Design and Power Budget Calculations for Radio over Fibre (ROF) and Optical Transmission System

Subject: Advanced Optical Communications Order id: 757091
1)
Introduction
Radio over fibre (ROF):
ROF is very attractive technique for wireless access network infrastructure, because
transmission of microwaves and millimetre-waves through optical fibres for a long distance is
very much simpler than the other existing techniques. ROF is a technique by which high
frequency signals are transmitted by means of optical components. A ROF system consists of
a Central Site (CS) and a Remote Site (RS)/ Base site (BS) user end connected by an optical
fiber link or network. The main optical components employed in RoF technology are the
laser transmitter, the Photo detectors and the optical fiber.
Basic Block Diagram of Radio over Fibre
Design criteria is depends upon two things
1) Data Rate
2) Link length
While at the time of a Design the following Parameters are required
Modulation format
System fidelity: BER, SNR
Cost
Upgradeability
Commercial availability
According task requirement design of a RoF as following as

As per given data
Bandwidth = 2 Gbits/sec
Length= 5000km
Selecting optical source:
LED at 850 nm is suitable for short distances. Its generates – 10 dBm optical power.
Selecting optical detector:
PIN-FER optical detector is reliable and has – 50 dBm sensitivity.
Selection optical fiber:
Step-index multimode fiber is selected. The fiber has bandwidth length product of
1000 (gb/s) km.
b)
Power Budget Calculations:
Link Power Budget:
The relation between the power margin between the optical transmitter output and the
minimum receiver sensitivity.
= Transmitter powerbin dBm
= Sensitivity of receiver in dBm for given BER
Maximum permissible loss
Power limited link length=

Rise Time/ Bandwidth Budget Calculation:
Rise-time budget:
The link power budget has been established, a system rise time analysis calculations are meet
the budget
=Detector
Above mentioned equation total rise time ‘tsys’ of the link is the root mean square of the rise
times from each contributor (ti ) to the pulse rise-time degradation
Bit Error Rate (BER):
Defined as the ratio of the number of errors in a given time interval (Ne) to the number of bits in that
time interval (Nt).
BER=
In general telecommunication applications the specified maximum BER falls in the range in
between .
For RZ data format
Bit rate R = B =1/ τ
Signal to Noise Ratio (SNR):
SNR is defined as the ratio of the average optical signal power to the average optical noise
power.
Here
I = Average Signal Power
= Optical Noise Power

Matlab code for BER, SNR
clear all
clc
r=randint(1,10000);
for i=1:10000
if r(i)==0
s(i)=-1;
else
s(i)=1;
end
end
k=1;
for snrdb=1:1:10;
v=1/(10^(snrdb/10));
x=awgn(s,snrdb,'measured');
y=x;
for j=1:10000
if y(j)>0
z(j)=1;
else
z(j)=0;
end
end
error=length(find(z~=r));
ber(k)=error/10000;
k=k+1;
end
snrdb=1:1:10;
snrlin=10.^(snrdb./10);
tber=0.5.*erfc(sqrt(snrlin));
semilogy(snrdb,ber,'-bo',snrdb,tber,'-mh')
grid on
title('task1');
xlabel('SNR');