akhirnya blog ini bisa dibuka lagi... -____-"

Huuuft...
finally I get back my gmail account and password...
I really miss this blog...

Ok nanti sharing2 lagi ya...
skarang mw cari cari materi dulu sebelum di share... :)

I was training Drive test using Nemo and Tems

Sorry...

Currently I can't update my blog,
because now I was training Drive test and case analize using Nemo and Tems 8.0.3
but when I have more experience about it, I'll update this blog as soon as possible.


thx
br,
Rama Apde

Dynamic Half Rate Allocation (DHA)

Dynamic Half Rate Allocation (DHA) – the feature used for new connections at TCH allocation that allows the possibility to direct traffic towards FR or HR connections resulting in a better flexibility to control traffic resources. The end user will experience less congestion and hence increased accessibility to the network.

1. Dynamic Half Rate Allocation

a. The feature is invoked if the parameter DHA is ON. At high traffic load TCH/HR have precedence and at low traffic load TCH/FR have precedence.

b. If the MS and the cell support AMR HR and the number of idle FR TCH divided by the total number of de-blocked FR TCH is equal or above DTHAMR FR TCH will have precedence over HR TCH. If the number of idle FR TCH divided by the total number of de-blocked FR TCH is less than DTHAMR HR TCH will have precedence over FR TCH.

c. If the MS or the cell do not support AMR HR and the number of idle FR TCH divided by the total number of de-blocked FR TCH is equal or above DTHNAMR FR TCH will have precedence over HR TCH. If the number of idle FR TCH divided by the total number of de-blocked FR
TCH is less than DTHNAMR HR TCH will have precedence over FR TCH.

2. Main Controlling Parameters
a. DHA is used to turn the feature Dynamic Half Rate Allocation ON orOFF. The parameter is set per cell.

b. DTHAMR is the threshold parameter for AMR HR capable MS:s at channel allocation below which an AMR MS will be allocated on a HR channel. The parameter expresses the ratio between idle and deblocked TCH:s in percent and is set per cell.

c. DTHNAMR is the threshold parameter for non AMR HR but DR capable MS:s at channel allocation below which a DR capable MS will be allocated on a HR channel. The parameter expresses the ratio between idle and de-blocked TCH:s in percent and is set per cell.

Commande to veiw parameter existing

RLDHP:CELL=cell;

CELL DYNAMIC HR ALLOCATION DATA



CELL     DHA  DTHAMR  DTHNAMR

cell     dha  dthamr  dthnamr

.        .     .        .

.        .     .        .

.        .     .        .

cell     dha  dthamr  dthnamr



/    \

|NONE|

\    /

/                   \

|EOT DURING PRINTOUT|

\                   /

/               \

|FAULT INTERRUPT|

|fault type     |

\               /

END

Commande to change parameter Halfrate

RLDHC:CELL=cell+[,DHA=dha][,DTHAMR=dthamr][,DTHNAMR=dthnamr]+;

CELL=cell	Cell designation This is a symbolic name of a defined cell.
DHA=dha	Dynamic Half Rate (HR) Allocation OFF Dynamic HR Allocation is disabled. ON Dynamic HR Allocation is enabled.
DTHAMR=dthamr	Dynamic HR Allocation threshold for Adaptive Multi Rate (AMR) capable mobiles This parameter indicates a percentage value of number of deblocked Full Rate (FR) Traffic Channels (TCHs) in the cell when Dynamic HR Allocation is enabled and the mobile supports AMR HR. When the number of idle FR TCHs in the cell is above or equal to the value, FR TCHs will have precedence over HR TCHs. When the number of idle FR TCHs in the cell is below to the value, HR TCHs will have precedence over FR TCHs. For the default value for DTHAMR see the Application Information for block Numeral 0 - 100
DTHNAMR=dthnamr	Dynamic HR Allocation threshold for mobiles not capable of AMR This parameter indicates a percentage value of number of deblocked FR TCHs in the cell when Dynamic HR Allocation is enabled and the mobile does not support AMR HR. When the number of idle FR TCHs in the cell is above or equal to the value, FR TCHs will have precedence over HR TCHs. When the number of idle FR TCHs in the cell is below to the value, HR TCHs will have precedence over FR TCHs. For the default value for DTHNAMR see the Application Information for block Numeral 0 - 100

Frequency Hopping

1. Pendahuluan

Selama koneksi Call, burst dapat dengan mudah hilang ketika mobile station berada pada lokasi kondisi fading untuk frekuensi tertentu atau jika terkena interferensi.Ada beberapa kemungkinan baik untuk burst berikutnya yang diterima, jika di kirim melalui frekuensi yang berbeda, dengan frekuensi hoping. Pengkodean dan susunan interleaving pada GSM terkonstruksi, bila kehilangan satu burst mempunyai pengaruh pada speech quality.

Dalam frekuensi hopping penentuan awal frekuensi digunakan pada masing-masing cell. Dimana Mobile Station merubah frekuensi satu kali setiap TDMA frame ( 217 kali perdetik).

2. Daftar istilah
Konsep

E-GSM
Extended GSM 900 Band termasuk Primary GSM900 bang dan G1.

Filter Combiner
Adalah narrow band Combiner, ketika filter pada masing-masing transmitter di tune pada frekuensi transmit-nya. Tuning ini dilakuakn secara otomatis tetapi membutuhkan waktu. Untuk alasan inilah filter combiner hanya dapat digunakan pada baseband hopping. Keuntungan dari filter Combiner dapat meng-combine lebih dari 2 TRX secara bersamaan dan total loss lebih -kurang 3 sampai 4 dB, kemudian Hybrid combiner berada dalam jumlah TRX yang sama.

G1
Band ekstension dibuat untuk GSM900 pada 880-890MHz (uplink) dan 925-935 Mhz (downlink).

Hybrid Combiner
Hybrid Combiner dapat meng-combine lebih dari 2 TRX, degan loss sekitar 3dB. Hybrid Combiner merupakan broad band combiner dan tidak memerlukan tuning. Sebab itu sesuai untuk synthesizer hopping dan baseband hoping. Ia membutuhkan satu port antenna setiap hybrid combiner.

MAIO
Adalah offset indek pada ARFCN dengan allocated frekuensi.

Multipath Fading
Multipath fading terjadi ketika signal yang diterima pada receiver ada dua, langsung dari transmitter dan tidak langsung sesuai obyek propagasi atau terjadi karena repleksi. Signal tersebut diterima sedikit berbeda waktu, dengan amplitude dan phasa yang berbeda. Mereka secara bersama-sama menjumlahkan dan juga sebaliknya (Fading dips). Fading Dips muncul pada lokasi ruang yang berbeda untuk frekeunsi yang berbeda. Fenomena ini disebut multipath fading. Fading dips terbagi kira-kira 17 cm untuk GSM 900 dan kira-kira 8 cm untuk GSM 1800 dan GSM 1900.
P-GSM
Adalah Primary GSM900 yang di difine pada 890-915 Mhx (uplink) dan 935-960 Mhz (downling).

TS0 to TS7
Posisi time slot dalam sebuah frame TDMA


3. Kemampuan

1. Frekuensi Diversity

Frekuensi Hoping dapat menekan efek dari multipath fading. Multi path Fading pada frekuensi dan tergantung lokasi. Dengan frekuensi Hoping, gerak lambat mobile station tidak akan mengkhususkan tetap pada specific fading dip yang panjang dalam satu frame TDMA.
Signal strength yang lemah, dalam multipath fading, mobile station akan melihat lebih keadaan radio secara sama.


Gambar-1 Sekema dari multipath Fading pada dua frekuensi yang berbeda dan pada frekuensi hoping antara dua frekuensi untuk pergerakan lambat dari mobile station.

2. Interference diversity
Interferensi tergantung dari waktu, frekuensi dan mobile station Tanpa frekuensi hoping, beberapa margin perencenaan cell harus di gabungkan, agar service pelayanan kualiatas yang cukup dapat disediakan dalam sistuasi yang ter-interference. Dengan perubahan frekuensi pada setiap frame TDMA. Mobile station hanya mengalami interference pada frekuensi tertentu satu kali dalam jumlah hops. Kemiripan interferensi frekuensi tertentu akan disebarkan oleh banyak lintasan mobile station. Ini disebut interferensi rata-rata (Interference averaging) dan hasinya dalam interferensi diversity. Dengan interferensi divercitry akan melihat lebih banyak lingkungan radio yang sama. Sebagai hasil dari frekuensi hopping. Perencanaan margin cell dapat ditekan yang memungkinkan untuk penerapan pada perecanaan frekuensi yang lebih handal.

Interferensi diversity tergantung dari kecepatan mobile station, tetapi tergantung pula pada mode dari hopping yaitu mode cyclic atau random dan type dari frekuansi hoopinng yang digunakan yaitu baseband atau synthesizer hopping. Untuk improvement terbaik adalah didapatkan ketika penginterferensinya dan koneksi peng-interferensi menggunakan hoping squen yang tidak berkorelasi. Korelasi yang rendah, merupakan yang tertinggi dari hopping gain. Jika keduanya pelayan dan peng-interferensi di set pada frekuensi yang sama dan juga cyclic hopping, itu memungkinkan bahwa beberapa mobile station akan hop “in phase”dengan yang lainnya. Efek jumlah total korelasi, seakan-akan tidak hopping dan hasil improvement akan menjadi sangat rendah. Dalam penanganan yang lain, random frekuensi hopping akan memeperlihatkan gain hopping, dalam pembebanan system secara penuh, sebab itu dari hopping yang tidak berkorelasi. Jumlah frekunsi hopping juga mempengaruhi gain dari interferensi diversity. Jika interferensi dapat disebarkan dalam bandwith yang luas, maka Tabrakan Interferensi akan lebih sedikit dan menhasilkan hopping gain yang tinggi.


3. Kesimpulan

Dari sisi subscriber point, frequensi hopping memberikan peningkatan speech kuality dalam banyak situasi. Sedngkan dari sisi operator akan mendapatkan keuntungan berupa:
• Frekuensi reuse yang handal dan meningkatkan capacity
• Lebih banyak mengetahui tengatng radio
• Memunkinkan untuk memberikan lebih banyak penyeragaman speech quality pada subscriber

4. Penjelasan Teknik

1. Methode frekuansi hopping

Ada dua type frekuansi hopping yaitu baseband dan synthesizer hopping. Parameter spesifik FHOP yang metodanya digunakan dala base station yang ada. Untuk setiap chanal group, parameter FHOP digunakan untuk meng switch on dan off fitur frekuansi hopping secara terpiah. Saat ini memungkainkan meng on kan hop dalam 16 frekuensi per cahanal group, frekuensi hopping dapat dibentuk pada Trafik Chanal (TCH), SDCCH dan Packet Data Channel (PBCCH dan PDCH). Bagaimanapun Broadcast dan Commnon Control Channel seperti misalnya BCCH tidak bias di hop, Channel-channel tersebut dim aping pada TS0 dari BCCH carrier.

Dalam Baseband dan synthesizer hopping di jelaskan dengan menggunakan contoh yang sama dam konfigurasi kombinasi antenna. Konfigurasi yang benar bagaimanapun tergantung pada base station (RBS200 atau RBS2000) dan type dari instalasi combiner-nya.

2. Baseband Hopping

Dalam baseband hopping, setiap transmitter ditetapkan dengan fix frekuensi. Pada transmisi semua burst, tidak me-respect dari yang koneksi, tetapi dirouting ke transmitter yang sesuai dari frekuesi yang sewajarnya dapat dilihat pad gambar-2


Gambar-2 Routing burst dari TRX ke transmitter pada baseband hopping

Keuntungan dengan mode ini adalah narrow band dapat menggunakan filter combiner yang dapat di-tuning. Combiner tersebut mempunyai sampai 12 input untuk RBS2000 dan 16 input untuk RBS200. Ini memunkinkan untuk menggunkan transceiver dengan satu combiner.


3. Synthesizer hopping
Synthesizer hopping artinya satu transmitter meng-handle semua burst yang mempunyai spesifik koneksi. Burst-burst tersebut dikirim “straight on forward” dan tidak dirout oleh Bus, Berbeda dalam baseband hopping, transmitter di-tuning pada frekuensi yang benar pada transmisinya setiap burst. Dapat dlihat pada gambar-3.


Gambar-3 Menunjukan pengiriman burst dari TRX ke Transmitter pada synthesizer hopping

4. Konfigurasi

Pada konfigurasi cell, Cell ditentukan dengan satu atau beberapa channel group (CHGRs). Ketersediaan frekuensi untuk cell yang dipecah dan di tentukan untuk satu channel group. Transceiver group dapat dikoneksikan pada satu atau lebih chananel group. Selain itu setiap channel group dapat ditentukan secara terpisah sebagai hopping dengan parameter HOP, sebagai contoh terdapat dua channel group dalam satu cell, dimana yang satu adalah hopping dan yang lainnya tidak. Dalam setiap channel group. Channel group akan hop lebih dari frekuensi yang ditentukan untuk channel group tertentu. SDCCH/8,TCH dan semua packet data channel dai meng hop. Time slot 0 pada BCCH tidak dapat dihop bahkan jika ia mempunyai satu channel group yang dikonfigurasi sebagai hopping.

BCCH harus selalu transmit, agar dapat mengizinkan mobile station pada neighbour ing –cells untuk melakukan pengukuran selama ative dan mode idle. Ketika tidak ada trafik burst, sebagai ganti akan dikirim dummy burst , hanya pada downlink saja dari BCCH carrier. Hal ini disediakanoleh transmitter itu sendiri, Jika dikonfigurasikan untuk single frekuensi, itu dapat di set-up, sebagai yang mentransmit dummy busrt kapanpun tidak ada yang datang dari kontrooler melalui bus. Itu disebut pengisian carrier-zero (Co) ketika dilakukan ke frekuensi BCCH fo. Pengisian Co adalah diperoleh secara otomatis untuk isi channel group BCCH.

RF Optimization Crash Course [SDCCH Congestion]

Probable Reasons of SDCCH Congestion

Low Availability
Action: Check SDCCH Availability. Check if the channels are manual, control or automatic blocked.
Solution: Change and repair faulty equipment. Review the O&M procedures.

Increasing Traffic Demand
The 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.
Solution: Increase the number of SDCCH channels. Note, that an increase may lead to the need for new transceivers. If combined SDCCH is used, non-combined channel configuration should be introduced.

Bad use of Adaptive configuration of Logical Channels
By 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
Solution: If ACSTATE is off, it is suggested to switch on.

Long Mean Holding Time
If the mean holding time is long, this generates a higher traffic load.
Action: Check SDCCH Mean Holding Time

Too Frequent Periodic Registration
Action: Check Random Access Distribution. Check the timer T3212 in the BSC and the parameters

BTDM and GTDM in the MSC
Solution: Decrease the periodic registration.

Location Area Border Cell
If 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.
Solution: If the site is located close to major road or railway, consider to move the Location Area border. Increase the hysteresis CRH. The CRH is the hysteresis value used when the MS in idle mode crosses a LA border. The default value for this parameter is 4. If a high number of Location Updatings occurs in a Location Area border cell, a higher CRH can be set in order to reduce the number of LUs.

Extensive SMS Usage
Extensive SMS usage increases the SDCCH traffic and could cause congestion if badly dimensioned SDCCH channels.
Action: Check SMS activity.
Solution: Re-dimension the SDCCH channels with consideration taken to SMS usage.

Cell Broadcast Used
Action: Check if Cell Broadcast is active. .If active, check if it is used by the operator.
Solution: Remove Cell Broadcast if not used.

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 Congestion
Action: Check SAE setting. High Ratio of Random Accesses
Action: Check Random Access performance

RF Optimization Crash Course [Handover]

Handover is a key function in a GSM network. If the handover performance is poor the subscriber will perceive the quality of the network as bad.

Handover performance statistics should preferably be measured on 24 hour data or longer.

The following checks should be performed:
1. Check for handover relations with low traffic (e.g. less than 10% of average number of handovers per relation).

2. Check for unbalanced handover relations (e.g. relations which have not approximate the same number of handovers in either direction. Remark: Unbalanced handovers relation indicate problem if measured on whole days, assuming that the same number of people go in and out of the cell coverage area.

3. Check if the reason for unbalanced handover is congestion.



Probable Reasons of Bad Handover Performance

Bad Locating Parameter Setting
A bad setting of locating control parameters might result that the locating will seldom rank the cell as a candidate.
Action: Check parameter setting.
Solution: Correct bad parameter setting.
Unnecessary Neighboring Cell Relation
None or very few handovers might indicate an unnecessary neighbouring cell relation.
Action: Check neighbor cell relations
Solution: Check if the relations really should be defined. Remove unnecessary cell relations.

The Base Station is Defined But Not in Service.
Action: Check reason for BTS not in service.
Solution: Take action to set the base station in service.

HW faults.
Action: Check BTS error log.

Missed measurement frequencies in BA-list
This will cause no handover decisions to the target cell.
Action: Check measurement frequencies list.
Solution: Add missed frequencies.

Permitted Network Color Code problem
If NCCPERM doesn’t include neighboring cell’s NCC, there will be no handovers.
Action: Check NCCPERM.
Solution: Add NCC of neighbors to NCCPERM.

Wrong Use of HCS
Action: Check HCS related parameters
Solution: Change to normal value.

Poor inter-MSC/BSC handover performance
If the cell is at the border of inter-BSC or inter-MSC, poor inter-MSC/BSC handover
performance will cause few or no handover attempts.
Action: Check inter-MSC/BSC handover performance

Unsuccessful Handovers
There can be two reasons why an attempt is counted as unsuccessful: either the mobile station was lost or the call was reverted to the old cell and channel.Unsuccessful handover may lead to a dropped call. Investigate if there is any difference between incoming and outgoing handovers. This can give further reasons of the problem area.

The lost handovers are registered at outgoing handover. Note that also dropped call counters are
stepped.


Congestion
A high congestion might lead to dragged calls (handover performed at a not intended location) and a lot of unsuccessful handovers.
Action: Check TCH congestion.
Solution: Add more TCH capacity. Activate DHA or DYMA.

Timer Expire After MS is Lost
The MS never answers the base station.
Action: Check coverage. Check interference.

Link Connection or HW Failure
Action: Check BTS error log. Perform site visit. Perform link performance measurements.
Solution: Repair faulty equipment.

Bad Antenna Installation
Action: Perform site survey and check antenna installation. Check antenna cabling.
Solution: Adjust antenna installation, antenna type or cabling.

Antennas Connected to Wrong Feeder
Action: Perform site survey and check antenna installation. Check antenna cabling.
Solution: Correct the antenna to the right sector.

Incorrect Down Tilt
Action: Perform site survey and check antenna installation.
Solution: Correct antenna tilting.

The MS Measures Signal Strength of Another Co- or Adjacent than Presumed.
Action: Check frequency plan..Perform drive tests.
Solution: Decrease interference.

Wrong Neighboring Cell is Defined

This can happen when a new site is added and old definitions are not undefined and new relations are not inserted.

Action: Check parameter setting. Run Undefined Neighboring Cell Recording.
Solution: Define or remove neighboring cells.

Missing Handover Relations

Missing handover relations will act as coverage holes. Suddenly the MS can not perform handover to the best server (i.e. not in the BA-list), instead a handover is performed to the second best candidate.

Action: Check existing handover relations. Check with actual site positions and coverage plots if more relations need to be added. Run Undefined Neighboring Cell Recording.
Solution: Add missing handover relations.

Wrong Output Power due to Faulty Transceiver
Action: Check output power setting. Check BTS error log

Poor Inter-MSC/BSC Handover Performance
For outer or external cell, wrong definitions in either MSC or BSC may be reason for the problem.
Action: Check inter-MSC/BSC handover performance.

Many Neighbors Defined

Many defined measurement frequencies defined (>16) will decrease the accuracy of the mobile measurements to locate the best six servers. Many measurement frequencies mean few samples per frequency and problem for mobiles to decode the BSIC.

Action: Check number of definitions.
Solution: Remove unnecessary definitions.

Too Many Measurement Channels Defined
Action: Check number of measurement channels
Solution: Remove unnecessary measurement channels.

Bad Use of Radio Network Features
Incorrect use of radio features such as Dynamic Power Control, Locating, Intra-Cell Handover, Frequency Hopping, etc.
Action: Check Feature parameter setting.
Solution: Correct strange and erroneous parameter setting.

Delayed Handover Decision
A delayed handover decision can be due to congestion in the target cell.
Action: Check handover parameters.

Wrong Locating Parameter Setting
Action: Check locating parameters
Solution: Correct parameter setting.

Bad Radio Coverage
Action: Check coverage plots.

High Interference, Co-Channel or Adjacent

The 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 base station.

Action: Check interference. Check if many handovers are performed due to downlink or uplink bad quality.
Solution: Change frequency plan.

Lower Output Power on TCH than on the BCCH in the Target Cell
Action: Check output power. Check BSTXPWR and BSPWR definition

Not good neighboring cell relation
Action: Delete the relation if not necessary.

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

RF Optimization Crash Course [Dropped Calls]

Dropped calls show the number of abnormal disconnections during call setup or during conversation. From a subscriber point of view, the most serious dropped calls are those that interrupts an ongoing conversation, i.e. a call dropped on the TCH. There are different counters for dropped calls, i.e. dropped calls due to low signal strength, bad quality, too high timing advance and miscellaneous that will give us indication of the reason for possible bad performance.

The mechanisms behind dropped calls on TCH and SDCCH are described below:

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 mobile station 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-Out

If 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 mobile station 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 Indication

When 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 mobile station 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. MSC Time-Out
Normal 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 TCH

Before 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 mobile station and a Clear Request to the MSC.

TCH Drop reason (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 Connection
5.Other Reasons

Excessive Timing Advance

The 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.


TCH Drop Reasons (2)
Low Signal Strength on Down or Uplink or Both Links

The 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

TCH Drop Reasons (3)
Poor Quality on Down or Uplink or Both Links

The 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 is used only for statistics purposes and does not affect the behavior 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.

TCH Drop Reasons (4)
Sudden Loss of Connection

Drops 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

TCH Drop Reasons (5)
TCH Drops due to Other Reasons
TCH 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 with hardware 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 reason of drop in SDCCH

Low Signal Strength on Down or Uplink
The 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 Uplink
Action: Check C/I and C/A plots. Check frequency plan. Perform drive tests.
Solution: Change frequency. Use available radio features.

Too High Timing Advance
Action: 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 Error
Some 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 Behavior
Poorly 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 Flaw
When 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 TCH
The 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.