OOK Modulation scheme

[Naazira Badar]

Hi everyone.
I have a query about On off keying based systems. We know it’s mostly used for its simple implementation and low cost. But due to a fixed threshold based detection at the receiver, it is susceptible to bit errors because the received optical power is mostly fluctuating. But to overcome this, dynamic thresholding is a solution.
We often use OOK on optisystem, could anyone of you confirm that is based on fixed threshold based detection on optisystem? ? Kindly respond.

Regards.
Naazira Badar.

[burhan num mina llah]

Hello Naazira Badar

I couldn’t find a direct example or tutorial in regards to this.. but i did find a paper in whch the have conducted simulations of optisystem itself and the have mentioned and infact confirmed the fixed threshold level taken when OOK is simulated on optisystem.. i believe you can carry on your simulation for OOK as it does take the fixed threshold level.. i am attaching the respective file along to give you better information and help..

Regards

Burhan

[Atul Sharma]

Hello Burhan. Greetings.

thank you for sharing the pdf document file. It should be really helpful for understanding this OOK concept. i hope naazira badar gets benefited from this all.

With regards
Atul Sharma

[Naazira Badar]

Hi Burhan num mina llah..

Thanks a lot for your response and for posting this link. even if based on this paper, I assume that in Optisystem , OOK detection is based on a fixed level thresholding ..the BER analyser results would still be confusing.I mean, the eye diagram.. on different OOK-based systems, the threshold on the eye diagram could been seen a different value. I don’t understand if it is not mid-point biasing , i.e. 0.5 units.. then ho is the fixed-threshold value for each system decided.

Best Wishes
Naazira Badar.

[Ranjeet Kumar]

Hellow ma’m
As you have posted a very nice and basic question related to fixed/ dynamic threshold based detection on optisystem.
I am not sure how to fix or vary the threshold level in detector.
I will suggest you to please refer to following link:

RZ-OOK

[Atul Sharma]

Hello Naazira. Greetings from my side.

Well here i would like to understand the concept of dynamic threshold. what does it mean? Does it somehow relate to the receiver sensitivity? I would like to know that. Shall be looking forward for your reply.

With Regards
Atul Sharma

[Ranjeet Kumar]

Hi Atul Sharma,
In order to minimize the signal distortion and to maximize dynamic range we use Dynamic threshold technique in which we employ Edge detection technique.
As in fixed threshold we use comparator.
Hope i could explain it correctly.

[Atul Sharma]

Hello Ranjeet. Greetings from my side side.

But can you tell me how do we implement it in the optisystem system for the design of a system. Do we have an option using it in the optisystem. Please share it. I would be looking forward for your response.

With regards
Atul Sharma

[Ranjeet Kumar]

Hi Atul
The adaptive threshold system is also called Dynamic threshold system,in response to varying channel
conditions, results in orders of magnitude improvement in probability of error, as compared to use of a fixed threshold itself is based on a robust channel identification system that uses average signal strengths to estimate the degree of fade and total attenuation,
and an RBF network for estimating pulse spreads, all with excellent accuracy.
Hope i have answered it correctly.

[Atul Sharma]

Hello Ranjeet.

The theoretical aspect is fine. Thanks for explaining that but here i want to know if we can implement it in the optisystem system for the design of a system. Do we have an option using it in the optisystem. lease share it. I would be looking forward for your response.

With regards
Atul Sharma

[SAHIL SINGH]

Hi Atul Sharma,

As mentioned by Ranjeet Kumar Dynamic Threshhold technique is used to minimise the signal distortion and to maximize the dynamic range.. Hope you understand it…

Thanks and Regards
Sahil Singh

[burhan num mina llah]

Hello Naazira Badar

That problem still exists , i just answered your query in regards to optisystem taking fixed value or not.. That clearly is the issue that at the reciever end the problem would still exist..

@ranjeet.. very well explained the concept of dynamic threshold..

Regards

Burhan

[Manoj Kumar]

Hi Naazira,

The adaptive threshold system is also called Dynamic threshold system,in response to varying channel
conditions, results in orders of magnitude improvement in probability of error, as compared to use of a fixed threshold itself is based on a robust channel identification system that uses average signal strengths to estimate the degree of fade and total attenuation,
and an RBF network for estimating pulse spreads, all with excellent accuracy.
Hope i have answered it correctly

[Naazira Badar]

hello everybody

thanks a lot for your responses. all of you have correctly explained the concept of adaptive or dynamic thresholding. But i was asking of optisystem does employ this or does it detect based on fixed thresholding. if that would have gotten confirmed, it would have been good.

Regards
Naazira Badar.

[Rajguru M. Mohan]

Hi Naazira,
We ahve various disadvantage of static threshold like: we observe a
penalty as we increase the number of hops even at minimum FCL, where the best transient suppression performance is
obtained. This arises from small power excursions caused by
burst add–drop at each node which are not fully suppressed
and these excursions accumulate with increasing number of
hops.
Also, the point at which the penalty starts to increase
sharply due to insufficient gain transient suppression shifts to
lower values of FCL as the number of hops traversed increases.
This occurs because there is insufficient power in the feedback
channel to compensate for the increasing amplitude fluctuations.
Thus, the transients caused by the adding and dropping
of bursts sharing link amplifiers accumulate with each hop and
a lower FCL is required to achieve optimum performance as
the network size grows.

So, we should opt Dynamic threshold.

[Rajguru M. Mohan]

Hi Naazira,
Moreover, A dynamic threshold data receiver uses a single comparator for both squelch and data detection.
It has various advatege over static threshold like:
The comparator has a high-magnitude threshold when the receiver is squelched and a low-magnitude threshold when the receiver is unsquelched.
Preferably the comparator is a differential line receiver, and each of the high and low magnitude thresholds has hysteresis.
he switching threshold is automatically adjusted in response to varying operation conditions such as changes in the received optical signal power. Nonlinear optical thresholding or decision thresholding are used to improve the system
performance and suppress the multiple access interferences in asynchronous
system. Using an encoding/decoding (E/D) technique and
optical thresholding multiple access interference (MAI) can be eliminated
effectively. In on-off keying (OOK) OCDMA, the interference level is
studied to be more and also requires high power level to maintain the desired
BER for the given number of users with direct detection. Even after
employing the optimum fixed decision threshold or adoptively varying the
decision threshold with the number of users, the performance of the
8
asynchronous OOK OCDMA system does not meet performance level of
differential phase shift keying (DPSK) OCDMA. Optical thresholding in
OOK OCDMA can eliminate MAI to the extent as that of DPSK
encoder/decoder in the system without sacrificing the BER and OSNR
required for proper operation of the receiver.

Thanks,

[Aabid Baba]

Hello Rajguru M Mohan,
I have a few questions here:
Firstly Can you explain what does squelch refer to?
Secondly as you have mentioned about that The comparator has a high-magnitude threshold when the receiver is squelched and a low-magnitude threshold when the receiver is un-squelched and it is a differential line receiver and each of the high and low magnitude thresholds has hysteresis. I want to ask you is this comparator available fro use in Optisystem. I am not talking about the theoretical aspect i mean is there a way where we could find it or implement it. I would be glad to see your response. Thanking you.
Regards

[Rajguru M. Mohan]

Hellow Aabid,
squelch refer to a circuit that suppresses the output of a radio receiver if the signal strength falls below a certain level.
As The signal detection threshold is set based on information
received from the intelligent agent, in the form of extracted
channel parameters.

I am sure that in dynamic threshold we use comparator for detection.
We have lots of advantage of dynamic threshold and the question was asked about dynamic threshold.
I am not whether i could implement this in optisystem, but dynamic threshold are frequently used in wireless comuunication because The adaptive threshold system itself is based on a robust
channel identification system that uses average signal
strengths to estimate the degree of fade and total attenuation,
and an RBF network for estimating pulse spreads, all with excellent
accuracy.
I apologize as i am unable to answer about its implementation in optisystem.
If you could, please share your idea about it.
Thanks

[Rajguru M. Mohan]

Hellow Aabid,
I want to share a research paper of IEEE with heading “An Adaptive Threshold Detector and Channel Parameter Estimator
for Deep Space Optical Communications”, which i like to share to you.
I have gained some idea about dynamic threshold and its advantages from this paper.
It is:
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=965078

Thank

[Aabid Baba]

Hello Rajguru M. Mohan,
I thought you posted it and you may have a slight idea about a comparator. I wanted to use a comparator in my design if available but i think there ain’t any component that can provide the usage of a comparator. Anyways thank you for the link of the paper you have posted.
I shall go through it and may be there is some evidence or any sort of component that can serve my purpose. I hope it is helpful in some way.
Thanking you.
Regards

[Naazira Badar]

Hi Rajguru M. Mohan..
you have put in a lot of effort explaining OOK.

Thanks alot for that.

Aabid baba, i was asking this for the same reason of errors due to fixed thresholding vis-a-vis signal detection and error.

Best Wishes
Naazira Badar

[Aabid Baba]

Hello Naazira,
I am not sure if it is confirmed. But yeah it can do wonders for me too if it is known. I myself was looking for some sort of comparator based on this fixed threshold detection.
I would appreciate if you can share any material you already have regarding this.
Thanking you.

Regards

[Hamza Ali Abbas Khan]

Hello Naazira,
If you are talking about the dynamic threshold detection associated with free space optics then here is a link to a paper which may help you. I suggest you to go through it.
https://dru5cjyjifvrg.cloudfront.net/wp-content/uploads/2016/04/1255-6871-1-PB.pdf?448a95
This article deals with the construction of a modulator and demodulator for Free-Space Optical (FSO) communication. In FSO optics, the modulated optical signal is propagated in the constantly changing environment (atmosphere). The optical signal is strongly influenced by the actual composition of air, which is directly linked to the change in refractive index in the turbulent cells. This article examines primarily
the appropriate modulation format for FSO. For this purpose, one type of an OOK-NRZ modulator and one type of a demodulator were designed. This article also describes the construction of two types of photo detectors the high impedance and the transimpedance ones). All electronic constructions were tested in the MicroCap simulator and they were experimentally measured as well. For the OOK NRZ modulation the, maximum transmission speed achieved the value of 160 Mbps. Measuring the quality of the modulation formats was carried out under mechanical and thermal turbulences. The last part of this work gives the results of the measurements of fog influences.

I hope this will help a little.

Thanks

[Hamza Ali Abbas Khan]

And about the OOK modulation i want to add that It is a type of the intensity modulation belonging to the ASK modulation, in which binary information is represented by the presence or absence of an optical signal. The decision level compensates the probability of the error log 0 and log 1 and is dependent on the received power and noise. This type of modulation is most widely used in free space optics. The production
of the transmitter and the receiver is simple. It is resistant to nonlinearity on the laser and the external modulator. The OOK is more sensitive to atmospheric turbulences and other disturbing influences when the fluctuations of the received level occur.
Hope this would help

Thanks

[Naazira Badar]

Hi Hamza Ali Abbas Khan..

Thank you for your replies.

Yes, the theoretical aspect is clear. All i was asking was if in optisystem , the thresholding was based on fixed-bias method.

Thanks anyway for your efforts.

Best Wishes

Naazira Badar

[Hamza Ali Abbas Khan]

You are welcome Naazira.
I hope your problem gets solved as soon as possible.

All the best.
Thanks

[Karan Ahuja]

Hello,
I would like to add that using an encoding/decoding (E/D) technique and optical thresholding multiple access interference (MAI) can be eliminated effectively. In on-off keying (OOK) OCDMA, the interference level is studied to be more and also requires high power level to maintain the desired BER for the given number of users with direct detection. Even after employing the optimum fixed decision threshold or adoptively varying the decision threshold with the number of users, the performance of the 8 asynchronous OOK OCDMA system does not meet performance level of differential phase shift keying (DPSK) OCDMA. Optical thresholding in OOK OCDMA can eliminate MAI to the extent as that of DPSK encoder/decoder in the system without sacrificing the BER and OSNR required for proper operation of the receiver.

Regards

[burhan num mina llah]

Hello everyone,

Thank you for your response. I appreciate your efforts but it would be appropriate if it is a discussion rather than repeating the same information. I hope we will see healthier discussions in future. Thanking you

Regards

Burhan

[Author]

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