Minimization of Drive Tests (MDT) in 3GPP Release-10

Another one that came from the SON conference.

At present, the network optimisation after it is operational is generally done by drive testing. In this an equipment (test mobile) that collects measurements and location information collects all the required information while the equipment is being driven in a car on the roads and this information is used offline to analyse the coverage in different locations and based on that the parameters, power, antenna locations, antenna tilts, etc. are optimised. After the changes to any of the optimisation paramaters, drive test has to be undertaken again to make sure that the impact of these changes are positive.

One more thing that has to be taken account of is that the drive tests have to be carried out at di9ffert times to be able to predeict the behaviour at different loads.

Using drive tests for network optimization purposes is costly and causes also additional CO2 emissions, so it is desirable to develop automated solutions, including involving UEs in the field, in 3GPP to reduce the operator costs for network deployment and operation. The studies done as part of the study item phase [1] have shown that it is beneficial to collect UE measurements to enable a more efficient network optimisation and it is feasible to use control plane solutions to acquire the information from devices. This information, together with information available in the radio access network can be used for Coverage Optimization purposes.

It should be remembered that drive tests form a big part of the Network opex and Deutsche Telekom for example expects a 40% cost saving with SON (and MDT is a part of that)

Goal of MDT in 3GPP Rel.10

– Automatic UE measurements collection and data logging used to replace the manual drive testing that the operators have to perform in their networks

– Evaluation of network performance per physical location

– For both HSPA & LTE

There are two different types of MDT:

Immediate MDT: MDT functionality involving measurement performance by UE in CONNECTED state and reporting of the measurements to eNB/RNC available at the time of reporting condition.

Logged MDT: MDT functionality involving measurement performance by UE in IDLE state at points in time when configured conditions are satisfied, its storage in measurement log for reporting to eNB/RNC at a later point in time.

The solutions for MDT shall be able to work independently from SON support in the network. Relation between measurements/solution for MDT and UE side SON functions shall be established in a way that re-use of functions is achieved where possible.

• Use cases

– 3GPP R10: Coverage optimization : Prio1

– For 3GPP > R10 :Capacity optimization, Mobility optimization, Parameterization of common channels, QoS verification, no specific measurements

- In Release-11 MDT Enhancements and evaluation of other MDT use cases, such as ”Parameterization of common control channels” and Positioning enhancements will be explored.

• MDT and SON

– MDT is about UE measurement collection for off-line processing No automatic mechanism is defined MDT

– SON is aiming at instantaneous/automated reaction on short to middle term network issues

It should be noted that MDT is a wide area and some of the boundaries between MDT and SON are a bit fuzzy. One of the other ways for SON is to enable detected cell measurements in the handset. This will give the indication about the cells that are not in the monitored set but the UE is able to see.

The RRC (control plane) measurements for LTE are not advanced enough and there are no measurements for UE position. On the other hand for UMTS/HSPA the UE positioning measurements could be used to report the exact location at the point of measurements. There are some discussions for enhancing the LTE measurements to include the longitude, latitude, altitude, velocity and even direction (too ambitious?).

Finally it should be pointed out that UE based reporting based on the User Plane Measurements (typically done by the operator installing a small application on the handset) can be performed by the operator in case a user is reporting poor coverage or failure in an area. Since these are proprietary applications, the operator can collect variety of information including but not limited to, position information, crrent cell and neighbour cell power levels, etc.

With all the control plane measurements and user plane measurements, the battery life could be severely affected and it has to be made sure that these are done very seldomly or with users permission.

Some of the things mentioned above may not be exactly true and if you know better please feel free to correct me.

[1] 3GPP TR 36.805 - Study on Minimization of drive-tests in Next Generation Networks

[2] 3GPP TS 37.320 - Universal Terrestrial Radio Access (UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRA); Radio measurement collection for Minimization of Drive Tests (MDT); Overall description; Stage 2 (Release 10)