rf dt basics
Post on 13-Apr-2015
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DESCRIPTIONOverview of RF DT
RF DT BasicsClick to edit Master subtitle style by
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 whats 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 networks performance on the field using certain tools. It3/13/13
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 Analysis3/13/13
Planned Drive By planned drive it suffices to say that an indebt
understanding of customers 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:v
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 (KPIs).
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 inverter3/13/13
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
Reasons for Tilting Antennav v v v v
Reduction of overshoot Removal of insular coverage Reducing interference Improving coverage quality in near areas Adjusting HO Types of Antenna Tilt
Mechanical Tilt Electrical Tilt3/13/13
EVENTS and KPI Measurements Events In RF DT, the events that will be required by the operator are:v v v v v v
MS Connected and Disconnected Blocked Calls Call Initiation Call Established Call Set-up3/13/13
v v v v v v
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 service3/13/13
Call Initiation: This happens when the originating MS seeks TCH allocation of resources. Its 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.3/13/13
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 QualitySudden Loss of Connection3/13/13
SDCCH Dropped calls
Low signal strength on down or uplink Poor quality on down or uplink Too high timing advance MS error Subscribers 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 welldefined 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 failuresv v
Congestion on the target cell No synchronization between equipments from manufacturers
v v v v