SAC ocdma

[LALIT VERMA]

Sir can any one help me on SAC OCDMA SPD technique,plz
iam not getting the results.
ihad also attached the work 30 july by name.

thanks and regards.

[LALIT VERMA]

Damian Marek Sir can u plz give some idea about what i am doing wrong in the sac ocdma technique i had used MDW code for this and the circuit is attached.

[alistu]

Hi Lalit, I took a look at your design and found nothing wrong at a cursory glance. But when ran the simulation, it took so long that I actually could not wait until it finishes! Is this your problem? Whenever I have had the simulation time duration problem, it has been because of the existence of too much power in the line. So please lower the power injected into the line in the first step and let me know if this helps.

[Ashu verma]

Hello Lalit
I suggest you go through the similar discussion started by Gurpreet in another forum.Read that carefully because discussion is very good and long to ,which sum up your akl the questions.Alisthu Gagan including me discussrd some important points.i think this file also from there..Rest also read the papers attached thn you will get the idea

[alistu]

Yes, that is most probably the problem! I removed the optical fiber channel and then ran your simulation. It went well and I managed to get the results this way. When you enter two much power into the fiber, it causes some nonlinear effects to influence the process and make the calculations more complex, which results in an increase in the time duration of the simulation.

[LALIT VERMA]

Thanks Sir well i had the problem of system taking a long time to run as well i will do reduce the power and see but also the eye diagram results were also not good.

Thanks & regards.

[alistu]

You’re welcome Lalit. The corruption of the received signal can also be caused by the undesirable nonlinear effects which take place in the optical fiber channel at high powers. I am not sure whether that is the case with your simulation or not, but you will find this out as soon as you reduce the power.

[LALIT VERMA]

Sir with -5 dBM or 0 dBm theckt iam going to see,which is specified in some papers on non coherent CDSMA optical techniques.

[alistu]

I didn’t exactly understand your statement, Lalit. Could you explain more? Thank you.

[Ashu verma]

As i understand from Lalits statement,he is asking about input power he would use in system.From my opinion you can use low power due to the fact that it will reduce calculation time as well as reduce non linear effects.-5 dBm and 0 dBm are not to high powers so you can analyze on both powers.even you can observe the system at different pwers .

[LALIT VERMA]

Sam sung u are saying it right i am using the power at the o/p of LED as 0 dBm or -5 dBm.

Thanks

[alistu]

Is your problem hopefully solved by using -5dBm to 0dBm? I have to add, I think the power being considered high or low highly depends on the your system. I am currently comparing MC-CDMA and WDM-OFDM. Even though I am using the same bandwidth and the same number of users, my WDM-OFDM results get worse and worse as I enhance the power from 0dBm. But for MC-CDMA I can get better results by increasing the power up to 8dBm.

[Ashu verma]

Welcome Lalit
Alisthu made a good point about the dependence of system performance by increasing power is not certain that increases .In case of transmission over fibwr high power degrades due to impairements of non linraties.Howevere if you are using non linear effects to realize some system then it increases.

[alistu]

That’s right Sam Sung! But even if you are realizing a system with nonlinear effects, it doesn’t necessarily mean that you have to go through this simulation time extension problem. I have experienced whenever this happens, I always get corrupted signals. However, sometimes the power threshold (before this problem occurs) is needed to evaluate system performance.

[alistu]

I think I understand why in MC-CDMA increasing the power does not make as much trouble as in WDM-CDMA if anyone is interested. In WDM CDMA in a specified bandwidth, there are data channels that are seperated from one another by a distance we call channel spacing. So the power we apply only exists in the channels and not between them. But in MC-CDMA the power is distributed throughout the whole bandwidth and therefore, the power peaks are lower than they are in WDM-OFDM.

[Ashu verma]

Hi Alisthu ,In my systems nonlinear effects use to convert wavelength i.e upconversion and downconvesion using EAM and SOA’s.System calcultes fast and doesnt take a more time but when it comes to HNLF,simulation time increases Too long.However Q-factor of converted wavelength increase with the increase of input power which gives more efficiency of conversion.

[alistu]

That’s right. I was also implying the same thing in my last reply in this forum. I meant it is possible to have nonlinear effects in your system and consider these effects (which actually exist in real fiber optic system) to make the simulated system more like a real one without the time extension. Time extension happens when a lot of power is injected into the line.

[LALIT VERMA]

Thanks alitsu ANd sam sung to both of u, i simulated three user SPD technique on sac ocdma with i/p power as -23.9 dBm and i was getting BER as 1.03569e-008 and Q factor 5.50452 at 200 Mbps

still i need to achieve the bit error rate of at least 10^-28 at 622 Mbps what i should i do.
thanks & regards.

[alistu]

You’re welcome Lalit! As for what you have asked, I think since your main problem that has been discussed in this forum up until now has been your high input power, it is possible when you might have lowered the power more than what is necessary when you were trying to solve the problem. So please start with increasing your power as much as possible without facing that problem again.

[Ashu verma]

Welcone Lalit,its been great to discuss the topic with forum members.As far as your system is concernd,as you said the input power is – 23 dB and gives you BER of 10^-10.To decrease the value of Ber and to increase value of Q factor,you can simply increase the input power.And see the results,i suggested you power increase due to the fact that you have entered very low power input value

[Ashu verma]

Also i got the basic idea that you wqnt to increase the data rate to 622 mbps,i have following question related to your system
1) How much link length you have covered with BER 10^-10?If you increase distance BER will increase simply.
2) Have you included any EDafA or optical amplifuer?
3) Have you used any dispersion compensation??
Give me these answers and then i will give you the further suggestions.Thank you

[alistu]

Hi Sam Sung, I think the parameters and components you have asked about are there in the simulation file that Lalit has attached and since he has not mentioned anything about changing parameters except for the input power, I assume these parameters have not changed and you can suggest your points. Thank you.

[LALIT VERMA]

Thanks Alitsu and Sam sung for responding,i am using the 622 Mbps data rate, along with this I am not using any EDFA or dispersion compensation.
length of fiber was 10- km,of smf with dark current 5 nA, thermal noise coeffecient as 1.8 * e-23,0.25 attn,etc.

also i varied i/p power from 10 to 30 micro watt but bit error rate not improved ,the code i am using is MDW.

Thanks & regards.

[alistu]

You’re welcome Lalit. You have increased the power but maybe not enough for the results to change. In one of my previous replies I asked you to increase the transmission power so much that you reach the threshold. The threshold power is reached when by increasing the power you start to get worse results.

[LALIT VERMA]

i increased the power from 10 microwatt to 300 microwatt but the results were still the same an BER of e-006
what next i should do.
thanks and regards Alitsu and sam sung.

[alistu]

Hi Lalit, Could you please tell me whether you have followed the procedure I asked you to follow in my previous comments or not? The 300uW power that you are injecting into the line right now does not seem to be so much that it would cause nonlinear effects. In other words, what would happen if you increase the power to more than 300uW?

[LALIT VERMA]

Alitsu
i constructed an sac ocdma system with FBG only so that i can look the problem w/o WDMux and also the power losses would be minimized but the problem is same.
plz look in to the matter where the problem is.

thanks and regards.

[alistu]

Hi Lalit, I am familiar with the system you are simulating and I believe we had a discussion about what to do in order to improve system performance, following the discussion we had about your simulation problem due to too much power injected into the line and the nonlinear effects induced by that. So please do as I mentioned in my previous reply and let me know of the result. Thank you.

[LALIT VERMA]

Sir i thought i was not able to attach the file now again i try.

[alistu]

Thank you for uploading your simulation file. While you experiment what I have suggested you, may I ask why you have not used any dispersion compensating fiber in your implemented system? Is it a system proposed in a particular paper that you are trying to reproduce the results? If so, could you introduce the paper? Thanks.

[LALIT VERMA]

Yes Sir i can introduce the paper since no DCF has been used in that.

[LALIT VERMA]

Sir the paper has been attach i will do same as you said, with the previous diagram.

thanks and regards.

[alistu]

Thank you Lalit for introducing the paper. While I found the answer to my question about dispersion compensating fiber in this paper, there was no mention of the power injected into the line. So I think you’d better find the maximum laser power by following the procedure I suggested to ensure the best results and closest to those in the paper.

[LALIT VERMA]

No sir but i have written in my synopsis to solve the problem by in coherent source. LED.

With regards
Thanks sir.

[alistu]

In this case you’d better consider the suggestion I gave you to be able to find the highest power possible before encountering any trouble because of nonlinear effects, in order for for results to get better than what you are getting now. Please let me know if you did that. I have no more way in mind to suggest other than that.

[LALIT VERMA]

How i can see that Mach zehender modulator is dividing the single bit in to 4 chips of different wavelength using MDW code of SAC OCDMA scheme.

Thanks and regards.

[alistu]

Hi Lalit, The Mach-Zehnder modulator does not divide the signal; the four signals with different wavelengths are combined using a power combiner to form one signal with different wavelength components and then modulated using the Mach-Zehnder modulator.

[LALIT VERMA]

Thanks Alitsu ,for ur response .
I simulated the the SPD SAC OCDMA circuit and was able to achieve bit error rate of 10e-12,10e-13 and 10e-22.for user 1,2,3, resp.This seems to be different results as BER should be achieved near by for all user.
The power uptill the receiver demux is same for all three user the FBG i used are uniform,but FBG are giving power at refelective and transmittive end are differnt for the three user .i also tried tuning of the FBG by changing the reflectivity.
how icsn achieve approx same BER at all the three user.
Thanks and regards.

[alistu]

Hi Lalit, Please attach your osd file so I would be able to check. I have faced more or less the same problem while working with electrical CDMA, but not in OCDMA.

[Ashu verma]

Can you attach your system file .Latest file i mean to say.

[LALIT VERMA]

Thanks Alitsu and samsung for responding.

Iam attaching my file.

regards.

[LALIT VERMA]

I had attached the file name spd2015.osd

[LALIT VERMA]

Plz see and if u can help me.

thanks.

[alistu]

Dear Lalit, The problem is every time the simulation is run, the amount of BER differs from the last time for every user. I think this is due to three main factors: randomness of noise, random seeds generation being chosen, and short bit sequence. I just increased the bit length to 4096 (and reduced samples per bit just to make simulation time shorter; you don’t have to do this) and got min. BER of about 10-4 to 10-6 for all users for three simulations. So I suggest that you increase it.

[LALIT VERMA]

Thanks alitsu for ur support i will look in to this using this suggestions.

regards.

[alistu]

You’re welcome Lalit. Let me know if your problem is solved.

[LALIT VERMA]

Alitsu gud evening i changed the random seed to 0 and also increased the sequence length but iwas not able to get result.

Thanks and regards.

[alistu]

Hi Lalit, Please run the simulation for the system in the attached file. I have just increased bit sequence. By the way, I was not talking about random seed index, I meant “generate random seeds” being ticked causes some variations, but you should be able to get results without unticking it. Please check the file.

[LALIT VERMA]

Thanks alitsu for ur response but iam not able to open the file i am having optisystem 13.but not being loaded.

with regards .

[alistu]

Then I am afraid I am using Optisystem 13.0.3. I just suggest trying once more by increasing bit sequence to 4096 without changing any other parameters.

[LALIT VERMA]

Is there any relation between sequence length and the o/p power of the LED source for getting a good BER.

[alistu]

There is no relation between the sequence length and system performance. But when a short sequence is used, you see more fluctuations in the results as you repeat the simulation (for example if you use 100 bits and one bit is incorrectly received, you get BER=0.01, while one bit error for a seuqence of 10000 bits gives BER=0.0001). So it is as if the use of longer bit sequences improves the measurement accuracy somehow.

[Ashu verma]

In optical communication system, generally the pseudorandom bit sequence (PRBS) are used as data signals for modulating the DWDM channels. The longer word length (WL) develops the more bit patterns in PRBS. The selection of number of bits in PRBS directly affects the system performance because longer the WL means easy to evaluate the performance, on the other hand, shorter the WL means condense the calculation time and the memory requirements. Therefore, it is essential to illuminate how long the WL is vital to estimate the nonlinear crosstalk’s precisely.
The SRS crosstalk can be increased due to the presence of successive number of “1” bits, which is directly proportional to the WL as it determines the maximum possible length of the successive ‘1’ bits. That means longer the WL, maximum the probability of occurrence in successive “1s”.

[Ashu verma]

Hello Alisthu ,i found this paper very interesting which defines effect of world length on non linearities.i am little confused now about the dependence of sl on system pergormance.Take a look at thishttp://www.sciencedirect.com/science/article/pii/S106852001300059X
This explaines SRS effect on system performance with wL .As WL increase there is increase in non linear effects

[alistu]

Hi Sam Sung, Thank you for introducing this interesting paper. However, we are discussing a specific case here. Lalit would like to know why I suggested a longer bit sequence and that if the reason for getting more acceptable results after lengthening the sequence can be interpreted as better system performance, and I proposed what Damian had formerly suggested in a few similar occasions. Neither lengthening the sequence would take up so much time and memory in here nor any hybrid optical amplifier has been used in his system. It’s a practical question rather than theoretical from Lalit, which is asked about a specific case discussed above. I suggest that you go through the whole discussion about the issue to avoid confusing it with the idea in the paper.

Regards

[Ashu verma]

Thank yoi alisthu.But i got lot of questions about this paper that word length only depend in case of where hybrid amplifiers are used? Is this due to raman fiber only? Or is it play some role in every system where fiber is used? I got your point about the discussion here of sequence length and varied results..And in paper author explained some interesting point of non linear effects depends upon WL..But every time i read similer discussion on forum ,increased seq. Length suggesred in order to get mote accurate results.Now i am bit confused? I will start new topic if required,if it confused here?

[LALIT VERMA]

Sir, in some tutorials GVD DAT file is being mentioned how to obtain it.

Thanks and regards.

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