Over-the-Air Performance Measurements of LTE MIMO
Terminals
John Åsberg, Charlie Orlenius
charlie.orlenius@bluetest.se
Bluetest AB, Gothenburg, SWEDEN
October 2011
© Bluetest AB
Outline
Who’s Bluetest?
Intro: Over-the-Air testing and MIMO
Reverberation chamber
Examples
–
–
–
–
–
SISO vs MIMO
Efficiency
Correlation
Drive test comparison
Noise interference
Conclusions
© Bluetest AB
Bluetest Background
Started in 2001 with the vision to
perform antenna testing
– Fast
– Easy
– Cost effectively
Antenna measurements based on
reverberation chamber technology
Patent protected solutions
Today:
– Measurement systems spread worldwide
– Used by main mobile phone
manufacturers
– World’s first active MIMO/LTE OTA
solution (2009)
© Bluetest AB
Base station
© Bluetest AB
Over-the-Air Testing
Traditional: Single antenna efficiency
Multipath emulation: Complete device test not only antenna
Requires multipath
scattering environment for
enhanced performance
Test environments
replicating real-use
environment
Base station
Indoor environment
© Bluetest AB
Multipath Creation in Lab Environment
Idea: Place unit in multipath field –
how well does it perform?
Create multipath
– Statistically (reverb chamber)
– Deterministically (multiple probes in
anechoic ch.)
– Synthetically (two-stage method)
DUT
* picture from 3GPP tdoc R4-112228 by Agilent
* picture from 3GPP TR 37.976 v1.5
© Bluetest AB
Reverberation Chamber – a Multipath Emulator
Received power (dB)‫‏‬
4
2
0
-2
-4
-6
-8
-10
0
0.5
1
1.5
Time
2
2.5
3
3.5
Statistical isotropic field
environment (ensemble property)
Rayleigh faded signal transmission
© Bluetest AB
Measurement Setup
Reverberation chamber
Fixed antennas
MIMO link
Measure MAC layer TPUT
during a full stirrer
sequence for a number of
power levels
Report average TPUT as a
function of average
available power
Mode stirrer
DUT
© Bluetest AB
Base Station
Alt. Measurement Setup
Fixed antennas
Reverberation chamber
SIMO link
DUT
Mode stirrer
Base Station
 Possibility of creating advanced channel delay profiles
© Bluetest AB
Channel
Emulator
Example 1: SISO/SIMO vs MIMO
© Bluetest AB
Modulation
QPSK and 64QAM
DL frequency
751 MHz (band 13)
Bandwidth
10 and 20 MHz
Example 2: RC vs Drive Test
Two antenna arrays with differing efficiency tested in
MIMO mode
Active LTE measurement setup in reverberation
chamber
Fixed MCS
Average throughput as function of available power
Drive test in live LTE network in Oslo, Norway
Adaptive modulation
Cumulative distribution of throughput values
Same grading of ”good” and ”bad” device!
Results from Bluetest-Samsung collaboration presented at EuCAP 2011
© Bluetest AB
Example 3: Better and Worse Correlation
Two external diversity antennas
provided by Sony Ericsson
– DUT C: High correlation
(intentionally bad design)
– DUT D: Lower correlation
Reverberation chamber
Fixed measurement
antennas
MIMO link
Mode stirrer
DUT antennas
Base
station
© Bluetest AB
Example 3: Better and Worse Correlation
DUT C (lower correlation,
lower efficiency) has
better throughput
performance than DUT D
The result is repeatable
Modulation
64QAM
DL frequency
2630 MHz
Bandwidth
10 MHz
© Bluetest AB
Example 4: Gain Imbalance
Gain Imbalance
– Attenuators
connected to one of
the branches of the
external antenna
Larger imbalance
gives lower
throughput
© Bluetest AB
Example 5: Noise Interference
Host laptop
computer source of
noise
– Display, hard drive
etc.
Significant effect
on USB dongle
performance
Noise effect
captured in RC
measurement
© Bluetest AB
Revisit: Measurement Method
Procedure:
Reverberation chamber
– Measure MAC layer TPUT
during a full stirrer sequence
for a number of power levels
– Report average TPUT as a
function of average available
power
– About 1 min per power level
Fixed antennas
MIMO link
Calibration:
– Measure average power
transmission
– (Tune power-delay-profile)
Mode stirrer
DUT
Simple, reliable, cost-efficient
© Bluetest AB
Base Station
Summary
Trend in community to test directly in multipath fading
environment
– Composite testing
– End-user metric (throughput)
Reverberation chamber a stable and repeatable solution for
creating multipath environment
Several examples of reverb chamber measurements,
possible to differentiate antenna configurations
– Radiation efficiency
– Antenna element decoupling (correlation)
– Gain imbalance
Noise interference important factor for USB dongle
measurements, effect captured in reverb chamber
© Bluetest AB