RFOTDOA Testing: Conformance and Equipment
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This page describes OTDOA testing, OTDOA test cases, and OTDOA conformance testing. It also mentions OTDOA test equipment used for OTDOA measurements. Test equipment vendors include Spirent Communications and Rohde & Schwarz.
About OTDOA
The term OTDOA stands for Observed Time Difference of Arrival. It’s a positioning technique used in LTE-compliant mobile phones. This technique is used to determine the location of a UE (User Equipment, i.e., mobile phone) in emergency situations.
It works effectively and accurately regardless of UE positions, such as indoors, in tall buildings, and even in forest locations surrounded by dense trees. This is because LTE signals can penetrate steel and concrete structures, as well as trees. Moreover, LTE has introduced a special reference signal referred to as PRS (“Positioning Reference Signal”) to provide better estimation performance to locate the UE.
OTDOA is similar to E-OTD (Enhanced Observed Time Difference) used in WCDMA and AFTL (Advanced Forward Link Trilateration) used in CDMA for location determination.
There are two main types of OTDOA: downlink and uplink.
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Downlink OTDOA: The UE receives downlink signals from the serving eNB (evolved NodeB, i.e., base station) and multiple neighboring eNBs and determines RSTD (Reference Signal Time Difference). This information is fed back to the network (i.e., eNBs) by the UE. Based on the RSTD information, the eNBs determine the position of the UE.
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Uplink OTDOA: The eNBs receive uplink transmissions from the UE and determine its position.
The OTDOA conformance test cases are defined in 3GPP TS 37.571 release documents.
Following table mentions OTDOA test equipment vendors with their offerings.
OTDOA testing involves test cases in the following areas:
- Conformance test specification
- Operator acceptance testing
- R & D performance testing
OTDOA Test Equipment
Following are the OTDOA test equipments used for OTDOA measurements.
| OTDOA Test Equipment | Description |
|---|---|
| CS8 interactive tester from Spirent | It is a network emulator which allows UE to connect with eNB as in realtime network scenario. It allows whether mobile gets registered with eNB(i.e. network) and whether it is sensing the PRS (Positioning Reference Signal) transmitted by eNBs and so on. This OTDOA equipment allows to conduct initial level of OTDOA testing of the UE. It is used for manual OTDOA testing. It allows to configure eNBs and PRS configurations. |
| 8100 LTS from Spirent | This LTE Location Technology Solution is designed for automated testing of the OTDOA feature in a mobile phone. It is a second level of testing which allows testing in three different modes as mentioned above. This testdrive LTS provides test cases as per TS 37.571 readily available to test the UE. These test cases can also be modified and configured. The GUI of testDrive LTS allows user to review all the messages exchanged between UE and eNBs. |
| TS-LBS Location Based Services Test System from Rohde & Schwarz | It supports all positioning technologies viz. A-GNSS, OTDOA, eCID and hybrid technologies. It supports technologies such as LTE FDD, LTE TDD, GERAN, HSPA, WCDMA, etc. |
