Performance Assessment ofOptical Networks with CDMA

Paulo M. Mendes

ConclusionsA new methodology for performance evaluation of optical DS/CDMA systems was developed;The prime codes are more sensitive to the fibre length than optical orthogonal codes;The dispersion tolerance depends of the relation between the code length and number of chips in the code and a longer code does not imply an improvement on dispersion tolerance;The codes to be used in DS/CDMA systems must be selected taking into consideration their dispersion tolerances;We simulated a system operating at 20 Gchip/s with a penalty < 2 dB, for L=10 km and Pe=10-9.

Th

10T

dtc

T NTc

Coding Sequence (1001101)

Data Sequence (1011)

Coded Sequence

L

nndb

ssDwbsDFss2

1)1(

0022 )()()(

2

1exp)()1(

0

APD input

MGF of V(ts)

( ) ( ) ( )

( )

,( )t

Tm h t lT jT

Th t lT jT

cl j

nc n

j

N

ln

L

cc n

j

N

ln

L

d

1 1

0

1

1

1

0

1

1

Simulation Methodology

Generation of the optical symbol sequence, propagation through linear fibre channel and reception with Butterworth low-pass filter;

Performance estimation using the moment generating function of the output distribution with the saddle point approximation.

Effect of Dispersion on Eye Opening

System Operating at 10 Gchip/s

0 0.5 1 1.5 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1x 10

-3

t/T0 0.5 1 1.5 2

0

1

2

3

4

5

6

7x 10

-4

t/T

PC with N = 121w = 11C = 11

TC with N = 129w = 3C = 6

-54 -52 -50 -48 -46 -44 -42

10-10

10-5

100

Pe

Chip Received Power [dBm]

PC with

N = 529 w = 23

-55 -50 -45 -40 -35

10-10

10-5

100

Pe

Chip Received Power [dBm]

PC and

OOC

PC with N = 529 L = 5

D = 37 Mbit/s

PC with N = 121 L = 5

D = 165 Mbit/s

-50 -45 -40 -35 -30

10-10

10-8

10-6

10-4

10-2

100

Chip Received Power [dBm]

Pe

-50 -45 -40 -35 -30

10-10

10-8

10-6

10-4

10-2

100

Chip Received Power [dBm]

Pe

DS/CDMA System Model

Developed Simulator

Effect of Dispersion on Probability of Error

System Operating at 20 Gchip/s

RX

TX