omf010001 system information issue1.4.ppt
TRANSCRIPT
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Wireless Curriculum Development Section
ISSUE
OMF010001
System Information
1.4
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Introduction to BSS Timers
System Information Overview
Parameters Introduction
Case Study
Course Contents
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System information (SYS INFO) contains network parameters
sent to MS through air interface(Um), including network identity
parameters, cell selection parameters, system control
parameters and network function parameters. By reading system
information, MS can access the network, perform cell selection,
fully utilize various services provided by the network, and
achieve favorable cooperation with the network. SYS INFO can
be divided into two parts:
SYS INFO sent on BCCH, including SYS INFO 1, 2, 2BIS, 2TER,
3, and 4, which are used by MS in idle mode.
SYS INFO sent on SACCH, including system information 5, 5BIS,
5TER, and 6, which are used by MS in dedicated mode.
Additionally Huawei BSC supports the system information 7 and
13 to support GPRS.
System Information Overview
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SYS INFO 1
SYS INFO 1 - - Cell Channel Desc.
(cell channel description format)
- - RACH Control Parameter
(random access channel control parameter)
Content
SYS INFO 1
It contains random access control information (RACH)
and cell frequency allocation table (i.e. CA table). It is
transmitted on BCCH.
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Bit8 Bit7 Bit4 Bit3 Bit2 Format Type
0 0 X X X bit map 0
1 0 0 X X 1024 range
1 0 1 0 0 512 range
1 0 1 0 1 256 range
1 0 1 1 0 128 range
1 0 1 1 1 variable bit map
The above cell channel description formats correspond to different
requirements on the configured frequencies in a cell.
SYS INFO 1 - CA Description Format
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SYS INFO 1 - RACH Control Parameter
These control parameters include:
Maximum re-transmitting times (MAX retrans)
Extended transmission timeslots (Tx_interger)
Cell Bar access (CBA, CELL_BAR_ACCESS)
Common access control level(AC)
Call reestablish permitted (RE)
Emergency call permitted (EC)
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SYS INFO 2
It contains access control information (RACH), network color code
permitted (NCC Permitted), and neighbor cell frequency allocation list
(BA1 list). It is transmitted on BCCH. Generally speaking, SYS INFO
2, 2BIS, 2TER contains different parts of the neighbor cell BCCH
frequencies. Via reading and decoding BA1 list, MS can perform cell
reselection in idle mode. For a MS of GSM900 PHASE I, it only reads
the neighbor cell BCCH frequencies defined in SYS INFO 2, and
ignores those carried by 2BIS and 2TER.
SYS INFO 2
Content
SYS INFO 2 - - Neighbor Cell Desc.
- - NCC permitted
- - RACH Control Parameter
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SYS INFO 2BIS
2BIS contains RACH control data and neighbor cell BCCH
frequencies (part of BA1 list). It is optional and transmitted on
BCCH. As the number of frequencies in BA1 list carried by SYS
INFO 2 is limited; SYS INFO 2BIS carries the rest of the BCCH
frequencies in the BA1 list that are from the same band as in SYS
INFO 2.
SYS INFO 2BIS
Content
SYS INFO 2BIS - - Neighbor Cell Desc.
- - RACH Control Parameter
(Same as that in SYS INFO 1.)
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2TER contains neighbor BCCH frequencies (part of BA1 list). It is
transmitted on BCCH. Only dual band MS can read this
information, and single band 900 or 1800 MS will ignore it. Since
this information carries BCCH frequencies that belong to differentband as those in SYS INFO 2, it is unnecessary for single band
MS to read.
SYS INFO 2TER - - Neighbor Cell Desc. (extended)
SYS INFO 2TER
Content
SYS INFO 2TER
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It contains LAI, cell identity, RACH and parameters related to cell
selection. It is transmitted on BCCH. It is one of the most
important information in SYS INFO.
SYS INFO 3 - - Cell Identity
- - LAI( location area identity)
- - Control Channel Desc
- - Cell OptionBCCH
- - Cell Selection Parameter
- - RACH Control Parameter
SYS INFO 3
Content
SYS INFO 3
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Cell Identity and Location Area Identity
Cell Global Identity (CGI) consists of Location Area Identity (LAI) and
Cell Identity (CI). And LAI includes Mobile Country Code (MCC),
Mobile Network Code (MNC), and Location Area Code (LAC). SYS
INFO 3, 6, and 4 contain all or part of the information of CGI.According to the received SYS INFO, MS decodes the CGI, and
decide whether it can register in the network based on the MCC and
MNC indicated by CGI. At the same time, it can judge whether the
current location area is changed, so as to decide whether it is
necessary to start the location updating process.
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Control Channel Description.
Control channel description includes the following parameters
IMSI Attach-Detach Allowed (ATT, Attach-Detach allowed)
Common Control Channel Configuration (CCCH-CONF)
Access Granted Blocks Reserved (BS_AG_BLKS_RES) Paging Channel Multi-frames (BS-PA-MFRAMS)
Periodic Location Updating Timer (T3212)
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Cell Option
Cell option contains the following parameters:
Power control indication (PWRC)
Discontinuous transmission (DTX)
Radio link timeout
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Cell Selection Parameter
Cell selection parameters indicate how the MS will behave
after the MS is powered on. It includes the following
parameters:
Cell Selection Hysteresis Maximum power level of control channel
(MS_TXPWR_MAX_CCH)
Minimum receiving level of MS permitted to access
(RXLEV_ACCESS_MIN)
Additional reselection parameter indicator (ACS)
Half-rate supported(NECI)
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SYS INFO 4
Content
SYS INFO 4 - - LAI
- - Cell Selection Parameter
- - RACH Control Parameter
- - CBCH Channel Desc. (optional)
- - CBCH Mobile Allocation(optional)
- - SI4 Rest Oct.(parameters related to cell reselection)
SYS INFO 4
It consists LAI, RACH, cell selection parameters and optional CBCH
channel information. It is transmitted on BCCH. When the system
supports cell broadcast function, CBCH together with the CBCH MA
describe the configuration of CBCH and the relevant frequency
information.
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CBCH Channel Desc. and CBCH MA
These two parameters are optional. When system supports
cell broadcast, CBCH Channel Desc. explains the CBCH
channel configuration situation. When CBCH Channel Desc.
is in frequency hopping mode, CBCH MA is also needed.
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SI4 Rest Oct.
It contains the following parameters:
Cell reselection parameter indicator (PI)
Cell Bar Qualify (CBQ)
Cell Bar Access (CBA) Cell_Reselect_Offset (CRO)
Temporary_Offset (TO)
Penalty_Time (PT)
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Content
SYS INFO 5 - - Neighbor Cell Desc.
SYS INFO 5
SYS INFO 5
It describes the neighbor cell BCCH frequencies(BA2 list). It is
mandatory and is transmitted on SACCH. Different from SYS
INFO 2, MS can read the frequency described in SYS INFO 5 in
dedicated mode, report the relevant information of neighbor cells
in measurement report, and use it as the basis for handover.
Similarly, for 900 MS of PHASE 1, it only recognizes the
neighbor cell frequency information described by SYS INFO 5,
and ignores that carried by SYS INFO 5BIS and 5TER.
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SYS INFO 5BIS
SYS INFO 5
5 BIS describes neighbor cells BCCH frequencies.These
frequencies are part of BA2 list. It is optional and is transmitted
on SACCH. Generally, as the number of frequencies which can
be described by SYS INFO 5 is limited, SYS INFO 5 BIS carries
the rest BCCH frequencies in the BA2 that are belong to the
same band as SYS INFO 5 for transmitting to MS.
Content
SYS INFO 5BIS - - Neighbor Cell Desc.
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SYS INFO 5
ContentSYS INFO 5TER - - Neighbor Cell Desc.(Extended)
SYS INFO 5TER
5 TER describes neighbor cells BCCH frequencies,these
frequencies are also part of the BA2 list. It is transmitted on
SACCH channel. Similarly, only dual band MS can read this
information, and single band GSM900 or GSM1800 MS will
ignore it. It carries the BCCH frequencies of neighbor cells
whose band are different from the serving cells.
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SYS INFO 6
Content
SYS INFO 6 - - Cell Identity
- - LAI
- - Cell Option
- - NCC Permitted
SYS INFO 6
It describes LAI, cell identity, and some parameters
describing functions of the cell. It is transmitted on
SACCH. It is also one of the most important informationin system information.
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Introduction to BSS Timers
System Information Overview
Parameters Introduction
Case Study
Course Contents
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Introduction to SYS INFO Parameters
Huawei GSM System Information Parameters:
Network Identity Parameters
System Control Parameters
Cell Option Parameters Network Functional Parameters
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Network Identity Parameter CGI
Network identity parameters mainly include cell global identity
(CGI) and base station identity code (BSIC).
CGI=MCC+MNC+LAC+CI
Once MS receives SYS INFO, it decodes the CGI information,and decides whether it can stay in the cell according to the MCC
and MNC indicated by CGI. At the same time, it judges whether
the current location area is changed, so as to decide whether to
execute location updating. During the location updating process,
MS will report the new LAI information to the network, so that
the network can know exactly the LA in which MS is currently
located.
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Network Identity Parameter BSIC
BSIC=NCC+BCC
In GSM system, each BTS is allocated with a color code, which
is called BSIC. MS can identify two cells with the same BCCH
by the help of BSIC, In network planning, effort should be made
to make sure that BCCH of neighbor cells different from the
serving cells BCCH to reduce the interference. Practically it is
still possible that a same BCCH is re-used in the surrounding
cells. For cells using the same BCCH in a relevant near distance,
their BSIC must be different so that MS can identify two
neighbor cells with same BCCH.
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Mobile Country CodeMCC
MCC is composed of 3 decimal numbers. The
coding range is decimal 000-999.
Definition
MCC consists of 3 decimal numbers. It
indicates the home country of the mobile
subscriber.
Format
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Mobile Network CodeMNC
MNC is composed of two decimal numbers. The
coding range is decimal 00-99.
MNC is used to uniquely identify a specific GSM
PLMN network in a certain country (decided by
MCC).
Definition
Format
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Location Area CodeLAC
LAI contains LAC, which is composed of two bytes. LAC
adopts hexadecimal coding. The available range is from
0001H to FFFEH. Code group 0000H and FFFFHcannot be used (please refer to specification GSM0303,
0408, and 1111). One location area can contain one or
more cells.
To locate the location of MS, the whole area covered by
each GSM PLMN is divided into different location areas.
LAC is used to identify different location areas.
Definition
Format
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Cell IdentityCI
CI is composed of 16 bits, The available range is
from 0 to 65535.
To uniquely identify each cell in the GSM PLMN, the
network operator needs to allocate one code for each
cell, which is the cell identity (CI). Cell identity, together
with LAI, is used for identity of each cell in the world.
(specification 0303).
Definition
Format
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Network Color CodeNCC
NCC is composed of 3 bits, with
coding capacity of 8.
NCC is part of BSIC. MS uses it to distinguish
adjacent BTS that belong to different GSM PLMN.
Format
Definition
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BS Color CodeBCC
BCC is composed of 3 bits. The available
range is from 0 to 7.
BCC is part of BSIC. For its function, please refer
to above sections.
Format
Definition
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ATT
CCCH-CONF
BS-AG-BLKS-RES
BS-PA-MFRAMST3212
Cell Channel Description format
Radio Link Timeout
Neighbor Cell Desc.
NCC Permitted
MS MAX re-trans
Tx-integer
CBA
Common Access Control Class
Wait-for-indication (T3122)MBR
ECSC
Power Deviation Indication
Power Deviation
CBCH Channel Description
CBCH Mobile Allocation
System Control Parameters
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ATT
Value range:Yes, No
ContentIt is Attach-Detach allowed (ATT) in Huawei data
management system. It is used to inform MS whether IMSI
attach-detach is allowed in this cell. If it is set to Yes, thenetwork will not process the connection to the subscriber called
when MS is power-off. Thus network processing time and
resource are saved. Otherwise the network will process the
connection even though the MS has been powered off.
RecommendationYes
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CCCH-CONF
Value range: 1 non-combined CCCH, 1 combined CCCH, 2 non-
combined CCCH, 3 non-combined CCCH, 4 non-combined CCCH.
Content: It is Common Control Channel Configuration.The number of
CCCH message blocks in one corresponding BCCH multi-frame are 9,
3, 18, 27, and 36 respectively. CCCH configuration determines the
capacity of PCH, AGCH and RACH.
Unit: None
Recommendation: When there is one TRX in the cell, one combined
CCCH is recommended (in a system with few paging messages in
location area). For others, it is configured according to the number of
TRX in the cell.
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BS-AG-BLKS-RES
Value range: 0~2 (1 combined CCCH), 0~7 (others)
Unit: Block
Content: It is also called Access Granted Blocks Reserved.It is the number of CCCH channel message blocks that are
reserved for access granted channels(AGCH).
Recommendation: 2
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BS-PA-MFRMS
Value range: 29
Unit: Multi-frame period (51 frames)
Content: It is Paging Channel Multi-frames. It defines the
number of multi-frames used as a loop of paging sub-
channels.
Recommendation: 2
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T3212
Value range: 0~255
Unit: 6 minutes
Content: It is Periodic Location Update Timer. It defines
the period length of location updating.
Recommendation: 30 (for urban area), 20 (for suburban
area)
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Application of T3212
Even if T3212 setting is less than the system(MSC)
query time, The system will still sometimes voice The
subscriber you dialed is powered off.
A B
T3212=4 T3212=8
LAC
Ping-pong Reselect
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Cell Channel Description Format
Value range: Bitmap, 1024, 512, 256, 128,
variable length
Content: That is CA table. Presently, the parameter
has been automatically selected by the program
according to actual CA configurations.
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Application of CA Table
Module ID Cell ID Effectivefrequency 0
Effective
frequency 1
Effective
frequency 2
Effective
frequency 3
Effective
frequency 5
...
2 51 45 59 68 77 86 ...
2 52 49 62 71 80 89 ...
2 53 53 65 74 83 92 ...
This table describes all the effective frequencies configured in a cell.
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Radio Link Timeout
Value range: 4~64, the step size is 4
Unit: SACCH period (480ms)
Content: This parameter is used for MS to decide down-linkdisconnection in case of SACCH decoding failures.
Recommendation: 20~56
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Application of Radio Link Timeout
Impact of radio link timeout
A B
P Q
Poor coverage
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Neighbor Cell Description
I.e. Huawei BA tables. There are table BA1 and table BA2.
Table BA1 describes BCCH frequencies of the adjacent cells
to be measured when the MS is in idle mode.
Table BA2 describes BCCH frequencies of the adjacent cellsto be measured when the MS is in dedicated mode.
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Application of Neighbor Cell Description
Theoretical Neighbor Cells Actual Neighbor Cells
B
CA
D
B
CA
D
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B
C
A
Application of Neighbor Cell Description
A
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NCC Permitted
Value range: Check box, including options 0~7.
Content: Network Color Code, to be sent in system messages
2 and 6. It lists NCC that need be measured by MS. If a
neighbor cell with NCC permitted, MS will report M.R. Of the
neighbor cell to the network.
Recommendation: Subject to the concrete conditions.
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MS MAX Re-trans
Value range: 1, 2, 4, 7
Unit: Times
Content: One of the parameters of random access control
information. i.e. MS MAX. Re-trans Times. It is the upper limit of
times that MS is allowed to send Channel Request in oneimmediate assignment procedure.
Recommendation: Set to 7:For areas with low traffic (suburban or
rural area) and the cell radius more than 3 km.Set to 4: For areas
with ordinary traffic (non-busy area in the city) and the cell radius
less than 3km. Set to 2: For micro-cellular Set to 1: For micro-
cellular with heavy traffic or with obvious congestion. And 4 or more
is recommended to set for satellite transmission BTS.
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Tx-integer
Value range: 3~12, 14, 16, 20, 25, 32, 50
Unit: Number of RACH timeslots (equivalent to one timeslot,
0.577ms)
Content: Extended Transmission Timeslots(T), used to calculate the
number of timeslots in the interval between two channel requests
sent by MS.
Recommendation: 25 (If the cell immediate assignment success
rate is low, set the S with a larger value. Select 32 for satellite
transmission, so as to reduce satellite transmission delay).
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Calculation of S
ST
Combined
CCCH
Non-combined
CCCH
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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CBA
Value range: Yes (0), No (1)
Unit: None
Content: Cell Bar Access, worked together with CBQ to set
the priority status of the cell in idle mode for cell selection and
reselection.
Recommendation: Yes
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Application of CBA
CBQ(A)= NO
CBA(A)= NO
A
C
B
D
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Common Access Control Class
Value range: Check box, including level 0 forbidden,lever 1
forbidden,till level 9 forbidden
Content: One of the parameters of random access control
information. i.e. 0~9 bits of AC. It is used for load control of
ordinary subscribers, to permit or forbid the network access of
some common level users. 1 stands for forbidden and 0 for
permitted.
Recommendation: 000000000
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Special Access Control Class
Value range: Check box, including level 11 forbidden,level12
forbidden,till level 15 forbidden
Content: I.e. 11~15 bits of AC. It is used for load control,
permitting or forbidding the network access of some special level
users. 1 stands for forbidden and 0 for permitted.
Recommendation: 00000
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When the network receives channelrequest message sent by MS,
if there is no appropriate channel assigned to MS, the network will
send immediate assignment rejection message to MS. To avoid the
congestion of radio channel which is caused by MSs frequently
sending of channel request, immediate assignment rejection
message contains the timer T3122 (the wait-indication). After MS
receives immediate assignment rejection message, only after T3122
is timeout MS can send a new channel request.
T3122
Definition
Format
T3122 is 8-bit binary. It indicates the time that MS has to wait before
sending the second request.Its timing length is 0-255 seconds.
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MBR
Value range: 0~3
Unit: None
Content: Multi-band Reporting. It is used to inform MS to
report the adjacent cells in a controllable way. It is sent in
the System Information 2ter and 5ter.
i i f
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Application of MBR
-92dBm-82dBm
AB
C -68dBm
D -90dBm
E -78dBm
F -88dBm
G -96dBm
H -84dBm
GSM1800
GSM900S
ECSC
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ECSC
Value range: Yes, No
Unit: None
Content: Early Classmark Sending Control. It informs MS in a
cell whether class-mark 3 should be sent in advance actively or
not.
Recommendation: No.
P D i i I di i
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Power Deviation Indication
Value range: Yes, No
Unit: None
Content: Determine whether to adjust the output the power for
class 3 MS of GSM1800.
Recommendation: None
P D i ti
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Power Deviation
Value range: 0~3, corresponding value: 0dB, 2dB, 4dB, 6dB
Unit: None
Content: After random access, when the initial power command is
not received, the power used by GSM1800 Class 3 MS is MS max.
transmitting power plus the value of power offset.
Recommendation: 1
C ll S l ti P t
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Cell Selection Parameter
MS_TXPWR_MAX_CCH
RXLEV_ACCESS_MIN
ACS(Additional Reselect Parameter
Indication)
PI(Cell Reselect Parameters Indication)
CBQ(Cell Bar Qualify)
CRO(Cell Reselection Offset)
TO(Temporary Offset)
PT(Penalty Time)
CRH( Cell Reselection Hysteresis)
C ll S l ti P
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Cell Selection Process
There are two kinds of cell selection.
Normal cell selection
Stored list cell selection
In fact, the process might be different for different MSs
C ll R l ti P
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Cell Reselection Process
Cell reselection for cells in same location area
If the C2 value of the target cell is higher than that of the serving cell and
last for longer than 5 seconds, a cell reselection process will be
performed and the MS tunes to the new cell.
Cell reselection for cells in different location areas
If the C2 value of the target cell is higher than that of the serving cell by
at least the value of CRH and last for longer than 5 seconds, a location
updating process and the cell reselection process will be performed.
Cell reselections caused by C2 have a time interval of 15 seconds
If current serving cell is prohibited, or down link fails, or C1 is less
than 0 continuously for 5s, cell reselection will also be triggered.
MS starts a cell reselection if the access times exceed the MAX
retrans .
MS TXPWR MAX CCH
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MS_TXPWR_MAX_CCH
Value range: 0~31
Unit: level
Content: This parameter determines the max. allowed output
power of the MS when it begins to access a cell and has not
yet received power command.
Recommendation: 5(900MHz), 0(1800MHz)
RXLEV ACCESS MIN
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RXLEV_ACCESS_MIN
Value range: 0~63
Unit: Level
Content: It means the minimum received signal level
required for MS to access a cell.
Recommendation: 8
ACS
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ACS
Value range:Yes, No.
Unit:None
Content: Additional Reselect Parameter Indication. It is
used to inform MS of the location of reselection parameter in
the cell.
Recommendation: No.
PI
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PI
Value range: Yes (1), No (0).
Unit: None
Content: Cell Reselect Parameters Indication, sent on the
broadcast channel of the cell. It is an indication of existenceof Cell Reselect Offset(CRO), Temporary Offset(TO)
and PenaltyTime(PT).
Recommendation: Yes.
CBQ
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CBQ
Value range: Yes(1) , No(0)
Unit: None
Content: Cell Bar Qualify. CBQ only affects the
selection of cells but is not related to cell reselection. It
works with CBA to define the access priorities of cells.
Recommendation: No.
Application of CBQ
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Application of CBQ
The traffic of cell A and B is heavy. Set these two cells with
CBA=No, CBQ=No.
A B
Application of CBA
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Application of CBA
B is a micro cell. Set B to Normal and A to Low.
B
A
CRO
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CRO
Value range: 0~63, the corresponding level value: 0~126dB,
stepped every 2dB.
Unit: None
Content: Cell Reselect Offset. It is a parameter in C2
calculation to give a manual modification in MS cell reselection.
Recommendation: 0
TO
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TO
Value range: 0~7 , the corresponding value is 0~60dB, 7
corresponds to Infinite
Unit: None
Content: Cell Reselect Temporary Offset. It is a parameter inC2 criterion to give a temporary modification within PT time.
Recommendation: 0
PT
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PT
Value range: 0~31, the corresponding time is 20~620s.
31 is to change the function direction of CRO on C2.
Unit: None
Content: Cell Reselect Penalty Time.
Recommendation: 0
CRH
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CRH
Value range: 0~14 , the step size is 2
Unit: dB
Content: Cell Reselection Hysteresis. It is the parameter
used when cell reselection happens between two location
areas.
Recommendation: 4
Network Function Parameter
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Network Function Parameter
PWRC (Power Control Permitted)
UL DTX(Uplink Discontinuous Transmission)
NECI(New-Establishment Cause Indication)
Call Re-establish Allowed(RE)
EC Allowed(Emergency Call Allowed)
Frequency Hopping
PWRC
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PWRC
Value range: Yes, No.
Unit: None
Content: It is used to indicate MS weather to reduce
received level value obtained from the timeslots of BCCH
when MS measures receiving level during base band
hopping mode. When it is set to No, it means the
influence of receiving level on BCCH is not in
consideration. If it is set to Yes, process it in the way
mentioned above.
Recommendation: Yes
UL DTX
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UL DTX
Value range: May use, Must use, Can not use.
Unit: None
Content: It is used to indicate whether MS uses DTX
function. In System Information 3, it is 2 bits coding. InSystem Information 6, 3 bits coding. It shows the DTX
state of the MS in the previous measurement period.
Recommendation: Must use.
NECI
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NECI
Value range: Yes, No.
Unit: None
Content: Informing MS whether half-rate service aresupported in the cell.
Recommendation: No
Call Re-establishment Allowed
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Call Re establishment Allowed
Value range: Yes, No
Unit: None
Content: RE, Informing MS whether call reestablishment is
supported or not.
Recommendation: No
EC Allowed
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EC Allowed
Value range: Yes, No
Unit: None
Content: Emergence Call Allowed . When EC is set to
Yes, it means emergency call is permitted.
Otherwise it is prohibited.
Recommendation: Yes.
Others in Data Management system
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Others in Data Management system
System Information Used
Regular Transmission
Regular Transmission Interval
System Information Used
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System Information Used
Value Range: It is a check box, including system information
1~12, 2bis, 2ter, 5bis, 5ter, 10bis.
Unit: None
Content: It is used to determine whether a type of systeminformation should be sent. A selected box means support,
Recommendation: Select system information: 1~6, 2bis, 2ter,
5bis, 5ter
Regular Transmission
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Regular Transmission
Value range: Yes, No
Unit: None
Content: It shows whether BSC chooses to perform timing
update of system information contents transmitted by BTS. If it
is Yes, BSC will send system information to BTS at a certain
interval (it is decided by timing updating interval.). Otherwise, it
must be transmitted through operating the BSC.
Recommendation: Yes
Regular Transmission Interval
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Regular Transmission Interval
Value range: 0~255
Unit: Minute
Content:It stipulates the time interval that BSC
sends system information to BTS.
Recommendation: 10 minutes
Course Contents
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Introduction to BSS Timers
System Information Overview
Parameters Introduction
Case Study
Cou se Co e s
Case Study
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y
Case Description
During the process of optimization in a certain area, it is found out that the signal
is poor in a certain section of suburban highway. The signal strength measured
is less than -95dBm.
Handling Procedure
Modify the data in BSC BA1 table. Cell A-3 and B-3 add adjacent data for each
other. The coverage problem is thus solved.
Summary and Suggestions
There is a lot of signals received in this area, it is difficult to solve the coverageproblem if we check data independently. Try to conduct frequency scanning in
highway sections where the signal is poor, find out the receiving frequency with
the highest signal level, check BA1 table, BA2 table, and the neighbor cell
relationship, and modify the data. In this way, problem can be solved quickly.
Case 1: Incorrect Configuration of BA Table
Case Study
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y
Case description
The subscriber complains that MS cannot register to the network, or
it is difficult to register to the network between BTS A and B, or no
network mark is displayed on the MS, but MS indicates that the
signal is very good. Some subscribers also complain that MS canmake MTC but cannot make MOC.
Cause analysis
CGI of the cell is modified. So the network register flow is not
normal. Although the signal is very good, MS cannot get registered
in the network.
Recommendation and summary
CGI is a very important parameter and should be configured
correctly, thus to ensured that the CGI data in BSC and MSC are
same.
Case 2: Incorrect CGI causes MS unable to register on the network.
Case Study
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Case description
SDCCH congestion rate is as high as 4.91% in 2 cells of an urban BTS. The
configuration of this BTS is S1/1/1. And the busy hour TCH traffic of each
cell does not exceed 3 Erl.
Handling procedure
Modify the LAC of this BTS into 0520, which is the same as the surrounding
cells. And the problem is solved.
Recommendation and summary
LAC configurations of all the cells in the same location area must be the
same. Different cells must have different CGI. When there is modification on
BSS side, corresponding modification should be made on MSC.
Case 3: Incorrect LAC configuration causes high SDCCH congestion rate.
y
Case Study
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y
Case description
After Huawei BSC has been running successfully in a network. Some subscribers
complain that they cannot be called. The system announcement that the subscriber
called is powered off. After they make a call, this phenomenon disappears.
Handling procedure 1. When analyzing the distribution of the complaining subscribers, it found the
distribution are very dispersed. So this should not be caused by poor coverage.
2. Use the complaining subscribers mobile for dial test, And the result shows tested
mobiles are okay.
3. Trace the cause from MSC. After checking location update time of MSC with the
operator, we reduce T3212 of BSC to 30 minutes.
Recommendation and summary
T3212 in BSC must be less than that in MSC.
Case 4: MSC T3212 is too small caused part of MS cannot be called.
Case Study
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y
Case description
Subscribers complain that the signal fluctuates in a certain area. On-site
tests shows that this phenomenon does exist. From the testing mobile,
we can see that there are a lot of cells signals in this area. Some
frequencies are the suburb BTS signals far away from this area. The cell
reselection of MS is rather frequent.
Handling procedure
Modify parameterRXLEV_ACCESS_MIN of all cells in urban area and
make them consistent with each other. The problem of signal fluctuation
is solved.
Recommendation and summary
In area with complicated coverage, the RXLEV_ACCESS_MIN of each
cell should be kept same.
Case 5: MS Min-access Level causes the fluctuation of MS signal.
Case Study
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y
Case description
A network operator finds that the SDCCH call drop rate is about 2% after
BSC cutover. This is far away from the acceptable standard.
Handling procedure
1. Modify relevant parameters in system information and cell attribute
tables. The modification helps to avoid the radio link failure which will
cause call drop, and to adjust the balance between uplink and downlink.
2. Check the situation of other indices, especially handover successful rate
and TCH related indices. Analyze hardware and parameters and see if
they are in compliance with the actual running situation of the network.
3.Check the performance of the hardware on-site. Analyze the drive test
result. Check and make proper adjustment to the azimuth and downtilt of
the antenna system. Check whether the connectors are loosened.
Case 6: High SDCCH call drop rate
Case Study
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Case description
In a dual-band network, performing GSM1800 single network drive test, during
the driver test, MS often lost connection with the network. But when MS
reconnects with the network, the signal level is very strong.
Handling procedure
After analyzing the actual traffic in each cell of GSM900 network in details, MS
minimum access level and cell reselection offset (CRO) of GSM1800 are
adjusted to make C2 of cells in GSM1800 close to one another when received
signal levels are the same. At the same time, the traffic carried by equipment of
other network is not reduced. After several times of adjustment, CRO of most
1800 cells are 30dB, MS minimum access level is -90dBm. For GSM900 cells,
CRO is 0, MS minimum access level is -100dBm. The cross-cell coverage
phenomenon is basically eliminated.
Case 7: Cell reselection caused fluctuation of signals.
y
Case Study
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Case description
A local GSM network has more than 6000 subscribers. There are four BTS. The
network has been working properly. But from sometime on, some MS often lost
connection with network suddenly. The complaint from subscribers in urban
area increased.
Handling procedure
Modify the time of BSC periodic location update (T3212) to 10, i.e. 60 minutes.
Modify the corresponding time of MSC to 180 minutes. Two days observation
shows no subscriber complains and the problem is solved.
Case 8Too small T3212 causes MS lose connection with network.
y
Course Contents
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Introduction to BSS Timers
System Information Overview
Parameters Introduction
Case Study
Some of the BSC Timers -T3101
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Definition It is used in the immediate assignment process. During the
process of immediate assignment, T3101 is activated when
BSC sends CHANNEL-ACTIVE to BTS, and reset when it
receives ESTABLISH INDICATION sent from BTS.
Value range 0~255s
Some of the BSC Timers -T3103
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Definition T3103 defines the time that BSC reserves the TCH of both the
target cell and the original cell simultaneously during the
handover process. T3103 starts when BSC originates handover
command and resets when handover complete (intra BSC
handover) or clear command is received (inter-BSC handover).
Value range
0~255s
Some of the BSC Timers -T3107
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Definition It is used in the TCH assignment process. BSC starts T3107.
when TCH assignment command is sent to BTS, and stop
after receiving assignmentcomplete from BTS.
Value range 0~255s
Some of the BSC Timers -T3109
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Definition SACCH release time allowed is indicated by this timer.
Value range
0~255s
Some of the BSC Timers -T3111
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Definition According to timer T3111, BSC delays the channel release
at BTS side. After BSC receives information of BTS
channel releasing, it start T3111. BSC will not send
channel release command to BTS until T3111 is timeout.
Value range 0~255s
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