MC CDMA channel estimation (CDMA and OFDM)

[ammaralwazzan]

hi

i am working on MC-CDMA channel estimation

cdma + OFDM(802.11a)

i try two types of channel estimation : Block type and Comb type

i am using MATLAB built in function (rayleighchan) more specificlly (stdchan) as follow:

bitrate = 20000000; % Bit Rate
ts = 1/bitrate; % ts is the sample time of the input signal, in seconds (bit rate is 10Mbps)
fd = 0.0001 ; % fd is the maximum Doppler shift, in Hertz
H = stdchan(ts, fd, 'itur3GPAx'); % Creat Channel
H.ResetBeforeFiltering = 0; % Continous Rayleigh Channel
H.StoreHistory = 1; % Plot Channel parameters
H.NormalizePathGains = 1;


the result gave me better performance for Comb type more than Block type:

my information said that Block type suitable for frequency selective fading while Comb type is suitable for Flat fading channel

and you can see that i insert the doppler frequency near to zero which is mean that the channel is very slow fading

so if i try to classify my channel i think it will be (flat or frequency selective) slow fading which is mean that Block type should have better performance than Comb

final note that i used a 16 pilot insertion for comb type , while in Block type i sent [complete OFDM Pilotsymbol then (6 DATA OFDM SYMBOL)]

so is the result correct and why?

please answer me as soon as possible

Best Regards

 

[ammaralwazzan]

Any Thoughts

 

[ammaralwazzan]

Any Body Here

 

[Mityan]

1. doppler freq Fd = -2*V/lambda.
For 802.11a (5 GHz) wavelength labda is about 0.06 m.
So V = 0.0001*0.06/2 - very very slow. Maybe you should take very very lot of time to detect any channel fading?

2. Your words:
a)the result gave me better performance for Comb type more than Block type
b)so if i try to classify my channel i think it will be (flat or frequency selective) slow fading which is mean that Block type should have better performance than Comb

It is not clear why you decided that 'Block type should have better' According to a) for slow fading it is not true. And at last how you implemented a frequency selective fading? This is not the same as doppler I think.