Sac ocdma with MD code

[Gurpreet Kaur]

i am designing SAC OCDMA with MD coding. can anyone help me out by telling how to choose the frequency for the codes for different users? is there any particular criteria for that?

[Ashu verma]

Hello Gurpreet
I just want to know more abut what you want to try in your system.Do you want to realize multidiagnal scheme with the help of laser or LED?On which paper you are working on,can you please share that with us?
Till then i suggest you a article to read fro MD codes using LED.Let me know i it helps
https://cdn.optiwave.com/wp-content/uploads/2014/09/30050934/elsvier-2.pdf

[Ashu verma]

Also visit these links as i found these topics very similar to your work

SAC-OCDMA

SAC-OCDMA system

[alistu]

Hi Gurpreet,

If you have N users and W weights (where W>1 is arbitrary), then you should create W diagonal NxN matrices. Put these matrices in a row to form one total matrice and the ones in each row of the total matrice determine the wavelengths (for the frequencies) that are used for each user. for example, 0 0 0 1 1 0 0 1 in a row shows that you will have lambda4,lambda5,lambda8 wavelengths for the user relating to that row.

That was a brief explanation, but if you want you can easily google it and find plenty of useful links on it within seconds.

[Gurpreet Kaur]

hello alistu and sam sung.
alistu i have implemented it the same way but my doubt is that what frequency values can i use?
i have implemented using 1550nm as centre frequency and gap of 1 nm.
i am using Laser as the input.
i implemented the same with LED as well but performance is better with laser. otherwise which source is preferred?

[alistu]

I believe the spacing between the frequencies depends on the overall bandwidth you want to use. The less spacing between the wavelengths, the better (as long as you get the desired bit-error-rate). So why don’t you simulate the system for different frequency spacings and then choose the most suitable one?

[alistu]

As for what you have asked about the type of light source to use, the coherent light from laser would definitely be the best choice. However, because SAC-OCDMA systems are used in some applications such as Fiber-to-the-Home as a low-cost solution, sometimes LEDs are used as a cheaper light source along with FEC schemes to reduce the costs. The paper “A Comparison of Optical Sources for Spectral
Amplitude Coding OCDMA” which could be found easily by google makes comparisons between the two, but I guess the above explanation would suffice.

[Ashu verma]

Basic difference of using the LED rather than laser is only cost of the system while laser wikl provide you better results due to more directinality,coherence and monochomatic nature.However LED along with multimode fibers are preferably used to decrease cost of the system.

[Gurpreet Kaur]

i am having three users and W=3. so what shall the bandwidth to be used?

[alistu]

As I mentioned before, if I were you I would have tried different bandwidth values to find the optimum one, which would be the one to give good system performance (with desired bit-error-rate) and yet have the least amount possible. I cannot think of any number right now, but I would do as what I said to find the proper value.

[Gurpreet Kaur]

thank you alistu for the information.i will follow what you said.
one more doubt is regarding the decoding. i am using direct detection in my system, using FBGs so which signal should be passed on to the photodetector? the transmission output or the reflected output? and as i am using W=3 so detection is to be done with 3 FBGs per user in series?
will be thankful if you can help me out in this.

[alistu]

You’re welcome Gurpreet. On the receiver side, the signal first passes through the same FBGs as it has passed through on the transmitter side before being launched into the channel, and then through the photodetector. And the number of FBG equals the number of wavelengths of the number of weights used. So if W=3, then you should use three FBGs. I suggest that you take a look at optisystem SAC OCDMA sample.

[Gurpreet Kaur]

and i am working with free space optical channel.

[Gurpreet Kaur]

ok. but read in few papers that as MD codes are Zero cross correlation codes so data can be recovered from any non overlapping chips. so shall i attach the FBGs in series, at receiver side, as per the wavelengths used for encoding and then send the last FBG’s transmission output to the photodiode?
or i can decode with the reflected output of any of the FBGs?
Please help me out.

[alistu]

I think you have to attach the FBGs in series the way shown in the attached Optisystem file. I have not seen otherwise in the papers but that doesn’t mean such a way would be wrong. The thing is, I didn’t get exactly the other way you are suggesting than the series attachment, but using FBGs in series works for sure.

[Gurpreet Kaur]

thanks a lot. n yes i have studied the given simulation file.
can you tell that till what distance we prefer using FSO link. In my system i have used for 2km and getting good results. shall i increase the distance? as FSO is used in last mile applications so what maximum distance can i go to?

[alistu]

You’re welcome. I recommend that you search into review papers to get more accurate answers for questions like this. I haven’t worked in free-space-optics field, but I know one thing for sure: The reach depends on the atmospheric situation of the channel. For example, in free space you can have longer links with the desied reliability than other FSO channels. 2Km link is enough, if not too much. You might want to increase the number of the users instead.

[Ashu verma]

Hello gurpreet
Most of the answers of your question already been given by Alisthu about sac ocdma and how to consider there parameters.I just want to add about FSO distance you acheived.You can enhance the transmission distance more ,but it strongly depends upon what values of fso parameters you are taking.beam divergence,scintillation,attenuation are some of the important factors to be considered.i would also suggest you to study effects if different atmospheric turbulences on your system by taking the effects of fog,light fog,heavy fog,haze and clear weather.you just need to set the values of attenuation to realize these turbulences on system

[Ashu verma]

I found these paper interesting for your topic

Design of multi user free space optical communication system for … – I am browsing [Design of multi user free space optical communication system for …]. Have a look at it! https://www.google.co.in/url?q=http://www.ijettjournal.org/2015/volume-24/number-2/IJETT-V24P218.pdf&sa=U&ved=0CA8QFjADahUKEwj-7buq3P3GAhXDUY4KHYH1A40&usg=AFQjCNGs70YQIUZ8S6q8UC7pb0DMpvY09w

http://www.mdpi.com/2304-6732/2/1/139

Let me know if it helps

[Gurpreet Kaur]

i have simulated taking clear weather conditions and the attenuation is taken to be 0.43db/km. shall i work with clear weather conditions only, as my main objective is to study the effect of multitransmitter on it? or shall i increase the users.

[alistu]

Since you are working in free-space-optic field, your choice of weather condition is related to the application of the system you are simulating. Is it used in inter-building communication or inter-satellite communication? I suggest that instead of increasing the distance, try to increase the number of users or the transmission bit rate because 2km is enough for many purposes, unless you know exactly about the application of your work.

[Ashu verma]

Yes you can study your system for clear weather only,so work on more no. Of users as Alisthu said.

[Gurpreet Kaur]

thanks a lot sam sung and alistu for the suggestions and help.

[alistu]

You’re welcome Gurpreet. Glad to be of any help.

[Ashu verma]

Welcome Gurpreet,i was out of place so couldnt participate more on your topic.But Alisthu helped you alot and nade very good points and suggestions.I think your problem is solved .In case you will have any problem ,kindly share with us.

[Gurpreet Kaur]

i am attaching my simulation file for the same with 5 users. kindly go through this and let me know if the setup is correct. then i will work further on increasing the number of users and data rate.
waiting for early reply

[Gurpreet Kaur]

file

[alistu]

It seems to be working OK, but may I ask why you haven’t used fiber bragg gratings on the transmission side as well as on the reception side of the FSO channel? As I pointed out, lasers are considered expensive components and this way you are using several of them. By doing as depicted in optisystem sample osd file, You only need to use one laser for each user on the transmission side.

[Gurpreet Kaur]

Can u please make changes in my file that how shall i implement with what you said and send me the file?and I have used FBGs on the reception side for filtering.

[alistu]

I saw them on the reception side. I think you can easily do it yourself. Change the design so that on the transmitter, the same FBGs are used (after the laser and before launching the signal into the line) as in the receiver of each user. Please refer to the SAC OCDMA sample osd file that I have mentioned several times for more clarification.

[Gurpreet Kaur]

the sample given is using hadmard code. and in my setup i am using MD codes. so can you tell me that can i implement MD codes using FBGs?
i tried but i am getting BER=1

[alistu]

I haven’t worked with SAC OCDMA (simulation work) but I think in case of MD codes, you just implement MD codes (instead of Hadamard codes) with FBGs and that should be it. There is a paper named “Development of a new code family based on SAC-OCDMA system with large
cardinality for OCDMA network” that I refer you to, which has not used FBG I think.

[Gurpreet Kaur]

yes they have not used FBGs. so i am confused about how to implement MD code. please help me out

[alistu]

In that paper, the number of users is 5 and the code weight is 4. Having these numbers in mind, try to simulate the scheme depicted in figure 6 of the paper. Try reading the simulation part of the paper before implementing it. here’s another picture from another paper, with W=4 and N=2 which is close to your own simulation. FBGs are uniform. Take a look at this and its paper “Simulation of a SAC-OCDMA 10 User ×15 Gb/s System Using MD Code”, which expalains the same stuff again. try to make something out of these two.

[Gurpreet Kaur]

and for detection also they have used bessel filters to filter out just one chip(non overlapping) and sent that to photodetector.

[Gurpreet Kaur]

i am unable to get to the paper u mentioned. can u please send me the pdf file?
thanks

[alistu]

I am not sure whether the paper is copyright protected or not, so I don’t upload it here. But here’s the google search in which you can easily find the paper:
https://www.google.com/?gws_rd=ssl#q=sac+ocdma+md+Morteza+Motealleh

And here’s the name of the file you want to download:
[pdf] SAC-OCDMA, MD code, Optisystem – Scientific & Academ…

[Gurpreet Kaur]

thanks a lot
but the paper u have suggested is using laser as the optical source.

[alistu]

You’re welcome!
Yes, so have you in your own simulation whose osd file you have attached in this forum. However, I suggested reading the two papers just to understand how the system is supposed to work in order to learn how to implement your own. Try to find answers to these questions in these papers.

[Gurpreet Kaur]

as you were asking me that i should go for led as optical source so i asked that in these papers they have used laser light. so shall i go for that? and the other thing they have used single FBG for detection rather that using 3(as weight is 3). so does it mean that we can decode the signal from any non overlapping chip?
this thing is still not clear to me.

[alistu]

I never told you to go for LED. If you disagree, please give me the number of the reply in which I have stated such a suggestion. I think they have used demultiplexer to distinguish between different wavelengths. But I am not sure what is exactly going on. Right now I am busy but I will be back in a few hours with an answer hopefully.

[Gurpreet Kaur]

sorry i got confused. so shall i use single laser and use FBGs to filter the wavelengths?
waiting for reply
and sorry for the confusion

[alistu]

I strongly suggest that you go through the whole paper, and then try to implement your own system in Optisystem like the one simulated in the paper. If FBGs are used in the paper, use them in the same way. Just the pictures and screenshots from the paper are not enough. You’ll need to read the text as well.

[Gurpreet Kaur]

ya i have studied the paper and thanks a lot for the help.

[alistu]

You’re welcome. Is your problem hopefully solved now?

[Gurpreet Kaur]

ya almost..

[Gurpreet Kaur]

ya sam sung alistu’s information was very helpful.
i have one more query that with a single laser how can we get a broader output so that we can filter out from it the required frequencies?
as in my system if the laser is set at 1550nm, the output spectrum has more power for 1550nm only. so how can i generate 20 nm band signal from laser? please help me out

[alistu]

You can generate signals with arbitrary bandwidth in the base band. For example, you generate a baseband OFDM signal using the OFDM modulator with a bandwidth of 20nm. Then by using the laser you will be able to upconvert it and change its center frequency to the laser frequency. When this happens, the spectrum has 20nm bandwidth in the laser frequency.

[Gurpreet Kaur]

i didnt get what you are trying to say. can you please elaborate it.

[alistu]

here’s more explanation on this at your request: You have asked how to generate a passband signal using laser diode, which includes a spectrum of frequencies (or wavelengths) and not just one frequency (which is the laser’s frequency). Here’s my answer: What laser actually does is upconverting the baseband signal that you have generated before. Now if that baseband signal has a bandwidth of 20nm, after it is upconverted by laser it still retains its bandwidth. I hope I have been more clear this time.

[Ashu verma]

Hello gurpreet
If you want to broad the spectrum of laser signals you can do the following things
1) use hnlf highly non linear fiber to broad spectrum over a freq. Band.using spm and xpm effects
2) you can use SOA as a non linear medium to broad the spectrum and distribute signal over different dreq. Signals
3) use EAM with the carving high freq. To upconvert or downconvert your signal
I think these suggedtion help you.if you need help to implement these systems,i can help you

[Gurpreet Kaur]

ya it will be of great help if you can implement this in my file as i have no knowledge of what you said…

[alistu]

Hi Gurpreet, May I ask why you want to broaden the spectrum from the laser signal? I have always noticed designers willing to have pass band signals as narrow as possible. By widening the signal spectrum, you need more allocated bandwidth to implement your system, and bandwidth is most of the time a costly factor, especially in today’s systems.

[Gurpreet Kaur]

if i want to generate say about 15 different wavelengths from a single laser output… then i will need a broader band.so i will need to broaden the output of laser. i am not sure about it but it just came as a thought and i asked here.

[alistu]

I see… So you are looking for something like frequency combs. One common way to do this is by four-wave mixing. In this method, two laser powers with slightly different frequencies are shined through a photonic crystal fiber to elicit four wave mxing nonlinear effect. But that is not what you should do in optisystem. I wonder if this can be achieved by increasing laser linewidth and then using filters.

[Ashu verma]

Hello Gaganpreet
First of all sorry for late reply,i was too busy in my academic work.Rest now your requirement is to generate the different wavelengths from a dingle laser source or broden the spectrum.Yes it is possible to get multiple wavelengths from single laser source.But for this your spacing between the channels plays a important role.You can get the 15 freq.,however you can get multiple few. from a brodened spectrum using EAM with appropriate bias carving signal.

[Gurpreet Kaur]

one more thing is that for combining the modulated codes of users i am using ideal mux and at reception side ideal de-mux is used. but i have seen papers that have used power combiner at transmitter and power splitters at reception side. which one should be preferred? some are using wdm mux and demux.
so its confusing

[alistu]

I think choosing between power splitters/combiners and multiplexers/demultiplexers depends on your system. A multiplxer adds signals and a demultiplxer divides the signals again. But in a power combiner, the signals are added so that in each branch of the splitter, we have an attenuated version of the whole signal. In a MUX there is no attenuation, unless you change the value of insertion loss from zero.

[Gurpreet Kaur]

ok i think its clear to me now. thanks…

[alistu]

Hi Sam Sung, Among some of the ways that you have proposed for broadening the laser signal’s frequency spectrum, I think some methods do not have an overall positive effect on the system’s performance. For example, XPM causes the phase to change with power and therefore, we somehow have random phase in the system. So I believe broadening the spectrum at the cost of corrupting the system’s performance in not recommendable. Do you agree with me?

[Ashu verma]

Hi Alisthu,there are very major role of these techniques for spectrum broadning.In case of OCDMA due to security concern and to increase the degree of security,these scehmes widely used.You can convert your signal wavelength with the help of soa EAM or HNLF to broad spectrum and then convert wavelength so that jamming and effect of evasdropping cant intrupt the system.Howevere with this systems performance decreases due to phase change ,but it depends for what purpose you are designing.if it is for millitory applications then security is very much important otherwize you can go for high perfoemance.So finally it is basically a trade off in performance and security.

[alistu]

Hi Sam Sung, Yes, I am well aware of spread spectrum and CDMA technics and so on. But in those cases, the signal is spread pseudo-randomly and not completely randomly. For example in CDMA, each user’s signal is multiplied by a code which is known at the corresponding receiver. But I didn’t know about spreading the spectrum using XPM.

[Ashu verma]

I have seen lot of work In this particular area,if gagan or alisthu need papers related to it,let me know.Otherwise google it and you will able to get the papers.I come out with the ways to broden the spectrum from my point of view ,so that work can be extended for more enhanced levels for Ocdma.

[Gurpreet Kaur]

yaa please can you share the link for papers.. n its gurpreet not gagan

[alistu]

Hi Gurpreet, Here are some useful links that I have found, which talk about the basic concepts:

http://www.optics.rochester.edu/workgroups/agrawal/publications/papers/paper_1989_10.pdf
http://core.ac.uk/download/pdf/11533984.pdf

And this one is more practical than theoretical:
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6813584

I suggest that you at least take a look at the last one. I hope these help.

[Ashu verma]

Hi Alisthu ,I have attached some papers here which i have read and found these very intersting from the study as well as application point of view
Gurpreet visit these links for better understanding of my statement i have given above
http://www.sciencedirect.com/science/article/pii/S1068520013000254
http://www.researchgate.net/publication/258688471_Isolated_user_security_enhancement_in_optical_code_division_multiple_access_network_against_eavesdropping
http://www.mijst.mju.ac.th/vol6/238-248.pdf

[alistu]

Thank you very much Sam Sung for the useful links. However, I think we have somehow deviated from the main problem Gurpreet stated. I think it would help him and me much more than a hundred links if you would very kindly make an osd file, demonstrating how to get multiple wavelengths from the same laser. Because you have read the papers you have introduced and sure know how to do that more than we do. I also have Gurpreet’s problem and it would be a real help if you do this for us. Thank you in advance.

[Ashu verma]

Hello Alidthu
Thank you for your suggestion,I will keep this in consideration from very next time.For now the basic idea is for sharing these papers is, the successive work of a particular author step by step from beginning to final proposal.So that it is easy to understand the real concept and application of wavelength conversion to enhance the system security.I coudnt get time today for forum replies,i am attaching a file here to get multiple wavelengths from one laser source by using EAM .

[Gurpreet Kaur]

thanks a lot alistu and sam sung… will go through these…

[Ashu verma]

There are many research articles from same author of above papers in OCDMA security domain.Dissertation if woek also present on internet.I found some more good papers of same author

http://col.org.cn/abstract.aspx?id=COL201109120602-05
http://www.sciencedirect.com/science/article/pii/S0030402610002470
http://www.sciencedirect.com/science/article/pii/S0030402610002494

[Gurpreet Kaur]

thanks a lot sam sung for these links… thay can be used by me for future work in same field…

[Gurpreet Kaur]

i noticed one thing in sac ocdma sample… the bit rate used for single user is set to 200mbps and there are 2 active users and the third user is off.
but the global bit rate parameter is having value 10gbps…
can you tell me why is it so?

[alistu]

In that example, another parameter is defined in the global parameters. that parameter is named “SignalBitrate” and this is the parameter that the bitrate of each user in the PRBS is referred to. So as far as I can tell, the global bitrate parameter is in practice replaced by this parameter in this example.

[Gurpreet Kaur]

ya a new parameter is added signalbitrate which is set to value of 200mbps. but the thing is that as 3 users are there each with 200mbps data, so the whole system is running on 600mbps. so as per me the global value for bit rate should be set to 600mbps…
plz correct me if i am wrong

[Ashu verma]

Good observation Gurpreet,In global parameter signal bit rate is defined i.e 200mbps and combined from 3 users is 600mbps as you said,but the bit rate used in global parameter is 10Gbps.I have run the system by varying the bi rate to 600mbps at bit rate ,but could not get any results.I think this data rate is taken to change the time window,since sequence length is large 1024.But i am not sure,i think Damian can give its right answer.
@Alsithu,i think there is some logic to take the value of Bit rate 10Gbps,otherwize system has to work on different data rates changed in Bit rate (by keeping signalrate constant)

[alistu]

I think if the “SignalBitrate” parameter is used in the script mode for all the users in their pseudo random bit sequence as the bit rate, then we will not have different data rate for different users. And this is the case right now. However, other global parameters such as Sample rate and Time window also change with the change of the “bit rate”.

BTW, would you please kindly consider my 23062 reply in this forum? Thank you.

Cheers!

[Damian Marek]

Defining the bit rate is a little subjective sometimes it can mean the entire systems performance and other times a single channel. Technically here it might have been better to call it the SignalBitrateperChannel. Normally, using a layout parameter to set the bit rate is a good idea because a lot of times there are low pass filters or optical bandpass filters that need to be optimized depending on the bit rate and using the TOTAL bit rate would not be correct.

[Ashu verma]

Thank you Damian,But why system stops working by changing Bit Rate?Is it specifically choose to take care about 200Signalbitrate?Because it works only for this particular data rate i.e 10Gbps

[Damian Marek]

This answer is tied to all your questions Alistu, Gurpreet and Samsung:

This gets deeper into signal theory, but the Layout Parameter Bit rate is tied to the Sample rate. Using the Samples per bit parameter in conjunction with the Bit rate the correct Sample rate is computed. Sampling is how the “real analog” signal is interpreted into a digital signal that the program can work with. Your sample rate has an effect on the largest frequency that the digital signal can represent, called the Nyquist rate. Since in our simulation our frequency signal is upconverted to the optical frequency you might say the sampling rate restricts the total bandwidth that can be represented.

What this means for this particular example is that while the bit rate per user is 200 Mbps, the bandwidth required to represent this signal is actually QUITE larger, since there are three users AND because of the format SAC-OCDMA being used. This is why lowered the bit rate changes the simulation, the sample rate is also reduced and now the signal cannot be represented entirely. However, you could lower the Bit rate layout parameter and increase the Samples per Bit parameter to balance it out.

[alistu]

Thank you Damian. However, I think I would rather change the sample rate by changing the “Sampler per bit” parameter.

[Gurpreet Kaur]

what is the effect of symbol rate on the performance?

[alistu]

You’re welcome, Gurpreet. The symbol rate is related to the type of coding that you use. For example, by using 4-QAM coder every two bits are represented by one symbol and therefore if the bit rate is 10 Gbps, then the symbol rate becomes 5 Gbps. Now this is a good thing but it might change the error rate somehow.

[Gurpreet Kaur]

thanks a lot damian for clarifying the things…
and thanks sam sung and alistu for participating in the query and helping me out….

[Ashu verma]

Thank you Damian for your elaborATION ON THIS topic.Now most of the doubts are cleared regarding BW and bit rate

[alistu]

Thank you Damian for the explanation, but i didn’t exactly get why we do not make the bit rate change to the already defined “bit rate” parameter and instead we are defining a new parameter. Can you please clarify this?

[Gurpreet Kaur]

thanks damian, sam sung and alistu
so is it necessary to set the global bitrate to 10gbps in this setup?
and for the filters used the signalbitrate is used i.e. 200mbps…

[Gurpreet Kaur]

i tried changing the sequence length to 128 but still i could not obtain the results..

[alistu]

With Damian’s explanation, I think it is all clear to you now. But if I were you, in order to avoid confusion I would have deleted the SignalBitrate Parameter and would have used the Bit rate parameter instead. At the same time, I would have multiplied Samples per bit parameter by 10G/200M=50 times the amount it has now to make everything more simple. Then you can compare filter cut-offs, bit rates and samples per bit to find the problem more quickly.

[Ashu verma]

Hello Gurpreet,As damian said i have just made some modifications in sample file of SAC OCDMA.It is working fine for 128 Seq. length and bit rate set to 1Gbps sample per bit to 512 to make total samples 65536.What type of problem you are facing?

[Gurpreet Kaur]

hi samsung
can you please attach the file in which you have made changes?

[Ashu verma]

Hello Gurpreet Kaur,
I have made very simple changes as i suggested above about setting bit rate sequence length and sample per bit. Find the file attached ↓ , it is working fine for me. Please let me know if you find it worth. Thank You.

[Damian Marek]

It doesn’t matter as far as I can tell, the person who made this sample just made it a certain way but both ways are equally valid

[Ashu verma]

Welcome Gurpreet ,and sorry for incorrectly spelling your name :/
This forum topic containes very important points ,even i have got to know many new concepts,specially security in ocdma.Thanks to Alisthu for joining this topic

[Gurpreet Kaur]

samsung can you please make the osd file for getting multiple wavelengths from single laser? as things are not much clear by reading.
it will be of great help

[alistu]

Yes, Sam Sung. You have very kindly introduced many papers in this topics, claiming they are related to Gurpreet’s question. I think demonstrating exactly what he and I have problem with, by creating an Optisystem file, would be better than a hundred links. Besides, you have read the papers and otherwise, you wouldn’t have recommended them. So please refer to my 23062 reply. Thank you in advance.

[Ashu verma]

Hello Alisthu and Gaganpreet
Thank you for your suggestion,I will keep this in consideration from very next time.For now the basic idea is for sharing these papers is, the successive work of a particular author step by step from beginning to final proposal.So that it is easy to understand the real concept and application of wavelength conversion to enhance the system security.I coudnt get time today for forum replies,i am attaching a file here to get multiple wavelengths from one laser source by using EAM .

[alistu]

Thank you very much Sam Sung for the explanations and the file attached. I think this is some of what me and Gurpreet were curious to know about the issue, aside from the papers and all the theoretical aspect of it. And we are waiting for more explanations plus the attached osd file after you find the time.

[Ashu verma]

Welcome Alisthu ,
I have already attached the file and a brief explanation is given with it about the system, however if you would like to know more then i will explain it. For now i can just explain it as:-
In this system a laser source externally modulated by MZM with data encoded by NRZ is fed to electro absorption modulator. A sine generator is used for the spectrum broadening causing cross absorption that is XAM. In second system EAM as a wavelength converter is same as we have described above , the only difference is i have used single laser source by not incorporating any data, rest you can see the system file i have given the annotations there. Thank You

[Ashu verma]

The system i have attached is divided into two systems.One for conversion of wavelength or multiple wavelenghts with modulated data steam and 2nd one from direct laser.
1)A 10G data stream modulated with NRZ followed by MZM is fed to EAM.Broad in spectrum can be seen i n OSA2
2)Direct laser fed to EAM and broadened spectrum realized at OSA4.
Note:- With change of sine gen. freq. the spectrum changes,so by adjusting the SINe Gen freq. more or less broaden spectrum can be observed.

[Gurpreet Kaur]

thank you for sharing the file with us…

[Ashu verma]

Welcome Gurpreet,
It is very obvious for me to attach the file but i would strongly recommend you to understand the concept and use it in your system by doing a proper study of the papers i have attached for the OCDMA security enhancement. All the anti-jamming and eavesdropping protection in the papers has been done using SOA as a wave length converter. You can implement save setups using EAM because in SOA FWM affect is prominent and to initiate it author had to use additional pumps. By using EAM requirements of these additional pumps maybe be eliminated, also you can compare the performance of two systems. Thank you and best of luck.

[Gurpreet Kaur]

thanks a lot sam sung for the help… and i will go through the papers and try to use it in my system….
thanks

[Gurpreet Kaur]

hello
i am using FBGs for decoding. but with the desired reflection i am getting other wavelengths too. can anyone tell me how to reduce the power of unwanted wavelengths in the reflection output?

[alistu]

Hi Gurpreet, Please attach the osd file if possible. Thank you.

[Gurpreet Kaur]

here is the file i have done with 2 users the code is 110, 011.

[alistu]

Hi Gurpreet, I ran your simulation and think it makes sense and you have made correct use of filters. If you are referring to the ripples as “other wavelengths”, you can never have just three impulse as in theory. However, you can reduce them by reducing your FBG bandwidth, sometimes at the cost of system performance.

[Gurpreet Kaur]

thank you for reviewing my file…. so is it ok and i can continue on the work?

[alistu]

You’re welcome! Yeah, no worries about the ripples.

[Abhishek Shrama]

Hi Gurpreet ,if i an getting you right.Then you try by reducing the bandwidth of FBG.i think if you are taking wider BW and wavelength you choosen with less spacing among them.This problem arises but i am no sure about it.

[Shreyas Nagendra]

Hi i have been able to simulate for 5 users and the BER result is being correctly obtained for the parameters which i have used for SAC ocdma MD codes .
But now how to get a graph for 100 users or for multi users for different weights as used in all the papers.
optisystem 13 is used for my simulation.

[Author]

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