mm-wave communication: ~30 - 300ghz recent release of ... · • ieee 802.11ad: ratified in 2013...
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• mm-Wave communication: ~30 - 300GHz
• Recent release of unlicensed mm-Wave spectrum − Frequency: 57 – 66 GHz (4.7 to 5.3mm wavelength)
− Bandwidth: 7 - 9 GHz (depending on region)
− Current Wi-Fi Frequencies: 2.4 GHz (100 MHz) and 5 GHz (555 MHz)
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10x times as much frequency spectrum available at mm-Wave frequencies than currently used for Wi-Fi.
2.4 5 57-66 (GHz)
• Free-space attenuation: 20-40 dB higher than on Wi-Fi frequencies
• Blockage: concrete and other materials cause very high attenuation
• Directional antennas to overcome limited range
• Signal energy is focused into direction of receiver
• Antenna size correlates with wavelength small form factor, many antennas
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Very directional communication improves spatial reuse
Phased Antenna Array
• Current Systems: Proprietary or not Wi-Fi capable − WirelessHD/WiGig
− Mobile backhaul links
• IEEE 802.11ad: ratified in 2013 − Throughput up to 7 Gbps (current Wi-Fi
~0.6 Gbps)
− Commercial devices under development (Qualcom, Intel, …)
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Wi-Fi about to take the step to mm-Wave frequencies, increasing throughput by a factor of 10.
• Attenuation: beam forming
• Mobility: beam tracking, retraining
• Blockage: relaying, communication using reflections
• Directional medium access
• Spectrum reuse: centralized scheduling of parallel transmissions
• Focus of this talk: beam steering
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Dynamic Nodes Require Antenna Focus Adjustment − IEEE 802.11ad devices have “sector” antennas
(e.g, phased antenna array)
− Up to 128 sectors per devices (3° beam width)
− First generation devices: 2 to 16
− Strongest Sector: Corresponds to direct path when unblocked (LOS)
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Two Stage Beam Training Process
− Sector Level Sweep (SLS): Coarse grained sector selection
− Receiver uses “quasi omni-directional” antenna pattern
− Beam Refinement Phase (BRP): Fine grained sector selection and receive sector selection
− One frame to probe multiple sectors
− Coarse grained direction must be known
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Two Stage Beam Training Process
− Sector Level Sweep (SLS): Coarse grained sector selection
− Receiver uses “quasi omni-directional” antenna pattern
− Beam Refinement Phase (BRP): Fine grained sector selection and receive sector selection
− One frame to probe multiple sectors
− Coarse grained direction must be known
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Two Stage Beam Training Process
− Sector Level Sweep (SLS): Coarse grained sector selection
− Receiver uses “quasi omni-directional” antenna pattern
− Beam Refinement Phase (BRP): Fine grained sector selection and receive sector selection
− One frame to probe multiple sectors
− Coarse grained direction must be known
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Two Stage Beam Training Process
− Sector Level Sweep (SLS): Coarse grained sector selection
− Receiver uses “quasi omni-directional” antenna pattern
− Beam Refinement Phase (BRP): Fine grained sector selection and receive sector selection
− One frame to probe multiple sectors
− Coarse grained direction must be known
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Two Stage Beam Training Process
− Sector Level Sweep (SLS): Coarse grained sector selection
− Receiver uses “quasi omni-directional” antenna pattern
− Beam Refinement Phase (BRP): Fine grained sector selection and receive sector selection
− One frame to probe multiple sectors
− Coarse grained direction must be known
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Two Stage Beam Training Process
− Sector Level Sweep (SLS): Coarse grained sector selection
− Receiver uses “quasi omni-directional” antenna pattern
− Beam Refinement Phase (BRP): Fine grained sector selection and receive sector selection
− One frame to probe multiple sectors
− Coarse grained direction must be known
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Two Stage Beam Training Process
− Sector Level Sweep (SLS): Coarse grained sector selection
− Receiver uses “quasi omni-directional” antenna pattern
− Beam Refinement Phase (BRP): Fine grained sector selection and receive sector selection
− One frame to probe multiple sectors
− Coarse grained direction must be known
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Two Stage Beam Training Process
− Sector Level Sweep (SLS): Coarse grained sector selection
− Receiver uses “quasi omni-directional” antenna pattern
− Beam Refinement Phase (BRP): Fine grained sector selection and receive sector selection
− One frame to probe multiple sectors
− Coarse grained direction must be known
• High Gain Devices Increase Overhead − Maximum Link Setup Overhead: 5.3ms (128 Sectors at both
devices, 3 BRP iterations)
− Overhead scales with number of nodes
• Mobility requires readjustment of antenna direction − Small misalignments can be corrected efficiently (Beam
Tracking/ BRP)
− Otherwise full retraining has to be done
• Misalignment depends on type of movement − Linear motion creates small misalignment
− Rotation easily breaks link (handheld devices)
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Beam forming training overhead for IEEE 802.11ad networks is a problem for more complex scenarios.
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Detect Incidence Angle of a Signal Using Multiple Receive Antennas
− Received phase difference at multiple antennas reveals path length
− Known antenna geometry allows to infer angle
1 2
λ/2
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Antenna 1
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X2 Antenna 2
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Detect Incidence Angle of a Signal Using Multiple Receive Antennas
− Received phase difference at multiple antennas reveals path length
− Known antenna geometry allows to infer angle
1 2 Θ=47°
BUT: Omni-directional signal needed!
Does not work with 802.11ad
• APs will almost always be multi-band
− Seamless fast session transfer from 60Ghz to lower frequency is part of the standard
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Use Angle of Arrival below 6 GHz to guide highly directional mm-Wave communication
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Omni-Directional N Antenna Array
Directional mm-Wave Antenna Array
Application Band
Detection Band Signal Samples
AoA Antenna Geometry
Legacy 802.11ac/n
802.11ad Request Sector
Sector ID
BBS
• Challenges to be Addressed
−Multipath on detection band
− Prevent beam steering on blocked direct path
−Minimize in-band sector refinement
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− Multiple signal energy peaks detected
− Main energy received on direct path
− Paths can interfere
AoA Spectrum
AoA Techniques Classify Signal Energy to Incidence Angle
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Detect Location Dependent Strong Multipath − Peak to average ratio reveals multipath strength
− Discard direction estimates with low peak to average ratio
Low Multipath Deviation High Multipath Deviation
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Less attenuation below 6 GHz compared to mm-Wave Frequencies
− Angle of arrival detection can lock on a blocked path
− Beam is steered into obstacle
− Discard direction estimates with low peak to average ratio
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Less attenuation below 6 GHz compared to mm-Wave Frequencies
− Angle of arrival detection can lock on a blocked path
− Beam is steered into obstacle
− Fall back to legacy beam training
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Estimated direct path can be inaccurate due to noise and multipath
− Direct path estimate substitutes coarse grained SLS
− Perform BRP phase on sectors around direct path estimate
AoA Estimate
Sectors for in-band refinement
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Estimated direct path can be inaccurate due to noise and multipath
− Direct path estimate substitutes coarse grained SLS
− Perform BRP phase on sectors around direct path estimate
AoA Estimate
Sectors for in-band refinement
How many sectors
need to be checked?
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Angular spread of the direct path peak correlates with precision of the estimate
− Wide spread indicates more sectors for refinement
− Scale factor to tune for high reliability or low overhead
Direction Estimate
Angular Spread
Direction Estimate
Angular Spread
Application Band
− Received signal power measurement at 62.64 GHz
− Bandwidth: 15 MHz
− Beamwidth: 80, 20 and 7 degree (5, 18 and 52 sectors)
− Rotating device to emulate sector sweeps
Mm-Wave Application Band Programmable
Rotation Table
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Detection Band
− WARP based AoA detection
− Antennas: 8 physical antennas, vary from 4-8 by data post processing
− AoA Aggregation: 50 AoA profiles
− AoA profile averaged over 192 samples
AoA Detection Band
WARP boards
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− Meeting Room: Clear direct path
− Measurement Locations:
− Fixed receiver
− Seven transmitter locations
− Maximum/Minimum distance: 1.5m/9m
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On average 97.8% accuracy over all transmitter locations
− Corresponds to 4° deviation
− Assuming at least 5 antennas
− Accuracy is location dependent (different multi-path environments)
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Discarding strongly deviated estimates by AoA peak to average ratio.
− Peak to average threshold of 4
(Reject estimates below 95% accuracy)
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− Two locations 1.5 and 9 meters
− Four obstacle types
− Desktop Computer
− Monitor
− Wooden Board (1.8cm)
− Human
Blockage
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− Peak to average ratio averaged over both locations
− Threshold of 4 to classify between blocked and unblocked direct path
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Strategy
− Scaling factor chosen to ensure optimum sector in refinement set
− Assuming correlation between number of antennas and number of sectors
AoA Estimate
Sector Refinement Set
Angular Spread
Detection Antennas
Application Sector Width
8 7°
6 20°
5 80°
• BBS overhead reduction given required number of refinement sectors to find optimum sector
• Overhead reduction of 81%, 68%, 100% for beamwidths of 7, 20, 80 degrees − No refinement necessary in most cases
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In-Band Sector Refinement
7 Degree 802.11ad SLS+BRP time = 1.54ms
20 Degree 802.11ad SLS+BRP time = 0.88ms
80 Degree 802.11ad SLS+BRP time = 0.63ms
BBS(ms) Time Reduced (ms)
% Reduction
BBS(ms)
Time Reduced (ms)
% Reduction
BBS(ms)
Time Reduced (ms)
% Reduction
0 0 1.54 100 0 0.88 100 0 0.63 100
2 0.28 1.26 81.42 0.28 0.6 67.55 0.28 0.35 54.66
4 0.29 1.25 81.03 0.29 0.59 67.21 0.29 0.34 53.72
10 0.31 1.23 79.87 0.31 0.57 64.85 - - -
20 0.34 1.20 77.94 - - - - - -
• Extremely promising area, data rates of tens of Gbit/s with very high spatial reuse − In the future: 300 GHz to THz systems
− Related area: visible light communication
• Conventional wireless network paradigms don’t work well − IEEE 802.11ad inefficiencies due to “802.11 compatible” design
• Rich field for new research
• Requires much closer collaboration of PHY layer and higher layer research
Looking for PhD students and engineers to work on this
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