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Fixed WiMAX modeling, baffling simulation results

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marvin42

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sui model wimax

Hi.

I'm doing a model of PHY interface of fixed Wimax in Simulink for my graduation project, and some of the simulation results are pretty baffling.
Using SUI 4 - 6 with any kind of modulation always produces a kind of, in lack of a better name, a saturation of BER in the BER vs. SNR plot, at around 5e-6, as illustrated here, with 16-QAM (coderate 3/4):

iddhu1.png


Also, when using BPSK, all of the implemented channel models behave the same (including AWGN). Here's the image:

20r9qhh.png


I am using the Communication Blocket built-in Multipath Rician Fading with the parameters of SUI models to model them - the only thing I am disregarding is the Doppler spectrum of the model description. But I doubt that causes the problems.

I checked every block in the model trying to figure out what's wrong, but still have no idea. Any help will be greatly appreciated.

Attached inside the archive is the model and all the needed supporting files, if it can help... The captions are all in Croatian, but I think the model is pretty self-explanatory. Nevertheless, if anyone cares, I can translate them to English.

TIA
 

wimax modeling in matlab

Me again :)

Solved the aforementioned problems - the "saturation" of the BER curve, i.e. it not following the common slope in SUI 4 - 6 is because the ISI is too severe to handle. And in the BPSK case - well, it sort of resolved itself after I shuffled the subsystems around :D

Now, I have new (and I presume, simpler) questions: the Least Squares pilot-aided estimator has very poor performance - it's useless, to be exact. At least in time-invariant channels - when the channel is time-variant, it performs better than preamble-aided LS (as expected), but it's still pretty much useless (BER is around 0.2).

And the MMSE equalizer that uses the LS estimate generated by the pilots has, well, even worse results.

This is the subsystem that does the LS estimate using pilots:
ab3yaf.png


... and this is the MMSE subsystem:

2yycos4.png


wimax_spline is an S-function that does the interpolation, this is its Outputs function, the only relevant one:

function Outputs(block)

x=block.DialogPrm(1).Data; % pilot locations
Y=block.InputPort(1).Data; % estimated transfer function
xx=block.DialogPrm(2).Data'; % length of the interpolated vector


yy=interp1(x,Y,xx,'spline');
block.OutputPort(1).Data=yy;

%end Outputs

So, my questions are: what am I doing wrong? Or is this the best I can get using only 8 pilots? This is an example of the result of the interpolation (the black stems are the uninterpolated estimates, the red plot is the result of cubic spline, the blue one of the linear interpolation, and the green one is the MMSE estimate):

oeo3d.png


Same plot, now with the real channel frequency response (the magenta-colored plot):

15d9cmf.png


Please help :)

ETA: oh, and, is there any way to optimize the m file S-functions without writing TLC files and compiling (that seems way too cumbersome), because using them slows down the simulation. A lot.
 

ber curve for wimax

I need a help regarding my MS thesis. I have read few papers on Wimax Handover.And decided to work on wimax handover. But still i am not getting any idea on which specific topic i should work. Also i dont know how to use matlab. I have to learn it as well. Also want to know can we do wimax handover related work in Matlab? Please help me as i have short time. If you have any Handover code in Wimax? Thanks in advance.
Naina
 

wimax handover simulations matlab

Well, I don't know if I'll be of much help, because I focused on fixed Wimax, where there is no handover. Searching Matlab Central (https://www.mathworks.com/matlabcentral/) had no results - usually you can find some good examples there.

First of all, I would recommend discussing it at length with your supervisor/instructor - mine was great in that respect.

Second, you have to decide if you want to do someting broad (like a simulation of the whole end-to-end system) or just a detail; and if you want to use Simulink or Matlab. Simulink is user-friendlier, but Matlab is more flexible (especially if you want to simulate just the handover).

Also, you should try to use the things you've read in those papers and use them to do a simulation...

As for learing Matlab, the basics are really not that hard and once you get the hang of them (there are a lot of tutorials and manuals round the net, including the ones from Mathworks), the specific functions/blocks/etc. you need you learn using through the built-in help system, which is pretty comprehensive.

Hope I could help.
 

simulation hand over + matlab

Thanks for your kind reply. Thats nice idea to simulate any of papers i read, If not whole but can go for some module simulation. So you mean matlab is preferable for handover rather simulink. What about stateflows? I even didnt find that much code examples on handover. Checked google code as well. Pleaase do let me know if you find any examples. Again thanks for your good points. My current status is i am learning matlab. I wont be able to go for simulating whole end-to-end system as i got short time of few months. As i am doing MS so part of it will be fine as well.
 

hi marvin42,

Hope you are fine. I need any matlab simulation code or model of wimax in mesh network. Anyone please help me the simulation code/model in matlab?

I am looking forward for any helping hand. Thank you.

farhad
 

Hi all lovers of Wimax,

As I see there are many people working on it and in my opinion end to end user system could be very tough to do in prefer to work in locally what I mean that optimize a part of system which has already done. So first thing to do is find a whole system example and partially modify it according to your goals. What do you think ?
 

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