Uncoordinated Optical Multiple Access using IDMA and Nonlinear TCM

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Uncoordinated Optical Multiple Access using IDMA
and Nonlinear TCM
UCLA Electrical Engineering Department-Communicati
on Systems Laboratory

• PIs Eli Yablanovitch, Rick Wesel, Ingrid
  Verbauwhede, Bahram Jalali, Ming Wu
• Students whose work is discussed here
• Juthika Basak, Herwin Chan, Miguel Griot, Andres
  Vila Casado, Wen-Yen Weng

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OCDMA Coding Architecture
1.2 Gbps
2 Gbps
60 Mbps
Reed Solomon (255, 237)
Trellis Code 1/20
int
OR channel
93 Mbps
5 other tx
Correct extra errors
Separate different transmitters
Asychronous Access code
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The system
Reed Solomon (255, 237)
Trellis Code 1/20
int
sync
5 other tx
For uncoor-dinated access
To distinguish between users
Initial synchroni-zation of tx-rx pair
OR channel
To bring final BER to 1e-9
Reed Solomon (255, 237)
Trellis Code 1/20
int
Bit align
BER Tester
sync
Large feedback loop for rx synchronization
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Experimental Setup
FPGA XMIT 1
AMP
AMP
Optical MOD
AMP
FPGA XMIT 2
AMP
Optical MOD
AMP
AMP
Optical MOD
FPGA XMIT 3
Optical to Electrical
AMP
AMP
Optical MOD
FPGA XMIT 4
D Flip-Flop
AMP
AMP
Optical MOD
FPGA XMIT 5
AMP
AMP
Optical MOD
FPGA XMIT 6
FPGA RCV 1
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Six Users
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(No Transcript)
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Probability of amplitudes for 6-users
Height Probability
0 4.4880e-001
1 3.8468e-001
2 1.3739e-001
3 2.6169e-002
4 2.8038e-003
5 1.6022e-004
6 3.8147e-006
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Asynchronous users
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Receiver Ones Densities for this code.
Number of Users Receiver Ones Density
1 0.125
2 0.234
3 0.330
4 0.413
5 0.487
6 0.551
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Performance results

• FPGA implementation
• In order to prove that NL-TCM codes are feasible
  today for optical speeds, a hardware simulation
  engine was built on the Xilinx Virtex2-Pro 2V20
  FPGA.
• Results for the rate-1/20 NL-TCM code are shown
  next.
• Transfer Bound
• Wen-Yen Weng collaborated in this work, with the
  computation a Transfer Function Bound for NL-TCM
  codes.
• It proved to be a very accurate bound, thus
  providing a fast estimation of the performance of
  the NL-TCM codes designed in this work.

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C-Simulation Performance Results 6-user OR-MAC
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6-user OR-MACSimulation, Bound, FPGA (no optics)
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Results observations

• An error floor can observed for the FPGA
  rate-1/20 NL-TCM.
• This is mainly due to the fact that, while
  theoretically a 1-to-0 transition means an
  infinite distance, for implementation constraints
  those transitions are given a value of 20.
• Trace-back depth of 35.
• Additional coding required to lower BER to below
  10-9.

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Dramatically lowering the BER Concatenation
with Outer Block Code

• Optical systems deliver a very low BER, in our
  work a is required.
• Using only a NL-TCM, the rate would have to be
  very low.
• A better solution is found using the fact that
  Viterbi decoding fails gradually, with relatively
  high probability only a small number of bits are
  in error.
• Thus, a high-rate block code that can correct a
  few errors can be attached as an outer code,
  dramatically lowering the BER.

Block-Code Encoder
NL-TCM Encoder
Z-Channel
Block-Code Decoder
NL-TCM Decoder
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Reed-Solomon NL-TCM Results

• A concatenation of the rate-1/20 NL-TCM code with
  (255 bytes,247 bytes) Reed-Solomon code has been
  tested for the 6-user OR-MAC scenario.
• This RS-code corrects up to 8 erred bits.
• The resulting rate for each user is
  (247/255).(1/20)
• The results were obtained using a C program to
  apply the RS-code to the FPGA NL-TCM output.

Rate Sum-rate p BER
0.0484 0.29 0.125 0.4652
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C-Simulation Performance Results NL-TCM only,
100-user OR-MAC
Rate Sum-rate p BER
1/360 0.2778 0.006944 0.49837
1/400 0.25 0.006875 0.49489
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Current Status

• Decreased optical speed from 2 to 1.2 Gbps
  because FPGA cant keep up at 2 Gbps.
• Single Amplifier Results
• 2-Amplifier system in progress.
• We need more amplifiers for six users. Last
  night, worked for 4 users, but two users need
  more power.

Users BER
1 lt 10-9
2 lt 10-9
3 10-8
4 510-6
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Results

• Demonstrated scalability to 100 users in a C
  simulation.
• Working on our 6-user optical implementation.