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Dual Header Pulse Interval Modulation (DH-PIM)
Dr. Nawras Aldibbiat
Professor Z Ghassemlooy
Optical Communications Research GroupSchool of Computing, Engineering & Information Sciences,
Northumbria UniversityEmail: [email protected]
Tel: 0191 227 3841
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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
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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?
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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
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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
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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.
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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
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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
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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
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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
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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
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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.
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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
,
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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
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DH-PIM Transmitter
MSB = 0?
No
Yes Enable
DH-PIM
M -bitLatch
Pulsegenerator 2sT
Pulsegenerator sT
d = BDCDelay
sTd 1
Enable
Ena
ble
OpticalSource
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DH-PIM Receiver
Matchedfilter
Decisioncircuit
sTt
Clockrecovery
Edgedetector
Slotcounter
Datalatch ( d )
M -bitdata out
Reset
Headeridentifier
DBC
Pre-detection filter
Slotsin
sT1Dealy
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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
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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
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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
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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
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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
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Power Spectral Density - cont.
DH-PIM1
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Power Spectral Density - cont.
DH-PIM2
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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
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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.
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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)
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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
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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)
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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
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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:
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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
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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
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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%
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Multipath Propagation
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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
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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
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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
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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 ____ .......
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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.
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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
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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.
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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
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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
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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
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THANK YOU