Experimental Demonstration of FEC in 2D λ-t OCDMA...
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1 1 Experimental Demonstration of FEC in 2D λ-t OCDMA Using a Receiver with CDR and Reed-Solomon Decoding Julien Faucher 1 , Simon Ayotte 2 , Ziad El-Sahn 2 , Mustansir Mukadam 1 , Leslie A. Rusch 2 , and David V. Plant 1 1 McGill University, Montréal, Canada 2 Université Laval, Québec, Canada 2 Outline Outline 1. Introduction - OCDMA - Need for CDR and FEC 2. λ-t OCDMA 3. Experimental setup 4. CDR-FEC receiver 5. BER results 6. Conclusion
Transcript of Experimental Demonstration of FEC in 2D λ-t OCDMA...
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Experimental Demonstration of FEC in 2D λ-t OCDMA Using a Receiver
with CDR and Reed-Solomon Decoding
Julien Faucher1, Simon Ayotte2, Ziad El-Sahn2, Mustansir Mukadam1, Leslie A. Rusch2, and David V. Plant1
1McGill University, Montréal, Canada2Université Laval, Québec, Canada
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OutlineOutline
1. Introduction- OCDMA- Need for CDR and FEC
2. λ-t OCDMA3. Experimental setup4. CDR-FEC receiver5. BER results6. Conclusion
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One code allocated to each channel
Codes can be based on time, wavelength, space, polarization or phase
OCDMA signals are broadcast to all users
Users transmit simultaneously and asynchronously
OCDMA:OCDMA:Optical Code Division Multiple AccessOptical Code Division Multiple Access
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OCDMA AdvantagesOCDMA Advantages
An alternative to WDMA and TDMA for PONs
Sub-Gb/s rates for FTTH
Potentially low cost components
Soft-capacity
Decentralized
Bursty traffic
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CDR and FECCDR and FEC
For the first time, we present a complete, standalone OCDMA receiver capable of achieving the following functions:
– Eliminating multiple-access-interference (MAI)– Clock and data recovery (CDR)– Forward error correction (FEC) to overcome
OCDMA noises
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2 dimensional codes: Time and wavelength
Time
Wav
elen
gth
Time
Wav
elen
gth
Bit time
Chip time
«1» «0» «1» «0»
Time
Wav
elen
gth
Desired userInterfererDetection windowBroadband source modulated by the data
Encoded OCDMA chips
The matched channelis correctly decoded
The interferer power is spread (MAI)
Power outside the detection window is discarded
WavelengthWavelength--time OCDMA time OCDMA
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WavelengthWavelength--time OCDMA time OCDMA with with FiberFiber Bragg GratingsBragg Gratings
The FBG periods determine the code wavelengthsThe FBG positions determine the induced delays
H. Fathallah, L. A. Rusch, and S. LaRochelle, J. Lightwave Technol. (1999)
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The The λλ--t OCDMA setupt OCDMA setup
EAM: electro-absorption modulatorEDFA: erbium doped fiber amplifierVOA: variable optical attenuator
Enc: encoderDec: decoderLPF: low pass filter
EAM 1 x 8
LPF
Enc 6
VOA
Broadband source
Delay lines
Photo-detector
Pattern generator
Error detector
Clock Data
Enc 2Enc 3Enc 4Enc 5
Enc 1
Dec 1
EDFA
EDFA
OCDMAreceiver
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OCDMA codesOCDMA codes
Codes:– Channel spacing = 50 GHz– Length = 29– Weight = 8
1551 1552 1553 1554 1555 1556 1557-75
-70
-65
-60
-55
-50
-45
-40
-35
-30
-25
Wavelength (nm)
PSD
(dB
m/0
.01n
m)
1 user6 users
Chip rate = 1.339 Gchip/s = 1.25 Gbchip/s * 15/14 (FEC)Bit rate = chip rate/8 = 167.4 Mb/s, 156.25 Mb/s before FEC
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Eye diagramsEye diagrams
Two Users
Interfering λs appear in the peak of user 1– Worst case scenario– OCDMA receiver tested under severe conditions
One User
Four Users
Six Users
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OCDMA receiverOCDMA receiver
Comma detector
+framer
1:8deserializer
8:1serializer
RS(255,239) decoder
1.339 Gb/sCDR
PLLs
Q
RZto
NRZconverter
167 Mb/sdata1.339 Gchip/s
OCDMA data
ON/OFF
FPGA
167 MHzclock
Quantizer: thresholds data to filter out MAICDR: clock and data recovery (chip rate)Reed-Solomon decoder on FPGA
Input Output
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BER measurementsBER measurements
Solid line: global clockDotted line: recovered clock (without FEC)
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-5
-4
-3
-2
-1
0
Useful power (dBm)
Log(
BER
)
1 user2 users3 users4 users5 users6 users
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-5
-4
-3
-2
-1
0
Useful power (dBm)
Log(
BE
R)
1 user2 users3 users4 users5 users6 users
Recovered clock with FECFloor eliminated for BERs better than 10-4,
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BER prediction after FECBER prediction after FEC
mBS PP )1(1 −−=
( ) j
Sj
Stj
m
mFECS
mm
PPj
jP −−−
+=
−⎟⎟⎠
⎞⎜⎜⎝
⎛ −−
≈ ∑ 1212
1_ 1
1212
1
mnPP FECSFECB /__ ×=
BER before FEC
Symbol error rate before FEC:
Symbol error rate after FEC:
BER after FEC:
m = 8 bits per symboln = # of bit errors per symbol error
(1: lower bound, 8: upper bound)t = 8 correctable symbols per block of 255
B. Sklar, Digital communications: Fundamentals and Applications, 2nd ed. (Prentice Hall, Upper Saddle River, 2001).
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BER prediction after FECBER prediction after FEC
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-5
-4
-3
-2
-1
0
Useful power (dBm)
Log(
BE
R)
1 user2 users3 users4 users5 users6 users
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-5
-4
-3
-2
-1
0
Useful power (dBm)
Log(
BER
)
1 user2 users3 users4 users5 users6 users
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-5
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-1
0
Useful power (dBm)
Log(
BER
)
1 user2 users3 users4 users5 users6 users
PB
PB_FEC
Lower bound (1 bit error per symbol)Upper bound (8 bit errors per symbol)
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ConclusionConclusion
Standalone receiver with– Quantizer that eliminates MAI– Automatic payload detection– Clock and data recovery– Reed-Solomon FEC decoding
FEC improves soft-capacity of λ-t OCDMA– Eliminates BER floors up to ~10-4
– Increases number of users from two to five
