07) gsm radio parameters-57

8/13/2019 07) GSM Radio Parameters-57

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ZXG10 – RADIOPARAMETERS




TOPICS FOR DISCUSSION

• NETWORK IDENTIFICATION PARAMETERS – CGI , BSIC, BCC/ NCC

• CELL SELECTION PARAMETERS

– C1 and C2

• SYSTEM CONTROL PARAMETERS

– RLT, CBA, CBQ and etc.

• NETWORK FUNCTIONAL PARAMETERS

– INTAVE, LIMITn




NETWORK IDENTIFICATION

PARAMETERS

• As a global cellular mobile communication

system, the GSM adopts a unique numbers to

every country, networks in every country,

location area of every network and cells ofeach location area.




ROLES OF IDENTIFICATION

PARAMETERS

Enable the MS to correctly identify the ID of thecurrent network so that it can correctly select the

network when the user (or telecom operator) wants to

access to in any conditions.

Enable the network to be real time informed of thecorrect geographical location of the MS so that the

network can normally connect various service

requests with the MS.

Enable the MS to report correctly the adjacent cellinformation during the conversation process so that

the network can hand-over the calls when necessary

to ensure the continuity of the conversation.




CELL GLOBAL IDENTITY (CGI)

MCC LAC

Cell Global Identity

MNC

3 Digi ts 2-3 Digits Max 16 Bits

CI

Max 16 bits

LAI

Cell Global Identity (CGI)

• It is used for identifying individual cells within an

LA




ROLES OF CGI

The CGI information is sent along the systembroadcasting information in every cell.

When the MS receives the system information, it will

extract the CGI information from it and determines whether

to camp on the cell according to the MCC and MNCspecified by the CGI.

It judges whether the current location area is changed,

then determines whether to take the location updating

process. During the location updating process, the MS willreport the LAI information to the network so that the

network is fully aware of the cell where the MS is currently

located.




SETTING OF CGI

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

～ 999.

MNC

Mobile Network Code

: consists of 3decimal 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.




BASE STATION IDENTITY CODE (BSIC)

NCC BCC

3 Bits 3 Bits

BSIC

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

BCC Base Station Color Code Value Range: 0~7

Base Station Identity Code (BSIC)

• It enables MSs to distinguish between neighboring

base stations




NCC and BCC ROLES

NCC: In the connection mode (during conversation), theMS must measure the signals in the adjacent cells and

report the result to the network. As each measurement

report sent by the MS can only contain the contents of six

cells, so it is necessary to control the MS so as to onlyreport the information of cells factually related to the cell

concerned. The high 3 bits (i.e. NCC) in the BSIC serve this

purpose.

BCC: The BCC is used to identify different BS using the

same BCCH in the same GSMPLMN.




BSIC CONFIGURATION PRINCIPLE

CBA

FED

In general, it is required that Cells A, B, C, D, E and F

use different BSIC. When the BSIC resources are not

enough, the cells close to each other may take the

priority to use different BSIC.




ROLES OF BSIC

1. Inform the MS the TSC used by the common signaling

channel of the cell.

2. As the BSIC takes part in the decoding process of the

random access channel (RACH), it can be used to

prevent the BS from mis-decoding the RACH, sent by

the MS to an adjacent cell, as the access channel of thiscell.

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 theresults to the BS. In the uplink measurement report, MS

must show BSIC of this carrier it has measured to every

frequency point.




BA LIST (BCCH ADJACENT LIST)

When a MS is turned on, it will scan from the BA

(Adjacent cell BCCH table) it remembered when

turned off last time. The MS will first search

carriers from this table and if none is found it willturns to find any of 30 carriers with highest levels,

then try to decode BCCH carriers one by one

according to their level sequences.




CELL SELECTION C1

When the MS is turned on, it will try to contact a

public GSM PLMN, so the MS will select a proper

cell and extract from the cell the control channel

parameters and prerequisite system messages.This selection process is called cell selection. The

quality of radio 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.




CELL SELECTION C1

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

where:

RXLEV_ACCESS_MIN is the minimum received level the MSis allowed to access the network

MS_TXPWR_MAX_CCH is the maximum power level of the

control 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）＝0; if Y X.




C1 PATHLOSS CRITERION

All the candidate cells for MS must meet the path

loss criterion, i.e C1>0. MS will select the cell with

the maximal C1 to access and will camp on this cellunless some key conditions has changed greatly.




RXLEV_ACCESS_MIN

In order to avoid providing unsatisfactory communicationquality and avoid the unnecessary waste of radio

resources if the MS accesses to the system (the

communication quality after the access often cannot

ensure the normal communication process) at the very

low received level, the GSM system regulates that, when

a MS is to access to a network, its receiving signal level

must be larger than a threshold level, i.e. the minimum

receiving level the MS is allowed to access to

RXLEV_ACCESS_MIN).

Default value is 0 (-110dBm).




CELL RESELECTION C2

1. Cell Reselection (C2) is a process when MS changeits service cell in idle mode.

2. When the MS selects a cell it will begin to measure

the signal levels of the BCCH TRX of its adjacent cells,

record 6 adjacent cells whose signal levels are the

strongest and extract from them various types of

system messages and control messages of each

adjacent cell.

3. When given conditions are met, the MS will move

from the current cell into another one. This process is

called cell reselection.




CELL RESELECTION C2

When C2 Parameter Indicator (PI) indicates YES，the MS will

get parameters [CRO(cell reselect offset), TO(temporary offset)and PT(penalty time)] , from BCCH to be used to calculate

C2(channel quality criterion), which serves as cell reselection

norm. 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 the

six strongest cells, timer starts counting, otherwise, T is reset to

zero.




PARAMETER INDICATOR (PI)

PI is used to notify the MS whether to use C2 as thecell reselect parameter and whether the parameters

calculating C2 exist.

PI consists of 1 bit. “1”means the MS should extract

parameters from the system message broadcasting in

the cell to calculate the C2 value, and use the C2

value as the standard for cell reselect; “0” means the

MS should use parameter C1 as the standard for cellreselect (equivalent to C2＝C1）.




CRO, PT AND TO

The cell reselection initiated by the radio channelquality regards C2 as the standard. C2 is a parameter

based on C1 plus some artificial offset parameters.

The artificial influence is to encourage the MS to take

the priority in accessing to some cells or prevent itfrom accessing to others. These methods are often

used to balance the traffic in the network.

In addition to C1, there are three other factors

influencing C2, namely: CELL_RESELECT_OFFSET(CRO), TEMPORARY_OFFSET (TO) and

PENALTY_TIME (PT).




C2 TYPICAL APPLICATIONS

1. In general, it’s not expected that MS access the cells

where the traffic is very heavy or the channel quality is

very low. In this case , the PT may be set 31, making TO

invalid, so C2=C1-CRO. Because the C2 is lowereddeliberately, the possibility that the cell will be

reselected by MS is lowered greatly. The greater the

CRO, the less possibility that the cell will be reselected,

and vice versa.




C2 TYPICAL APPLICATIONS

2. It’s expected that MS stay as much as possible in cells

where the system utilization are very low and the trafficload is light. In this case, it’s recommended that CRO

be ranged from 0 to 20dB. The greater the CRO, the

more possible the cells will be reselected ,and vice

versa. It’s also suggested that TO is equal or a littlehigher than CRO. PT, whose main role is to avoid

frequent cell reselection by MS, is generally

recommended to be set at 20 seconds or 40

seconds.(20-640).

3. For cells where the traffic is moderate, the recommended

value for CRO is zero and PT=31, thus causing C2=C1,

i. e. no artificial impact will be imposed.




CELL SELECTION HYSTERESIS (1)

1. When a MS reselects a cell, if the old cell and the

target cell are in different locations, then the MS must

initiate a location updating process after cell

reselection.

2. Due to the fading features of the radio channel, the C2

values of two adjacent cells measured along theirborders will fluctuate greatly.

3. MS will frequently conduct the cell reselection, which

will not only increase the network signaling flow and

lead to low efficiency use of radio resources, butreduces the access success rate of the system, as the

MS cannot respond to paging calls in the location

updating process.




CELL SELECTION HYSTERESIS (2)

4. To minimize the influence of this issue, the GSMspecifications put forward a parameter called cell

selection hysteresis (CSH), which requires that the

signal 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

cell selection hysteresis. In this case, the MS will start

the cell reselection.

5. The cell selection hysteresis is represented in decimal

numerals, its unit is dB, its range is 0～14, its step

length is 2dB, and its default value is 4.




CELL RESELECTION PRINCIPLE

1. If the MS calculates that the C2 value of an adjacent cell

(Same location area) surpasses the C2 value of theserving cell and maintains for 5s or longer, the MS will

start cell reselection and access to the adjacent cell.

2. If the MS detects a cell that is not in the same location

area with the current cell, the calculated C2 valuesurpasses the sum of the C2 value of the current cell

and the cell selection hysteresis (CSH) parameter and if

it remains for 5s or longer, the MS will start the cell

reselection and access to the new cell.

3. Note that the cell reselection caused by the parameter

C2 should be originated at least at the interval of 15s so

as to avoid the frequent cell reselection by MS.




CELL BAR ACCESS (CBA)

In the system message broadcasting in each cell, there is a bit

information indicating whether to allow the MS to access to it, which is

called cell bar access (CBA). The parameter CBA is to indicate whether

the 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 access

NO: the cell is not barred for access

The CBA bit is a parameter for the network operator to set. Usually all thecells 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 cells

for handover service only, then the bit can be set YES.




CELL BAR ACCESS (CBA)

Area A

BTS A

BTS B

BTS C




CELL BAR QUALIFY (CBQ)

In areas where the cells overlay with each other and differ incapacity, traffic and functions, the telecom operator often

hopes that the MS can have priority in selecting some cells,

that is, the setting of cell priority. This function is set by way of

the parameter "Cell Bar Qualify" (CBQ).

YES: The cell has low priority

NO: The cell has normal priority




CELL BAR QUALIFY (CBQ) 2

C1 and C2 States with CBA and CBQ

Configurations

CBQ CBA Cell SelectionPriority

Cell ReselectionState

No No Normal Normal

No Yes Barred Barred

Yes No Low Normal

Yes Yes Low Normal




EXAMPLE OF CBQ SETTING

For some reasons, the traffic of Cells A and B is apparently higher

than that of other adjacent cells. To balance the traffic in the wholearea, you can 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 by adjacent cells. It must be noted that the result of

this setting is that the actual coverage of Cell A and Cell B is narrowed.However, this is different from reducing the transmitting power of Cell

A and Cell B, the latter may cause blind areas of the network coverage

and the reduction of communication quality.。

B




RANDOM ACCESS

Random access is the process that messages being transmittedon RACH when a MS turns from “idle” to “specialized” mode.

The main parameters includes:

MAXRETRANS AC

RE (Re-establishment Enable)




MAX RETRANS

When starting the immediate assignment process (e.g, when

MS needs location updating, originating calls or responding to

paging calls), the MS will transmit the "channel request"

message over the RACH to the network. As the RACH is an

ALOHA channel, in order to enhance the MS access successrate, the network allows the MS to transmit multiple channel

request messages before receiving the immediate assignment

message. The numbers of maximum retransmission (MAX

RETRANS) are determined by the network.




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 set 11 (i.e. the MAX RETRANS is 7).

For areas (not bustling city blocks) where the cell radius isless than 3km and the traffic is moderate, the MAX RETRANS

can be set 10 i.e. the MAX RETRANS is 4).

For micro-cellular, it’s recommend that the MAX RETRANS

be set 01 i.e. the MAX RETRANS is 2).

For microcellular areas with very high traffic and cells with

apparent congestion, it’s recommend that the MAX RETRANS

be set 00（i.e. the MAX RETRANS is 1).




ACCESS CONTROL AC

In some special conditions, the telecom operator wants to barall or part of MS from sending out the access request or paging

response request in some special areas. For example, in case

some areas are in emergency state or in case a GSM PLMN

encounters a serious fault. For this reason, GSM Specification

（ 02.11 ） stipulates that each GSM subscriber (ordinarysubscriber) is allocated with an access level. The access level

ranges from 0 to 9 and is stored in the SIM card of the

subscriber. The GSM Specifications reserves 5 special access

levels for some special subscribers, which range from 11 to 15.These levels usually have higher access priority. Special

subscribers can have one or more access levels (11~15), and

their access levels are also stored in the SIM cards.




SETTING OF AC

In the BS installation and commissioning process or in theprocess of maintaining or testing some cells, the operator

can set C0～C9 as 0 to forcedly forbid the access of

ordinary subscribers so as to reduce the unnecessary

effects on the installation or maintenance work.

In some cells with very high traffic, the congestion will occur

in busy hours. For example, the RACH conflict happens

frequently, the AGCH is overloaded and the Abis interfaceflow is overloaded. The network operator can set proper

access control parameters（C0～C15）to control the traffic

of some cells.




RE-ESTABLISHMENT ENABLE (RE)

1. For the drop calls caused by the radio link fault, the MS can startthe call reestablishment process to resume the conversation, but

the network is entitled to determine whether the call

reestablishment is allowed or not. “0”=Yes, “1”=No.

2. In some special circumstances, the drop call may occur when the

MS goes through a blind area during the conversation. If the callreestablishment is allowed, the mean drop call rate will be

reduced. However, the call reestablishment process will occupy a

longer period of time, most of the subscribers have hung up

before the reestablishment process is over, as a result, the call

reestablishment failed to achieve its purpose and wasted manyradio resources. We recommend that the call reestablishment be

not allowed in the network except for some individual cells.




LIMITn

1. According to GSM Specification 05.08, the BTS mustmeasure the interference levels of the upward links of all

the free channels for the purpose of providing basis for

managing and allocating radio resources.

2. Moreover, the BTS should analyze its measured results,divide the interference levels into 5 grades and report

them to the BSC. The division of the 5 interference

grades (i.e. the so-called interference bands) is set by the

operator through the man-machine interface. Theparameter "Interference band border(LIMITn)” determines

the borders of the 5 interference bands.




LIMITn

Value Range Specified dBm Level

0 <-110 dBm

1 -110 dBm ~ -109 dBm

2 -109 dBm ~ -108 dBm

…

61 -50 dBm ~ -49 dBm

62 -49 dBm ~ -48 dBm

Default: LIMIT1：4 LIMIT2：8 LIMIT3：15 LIMIT4：25

The division of the interference bands should be favorable in describing the

interference in the system. Generally the default values are recommended. Inthe ordinary situations, the free channel interference level is smaller, so the

LIMIT1～4 value should be smaller. When apparently large interference

appears in the system, you can properly increase the LIMIT1~4 values in

order to know the exact interference.




IMSI ATTACH/ DETACH (ATT)

1. An ATT mark should be set as YES so that the network will no longer

process the paging process for the called MS after the MS shutsdown, thus saving the processing time of the network entities and

saving lots of network resources.

2. Please note that the ATT in different cells but in the same location

area should be set the same. Because the shutdown of the MS incells where the ATT is YES will start the IMSI detach process, and

the network will record the fact that the MS is in the non-working

state and reject all the connection requests when using MS as the

called. When the MS restarts and is in the same location area (so the

location update process is not started) as when it shuts down but isin a different cell and the ATT of the cells 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 the location updating process.






The IMSI detach process is that: the MS notifies the network that it is

moving 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 indicate the

IMSI subscriber to be in the non-working state, so the connection request

ending the subscriber as the called party will be rejected. The

corresponding IMSI attach process is that the MS notifies the network that

it has been in the working state , or the SIM card is re-inserted into the MS.

When the MS re-enters the working state, it will detect whether the

current 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 will startthe location updating process (instead of the IMSI attach process). When

receiving the location updating or IMSI attach process, the network will

indicate the IMSI subscriber being in the working state.




CCCH_CONF

The CCCH can be one or more physical channels. The CCCH

and SDCCH can share the same physical channel. Thecombination mode of the common control channel in a cell is

determined by the CCCH_CONF

CCCH_CONF

CodingMeanings

CCCH message

blocks in one

BCCH

0 CCCH use one basic physical channel, not shared with SDCCH 9

1 CCCH use one basic physical channel, shares with SDCCH 3

10 CCCH use two basic physical channels, not shared with SDCCH 18100 CCCH use three basic physical channels, not shared with SDCCH 27

110 CCCH use 4 basic physical channels, not shared with SDCCH 36

Others Reserved




CCCH_CONF

The CCCH_CONF is determined by the telecom operationdepartment according to the traffic model of a cell. It is often

decided in the system design period. The common configurations

in practice are the following:

If a cell has 1 or 2 TRX, we recommend that the CCCH

uses one basic physical channel and shares it with the

SDCCH

If a cell has 3 or 4 TRX, we recommend that the CCCHuses one basic physical channel but does not share it

with the SDCCH.

AGBLK




AGBLK

Since the CCCH consists of the access grant channel

(AGCH) and paging channel (PCH), it is necessary to set

how many blocks of the CCCH information blocks are reserved

and dedicated to the AGCH. To let the MS know about the

configuration information, the system message of every cell

contains a configuration parameter, that is, the access grantreserve blocks (AGBLK).

AGBLK is represented in decimal numerals, and its value

range is:

CCCH is not combined with SDCCH: 0～7.

CCCH is combined with SDCCH: 0～2.




AGBLK

The AGBLK setting principle is: given that the AGCH is not

overloaded, try to reduce the parameter as much as

possible to shorten the time when the MS responds to the

paging and improve the quality of service of the system.

The recommended value of AGBLK is usually 1 (when the

CCCH is combined with the SDCCH), 2 or 3 (when the

CCCH is not combined with the SDCCH).

SETTING AND IMPACT OF AGBLK




BS-PA-MFRMS (2)BS-PA-MFRMS is represented in decimal numerals and its value

range is 2～9, its unit is multiframe 51 frames）, its defaultvalue is 2

BS-PA-MFRMS

Multiframes of the same

paging group that cycle

on the paging channel2 2

3 3

4 4

5 5

6 6

7 7

8 8

9 9




PERIODIC UPDATING TIMER (T3212)

The reasons for the location update in the GSM system are

of two types: one is that the MS finds its location areachanged (with a different LAC), the other one is that the

network requires the MS to periodically update its location.

The frequency of periodic location update is controlled via

the network and the period length is determined by theparameter T3212.

In general, in areas with larger traffic and signaling flow, you

should select the larger T3212（e.g. 16 hours, 20 hours or

even 25 hours）, but in areas with smaller traffic and lowersignaling flow, you can set the smallerT3212 (3 hours or 6

hours, etc.). In areas where traffic is far beyond the system

capacity, we recommend that you set T3212 as 0.




NCCPERM

In the connection mode (during the conversation), the MS willreport the measured signals of the adjacent cells to the BS, but

each report may contain at most 6 adjacent cells, Therefore, let

the MS only report the information of the cells that may become

the hand-over target cells, do not let the MS report the information

merely 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 merely

measure the cells whose NCC have been specified. The

NCCPERM lists the NCCs of cells to be measured by the MS.




NCCPERM (2)

In general, each area is allocated with one (or

several) NCC. The NCCPERM of each cell in the area

should contain the NCC of the area, otherwise a large

number of cross-cell drop calls will occur and the cellreselection will fail. To ensure the normal roaming

between different areas, the border cells of an area

should contain the NCC of its adjacent areas




RADIO LINK TIMEOUT (RLT)

During the MS conversation, when the downward voice (or

data) quality is degraded to be unacceptable and cannot be

improved through the RF power control or handover (i.e. the so-

called radio link fault), the MS will either start the call re-

connection or forcedly disconnect the link.

As the forced disconnection actually means a "drop call"process, the MS will regard it as a downward radio link fault

when the communication quality is unacceptable (usually the

user has to hang up). In this case, it is provided in the GSM

specifications that the MS needs a counter S to assign an initial

value--"downward radio link timeout"--. When S is counted to 0,

the MS will report the downward radio link fault.




MBCR (1)

In the single band GSM system, when the MS reports the

adjacent cell measurement result to the network, it only needs

to report the contents of the 6 adjacent cells with the strongest

signals in a band. When multiple bands form a network, the

telecom operator often, according to the actual situation of the

network, wants the MS to access to a frequency band withpriority during the handover, so the operator hopes that the

MS will report the measurement result on the basis of not only

signal strength but signal band as well. The parameter

"multiband indication (MBCR)" is used to notify the MS that itshould report the multiband adjacent cell contents.

The value is 0-3




MBCR (2)

0: Based on the signal strength of adjacent cells, the MS

reports the measurement results of 6 adjacent cells whosesignals are the strongest, whose NCC are known and

allowed no matter in which band the adjacent cells lie. The

default value is “0”

1: The MS should report the measurement result of anadjacent cell in each band (not including the band used by

the current service area) in the adjacent table, whose

signal is the strongest and whose NCC is already known

and allowed. It should also report in the rest position the

adjacent cells in the band used by the current service area.

If there are still rest positions, it will report the information of

the rest adjacent cells no matter in which band these

adjacent cells lie.




MBCR (3)

2: The MS should report the measurement results of two

adjacent cells in each band (not including the band used bythe current service area) in the adjacent table, whose signals

are the strongest and whose NCC are already known and

allowed. It should also report in the rest position the adjacent

cells in the band used by the current service area. If there

are still rest positions, it will report the information of the rest

adjacent cells no matter in which band these adjacent cells

lie.

3: The MS should report the measurement results of three

adjacent cells in each band (not including the band used by

the current service area) in the adjacent table, whose signals

are the strongest and whose NCC are already known and

allowed.

07) gsm radio parameters-57

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