rf dt basics
DESCRIPTION
Overview of RF DTTRANSCRIPT
RF DT BASICS
by
Chika Albert
Gil
RF DT is the most common and maybe the best
way to analyze Cellular Network performance by
means of coverage evaluation, system
availability, network capacity, network
retainibility and call quality. Although it gives idea
only on downlink side of the process, it provides
huge perspective to the service provider about
what’s happening with a subscriber point of view.
It is the testing of a network in a particular area to get
the real picture of the network’s performance on the
field using certain tools. It brings about Planning,
Implementation of the plan and optimizing where
necessary.
While statistics give an idea about the real behavior
faced by all end users regardless of their geographical
location, drive testing bring a simulation of end user
perception of the network on the field from one call
perspective. Drive tests give the ‘feel’ of the designed
network as it is
experienced in the field. The testing process starts
with selection of the ‘live’ region of the network
where the tests need to be performed, and the drive
testing path. Before starting the tests the engineer
should have the appropriate kits that include mobile
equipment (usually three mobiles), drive testing
software (on a laptop), and a GPS (global positioning
system) unit.
The purposes of RF DT are:
Since RF DT service tools (MS & BTS) are always in
use, the BTS needs constant maintenance to
improve its performance.
The performance of an RF network is only assessed
by collecting and analyzing DT logs.
As a business venture, troubleshooting and
optimization by the operators is needful and can
only be done when DT logs are collected.
Generally, RF DT is captioned as a planned drive
aimed at testing events, measure KPIs and draw
analysis between the MS and BTS in real time
using pre-defined testing tools.
Based on the above definition, I will discuss RF DT
under the following headings:
Planned Drive
Pre-defined testing tools
MS and BTS
Events KPIs Measurements
Drawing Analysis
Planned Drive
By planned drive it suffices to say that an indebt
understanding of customer’s demand of what type
of RF DT to be carried-out, pre-defined routes and
updated cell file are really necessary. I will again
discuss planned drive in the following sub-headings:
Types of RF DT
Pre-defined Routes
Updated Cell File
Types of RF DT
The types of RF DT are generally summarized into
the following:
VIP RF DT: This RF DT normally comes up after
problems of a particular site/cell have been reported
by statistical analyst from the logs of an SSV RF DT.
These areas are also called hotspots and the
analysis is performed simultaneously with the DT.
Benchmark RF DT: In a region where there is more than
one operator, BM RF DT is used to compare the network
performance of these operators. This RF DT is mostly
done in clusters.
SSV RF DT: Single Site Verification RF DT can also be
called cell coverage analysis DT or the routine DT. It
is a DT used to monitor network performance on
regular basis and on new planned sites in the
network. It tells the coverage area of each sector of
the site.
Pre-defined Routes
Every operator has their coverage area i.e the area
the sites are expected to cover. Before performing
RF DT, knowledge of the expected area to be
covered is largely important to the RF DT Engineer.
Also, if it is a cluster DT, proper definition of each
cluster route is necessary as a repeated drive of any
route we surely affect the Key Performance
Indicators (KPI’s).
Updated Cell file
This is an excel sheet showing details of all the sites
of an operator. The sheet contains the cell name,
Absolute Radio Frequency Channel Number (ARFCN),
Base Station Identity Code (BSIC), Latitude,
Longitude, Mobile Network Code (MNC), Mobile
Country Code (MCC), Location Area Code (LAC), Cell
Identity (CI), antenna direction, antenna beam,
mechanical tilt, electrical tilt e.t.c. It is converted to
a cell file format (this is the format TEMS
understands) using the following steps:
Open another excel sheet
Copy the sheet introduction on the top left of the
sheet also in the first row of the sheet. e.g 2 TEMS_-
_Cell_names
Copy needed information such as cell name, ARFCN,
BSIC, Lat, Lon and antenna direction to the new
sheet.
Save the excel sheet using the text tab delimited
format.
Open the saved file and rename it “any name.cel”
and save.
Pre-defined Testing Tools
There many testing tools for DT. But when carrying-
out an RF DT project, the testing tools are in most
cases defined by the client/customer. The most used
testing tools are the general products of TEMS. The
acronym expands as Testing Equipments for Mobile
Systems. Her products are grouped into:
Real time diagnosis tools
Network planning tools
Network monitoring tools
Network Performance Management tools
Also with the TEMS products are:
A laptop the meets task specification.
At least a mobile phone
One (1) GPS
An extension box
AC to DC inverter
A well-ventilated car
MS and BTS
MS: Mobile Station (MS) is made up of the Mobile
Equipment (International Mobile Equipment Identity
IMEI) and Subscriber Identity Module (International
Mobile Subscriber Identity IMSI). The MS used for RF
DT can either be K790, W995 e.t.c
Both the K790 and W995 have an almost the same
user approach as the steps below shows:
Power-up the phone (NB: Always remove the battery
from the phone when not in use)
Connect the cable first to the phone and then to the
laptop when already the license (dongle) is up and
running.
K790
Purely designed for GSM network testing.
W995
It has the capabilities of perform test on GSM (2G),
WCDMA (3G), GSM and WCDMA (IRAT), Video
streaming e.t.c. It is the MS in vogue as testing for
WCDMA is now everywhere since its deployment.
BTS: The Base Transceiver Station (BTS) is made up
of the following:
BTS Shelter
BTS Tower
Reasons for Tilting Antenna
Reduction of overshoot
Removal of insular coverage
Reducing interference
Improving coverage quality in near areas
Adjusting HO
Types of Antenna Tilt
Mechanical Tilt
Electrical Tilt
EVENTS and KPI Measurements
Events
In RF DT, the events that will be required by the operator are:
MS Connected and Disconnected
Blocked Calls
Call Initiation
Call Established
Call Set-up
Call end
Cell Reselection
Dedicated Mode
Idle Mode
Dropped Calls
HO success and failure
PS attached and detached
PDP Context Activated and Deactivated
Location Area Update
Routing Area Update
MS Connected and Disconnected: This is the voice
prompt when an MS is activated and deactivated on
TEMS.
Blocked Calls: Calls that cannot find their way into the
network are classified as blocked calls. They are used
to ascertain the accessibility of the network. Causes of
blocked calls will be generally classified into the
following:
• Terminating MS is engaged
• System Busy
• No service
• Other causes
Call Initiation: This happens when the originating MS
seeks TCH allocation of resources. It’s simply put as
when a number is dialed by the originating MS.
Call set-up: This occurs when the terminating MS
receives signal from the BTS of an in-coming call.
This measures the successful TCH assignment to the
total number of TCH assignment attempts.
Call Established: This occurs when both the
originating and the terminating MSs are carrying
traffic.
Call end: This occurs when the transfer of traffic
between the originating and terminating MSs is
stopped by the users.
Cell Reselection: This occurs when the MS is in idle
mode. The MS measures the kpis of cells it can camp
on while in transit.
Dedicated Mode: When an MS is carrying
traffic/making calls, the MS is said to be in a
dedicated mode.
Idle Mode: A drive test activity in which, the MS is
“ON” but no call occur. A powered on mobile station
(MS) that does not have a dedicated channel
allocated is defined as being in idle mode.
While in idle mode it is important that the mobile is
both able to access and be reached by the system.
The idle mode behavior is managed by the MS. It is
the mode for performing scanning.
Dropped Calls: This shows 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.
This indirectly also defines retainability as a
higher retainability value indicates less dropped
calls.
The causes of dropped calls can be classified into
two viz
Traffic Channel (TCH) Dropped calls
• Excessive Timing Advance
• Low Signal Strength
• Bad Quality
• Sudden Loss of Connection
• Other Reasons
SDCCH Dropped calls
• Low signal strength on down or uplink
• Poor quality on down or uplink
• Too high timing advance
• MS error
• Subscriber’s behavior
• MS Battery flaw
• Congestion on TCH
HO Success and Failure: When a call is made
continuously in transit, it expected that the cell
where the call was initiated and camped-on will not
be cell where the call is terminated. The call is
transferred from one cell to another as the MS is in
transit. Therefore, HO success is the process where
a dedicated call is transferred from one cell to
another without any voice quality dropping using
some well-defined network HO parameter
configuration. If the quality of the call drops or the
call ends impromptly, then the call is said to have
experience HO failure.
Causes of HO failures
Congestion on the target cell
No synchronization between equipments from
manufacturers
Poor HO parameter configuration
Missing Neighbors
Problem from antenna and feeder system
PS Attached and Detached: It is used to measure the
accessibility in and out of any network while testing
for data service.
PS Attach and Detach: It is an event used by the MS
to access the network for GRPS service over a
channel. This channel focuses on that packet alone
been transmitted. It can be used to ascertain the
level of accessibility of a network in performing
GPRS service.
PDP Context Activation and Deactivation: In order for
the MS to send and receive GPRS data the MS must
perform a PDP context activation after the GPRS
attach. The PDP context activation makes the MS
known in the concerned GGSN and communication to
external networks is made possible. The PDP context
activation corresponds from the end users
perspective to "Logging On" to an external network.
The difference from using a dial-up connection over
circuit switched is that in GPRS the end user can have
several PDP contexts activated simultaneously if the
terminal supports several IP addresses.
Location Area Update: A GSM network is divided into
cells. A group of cells is considered a location area. A
mobile phone in motion keeps the network informed
about changes in the location area. If the mobile
moves from a cell in one location area to a cell in
another location area, the mobile phone should
perform a location area update to inform the
network about the exact location of the mobile
phone.
Routing Area Update: A routing area is sub-divided
into location area. It is an event used by the MS for
PS attach and detach and PDP context activation
and deactivation services.
KPI Measurements
RxLev: Rx-Level is define as The power level
corresponding to the average received signal level
of the downlink as measured by the mobile station.
The range of Rx-level is between -55 to -110.It is
been further classified as Rx-Level Sub and Rx-level
Full. Where Rx-Level sub is based on the mandatory
frames on the SACCH multi frame. These frames
must always be transmitted which means that they
carry intelligent signaling data. Whereas The FULL
values are based upon all frames on the SACCH
multi frame, whether they have been transmitted
from the base station or not.
This means that if DTX DL has been used, the FULL
values will be invalid for that period since they include
bit-error measurements at periods when nothing has
been sent resulting in very high BER.
RxQual: Rx-Qual is define as the level corresponding to
the mobile station's perceived quality of the downlink
signal. Rx Quality is a value between 0 and 7, where
each value corresponds to an estimated number of bit
errors in a number of bursts. The Rx Quality value
presented in TEMS is calculated in the same way as
values reported in the measurement report sent on the
uplink channel to the GSM network.
Frame Error Rate (FER): It shows the number of
frames that dropped due to too many bit errors in
the frame. It is the ratio of the number of frame
error to the transmitted frames. It is expressed in
percent. The smaller the speech codec bit rate, the
more sensitive it becomes to frame erasures. FER
plays a major role in troubleshooting of Interference.
Bit Error Rate (BER): It measures the quality of the
network. It is the ratio of the number of bits errors to
the transmitted bits. It is expressed in percent.
Speech Quality Index (SQI): It measures the voice
quality beyond the RxQual because it also considers
the FER and BER. SQI is an estimate of the perceived
speech quality as experienced by the mobile user, is
based on handover events and on the bit error and
frame erasure distributions.
However, the Rx Quality measure is based on a
simple transformation of the estimated average bit
error rate, and two calls having the same Rx Quality
ratings can be perceived as having quite different
speech quality.
One of the reasons for this is that there are other
parameters than the bit error rate that affects the
perceived speech quality. Another reason is that
knowing the average bit error rate is not enough
to make it possible to accurately estimate the
speech quality.
Generally Speech Quality Index, which is an
estimate of the perceived speech quality as
experienced by the mobile user, is based on
handover events and on the bit error and frame
erasure distributions.
The quality of speech on the network is affected by
several factors including what type of mobile the
subscriber is using, background noise, echo
problems, and radio channel disturbances.
Extensive listening tests on real GSM networks have
been made to identify what type of error situations
cause poor speech quality. By using the results from
the listening tests and the full information about the
errors and their distributions, it is possible to
produce the Speech Quality Index. The Speech
Quality Index is available every 0.5 second in and
predicts the instant speech quality in a phone
call/radio–link in real–time.
DRAWING ANALYSIS
In RF DT, the major analyses to be drawn are:
Coverage Analysis
Interference Analysis
HO Analysis
Neighbor Analysis
Call Analysis
Data throughput rate
THANK YOU
Failure establishes one thing; that your zeal to succeed was not strong enough.
Gil