Compilation Case and Analysis Rf Optim 2g 1stedition

8/9/2019 Compilation Case and Analysis Rf Optim 2g 1stedition

http://slidepdf.com/reader/full/compilation-case-and-analysis-rf-optim-2g-1stedition 1/28

COMPILATION OF

RFOPTIMIZATION

PROBLEM CASEAND ANALYSIS(CELLULAR2GNETWORKS)

compiled by

HerySupriyanto

[email protected]

[email protected]

http:/ / www.linkedin.com/ in/ herysupriyanto

these document compilation from many resource feel free to share for knowledges purpose

1st Edition

March 10, 2010

Create PDF with GO2PDF for free, if you wish to remove this line, click here to buy Virtual PDF Printer

http://www.linkedin.com/in/herysupriyanto

http://www.go2pdf.com/


http://www.linkedin.com/in/herysupriyanto



SDCCH drop reasons

1)High intreference of freq.,like co-channel

2)SDCCH time slot faulty

3)Poor TRX DL quality

4)Hardware fault like antenna or duplexer malfunction5)May be feeder cable and connectors are faulty.

6)Site taking calls from a very far distance.

Dropped Call(TCH Drop-SDCCH Drop)

1. Radio Link Time-Out

Every time a SACCH message can not be decoded the radio link time-out counter is decreased

by 1. If the message can be decoded the counter is incremented by 2. However, the value can

not exceed the initial value. The initial value is set by the parameter RLINKT for radio link time-

out in the mobile station and by RLINKUP for timeout in the BSC. If the mobile moves out of

coverage and no measurement reports are received in the BSC, there will be a radio link time-

out and the message Channel Release (cause: abnormal release, unspecified) is sent to the

mobilestation and the SACCH is deactivated in the BTS. A Clear Request message is sent to the

MSC. To be sure that the mobile has stopped transmitting, the BSC now waits RLINKT SACCH

periods before the timeslot is released and a new call can be established on the channel.

2. Layer 2 Time-OutIf the BTS never get an acknowledge on a Layer 2 message after the time T200XN200, the BTS

will send Error Indication (cause: T200 expired) to the BSC, which will send Channel Release

(cause: abnormal release, timer expired) to the mobilestation and a Clear Request to the MSC.

The SACCH is deactivated and the BSC waits RLINKT SACCH periods before the timeslot is

released and a new call can use the channel. This is only valid if the call is in steady state, i.e. not

during handover or assignment.






3. Release IndicationWhen the BTS received a layer 2 DISC frame from the mobile it replies with a Layer 2 UA frame

to the mobile station and a Release Indication to the BSC. The system does only react on

Release Indication if it is received during a normal disconnection situation. If such a message is

received unexpectedly this will usually cause radio link time-out or timer T200 expiration as the

mobilestation stops the transmitting of measurement reports. It is also possible that the release

will be normal depending on when the Release Indication is received.

4. MSCTime-OutNormal Release:

If the MSC never received a response on a message (e.g. Identity Request) and there is no radio

link time-out or layer 2 time-out, the MSC will send a Clear Command to the BSC. The time-out

is depending on the message. When receiving Clear Command, the BSC will send a Channel

Release (cause: normal release) and then deactivates the SACCH.

Reject (only SDCCH):

If the MSC never receives a response on the first message after Establish Indication, the MSC

will send a reject message. If the connection was a Location Update it will be a Location Update

Reject (cause: network failure) and if the connection was a mobile originating call (CM Service

Request) a CM Service Reject (cause: network failure) will be sent. The MSC will then send a

Clear Command to the BSC and the call is cleared by Channel Release (cause: normal release).

5. Assignment to TCHBefore sending an Assignment Command from the BSC at TCH assignment, the following two

criterion have to be fulfilled:

a. There must be a TCH channel available, i.e. no congestion

b. The locating algorithm must have received at least one valid measurement report.

If either of the criterion is not fulfilled, Assignment Command will not be sent and a Channel

Release (cause: abnormal release, unspecified) will be sent to the mobilestation and a Clear

Request to the MSC.






TCHDropreason(1)The classification of TCH Drop Reasons are arranged in the order of priority:

1.Excessive Timing Advance

2.Low Signal Strength

3.Bad Quality

4.Sudden Loss of Connection5.Other Reasons

Excessive TimingAdvanceThe TCH Drop counters due to Excessive Timing Advance will pegged when the during the time

of disconnection, the last Timing Advance value recorded was higher than the TALIM Parameter.

This drop reason is commonly apparent to isolated or island sites with a wide coverage area.

Action:Check if the cell parameter TALIM is < "63"

Solution:

Set TALIM to a value close to 63.Tilt antenna/reduce antenna height/output power, etc. for co-channel cells.

TCHDrop Reasons(2)Low Signal Strength onDown or Uplink or Both LinksThe drops counters due to Low Signal Strength will be pegged when the Signal Strength during

the last Measurement Report before the call dropped is below the LOWSSDL and/or LOWSSUL

Thresholds. LOWSSDL and LOWSSUL are BSC Exchange Property parameters which is used only

for statistics purposes and does not affect the behavior of calls. If both UL and DL Signal

Strength are below the thresholds, only Drop due to Low SS BL will pegged. Normally a call is

dropped at the border of large rural cell with insufficient coverage. Bad tunnel coverage cause

many dropped calls as well as so called coverage holes. Bad indoor coverage will result in

dropped calls. Building shadowing could be another reason.

Action:Check coverage plots.

Check output power.

Check power balance and link budget.

Check if Omni site.

Check antenna configuration & type.

Check antenna installation.

Perform drive tests & site survey.

Check TRX/TS with high CONERRCNT.

Solution:Add a repeater to increase coverage in for example a tunnel.

Change to a better antenna (with higher gain) for the base station.

Add a new base station if there are large coverage holes.

Block/Deblock TRX






TCHDrop Reasons(3)Poor Quality on Down or Uplink or Both LinksThe drops counters due to Bad Quality will be pegged when the Signal Strength during the last

Measurement Report before the call dropped is above the BADQDL and/or BADQUL Thresholds.

BADQDL and BADQUL (expressed in DTQU) are BSC Exchange Property parameters which isused only for statistics purposes and does not affect thebehavior of calls. If both UL and DL

Quality are above the thresholds, only Drop due to BAD Quality BL will pegged.

Problem on Bad Quality is usually associated with Co-channel Interference on BCCH or TCH.

Faulty MAIO assignment can cause frequency collisions on co-sited cells especially on 1x1 Reuse.

External interference is also one possible cause of problem on quality.

Action:Check C/I and C/A plots.

Check Frequency Plan (Co-BCCH or Co-BSIC Problem).

Check MAIO, HOP, HSN parameters.

Check FHOP if correctly configured (BB or SY).Check for External Interference.

Perform drive tests.

Solution:Change BCCH frequency.

Change BSIC.

Change MAIO, HOP, HSN.

Change FHOP.

Record RIR or on-site Frequency Scanning to identify source of interference.

Use available radio features.

TCHDrop Reasons(4)Sudden Lossof ConnectionDrops due to Sudden Loss are drops that have not been registered as low signal strength,

excessive timing advance, bad quality or hardware (other) reasons, and the locating procedure

indicates missing measurement results from the MS.

There are some common scenarios that could lead to Sudden Loss of connections such as very

sudden and severe drops in signal strength, such as when subscribers enter into buildings,

elevators, parking garages, etc., very sudden and severe occurrence of interference, MS runs

out of battery during conversation, Handover Lost, BTS HW faults, Synchronization or A-bis link

fault (transmission faults), and

MS Faults.

Action:Check BTS Error Logs, Alarms and Fault Codes.

Check CONERRCNT per TRX and TS.

Check Transmission Link (A-bis).

Check for DIP Slips.

Check LAPD Congestion.

Correlate Handover Lost to Drops due to Sudden Loss

Solution:Fix Hardware Faults and Alarms.

Reset TRX with high CONERRCNT.






Ensure that Synchronization and A-bis Link are stable.

Change RBLT with high DIP Slips.

Change CONFACT or increase Transmission Capacity

Investigate HO Lost Problem

TCHDrop Reasons(5)TCHDropsdue to Other ReasonsTCH drops due to Other Reasons are computed by subtracting the sum of drops due to

Excessive TA, Low SS, Bad Quality and Sudden Loss from the Total TCH Drop Counts. Drops due

to Other Reasons are generally associated withhardware problems, transmission link problems

on A-bis, Ater or Ainterfaces, and sometimes Handover Lost.

Action:Check BTS Error Logs.

Check Alarms and Fault Codes.

Check CONERRCNT per TRX and TS.

Check Transmission Link (A-bis).Check for DIP Slips.

Correlate Handover Lost to Drops due to Other Reasons

Solution:Fix Hardware Faults and Alarms.

Reset TRX with high CONERRCNT.

Ensure that Synchronization and A-bis Link are stable.

Change RBLT with high DIP Slips.

Investigate HO Lost Problem

Problem reasonof drop in SDCCHLow Signal Strength onDown or UplinkThe reason for poor coverage could be too few sites, wrong output power, shadowing, no

indoor coverage or network equipment failure.

Action: Check coverage plots.Check output power. Perform drive tests. Check BTS error log

Solution: Add new sites. Increase output power. Repair faulty equipment.

Poor Quality on Down or UplinkAction: Check C/I and C/A plots. Check frequency plan. Perform drive tests.

Solution: Change frequency. Use available radio features.

Too High TimingAdvanceAction: Check if the cell parameter TALIM is < style="font-weight: bold;">Solution: Set TALIM to

a value close to 63. Tilt antenna/reduce antenna height/output power, etc. for cochannel cells.

Mobile ErrorSome old mobiles may cause dropped calls if certain radio network features are used. Another

reason is that the MS is damaged and not working properly.

Action: Check MS fleet.

Solution: Inform operator.






Subscriber BehaviorPoorly educated subscribers could use their handsets incorrectly by not raising antennas,

choosing illadvised locations to attempt calls, etc.

Action: Check customer complaints and their MS.

Battery FlawWhen a subscriber runs out of battery during a conversation, the call will be registered as

dropped call due to low signal strength or others.

Action: Check if MS power regulation is used. Check if DTX uplink is used.

Congestion on TCHThe SDCCH is dropped when congestion on TCH.

Action: Check TCH congestion

Solution: Increase capacity on TCH or using features like Assignment to another cell, Cell Load

Sharing, HCS, Dynamic Half-Rate Allocation and FR-HR Mode Adaptation etc

TCH ASSIGNMENT SUCCESSRATE

Probable Reason:1) No dominant serving cell: The serving cell cannot cope with the TCH traffic.

2) Severe congestion on TCH: Failing TCH allocation for assignment or handover due to

congestion

3) Low signal strength for call access: The signal strength might be higher on the BCCH than onthe TCH.

4) Interference: Disturbance on SDCCH or target TCH

5) Faulty transceiver: Faulty equipment

Probable Reasonsof SDCCH Congestion

---Low AvailabilityAction: Check SDCCH Availability. Check if the channels are manual, control or automatic

blocked.

---IncreasingTrafficDemandThe high traffic could be related to an occasional event or due to a long term growth.

Action: Check if short term traffic growth. Make trend comparisons. Check if combined SDCCH is

used. Check SDCCH dimensioning.

---Bad use of Adaptive configuration of Logical ChannelsBy using the Adaptive configuration of logical channels feature, the basic SDCCH configuration in

a cell will be under-dimensioned. If this feature is not used correctly, it will cause SDCCH

congestion.

Action: Check if ACSTATE is on. Check parameters related to Adaptive configuration of logical

channels






---LongMeanHoldingTimeIf the mean holding time is long, this generates a higher traffic load.

Action: Check SDCCH Mean Holding Time

---Too Frequent PeriodicRegistrationAction: Check Random Access Distribution. Check the timer T3212 in the BSC and the

parameters

---BTDM andGTDM in the MSCSolution: Decrease the periodic registration.

---Location Area Border CellIf the cell is situated on a misplaced Location Area border, this means that unnecessary many

normal LUs are performed.

Action: Check site position and location area border. Check Location Update Performance.

Check parameter CRH etc.

---Extensive SMSUsageExtensive SMS usage increases the SDCCH traffic and could cause congestion if badly

dimensioned SDCCH channels.

Action: Check SMS activity.

---Cell Broadcast UsedAction: Check if Cell Broadcast is active. .If active, check if it is used by the operator.

---IMSI Attach/ Detach in Use.An introduction of IMSI attach/detach will increase the traffic on SDCCH. However, the benefits

are that the paging success rate will increase. The recommendation is to use Attach/Detach.

---Cell Software File CongestionAction: Check SAE setting. High Ratio of Random Accesses

Action: Check Random Access performance

Probable Reasonsof Bad Handover Performance






---NeighboringCell RelationAction:Add neighbor cell relation.

---Missed measurement frequenciesin BA-listAction:Check measurement frequencies list.

---Permitted NetworkColor Code problemAction:Check NCC Permitted

---HW faults.

Action: Check BTS error log.

---BlockingonTarget CellAction:Remove Blocking on Tager Cell

---CongestionA high congestion might lead to dragged calls (handover performed at a not intended location)

and a lot of unsuccessful handovers.

Action: Check TCH congestion.

---Timer Expire After MSis LostThe MS never answers the base station.

Action: Check coverage. Check interference.

---Link Connection or HW FailureAction: Check BTS error log. Perform site visit. Perform link performance measurements.

---Bad Antenna InstallationAction: Perform site survey and check antenna installation. Check antenna cabling.

---Many NeighborsDefinedMany defined measurement frequencies defined (>16) will decrease the accuracy of the mobile

measurements to locate the b est six servers. Many measurement frequencies mean few

samples per frequency and problem for mobiles to decode the BSIC.

Action: Check number of definitions.---Delayed Handover DecisionA delayed handover decision can be due to congestion in the target cell.

Action: Check handover parameters.

---WrongLocatingParameter SettingAction: Check locating parameters.

---Bad Radio CoverageAction: Check coverage plots.






---High Interference, Co-Channel or AdjacentThe potential handover candidate is disturbed by interference. Outgoing handover due to bad

uplink quality may indicate interference from co-channel another MS. On the border, the quality

may be rather bad and the signal strength low. Bad downlink quality may indicate interference

from another co-channel basestation.

Action: Check interference. Check if many handovers are performed due to downlink or uplink

bad quality.

---Receiver Antenna Problem or RBSHW problems(in candidate cell)Action: Check antenna installation. Check RBS HW and Error log of the target cell

---Poor Inter-MSC/ BSCHandover PerformanceFor outer or external cell, wrong definitions in either MSC or BSC may be reason for the

problem.

Action: Check inter-MSC/BSC handover performance.

---Incorrect Down TiltAction: Perform site survey and check antenna installation.

Solution: Correct antenna tilting.

PingPongHandover

As the cellular network growing, it requires addition of new sites to expand capacity and or

coverage services. New mobile operators were expecting to grow their network in exponential

order to gain market share against mature competitors. Without any intensive network

performance maintenance, common problem such ping pong handover would be degrade user

experience like bad voice quality ( SQI speech quality index, MOS mean opinion score ) or even

dropped call.

Ping Pong handover is shown from the successful handover back to old cell within pre-defined

time of total handover, e.g. less than 10 seconds. Since not all BSS vendors provide such

performance counters it might be identified by simple metric that shall be expressed as total

successfulhandover over number of call or connection, e.g. more than 200% indicates ping ponghandover.






The actual ping pong handover is easily identified through drive test with sense of optimization

engineer without require any calculation. Coverage holes might lead to Ping-Ponghandover

especially for slow moving mobiles. It may be cause by shadowing by high building. Several

possible equal signals from two or more base stations might lead to Ping-Ponghandover as well

which is so called not optimized cell dominance.

The following action items shall be used for optimization solutions:

• Check the parameter setting such as hysteresis, offset, priority layer in dual-band case,

etc. If poor parameters setting found, then correct the related parameters. Compare to

default parameters design.

• Check the output power BSPWR and BSPWRT which normally put on maximum value or

compare to design.

• Check path balance on transceiver link, e.g. loss in uplink and downlink chain. Defective

RF modules might be the reason of imbalanced link.

• Check the site location such as possible coverage holes or no dominant cells.

• Perform drive test on that particular area to check the signal strength, if the average of signalstrength of the neighbors are the same, no dominant cell is found.

• For Long term action if no dominant cell shall be adding new site, while short term action shall

be uptilt the most dominant cell as the serving cell for that area and reduce coverage for others.

Drive Testing

ThePurpose of Drive Testing

Drive testing is principally applied in both the planning and optimisation stage of network

development. However, there are other purposes for which drive testing can be used:

•To provide path loss data for initial site survey work

•To verify the propagation prediction during the initial planning of the network.

•To verify the network system parameters, as defined in the EG8: GSM/DCS

System-Specific Parameters.

•To provide the initial test parameters used in Benchmarking (as defined in the

“Analysis” section of the Network Performance and Monitoring Guideline).

•To verify the performance of the network after changes have been made e.g.When a new TRX is added; the removal or addition of a new site; any power

Adjustments or changes to the antenna; any changes in clutter or traffic habits






such as the addition of new roads etc.

•To measure any interference problems such as coverage from neighboring

Countries.

•To locate any RF issues relating to traffic problems such as dropped or blocked

calls.

•To locate any poor coverage areas.

•To monitor the network against a slow degradation over time, as well as

Monitoring the network after sudden environmental conditions, such as gales

or electrical storms.

•To monitor the performance of a competitor’s network.

Whento Drive Test

Drive testing can take place during the day or at night and is dependant upon the

Operator’s requirements and subscriber habits.

Drive testing during the day will mimic the conditions as seen by subscribers, but may

clog up the network if call analysis is being performed.

Drive testing during the night will allow a greater area to be surveyed due to the reduction

in vehicular congestion. It will also allow for certain test signals to be transmitted and

tested, particularly when setting up a new site, without interrupting normal operation.

However, night-time testing does not mimic the conditions experienced by subscribers.

For planning purposes, drive testing is typically performed at night and for maintenance

purposes, drive testing is performed during the day.

Where to Drive Test

Some areas of a network will have greater performance problems than others. Drivetesting should not be uniform throughout the whole network, but should be weighted

towards areas where there are significant RF problems.

There may be other areas of the network that require temporary coverage during a certain

time of the year e.g. an exhibition centre or a sports stadium. These areas should be

examined and planned in greater detail.

It is important that a drive test is documented. This is specified by the Operator and can

either take the form of creating a new item of documentation or filling in an existing

document. All documentation will be passed to Analysts and Engineers, who will need

accurate records of any test work carried out.

----Route PlansThe area to be drive tested is ascertained before leaving the office. There are three levels

of drive testing depending on the purpose of the test:

Primary Route: This includes all major roads, highways and throughfares and should be

given priority to all other roads when conducting a coverage test, unless a new site is put

into service for a specific objective.

Secondary Route: This includes all streets, by-streets and compounds, where accessible,

such as a University Campus. Secondary routes are used in areas where problems have

been located during a primary route test and further investigation is needed.Miscellaneous Routes: This includes in-building and non-access routes to vehicles such

as shopping malls, golf courses, airports, hotels, conference centres etc.






A route is prepared by photocopying a map and highlighting the route to be driven. For

primary routes, a map of scale no less than 1:20,000 should be used, and a map of scale

1:10,000 is recommended for secondary routes. It is recommended that the route is

marked in a contiguous circuit, taking account of one-way streets at this stage.

A drive test should be planned in both directions, where possible, and at the same speed.

This minimises any errors and checks the point of handovers and cell dimensioning. For

new sites that are being tested, it is recommended that the transceiver is forced to camp

onto the cell (forbidding any handovers) in order to ascertain the full coverage of the cell.

The test should be re-driven with any forced handovers removed.

Layer 1 Messages

Other Layer 1 criteria that is useful for field measurements include:

C1 criteria •

ARFCN of Serving Cell - (TCH in dedicated mode, BCCH in idle mode)) •

Time Slot (TS) •

Layer 3 Messages

All Layer 3 messages should be collected where possible. Layer 3 Messages are used by

Analysts to determine more accurately the cause of a problem within the network.

Some field test equipment can perform basic analysis of particular Layer 3 messages

during data collection. This enables certain conditions such as call classification or

handovers to be flagged to the survey technician.

Call ClassificationIn principle there are five call classifications, some of which can be sub-divided further.

Good Calls: These are calls that are successfully placed on the network and maintained

for the required duration.

Dropped Calls: These are calls that are successfully placed on to the network but are

terminated without authorisation. Using Layer 3 Messages, these calls can b e sub-divided

into:

End User Hang-up •

System Hang-up •

Other •

Blocked Calls: These are calls that cannot be placed on to the network. Again, using

Layer 3 messages, these can be sub-divided as follows:

System Busy •

End User Engaged •

No Service •

Other •

Roamed Calls: These are calls that are successfully placed on another network. Roamed

calls may also be good calls or dropped calls.

Noisy Calls: These are calls which have been successfully completed for the duration of

the call but which experienced a number of noise bursts that a subscriber may find

intolerable. The threshold for determining the level of poor audio is programmed during

the set-up of the test.






In GSM, this particular classification is very difficult to determine with great accuracy. It

should be noted that it is not enough to monitor just the RxLEV and the RxQUAL.

Troubleshooting

No Data CollectedOccasionally, the equipment fails to trigger the collection device to save the data to file.

Check • all cables

Ensure the Processing Unit is powered •

Re-start the laptop computer •

Re-start the equipment •

Re-drive the test. •

No Positional InformationCollectedIf data is collected using GPS only, it may be possible that satellite reception was lost

during a drive through a tunnel etc. It is important that back-up equipment is used, such asa Dead-Reckoning device, since a GPS receiver will re-transmit the last known position

until it receives an update. If the vehicle moves without GPS cover, the data will be

inaccurate and cannot be analysed.

Check the • GPS antenna cable to the receiver

Drive to an open area and ensure that the GPS system is working correctly •

If required, install a back-up positional device to safeguard against lost GPS •

Coverage Holes

If there are patches of poor coverage in unexpected areas, it may indicate the fringes of a

coverage hole. It is important to re-drive this particular area.

Complete a route plan using secondary roads as far as possible •

Make notes of any buildings / obstructions that may cause shadowing •

Take note of pedestrian / vehicular habits in the area •

Dropped Calls

Dropped calls can be caused by either RF environments or incorrect system parameters.

The following data should be checked to ensure that it has been collected properly.

Layer 3 Messages •

Neighbour Cell List (BA Table) •

RxLEV (Server • & Neighbour)

RxQUAL (Server • & Neighbour)

Finally, ensure that the automatic setting for the call length is not shorter than that for the

timer monitoring for unauthorised call drop-outs. The setting should be a minimum of 30

seconds.

Handover Problems

Handover problems are generally caused by inaccurate settings of the handover boundary.

This can cause ping-ponging, where the server will keep changing, and congestion at the

switch. Check the following.

The transceiver antenna is fitted correctly •

Collection of Layer 3 Messages •






Collection of Neighbour Cell List (BA Table) •

Collection of Scanning Information •

Collection of Cell Identities •

Collection of T.Adv for the Serving Cell •

Also, ensure that the collection of data from the new serving cell immediately after the

handover has occurred (particularly RxLEV and RxQUAL) is not timed to occur prior tothe-synchronisation of the transceiver itself.

If a particular serving cell can be isolated as a potential cause of handover problems,

slowly drive around the cell in a radius of around 500m - 1km, checking when handovers

occur.

Blocked Calls/ System BusyIf calls are repeatedly classified as blocked, it is recommended that the drive test is

temporarily halted in order to try and locate the cause.

Check that the number called is fully functional •

Check that there is adequate coverage from the expected serving BTS •

Check the equipment transceiver is functioning correctly by using an ordinary •

mobile to call the office

If all appears functional, try to place calls through an alternative BTS. If this •

succeeds, inform the office immediately and re-suspend the drive test.

Timersandcountersfor Radio Resource Management

Timers on the Mobile Station Side

T3122: This timer is used during random access, after the receipt of an IMMEDIATE ASSIGNREJECT message.Its value is given by the network in the IMMEDIATE ASSIGN REJECT message.

T3124: This timer is used in the seizure procedure during a hand-over, when the two cells are

not synchronized.Its purpose is to detect the lack of answer from the network to the special

signal. Its value is set to 675 ms if the channel type of the channel allocated in the HANDOVER

COMMAND is an SDCCH (+ SACCH); otherwise its value is set to 320 ms.

T3126:This timer is started either after sending the maximum allowed number of CHANNEL

REQUEST messages during an immediate assignment procedure. Or on receipt of an IMMEDIATE

ASSIGNMENT REJECT message, whichever occurs first. It is stopped at receipt of an IMMEDIATEASSIGNMENT message, or an IMMEDIATE ASSIGNMENT EXTENDED message. At its expiry, the

immediate assignment procedure is aborted. The minimum value of this timer is equal to the

time taken by T+2S slots of the mobile station's RACH. S and T. The maximum value of this timer

is 5 seconds.

T3128:This timer is started when the mobile station starts the uplink investigation procedure

and the uplink is busy.It is stopped at receipt of the first UPLINK FREE message. At its expiry, the

uplink investigation procedure is aborted. The value of this timer is set to 1 second.

T3130:This timer is started after sending the first UPLINK ACCESS message during a VGCS uplink

access procedure.It is stopped at receipt of a VGCS ACCESS GRANT message.At its expiry, the

uplink access procedure is aborted.The value of this timer is set to 5 seconds.






T3110:This timer is used to delay the channel deactivation after the receipt of a (full) CHANNEL

RELEASE. Its purpose is to let some time for disconnection of the main signalling link. Its value is

set to such that the DISC frame is sent twice in case of no answer from thenetwork. (It should be

chosen to obtain a good probability of normal termination (i.e. no time out of T3109) of the

channel release procedure.)

T3134:This timer is used in the seizure procedure during an RR network commanded cell change

order procedure. Its purpose is to detect the lack of answer from the network or the lack of

availability of the target cell. Its value is set to 5 seconds.

T3142:The timer is used during packet access on CCCH, after the receipt of an IMMEDIATE

ASSIGNMENT REJECT message. Its value is given by the network in the IMMEDIATE

ASSIGNMENT REJECT message.

T3146:This timer is started either after sending the maximum allowed number of CHANNEL

REQUEST messages during a packet access procedure. Or on receipt of an IMMEDIATEASSIGNMENT REJECT message during a packet access procedure, whichever occurs first. It is

stopped at receipt of an IMMEDIATE ASSIGNMENT message, or an IMMEDIATE ASSIGNMENT

EXTENDED message. At its expiry, the packet access procedure is aborted. The minimum value

of this timer is equal to the time taken by T+2S slots of the mobile station's RACH. S and T are

defined in section 3.3.1.2. The maximum value of this timer is 5 seconds.

T3164:This timer is used during packet access using CCCH. It is started at the receipt of an

IMMEDIATE ASSIGNMENT message. It is stopped at the transmission of a RLC/MAC block on the

assigned temporary block flow, see GSM 04.60. At expire, the mobilestation returns to the

packet idle mode. The value of the timer is 5 seconds.

T3190:The timer is used during packet downlink assignment on CCCH. It is started at the receipt

of an IMMEDIATE ASSIGNMENT message or of an PDCH ASSIGNMENT COMMAND message

when in dedicated mode.It is stopped at the receipt of a RLC/MAC block on the assigned

temporary block flow, see GSM 04.60. At expiry, the mobile station returns to the packet idle

mode. The value of the timer is 5 seconds.

Timers on the network sideT3101:This timer is started when a channel is allocated with an IMMEDIATE ASSIGNMENT

message. It is stopped when the MS has correctly seized the channels. Its value is network

dependent. NOTE: It could be higher than the maximum time for a L2 establishment attempt.

T3103:This timer is started by the sending of a HANDOVER message and is normally stopped

when the MS has correctly seized the new channel. Its purpose is to keep the old channels

sufficiently long for the MS to be able to return to the old channels, and to release the channels

if the MS is lost. Its value isnetwork dependent. NOTE: It could be higher than the maximum

transmission time of the HANDOVER COMMAND, plus the value of T3124, plus the maximum

duration of an attempt to establish a data link in multiframe mode.)

T3105:This timer is used for the repetition of the PHYSICAL INFORMATION message during thehand-over procedure. Its value is network dependent. NOTE: This timer may be set to such a

low value that the message is in fact continuously transmitted.






T3107:This timer is started by the sending of an ASSIGNMENT COMMAND message and is

normally stopped when the MS has correctly seized the new channels. Its purpose is to keep the

old channel sufficiently long for the MS to be able to return to the old channels, and to release

the channels if the MS is lost. Its value isnetwork dependent. NOTE: It could be higher than the

maximum transmission time of the ASSIGNMENT COMMAND message plus twice the maximum

duration of an attempt to establish a data link multiframe mode.

T3109:This timer is started when a lower layer failure is detected by the network, when it is not

engaged in a RF procedure. It is also used in the channel release procedure. Its purpose is to

release the channels in case of loss of communication. Its value is network dependent. NOTE: Its

value should be large enough to ensure that the MS detects a radio link failure.

T3111:This timer is used to delay the channel deactivation after disconnection of the main

signalling link. Its purpose is to let some time for possible repetition of the disconnection. Its

value is equal to the value of T3110.

T3113:This timer is started when the network has sent a PAGING REQUEST message and is

stopped when the network has received the PAGING RESPONSE message. Its value is network

dependent. NOTE: The value could allow for repetitions of the Channel Request message and

the requirements associated with T3101.

T3115:This timer is used for the repetition of the VGCS UPLINK GRANT message during the

uplink access procedure. Its value is network dependent. NOTE: This timer may be set to such a

low value that the message is in fact continuously transmitted.

T3117:This timer is started by the sending of a PDCH ASSIGNMENT COMMAND message and isnormally stopped when the MS has correctly accessed the target TBF. Its purpose is to keep the

old channel sufficiently long for the MS to be able to return to the old channels, and to release

the channels if the MS is lost. Its value isnetwork dependent. NOTE: It could be higher than the

maximum transmission time of the PDCH ASSIGNMENT COMMAND message plus T3132 plus

the maximum duration of an attempt to establish a data link in multiframe mode.

T3119:This timer is started by the sending of a RR-CELL CHANGE ORDER message and is

normally stopped when the MS has correctly accessed the new cell. Its purpose is to keep the

old channels sufficiently long for the MS to be able to return to the old channels, and to release

the channels if the MS is lost. Its value isnetwork dependent.NOTE: It could be higher than the

maximum transmission time of the RR_CELL CHANGE ORDER, plus T3134, plus the maximum

duration of an attempt to establish a data link in multiframe mode.

T3141:This timer is started when a temporary block flow is allocated with an IMMEDIATE

ASSIGNMENT message during a packet access procedure. It is stopped when the mobile station

has correctly seized the temporary block flow. Its value is network dependent.






GSM Mobile Terminated Call

?áThe PSTN subscriber dialsthe MS’stelephone number (MSISDN), the MSISDNisanalyzed inthe PSTN, which identifiesthat thisisa call to a mobile network subscriber. A connectionis

established to the MS’shome GMSC. The PSTN sendsan Initial Addressmessage(IAM) totheGMSC.?úThe GMSCanalyzesthe MSISDNto findout which HLR, the MSisregisteredin, and queriesthe HLRforinformationabout how to route the call to the servingMSC/ VLR. The HLRlooksupthe MSISDN and determinesthe IMSI and theSS7 addressfor the MSC/ VLRthat isservicingthe MS. The HLRalso checksif theservice, “call forwardingto C-number” isactivated, if so, thecall isrerouted bythe GMSCto that number.?‚ The HLRthencontactsthe servicingMSC/ VLRand asksit to assign a MSRN to thecall. [MSRN -MobileStationRoutingNumber].The MSC/ VLRreturnsanMSRN viaHLRto theGMSC.

?ÖThe GMSCsendsan Initial Addressingmessage(IAM) to the servicingMSC/ VLRand usestheMSRN to route the call to the MSC/ VLR. Once the servicingMSC/ VLRreceivesthe call, theMSRN canbe released and may be made available for reassignment.?+The MSC/ VLRthenordersallof itsBSCsand BTSsto page the MS. Since the MSC/ VLRdoesnot know exactly which BSCand BTSthe MSis monitoring, the page will besent out acrossthe entireLocationArea(LA).?{When the MSdetectsthe pagingmessage to the BTS’sin the desired LA. The BTS’stransmitthe message over the air interface usingPCH. To page the MS, the networkusesan IMSI orTMSI validonly in the current MSC/ VLRservice area.?ÐWhenthe MSdetectsthe pagingmessage, it sendsa request onRACH for a SDCCH.?ÛThe BSCprovides a SDCCH, usingAGCH.

? SDCCH isused for the call set-up procedures. Over SDCCH all signalingprecedinga call takesplace. Thisincludes: Markingthe MSas“active” in the VLR. Authentication procedure (Startciphering, Equipment identification).?· The MSC/ VLRinstructs the BSC/ TRCto allocate an idle TCH. The BTSandMSare toldtotune to the TCH. The mobile phone rings. If the subscriber answers, the connectionisestablished.






GSM Mobile OriginatingCall Flow

Mobile User callinga LandLine Subscriber.

1. MS after dialing a number & pressing SEND key, sends Channel

Request(Chan_Req) message on RACH to ask for a signalingchannel (Radio Resources).

[RACH - Random Access channel]

2. The BSC allocates a Traffic Channel(TCH) using AGCH. TCH allocation assigns a specific

Frequency & a Timeslot on that frequency. [AGCH - Access Grant Channel]

3. The MS sends a call setup request through SDCCH, to the MSC/VLR. [SDCCH - slow

dedicated control channel]. Over SDCCH, all signaling takes place. This includes: marking

the MS status as active in the VLR

4. Then comes Authentication Procedure which includes Ciphering (The channel is ciphered

so as to protect the call), Equipment Identification, etc.

5. The MSC/VLR instructs the BSC to allocate an Idle TCH (this message contains the dialed

digits and other information needed for call establishment). The BTS and MS are told to

tune to the TCH.

6. The MSC allocates a voice circuit on one the digital trunks between the MSC and the BSS.

7. MSC informs the BSS about the allocated voice circuit. The call is also switched from

signaling to voice.

8. The BSS notifies the Mobile about the changeover to voice mode.

9. The MSC routes the call and sends the call towards the called subscriber.

10. The PSTN indicates to the MSC that it has received all the digits and the called subscriber

is being rung.

11. The MSC informs the mobile that the called subscriber is beingalerted via a ring.

12. The called subscriber answers the call.

GSM IDENTITYNUMBERS(IMSI,TMSI,CGI,MSRN,IMEI)

GSM identities

The GSM network is complex and consists of the Switching System (SS) and the Base Station

System (BSS). The switching system, which consists of HLR, MSC, VLR, AUC and EIR, interfaces

both the Base Station System and also other networks like PSTN/ISDN, data networks or other

PLMNs.






In order to switch a call to a mobile subscriber, the right entities need to be involved. It is

therefore important to address them correctly. The numbers used to identify the identities in a

GSM/PLMNnetwork is described in this chapter. See also Figure 56.

Numbering plans are used to identify different networks. For a telephone number in the

PSTN/ISDN network, numbering plans E.164 is used.

Mobile Station ISDNNumber (MSISDN)

The MSISDN is a number which uniquely identifies a mobile telephone subscription in the public

switched telephone network numbering plan. According to the CCITT recommendations, the

mobile telephone number or catalogue number to be dialled is composed in the following way:

MSISDN = CC + NDC + SN

CC = Country Code

NDC = National Destination Code

SN = Subscriber Number

A National Destination Code is allocated to each GSM PLMN. In some countries, more than one

NDC may be required for each GSM PLMN. The international MSISDN number may be of

variable length. The maximum length shall be 15 digits, prefixes not included.

Each subscription is connected to one Home Location Register (HLR).

The length of the MSISDN depends on the structure and numbering plan of each operator, as an

application of CCITT recommendation E.164.

The following is an example of dialling a GSM subscriber.

International Mobile Subscriber Identity (IMSI)

The IMSI is the information which uniquely identifies a subscriber in a GSM/PLMN.

For a correct identification over the radio path and through the GSM PLMN network,

a specific identity is allocated to each subscriber. This identity is called the

International Mobile Subscriber Identity (IMSI) and is used for all signalling in the






PLMN. It will be stored in the Subscriber Identity Module (SIM), as well as in the

Home Location Register (HLR) and in the serving Visitor Location Register (VLR).

The IMSI consistsof three different parts:IMSI = MCC + MNC + MSIN

MCC = Mobile Country Code (3 digits)

MNC = Mobile Network Code (2 digits)

MSIN = Mobile Subscriber Identification Number (max 10 digits)

According to the GSM recommendations, the IMSI will have a length of maximum 15

digits.

All network–related subscriber information is connected to the IMSI. See also Figure

56.

Mobile Station RoamingNumber (MSRN)

HLR knows in what MSC/VLR Service Area the subscriber is located. In order to

provide a temporary number to be used for routing, the HLR requests the current

MSC/VLR to allocate and return a Mobile Station Roaming Number (MSRN) for thecalled subscriber, see Figure 56.

At reception of the MSRN, HLR sends it to the GMSC, which can now route the call to

the MSC/VLR exchange where the called subscriber is currently registered.

The interrogation call routing function (request for an MSRN) is part of the Mobile

Application Part (MAP). All data exchanged between the GMSC - HLR - MSC/VLR for

the purpose of interrogation is sent over the No. 7 signalling network.

The Mobile Station Roaming Number (MSRN), according to the GSM

recommendations, consists of three parts:

MSRN = CC + NDC + SN

CC = Country Code

NDC = National Destination Code

SN = Subscriber Number

Note: In this case, SN is the address to the serving MSC.






Temporary Mobile SubscriberIdentity (TMSI)

The TMSI is a temporary number used instead of the IMSI to identify an MS. It raises the

subscriber’s confidentiality and is known within the serving MSC/VLR-area and changed at

certain events or time intervals. The structure of the TMSI may be chosen by each

administration but should have a maximum length of four octets (8 digits).

International Mobile station Equipment Identity (IMEI)

The IMEI is used for equipment identification. An IMEI uniquely identifies a mobile station as a

piece or assembly of equipment. (See IMEI, chapter 5.)

IMEI = TAC + FAC + SNR + sp

TAC = Type Approval Code (6 digits), determined by a central GSM body

FAC = Final Assembly Code (2 digits), identifies the manufacturer

SNR = Serial Number (6 digits), an individual serial number of six digits uniquely identifying all

equipment within each TAC and FAC

sp = spare for future use (1 digit)

According to the GSM specification, IMEI has the length of 15 digits.

Location Area Identity (LAI)

LAI is used for location updating of mobile subscribers.

LAI = MCC + MNC + LAC

MCC = Mobile Country Code (3 digits), identifies the country. It follows the same numbering

plan as MCC in IMSI.

MNC = Mobile Network Code (2 digits), identifies the GSM/PLMN in that country and follows

the same numbering plan as the MNC in IMSI.

LAC = Location Area Code, identifies a location area within a GSM PLMN network. The maximum

length of LAC is 16 bits, enabling 65 536 different location areas to be defined in one GSM

PLMN.

Cell Global Identity (CGI)

CGI is used for cell identification within the GSM network. This is done by adding a Cell Identity

(CI) to the location area identity.CGI = MCC + MNC + LAC + CI






CI = Cell Identity, identifies a cell within a location area, maximum 16 bits

Base Station Identity Code (BSIC)

BSIC allows a mobile station to distinguish between different neighboring base stations.

BSIC = NCC + BCC

NCC = Network Colour Code (3 bits), identifies the GSM PLMN.

Note that it does not uniquely identify the operator. NCC is primarily used to distinguish

between operators on each side of border.

BCC = Base Station Colour Code (3 bits), identifies the Base Station to help distinguish between

BTS using the same BCCH frequencies

Location Number (LN)

Location Number is a number related to a certain geographical area, as specified by the network

operator by ”tying” the location numbers to cells, location areas, or MSC/VLR service areas.

The Location Number is used to implement features like Regional /Local subscription and

Geographical differentiated charging.

Dropped Call due to Sudden DropOn circuit switch service, when a call is abnormally disconnected, a Clear Message with cause

code Call Control be treated as normal Disconnection is sent to the MSC – named Clear Request

Message.

Refer to Ericsson system, the following Urgency condition is checked at that time and the

relevant counter is incremented as a consequence:

1. Excessive TA

2. Low Signal Strength

3. Bad Quality

4. Sudden Drop

As named, stright forward meaning for the dropped call is described for the first three items.

However, Sudden Drop is quite not easy to understand.

Sudden Loss are drops that have not been registered as bad quality, signal strength, timing

advance. The term Sudden Loss is used because if the network cannot establish a connection

with the lost MS after a pre-defined period, the sudden loss counter is incremented if the last

reported measurement from the MS does not fulfill any of the reasons mentioned.

A connection is marked as Sudden loss if none of the three types of urgency states (that isexcessive TA, low signal strength or bad quality) are indicated and the locating procedure

indicates missing measurement results from the MS.






Drops due to ‘Other’ reasons are generally associated with hardware problems and

disturbances, number of drops due to ‘Other’ reasons is obtained by subtracting the drops with

known reasons from the total number of drops.

Main contributors in sudden and other TCH drop:

• Very sudden and severe drop in signal strength, such as when subscribers enter into

buildings, elevators, parking garages, etc.

•

Very sudden and severe occurrence of interference or bad quality.

MS running out of battery during conversation.

• Handover Lost.

• BTS HW faults.

• Synchronization or Abis link fault (transmission faults).

• MS Faults.

SMS(SHORTMESSAGESSERVICES)* *mostlyof term

SMS is a service that allows subscribers to send short messages (up to 160 characters) to other

mobile subscribers. Rather than having to set up a call on a traffic channel, SMS uses spare

capacity on the Standalone Dedicated Control Channel (SDCCH).

SMS is classified as a GSM Teleservice and three SMS teleservices (TS21-23) have been defined:· TS21 – Mobile terminated point-to-point messaging. A mobile can terminate an SMS

message either from another MS or from the fixed network.

· TS22 – Mobile originated point-to-point messaging. A mobile can send a message either to

another MS or into the fixed network (as an Email for example).

· TS23 – SMS Cell Broadcast (SMSCB). A more recent variation of SMS is SMSCB. SMSCB

messages are generally broadcast only in a specific network region. An MS cannot initiate such

a message and does not acknowledge receipt of one. Only MSs in idle mode can receive SMSCB

messages. These messages differ from standard SMS messages in that they are only 92

characters long. However, procedures exist to concatenate up to 15 SMSCB messages using a

special reassembly mechanism.In order to implement SMS, a network operator must establish a SMS Service Centre which

receives and processes SMS messages in a store-and-forward mode. Messages can be initiated

in the fixed or mobile network and delivered to either the fixed or mobile network.






Short MessagingEntitiesShort messaging entity (SME) is an entity which may receive or send short messages. The SME

may be located in the fixed network, a mobile station, or another service centre.

Short Message Service CentreShort message service centre (SMSC) is responsible for the relaying and store-and-forwarding of

a short message between an SME and mobile station.

SMSGateway Mobile SwitchingCentreThe SMS–gateway mobile switching centre (SMS–GMSC) is an MSC capable of receiving a short

message from an SMSC, interrogating a home location register (HLR) for routing information,

and delivering the short message to the visited MSC of the recipient mobile station. The SMS

interworking MSC (SMS–IWMSC) is an MSC capable of receiving a short message from the

mobile network and submitting it to the appropriate SMSC. The SMS–GMSC/SMS–IWMSC are

typically integrated with the SMSC.

Home Location RegisterThe HLR is a database used for permanent storage and management of subscriptions and

service profiles. Upon interrogation by the SMSC, the HLR provides the routing information for

the indicated subscriber. The HLR also informs the SMSC, which has previously initiated

unsuccessful short message delivery attempts to a specific mobile station, that the mobile

station is now recognized by the mobile network to be accessible.

Mobile SwitchingCentreThe MSC performs the switching functions of the system and controls calls to and from other

telephone and data systems.

Visitor Location RegisterThe visitor location register (VLR) is a database that contains temporary information about

subscribers. This information is needed by the MSC to service visiting subscribers.

The Base Station SystemAll radio-related functions are performed in the base-station system (BSS). The BSS consists of

base-station controllers (BSCs) and the base-transceiver stations (BTSs), and its primary

responsibility is to transmit voice and data traffic between the mobile stations.






The Mobile StationThe mobile station (MS) is the wireless terminal capable of receiving and originating short

messages as well as voice calls. The wireless network signalling infrastructure is based on

signalling system 7 (SS7). SMS makes use of the mobile application part (MAP), which defines

the methods and mechanisms of communication in wireless networks, and uses the services of

the SS7 transaction capabilities application part (TCAP). An SMS service layer makes use of the

MAP signalling capabilities and enables the transfer of short messages between the peer

entities.

GSM Interfaces

Interface between the MSCand Base StationSystem (A-interface)The interface between the MSC and its BSS is specified in the 08-series of GSM Technical

Specifications. The BSS-MSC interface is used to carry information concerning:

· BSS management;

· call handling;

· mobility management.

A-BISINTERFACE(BSC- BTS)When the BSS consists of a Base Station Controller (BSC) and one or more Base Transceiver

Stations (BTS), this interface is used between the BSC and BTS to support the services offered tothe GSM users and subscribers. The interface also allows control of the radio equipment and

radio frequency allocation in the BTS.

This interface is specified in the 08.5x-series of GSM Technical Specifications.

BINTERFACE(MSC- VLR)The VLR is the location and management data base for the mobile subscribers roaming in the

area controlled by the associated MSC(s). Whenever the MSC needs data related to a given

mobile station currently located in its area, it interrogates the VLR. When a mobile station

initiates a location updating procedure with an MSC, the MSC informs its VLR which stores the

relevant information. This procedure occurs whenever an MS roams to another location area.Also, when a subscriber activates a specific supplementary service or modifies some data






attached to a service, the MSC informs (via the VLR) the HLR which stores these modifications

and updates the VLR if required.

CINTERFACE(HLRand the MSC)The Gateway MSC must interrogate the HLR of the required subscriber to obtain routing

information for a call or a short message directed to that subscriber.

D INTERFACE(HLR- VLR)This interface is used to exchange the data related to the location of the mobile station and to

the management of the subscriber. The main service provided to the mobile subscriber is the

capability to set up or to receive calls within the whole service area. To support this, the

location registers have to exchange data. The VLR informs the HLR of the location of a mobile

station managed by the latter and provides it (either at location updating or at call set-up) with

the roaming number of that station. The HLR sends to the VLR all the data needed to support

the service to the mobile subscriber. The HLR then instructs the previous VLR to cancel the

location registration of this subscriber. Exchanges of data may occur when the mobile

subscriber requires a particular service, when he wants to change some data attached to hissubscription or when some parameters of the subscription are modified by administrative

means.

EINTERFACE(MSC– MSC)When a mobile station moves from one MSC area to another during a call, a handover

procedure has to be performed in order to continue the communication. For that purpose the

MSCs have to exchange data to initiate and then to realize the operation. After the handover

operation has been completed, the MSCs will exchange information to transfer A-interface

signalling as necessary. When a short message is to be transferred between a Mobile Station

and Short Message Service Centre (SC), in either direction, this interface is used to transfer themessage between the MSC serving the Mobile Station and the MSC which acts as the interface

to the SC.

FINTERFACE(MSCand EIR)This interface is used between MSC and EIR to exchange data, in order that the EIR can verify

the status of the IMEI retrieved from the Mobile Station.

GINTERFACE(VLR– VLR)When a mobile subscriber moves from a VLR area to another Location Registration procedure

will happen. This procedure may include the retrieval of the IMSI and authentication

parameters from the old VLR.

H INTERFACE(HLR- AuC)When an HLR receives a request for authentication and ciphering data for a Mobile Subscriber

and it does not hold the requested data, the HLR requests the data from the AuC. The protocol

used to transfer the data over this interface is not standardized.

Um INTERFACE(MS- BTS)The interface between the MS and the BSS is specified in the 04- and 05-series of GSM Technical

Specifications.






Date post:	30-May-2018
Category:	Documents
Upload:	herybruce
View:	226 times
Download:	0 times

Compilation Case and Analysis Rf Optim 2g 1stedition

Documents