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GSM RN Optimization

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GSM RN Optimization Powered By Docstoc
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Notes:

Three main elements of any mobile network is capacity, quality and coverage. The
main goal to achieve in network optimization is to create a balance between capacity,
quality and the coverage of the network. This should be done by optimizing the
usage of available network resources at the time.




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Many factors affect the quality of network, such as uncertainty of radio wave
propagation,                        (e.g.                               area, re-planning
propagation changes of building (e g newly developed downtown area re planning
of the streets and city blocks), traffic load varying with place and time (e.g. stadium),
increased subscriber’s requirements.




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Network optimization is long-term process throughout the network development.

To satisfy the requirements of increasing mobile subscribers, the network quality
should be improved all the time.

During network optimization, network information can be collected via OMC traffic
statistics, driving test, subscriber complaints and OMC alarm information.

If the network quality have some cases such as KPI is as low as unacceptable, too
                    complaints,                      increased, etc.
many subscribers complaints number of subscriber increased etc The network
need optimization now.




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The input for Radio Network Optimization can be obtain from several sources:
         complaints,                            statistics.
Customer complaints Drive test and also traffic statistics

All these data can be co-related to each other to have a more deeper understanding
on the problems that are faced in the network.




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Note:

The KPI is a good way to measure the overall performance of the network. Several
KPI parameters will be defined in the network to enable the operator to monitor the
network performance throughout important events, upgrades etc.




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Normally the formula of KPI are defined by operator, and usually different operator
                                                 formula.
maybe consider different KPI and using different formula The KPI can be derived
from driving test and OMC traffic statistics.




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The raw date for network evaluation include Network Statistic, Drive Test and
                                                                  condition.
Trouble Ticket are obtained to determine the current network condition Then the
KPI Targets is set based on the consideration from all the data collected and agreed
by both parties. The Action Plan is proposed based on the studies of the network.
The Action Plan should be agreed by both parties before the optimization is started.
The Frequency, Cell Parameters/Configuration and Hardware Changes may
proposed in the Action Plan. For Implementing the Action Plan, the operation may
include cells frequencies changes, cell parameters retune and Cell Hardware
Reconfiguration. After all the works are done as per Action plan, the network
statistic and Drive Test is performed again to determine the KPI achieve the required
Target. For the case where the KPI target is not achieved as requirements, the
optimization work is repeated again until the achievement of KPI targets. The KPI
Acceptance report is prepared and signed by the customer to indicate the
optimization process is ended. An further improvement plan may summated to
customer for future reference in order to bring the network performance to greater
heights in the future.




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Notes:

It is important to understand the actual problems before changes are proposed and
implemented. It should be confirmed that the identified problem is a valid radio
network problem and not related to hardware faults. After any parameter changes are
implemented, the performance of the corresponding cell(s) should be monitored for
any improvement or else need to reverted.




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Notes:

Parameter types can be divided into 2 types, Radio Parameters (BSS) and the site
engineer parameter (Antenna). The radio parameter changes are done in the OMC
while the site engineering parameters will be done at the site.




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Notes for radio parameter adjustment:

In GSM system, most of radio parameters are based on cells or some areas, while
parameters between areas are closed related, we should consider the negative
influence for the the adjacent areas before adjust the parameters.

Usually , if there are problems in some areas, first confirm whether there is
equipment faulty (including connection problem), second make sure the problem is
caused by the parameters, and then radio parameters can be adjusted.




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ANT and TEMS driving test tools are suggested. The test methods can be cell
selection, reselection,                                  mode,
selection reselection frequency scanning in idle mode regular dial test and
continuous conversation test in dedicate mode. The data include Rx-level, Rx-quality
and others. In the meantime, the actual installation of antenna and feeder system can
be verified.




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Notes:

The drive test tool unlike the traffic statistics analysis, enables the investigation of
more specific network optimization problems. These problems might not be obvious
in the traffic statistics since they might be localized in a specific area of a cell.




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Notes:

The drive test tool unlike the traffic statistics analysis, enables the investigation of
more specific network optimization problems. These problems might not be obvious
in the traffic statistics since they might be localized in a specific area of a cell.




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Usually, RF engineers use the MA-10 signaling analyzer collect and analyze the data
                        interface,                                             flow,
of Abis interface and A interface and observe the entire signaling connection flow
draw out measurement reports and compare them with the Um interface signaling
obtained in the driving test, so as to get a comprehensive information of the on
service network.

In this way, the main causes and locations can be found for problems such as call
drop, handover failure and congestion, etc.




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In general network, inter-modulation interference upon GSM network often caused
                             repeaters.
by analog system and illegal repeaters So the interference source can be located by
using of the spectrum analyzer.




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Notes:

The OMC traffic statistics tool provide the means to capture the performance of the
network 24hrs of the day.

Analysis can be done to solve gradual problems in the network. Unlike drive test,
where the data collected are only valid for the time the drive test was conducted.




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Notes:

Huawei OMC provide advance traffic statistics monitoring functions. This provides
flexibility in terms of getting additional information for network optimization.




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As for signal coverage hole:

Improve the coverage of BTS or add new BTS, we should consider the co-channel
and adjacent-channel interference may occur after the coverage is extended. The
coverage holes in valleys and slopes can be covered by using of new BTS or
repeaters, we should consider the interference also.

For tunnels, underground garage and high buildings coverage, the repeater , leaking
cable technology and micro-cell technology can be used.

For over shooting:

Adjust the antenna downtilt and output power of TRX. Change the azimuth of
antenna to avoid the direction of antenna facing to the road, so as to reduce the
coverage radius.

Add missing adjacent cells for the cell.

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How to make a judgment:

In power control measurement function, the average uplink/downlink signaling
strength is too low.

In power control measurement function, whether the average distance between MS
and BTS is consistent with designed.

In power control measurement function, the maximum distance between MS and
                                     periods.
BTS goes abnormal in many continuous periods

In receiving level measurement function, poor signal account for a high percentage.

In cell measurement function and inter-cell handover measurement function, the
average receiving level are too low when trigger handover.




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In call drop measurement function, the level is too low when call drop, and the TA
                            drop.
value is normal before call drop

In defined adjacent cell measurement function, the specific adjacent cell with too low
average level can be found.

In undefined adjacent cell measurement function, there are many undefined adjacent
cells with too high average receiving level.

In defined adjacent cell measurement function , the average receiving level of the
defined adjacent cell is too high (over shooting).

In out-going inter cell handover measurement function, there are few handover to
some certain neighbor cell




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Adjust network parameters (BTS transmitting power, antenna downtilt and height, the
                            MS,                            cells,
minimum access level of MS adjacent relationship between cells minimum access
level of candidate cells for handover)




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Approach for traffic adjustment

1. Change the downtilt and height of the directional antenna, adjust the cell
   parameters, e.g., transmitting power of the cell, change the the coverage area, so
   as to implement the traffic adjustment. For the increase of accidental traffic, the
   signal coverage range can be changed by adding more carriers temporarily or
   increasing the transmitting power, so as to change the signal coverage areas.

2. Change number of cell TRX is one of the most popular methods for traffic
   adjustment.

3. Check the RXLEV_ACCESS_MIN value. According to the cell reselection test,
   adjust the cell reselection offset parameter CRO; adjust the handover threshold
   and hysteresis, change the normal handover threshold for traffic load sharing;
   enable direct retry and load handover.

4. Dual band                   adjustment.
4 Dual-band network traffic adjustment Adopt layered cell structure on GSM900 and
    GSM1800 systems(HCS). Settings different priority for the layers, layer handover
    threshold and layer handover hysteresis, then the GSM1800 cell can successfully
    absorb the traffic of the dual-band mobile phones.




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Interference location

1.Analysis of the rules of interference band in TCH measurement function.

Interference usually occurs when more than one idle channel appear in the
interference band 3, 4 and 5. If the interference is internal, it will usually increase with
the growth of traffic. If the interference is from external, it is usually not related to
traffic, but it may increase with the traffic growth if the interference is from the close
analog network.

Note that the interference band is reported to BSC by BTS via RF resource indication
message for idle channel. If the current channel are all busy, the interference can not
be measured. Therefore, the measurement of interference bands should be taken
into comprehensive consideration with others..

2. Receiving level measurement function

This is a measurement task statistics for TRX. If there are high Rx-level but bad
quality existing frequently, it indicates that there are co-channel and adjacent-channel
interference existed.




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3. Ratio of handovers for uplink/downlink quality.

In inter-cell handover measurement function, or in outgoing inter-cell handover
measurement function, the outgoing handover attempt times for various reasons are
kept in the statistics. If the handover caused by bad quality frequently, it indicates that
there is possible interference. Moreover, it tells the interference status of
uplink/downlink have relationship with handover times caused by bad uplink quality
and bad downlink quality.

4. Receiving quality measurement

For TRX, measure the average receiving quality rank for reference.

5. Call drop measurement function

It records the average level and quality in case of call drop. this is for reference.

6.                                              too.
6 Too many handover and reestablishment failure too

It is most likely caused by interference in the target cell. This is for reference.




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1. Perform driving test, check the quality of interferential. Analyze the interference
                  shooting.
caused by over shooting Avoid interference through adjusting the downtilt of
antenna , transmitting power, relationship between adjacent cells, handover
parameters, or by adjusting the frequency planning.

2. Analyze with a spectrum analyzer, locate the interferential frequency, and find out
the interference’s source.

3. Frequency hopping, DTX and power control can decrease the interference within
GSM system..

4. Resolve equipment problems (e.g. TRX, tower mount amplifier, filter)




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When we perform continuous conversation driving test, such problems as handover
failure,                                                  captured.
failure handover delay or frequently handover can be captured Through traffic
statistic, cell handover success rate and the ratio of outgoing and incoming also
handover can be found.




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How to make a judgement:

Check the handover parameters: threshold, hysteresis, period and etc.

Inter-cell handover measurement function: too many handover failure and
reestablishment failures too.

Inter cell handover measurement function: too many handover failures, and many
reestablishment successes as well.

Undefined adjacent cell measurement function : the number of reports of undefined
adjacent cell level goes beyond the threshold.

Outgoing inter cell handover measurement function : When successful rate of
outgoing handover is low (for some specific cell), and then find out the successful
rate of which target adjacent cell is low , further search the target cell for cause.

                                                 low,
When the successful rate of incoming handover is low the parameters setting in the
original cell are improper.

TCH measurement function : handover times is out of proportion to TCH seizure for
call successful times. (handover/call>3).




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The analysis and location of the handover failure must be carried out in conjunction
                                   indices.
with analysis of other performance indices

First, check whether the target cell is congested, or there is any hardware fault or
transmission fault.

Second, analyze whether the interference cause MS can not seizure the channel
assigned by system.

Third,                             parameters,
Third confirm whether the handover parameters definition of adjacent cells are
correct.

Last, check whether the NSS part data or router definition is incorrect.




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The causes for radio link failure include:

1.When the MS is in the coverage hole, call drop will be resulted from poor signal.

2.Internal or external interference of uplink leads to SACCH frame decoding failure,
this can cause call drop too.

3.When the MS move to the border of the coverage area, BSC will judge whether
need handover or not. But because the adjacent cell congestion or adjacent cell had
                            data,                    performed,
not been defined in the BSC data no handover can be performed MS will call drop in
this case.

4.Call drop after handover in case of unbalance between uplink and downlink: MS is
in serving CELL1. Uplink/downlink unbalance exists in the adjacent cell CELL2
(suppose CELL2 downlink signal strength is enough before handover, but the uplink
is poor after handover). This can lead to call drop after handover because of poor
       signal.
uplink signal

5.Some other call drops are caused by Abis interface failure, A interface failure.




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We should pay more attention to the inter-band handovers. Properly set the
           threshold,
handover threshold and avoid frequent location update caused by inter band  inter-band
handovers. When there are not many dual-band MS on the network, M1800
construction are expected to absorb traffic effectively, so the parameters should be
set as conducive for GSM 900 handover to GSM 1800. When the dual-band mobile
phones on the network are balanced relatively with the actual traffic, we should avoid
inter-band handovers to decrease the signaling load of the system.

                                                              LAC,
When GSM 900M and GSM 1800M cells are different BSC but same LAC we should
consider some timer such as T3212, It will cause some problem for MTC when
T3212 values in cells are different.




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We should pay more attention to the inter-band handovers. Properly set the
           threshold,
handover threshold and avoid frequent location update caused by inter band  inter-band
handovers. When there are not many dual-band MS on the network, M1800
construction are expected to absorb traffic effectively, so the parameters should be
set as conducive for GSM 900 handover to GSM 1800. When the dual-band mobile
phones on the network are balanced relatively with the actual traffic, we should avoid
inter-band handovers to decrease the signaling load of the system.

                                                              LAC,
When GSM 900M and GSM 1800M cells are different BSC but same LAC we should
consider some timer such as T3212, It will cause some problem for MTC when
T3212 values in cells are different.




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posted:12/21/2011
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