mm-wave communication: ~30 - 300ghz recent release of ... · • ieee 802.11ad: ratified in 2013...

• 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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• 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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Q X1

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



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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mm-wave communication: ~30 - 300ghz recent release of ... · • ieee 802.11ad: ratified in 2013...

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