06 go_na08_e1_1 gsm basic radio parameters-60

8/18/2019 06 GO_NA08_E1_1 GSM Basic Radio Parameters-60

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GSM Basic Radio parameters

ZTE University


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Objectives

At the end of this course, you will be able to:

Understand the meaning of various radio parameters

Grasp the setting of radio parameters

State the effect to radio network performance of various

kind of radio parameters


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Content

Network identification parameters

System control parameters

Cell selection parameters

Network function parameters


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Roles of identification parameters

Enable the MS to correctly identify the ID of the current

network

Enable the network to be real time informed of the correct

geographical location of the MS

Enable the MS to report correctly the adjacent cell

information during the conversation process


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MCC LAC

Cell Global Identity

MNC

3 Digits 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 broadcasting

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.


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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)

Base Station Identity Code (BSIC)

It enables MSs to distinguish betweenneighboring base stations


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NCC and BCC ROLES

NCC:

In the connection mode (during conversation), the MS

must measure the signals in the adjacent cells andreport 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 toonly report 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.


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CBA

FED

BSIC CONFIGURATION PRINCIPLE

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

F use different BSIC when they have same BCCH

frequency. When the BSIC resources are notenough, the cells close to each other may take the

priority to use different BSIC.


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ROLES OF BSIC

Inform the MS the TSC used by the common signaling

channel of the cell.

As the BSIC takes part in the decoding process of therandom 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 this cell.

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 measurement report, MS must showBSIC of this carrier it has measured to every frequency

point.


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BA LIST (BCCH ADJACENT LIST)

Adjacent cell BCCH table

At most 32 adjacent cell

Carried by BCCH when MS is idle, by SACCH

when MS is dedicated

The MS will first search carriers from this tableand if none is found it will turns to find any of 30

carriers with highest levels.


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Content






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RANDOM ACCESS

Random access is the process that messages

being transmitted on RACH when a MS turns

from “idle” to “dedicate” mode. The mainparameters includes:

MAXRETRANS

Tx_Integer

AC


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MAX RETRANS

When starting the immediate assignment process

(e.g, when MS needs location updating,

originating calls or responding to paging calls), theMS will transmit the "channel request" message

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

ALOHA channel, in order to enhance the MSaccess success rate, the network allows the MS to

transmit multiple channel request messages

before receiving the immediate assignmentmessage. The numbers of maximum

retransmission (MAX RETRANS) are determined

by the network.


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

For areas (not bustling city blocks) where the cell radius is less

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).


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Transmission Distribution Timeslots

(Tx_integer)

The Tx_integer parameter is the interval in timeslots at which

the MS continuously sends multiple channel request messages.

The parameter S is an intermediate variable in the accessalgorithm, and is to be determined by the Tx_integer parameter

and the combination mode of the CCCH and SDCCH


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Format of Tx_Integer

MS starts the first channel request message : {0, 1, ...,

MAX (Tx_integer, 8)-1}

The number of timeslots between any two adjacentchannel request messages {S, S+1, ..., S+Tx_integer-1}

The Tx_integer is a decimal number, which can be 3~12,

14, 16, 20, 25, 32 and 50 (default). The values of theparameter S are shown as below:

Tx_integer CCH Combination Mode

CCCH Not Shared with SDCCH CCCH Shared with SDCCH

3, 8, 14, 50 55 41

4, 9, 16, 76 52

5, 10, 20, 109 58

6, 11, 25, 163 86

7, 12, 32, 217 115


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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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CCCH_CONF

Coding Meanings

CCCH message

blocks in oneBCCH

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 can be one or more physical channels. The

CCCH and SDCCH can share the same physical channel.

The combination mode of the common control channel in a

cell is determined by the CCCH_CONF


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CCCH_CONF

The CCCH_CONF is determined by the telecom

operation department according to the traffic

model of a cell. If a cell has 1 TRX, we recommend that the CCCH

uses one basic physical channel and shares it with the

SDCCH If a cell has 2 ~ 8 TRX, we recommend that the CCCH

uses one basic physical channel but does not share it

with the SDCCH.


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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 blocks of the CCCHinformation blocks are reserved and dedicated to

the AGCH, the access grant reserve 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.


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BS-PA-MFRMS

According to the GSM specifications, every mobile

subscriber belongs to a paging group. the MS calculates

the paging group to which it belongs by its own IMSI.

In an actual network, the MS only "receives“ the contents

in the paging subchannel to which it belongs but ignores

the contents in other paging subchannels. (i.e. DRX

source).

The BS-PA-MFRMS refers to how many multi-frames are

used as a cycle of a paging subchannel. This parameter in

fact determines how many paging sub-channels are to bedivided from the paging channels of a cell.


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BS-PA-MFRMS

Multiframes of the same

paging group that cycle

on the paging channel

2 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 range is 2～9, its unit is

multiframe（51 frames）, its default value is 2


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NCCPERM

In the connection mode (during the conversation),the MS will report the measured signals of the

adjacent cells to the BS, but each report maycontain at most 6 adjacent cells.

Therefore, let the MS only report the information of

the cells that may become the hand-over targetcells.

The above functions can be fulfilled by limiting the

MS to merely measure the cells whose NCC havebeen specified. The NCCPERM lists the NCCs ofcells to be measured by the MS.

NCCPERM will affect handover


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RADIO LINK TIMEOUT (RLT)

GSM specification stipulates that the MS must have a timer

(S), which is assigned with an initial value at the start of

the conversation, that is, the “downlink radio link timeout”

value.

Every time the MS fails to decode a correct SACCH

message when it should receive the SACCH, the S is

decreased by 1. On the contrary, every time the MS

receives a correct SACCH message, the S is increased by

2, but the S should not exceed the downlink radio link

timeout value. When the S reaches 0, the MS will reportthe downlink radio link failure.

The radio link timeout is a decimal number, within the

range of 4 ~ 64, at the step of 4, defaulted to 16.


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MBCR (1)

The parameter "multiband indication (MBCR)" is

used to notify the MS that it should report the

multiband 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 reports the

measurement results of 6 adjacent cells whose signals 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 one adjacent 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.


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MBCR (3)

2: The MS should report the measurement results of two 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.

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.


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Application of MBCR


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Content






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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 channelparameters 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 definesthe 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 is 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）＝Y; if Y≥ X.


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RxLevAccessMin

The RXLEV_ACCESS_MIN is a decimal number,

within the range of -110dBm ~ -47dBm

Default value is 0 (-110dBm).

RXLEV_ACCESS_MIN Meaning

-47 dBm > -48 dBm (level 63)

-46 dBm -49 ~ -48 dBm (level 62)

... ...

-108 dBm -109 ~ -108 dBm (level 2)

-109 dBm -110 ~ -109 dBm (level 1)

-110 dBm


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Setting and Influence

For a cell with traffic overload, you can appropriately

increase the RXLEV_ACCESS_MIN

RXLEV_ACCESS_MIN value cannot be set to too high a

value. Otherwise, “blind areas” will be caused on the

borders of cells.

It is suggested that the RXLEV_ACCESS_MIN value

should not exceed -90 dBm.


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CELL RESELECTION C2

Cell Reselection (C2) is a process when MS change its

service cell in idle mode.

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

signal levels of the BCCH TRX of its adjacent cells (at

most 6)

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

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


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

will get parameters (CRO, TO and PT) , from BCCH, to be

used to calculate C2(channel quality criterion), which serves

as cell reselection norm. The equation is as follows:

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.

C2＝

C1＋

CRO－

H（

PT－

T）×

TO, when PT≠

31

C2＝

C1－

CRO , when PT= 31

CELL RESELECTION C2


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PARAMETER INDICATOR (PI)

PI is used to notify the MS whether to use C2 as the cell

reselect parameter and whether the parameters calculating

C2 exist.

PI consists of 1 bit. “1”means the MS should extractparameters 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 cell reselect (equivalent

to C2＝C1）.


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CRO, PT AND TO

The cell reselection initiated by the radio channel quality 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 it from 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).


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Format of CRO, PT and TO

The CRO is a decimal number, in dB, within the range

of 0 ~ 63, meaning 0 ~ 126 dB, at the step of 2 dB.

The TO is a decimal number, in dB, within the range of

0 ~ 7, meaning 0 ~ 70 dB, at the step of 10 dB, where

70 means infinite.

The PT is a decimal number, in seconds, within the

range of 0 ~ 31, meaning 20 ~ 620 seconds for 0 ~ 30,and at the step of 20 seconds. The value of 31 is

reserved to change the direction of effect that the CRO

works on the C2 parameter.


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C2 TYPICAL APPLICATIONS

For cells where the traffic is very heavy or the

channel quality is very low. the PT may be set 31,

making TO invalid, so C2=C1-CRO.

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.


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CELL SELECTION HYSTERESIS (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.

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

values of two adjacent cells measured along their borders

will fluctuate greatly.

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, but reduces the

access success rate of the system, as the MS cannotrespond to paging calls in the location updating process.


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CELL SELECTION HYSTERESIS (2)

To minimize the influence of this issue, the GSM

specifications put forward a parameter called

ReselHysteresis,

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.


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CELL RESELECTION PRINCIPLE

If the MS calculates that the C2 value of anadjacent cell (Same location area) surpasses theC2 value of the serving cell and maintains for 5sor longer, the MS will start cell reselection .

If the MS detects a cell that is not in the same

location area with the current cell, the calculatedC2 value surpasses the sum of the C2 value of thecurrent cell and the ReselHysteresis parameterand if it remains for 5s or longer, the MS will startthe cell reselection .

The cell reselection caused by C2 should be

originated at least at the interval of 15s.


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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 CBA bit is a parameter for the network operator to set. Usually

all the cells are allowed to be accessed by MS , so the bit is setNO. 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)


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Area A

MS 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 and differ in capacity, traffic and

functions, the telecom operator often hopesthat 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).


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C1 and C2 States with CBA and CBQ Configurations

CBQ CBACell Selection

Priority

Cell Reselection

State

No No Normal Normal

No Yes Barred Barred

Yes No Low Normal

Yes Yes Low Normal

CELL BAR QUALIFY (CBQ) 2


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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 whole

area, 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 Bis 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.


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Content






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LIMITn

According to GSM Specification 05.08, the BTS must

measure the interference levels of the upward links of all

the free channels for the purpose of providing basis for

managing and allocating radio resources.

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. The parameter

"Interference band border(LIMITn)” determines the bordersof the 5 interference bands.


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Value Range Specified dBm Level

0


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INTAVE

Due to the randomness of the radio channel

interference, the BTS must average the measured

uplink interference levels within the specifiedperiod, and this average cycle is determined by

the INTAVE parameter.

This parameter is a decimal number, in SACCHmulti-frames, within the range of 1 ~ 31.


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New Cause Indication (NECI)

The NECI is a decimal number, within the range of

0 ~ 1, with the meaning described as below:

When the NECI is 0, it means that the cell does notsupport the access of half-rate services.

When the NECI is 1, it means that the cell supports the

access of half-rate services.


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RE-ESTABLISHMENT ENABLE (RE)

For the drop calls caused by the radio link fault, the MScan start the call reestablishment process to resume theconversation, but the network is entitled to determinewhether the call reestablishment is allowed or not.

“0”=Yes, “1”=No.

In some special circumstances, the drop call may occurwhen the MS goes through a blind area during the

conversation. If the call reestablishment is allowed, themean drop call rate will be reduced. However, the callreestablishment process will occupy a longer period oftime, most of the subscribers have hung up before the

reestablishment process is over, as a result, the callreestablishment failed to achieve its purpose and wastedmany radio resources. We recommend that the callreestablishment be not allowed in the network except forsome individual cells.


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06 go_na08_e1_1 gsm basic radio parameters-60

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