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Alper Akbilek, Dr. Florian Pfeiffer, Manzar Hussain
perisens GmbH
Analysis of Multi-Path Channels Using
the WLAN Packet Preamble
Analysis of Multi-Path Channels Using the WLAN Packet Preamble
Agenda
1. About perisens
2. Motivation
3. Background
4. Implementation and Results
5. Conclusion
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Agenda
1. About perisens
2. Motivation
3. Background
4. Implementation and Results
5. Conclusion
24.05.2019 Analysis of Multi-Path Channels Using the WLAN Packet Preamble 3
About perisens…
perisens GmbH
Founded in 2009 as Spin-Off from the Technical University of Munich(TUM) with ongoing cooperation
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Services
• Technical Consulting / Studies
• RF measurements & Simulations (up to 90 GHz)
• Development and Evaluation of Wireless
Communication Systems
• Signal Processing
• Development of RF Prototypes
• Solutions in Automotive Radar Sensors
Products
• In-House Development, Production and Sale of
Radar Target Simulators (RTS)
Analysis of Multi-Path Channels Using the WLAN Packet Preamble
Agenda
1. About perisens
2. Motivation
3. Background
4. Implementation and Results
5. Conclusion
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Motivation
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▪ Wifi is everywhere
▪ Higher data rates enabled by new amendments
▪ High data rates require very favorable channel
conditions
▪ Evaluating the wireless channel is required to
determine if implementing new wireless standards
(e.g IEEE 802.11ax) would bring improvement
Analysis of Multi-Path Channels Using the WLAN Packet Preamble
Goal:
Evaluating IEEE 802.11ax (Wi-Fi 6) without Commercial WLAN Hardware
▪ Matlab models allow evaluation of WLAN standards
before commercial hardware hits the market
▪ We aim to evaluate the standard for specific
environment (e.g. in-vehicle environments)
▪ Simulations and over-the-air testing with Matlab
➢ IEEE 802.11ax models are available in MATLAB WLAN
Toolbox since 2018
Timeline
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May
2014
Start
TGax
March
2016
Draft
0.1
Nov.
2016
Draft
1.0
Sept.
2017
Draft
2.0
May
2018
Draft
3.0
Jan.
2019
Draft
4.0
Jan.
2020
Final
Approval
Jun.
2020
Publication
MATLAB R2018a
802.11ax Models in WLAN Toolbox
Agenda
1. About perisens
2. Motivation
3. Background
4. Implementation and Results
5. Conclusion
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OFDM
▪ Orthogonal frequency-division multiplexing
▪ Data is transmitted over independent sub-carriers with some redundancy (channel coding)
▪ Able to cope with severe channel conditions (frequency-selective fading, narrowband interference…)
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WLAN sub-carrier distance:
IEEE 802.11a/g/n/ac: 312.5 kHz
IEEE 802.11ax : 78.125 kHz
BW: 20, 40, 80 or 160 MHz
Enabling High Throughput
Higher Modulation and Coding Schemes
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6 Bits/Symbol/Carrier
MCS 5,6,7
IEEE 802.11a/g/n
8 Bits/Symbol/Carrier
MCS 8,9
IEEE 802.11ac
10 Bits/Symbol/Carrier
MCS 10,11
IEEE 802.11ax
Analysis of Multi-Path Channels Using the WLAN Packet Preamble
Received Signal Strength
▪ Total received signal power in the channel
▪ Available at the receiver
▪ Conventional way to evaluate the link
▪ High data rates require high signal power at the receiver
▪ Signal strength is NOT the only factor determining the link speed
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Multi-Path Channel
▪ Several echoes of the signal is detected at receiver
▪ Signal power and SNR are not equally distributed in the channel
▪ Causes frequency-selective fading which increases the required SNR
▪ Sensitive to moving objects on the signal path
▪ Channel models available for IEEE 802.11 simulations
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Transmitter Receiver
time
frequency
h(t
)H
(f)
Noise floor
High SNR
Low SNR
Analysis of Multi-Path Channels Using the WLAN Packet Preamble
IEEE 802.11 Packet Preamble
Channel Estimation by HE-LTF for Equalization
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Wireless
Channel
HE-LTF at TX HE-LTF at RX
Channel State
Information
(CSI)
Analysis of Multi-Path Channels Using the WLAN Packet Preamble
Agenda
1. About perisens
2. Motivation
3. Background
4. Implementation and Results
5. Conclusion
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WLAN PHY Simulations in MATLAB
▪ Simulation loop is already included in MATLAB
WLAN Toolbox
▪ IEEE channel models available for example
scenarios (small office, conference room etc.)
▪ Output: SNR requirement for a definite WLAN
packet format
▪ We use simulations for link budget calculations for
specific scenarios in which the path loss is known
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IEEE802.11
Baseband
Waveform Creation
TX bits
Channel Model
Synchronization,
Equalization and
Demodulation
RX bits
Baseband IQ
(TX)
Baseband IQ
(RX)
Packet Error
Rate (PER)
Opening the Simulation Loop
Measurements Over the Air
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▪ Sending WLAN packets over the RF channel
▪ Evaluate the real wireless channel
▪ Requires RF instruments or Software-Defined-Radios
(SDRs) as TX and RX
▪ Can measure the PER for a definite packet type
▪ Drawback: Long measurement time
Analysis of Multi-Path Channels Using the WLAN Packet Preamble
IEEE802.11
Baseband
Waveform Creation
TX bits
Channel Model
Synchronization,
Equalization and
Demodulation
Baseband IQ
(TX)
Baseband IQ
(RX)
RX bits
Packet Error
Rate (PER)
IEEE802.11
Baseband
Waveform Creation
TX bits
Synchronization,
Equalization and
Demodulation
RX bits
RF Signal
over the air
Channel Sounding
Extracting the Channel State Information (CSI)
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▪ Instead of making PER measurements, we only
extract the Channel State Information (CSI) and signal
power
▪ We collect several CSI samples to use in simulations
▪ Packet type & modulation are varied in simulations to
determine the highest achievable data rates
Analysis of Multi-Path Channels Using the WLAN Packet Preamble
Baseband IQ
(TX)
IEEE802.11
Baseband
Waveform Creation
Synchronization,
Equalization and
Demodulation
Channel State Information (CSI)
RF Signal
over the air
Channel Sounding Method
Using the CSI in Simulations
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Channel State Information
Extraction
Analysis of Multi-Path Channels Using the WLAN Packet Preamble
IEEE802.11
Baseband
Waveform Creation
Baseband IQ
(TX)
RF Signal
over the air
Synchronization,
Equalization and
Demodulation
IEEE802.11
Baseband
Waveform Creation
Multiplication
in
frequency domain
AWGN
channel
simulation
Synchronization,
Equalization and
Demodulation
RX bitsTX bits
Packet Error
Rate (PER)
Baseband IQ
(RX)
Channel State Information
Channel Frequency Response & Error Vector Magnitude (EVM)
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Simulation using
the measured
channel response
EVM threshold
for 1024-QAM:
-35 dB
Channel Sounding with WLAN Packets
Measurement Setup
▪ Measurement in a closed room
▪ IEEE 802.11ax waveforms generated in MATLAB
▪ First transmission with line of sight channel
➢ Measured path loss: 53 dB
▪ Second transmission with non line of sight channel
➢ Measured path loss: 59 dB
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TX
RX
Line of sight
distance:
4.3m
BLOCK
Channel Sounding with WLAN Packets
Measurement Setup
▪ Measurement in a closed room
▪ IEEE 802.11ax waveforms generated in MATLAB
▪ First transmission with line of sight channel
➢ Measured path loss: 53 dB
▪ Second transmission with non line of sight channel
➢ Measured path loss: 59 dB
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TX
RX
BLOCK
Channel Sounding with WLAN Packets
Results
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Amplitude variation in the
line of sight (LOS) channel:
6 dB
Amplitude variation in the
non line of sight (NLOS) channel:
28 dB
Simulation Using the LoS and NLoS Channel Responses
Results
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~8 dB
Agenda
1. About perisens
2. Motivation
3. Background
4. Implementation and Results
5. Conclusion
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Conclusion
Summary
▪ New wireless standards can be evaluated with MATLAB before the hardware hits the market
▪ Wireless channels can be analyzed using the WLAN signals
▪ Energy is not evenly distributed in a non line of sight (NLOS) channel
▪ Receiver needs higher signal power to decode the signal in NLOS scenarios
▪ The channel state information (CSI) changes if there are moving objects in the room
Future Work
▪ Other applications using the channel state information (CSI) of WLAN signals:
➢ Human presece detection
➢ Vital signal monitoring (breathing & heart rate)
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