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
Network identification parameters
System control parameters
Cell selection parameters
Network function parameters
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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
Network identification parameters
System control parameters
Cell selection parameters
Network function parameters
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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
Network identification parameters
System control parameters
Cell selection parameters
Network function parameters
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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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