Dual Header Pulse Interval Modulation (DH-PIM)

Dr. Nawras Aldibbiat

Professor Z Ghassemlooy

Optical Communications Research GroupSchool of Computing, Engineering & Information Sciences,

Northumbria UniversityEmail: Nawras.Aldibbiat@unn.ac.uk

Tel: 0191 227 3841

Outline of the Presentation

• Introduction• DH-PIM principles• Power spectral density• Artificial light interference• Slot & packet error probabilities• Optical power & B/W requirements.• Multipath propagation• Conclusions

Introduction

DH-PIM was first introduced in 2000: N. M. Aldibbiat & Z. Ghassemlooy: “Dual header-pulse interval modulation (DH‑PIM) for optical communication systems”, CSNDSP 2000, Bournemouth, UK, pp. 147-152, July 2000.

Why DH-PIM?

Is it ideal for Indoor optical wireless systems?

RX

TX

TX RX

TX

RX

TX RX

(Diffuse)

TX

RX

TX RX

Introduction

Line-of-SiteLine-of-Site

Non-Line-of-SiteNon-Line-of-Site

HybridHybridDirectedDirected Non-directedNon-directed

Pulse Time Modulation Tree

DH-PIM

Pulse Time Modulation

Analogue Digital

Isochronous Anisochronous

DPWM

MPPM

PPM

PCM

DPIWM

DPPM

DPIM

AnisochronousIsochronous

PIWM

PIM

PFM

SWFM

PWM

PPM

Pulse Modulation Symbol Structure

Symbol1

Symbol2

Symbol3

OOK

PPM

DPIM

DH-PIM 2

Time

bT

sT2sT

0 0 0 0 0111 1 11 1

H2H1

Redundantspace

M = 4 bits

L = 2 M = 16 slotsInformation

Information

Info.

DH-PIM symbol structure

H 1

nT sn TT )1(

symbol

Information slots

t

V

n th

v

Guardband

2/sT

snTd

1nT

sg TT )12/(

H 2

symbol

Information slots

t

n th

v

sn TT )1(

Guardband

nT

sT

snTd

1nT

sg TT 1V

0 2

3)(2rect

2

1)(2rect)(

n s

nn

s

n

T

Tth

T

TtVtx

1

00 )1(

n

kksn dnTTT

Symbol Length

minL maxL L

PPM M2 M2 M2

DPIM 2 12 M 2/32 M

DH-PIM 1 12M 2/212 1 M

OOK PPM DPIM DH-PIM2

0 0 0 1 0 0 0 0 0 0 0 1 0 1 0 0

0 0 1 0 1 0 0 0 0 0 0 1 0 0 1 0 0 0

0 1 0 0 0 1 0 0 0 0 0 1 0 0 0 1 0 0 0 0

0 1 1 0 0 0 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0

1 0 0 0 0 0 0 1 0 0 0 1 0 0 0 0 0 1 1 0 0 0 0

1 0 1 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0 1 10 0 0

1 1 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 1 1 0 0

1 1 1 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 0

3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 80

50

100

150

200

250

M [slot]

Ave

rag

e s

ymb

ol l

en

gth

[T

s]

PPM DPIM DH-PIM 1DH-PIM 2

Average Symbol Length

Transmission bandwidth

DH-PIM

requires less

bandwidth

compared

with PPM

& DPIM.

Bandwidth normalised to OOK:

3 4 5 6 7 80

4

8

12

16

20

24

28

32

M [slot]

No

rma

lise

d b

an

dw

idth

re

qu

ire

me

nts

DH-PIM1 DH-PIM2

DH-PIM3

DPIM

PPM

)32(

2

M

bDPIMreq R

MB

Mb

PPMreq R

MB

2

M

RB

Mb

req )122( 1

Transmission Packet Rate

2 3 4 5 6 7 8 9 100.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

M [bit]

Nor

mal

ised

pac

ket

tran

smis

sion

rat

e

DH-PIM3

DH-PIM1

DH-PIM2

DPIM

PPM

Breq = 1 MHz

)122( 1

M

reqpkt N

MBR

)32(

2

M

DPIMreqDPIMpkt N

MBR

M

PPMreqPPMpkt N

MBR

2

1 2 3 4 5 6 7 8 9 10

x 106

0

100

200

300

400

500

600

700

800

Breq [Hz]

pa

cke

t tr

an

smis

sio

n r

ate

[p

ack

et/

sec]

M = 5

PPM

DH-PIM3

DH-PIM2

DH-PIM1

DPIM

Transmission Packet Rate - cont.

Transmission Capacity

codes validof no.2max LogRL

LC bT

3 4 5 6 7 8 9 100

2

4

6

8

10

12

M [slot]

No

rma

lise

d t

ran

smis

sio

n c

ap

aci

ty

DH-PIM 1

DH-PIM 2

DH-PIM 3

DPIM

PPM

21

12

122

22

M

Mreq

T

BMC

22

,32

124

M

Mreq

DPIMT

BMC

M

reqPPMT

BMC

2

2

,

DH-PIM system block diagram

TransmitterTransmitter ChannelChannel ReceiverReceiver

M bitsdata out

M bitsdata in

Pre-detectionfilter

OpticalChannel

Optical TX Optical RXDH-PIM

ModulatorDH-PIM

Demodulator

Whitenoise

Clockrecovery

DH-PIM Transmitter

MSB = 0?

No

Yes Enable

DH-PIM

M -bitLatch

Pulsegenerator 2sT

Pulsegenerator sT

d = BDCDelay

sTd 1

Enable

Ena

ble

OpticalSource

DH-PIM Receiver

Matchedfilter

Decisioncircuit

sTt

Clockrecovery

Edgedetector

Slotcounter

Datalatch ( d )

M -bitdata out

Reset

Headeridentifier

DBC

Pre-detection filter

Slotsin

sT1Dealy

Simulation Waveforms (16-DH-PIM1 )

0 2 4 6 8 10 12 14 160

0.5

1

t [Sec]

Inp

ut

da

ta

0 2 4 6 8 10 12 14 160

0.5

1

t [Sec]

Tra

nsm

itte

d D

H-P

IM

0 2 4 6 8 10 12 14 16-0.5

0

0.5

1

t [Sec]

Re

ceiv

ed

DH

-PIM

Simulation Waveforms (16-DH-PIM1 ) - cont.

0 2 4 6 8 10 12 14 16-0.5

0

0.5

t [Sec]

Mat

ched

Filt

er o

utpu

t

0 2 4 6 8 10 12 14 160

0.5

1

t [Sec]

Rec

eive

d D

H-P

IM

0 2 4 6 8 10 12 14 160

0.5

1

t [Sec]

Out

put d

ata

Simulation Model

Transmitterfilter p (t)

Input Mbits Multipath

channelh(t)

DH-PIMencoder X

34 PL

X

RShot noise

n (t)

DH-PIMdecoder

OutputM bits

Matchedfilter r(t)

sTt

Sample

y ic count

Power Spectral Density

oddanoddbothand2

;

evenoreveneitherand2

;0

2;

122

1Re

4sin89

4sin45

4sin4

)(

12

2222

dKT

K

KT

K

T

K

T

GGTTT

V

P

s

s

sM

s

sss

1

)1(2

21

11

M

Tj

Tj

Tj s

s

Ms e

e

eG

Power Spectral Density - cont.

0 1 2 3 410

-8

10-6

10-4

10-2

100

102

F [Hz]

PS

D [

Wa

tts/

Hz]

Predited result Simulated result

8-DH-PIM 2

Power Spectral Density - cont.

DH-PIM1

Power Spectral Density - cont.

DH-PIM2

2 3 4 5 6 7 80

1

2

3

4

5

6

7

8

9

10

M [bit]

PDC

-nor

DH-PIM1

DH-PIM5

DH-PIM4

DH-PIM3

DH-PIM2

DC component of the PSD

2 3 4 5 6 7 80

0.2

0.4

0.6

0.8

1

M [bit]

P sl0t

-nor

DH-PIM1

DH-PIM3

DH-PIM5

Slot component of the PSD

Artificial light interference

• Artificial light (e.g. Fluorescent) induces periodic interference that contain harmonics at low frequencies

• This interference can be reduced by employing a high-pass filter, but …

• this results in baseline wander, which is more severe in modulation schemes that contain high power at DC and low frequencies. Therefore …

• there is a trade-off between the extent of artificial light interference rejection and the severity of baseline wander

Artificial light interference

0 1 2 3 4 5 60

0.2

0.4

0.6

0.8

1

Normalised frequency (f / Rb

)

PS

D (

linea

r un

its)

M = 4 (L = 16)

DH-PIM (alpha=2)

DH-PIM (alpha=1)

DPPM

OOK-NRZ

PSD for OOK, DPPM and DH-PIM (=1 and = 2) for M = 4

Artificial light interference – cont.

Simulation block diagram

1

Transmitterfilter p (t)

Input Mbits Channel

h(t)DH-PIMencoder X

pI Shot noisen (t)

Matchedfilter r (t)

DH-PIMdecoder

OutputM bits

sTt

SampleHPF f(t)

Assumptions:

-a rectangular pulse shape

-an equal average transmitted optical power for all systems

Artificial light interference – cont.

10-5

10-4

10-3

10-2

10-1

100

-4

-2

0

2

4

6

8

10

fc/R

b

Opt

ical

pow

er re

quire

men

ts (d

B)

8-DH-PIM1 (no multipath dispersion)

Rb=10Mbps

Rb=100Mbps

Rb=1Mbps

- 8-DH-PIM1 on non-dispersive channel

- For fc/Rb < 0.01, an additional 5 dB of power is required when Rb is increased from 1 Mbps to 10 Mbps and from 10 Mbps to

100 Mbps.

- for fc/Rb > 0.01, the power requirement starts to increase

more swiftly for 1 Mbps than 10 Mbps and 100 Mbps.

Artificial light interference – cont.

10-5

10-4

10-3

10-2

10-1

100

-3

-2

-1

0

1

2

3

fc/R

b

Opt

ical

pow

er re

quire

men

ts (d

B)

8-DH-PIM1 (R

b=1Mbps)

NDS=0.10

NDS=0.01

NDS=0.05

- 8-DH-PIM1 assuming multipath propagation

-Normalised delay spread (NDS) = RMS delay spread (DT) / Bit rate (RB)

- For fc/Rb < 0.01, the power requirements are constant for all values of NDS with NDS of 0.1 displaying the highest value

- For fc/Rb > 0.01, the power requirements increase exponentially reaching the same value for fc/Rb > 0.5

Artificial light interference – cont.

10-4

10-3

10-2

10-1

100

101

0

1

2

3

4

5

6

7

8

9

fc/Rb

Opt

ical

pow

er p

enal

ty (d

B)

OOK8-DPIM8-PPM8-DH-PIM1

8-DH-PIM2

-Rb = 1Mbps and no multipath dispersion

-DH-PIM1 has marginally higher power penalty than DPIM and PPM but lower than OOK

- For fc/Rb = 0.1: DH-PIM displays far less power penalty than OOK but 1.6 dB and 1 dB additional power penalty compared with PPM and DPIM, respectively. This is because at low frequency region, the PSD of DH-PIM is higher than PPM and DPIM and lower than OOK

Slot/packet error rate

Assumptions:

•The input signal is composed of binary independent, identically distributed bits of ‘1’s and ‘0’s

• The matched filter is sampled at the slot frequency fs

• The channel is a distortion free channel

• No bandwidth limitations imposed by the transmitter and receiver

• The dominant noise source is the background shot noise

• No interference due to artificial light

• Packet length G = 1KB bits

• Equal occurrence of H1 and H2

Slot error rate

for DH-PIM is given by:

for PIM:

ooslote N

PRLMkQ

N

PRLMkQL

LP

2

222

2

222

9

)1(323

9

3234

4

1

o

PIM

o

PIMPIM

PIMPIMslote N

PRLMkQ

N

PRLMkQL

LP

222222

,

)1(221

1

: average transmitted optical power, R: a photodetector responsivity. 0 < k < 1 is the threshold factor.

P

where

Slot error rate Vs. SNROOK

• The higher the M, the better the slot error rate performance.

• Simulated results

match the predicted ones.

-5 -3 -1 1 3 5 7 9 1110

-5

10-4

10-3

10-2

10-1

100

SNROOK [dB]

Slo

t err

or r

ate

M = 3

M = 4

M = 5

DH-PIM (alpha=1)*** Simulated__ Predicted o

OOK N

PRSNR

222

• 12,000 consecutive random bits were used in simulation.

• Slot error rate is shown down to 10-5 due to computational power.

Slot error rate - cont.

• DH-PIM and DPIM offer improved slot error performance compared with OOK, but inferior to that of PPM.

• At slot error rate of 10-9 PIM and DH-PIM ( = 1) display an improvement of ~5 dB over DH-PIM ( = 2).

-10 -8 -6 -4 -2 0 2 4 6 8 10 12 14

10-8

10-6

10-4

10-2

100

SNROOK

[dB]

Slo

t er

ror

rate

OOK

DH-PIM (alpha=2)

PIM PPM

L=16 slot (M=4 bits)

DH-PIM (alpha=1)

Packet error rate

• For DPIM:

• For DH-PIM:

oopkte N

PRLMkQ

N

PRLMkQL

M

GP

2

222

2

222

9

)1(323

9

3234

4

o

PIM

o

PIMPIMPIMpkte N

PRLMkQ

N

PRLMkQL

M

GP

222222

,

)1(221

G is the packet length in bits.

MLGslotepkte PP /11 The packet error rate is given by

Packet error rate Vs. SNROOK

G = 1KB bits.

• DH-PIM and DPIM offer improved packet error performance compared with OOK, but inferior to that of PPM.

• At packet error rate of 10-6 PIM and DH-PIM ( = 1) display an improvement of ~5 dB over DH-PIM ( = 2).

0 2 4 6 8 10 12 1410

-6

10-5

10-4

10-3

10-2

10-1

100

SNROOK

[dB]

Pac

ket

erro

r ra

te

OOK

DH-PIM (alpha=2)

PIM PPM

L=16 slots (M=4bits)

DH-PIM (alpha=1)

DH-PIM packet error rate - cont.

G = 1KB bits

• The higher the M, the better the packet error rate performance.

• The smaller the , the better the packet error rate performance.

0 2 4 6 8 10 12 1410

-6

10-5

10-4

10-3

10-2

10-1

100

SNROOK

[dB]

Pac

ket

erro

r ra

te

M=4 & alpha=1M=4 & alpha=2M=5 & alpha=1M=5 & alpha=2

DH-PIM

Retransmission

Parameters:ret = 1, 3, 4 and 5 Majority decision scheme retransmission rateM = 2, 3, 4 and 5 Bit resolutionα = 1 and 2 No of slots in the wide pulse of the headerN_bits = 60,000 No of bits in the simulationK = 50% Threshold factorRb = 1 MB/S Bit rateη = 6.4000e-023; One-sided PSD of the noiseI_bg = 200 µAmp Background noise currentR = 0.6 Receiver responsivity.SNR = -10:14 signal-to-noise ratio in dB.

Decoder

OutputM bitsOptical

transmitter

Input Mbits Non-

dispersivechannel h (t)

Encoder X

pIx(t)

Opticalreceiver X

R Shot noisen (t)

Matchedfilter r(t)

sTt

Sample

y(t)

MDS

Simulation block diagram:

Retransmission - cont.

-55 -54 -53 -52 -51 -50 -4910

-6

10-5

10-4

10-3

10-2

10-1

100

Average TX Optical Power [dBm]

Slo

t er

ror

rate

16-DH-PIM1

Ret = 1

Ret = 3

Ret = 5

Ret = 4

• At SER = 10-4

• DH-PIM with Ret = 3 gives an improvement of ~ 1 dBm over standard DH-PIM

• DH-PIM with Ret = 5 gives an improvement of ~ 2 dBm over standard DH-PIM

Retransmission - cont.

-55 -54 -53 -52 -51 -50 -49 -48 -4710

-5

10-4

10-3

10-2

10-1

100

Average TX Optical Power [dBm]

Slo

t er

ror

rate

16-DH-PIM2

Ret = 1Ret = 5

Ret = 3

Ret = 4

• At SER = 10-4

• DH-PIM with Ret = 3 gives an improvement of ~ 1 dBm over standard DH-PIM

• DH-PIM with Ret = 5 gives an improvement of ~ 2 dBm over standard DH-PIM

Optical Power Vs. bandwidth requirements

• The average optical power is calculated at packet error rate of 10-6 for a packet length of 1KByte.

• To minimise the optical power and bandwidth, the parameter combinations are:

DH-PIM (L=16, =1)

DH-PIM (L=64, =2)

DPIM L = 161 2 3 4 5 6 7 8 9

-10

-8

-6

-4

-2

0

2

4

Normalised bandwidth requirements

No

rma

lise

d o

ptic

al-p

ow

er

req

uire

me

nt

[dB

]

DH-PIM (alpha=1)DH-PIM (alpha=2)PIM OOK

L=2

2 2 4

8

16

32

64

128

256

4

8

16

32

64

4

8

16

32

64

100%

50%

33.33%

25%

Multipath Propagation

Multipath Propagation

Calculate prob ofoccurrence &

multiply

'1' detected?

Calculate prob for'1' or '10' or '11' &

multiply

Segment of m slots: { si,1, s i+2, ..., s i+m}

Count No. of 0's

'1' detected at start of full DH-PIM symbol

Start

Leading slot = 0?

Next slot = 1?

Calculate prob ofoccurrence

Acceptable?

Count No. of 0's

Could be H1 or H2

Acceptable?

Set initial prob

Calculate prob ofoccurrence

Hence H 2 & start offull DH-PIM symbol.

Reset to start ofsegment.No Yes

No

No

Yes

At least 3 moreslots?

Invalid segmentprob = 0.

Acceptable?

Calculate no. of 0's

Acceptableheader?

Calculate prob ofoccurrence &

multiply

All done

Yes

Yes

No

No

No

No

No

Yes

Yes

Yes

Yes

Select

Completsymbol?

NoYes

Calculate prob ofoccurrence

0 1 2 3 4 5 6 7 8 90

1

2

3

4

5

6

7

8x 10

-6

Ts

Ca

sca

de

d s

yste

m im

pu

lse

re

spo

nse

32-DH-PIM1, Rb = 1 Mbps

DT = 0.001DT = 0.01 DT = 0.1 DT = 0.2

_____ __ __ ___ _ ........

Impulse Response

Diffuse Systems - Eye Diagram

NDS = 0.01

1 2 3 4 5 6 7 80

0.2

0.4

0.6

0.8

1

1.2x 10

-3

NDS = 0.1

1 2 3 4 5 6 7 80

0.2

0.4

0.6

0.8

1

x 10-3

Optical Power Requirements

10-3

10-2

10-1

100

-7

-5

-3

-1

1

3

5

7

9

11

RMS delay spread / T b

No

rma

lise

d o

ptic

al p

ow

er

req

uir

em

en

ts (

dB

)

L = 4

8

16

32

8

16

32

4

DH-PIM1 DH-PIM2

L = 32 ____ .......

10-3

10-2

10-1

100

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

RMS delay spread / T b

No

rma

lise

d o

ptic

al p

ow

er

req

uir

em

en

ts (

dB

)

DH-PIM1DH-PIM2DPIM PPM OOK

L = 32

Optical Power Requirements - cont.

Optical Power Penalty

10-3

10-2

10-1

100

0

2

4

6

8

10

12

RMS delay spread / T b

No

rma

lise

d o

ptic

al p

ow

er

pe

na

lty (

dB

) _____ L = 4 .......... L = 8 --o--o-- L = 16 __ __ L = 32

DH-PIM1 DH-PIM2

10-3

10-2

10-1

100

0

2

4

6

8

10

12

14

RMS delay spread / T b

Op

tica

l po

we

r P

en

alty

(d

B)

DH-PIM1DH-PIM2DPIM PPM OOK

L = 32

Optical Power Penalty - cont.

Conclusions

• Compared with PPM and DPIM, DH-PIM offers:– shorter symbol length

– higher transmission rate

– less bandwidth requirements

– simple slot synchronisation

– built-in symbol synchronisation

• DH-PIM offers improved error performance compared with OOK, but inferior to PPM and similar to DH-PIM

Conclusions - cont.

• The optimum system performance in terms of optical power and bandwidth requirements is achieved at DH-PIM (L=16, =1), DH-PIM (L=64, =2) and DPIM L = 16.

• A trade-off between the extent of artificial light interference rejection and the severity of baseline wander.

• Retransmission of DH-PIM symbols for 3 times or more gives significant improvement to the probability of errors at the expense of reducing the throughput

Final Remarks

• Acknowledgements:– Professor Fary Ghassemlooy (Associate Dean For Research)– Dr. R. McLaughlin (Sheffield Hallam University)

• Two MSc students are working on DH-PIM:– Wasiu Popoola: Equalisation– Olusegun Sanyaolu: Coding

• We’re seeking collaboration with staff or students from Informatics regarding mathematical analysis

THANK YOU