Uncoordinated Optical Multiple Access using IDMA and Nonlinear TCM

Uncoordinated Optical Multiple Access using

IDMA and Nonlinear TCM

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

UCLA Electrical Engineering Department-Communication Systems LaboratoryUCLA Electrical Engineering Department-Communication Systems Laboratory

UCLA Electrical Engineering Communication Systems Laboratory 2

OCDMA Coding Architecture

OR channel

5 other tx

Reed Solomon(255, 237)

Trellis Code1/20

int

Correct extra errors

AsychronousAccess code

Separate different transmitters

2 Gbps

93 Mbps

60 Mbps

1.2 Gbps


The system


Trellis Code1/20

intsync


Trellis Code1/20

int

sync

Bitalign

OR channel

5 other tx

Large feedback loopfor rx synchronization

BERTester

For uncoor-dinatedaccess

To distinguishbetween users

To bring final BER to 1e-9

Initial synchroni-zation of tx-rx pair


Experimental Setup

FPGAXMIT 1

FPGAXMIT 2

FPGAXMIT 3

FPGAXMIT 4

FPGAXMIT 5

FPGAXMIT 6

AMP

AMP

AMP

AMP

AMP

AMP

AMP

AMP

AMP

AMP

AMP

AMP

OpticalMOD

OpticalMOD

OpticalMOD

OpticalMOD

OpticalMOD

OpticalMOD

FPGARCV 1

Optical toElectrical

D Flip-Flop


Six Users

0 10 20 30 40 50 60


0 10 20 30 40 50 600

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 600

0.5

1

1.5

2

2.5

3

3.5

4

0 10 20 30 40 50 600

0.5

1

1.5

2

2.5

3

3.5

4


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


Asynchronous users

7.5 8 8.5 9 9.5 10 10.5 11 11.50

0.5

1

1.5

2

2.5

3

3.5

4


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


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.


C-Simulation Performance Results: 6-user OR-MAC

4 5 6 7 8

10-6

10-5

10-4

10-3

users

BE

R

NL-TCM 1/17

NL-TCM 1/18NL-TCM 1/20

6-user BER 10-5


6-user OR-MAC:Simulation, Bound, FPGA (no optics)

0.2 0.3 0.4 0.5 0.6 0.7

10-8

10-6

10-4

10-2

100

BE

R

NL-TCM 1/17NL-TCM 1/18

NL-TCM 1/20

NL-TCM 1/20 FPGA

Bound 1/17

Bound 1/18Bound 1/20

6-user BER 10-5


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.


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.

910BER

Block-Code Encoder NL-TCM Encoder

Z-Channel

Block-Code Decoder NL-TCM Decoder


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

102.48 10


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

64.54 10

79.45 10


Current Status

Decreased optical speed from 2 to 1.2 Gbps because FPGA can’t 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 < 10-9

2 < 10-9

3 10-8

4 5×10-6


Results

Demonstrated scalability to 100 users in a C simulation.

Working on our 6-user optical implementation.

Uncoordinated Optical Multiple Access using IDMA and Nonlinear TCM

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