thesis_presentation

Introduction
System Model for FSK
Bistatic Scatter Radio FSK Demodulation
Composite Hypothesis Testing Receivers for Noncoherent FSK
Simulation Results and Experimental Measurements
Conclusion
Channel Coding and Detection for Increased Range
Bistatic Scatter Radio
Panos Alevizos
School of Electronic & Computer Engineering T.U.C. Chania, Greece
Telecommunications Laboratory
May 14, 2015
Panos Alevizos Master Thesis Presentation 1 / 35

Introduction
Conclusion
Motivation
Scatter Radio: Problems and Solution
Bistatic Scatter Radio WSNs
Outline
1 Introduction
Motivation
2 System Model for FSK
Fading Characteristics
Bistatic Scatter Radio: Transmission and Reception
3 Bistatic Scatter Radio FSK Demodulation
4 Composite Hypothesis Testing Receivers for Noncoherent FSK
Noncherent Uncoded Reception in Bistatic Scatter Radio
Noncoherent Coded Reception in Bistatic Scatter Radio
5 Simulation Results and Experimental Measurements
6 Conclusion

Introduction
Conclusion
Motivation
General Goal
Low-power, low-cost, large-scale, dense WSNs.
Existing WSNs:
Complex RF front-ends =⇒ prohibit dense deployments.
Scatter radio: communication by means of reﬂection.
Low monetary cost.
Low energy requirements.
Scatter radio: key-enabling technology for ubiquitous sensing.

Introduction
Conclusion
Motivation
Scatter Radio: Problems
Scatter radio testbeds:
Passive RF tags.
Monostatic architectures.
Ultra high bit-rates.
SDR
Reader Tag
Figure: Monostatic.
Carrier
Emitter
SDR
Reader
Tag
Figure: Bistatic.

Introduction
Conclusion
Motivation
Solutions
Tag-SDR reader range
maximized.
Bistatic scatter radio
architecture [1].
Semi-passive RF tags [1],[2].
Relative low bit-rates [2].
Channel coding [3],[4].
Carrier
Emitter
Tag
SDR Reader
Figure: Bistatic architecture.
[1] J. Kimionis, A. Bletsas, and J. N. Sahalos, “Increased range bistatic scatter radio,” IEEE Trans. Commun., vol.
62, no. 3, pp. 1091–1104, Mar. 2014.
[2] G. Vannucci, A. Bletsas, and D. Leigh, “A software-deﬁned radio system for backscatter sensor networks,” IEEE
Trans. Wireless Commun., vol. 7, no. 6, pp. 2170–2179, Jun. 2008.
[3] P. N. Alevizos, N. Fasarakis-Hilliard, K. Tountas, N. Agadakos, N. Kargas, and A. Bletsas, “Channel coding for
increased range bistatic backscatter radio: Experimental results,” in Proc. IEEE RFID-TA, Tampere, Finland, Sep.
2014.
[4] N. Fasarakis-Hilliard, P. N. Alevizos, and A. Bletsas, “Coherent detection and channel coding for bistatic scatter
radio sensor networking,” Submitted in IEEE Trans. Commun.

Introduction
Conclusion
Motivation
Bistatic scatter radio WSNs:
Several carrier emitters.
Tags: FSK [1],[3],[4] or MSK
[2] for FDMA.
Single SDR reader.
Extended ﬁeld coverage.
Link budget gains.
Analyzed and shown to be
feasible [5].
Backscatter
Cells
Reader
Carrier
Emitter
Tag
Tag
Tag
Carrier
Emitter
Tag
Tag
Tag
Figure: Bistatic scatter radio WSNs.
[5] A. Bletsas, S. Siachalou, and J. N. Sahalos, “Anti-collision backscatter sensor networks,” IEEE Trans. Wireless
Commun., vol. 8, no. 10, pp. 5018–5029, Oct. 2009.

Introduction
Conclusion
System Model
For duration of Tcoh,
hl (t) = hl = al e−jφl
,
with l ∈ {CR, CT, TR}.
Carrier
Emitter
SDR
Reader
Tag
hCR(t)
hCT(t) hTR(t)
Figure: Bistatic scatter radio link.
Outdoors environment: strong LOS =⇒ Rician fading.
al ∼
κl
κl + 1
σl + CN 0,
σ2
l
κl + 1
, l ∈ {CR, CT, TR}, (1)
φl ∼ U[0, 2π), l ∈ {CR, CT, TR}. (2)

Introduction
Conclusion
Carrier Emission
Carrier
Emitter
SDR
Reader
Tag
Carrier emitter at frequency Fc
c(t) = 2PC e−j(2π∆Ft+∆φ)
. (3)
PC : carrier transmitting power at passband.
∆F: carrier emitter–SDR reader CFO.
∆φ ∼ U[0, 2π): carrier emitter–SDR reader phase oﬀset.

Introduction
Conclusion
Tag Scatters the Incident Signal (1/2)
Carrier
Emitter
SDR
Reader
Tag
Tag receives and scatters back
ui (t) = s v0 +
Γ0 − Γ1
2
bi (t) aCTe−jφCT
c(t), i ∈ B. (4)
Γ0, Γ1: 2 load values bit “0” and bit “1”.
s: scattering eﬃciency.
v0: DC constant depending on structural mode and Γ0, Γ1.

Introduction
Conclusion
Tag Scatters the Incident Signal (2/2)
Carrier
Emitter
SDR
Reader
Tag
Fundamental freq. component 50% duty cycle
bi (t) =
4
π
cos (2πFi t + Φi ) ΠT (t), i ∈ B. (5)
Fi : subcarrier frequency for bit i ∈ B.
Φi : tag–SDR reader phase mismatch for bit i ∈ B.
T: nominal bit period.
ΠT (t): ideal square pulse of duration [0, T).

Introduction
Conclusion
SDR Reader Receives DC and the Scattered Signal
Carrier
Emitter
SDR
Reader
Tag
hCRc(t)
hTRui(t)
SDR reader receives through hCR and hTR
y(t) = DC + µae−jφ
cos (2πFi t + Φi ) ΠT (t) e−j2π∆Ft
+ n(t),
(6)
with φ φCT + φTR + ∆φ + Γ0 − Γ1, a aCTaTR and
µ
√
2Pc|Γ0 − Γ1| 2
π s.

Introduction
Conclusion
SDR Reader Processes the Received Signal
SDR estimates/compensates CFO.
Eliminates DC-oﬀset.
Applies synchronization.
Perfect synchronized, DC-blocked, CFO-free signal
˜y(t) = µae−jφ
cos (2πFi t + Φi ) ΠT (t) + n(t) (7)
=
µh
2
ej(2πFi t+Φi )
+ e−j(2πFi t+Φi )
ΠT (t) + n(t), (8)
where h ae−jφ.

Introduction
Conclusion
Bandlimited Noise Process and SNR
n(t): complex baseband Gaussian noise process:
Snn(F) =
N0
2 , |F| ≤ WSDR
0, otherwise.
(9)
Instantaneous and average received energy per bit:
E(aCT, aTR)
T
0
µae−jφ
cos(2πFi t + Φi )
2
dt =
Tµ2a2
2
,
E = E
aCT,aTR
[E(aCT, aTR)] =
Tµ2
2
. (10)
Average received SNR:
SNR
E
N0
2
=
Tµ2
N0
. (11)

Introduction
Conclusion
Classic VS Bistatic Scatter Radio Demodulation
F0 F1
0 F
F0 F1-F0-F1
0
F
Carrier
Figure: Classic VS bistatic scatter radio FSK complex baseband
spectrum.
Classic FSK demodulator =⇒ 3 dB loss of information [1].

Introduction
Conclusion
Optimal Bistatic Scatter Radio FSK Demodulation
Correlator demodulators: maximizes received SNR.
Utilized orthonormal basis:
1
√
T
e+j2πFi t
ΠT (t),
1
√
T
e−j2πFi t
ΠT (t)
i∈B
. (12)
For Fi
1
T
:
r =




r+
0
r−
0
r+
1
r−
1



 = h
E
2




e+jΦ0
e−jΦ0
e+jΦ1
e−jΦ1



 si +




n+
0
n−
0
n+
1
n−
1



 , si ∈







1
1
0
0



 ,




0
0
1
1







.
For WSDR > Fi :
n = [n+
0 n−
0 n+
1 n−
1 ] ∼ CN 04,
N0
2
I4 . (13)

Introduction
Conclusion
Composite Hypothesis Noncoherent FSK Detection
ML detector
E
h,Φ0
fr|s0,h,Φ0
(r|s0, h, Φ0)
H0
H1
E
h,Φ1
fr|s1,h,Φ1
(r|s1, h, Φ1) . (14)
Proposition
For uncoded bistatic scatter radio noncoherent FSK we propose
E
Φ0
maxh∈C ln fr|s0,h,Φ0
(r|s0, h, Φ0)
E
Φ1
maxh∈C ln fr|s1,h,Φ1
(r|s1, h, Φ1)
H0
H1
1, (15)
that can be simpliﬁed to
z0 |r+
0 |2
+ |r−
0 |2
H0
H1
|r+
1 |2
+ |r−
1 |2
z1. (16)

Introduction
Conclusion
Performance Analysis for Rayleigh Fading
(κCT = κTR = 0)
Lemma
For Rayleigh fading (κCT = κTR = 0), the detector of (16) oﬀers
Pr(e) = −
SNR + e
2
SNR 5SNR + 2 Ei − 2
SNR
4SNR2
, (17)
where for x > 0, Ei(−x) = −
∞
x
e−t
t dt.

Introduction
Conclusion
Encoding at Tags: Redundancy is Introduced.
Generator of code C
G g1 g2 . . . gK .
Generated codeword
c ∈ C ⇐⇒ ∃ b ∈ BK
: c = bG.
Rate and minimum distance
r =
K
N
, dC
min = min
c∈C{0}
wH(c).
Limited storage and processing
capabilities =⇒ N, K small.
Carrier
Emitter
G
Tag
01001.....01110....00111....
information
sequence
Encoder
coded
sequence
...,b2,b1 ...,c2,c1
SDR
Reader
Figure: Encoding at Tags [3].

Introduction
Conclusion
Deep Fading - Solution
Wireless environment: errors occur in long bursts.
Small N, K =⇒ no error correction.
Idea: interleaving in conjunction with channel coding.
Interleaving depth d: dT ≥ Tcoh =⇒ diversity order dC
min [6].
. . .
. . .
. . .
. . .
.
.
.
.
.
.
.
.
.
.
.
.
c11 c12 c1n
c21 c22 c2n
cd1 cd2 cdn
. . .
[6] J. G. Proakis and M. Salehi, Digital Communications, 5th ed. Upper Saddle River, NJ, USA: Prentice-Hall,
November 2007.

Introduction
Conclusion
Composite Hypothesis Testing Decoding (1/2)
If dT ≥ Tcoh, N de-interleaved symbols asossiated with c = [c1 c2 . . . cN ] ∈ C
of a single row
r1:N =





r1
r2
...
rN





=





h1tc1 (Φc1 )
h2tc2 (Φc2 )
...
hN tcN (ΦcN )





+





n1
n2
...
nN





, (18)
where, [n1 n2 . . . nN ] ∼ CN 04N , N0
2
I4N , ∀n ∈ {1, . . . , N}:
rn = r+
0 (n) r−
0 (n) r+
1 (n) r−
1 (n) , (19)
tcn (Φcn ) =
E
2
eΦ0
e−Φ0
eΦ1
e−Φ1
[1 − cn 1 − cn cn cn] , (20)
and h1, h2, . . . , hN independent each other.

Introduction
Conclusion
Composite Hypothesis Testing Decoding (2/2)
Theorem
For bistatic scatter radio noncoherent FSK decoding, we propose
c = arg max
c∈C
E
Φ0,Φ1
max
h∈CN
ln fr1:N |c,h,Φ0,Φ1
(r1:N|c, h, Φ0, Φ1) , (21)
h = [h1 h2 . . . hN] . If dT ≥ Tcoh, then Eq (21) is simpliﬁed to
c = arg max
c∈C
wc , (22)
where, w = [w(1) w(2) . . . w(N)] {z1(n) − z0(n)}N
n=1,
zi (n) |r+
i (n)|2 + |r−
i (n)|2, i ∈ B.

Introduction
Conclusion
Noncoherent Detection over Rayleigh Fading
0 5 10 15 20 25 30 35 40
10
−4
10
−3
10
−2
10
−1
10
0
Average Received SNR (dB)
BER Noncoherent Detection − Backscatter FSK − Rayleigh
Simulation
Theory

Introduction
Conclusion
Rayleigh Fading: Impact of Interleaving Depth
0 5 10 15 20 25 30
10
−6
10
−5
10
−4
10
−3
10
−2
10
−1
10
0
BERNoncoherent Backscatter FSK − Impact of Interleaving − Rayleigh
Uncoded
Coded, d = 5, Tcoh
= 100T
Coded, d = 20, Tcoh
= 100T
Coded, d = 50, Tcoh
= 100T
Coded, d = 100, T
coh
= 100T

Introduction
Conclusion
Rician Fading: Impact of CFO mismatch
0 5 10 15 20
10
−4
10
−3
10
−2
10
−1
10
0
Noncoherent Backscatter FSK − Impact of CFO Mismatch − RiceBER
Uncoded, e
∆F
= 1 Hz
Uncoded, e
∆F
= 0.2 Hz
Uncoded, e∆F
= 0.001 Hz
Coded, e∆F
= 1 Hz, d = 10
Coded, e
∆F
= 0.2 Hz, d = 10
Coded, e∆F
= 0.001 Hz, d = 10
κCT
= 7, κTR
= 2,
T
coh
= 50T

Introduction
Conclusion
Rician Fading: Comparison of RM with BCH
0 5 10 15 20
10
−5
10
−4
10
−3
10
−2
10
−1
10
0
BER Reed Muller vs BCH − Noncoherent Backscatter FSK − Rice
RM, κ
CT
= 0.05, κ
TR
= 0.01
RM, κCT
= 5, κTR
= 0.5
RM, κCT
= 20, κTR
= 5
BCH, κ
CT
= 0.05, κ
TR
= 0.01
BCH, κCT
= 5, κTR
= 0.5
BCH, κ
CT
= 20, κ
TR
= 5
d = 30, T
coh
= 50T

Introduction
Conclusion
Rician Fading: Uncoded Noncoherent VS Coherent [4]
Tcoh = 70T
Ntr = 30
ENC = E
ECoh = 4
7E
0 5 10 15 20
10
−5
10
−4
10
−3
10
−2
10
−1
10
0
Average Received SNR [dB]
BER
Bistatic Scatter Radio FSK − Detection − Impact of Fading
Noncoherent, Rayleigh
Noncoherent, Rician
Noncoherent, Rician
Noncoherent, Rician
Coherent − LS, Rayleigh
Coherent − LS, Rician
κ
CT
= 0 − κ
TR
= 0
κCT
= 20 − κTR
= 5
κ
CT
= 150 − κ
TR
= 80
κCT
= 40
κTR
= 20

Introduction
Conclusion
Bistatic Scatter Radio Setup
Carrier Emitter (CE)
RF Tag
Software Defined Radio
(SDR)
Figure: Bistatic scatter radio setup.

Introduction
Conclusion
Experimental Outdoor Deployment
Carrier emitter: 13 dBm.
Semi-passive RF tag: 8 bit
micro-controller at 1kbps with
FSK.
SDR reader: USRP.
Omnidirectional antennas.
Carrier
Emitter
RF Tag SDR
Reader
Figure: Experimental setup outdoor
deployment.

Introduction
Conclusion
Achieved Ranges (1/2)
Carrier
Emitter
Tag SDR
Reader
dCT
dCR
Figure: Scenario 1.
Carrier
Emitter
Tag SDR
Reader
dCT
dCR
Figure: Scenario 2.
Carrier
Emitter
Tag
SDR
Reader
dCT
dCR
Figure: Scenario 3.

Introduction
Conclusion
Achieved Ranges (2/2)
Table: BER performance for diﬀerent scenarios
Sc. dCR(m) dCT(m) dTR(m) BER coded BER uncoded
1 134 m 2.8 131.2 3.03% > 15%
1 128 m 2.8 125.2 0% 6.4%
2 128 m 4.8 132.8 3.24% 12.11%
3 134 m 2.6 134.025 5.07% > 15%
3 120.4 m 2.6 120.43 0% 8.04%

Introduction
Conclusion
Conclusion
Noncoherent FSK receiver with channel coding for bistatic
scatter radio derived.
Performance is rigorously examined (simulation, analysis and
experimental results).
Proposed coded noncoherent receiver increased
communication range.

Introduction
Conclusion
Publications (Submitted)
P. N. Alevizos, E. Vlachos, and A. Bletsas, “Factor
Graph-based Distributed Frequency Allocation in Wireless
Sensor Networks”, submitted to IEEE Trans. Wireless
Commun.
N. Fasarakis-Hilliard, P. N. Alevizos, and A. Bletsas,
“Coherent Detection and Channel Coding for Bistatic Scatter
Radio Sensor Networking”, submitted to IEEE Trans.
Commun.

Introduction
Conclusion
Publications (Submitted)
P. N. Alevizos and A. Bletsas, “Noncoherent Composite
Hypothesis Testing Receivers for Extended Range Bistatic
Scatter Radio WSNs”, submitted to IEEE ICC 2015.
“Coherent Detection and Channel Coding for Bistatic Scatter
Radio Sensor Networking”, submitted to IEEE ICC 2015.
N. Kargas, P. N. Alevizos, and A. Bletsas, “Boosting
Anti-collision Gen2 Performance with Software Deﬁned
Radio”, submitted to IEEE ICC 2015.

Introduction
Conclusion
Publications (Accepted/Published)
P. N. Alevizos, E. Vlachos, and A. Bletsas, “Factor
Graph-based Distributed Frequency Allocation in Wireless
Sensor Networks”, accepted to IEEE GLOBECOM 2014.
“Cooperative Localization with Narrow-Band Radios”,
accepted to IEEE GLOBECOM 2014.
P. N. Alevizos, N. Fasarakis-Hilliard, K. Tountas, N. Agadakos,
N. Kargas, and A. Bletsas, “Channel Coding for Increased
Range Bistatic Backscatter Radio: Experimental Results,” in
Proc. IEEE RFID-TA, Tampere, Finland, Sep. 2014.

Introduction
Conclusion
Questions?
Thank You!!
Dedicated to my grandparents.

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