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I have to transmit Walsh sequence (spreading codes) modulated with 8 psk with a channel impaired by intersymbol interferences, fast fading .

Suppose i have a stream of data for instance 1 0 1 1, 0 0 0 1

With the 16 walsh spreading, I get 1 0 1 1 ==> -1 1 -1 1 1 1 1 -1 -1 -1 1 1 1 1 1, And 0 0 0 0 1 ==> -1 -1 -1 -1 1 1 1 1 -1-11 1 1 1 11 (just to illustrate).

The 32 symboles are then scrambled with 8 psk symbols and then sent to channel with ies ( mainly two taps, with a known delay).

To demodulate,

  1. first I made synchronisation with known symbols(pilots),
  2. I descramble to obtain symbols in {-1,1}
  3. I use correlation for all the possible walsh codes, and I choose the maximum to determine the four bits.
  4. I use correlation on a offset version of the walsh code for the second finger of the rake receiver.
  5. I use Maximal Ratio Combiner to combine the results

What is wrong in my algorithm since i am not getting the good ber ?

Thanks experts

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