Hello Aditya:
I think it should be shifted.In the transmitter of the
OFDM,the ifft operation is adopted.
Another phenomenon I have found that the result of the input
data go through the FFT block (gnuradio)isn't same to the result in
matlab(just ifft(data)).Can you explain it?
Best regards,
Kun
At 2014-11-03 00:00:29, "Aditya Dhananjay" <[email protected]> wrote:
Hello Kun,
Could you please verify whether the input to the FFT call are supposed to be
shifted or not?
Best,
Aditya
On Sun, Nov 2, 2014 at 10:44 AM, xianda <[email protected]> wrote:
Hello all:
Thank you in advance.I have two questions about the symbol used in
ofdm example.
1.The first synchronization symbol is:
n1=00000001.414213538169860-1.4142135381698601.414213538169860-1.414213538169860-1.414213538169860-1.4142135381698601.414213538169860-1.4142135381698601.414213538169860-1.414213538169860-1.414213538169860-1.414213538169860-1.4142135381698601.414213538169860-1.4142135381698601.4142135381698601.4142135381698601.414213538169860-1.4142135381698601.4142135381698601.4142135381698601.414213538169860-1.4142135381698601.4142135381698601.4142135381698601.41421353816986000000
As the algorithm said,the first half of the symbol is same to the
second half of the symbol.
But i do ifft(n1) in matlab,and the result is
0.0441941730678082 + 0.00000000000000i0.0644254533894132 +
0.175326551876726i-0.0367461119467220 - 0.0453679674017572i0.0265416620395810 +
0.0320366536443552i-0.0985725617473446 - 0.0915672254739864i-0.0570202679872770
+ 0.0717009594634221i0.00862185545503520 -
0.0331748224844260i0.0431267759560735 - 0.101430672698735i0.0937499983955371 +
0.0624999989303581i-0.116910980048072 + 0.0875939237146428i0.0433449944244991 +
0.00659888247777708i0.0708002546250446 -
0.00739045916472342i0.00700533627335824 - 0.105577898020703i-0.0292347816053780
+ 0.0541379637893818i0.0245529670293908 - 0.0678979614538899i-0.237561871221452
+ 0.0681675029413550i0.00000000000000 + 0.00000000000000i0.237561871221452 +
0.0681675029413550i-0.0245529670293908 - 0.0678979614538899i0.0292347816053780
+ 0.0541379637893818i-0.00700533627335823 -
0.105577898020703i-0.0708002546250446 - 0.00739045916472342i-0.0433449944244991
+ 0.00659888247777708i0.116910980048072 +
0.0875939237146428i-0.0937499983955371 + 0.0624999989303581i-0.0431267759560735
- 0.101430672698735i-0.00862185545503520 -
0.0331748224844260i0.0570202679872771 + 0.0717009594634221i0.0985725617473446 -
0.0915672254739864i-0.0265416620395810 + 0.0320366536443552i0.0367461119467220
- 0.0453679674017572i-0.0644254533894132 +
0.175326551876726i-0.0441941730678082 + 0.00000000000000i-0.0644254533894132 -
0.175326551876726i0.0367461119467220 + 0.0453679674017572i-0.0265416620395810 -
0.0320366536443552i0.0985725617473446 + 0.0915672254739864i0.0570202679872770 -
0.0717009594634221i-0.00862185545503520 +
0.0331748224844260i-0.0431267759560735 + 0.101430672698735i-0.0937499983955371
- 0.0624999989303581i0.116910980048072 - 0.0875939237146428i-0.0433449944244991
- 0.00659888247777708i-0.0708002546250446 +
0.00739045916472342i-0.00700533627335824 + 0.105577898020703i0.0292347816053780
- 0.0541379637893818i-0.0245529670293908 + 0.0678979614538899i0.237561871221452
- 0.0681675029413550i0.00000000000000 + 0.00000000000000i-0.237561871221452 -
0.0681675029413550i0.0245529670293908 + 0.0678979614538899i-0.0292347816053780
- 0.0541379637893818i0.00700533627335823 + 0.105577898020703i0.0708002546250446
+ 0.00739045916472342i0.0433449944244991 -
0.00659888247777708i-0.116910980048072 - 0.0875939237146428i0.0937499983955371
- 0.0624999989303581i0.0431267759560735 + 0.101430672698735i0.00862185545503520
+ 0.0331748224844260i-0.0570202679872771 -
0.0717009594634221i-0.0985725617473446 + 0.0915672254739864i0.0265416620395810
- 0.0320366536443552i-0.0367461119467220 +
0.0453679674017572i0.0644254533894132 - 0.175326551876726i
The first half of the symbol in time domain isn't same to the
second half of the symbol.It is a fault?
2.I read the document fft_vcc_fftw.cc
gr_complex *dst = d_fft->get_inbuf();
unsigned int len = (unsigned int)(floor(d_fft_size/2.0)); // half
length of complex array
memcpy(&dst[0], &in[len], sizeof(gr_complex)*(d_fft_size - len));
memcpy(&dst[d_fft_size - len], &in[0], sizeof(gr_complex)*len);
Before doing the ifft operation,should I first do this?
Thank you very much.
Best regards,
kun
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