Minimization of Drive Tests (MDT)
1. What is Minimization of Drive Tests (MDT)
Minimization of driving test (MDT) is a standardized mechanism introduced in 3GPP Release 10 to provide operators with network performance optimization tools in a cost-efficient manner. The main characteristics of MDT can be summarized below:
o The operator shall be able to configure the UE measurements independently from the network configuration.
o The UE reports measurement logs at a particular event (e.g. radio link failure).
o The operator shall have the possibility to configure the logging in geographical areas.
o The measurements must be linked with information which makes it possible to derive the location information.
o The measurement shall be linked to a time stamp.
o The terminal for measurements shall provide device type information, for selecting the right terminals for specific measurements.
2. Most important reasons for DT and MDT
The most important reasons for drive and driveless tests performed in the networks can be summarized below:
o Capacity optimization: The operators need to identify areas where new base stations needed. Tests can help and provide insight for better capacity planning.
o Coverage optimization: Tests can help identify weak coverage areas, interference, overshooting, uplink coverage issues, coverage holes.
o Mobility optimization: The mobile devices try to handover to different cells under certain circumstances. It is critical to minimize any kind of handover failures in a mobile network. The tests provide useful information regarding the source and target cells and measurement levels under which the failures occurred.
o QoS verification: QoS is related with delay, service response time, data rate and packet loss. QoS usually measured through KPIs and can be identified through the tests process.
3. Disadvantages of drive testing
The main shortcomings related with the drive tests can be summarized below:
o Extended human effort needed in order to collect measurement data.
o Long time for testing needed. The vehicles should cover long distance in order to get the measurements needed. This approach is time consuming.
o High volume of data. During the drive tests the measurement logs should be downloaded from measurements devices and uploaded for processing. The amount of data needed is very high.
o Sampling limitation. There are specific cases where we cannot reproduce possible drops or failures. There might be issues that the drive test could not catch.
o Indoor issues. Even if there are indoor walk test solutions, the accuracy provided is not so high.
o High cost. The drive test solution is costly as we need to consider the buy/rent of vehicles, vehicles maintenance and fuels cost.
However, there are very specific reason making the drive tests very important. In below cases the drive testing is recommended:
o New sites build, where we need to investigate the general performance of the sites
o When a new technology or frequency introduced to the network, usually the users have not the most updated mobile devices. In these cases, we can test the new frequencies using dedicated UE devices for this.
4. Advantages of MDT
There are many advantages of MDT solution and some of them summarized below:
o Accuracy: less than 10m accuracy in outdoor environment. Plain GPS data with high precision
o Simplicity: no use of special terminal or probes
o Convenience: effective methodology for drive test minimization
o Short lead time: data are collected fast and available for analysis
o Statistical relevance of georeferenced data
o Flexibility: graphical reports, plots and data available to optimization engineers in order to identify proper operation of the network
o No Impact on User Plan data throughput or extra billing for final user
5. Positioning information source
There are two MDT functionalities:
a. Immediate MDT: MDT functionality involving measurements performed by the UE in CONNECTED state and reporting of the measurements to eNB/RNC available at the time of reporting condition as well as measurements by the network for MDT purposes.
b. Logged MDT: MDT functionality involving measurement logging by UE in IDLE mode, CELL_PCH and URA_PCH states (when UE is in UTRA) for reporting to eNB/RNC at a later point in time.
6. Comparison of MDT alternatives
The table below can give us a very good overview of the use of MDT solutions in comparison with classical drive test, probe and common geolocation solutions:
Figure 2: Comparison MDT alternatives
Figure 3: Geolocation and MDT solutions
7. Potential for Operators, telecommunication companies and vendors
There are many potentials related with the use of MDT for operators, vendors and telecommunication companies. Using MDT solutions, the drive tests can be replaced or at least reduced. The coverage analysis can be more detailed and areas for capacity upgrades can be faster identified. Issues related even to specific users can be tracked and detailed solutions and troubleshooting can be provided.
8. What’s next
The MDT solutions expected to be improved the following years based on the following considerations:
o 5G deployment
o Additional information reporting from UEs like temperature, humidity, thermal noise etc. Nowadays the UE devices have multiple sensors.
o Improvement of GPS penetration
o Faster and more reliable measurements at UE devices. The quality of the UE devices is improved which means that the data provided will be more accurate, reliable while the time needed for data collection will be decreased.