Home Forums SYSTEM how to implement sac ocdma?

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    • #25544
      Swapandeep Kaur
      Participant

      i am a beginner. please help me with the basics…

    • #25552
      LALIT VERMA
      Participant

      What type of SAC ocdma u want to implement and what is ur base paper on which u are working b coz sac ocdma is implemented in many ways.

    • #25567
      Swapandeep Kaur
      Participant

      Sir i am implementing the attached paper . please guide..

      • #25570
        alistu
        Participant

        Hi Swapandeep,

        Can you please tell me if you have gone through my very basic explanation of the SAC OCDMA in your topic optiwave.com/forums/topic/problem-while-installing-optisystem-13/ . I believe it will help with implementing your attached paper system, as it gives some basic information. Then you can ask about more specific details.

        Regards

    • #25572
      Swapandeep Kaur
      Participant

      Alistu sir i have gone through everything you sent in the link but it does not provide the basic explanation and i am not getting how actualy the sac ocdma is being implemented… we are using fbg but where in optisystem is the option that generates the codes like 101011.? This is the first time i am using optisystem.

      Regards

    • #25573
      Taiwo Ambali Abiola
      Participant

      First of all, you are welcome to the forum the same way I would equally welcome myself after a long break due to a number of task at hand. Just as Lalit Verma has already said, the forum is more of a way to implement your design using optisystem softwares and some others. There are some factors you need to consider when talking about SAC-OCDMA. One is how many users, which light source do you want to use (LED or multi-wavelenght laser,white light), which code do you plan to use, (eg, OOC, MQC, KS, MS code) and also the decoding techniques you have chosen to use.

      Whichever way, You have the light source (example LED), the spliter(divide into number of users), the FBG to implement the chosen code, modulator to modulate the light using the bit sequence from the PRBS with a specific modulation format ( such as NRZ, RZ, and other advance modulation formats such as QPSK, DPSK etc). Then you need a power combiner/coupler to couple the signal from different users. then you select your channel of communication (free space optics (FSO) or fiber). At the receiver, you equally need a splitter, to divide the combined signals into the number of receivers. Then you apply your chosen decoding techniques e.g(direct decoding, complementary, AND decoding or any other you have chosen). after selecting the decoding measure, you need a photodetector (to convert to electrical signal), low pass filter (to remove noise) and also BER analyzer (which gives you error rate by comparing your received signal with the transmitted one, then gives you the rate of error in your system. If you can recollect, A minimum BER of 10^-9 and below e.g (10^-10, 10^-15, 10^-18, 10^-30 etc) is the standard for effective communication. You can modify the parameters to suit your design. I hope the explanation helps. Kindly signify if you need more help. There are professionals like Ravil, Samson, Optiwaves teams, and others to help with more information.

    • #25574
      Swapandeep Kaur
      Participant

      Thank you so much sir for the useful explanation. since i am a beginner , i am not making any changes to the sac-ocdma given in the sample of optisystem 13 and with its help implementing my paper. it involves the use of white light, i want to know why we have used white light?how the fbgs are used to generate the hadamard codes . since the sample involves the use of three users, i too want to implement the same. only after getting what is being done , i can think of changing the users or other parameters….

      • #25578
        alistu
        Participant

        So I assume you have understood how the code is actually generated, and you just wish to know how to implement it. Imagine a codeword obtained for a user to be, for example, 101000. As you can see, only the first and the third elements are ‘1’ and the rest are zero. This shows that for this specific user, you have to use two FBGs whose wavelengths are tuned at lambda1 and lambda3 (Why? Because only the first and the third elements were non-zero at 1010000). That’s it!

        Now how are lambda1 and lambda3 chosen? For example, you can start from lambda1=1550.1, lambda2=1550.2,… .So lambda7 would be 1550.7. This is arbitrary. You just choose a starting and and step wavelength (And you’d better you LEDs wavelength the middle frequency of the lambda range). Please tell me if this explanation helped.

        Regards

    • #25579
      Swapandeep Kaur
      Participant

      sir this information is really useful. but actually i did not get how codes are generated ,so please help me with that. and why white light is chosen?

      • #25592
        alistu
        Participant

        White light is a combination of different wavelength, and here also we need a spectrum so that some wavelengths would be filtered in it.

        I guess now my explanation in the link below:

        optiwave.com/forums/topic/sac-ocdma-with-md-code/#post-22736

        along with the paper “Development of a new code family based on SAC-OCDMA system with large cardinality for OCDMA network” are going to be very useful in understanding how codes are generated. I have also explained it very simple there, so you will hopefully find that useful too and if not, please let me know.

    • #25580
      Swapandeep Kaur
      Participant

      sir the concept you just explained i have understood. thank you.

    • #25593
      Swapandeep Kaur
      Participant

      thank you sir for the information. but i have to implement hadamard codes in my paper ad in sac -ocdma sample also it is hadamard code not md code

      • #25595
        alistu
        Participant

        Generating Walsh-Hadamard codes from Hadamard matrix is much easier. Please look at the following matrix:

        1 1
        1 0

        The next Hadamard matrix would be a 4×4 one being generated by putting the above matrix instead of each of the elements of it. But for the zero elements, you would have to change ones to zeros and zeros to ones. Look:

        1 1 1 1
        1 0 1 0
        1 1 0 0
        1 0 0 1

        The above matrice is composed of for matrices as depicted above and shown below:

        1 1 – 1 1
        1 0 – 1 0

        1 1 – 0 0
        1 0 – 0 1

        I hope the explanation is clear. Please compare the two matrices to find the relation. Now every row or column of the above matrices is a code for one user.

    • #25597
      Swapandeep Kaur
      Participant

      yes sir it is clear thank you sir

    • #25601
      Swapandeep Kaur
      Participant

      sir suppose in the paper its shown at the encoder 11001100 (has that been chosen by choice or how by codind?) it will require 4 fbg. each 1 wil require 1 fbg and correspondingly frequency we will set, that i have understood. but the code at the encoder, how that has been chosen??

      • #25609
        alistu
        Participant

        The 11001100 code is the third column of the 8×8 Hadamard code (you could just use the code “hadamard(8)” in Matlab to see this).

        I don’t understand your question. Based on the number of users, you can choose hadamard code length (for example for 8 users, you can use each of the rows or columns of the 8in8 hadamard matrice as a code for one user). If this is not your answer, please elaborate more on your question.

    • #25620
      Swapandeep Kaur
      Participant

      Three users are there and the chosen codes at the encoder are 10101010,11001100,10011001 in the paper i am implementing.They have been chosen from the 8×8 hadamard matrix? one is second column,third column and 4th row. Why 8×8 matrix is chosen? and any row and column can be chosen thereafter i think as we want

      • #25624
        alistu
        Participant

        The most probable reason for doing such a thing is better performance I suppose, as in the electrical CDMA (not always, though). And I made an 8in8 matrix for an 8 user system just as an example. But obviously the number of rows or columns cannot be less than the number of users.

        All vectors created from matrix rows are orthogonal to each other, hence all vectors from columns. So you can pick any rows or columns.

    • #25621
      Swapandeep Kaur
      Participant

      hadamardMatrix =

      1 1 1 1 1 1 1 1
      1 -1 1 -1 1 -1 1 -1
      1 1 -1 -1 1 1 -1 -1
      1 -1 -1 1 1 -1 -1 1
      1 1 1 1 -1 -1 -1 -1
      1 -1 1 -1 -1 1 -1 1
      1 1 -1 -1 -1 -1 1 1
      1 -1 -1 1 -1 1 1 -1
      will be as above (zeroes instead of -1)

    • #25800
      Swapandeep Kaur
      Participant

      please explain the attached ber analyser graph.what does it signify?

      • #25802
        alistu
        Participant

        Hi Swapandeep,

        Generally speaking, here is the way to interpret the eye diagram:

        – The eye opening corresponds to the additive noise in the signal.
        – The eye overshoot or undershoot correspond to the peak distortion in the signal path.
        – The eye width corresponds to timing synchronization and jitter effects
        – Eye closure corresponds to inter-symbol interference in your system.

        With regards to the above factors, you can identify the destructive effects in your system from the information in the eye pattern.

        Regards

    • #25808
      Swapandeep Kaur
      Participant

      what does the blue curve in the figure i have attached signify? its not part of the eye diagram

      • #25849
        Damian Marek
        Participant

        The light blue curve you mentioned plots the Q factor as a function of the decision instant. Normally the Q factor is the highest in the center of the eye diagram which corresponds to the largest different in the signal amplitudes and near the edge of the eye it drops off. By changing the tabs at the bottom of the figure you can plot other results as a function of the decision instant, for example BER.

    • #25833
      Swapandeep Kaur
      Participant

      what does max Q factor , min ber, eye height , threshold signify? whether they should be high or low?

      • #25842
        alistu
        Participant

        In order to have a comprehensive understanding of the factors mentioned above, please go through the file attached in my comment given in the below link:

        BER manual calculation

        In the meanwhile, let me point out that the more eye height, the more Q-factor and the less BER, hence the signal better. Please read the paper and ask any questions you have.

    • #25945
      Swapandeep Kaur
      Participant

      Thank you sir. sir i implemented sac ocdma with long reach passive optical network. i am not getting the output. please guide. the figure was large, so i am attaching the file in two parts.

      • #25953
        alistu
        Participant

        The snapshots you have attached help me implement the system and then try to troubleshoot it, but it would be more helpful if you kindly upload your own implementation of the design in optisystem (the corresponding osd file). . Please attach the file and I will look into it. Are you using the latest version?

    • #25948
      Swapandeep Kaur
      Participant

      sir i used fiber bragg grating. i think i should use uniform fiber grating

    • #25949
      Swapandeep Kaur
      Participant

      sir didnt get the output with uniform fiber grating too..

    • #25954
      Swapandeep Kaur
      Participant

      sir these are snapshots of the file that i implemented..what does osd file mean?

    • #25955
      Swapandeep Kaur
      Participant

      yes sir i am using the latest version optisystem 13

    • #25957
      Swapandeep Kaur
      Participant

      osd format

    • #26002
      Swapandeep Kaur
      Participant

      sir were you able to find out where I am going wrong?

      • #26005
        alistu
        Participant

        Not unfortunately, as I am not familiar with the receiver structure and the basis on which the wavelength for each of the fiber bragg gratings for each user is being chosen. I only know you have used hadamard matrix to produce the code words. Can you elaborate on that please?

    • #26006
      Swapandeep Kaur
      Participant

      sir I have chosen the wavelengths as you had guided and taking the sac-ocdma simulation as the reference. i took 1550.1 nm as the first wavelength and 0.3 nm as the bandwidth and corresponding to that according to the rows and columns of the hadamard code selected in the paper like 10101010 , selected the next wavelength as 1550.7 nm and so on. at the receiver side, the upper decoder wavelengths for code 10101010 were starting from 1550.1nm and the lower decoder as 1548.5 nm

    • #26012
      Swapandeep Kaur
      Participant

      sir will this information help?

      • #26016
        alistu
        Participant

        I hope so. I haven’t got the results yet and I will let you know if I manage to do so. Can you please tell me how you chose the lower decoder wavelength?

        By the way, please have a closer look at the bit rate of your channels. You may want to set them again, as one is not set properly and the others are set at the global bit rate (and not at 200Mbps, as in the Optisystem example which you might have been trying to set to).

    • #26015
      Swapandeep Kaur
      Participant

      sir please reply. this is my college project and i am not getting the output………..

    • #26017
      Swapandeep Kaur
      Participant

      sir i chose the lower decoder wavelength with reference to the sac- ocdma sample, 1548.5 as the initial and the next with .3 as the bandwidth and 10101010 code.

    • #26098
      Swapandeep Kaur
      Participant

      sir did you get any output?

      • #26099
        alistu
        Participant

        Not unfortunately. And I am not still sure about the basis on which the wavelengths of the fiber bragg gratings on the receiver side should be chosen. I will let you know if I make any progress. I think members with an experience in this area such as Lalit (with whom we formerly discussed a SAC OCDMA system in another topic) may provide valuable insight.

    • #26251
      Swapandeep Kaur
      Participant

      Sir did you get any output? I asked the authors of the paper, they sent a snapshot of the parameters, i am attaching that, see if that helps

      Regards

      • #26257
        alistu
        Participant

        Hi Swapandeep, I have done the simulation with a bit rate of less than this in a back-to-back system and have not managed to get the results. I think the information we need is the wavelength of the lasers and the wavelength of FBGs both on transmitter side and on the receiver side, as I am not sure about the theoretical basis of choosing wavelengths in the receiver.

    • #26262
      Swapandeep Kaur
      Participant

      sir is there nobody who could help us…

    • #26361
      Swapandeep Kaur
      Participant

      Sir in the OCDMA network design I read this line “The diagram below shows the receiver-end for one of the users, where the received signal is split into an upper branch (FBGs are the same as the encoder) and lower branch (FBGs are the complement of the encoder)”.
      According to this the wavelength is set i think

    • #26363
      Swapandeep Kaur
      Participant

      Sir what i took in my simulation was wrong , since i didn’t know this concept.

      • #26365
        alistu
        Participant

        You’re right. And now that I wanted to correct it according to your statement, I realized you have used 1550.1 and 1550.9 while you have taken the steps as 0.1 nm. Therefore your code length must have been longer than 8. If I am wrong, please tell me how you have created the code so that we would be able to correct the system.

    • #26384
      Swapandeep Kaur
      Participant

      Sir i constructed the code like this : if code is 10101010 , then if first wavelength is 1550.1 and bandwidth is .3, the next would be 1550.7nm , though know i think that the steps and the bandwidth have no relation with each other ( as seen from the image that i sent yesterday that was sent by the authors of the paper) they have used 1550 , 1550.5 , 1551 ( say for 11110000) while bandwidth is 0.3 nm

      • #26501
        alistu
        Participant

        You have named three wavelengths for a code of length 8 and with four ‘1’s, while four FBGs with four different wavelengths should have been used. Are you sure about the wavelengths used in the paper?

        I suggest that you design the system with central wavelength of 1550.5 with steps of 0.5nm and bandwidth of 0.3nm and choose the receiver FBG wavelengths as you earlier mentioned (by using complements). If you did not get the answer, please attach the file here.

    • #26399
      Swapandeep Kaur
      Participant

      sir any hopes of getting result? i am confused…

    • #26401
      Swapandeep Kaur
      Participant

      i am confused what will be the codes at decoder if the lower fbg are complement of upper ..

    • #26499
      Swapandeep Kaur
      Participant

      sir this is what i got from a thesis work
      The fbg cut off freq is chosen randomly within the broadband light source bandwidth. Furthermore, to take in notice on choosing the cut
      off frequency is not to choose a cut off frequency that is close to another bit and not choosing the cut off frequency that is outside or too near to the upper and lower side of the broadband lights source bandwidth.
      The Specification of the Output from the spectrum is stated below:
      White Light Specification
      white light source freq 1550.5nm
      white light source power -115dbm
      fbg cut off freq 1548.5nm,1550.1nm 1550.9nm 1552.5nm
      bandwidth .6nm
      reflectivity .9998

      • #26502
        alistu
        Participant

        Please attach the thesis you are referring to, or address it by giving the name, name of the author and name of the university. As for what you mentioned about the bandwidth, I also think 0.3nm is a small amount for the bandwidth. But it would be better if you use script mode to set bandwidths, so that if we have to change it, we wouldn’t have to change them one by one.

    • #26500
      Swapandeep Kaur
      Participant

      It is given that for smaller bandwidth, there can be more users involved but the ber is high . best results are obtained at bandwidth of 0.6nm

    • #26505
      Swapandeep Kaur
      Participant

      the thesis

      • #26510
        alistu
        Participant

        Thank you for the thesis. It is somehow expected the less bandwidth is used, the more error might be made in the system. So you’d better use the script mode so as to be able to see what difference the change of bandwidth makes in your system. Please also consider my reply #26501 on this topic.

        Regards

    • #26519
      Swapandeep Kaur
      Participant

      yes ill consider your reply . ill chose the central wavelength as 1550.5 and steps as 0.5 nm . because i didnt get what step size has been chosen in the sac- ocdma example.

      one more thing i learnt from the thesis was that we can check the code with the spectrum analyser after the encoder..

    • #26522
      Swapandeep Kaur
      Participant

      what white light freq should i choose? 1550.5 nm? and what about the layout parameters?

    • #26523
      Swapandeep Kaur
      Participant

      please explain how to take complement of the codes at the decoder?

      • #26525
        alistu
        Participant

        You can choose white light frequency the same as the center frequency that you have chosen for your codes. The complement codes are formed from the code used at the transmitter when ones turn to zero and zeros turn to one. For example, if your code line is “11110000”, the complement is “00001111”.

    • #26529
      Swapandeep Kaur
      Participant

      sry sir one more question what does central wavelength mean? it is 8 bit code , so what will be the centre frequency?

      • #26532
        alistu
        Participant

        What I refer to as the center frequency is the frequency which is in the middle of the frequency range used for the fiber bragg gratings. For example, for a code of length 8 starting from 1550 with steps of 0.5 nm, lambda1 would be 1550 nm and hence lambda8 1553.5 nm. So the middle wavelength is 1551.75 nm.

    • #26552
      Swapandeep Kaur
      Participant

      sir what if i choose the centre freq as 1550 nm bcoz 1550.5 is getting tough to be chosen as centre freq

    • #26553
      Swapandeep Kaur
      Participant

      sir im selecting the freq as 1549 1549.5 1550 1550.5 1551 1551.5 1552 1552.5

    • #26554
      Swapandeep Kaur
      Participant

      sir there is something wrong. im not getting correct diagram of spectrum analyser after encoder like of code 10101010 . im getting the result as attached

      • #26556
        alistu
        Participant

        Hi Swapandeep,

        While I was trying to open your file, I encountered an error stating the file could not be opened. I have attached the screenshot of the folder here. And i am using the last version of OptiSystem. can you please upload your file again? Thank you.

        Regards

    • #26562
      Swapandeep Kaur
      Participant

      i attached the word file

    • #26564
      Swapandeep Kaur
      Participant

      should i attach the osd file?

      • #26568
        alistu
        Participant

        Oh, I thought that was an Optisystem file… So yes, please attach the OptiSystem file and I will check the results to see if there is a problem. Thank you.

    • #26574
      Swapandeep Kaur
      Participant

      sir i am attaching the osd file. i am not getting the results, there is some problem with the code generation as the spectrum analyser is not giving correct results of the encoder

    • #26576
      Swapandeep Kaur
      Participant

      the osd file

    • #26582
      Swapandeep Kaur
      Participant

      sir did you come to know the problem?

      • #26595
        alistu
        Participant

        Have you set the parameters according to our former discussion? Can you please tell me about them, the starting wavelength, the codes used and the step frequency? Thank you.

    • #26597
      Swapandeep Kaur
      Participant

      sir i made changes in the sac- ocdma example and have got some success in the first code and a very good eye diagram…thanks to you….
      looking forward to more of your expert comments…. i am attaching the osd file… though second code at the encoder is not correct

      • #26600
        alistu
        Participant

        Sure! But please address the problem and provide the information I asked for in #26595 in case.

    • #26602
      Swapandeep Kaur
      Participant

      the starting wavelength is 1549nm, step size is 0.5nm the first code is 10101010..
      second code is 11001100, though im not getting that correct, still working on that…

    • #26644
      Swapandeep Kaur
      Participant

      Sir i have got the rest of the codes as well. it depends on how we choose the cut off wavelengths.

      Sir i am not understanding how to obtain the results portion of the paper i am implementing. please help me with that. i have made the basic simulation of sac- ocdma using lr-pon. i am attaching the paper. please help.

      • #26652
        alistu
        Participant

        Did you get the suitable results for the rest of the users in your system as well? If not, please mention the problem you have faced. May I also ask you to upload your implementation file so that I would be able to see the system while considering the paper you have attached? Thank you.

    • #26653
      Swapandeep Kaur
      Participant

      yes sir i have got the suitable results for the resr of the users as well. i am attaching the osd file

    • #26659
      Swapandeep Kaur
      Participant

      sir i am not getting how ber varies with the transmitted power for different values of edfa gain? how are we getting different values of edfa gain ? from which option? and from where we get with and without ase noise? please reply…

      • #26682
        alistu
        Participant

        You should put a power meter before the transmission line to measure the transmitted power. Put two power meters before and after the EDFA to measure the component gain (or however you measure it). And then you just set and/or change the parameters to achieve the results. You can use sweep iteration capability to get the results easier. I suggest that you do that.

        P.S. For EDFA, you can also use the black box to be able to control gain easily.

    • #26705
      Swapandeep Kaur
      Participant

      sir if i put the power meter before the optical fiber , i will get a fixed transmitted power. how to get different values of transmitted power versus ber?

    • #26706
      Swapandeep Kaur
      Participant

      and we have to calculate ber with and without ase, for that we will enable and disable the option in the photodiode?

      • #26709
        alistu
        Participant

        The transmitted power is not the one controlled by the optical amplifier in your design. In order to change the transmitted power, you are going to have to change the power of the white light source lasers. And you can enable or disable the ASE noise by changing the potion in the photodetector.

    • #26716
      Swapandeep Kaur
      Participant

      sir but we have to see the effects of edfa noise ,ASE ;; Is it same as changing noise of photodiode?

    • #26718
      Swapandeep Kaur
      Participant

      sir may i ask you a couple of more questions regarding the project ?? such as why we chosen white light freq as 1550.5 nm? why mach zehnder modulator extinction ratio is 30 db

      we took edfa so as to avoid the losses. but in the simulation the Q factor does not improve and ber does not decrease with edfa in comparison to without edfa. so what is the importance of edfa??
      my paper is like i earlier said The Effects of EDFA Noise on the Performance of Multi-wavelength OCDM-based Long-Reach Passive Optical Networks

      • #26726
        alistu
        Participant

        If the wavelength of the white light laser is chosen to be at the center of the range of wavelengths used for the fiber bragg gratings, there would somehow be a symmetry in the way the wavelengths far from the center receive power. So it had better be chosen that way.

        The chosen extinction ratio has been chosen as the default value. But you can change it according to your paper (if there is any mention of it).

        Don’t you see any difference in the performance by changing the EDFA gain?

    • #26727
      Swapandeep Kaur
      Participant

      sir how to change the edfa gain? i dont know the concept of black box

      • #26732
        alistu
        Participant

        Chnaging the EDFA gain needs designing it for the gain you want it to have. However, in the EDFA black box, you can simply choose the gain you want EDFA to have and that’s it. In case you want to use it, set the operation mode in the EDFA black box properties to “gain control” and apply the gain value you want.

    • #26730
      Swapandeep Kaur
      Participant

      sir why fbg reflectivity chosen as .9998? noise dynamic 5 db? prbs generator bit rate as signal bit rate?

      • #26734
        alistu
        Participant

        The default value for reflectivity of the fiber bragg gratings is 0.99 in OptiSystem. And noise dynamic default value is 3dB for this component. However, you can change the value of these parameters along with other parameters to any other value you desire according to the paper you work on or so.

    • #26738
      Swapandeep Kaur
      Participant

      sir you said that the transmitted power is the power from the white light source. it has been chosen as -115 dbm. if i am changing it like to 0 to bring a plot vs ber , the simulation is taking too long,the calculation is not ending..

      for the edfa black box, we can also select the option of ase noise, since it has the option .

      if i am asked regarding the values of the parameters in the viva which is on monday, i can say that a particular combination of values is chosen to bring about the simulation

      • #26742
        alistu
        Participant

        I think the transmitted power in the paper you are working on refers to the power that enters the optical fiber (after the power combiner), so you can read the transmitted power by a power meter placed there.

        Unfortunately, I did not understand your last sentence and would be grateful if you explain it again.

    • #26740
      Swapandeep Kaur
      Participant

      Why have we chosen the complement of the wavelengths at the lower decoder at the decoder side?

    • #26743
      Swapandeep Kaur
      Participant

      i mean to say like the parameters like reflectivity .9998 are chosen to bring about a particular simulation

      why is the complement of wavelengths chosen at the lower decoder on the decoder side.

      thank you so much sir for your help….

    • #26744
      Swapandeep Kaur
      Participant

      but sir that was the problem, if i use a power meter for the transmitted power it will give one fixed value of power

      • #26745
        alistu
        Participant

        Unfortunately, I don’t know much about the theory regarding complementary subtraction detection technique. The fixed power you are referring to would change when you change the power of the white light sources (I suggest you make changes to their power equally). It is not dependent on the EDFA, as EDFA is placed after it.

    • #26746
      Swapandeep Kaur
      Participant

      no problem sir… thank you so much for your help and guidance…

    • #26751
      Swapandeep Kaur
      Participant

      sir by changing the power of white light sources the simulation is not getting compltetd. and on changing gain, the transmitted power is getting changed.

      • #26757
        alistu
        Participant

        How much do you change the power of lasers? If you make a huge increase in the input power, the simulation will take a lot of time to be done. However, you won’t need such an increase, as you are trying to reproduce the results mentioned in the paper. I increased and decreased the power of each laser by 3dB and it was run smoothly.

    • #26766
      Swapandeep Kaur
      Participant

      thank you sir. sir we chose white light but could we have chosen any other source? what would have been the advantages? and why we chose fbgs?

    • #26767
      Swapandeep Kaur
      Participant

      sir i read that ocdma uses broadband light source and not cw laser? what are broadband light sources and why they are used?

      • #26772
        alistu
        Participant

        As you can see, this component have one input and two outputs. You set the frequency that you want to filter along with the bandwidth and then that part of the signal would be in one of the outputs, and the other part of the signal outside of the bandwidth would be in the other output. Why do we use it? Because it simply suits our design.

    • #26768
      Swapandeep Kaur
      Participant

      why have we chosen walsh hadamard code?

      • #26774
        alistu
        Participant

        Walsh-Hadamard codes used for this purpose are orthogonal to each other. It means that the dot product of each two of the codes equals zero. This is the most prominent feature of these codes. I think if you study the theory thoroughly, you will get a better understanding of how this orthogonality comes to use.

    • #26773
      Swapandeep Kaur
      Participant

      sir you are talking about which compnent?white light has only one output and fbg two inputs ang one output

      • #26775
        alistu
        Participant

        I was talking about fiber bragg gratings. As for the white light source, it can be used when you need a light source with a wide wavelength spectrum, and although CW lasers have a linewidth, they are supposed to generate one frequency. That’s why white light source is better for this purpose.

    • #26776
      Swapandeep Kaur
      Participant

      thank you sir. sir last question. what is spectral amplitude coding? i am not getting it. it is an incoherent ocdma. but exactly what is it?

    • #26777
      Swapandeep Kaur
      Participant

      In SAC-OCDMA format, frequency components of the signal from a broadband
      optical source are encoded by selectively blocking or transmitting them in accordance
      with a signature code .sir i got this definition , what will be the signature code in terms of our project???

      • #26778
        alistu
        Participant

        Signature code is a code that is dedicated only to one user, like a signature that belongs only to one person. For example, signature code for your first user is 10101010, which means only this user is using this code and using it at the transmitter and receiver, the user can recover its own data from the received signal (I strongly recommend you to go through some basic papers in this regard to solve all your basic questions).

        Regards

    • #26779
      Swapandeep Kaur
      Participant

      ok sir. thank you sir

      • #26781
        alistu
        Participant

        You’re welcome, Swapandeep!

    • #26793
      Swapandeep Kaur
      Participant

      sir there is definitely some problem with the edfa black box. each time i run the simulation ,even with same parameters it gives different results

    • #26795
      Swapandeep Kaur
      Participant

      sir why does in absence of ASE , BER increase with length?

    • #26799
      Swapandeep Kaur
      Participant

      sir i replaced the black box with normal edfa, still the values are not constant. and i am not getting the desired results for with and without ase operations

      • #26828
        alistu
        Participant

        Thank you for the file. there are no power meters or visualizers before or after the EDFA component, so how would you know the EDFA gain changes each time the simulation is run? The EDFA amplification seems to be around 17dB and will not have any significant changes when you repeat the simulation.

    • #26836
      Swapandeep Kaur
      Participant

      sir my optisystem 13 will expire in 3 days , what should i do?

      • #26838
        alistu
        Participant

        As I told you, the EDFA gain is not random the way you have stated in your former post. I simply put two optical power meters before and after the EDFA component and for a couple of times running the simulation, the gain was almost the same. So please connect power meters and proceed with the rest of your work, as there are no worries about this issue.

        Regards

    • #26841
      Swapandeep Kaur
      Participant

      sir its not the gain that is changing but the BER at the output…however i will check again.
      my optisystem will expire in 3 days, what should i do?

      • #26845
        alistu
        Participant

        I increased your sequence length to 4096 and ran the simulation for a few times. The results did not have any significant changes. I suggest you do this. (I reduced the samples per bit parameter to decrease the simulation time, but that causes signal degradation).

    • #26872
      Swapandeep Kaur
      Participant

      sir can i download optisystem 13 using different id on the same system?

      • #26875
        alistu
        Participant

        OptiSystem can only be installed on each hard drive one time as far as I know, even if you reinstall your windows. However, the OptiSystem setup you have formerly downloaded can be installed on other computers (provided that OptiSystem had not formerly been installed on them).

    • #26941
      Swapandeep Kaur
      Participant

      sir is there sac- ocdma example simulation file on optisystem 7?

      • #26943
        alistu
        Participant

        Unfortunately, I don’t know whether the SAC-OCDMA example is available in that version. However, as far as I know, all the components necessary to implement your design are available in OptiSystem 7, so I think you would be able to implement it in OptiSystem 7 as well.

        Regards

    • #27254
      Swapandeep Kaur
      Participant

      sir i have implemented a three user system, why is that the ber of the user 2 is lesser than the others?

      • #27272
        alistu
        Participant

        Hi Swapandeep,

        Which version of OptiSystem are you currently using? Are you still using version 13.0.3 or have you implemented it with version 7? Please attach your implementation file so that I would be able to check it. If the BER changes significantly with each simulation, simply increase sequence length.

        Regards

    • #27271
      Swapandeep Kaur
      Participant

      sir in the paper its given that ber reduces with increase in length in absence of ase, but there is not a significant change in the values when i am increasing the length . in fact , the results are almost same for with and without ase. for ase , we have to enable and disable the options in the photodetector pin? that is what i have done…

    • #27273
      Swapandeep Kaur
      Participant

      sir i am using optisystem 7 and ber is not changing significantly. there is very little change with length. sequence length is 1024. should i increse it?

      • #27296
        alistu
        Participant

        No, I don’t think it is necessary. I thought the sequence length was shorter. In that case, the results might change every time the simulation is done and that’s when the results are not reliable. Even if a short sequence is used, there is no need to change sequence length when the results don’t change.

    • #27274
      Swapandeep Kaur
      Participant

      osd file

    • #27276
      Swapandeep Kaur
      Participant

      sir i am getting this graph for channel 2. i can take it that ber is decreasing with length without ase and increasing for with ase.

      Sir what is the reason for the increase and decrease?

      • #27297
        alistu
        Participant

        If you are referring to fig.5 of the paper, the BER does not decrease with the increase in length, but rather stays the same. And I think the figure yielded from your won simulation is pretty much similar to the one in the paper, perhaps except for the fact that the blue curve (belonging to the state with no ASE) should be below the red one.

    • #27315
      Swapandeep Kaur
      Participant

      sir in this architecture which we have implemented , communication is possible only in downstream direction?

      • #27319
        alistu
        Participant

        You can only transmit the downstream data as long as you only implement the downstream part of the system (or network) which you actually have. For upstream, you need to choose the scheme and then if you are willing to use a bidirectional fiber, you need to specify the proper wavelengths for DS and US.

    • #27399
      Swapandeep Kaur
      Participant

      sir please could you guide about the latest topics in optics for thesis purpose?

      • #27407
        alistu
        Participant

        Hi Swapandeep,

        I’d rather we discuss this in a topic related to this subject, or in a new topic so as not to deviate from the main subject of the topic in here. However, Space-Division-Multiplexing is an emerging and very promising research topic. It deals with few mode fibers or few core fibers to increase the channel capacity.

        Regards

    • #38635
      Irfan Morshed
      Participant

      Hi everyone,

      My project is similar to Miss Swapandeep’s. Its a 3 user OCDMA system, done using walsh coding. It is almost working. But however, its not giving me the desired results. Anybody kind enough to please help me out? Please. I am helpless, and it’s a request.

      This is my project link :

      3 user OCDMA

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