Emerging Radio

1
Emerging Radio and the World

• Aggelos BletsasDepartment of Electronic and
  Computer Engineering,Technical University of
  Crete (TUC), Greece

Collaborators Prof. Sahalos, Prof. Win, Prof.
Lippman Dr. Dimitriou
TUC Telecom Seminars 2008-2009 June 1, 2009
2
Outline

1. RFIDs
2. Emergency Radio
3. Emerging Relaying in Wireless Access Networks
4. Education and integration

3
Backscatter Radio/RFIDs are used everywhere!
4
Brief Intro Basic Principle
Tag
Reader
G. Vannucci, A. Bletsas and D. Leigh, "A
Software-Defined Radio System for Backscatter
Sensor Networks", IEEE Transactions on Wireless
Communications (TWC), Vol. 7, No. 6, pp.
2170-2179, June 2008.

• Communication from Tag to Reader Backscatter
  Radio binary modulation on tag antenna-tag
  load reflection coefficient!

5
Problem Formulation

• Focus on Tag-to-Reader Communication
• For given tag antenna, what are the optimal
  tag loads Z1(for bit 0), Z2 (for bit 1)?

6
Prior Art focus on minimum scattering antennas
only

• Nikitin et al Electronics Letters 2007 Since
  the scattered field is proportional to the
  complex current in the antenna, the system
  designer should maximize G1-G22(where Gi is
  the reflection coefficient for load Zi)
• As stated by Nikitin et al, this is only true for
  minimum scattering antennas.
• We derive the solution for the general tag
  antenna case.

7
Basic Quantities
E0 Antenna specific As Tag Antenna Structural
Mode Parameter si Radar Cross Section (RCS) at
load ZLZi
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Optimality Definition Constraint 1

• Must maximize average backscattered (carrier)
  power per bit P0
• P0 ? s1 s2 (scalar)
• si Radar Cross Section (RCS) at load ZLZi

9
Optimality Definition Constraint 2

• Must minimize variance of Backscattered
  (carrier) power Var(P0), due to different
  bits for M-bit message
• Var(P0) ? (s1 - s2)2/M (scalar)
• M96 for Gen2. We (can) drop this constraint!

10
Optimality Definition Constraint 3

• Must minimize Reader bit-error probability (BER)

11
Design Example for Given Tag Antenna Passive Tag

• Solutions I and II provide the same error
  detection probability (Constraint 3).
• Solution II provides higher backscattered
  carrier power per bit (Constraint 1).

12
Tag Design

• Experimentation with meander-type antennas,
  proposed in the literature for passive tags
• Battery-assisted tags no need for power
  transfer gt different problem

13
Tag Design and Experimentation

• Prototype

• Design

• Radar Cross Section can be increased compared to
  passive case (perfect matching).

14
Experimentation

• Carrier transmitted

• Tag modulating waveform

• Received (backscattered) waveform

15
Remarks
BUSTED

• Tag design should maximize G1-G2 only
• Research is over in RFIDs
• Selection of best reflection coefficients was
  given for any As (and tag antenna, not
  necessarily minimum scattering).
• As can be easily computed in closed-form, given
  measurements of scalar RCS!

BUSTED
Method for closed-form calculation of As was
omitted due to time constraints
16
Current Focus

1. Read Range (frequency dependent)
2. Communication throughput (bps/sensor)
3. Scalability (number of RFID sensors) gt
   anti-collision ability
4. Reading speed (number of sensors/sec) 40
   tags/sec current state of the art
5. Antenna size (as small as possible)
6. Packaging material environment (affect
   reader/tag coupling)
7. Efficient tag manufacturing programming
8. Tag/Reader Cost
9. Integration addressing all (or most of) the
   above in an application!

17
Scalability of Backscatter Sensor Networks

• For agricultural fields, sensor density is large
  (1-1.5 sensor/m2)
• Large number N of sensors is needed
• Required bandwidth is proportional to Nd
• Anti-collision performance depends on available
  bandwidth
• tradeoff between anticollision performance and N
  (or bandwidth)

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Why not Zigbee (with 802.15.4)?

• 5-10 each in quantity of 1000)
• however, the target is 1 per node
• tx current 30 mA _at_ 10 dBm, rx current 40 mA.
• Speed 20kbps (868 Mhz), 40kbps (900MHz), up to
  240 kbps (2.4GHz) routing overhead?

ZigBee Architecture Overview, available from
ZigBee.org

• cost of an MCU (1.5(each) in quantity of
  1!however, the target is 0.1 per node with
  ASIC
• tx current 0.6 mA _at_ 1 MHz, no receiver
• Speed a few bps no routing overhead

19
Reader Antenna Capacity Enhancement
Beamforming antenna Tag Collision occurs when
tags close in modulating frequency AND close in
geographical space gt Larger number of sensors
for given bandwidth (compared to omni)!
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BSN Capacity Enhancement with smart Reader
Antenna
Edge Collision probability is analytically
derived as a function of various uncertainties
21
Anti-Collision with Reader Antennas

• modulations utilized in Gen2 inappropriate for
  high-density, extended range semi-passive tags
• that is due to round trip nature of
  backscatter com
• quantified collision for any modulation, number
  of tags and given spectrum
• (useful for epc class 3 standard)
• A. Bletsas, S. Siachalou, J.N. Sahalos,
  "Anti-collision Tags for Backscatter Sensor
  Networks", 38th European Microwave Conference
  (EuMC), October 2008, Amsterdam, Netherlands.
• Bletsas, J.N. Sahalos, "Antenna Enhancements for
  Backscatter Sensor Networks", COST Antenna
  Systems Sensors for Information Technology
  Societies (ASSIST) Workshop, April 2008,
  Limassol, Cyprus.
• A. Bletsas, S. Siachalou and J.N. Sahalos,
  "Anti-collision Backscatter Sensor Networks",
  submitted June 2008, IEEE Transactions on
  Wireless Communications (TWC).

22
Reader Antenna Design in Practice
Butler Matrix Feeding Network (BFN)

• E. Vaitsopoulos, A. Bletsas, J.N. Sahalos, "On
  the RFID Design with Passive Tags and a Butler
  Matrix Reader", 13th Biennial IEEE Conference on
  Electromagnetic Field Computation (CEFC), May
  2008, Athens, Greece.

23
6-month focus RFID in HealthcareMotivation
Medical Errors Electronic Inventory Control

• Paper-based environments medical errors approach
  40
• In-hospital Medication errors 44,000 deaths per
  year in the US, 700 deaths per year in Canada.
  (Institute of Medicine, National Academic Press,
  1999)
• Theft of equipment/supplies 4,000 per hospital
  bed each year (3.9 billion annually in the US)
• Asset Tracking One third of personnel time is
  wasted in searching. 10 of inventory is lost
  annually.

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RFID Reader Antenna Transmit Diversity
z slice, z-field
z slice, z-field
x slice, z-field
x slice, z-field
1 Reader Antenna
2 Reader Antennas with passive splitter (3-dB Tx
power loss per antenna)
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References
G. Vannucci, A. Bletsas, D. Leigh, "Implementing
Backscatter Radio for Wireless Sensor Networks",
IEEE Personal Indoor Mobile Radio Communications
Conference (PIMRC), September 2007, Athens,
Greece, pp. 1-5. G. Vannucci, A. Bletsas and D.
Leigh, "A Software-Defined Radio System for
Backscatter Sensor Networks", IEEE Transactions
on Wireless Communications (TWC), Vol. 7, No. 6,
pp. 2170-2179, June 2008. E. Vaitsopoulos, A.
Bletsas, J.N. Sahalos, "On the RFID Design with
Passive Tags and a Butler Matrix Reader",13th
Biennial IEEE Conference on Electromagnetic Field
Computation (CEFC), May 2008, Athens, Greece. A.
Bletsas, J.N. Sahalos, "Antenna Enhancements for
Backscatter Sensor Networks", COST Antenna
Systems Sensors for Information Technology
Societies (ASSIST) Workshop, April 2008,
Limassol, Cyprus. A. Bletsas, S. Siachalou, J.N.
Sahalos, "Anti-collision Tags for Backscatter
Sensor Networks", 38th European Microwave
Conference (EuMC), October 2008, Amsterdam,
Netherlands. A. Bletsas, S. Siachalou and J.N.
Sahalos, "Anti-collision Backscatter Sensor
Networks", IEEE Transactions on Wireless
Communications (TWC), submitted June 2008. A.
Bletsas, A. G. Dimitriou, J. N. Sahalos,
Improving Backscatter Radio Tag Efficiency,
COST RF/Microwave Communication Subsystems for
Emerging Wireless Technologies (RFCSET) Workshop,
April 2009, Brno, Czech Republic. A. Polycarpou,
A.G. Dimitriou, A. Bletsas and J.N. Sahalos,
"RFID in Healthcare", COST Antenna Systems
Sensors for Information Technology Societies
(ASSIST) Workshop, May 2009, Valencia, Spain.
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Outline

1. RFIDs
2. Emergency Radio
3. Emerging Relaying in Wireless Access Networks
4. Education and integration

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Motivation
2001 _at_ MIT Distributed phased arrays Code
name Marblehead Island problem (note
Marblehead is north of Boston)
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Problem Formulation (1)
Very stringent requirements as in Emergency Radio

• 2009 make it more interesting.
• No CSI at the transmitters
• No feedback from the destination
• No carrier sync availability

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Intuition
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Problem Formulation (2)
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Alignment Probability Calculation
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Alignment Probability Results
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Steady-State Alignment Probability Phase Offset
Independence
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Steady-State Alignment Probability Clock
Frequency Skew Independence
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Transient Alignment Probability Clock Frequency
Skew Dependence
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and finally beamforming gain and delay
Example fc2.4 GHz R 1 Mbps gt Ts 1 µsec Tc
gt 100 µsec gt u lt 1.25 km/sec _at_ f0 p/4
gt Lbf 8.6 dB gt 4
symbols out 100 Thus, effective rate 1
Mbps x 4/100 _at_ Lbf 8.6 dB 40 kbps _at_ Lbf 8.6
dB! 8.6 dB in power is a factor of 7.24 (!!!)

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Remark (1)

• Distributed Beam-forming REQUIRES Carrier
  Synchronization and/or feedback from the
  destination.
• We provided zero-feedback, zero-CSI distributed
  beam-forming, based on unsynchronized
  carriers!
• The proposed scheme could complement rescue
  workers (emergency radio) or reachback
  communication in wireless networks (e.g. low-cost
  sensor networks).

BUSTED
38
Remark (2)
Marblehead Island problem ? Marathi Island
Problem
39
References
A. Bletsas, A. Lippman and J.N. Sahalos,
"Simple, Zero-Feedback, Distributed Beamforming
with Unsynchronized Carriers", submitted April
2009, IEEE Journal on Selected Areas of
Communication (JSAC), Special Issue on Simple
Sensor Networking Solutions. A. Bletsas, A.
Lippman and J.N. Sahalos, "Simple, Zero-Feedback,
Distributed Beamforming for Emergency Radio",
submitted April 2009, IEEE ISWCS 2009, Tuscany,
Italy.
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Outline

1. RFIDs
2. Emergency Radio
3. Emerging Relaying in Wireless Access Networks
4. Bibliometrics the Hirsch Index
5. Education trends and integration

41
The problem

1. One source, K half-duplex relays, several
   destinations
2. Quasi-static SLOW fading (no temporal
   diversity)
3. Network (global) CSI at relays or destinations
   NOT AVAILABLE
4. Low-complexity protocol reduced coordination
   overhead (its a network problem)
5. Low-complexity receivers, cheap radios(in-band
   multiple transmissions noise)

42
Approach

• always exactly two (2) in-band transmissions
• Source-to-destination
• best relay-to-DIFFERENT destination!
• best relay selected opportunistically,
  reactively, in a distributed manner at MAC (no
  global CSI anywhere in the network)
• best relay best for epoch n-1, interfering for
  next epoch n

43
Approach

• best relay best b for epoch n-1, interfering i
  for next epoch n.
• b?i due to half duplex radios
• Scheduling invariant
• Reactive opposed to Proactive The latter is
  energy-efficient but needs additional CSI.
• Efficient MAC for opportunistic selection A
  Simple Cooperative Diversity Method based on
  Network Path Selection, IEEE JSAC, March 2006.
• Optimality proof for DF Relays Cooperative
  Communications with Outage-Optimal Opportunistic
  Relaying, IEEE TWC, September 2007.

Major difference with prior art interference is
allowed, NO network/superposition/dirty-paper
coding (low complexity protocol/receivers)!
44
Analysis

1. discrete, narrow-band, constant total tx
   power,flat-fading model under Rayleigh Fading.

2. reactive, opportunistic selection
3. performance dependent on previous Epochs!
(non-memoryless) gt fix this by using bounds!

45
Analysis

• Need to compute all relevant outage probs,
  conditioned to (any) interfering relay i.

• Example 1

• Example 2 (little more involved)

46
Results

• (more than) acceptable performance with weak or
  no SD link, weak inter-relay links!

47
Results

• Opportunistic Relaying provides cooperative
  diversity and engineers the required outage
  probability plateau!
• thus, more efficient use of spectrum, no need
  for scheduling (from source) delays!

48
Remarks

• Notion of useful relays in IaOR is redefined
  relays with strong paths towards source and
  destinations but weak links with each other!
• Opportunistic, reactive relaying engineers the
  appropriate plateau to mitigate interference
  and reduce scheduling delays!
• No need for fancy coding (superposition or
  dirty-paper)but need for efficient
  opportunistic selection (examples exist, more
  research is required and welcomed! )

49
Discussion

• relays with strong paths towards source and
  destinations but weak links with each other!
• Approach 1 find such relays given existing
  relaying densities in urban environments!
• Existing Urban Environments provide wifi
  terminal densities on the order of 1000
  nodes/km2 Jones and Liu 2007.
• Approach 2 use directive antennas AT THE RELAYS!

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Classic relaying vs classic network coding vs
2-way physical network coding
Classic network coding
(classic) 2-way physical network coding (PNC)
Classic relaying
figure from Katti, Gollakota and Katabi, ACM
Sigcomm 2007
51
Classic network coding vs 2-way physical network
coding
Classic network coding
(classic) 2-way physical network coding (PNC)
figure from Popovski and Yomo, IEEE ICC 2007
52
2-way physical network coding 2-source
separation
figure from Katti, Gollakota and Katabi, ACM
Sigcomm 2007
J. Hamkins, "An analytic technique to separate
cochannel FM signals"IEEE Transactions on
Communications, vol. 48, no. 4, April 2000, p.
543-546.
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Our contribution 3-way Physical Network Coding

• Generalize the Hamkins Algorithm to the case of
  3 sources

• 3-way PNC becomes possible

• Hamkins states in his paper that such
  generalization is easy.

• Aggelos states that such generalization is not
  easy...

• try it

Must read Hamkins 2000, Zhang, Liew, Lam
2006, Katti, Gollakota, Katabi 2007
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Remarks (2)

• Interference is veeeeeryyyy baaaaaaaaddddd.
• We cannot live in interference

BUSTED
55
References
A. Bletsas, A.G. Dimitriou and J.N. Sahalos,
"Interference-Aware Opportunistic Relaying with
Reactive Spectrum Sensing", submitted August
2008, IEEE Transactions on Wireless
Communications (TWC). A. Bletsas, J.N.
Sahalos, "Interference-Aware Opportunistic
Relaying with Reactive Spectrum Sensing", invited
paper, IEEE Personal Indoor Mobile Radio
Communications Conference (PIMRC), September
2008, Cannes, France. A. Bletsas, A.G.
Dimitriou, J.N. Sahalos, "Reduced-Delay
Interference-Aware Opportunistic Relaying", to
appear, IEEE International Conference on
Communications (ICC) 2009, Dresden, Germany.
A. Bletsas, J.N. Sahalos, 3-way Physical
Network Coding, in preparation.
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Outline

1. RFIDs
2. Emergency Radio
3. Emerging Relaying in Wireless Access Networks
4. Education and integration