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Emerging Radio …and the World
Aggelos Bletsas
Department of Electronic and Computer Engineering,Technical University of Crete (TUC), Greece
TUC Telecom Seminars 2008-2009
June 1, 2009
Collaborators: Prof. Sahalos, Prof. Win, Prof. Lippman & Dr. Dimitriou
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June 1, 2009 TUC Telecom Seminars 2008-2009 2
Outline
1. RFIDs
2. Emergency Radio
3. Emerging Relaying in Wireless Access Networks
4. Education and integration
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June 1, 2009 TUC Telecom Seminars 2008-2009 3
Backscatter Radio/RFIDs are used everywhere!
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June 1, 2009 TUC Telecom Seminars 2008-2009 4
Brief Intro: Basic Principle
Reader
Tag
Communication from Tag to Reader = Backscatter Radio = = binary modulation on tag antenna-tag load reflection coefficient!
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.
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June 1, 2009 TUC Telecom Seminars 2008-2009 5
Problem Formulation
Bit ‘0’ ( )Z1ZL= Bit ‘1’ ( )Z2ZL=
Carrier
Backscattered Signal from Tag to Reader
Z1 Z2
Reader
Tag
Focus on Tag-to-Reader Communication
For given tag antenna, what are the ``optimal’’ tag loads Z1
(for bit ‘0’), Z2 (for bit ‘1’)?
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June 1, 2009 TUC Telecom Seminars 2008-2009 6
Prior Art: focus on minimum scattering antennas only
AC ZL
Tag
ZL
Equivalence is true only for minimum scattering antennas
Za
Z1 Z2
Reader
Tag
[Nikitin et al Electronics Letters 2007]: “Since the scattered field is proportional to the complex current in the antenna…”, the system designer “should maximize |Γ1-Γ2|2…”(where Γi 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.
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June 1, 2009 TUC Telecom Seminars 2008-2009 7
Basic Quantities
Bit ‘0’ ( )Z1ZL= Bit ‘1’ ( )Z2ZL=
Carrier
Backscattered Signal from Tag to Reader
E0: Antenna specific…
As: Tag Antenna
Structural Mode Parameter
σi: Radar Cross Section
(RCS)
at load ZL=Zi
AC ZL
Tag
ZL
Equivalence is true only for minimum scattering antennas
Za
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June 1, 2009 TUC Telecom Seminars 2008-2009 8
``Optimality’’ Definition: Constraint 1
Bit ‘0’ ( )Z1ZL= Bit ‘1’ ( )Z2ZL=
Carrier
Backscattered Signal from Tag to Reader
Must maximize
average backscattered
(carrier) power per
bit P0:
P0 σ1 + σ2 (scalar)
σi: Radar Cross Section
(RCS) at load ZL=Zi
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June 1, 2009 TUC Telecom Seminars 2008-2009 9
``Optimality’’ Definition: Constraint 2
Bit ‘0’ ( )Z1ZL= Bit ‘1’ ( )Z2ZL=
Carrier
Backscattered Signal from Tag to Reader
Must minimize
variance of
Backscattered (carrier)
power Var(P0),
due to different bits
for M-bit message:
Var(P0) [(σ1 - σ2)2]/M
(scalar)
M≥96 for Gen2. We (can) drop this constraint!
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June 1, 2009 TUC Telecom Seminars 2008-2009 10
``Optimality’’ Definition: Constraint 3
1G
2G
As
O (0,0)
Bit ‘1’ ( )Z2ZL=
Bit ‘0’ ( )Z1ZL=
Must minimize Reader bit-error
probability (BER):
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June 1, 2009 TUC Telecom Seminars 2008-2009 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).
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June 1, 2009 TUC Telecom Seminars 2008-2009 12
Tag Design
Experimentation with meander-type antennas, proposed in the literature for passive tags…
Battery-assisted tags: no need for power transfer => different problem…
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June 1, 2009 TUC Telecom Seminars 2008-2009 13
Tag Design and Experimentation
Design…
Prototype…
Radar Cross Section can be increased compared to passive case (perfect matching).
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June 1, 2009 TUC Telecom Seminars 2008-2009 14
Experimentation
Carrier transmitted…
Tag modulating waveform…
Received (backscattered) waveform…
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June 1, 2009 TUC Telecom Seminars 2008-2009 15
Remarks
Tag design should maximize |Γ1-Γ2|
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!
Method for closed-form
calculation of As was
omitted due to time constraints
BUSTE
DBUSTE
D
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June 1, 2009 TUC Telecom Seminars 2008-2009 16
Current Focus
1. Read Range (frequency dependent)
2. Communication throughput (bps/sensor)
3. Scalability (number of RFID sensors) => 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!
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June 1, 2009 TUC Telecom Seminars 2008-2009 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 Nδ…
Anti-collision performance depends on available bandwidth
…tradeoff between anticollision performance and N (or bandwidth)
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June 1, 2009 TUC Telecom Seminars 2008-2009 18
Why not Zigbee (with 802.15.4)?
1. 5-10$ each in quantity of 1000) –
[however, the target is 1$ per node]
2. tx current ~30 mA @ 10 dBm,
rx current ~40 mA.
3. Speed 20kbps (868 Mhz), 40kbps (900+MHz),
up to 240 kbps (2.4GHz) – routing overhead?“ZigBee Architecture Overview”, available from ZigBee.org
1. cost of an MCU (1.5$(each) in quantity of 1!
[however, the target is 0.1$ per node with
ASIC]
2. tx current ~0.6 mA @ 1 MHz, no receiver
3. Speed a few bps – no routing overhead
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June 1, 2009 TUC Telecom Seminars 2008-2009 19
Reader Antenna Capacity Enhancement
Beamforming antenna: Tag Collision occurs when tags close in modulating frequency AND close in geographical space…
=> Larger number of sensors for given bandwidth (compared to omni)!
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June 1, 2009 TUC Telecom Seminars 2008-2009 20
BSN Capacity Enhancement with smart Reader Antenna…
Edge Collision probability is analytically derived as a function of
various uncertainties
fading uncertainty
modulation
location uncertainty
observation direction uncertainty
antenna directivity pattern
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June 1, 2009 TUC Telecom Seminars 2008-2009 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).
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June 1, 2009 TUC Telecom Seminars 2008-2009 22
Reader Antenna Design in Practice
1
2
3
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.
Butler Matrix Feeding Network (BFN)
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June 1, 2009 TUC Telecom Seminars 2008-2009 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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June 1, 2009 TUC Telecom Seminars 2008-2009 24
RFID Reader Antenna Transmit Diversity
1 Reader Antenna
2 Reader Antennas with passive splitter (3-dB Tx power loss per antenna)
z slice, z-field z slice, z-field
x slice, z-fieldx slice, z-field
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June 1, 2009 TUC Telecom Seminars 2008-2009 25
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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June 1, 2009 TUC Telecom Seminars 2008-2009 26
Outline
1. RFIDs
2. Emergency Radio
3. Emerging Relaying in Wireless Access Networks
4. Education and integration
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June 1, 2009 TUC Telecom Seminars 2008-2009 27
Motivation
~2001 @ MIT: Distributed phased arrays…Code name: “Marblehead Island problem” (note: Marblehead is north of Boston)
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June 1, 2009 TUC Telecom Seminars 2008-2009 28
Problem Formulation (1)
2009: make it more interesting…. No CSI at the transmitters… No feedback from the destination… No carrier sync availability…
Very stringent requirements as in Emergency Radio
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June 1, 2009 TUC Telecom Seminars 2008-2009 29
Intuition
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Problem Formulation (2)
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June 1, 2009 TUC Telecom Seminars 2008-2009 31
Alignment Probability Calculation
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June 1, 2009 TUC Telecom Seminars 2008-2009 32
Alignment Probability Results
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June 1, 2009 TUC Telecom Seminars 2008-2009 33
Steady-State Alignment Probability Phase Offset Independence
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June 1, 2009 TUC Telecom Seminars 2008-2009 34
Steady-State Alignment Probability Clock Frequency Skew Independence
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June 1, 2009 TUC Telecom Seminars 2008-2009 35
Transient Alignment Probability Clock Frequency Skew Dependence
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June 1, 2009 TUC Telecom Seminars 2008-2009 36
…and finally: beamforming gain and delay
Example:fc=2.4 GHzR = 1 Mbps => Ts = 1 μsecTc > 100 μsec => u < 1.25 km/sec
@ φ0 = π/4 => Lbf = 8.6 dB => ~4 symbols out 100
Thus, effective rate: = 1 Mbps x 4/100 @ Lbf = 8.6 dB= 40 kbps @ Lbf = 8.6 dB!
8.6 dB in power is a factor of 7.24 (!!!)
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June 1, 2009 TUC Telecom Seminars 2008-2009 37
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).
BUSTE
D
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June 1, 2009 TUC Telecom Seminars 2008-2009 38
Remark (2)
“Marblehead Island problem” “Marathi Island Problem”
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June 1, 2009 TUC Telecom Seminars 2008-2009 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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June 1, 2009 TUC Telecom Seminars 2008-2009 40
Outline
1. RFIDs
2. Emergency Radio
3. Emerging Relaying in Wireless Access Networks
4. Bibliometrics & the Hirsch Index
5. Education trends and integration
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June 1, 2009 TUC Telecom Seminars 2008-2009 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… (it’s a network problem)
5. Low-complexity receivers, cheap radios…(in-band multiple transmissions = noise)
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June 1, 2009 TUC Telecom Seminars 2008-2009 42
Approach
…always exactly two (2) in-band transmissions:
a) Source-to-destination
b) “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
t
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June 1, 2009 TUC Telecom Seminars 2008-2009 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.
t
Major difference with prior art: interference is allowed, NO network/superposition/dirty-paper coding (low complexity protocol/receivers)!
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June 1, 2009 TUC Telecom Seminars 2008-2009 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) => fix this by using bounds!
Outage probability given specific
interfering relay
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June 1, 2009 TUC Telecom Seminars 2008-2009 45
Analysis
Need to compute all relevant outage probs, conditioned to (any) interfering relay i.
Example 1:
Example 2 (…little more involved):
Signal of interest (SOI) and Interfering Signal (IS)are fully correlated!!!
Selection Receiver (SR): simplest receiver, other simple receivers are also possible!
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June 1, 2009 TUC Telecom Seminars 2008-2009 46
Results
…(more than) acceptable performance with weak or no SD link, weak inter-relay links!
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June 1, 2009 TUC Telecom Seminars 2008-2009 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!
Outage probability plateau!
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June 1, 2009 TUC Telecom Seminars 2008-2009 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! )
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June 1, 2009 TUC Telecom Seminars 2008-2009 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!
Low complexity switched-beam antenna designs are possible [Vaitsopoulos, Bletsas and Sahalos, IEEE CEFC 2008]
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June 1, 2009 TUC Telecom Seminars 2008-2009 50
Classic relaying vs classic network coding vs 2-way
physical network coding Classic network coding
(classic) 2-way physical network coding (PNC)
[figure from Katti, Gollakota and Katabi, ACM Sigcomm 2007]
Classic relaying
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June 1, 2009 TUC Telecom Seminars 2008-2009 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]
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2-way physical network coding = 2-source separation
J. Hamkins, "An analytic technique to separate cochannel FM signals"IEEE Transactions on Communications, vol. 48, no. 4, April 2000, p. 543-546.
[figure from Katti, Gollakota and Katabi, ACM Sigcomm 2007]
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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]
][niCe
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Remarks (2)
“Interference is veeeeeryyyy baaaaaaaaddddd”….
“We cannot live in interference”…BUSTE
D
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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