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Radio Propagation and Networks Research
Costas ConstantinouSchool of Electronic, Electrical & Computer Engineering10 June 2013
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Introduction
Healthcare– 40 % of critical-care
time spent manually recording patient data in hospitals can be automated using BANs
– ICU spaghetti syndrome
Defence– Monitor vital soldier
signs, provide on-body hi-res video links
Why mm wave BANs?– Good covertness– Reduced interference– Unobtrusiveness– Expensive (not for
long)– Strong shadowing
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Experimental facilites Rhode&Schwarz ZVA67 20dBi horns & monopoles Flexible 2m coaxial cables Laboratory, outdoor and
anechoic chamber environment
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On-body path gain distance dependence
0 10 20 30 40 50-80
-60
-40
-20
0
20
Tx-Rx separation / cm
Path
gai
n / d
B
perpendiculartangentialfree space
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Signal variability
0 5 10 15 20 25 30 35 40
-100
-80
-60
-40
-20
0
Time (s)
Pat
h G
ain
(dB
)
Raw dataLong-term fadingShort-term fading
Moving body; waist to chest channel
Two types of fading cannot be unambiguously attributed to unique physical mechanisms
The time-scales that characterise these can be comparable for fast-moving bodies
Mechanisms include: Small and large-scale
movements of body Motion-induced antenna
misalignment and depolarisation
On-body multipath , |p s l p l p s l
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Signal variability – long-term fading
-100 -80 -60 -40 -20 00
0.02
0.04
0.06
0.08
0.1
Path Gain (dB)
(a)
Waist to chest shadowing
Blue – monopolesGreen – hornsCurve fits – lognormal
2
2
1 exp24
dBdB
lp l
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Signal variability – short-term fading
-10 -5 0 5 100
0.2
0.4
0.6
0.8
Magnitude (dB)
PD
F
DataCauchy fit
2 2
/|p s p s l dls
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Off-body paths: Covertness
Body channel: BAN + local multipath scattering environment
Propagation channel: free-space
Detection channel
Empirical Observability Study– Characterise an off-body channel of a 60 GHz BAN within a
variety of scattering environments– Propose an observability estimation model using channel
decomposition
R T OB D SW W G G FX
F
OB SG X
DG
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Off-body paths: Covertness
No strong distance dependence implies immersion in scattering environmentAntenna de-embedding is not possible
OB SX G X
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Observability: 60 GHz vs. 2.45 GHz The 60 GHz 1% observability probability threshold
distance for a realistic system both indoors and outdoors was estimated from measurement to be 48 m
The corresponding open environment threshold distance at 2.45 GHz keeping all system parameters unchanged was found to be 808 m
Assuming a more realistic microwave system at 2.45 GHz, the 1% observability distance threshold is 1,437 m (or using a two ray model 576 m)
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Off body paths: Interference
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Off-body paths: Interference
Head-to-belt channel with belt-to-belt channel: CDF of directly measured SIR on 4-port VNA
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Subject: male (178cm, 74 kg) wearing wetsuit
Groups of 3 or 4 markers (“virtual antennas”) placed on head, chest, waist, knee and 4 positions on the right arm
Movements:– Simple repeated movements
(e.g. twisting or tilting body or head, raising or twisting arms etc.) – 20s
– Random movements – 180s
Motion Capture Setup
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GO Predictions vs Measurements
0 2 4 6 8 10 12 14 16 18 20
-80
-60
-40
Time (s)
Path
Gai
n (d
B)
Chest - Wrist: Arms Sideways-Up
PredictionMeasurement
12 12.5 13 13.5 14 14.5 15-90
-80
-70
-60
Time (s)
Path
Gai
n (d
B)
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Time-varying on-body link geometry
Tx qT
(deg)fT
(deg)DT
(dBi) Ant Rx qR
(deg)fR
(deg)DR
(dBi) Ant
Head 64 74 8.7 Low gain
Upper Arm 36 49 23.4 High
gain
Head 72 360 1.6 Omni Wrist 51 103 7.8 Low gain
Upper Arm 48 59 14.4 High
gain Wrist 27 40 38.0 High gain
The elevation and azimuth direction variability of the markers translates to antenna beamwidth requirements and thus
directivity
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BAN antennas for 60 GHz on body paths Channel features
– Path loss high so only short link viable
– Need high gain antennas so fading due to beam misalignment
Printed Yagi-Udaarray gain ~20 dBi
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Novel SIW Yagi-Uda Array
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Linearly Polarised SIW Frequency Scanning Antenna: Fabrication and Measurement
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State4 State3 State2 State1 State0 State-1 State-2 State-3 State-4
SIW antenna -43.1 -43.4 -41.3 -32.9 -50.9 -45.8 -51.8 -53.2 -52.1
Horn × × -59.7 -45.2 -50.8 -50.1 -57.9 -58.3 ×
Mono × -60.8 -51.4 -43.8 -56.9 -51.3 -54.2 -63.9 ×
SIW Antenna vs. Horn & Monopole
State 4 State 1 State -4Max. Path Gain (dB)
Offsets body movement for highly mobile antenna locations (e.g. on wrist)
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Conclusions
60 GHz/mm wave technologies– Advantages
Good BAN-BAN isolationGreatly reduced EM emissions signature
– DisadvantagesQuasi-optical links necessitate multi-hop BANsGood radiation control requires careful antenna
design
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Future challenges
Electromagnetic modelling is a challenge & lags behind empirical work– Time-varying boundary conditions– Electrically large problems– Unexpected polarisation independence of attenuation
for near LOS paths Variability of body geometries and of electrical
properties of skin and clothing layers is largely unexplored
More realistic (small, conformal) adaptive antennas for better radiation control?