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Uncoordinated Optical Multiple Access using IDMA and Nonlinear TCM

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UCLA Electrical Engineering Department-Communication Systems Laboratory Uncoordinated Optical Multiple Access using IDMA and Nonlinear TCM PIs: Eli Yablanovitch, Rick ... – PowerPoint PPT presentation

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Title: Uncoordinated Optical Multiple Access using IDMA and Nonlinear TCM


1
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

2
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
3
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
4
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
5
Six Users
6
(No Transcript)
7
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
8
Asynchronous users
9
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
10
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.

11
C-Simulation Performance Results 6-user OR-MAC
12
6-user OR-MACSimulation, Bound, FPGA (no optics)
13
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.

14
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
15
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
16
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
17
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
18
Results
  • Demonstrated scalability to 100 users in a C
    simulation.
  • Working on our 6-user optical implementation.
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