach process, the networkwill indicate the IMSI subscriber being in the working state.


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CCCH_CONFCoding

MeaningsCCCH messageblocks in one

BCCH0 CCCH use one basic physical channel, not shared with SDCCH 91 CCCH use one basic physical channel, shares with SDCCH 3

10 CCCH use two basic physical channels, not shared with SDCCH 1100 CCCH use three basic physical channels, not shared with SDCCH 110 CCCH use 4 basic physical channels, not shared with SDCCH 3

Others Reserved

CCCH_CONF

The CCCH can be one or more physical channels. The CCCHand SDCCH can share the same physical channel. Thecombination mode of the common control channel in a cell isdetermined by the CCCH_CONF


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CCCH_CONF

The CCCH_CONF is determined by the telecomoperation department according to the traffic model ofa cell. It is often decided in the system design period.The common configurations in practice are thefollowing:

If a cell has 1 or 2 TRX, we recommend that the CCCH usesone basic physical channel and shares it with the SDCCH

If a cell has 3 or 4 TRX, we recommend that the CCCH uses

one basic physical channel but does not share it with theSDCCH.


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AGBLK

Since the CCCH consists of the access grant channel (AGCH)and paging channel (PCH), it is necessary to set how many blocksof the CCCH information blocks are reserved and dedicated to theAGCH. To let the MS know about the configuration information, thesystem message of every cell contains a configuration parameter,that is, the access grant reserve blocks (AGBLK).

AGBLK is represented in decimal numerals, and its value rangeis:

CCCH is not combined with SDCCH: 0 7.CCCH is combined with SDCCH: 0 2.


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AGBLK

SETTING AND IMPACT OF AGBLKThe AGBLK setting principle is: given that the AGCH is not

overloaded, try to reduce the parameter as much as possible toshorten the time when the MS responds to the paging andimprove the quality of service of the system.

The recommended value of AGBLK is usually 1 (when theCCCH is combined with the SDCCH), 2 or 3 (when the CCCH isnot combined with the SDCCH).


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BS-PA-MFRMSMultiframes of the samepaging group that cycle

on the paging channel2 2

3 3

4 4

5 5

6 6

7 7

8 8

9 9

BS-PA-MFRMS (2)

BS-PA-MFRMS is represented in decimal numerals and its value rangeis 2 9, its unit is multiframe 51 frames , its default value is 2


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PERIODIC UPDATING TIMER (T3212)

The reasons for the location update in the GSM system are oftwo types: one is that the MS finds its location area changed (witha different LAC), the other one is that the network requires the MSto periodically update its location.

The frequency of periodic location update is controlled via thenetwork and the period length is determined by the parameterT3212.

In general, in areas with larger traffic and signaling flow, youshould select the larger T3212 e.g. 16 hours, 20 hours or even 25

hours , but in areas with smaller traffic and lower signaling flow,you can set the smallerT3212 (3 hours or 6 hours, etc.). In areaswhere traffic is far beyond the system capacity, we recommendthat you set T3212 as 0.


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NCCPERM

In the connection mode (during the conversation), the MS willreport the measured signals of the adjacent cells to the BS, buteach report may contain at most 6 adjacent cells, Therefore, let theMS only report the information of the cells that may become thehand-over target cells, do not let the MS report the informationmerely according to the signal level without selection (usually donot let the MS report other GSMPLMN cells).

The above functions can be fulfilled by limiting the MS to merelymeasure the cells whose NCC have been specified. The NCCPERMlists the NCCs of cells to be measured by the MS.


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NCCPERM (2)

In general, each area is allocated with one (or several)NCC. The NCCPERM of each cell in the area shouldcontain the NCC of the area, otherwise a large numberof cross-cell drop calls will occur and the cellreselection will fail. To ensure the normal roamingbetween different areas, the border cells of an areashould contain the NCC of its adjacent areas


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RADIO LINK TIMEOUT (RLT)

During the MS conversation-, when the downward voice (or data)quality is degraded to be unacceptable and cannot be improvedthrough the RF power control or handover (i.e. the so-called radiolink fault), the MS will either start the call re-connection or forcedlydisconnect the link.

As the forced disconnection actually means a "drop call"process, the MS will regard it as a downward radio link fault whenthe communication quality is unacceptable (usually the user has tohang up). In this case, it is provided in the GSM specifications thatthe MS needs a counter S to assign an initial value--"downwardradio link timeout"--. When S is counted to 0, the MS will report thedownward radio link fault.


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MBCR (1)

In the single band GSM system, when the MS reports theadjacent cell measurement result to the network, it only needs toreport the contents of the 6 adjacent cells with the strongestsignals in a band. When multiple bands form a network, thetelecom operator often, according to the actual situation of thenetwork, wants the MS to access to a frequency band with priorityduring the handover, so the operator hopes that the MS will reportthe measurement result on the basis of not only signal strengthbut signal band as well. The parameter "multiband indication(MBCR)" is used to notify the MS that it should report themultiband adjacent cell contents.

The value is 0-3


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MBCR (2)

0: Based on the signal strength of adjacent cells, the MS reportsthe measurement results of 6 adjacent cells whose signals are thestrongest, whose NCC are known and allowed no matter in whichband the adjacent cells lie. The default value is 0

1: The MS should report the measurement result of an adjacentcell in each band (not including the band used by the currentservice area) in the adjacent table, whose signal is the strongestand whose NCC is already known and allowed. It should alsoreport in the rest position the adjacent cells in the band used bythe current service area. If there are still rest positions, it willreport the information of the rest adjacent cells no matter in whichband these adjacent cells lie.


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MBCR (3)

2: The MS should report the measurement results of twoadjacent cells in each band (not including the band used by thecurrent service area) in the adjacent table, whose signals are thestrongest and whose NCC are already known and allowed. Itshould also report in the rest position the adjacent cells in theband used by the current service area. If there are still restpositions, it will report the information of the rest adjacent cells nomatter in which band these adjacent cells lie.

3: The MS should report the measurement results of threeadjacent cells in each band (not including the band used by thecurrent service area) in the adjacent table, whose signals are thestrongest and whose NCC are already known and allowed.


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06) GSM Radio Parameters.ppt