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

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

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

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

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

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

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

Handset Test Configuration - Example Source: 3GPP 34.109 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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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 www.octoscope.com