Magneto-Inductive NEtworked Rescue System (MINERS): Taking Sensor Networks Underground
Andrew Markham and Niki TrigoniDepartment of Computer ScienceUniversity of Oxford
>2500 large underground mines
Mining disasters
Collapse: Chile
Fire/Explosion: Sago, USA
Flooding: Wales
Existing approaches
Wired
Wired
Wired
! !
?
Wireless
Wireless
Wireless
! !
?
Need
Need
! !
Need
! !
Solution: Magneto-Inductive
Overview
• Motivation• System Requirements and Design• Challenges and Solutions• Implementation and Results• Summary
System Requirements
• Nodes should not require precise positioning
• Nodes should be able to communicate over 30m through rock
• Information must be relayed to surface with minimal latency
Magneto-Induction
Magneto-Induction
Magneto-Induction
V
Overview
• Motivation• System Requirements and Design• Challenges and Solutions• Implementation and Results• Summary
Challenges
• Placement• Path loss and noise• Limited bandwidth• Latency
Challenge: Placement
1.00 V
𝑉 ∝𝐵 cos𝜃
Challenge: Placement
0.70 V
𝑉 ∝𝐵 cos𝜃
Challenge: Placement
0.00 V
𝑉 ∝𝐵 cos𝜃
Solution: Triaxial Receivers
𝑉 ∝|𝐵|
1.00 V
Solution: Triaxial Receivers
𝑉 ∝|𝐵|
1.00 V
Solution: Triaxial Receivers
𝑉 ∝|𝐵|
1.00 V
Solution: Triaxial Receivers
𝑉 ∝|𝐵|
1.00 V
Rotationallyinvariant
Challenges
• Placement• Path loss and noise• Limited bandwidth• Latency
Challenge: Path loss and noise
Frequency (Hz)
Noi
se (d
B)
Background noise
Challenge: Path loss and noise
Frequency (Hz)
Atten
uatio
n (d
B)
Skin effect
Solution: VLF Narrowband
Frequency (Hz)Pow
er S
pect
ral D
ensi
ty
32 Hz
2500 Hz
Avoid LF noise Minimize skin effect
Solution: VLF Narrowband
Frequency (Hz)Pow
er S
pect
ral D
ensi
ty
32 Hz
2500 Hz
Avoid LF noise Minimize skin effect
Sweet Spot
Challenges
• Placement• Path loss and noise• Limited bandwidth• Latency
Challenge: Limited bitrate
32 Hz
BPSK: 32 bps!
Vector fields
Vector fields
Vector fields
Vector fields
=[2;0;0]
Vector fields
=[0;0;-1]
Vector fields
=[0;-1;0]
Electrically Rotating Transmitter
X = +1Amp
Sending symbol 0
Transmitter Receiver
Electrically Rotating Transmitter
Y = +1Amp
Sending symbol 1
Transmitter Receiver
Electrically Rotating Transmitter
Z = +1Amp
Transmitter Receiver
Sending symbol 2
Electrically Rotating Transmitter
X = -1Amp
Sending symbol 3
Transmitter Receiver
Solution: Magnetic Vector Modulation
BPSK:2 symbols: 32bps 01
Solution: Magnetic Vector Modulation
BPSK:2 symbols: 32bps
Magnetic vector modulation:6 symbols: 80bps
01
2
3
4
01
Solution: Magnetic Vector Modulation
BPSK:2 symbols: 32bps
Magnetic vector modulation:6 symbols: 80bps
~2.5 times increase inbitrate
Same energy
Solution: Magnetic Vector Modulation
BPSK:2 symbols: 32bps
Magnetic vector modulation:6 symbols: 80bps
01
2
3
4
01
Solution: Magnetic Vector Modulation
BPSK:2 symbols: 32bps
Magnetic vector modulation:6 symbols: 80bps
01
2
3
4
01
Solution: Magnetic Vector Modulation
BPSK:2 symbols: 32bps
Magnetic vector modulation:6 symbols: 80bps
01
2
3
4
01
Need to train channel
Challenges
• Placement• Path loss and noise• Limited bandwidth• Latency
Challenge: Latency
• Rapid query response essential• How many miners are trapped
underground?• What is the maximum methane
concentration?
Challenge: Latency
A B
Challenge: Latency
A B
Challenge: Latency
A B
Challenge: Latency
A B
2 units of time
Challenge: Latency
Depth
Breadth
T≈ Breadth x Depth
Narrow transmitter bandwidth
Frequency (Hz)Pow
er S
pect
ral D
ensi
ty
32 Hz
2500 Hz
Wider receiver bandwidth
Frequency (Hz)Pow
er S
pect
ral D
ensi
ty
1000 Hz
1 2 20
Solution: Broadcatching
A B
Solution: Broadcatching
A B
1 unit of time
Solution: Broadcatching
Depth
Breadth
T≈ Depth
Solution: Broadcatching
Depth
Breadth
T≈ Depth
Reduced latency
Overview
• Motivation• System Requirements and Design• Challenges and Solutions• Implementation and Results• Summary
Implementation: System
Implementation: System
Implementation: Miner unit
Implementation: Miner unit
Implementation: Transmitter
Implementation: Receiver
Message format
Message format
Phase lock
Message format
Training
Message format
Data
Received Message
Received Message
Strongest on y channel
Training: Transmit on X
Bx
By
Bz
0
3
Training: Transmit on Y
Bx
By
Bz
1
4
Training: Transmit on Z
Bx
By
Bz2
5
Symbol Constellation
Symbol Constellation
Symbol Constellation
Increase in data rate
Latency
Latency
Latency
Latency
5 fold decrease in latency
Real world trials
Real world trials: BER
Real world trials
• Communication through solid rock• 25m range at 80 bps• 75m range at 0.1 bps
Real world trials
• Communication through solid rock• 25m range at 80 bps• 75m range at 0.1 bps
MI is a viable technique
Future Directions
• ARM based SDR• More sensitive receiver• Mobile MI nodes• Testing in operational mines
Conclusion
• Need for robust communication in mining• Modulate vector field to increase bitrate• Broadcatching to reduce latency• Prototype SDR transceiver• First real world test of MI sensor network• Potential lifesaving technology
Thanks
• JP van de Ven• Oxford Martin School• EPSRC SUAAVE
Questions?