Download MapBasic User Guide

Download MapBasic User Guide

What is Slow Fading

Slow fading is also called shadowing. When a UE moves away from a cell the signal strength drops down slowly.

What is Fast Fading

Fast fading is also called multi-path fading, as a result of multi-path propagation. When multi-path signals arriving at a UE, the constructive and destructive phases create a variation in signal strength.

SDCCH Congestion Reason

---Low Availability

Action: Check SDCCH Availability. Check if the channels are manual, control or automatic blocked.

---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.

---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

---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.

---Extensive SMS Usage

Extensive SMS usage increases the SDCCH traffic and could cause congestion if badly dimensioned SDCCH channels.

Action: Check SMS activity.

---Cell Broadcast Used

Action: 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 Congestion

Action: Check SAE setting. High Ratio of Random Accesses

Action: Check Random Access performance

GPRS Mobility Management States or GPRS MM States

GPRS MM states :

* Idle state - The GPRS/EGPRS MS is turned on but not GPRS attached. The GPRS/EGPRS MS is "invisible" to GPRS/EGPRS, i.e. outside the GPRS/EGPRS coverage area.

* Stand by state - The GPRS/EGPRS MS is attached to the GPRS MM and sends RA updates to the SGSN and performs GPRS/EGPRS cell selection and re-selection.

* Ready state - A packet transfer is ongoing or has recently ended. A READY timer with fixed value defines how long time the GPRS/EGPRS MS shall remain in ready state after transfer. The GPRS/EGPRS MS performs cell update when changing cell in ready state.

Mode of Operation for GPRS/EDGE

Mode of operation :

* Class A- The GPRS/EGPRS MS may have a CS connection and a GPRS/EGPRS transfer at the same time.

* Class B- The GPRS/EGPRS MS may be GPRS and IMSI attached simultaneously but it cannot use both services at the same time.

* Class C - The GPRS/EGPRS MS is only allowed to be attached to one service at a time. A GPRS/EGPRS MS that only supports GPRS/EGPRS and not CS traffic will always work in class C mode of operation.

Range of Timing Advance (TA) in GSM

Range of Timing Advance (TA) in GSM = 0-63

The purpose 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.
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When to 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. Drive
testing 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.

SDCCH Drop Call Reason

SDCCH Drop Call Reason

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

TCH Drop Call Reason

TCH Drop Call Reason

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

Radio Link Time-Out or RLINKT

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.

Terms in Key Performance Indicators or KPI

1. CSSR (CALL SETUP SUCCESS RATE)
Definition: Rate of calls going until TCH successful assignment

2. SCR (SUCCESSFULL CALL RATE)
Definition: Rate of calls going until normal release that is not interrupted by SDCCH DROP, neither by assignment failures, and neither by CALL DROP.


3. CALL DROP RATE (CDR)
Definition: Rate of all losses of TCH connections during a call in relation to the number of successful Call Setups
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4. HOSR (HAND OVER SUCCESS RATE)
Definition: Successful internal and external outgoing handovers of total number of internal and external outgoing handover attempts

Also See: Steps to Improve HOSR

5. PSR (PAGING SUCCESS RATE)
Definition: Rate of successful paging attempts of total number of paging attempts.The formula is based on NSS point of view (based on MSC or LAC)

6. LOCATION UPDATE SUCCESS RATE
Definition: Successful location update
attempts of total number of location update attempts. The formula is based on NSS point of view.

7. SDCCH BLOCK RATE
Definition: SDCCH congestion of total number of SDCCH seizure attempts

8. SDCCH DROP RATE
Definition: Dropped SDCCH connections of total number of SDCCH connections without TCH congestion.


9. TCH ASSIGNMENT BLOCK RATE
Definition: Rate of TCH unsuccessful seizures during assignment procedure due to congestion


10. TCH Assignment Failure Rate (exclude blocking)
Definition: Rate of RTCH seizure failed (system + radio) during normal assignment procedure over the total amount of RTCH request for normal assignment procedure

11. EMD (Erlang Minute per Drop)
Definition: Total of Erlang minutes (TCH occupation) in one period measurement per drop call (after TCH Assignment).

12. TCH Availability
Definition: Available TCH of total number of defined TCH

13. RACH Success Rate
Definition : Rate of Successful RACH over the total number of channel required message received

Location Number or LN

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.

Base Station Identity Code or BSIC

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

Cell Global Identity or CGI

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

Location Area Identity or LAI

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.

International Mobile station Equipment Identity or IMEI

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.

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.

Temporary Mobile Subscriber Identity or TMSI

Temporary Mobile Subscriber Identity (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).

Mobile Station Roaming Number or MSRN

Mobile Station Roaming Number (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 the called subscriber.

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.

International Mobile Subscriber Identity or IMSI

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 consists of 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.

Mobile Station ISDN Number or MSISDN

Mobile Station ISDN Number (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.

Why Ec/Io is always negative

Pilot channel power or Ec is always less than the Total Cell Power, the ratio of the Pilot power (Ec) to the Total Cell power (Io) is always less than one.

Thus, when measured in Decibels,the value of Ec/Io is always negative.

Here is the calculation.

Ec = Pilot Channel Power or Effect Energy Channel
Io = Total Energy and Noise.

Ec/Io = 10.log [Pilot Channel Power / (Total Energy with Noise)] < 10.log(1) = 0

so Ec/Io always negative