Do we need drive test in LTE?
In Long Term Evolution (LTE), as with other cellular technologies, drive testing is a part of the network
deployment and management life cycle from the early onset. Drive testing provides an accurate real-world
capture of the RF environment under a particular set of network and environmental conditions. The main
benefit of drive testing is that it measures the actual network coverage and performance that a user on the
actual drive route would experience. It is argued that in today’s networks with modern simulations, network
engineers can mathematically model how a network will perform. While this is true to a certain extent, it
is also essential to conduct drive testing as network parameter settings alter how the user equipment (UE)
interacts and deals with the network environment. Such interactions cannot be wholly predicted through
mathematical modeling. Figure 1 shows how drive test is used in the network planning life cycle.
Components of a Drive Test System
Drive test systems are generally built around two measurement components, instrumented mobile phones (test
engineering phones) and measurement receivers. Each component has its own characteristics with associated
benefits and drawbacks. Phone-based systems can respond to problems within network-controlled constraints.
Receiver-based systems give a complete overview of RF activity but cannot duplicate network-related problems.
These measurement devices are controlled with data-logging software on a laptop PC together with a global
positioning system (GPS) to provide geo-location of the collected data. The collected data can be analyzed using
software that allows for plotting the results on digital maps enabling visualization of the RF environment.
The measurements carried out during drive testing have evolved over time — from the early days when
the focus was purely on parametric RF measurements to the wide variety of application-based data performance measurements integrated into modern drive test systems. Many of these changes have been driven
by the change in services provided from a simple voice carrier to the multi-service, data-centric wireless
networks that LTE intends to enable. Network operators have shifted their focus from purely measuring RF
performance to measuring customer experience, and this has driven the integration of many data application tests such as video streaming and voice over IP (VoIP) into drive test systems so that engineers can
correlate end-user application performance with detailed RF measurements. With LTE, many of the measurements themselves have had to adjust to take into account the much higher data rates that LTE provides.
Another evolution is the move from single-band single-technology networks to multi-band multi-technology networks. LTE is not going to exist as an island technology, but will be overlaid and integrated with
the existing universal mobile telecommunications system/high-speed packet access (UMTS/HSPA) and
third-generation code-division multiple access (cdma2000) 1xRTT and high-rate packet data (HRPD) 1x
Evolution-Data Only (1xEV-DO) networks. Drive test tools need to embrace this multi-technology multiband environment. An area of key interest to cellular operators will be the interaction of LTE with their
existing infrastructure and, in particular, the crossover points where handovers take place.
Importance of Drive Test for LTE
Many different strategies and methods to monitor network performance have been described. Network
“probing” in which the signaling traffic is monitored at control points and then centrally analyzed can
provide valuable insights into the overall network health. This strategy works well where, as in Global
System for Mobile Communications (GSM) and UMTS networks, much of the control traffic is consolidated through radio network controllers (RNCs) or base station controllers (BSCs) so that by monitoring
relatively few major interfaces, a good view of a wide range of base station end-points can be obtained.
As the industry has moved ahead with HSPA and now LTE technologies, more and more of the network
intelligence has moved out from the core to the edge of the network and into the E-UTRAN Node Bs
(eNBs), also taking the traffic management toward the network edge (see Figure 2). This means that
much of the control and decision making is now deployed within the eNBs, and interaction between the
UE and base stations can be most effectively monitored by instrumented phones involved in the actual transactions. This move of the decision point in traffic management has been needed to realize the
reduced latency requirements for LTE performance — signaling control traffic no longer has to traverse
multiple network nodes when a change is made for a UE.
While the name “drive test” comes from the fact that the measurement equipment is generally “driven” in
a vehicle, we should also mention that measuring indoor coverage is becoming increasingly important.
Indoor performance measurements do not rely on views of the sky nor GPS for positional information. Instead, users indicate their measurement location on a scanned floor plan of the building using a
point-and-click navigation method. The logging software allows for true geo-location of a corner of the
floor plan so that the indoor results can be combined with the outdoor results in the final overall analysis. The considerable increase in the processing power available on smartphones has led to the creation
of handheld drive test devices that can be used when extreme portability takes priority over depth of
functionality. Handheld devices lend themselves very well to indoor measurement environments where
discretion of collection is also a factor. The range of measurements on a handheld device is as extensive as
on a full drive test system and data may be analyzed and amalgamated in post-processing.
Drive Test Solutions for LTE
Comprehensive drive test systems such as the JDSU E6474A Wireless Network Optimization Platform
address the challenges of optimizing LTE network performance by quickly and accurately identifying
problems. The E6474A system shown in Figure 7 can be used in spectrum clearing, site evaluation, cluster and initial optimization, system acceptance, and ongoing optimization and troubleshooting. The
system can be scaled from a single phone-based solution to a multi-phone, multi-technology receiver
and phone combined system covering all the major technologies that are deployed in wireless networks
worldwide: LTE, HSPA, UMTS, GSM, general packet radio service (GPRS), enhanced data rates for
global evolution (EDGE), 1xEV DO, cdma2000, time-division synchronous code-division multiple
access (TD-SCDMA), integrated digital enhanced network (iDEN), and worldwide interoperability
for mobile access (WiMAX). The system also encompasses a wide range of application tests including
TCP/UDP, messaging, analog and VoIP testing, web-oriented, and video streaming components and is
designed for both indoor and outdoor use.
Figure 7. JDSU E6474A Drive Test System for network planning, deployment, and maintenance
With the flexibility to combine multiple phones and the JDSU multi-band multi-technology receiver, this
drive test system lets users measure multiple technologies simultaneously with a single computer. The
unique graphical data test sequencer facilitates construction of a range of end-user scenarios to simplify
network optimization and to determine a customer’s quality of service.
To simplify configuration and reduce costs, the JDSU W1314A Measurement Receiver used in the
E6474A Drive Test System can measure up to eight frequency bands in a single drive, allowing verification
of multi-band multi-technology coverage using a single piece of measurement hardware. Powerful digital
signal processing (DSP) technology allows for software upgrades to keep the measurements current as the
JDSU has a range of smartphone-based drive test solutions that seamlessly integrate with the full laptop
solution for in-depth analysis where extreme portability and ease of use are paramount considerations.