LED base PAM system

[fairul anwar]

Im working on VLC project which use LED as an optical source. My aim is to simulate LED PAM system using optisystem to get the eye diagram and BER. Recently, i found it is almost impossible to get a good measurement using optisystem. anyone can help me with my project?

[Ravil]

Hi fairul,

First, I just want to do few clarifications: are you planning to use intensity modulation and direct detection in your project? Can you, please, also decrypt the abbreviation of your project?

[Alessandro Festa]

Hi Fairul, what do you mean by “impossible to get good measurement”?

[Abhishek Shrama]

Already there had been a discussion regarding use of LED sources and VLC systems. a number of common doubts were clarified and systems were attached. check the link and read the discussion carefully. hope u will get to understand the use.
let me know if any help still required.!!

awgn noise

[Ashu verma]

Hi Fairul,Can you please attach your system or share your objectives in detail,so that we will able to help you .

[Ravil]

Dear fairul anwar,

I agree with Alessandro: please, specify the main issues that you have with the measurements of the system that you are trying to design in OptiSystem environment…

[Dr. MohammadMahdi Ariannejad]

what is the main issue for measurement? and which parameters can influence?

[fairul anwar]

hi guys, thanks for the attention and sorry for the late reply. im a student so im still in learning process of this simulation system. so my objective is to simulate the 4 level PAM technique using optisys and to get all the performance measurement such as BER, SNR, constellation etc. i have constructed the layout (attached) and im not sure which part i did wrongly. there are a few different way i have tried to construct this project

Attachments:

1. with-clock-working.osd
2. PAM-with-BER-PRBS-working-with-test-set.osd
3. OOK.osd

[fairul anwar]

since i try to construct the PAM system in ideal cases, the only factors that affect my simulation is the timing jitter and the overshoot of the binary transition so the system suppose to show a good eye diagram. in reference to the OOK system, the PAM systems are suppose to have a higher data rate. i have been thinking that maybe the inter symbol interference (ISI) are the major limits for the LED PAM system. so now im stucked 🙁

[Damian Marek]

Directly modulating an LED introduced a lot of distortion as well to a signal due to its incoherent nature. I believe that is largest source of noise.

I changed the Laser driver component in your first project to range from 0.1 to 1 units to lower the bias and the results were much better.

Regards

[fairul anwar]

oh okay thats helping since my objective is to use IM/DD. i also got another question, instead of sending the binary of 1 bit per microsec, i use m-ary signal to send more and that should reduce the time, am i right? but when i analyze the time domain the transmitted and received binary have a same range of time.

thanks

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