1. Testing Wireless Devices and Systems Part II: R&D Test
10-July-2012
Fanny Mlinarsky
octoScope, Inc.

2. Open Air vs. Controlled RF Environment Measurements
Variability from test to test due to noise and interference
Throughput (frames per sec)
Stable, repeatable results in the controlled RF environment

3. Controlled Environment Conducted Test
Signal coupled via cabling, antennas are removed
Feed-through filters
Ethernet
USB
RF isolation box
Programmable attenuator
Master and DUT are isolated from each other to achieve wide dynamic range of the measurement by eliminating crosstalk
Distance and motion emulated using a programmable attenuator to model path loss (flat fading) or a channel emulator to model multipath and Doppler fading

4. Controlled Environment Measurement Example
Wi-Fi DUT’s data rate adaptation behavior vs. RSSI all the way down to the RSSI level of -95 dBm.
Data rate adaptation
vs.
Noise, interference and Master to DUT coupling must be well below intended signal level at DUT for metrics such as rate/MCS adaptation or roaming performance
Measured DUT RSSI is less than -95 dBm. This means Master to DUT coupling of less than -100 dBm.
802.11b (DSSS-CCK)
– 1, 2, 5.5, 11 Mbps; 2.4 GHz
802.11a (OFDM)
– 6, 9, 12, 18, 24, 36, 48, 54 Mbps; 5 GHz
802.11g
– both 11b and 11a rates; 2.4 GHz
802.11n
– up to 600 Mbps; 2.4 and 5 GHz
RSSI
MCS = modulation coding scheme
DUT = device under test
RSSI = receive signal strength indicator

5. Radio Performance Testing
RX sensitivity
TX spectrum, EVM
Range
Adaptive Modulation
Roaming behavior
Performance in the presence of noise and interference
Master
Isolation box
Noise/interference generator
Variable RF attenuator
RF combiner
DUT
DUT = device under test
EVM = error vector magnitude

6. Transmitter Tests EVM – constellation plots 802.11n 4x4 MIMO TX
Source: National Instruments WLAN Toolkit
EVM – constellation plots
802.11n 4x4 MIMO TX
OFDM spectrum plots
802.11n 4x4 MIMO TX
Test equipment: VSA, spectrum analyzer
VSA = vector signal analyzer
OFDM = orthogonal frequency division multiplexing

7. RX Sensitivity Test Setup - Example
Agilent N4010A
LDA-602 Programmable Attenuator w/20dB pad
RF (-20dBm)
Windows PC
LabVIEW
33dB total RF cable losses when Attenuator = 0dB
USB
DUT
Conducted connection shown; OTA connection also possible in the octoBox via antenna on the bottom
Linux Host PC with Wireshark Sniffer
USB
octoScope’s octoBox

8. Handset Test Configuration - Example
Source: 3GPP
EMMI
USB
System
Simulator SS
DUT UE RX TX
UE DUT TX RX
Anritsu MT8820C eNB emulator
MM/CC/SM TC TC
MM/CC/SM
MM = mobility management
CC = call control
SM = session management
TC = test control
RRC = radio resource control
RLC = radio link control
MAC = medium access control
PHY = physical layer
UE = user equipment (handset)
DUT = device under test
SS = system simulator (base station emulator)
EMMI = Electrical Man Machine Interface
eNB = enhanced Node B (LTE base station)
RLC
RLC
MAC
MAC
PHY
PHY UE
SS (eNB emulator)

9. Handset Test Protocol and PHY Layers
eNB emulator (call box)
Test script libraries, TTCN-3
Protocol Software
MAC, RLC, MM, CC, SM, TC Layers
Baseband signal generator
Interference and spectrum tests (e.g. blocking, spurious, etc.)
Baseband signal analyzer
Interference and noise generator
Channel emulator
RF Spectrum Analyzer
RF combiner
RF VSA
RF VSG
VSA = vector signal analyzer
VSG = vector signal generator
MAC = medium access control
RLC = radio link control
MM = mobility management
CC = call control
SM = session management
TC = test control
Wi-Fi AP/AP emulator
TTCN = testing and test control notation
UE = user equipment
eNB = enhanced node B
PHY = physical layer

10. Wireless Channel Multipath clusters Composite angular spread
Per path angular spread
Composite angular spread
Line of sight
Multipath and Doppler fading in the channel

11. Wireless Channel … Frequency and time variable wireless channel
Multipath creates a sum of multiple versions of the TX signal at the RX
Frequency …
Channel Quality
Frequency-variable channel appears flat over the narrow band of an OFDM subcarrier.
OFDM = orthogonal frequency division multiplexing

12. MIMO Systems
MIMO systems are typically described as NxM, where N is the number of transmitters and M is the number of receivers. TX RX
2x2
MIMO radio channel
2x2 radio
MIMO = multiple input multiple output

13. MIMO Based RX and TX Diversity
When 2 receivers are available in a MIMO radio MRC can be used to combine signals from two or more antennas, improving SNR
MIMO also enables transmit diversity techniques, including CDD, STBC, SFBC
TX diversity spreads the signal creating artificial multipath to decorrelate signals from different transmitters so as to optimize signal reception
Peak
Null
A MIMO device with multiple radios can implement transmit diversity in addition to receive diversity. Receive diversity on a MIMO device can also more sophisticated than on a single-radio device because the complete packet and not just preamble can be received by multiple receivers and then the receive source can be selected based on signal quality or by combining multiple received signals. This technique is known as maximal ratio combining (MRC).
One can think of receive diversity as analogous to having two ears and transmit diversity as analogous to having two mouths. Transmit diversity techniques aim to produce multiple versions of the same signal and they are specifically designed to carefully control the relationship of these multiple versions of the signal so as to optimize signal reception.
Transmit and receive diversity techniques can be used independently or together.
When channel conditions allow, MIMO radios can also use spatial multiplexing whereby multiple radios are used to transmit more than one simultaneous data stream thereby multiplying the capacity of the airlink.
MIMO = multiple input multiple output
SIMO = single input multiple outputs
SM = spatial multiplexing
SFBC = space frequency block coding
STBC = space time block coding
CDD = cyclic delay diversity
MRC = maximal ratio combining
SM = Spatial Multiplexing
SNR = signal to noise ratio
Delay is inside the TX

14. Wireless Channel Emulator
Used to emulate multipath and Doppler fading in order to test radio performance and adaptive behavior
Azimuth ACE channel emulator
4x4 MIMO
Controlled programmable channel conditions
Multipath
Doppler
Noise
Channel Emulator

15. Conducted vs. OTA Conducted OTA Antenna field To antenna port
Repeatable measurements, but antennas are not included in the test; impractical to disconnect antennas for measurement in devices like smartphones and consumer electronics
Antenna field
All energy couples into the coax
Energy propagates in 3 dimensions
To antenna port
Coaxial cabling
Antennas are included in the test and small devices with printed antennas can be measured through antennas, but the test set up requires controlled conditions to support 3D OTA metrics. Signal power and integrity at test antennas varies with DUT orientation, reflections and interference.
OTA = over the air
DUT = device under test
OTA = over the air
DUT = device under test

16. RF Anechoic Chamber for OTA coupling
Isolation
Prevents errors caused by noise and by crosstalk between Master and DUT
Absorption
Eliminates standing waves that cause nulls in the signal
Nulls result in high power gradients vs. antenna position
Cross-section view of octoBox Stackable
Standing waves create fluctuations in the signal
Absorptive foam with layers of gradient impedance dampens signal fluctuations by attenuating standing waves

17. Wireless Mesh Testing - Example
PC in open air #2 #2
Console
bc:77:37:ab:33:5d
Antenna
bc:77:37:ab:33:5d #1
94:39:e5:01:3d:62
94:39:e5:01:68:ed #3
RF Attenuator
octoBox
RF Switch
RF Combiner #1
USB cable going through data filter to control Pingblaster running on #3 #3
Ping request - response traffic #2
94:39:e5:01:3d:62
94:39:e5:01:68:ed
octoBox upper chamber #1
octoBox lower chamber #3

18. Delay Through Mesh One hop Ping round trip delay (ms) Seconds
bc:77:37:ab:33:5d
Ping round trip delay (ms)
94:39:e5:01:3d:62
94:39:e5:01:68:ed
~ 12 msec delay with bursts of long delays (>1 seconds)
~ 2 msec delay
Seconds
bc:77:37:ab:33:5d
94:39:e5:01:3d:62
94:39:e5:01:68:ed
BATMAN = better approach to mobile ad hoc networking
Zero hops

19. Wireless Mesh Testing Measure
Self-healing, self-forming
Throughput, QoS vs. hops
Throughput, QoS vs. range
Routing efficiency
Dealing with interference
Consider using multi-radio mesh nodes to communicate on different channels with multiple neighbors simultaneously
Throughput is cut in half per hop in a single-channel mesh

20. Testing Networking Layers
Voice, video, security based performance testing
Wireless Device
Traffic emulation based measurement of throughput, latency and jitter
Mesh testing (routing, self-forming, self healing)
Roaming performance
Upper layers (IP, applications, etc.)
MAC
Control and management
Baseband
RF front end
TX spectrum
RX sensitivity
Automatic MCS selection vs. channel emulation and vs. path loss
MCS = modulation coding scheme
MAC = medium access control

21. Other Testing Beyond Radio
Voice, video and data performance
IETF RFC 2285, 2544, 2889 (throughput, packet loss, latency, jitter);
ITU-T P.800, P.862, G.107 (voice quality)
IETF RFC 4445 (video quality)
AP/BS handling of data load; association capacity
QoS
Security
Regulatory compliance
AP = access point
BS = base station
QoS = quality of service

22. Please see more info and white papers at www.octoscope.com
Next Session
Part III: Quality Assurance Test
When: April 11th at 2 p.m.
Thank you!
Please see more info and white papers at