8 mohammed olama

Performance Study of Hybrid DS/FFH Spread-Spectrum Systems in the Presence of Multipath Fading and Multiple-Access Interference

Mohammed M. Olama

Teja P. Kuruganti

Steven F. Smith

Computational Sciences & Engineering Division Oak Ridge National Laboratory

Xiao Ma

Electrical Engineering and Computer Science Dept. University of Tennessee

IEEE CQR 2012

2 Managed by UT-Battelle for the Department of Energy

Outline

Introduction

Types of SS Systems

Multipath Fading Channel

Direct Digital Synthesizers (DDS)

Performance Evaluation of DS/FFH

Numerical Results

Conclusion


ORNLs Solution: Hybrid Spread Spectrum Novel technique (3 Patents); adaptive, programmable.

HSS: a synergistic combination of DS, FH, and TH.

Advantages: Adaptive Hybrid Spread-Spectrum (HSS) modulation format

combines DSSS and frequency/time hopping in a multi-dimensional, orthogonal signaling scheme.

Capable of excellent LPI, LPD & security properties (programmable).

Adaptive, robust protocol for high QoS applications. Can be operated in burst mode for very low power drain. Superior resistance to multipath and jamming (high process

gain). Easily deployed with modern chip technology. Compliant with existing FCC/NTIA/ETSI rules for ISM bands. Ideally implemented via modern FPGA-based electronics, ASICs,

and SDR techniques.


Typical HSS Applications


Data

PN Clock

Data

Data Clock

PN Sequence Generator

Carrier

1


Wide BP Filter Narrow BP Filter Phase Demod

Local PN Clock

Local Carrier

1

1

Frequency

Power Spectral Density

fc Frequency


fc Frequency


fc

DIRECT-SEQUENCE SPREAD-SPECTRUM

Narrow spectrum at output of modulator

before spreading

Spectrum has wider bandwidth and lower power density after spreading with PN sequence

(PN Rate >> Data Rate)

Original narrowband, high power density spectrum is

restored if local PN sequence is same as and lined up with

received PN sequence

RFI Spread

RFI

DS Signal


Data

PN Clock

Data

Data Clock

PN Sequence Generator FH

Signal


Wide BP Filter

Narrow BP Filter

Data Demod.

Local PN Clock

1

Frequency


fc Frequency


fc Time (hops) t

FREQUENCY-HOPPING SPREAD-SPECTRUM

Narrow spectrum at output of modulator while hopping

Spectrum has same bandwidth and power density after hopping with PN sequence (PN Rate


Data

PN Clock

Data

Data Clock

PN Sequence Generator DS/FH

Signal


Wide BP Filter

Narrow BP Filter

Data Demod.

Local PN Clock

1

Frequency


fc Frequency


fc Time (bits) t

SLOW HYBRID SPREAD-SPECTRUM (DS/SFH)

DS (wide) spectrum at output of modulator while hopping

Spectrum has same bandwidth and power density after hopping with PN sequence (PN Rate > for FastHSS)

Original narrowband, high power data stream is restored if local PN sequence is same as and lined up with received PN sequence

RFI

RF Frequency

Synthesizer

t0 t4 t3 t5 t1 t2

RF Frequency

Synthesizer

Data Output

t4 t2 t6 t1 t5 t3 t0

RFI Reduced

by DS PG t6


Data

PN Clock

Data

Data Clock

PN Sequence Generator DS/FH

Signal


Wide BP Filter

Narrow BP Filter

Data Demod.

Local PN Clock

1

Frequency


fc Frequency


fc Time (chips) t

FAST HYBRID SPREAD-SPECTRUM (DS/FFH)

DS (wide) spectrum at output of modulator while hopping

Spectrum has same bandwidth and power density after hopping with PN sequence (PN Rate >> Data Rate for FastHSS; e.g., as above, 2 hops per bit).

Original narrowband, high power data stream is restored if local PN sequence is same as and lined up with received PN sequence

RFI

RF Frequency

Synthesizer

t00 t11 t30 t01 t10 t20

RF Frequency

Synthesizer

Data Output

t00

RFI Reduced

by DS PG! t21

FastHSS

t01 t10 t11 t20 t21 t30 t31 t40 t40 t61 t60 t31 t41 t50 t51 t50 t51 t60 t61 t41

Gp(FH/DS) dB = Gp(FH) dB + Gp(DS)dB = 10 log (no. of hopping channels) + 10 log (BWDS/Rinfo)


HSS is a Multidimensional Signal

Code

Frequency

Time

(C4,F2,t0)

HSS can be defined in 3 axes (code, frequency, and time). Each dimension is orthogonal with the others. Permissible signal spaces along an axis may also be ~

orthogonal. Codes Frequencies Time slots

Easily adaptable to exploit

many degrees of freedom to

meet system requirements.

Some signal overlaps may be orthogonal.

(C2,F1,t0)

(C3,F0,t1)

(C1,F2,t2) (C0,F0,t0)


MULTIPATH PROPAGATION

TRANS. RCVR.

LONG-PATH REFLECTION

SHORT-PATH REFL. Differential delays are approx. 1 ns per foot Short-path delays (indoors) are typically < 0.1s Spread-spectrum modulation can largely cancel long-path effects

ORNL is developing new techniques to mitigate short-path degradations!


Direct Digital Synthesizers (DDS)

The implementation of a DDS has two distinct parts: A phase accumulator accumulates the phase

increment and adds in the phase offset. The DDS output is then calculated by quantizing the

results of the phase accumulator section and using them to select values from a lookup table.

Phase

Increment

Phase

Offset

Dither

Delay Adder Phase

Quantization

Lookup

Table NCO Adder Adder

Phase

Quantization

Error

Stored Phase


RF Coexistence Multi-User, Jamming, and Multipath Fading Performance

ML

bTTL

=

bc

TTNL

= PN

N PN

DSW

JW

Wp

JW

Number of FH channels

Number of hops per bit

Duration of each hop

Chip duration for sequence

Period of the

Bandwidth of DS waveform

Bandwidth of the wideband jamming

Number of hopping channels corrupted by jamming

Part of the bandwidth of the channel partially corrupted by jamming

sequence

1

0

1

0

( )

{ ( , ) ( , ) ( , )}

Kk

hj

Kk k k

j

P P j users

P j users no jam P j users ful jam P j users partial jam

=

=

=

= + +

1

0{ ( , ) ( | , )

( , ) ( | , )( , ) ( | , )}

Kk

j

k

k

P j users no jam P j users no jam

P j users ful jam P j users ful jamP j users partial jam P j users partial jam

=

=

+

+

The error probability of one hop is:

The error probability of one bit is:

12

( ) (1 )L

d L db h h

Ld

LP P P

d

+=

=

K Number of users


RF Coexistence Multi-User, Jamming, and Multipath Fading Performance

ML

bTTL

=

bc

TTNL

= PN

N PN

DSW

JW

Wp

JW

Number of FH channels

Number of hops per bit

Duration of each hop

Chip duration for sequence

Period of the

Bandwidth of DS waveform

Bandwidth of the wideband jamming

Number of hopping channels corrupted by jamming

Part of the bandwidth of the channel partially corrupted by jamming

sequence

From the problem formulation, we have 1

1

1

1 1 1 1( , ) 1

1 1 1( , ) 1

1 1 1 1( , ) 1

j K j

j K j

j K j

K M WP j users no jamj M M M

K WP j users full jamj M M M

KP j users partial jam

j M M M

=

=

=

1( | , )/ 2

k

kj

P j users no jam QNSR I

= + Noise-to-signal ratio

Interference to signal ratio introduced by the other users hopping in user ks channel

No Jamming

Full Jamming

1( | , )/ 2 / 2

k

kj

P j users full jam QNSR JSR I

= + +

Jamming-to-signal ratio

Partial Jamming ( | , ) ( | , , ) (1 ) ( | , , )k k kP j users partial jam q P j users partial jam corrupted portion q P j users partial jam uncorrupted portion = +

/pJ DSq W W= Fraction of the channel jammed

0 / 2NSR N PT=

/ 2JJSR N PT=

P Transmitted signal power


Hybrid DS/FFH Multi-user Simulation Severe (~worst-case)

channel conditions: K = 20-120 users, 100%

duty cycle L = 5 hops/bit M = 20 channels N = 127 PN code length DS PG = 21 dB JNR = 13 dB Rician coeff. = 0.1 Chan. covariance = 10 Jammed chan. = 5 Channel portion

partially corrupted = 0.4

Represents user flooding in rough terrain.

Performance of a hybrid DS/FFH system: Effect of different number of

users (multi-user interference).

5 10 15 2010-8

10-7

10-6

10-5

10-4

10-3

10-2

SNR(dB)

Erro

r Pro

babi

lity

20 users40 users60 users80 users100 users120 users



channel conditions: K = 100 users, 100%

duty cycle L = 5 hops/bit M = 20 channels N = 127 PN code length DS PG = 21 dB JNR = 10-16 dB Rician coeff. = 0.1 Chan. covariance = 10 Jammed chan. = 5 Channel portion



Performance of a hybrid DS/FFH system: Effect of different jamming-to-

noise ratios (JNRs).

5 10 15 2010

-4

10-3

10-2

10-1

SNR (dB)

Erro

r Pro

babi

lity

JNR=16 dBJNR=14.7 dBJNR=13 dBJNR=10 dB




duty cycle L = 5 hops/bit M = 20 channels N = 127 PN code length DS PG = 21 dB JNR = 13 dB Rician coeff. = 0.1 Chan. covariance = 10 Jammed chan. = 2-8 Channel portion



Performance of a hybrid DS/FFH system: Effect of different number of

fully-jammed channels.

5 10 15 2010

-4

10-3

10-2

10-1

SNR (dB)

Erro

r Pro

babi

lity

8 channels fully jammed6 channels fully jammed4 channels fully jammed2 channels fully jammed




duty cycle L = 1-7 hops/bit M = 20 channels N = 127 PN code length DS PG = 21 dB JNR = 13 dB Rician coeff. = 0.1 Chan. covariance = 10 Jammed chan. = 5 Channel portion



Performance of a hybrid DS/FFH system: Effect of different numbers of

frequency hops per bit.

5 10 15 2010

-4

10-3

10-2

10-1

100

SNR (dB)

Erro

r Pro

babi

lity

1 hop/bit3 hops/bit5 hops/bit7 hops/bit




duty cycle L = 5 hops/bit M = 10-40 channels N = 127 PN code length DS PG = 21 dB JNR = 13 dB Rician coeff. = 0.1 Chan. covariance = 10 Jammed chan. = 5 Channel portion



Performance of a hybrid DS/FFH system: Effect of different numbers of

available hopping channels.

5 10 15 2010

-4

10-3

10-2

10-1

SNR (dB)

Erro

r Pro

babi

lity

10 hopping channels20 hopping channels30 hopping channels40 hopping channels




duty cycle L = 5 hops/bit M = 20 channels N = 4-64 PN code length DS PG = 21 dB JNR = 13 dB Rician coeff. = 0.1 Chan. covariance = 10 Jammed chan. = 5 Channel portion



Performance of a hybrid DS/FFH system: Effect of different DS PN code

lengths.

0 1 2 3 4 5 6 7 8 9 1010

-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

SNR

BE

R

4 PN Code Length8 PN Code Length16 PN Code Length32 PN Code Length64 PN Code Length




duty cycle L = 5 hops/bit M = 20 channels N = 127 PN code length DS PG = 21 dB JNR = 13 dB Rician coeff. = 0.1-0.7 Chan. covariance = 10 Jammed chan. = 5 Channel portion


Represents user flooding in rough terrain

Performance of a hybrid DS/FFH system: Effect of different Rician fading

channel parameters.

5 10 15 2010

-4

10-3

10-2

10-1

SNR (dB)

Erro

r Pro

babi

lity

gamma=0.7gamma=0.5gamma=0.3gamma=0.1




duty cycle L = 5 hops/bit M = 20 channels N = 127 PN code length DS PG = 21 dB JNR = 13 dB Rician coeff. = 0.1 Chan. covariance = 10 Jammed chan. = 5 Channel portion



Performance of a hybrid DS/FFH system: Effect of different hitting rates.

0 1 2 3 4 5 6 7 8 9 1010

-6

10-5

10-4

10-3

SNR

BE

R

No Hit2% Hit4% Hit6% Hit10% Hit


Hybrid DS/FFH Comparative Simulation Severe (~worst-case)

channel conditions: Two-path Rayleigh

chan. P1: = 0, gain = 0.7 P2: = 0.3 s, gain =

0.4 Equal-bandwidth cases DS SF = 16 FH: 16 ch., 4 b/hop DS/FH: SF = 16, 4

hopping freqs.

Represents the fixed-bandwidth advantage of DS/FFH format over other modulations.

Comparative performance of a hybrid DS/FFH versus other forms in Rayleigh

fading.

0 1 2 3 4 5 6 7 8 9 1010

-7

10-6

10-5

10-4

10-3

10-2

10-1

100

SNR

BE

R

2-Path Rayleigh BPSKDSSFHFFHHybrid DS-SFHHybrid DS-FFH


The performance of a hybrid DS/FFH system was analytically evaluated in a worst-case use scenario.

We derived the average BER for a hybrid DS/FFH system that includes the effects from wide-band and partial-band jamming, multi-user interference and/or varying degrees of Rician/Rayleigh fading.

Numerical results exploring the parameter space of the HSS system have been presented to demonstrate its effectiveness under different conditions and scenarios.

The detailed performance and security aspects of HSS signals will be further analyzed in a future paper.

Conclusions


Performance Study of Hybrid DS/FFH Spread-Spectrum Systems in the Presence of Multipath Fading and Multiple-Access InterferenceOutlineORNLs Solution: Hybrid Spread SpectrumTypical HSS ApplicationsSlide Number 5Slide Number 6Slide Number 7Slide Number 8HSS is a Multidimensional SignalSlide Number 10Direct Digital Synthesizers (DDS) RF Coexistence Multi-User, Jamming, and Multipath Fading PerformanceRF Coexistence Multi-User, Jamming, and Multipath Fading PerformanceHybrid DS/FFH Multi-user SimulationHybrid DS/FFH Multi-user SimulationHybrid DS/FFH Multi-user SimulationHybrid DS/FFH Multi-user SimulationHybrid DS/FFH Multi-user SimulationHybrid DS/FFH Multi-user SimulationHybrid DS/FFH Multi-user SimulationHybrid DS/FFH Multi-user SimulationHybrid DS/FFH Comparative SimulationConclusionsSlide Number 24

8 mohammed olama

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