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上传时间: 2019-08-24
详细说明：在开发wifi芯片的过程中由于成本的因素存在采样频率偏移，理论分析了如何通过FFT窗口的移动来补偿采样频偏的影响2T·Ns
0(k)≈2T·△f·N。T·M+M
k·n=6c+6
we can see the typical value of cFo first, we assume the residue ppm=2, then the phase error be:
M
日ao=2·△fNT·M=2m:4800.80
=0.1206*M
20000000
2
0
50
150
200
250
300
350
we then see the typical value of Sco, we assume the ppm=50, then the phase error be
if new sampling frequency be fn, and the standard sampling frequency be fs so it will accumulate
and assume that the ppm be-50, then fn=19999000Hz, fs 20000000Hz
T-T20000000
19999000
1=50003*10-5
A8·k:n=M.2m:80
2T·N
M
64*k*5.0003*105=39272*10-4*k*M
We select k=-21, which is the one pilot subcarrier to see its phase change
3
2.5
0.5
0
0.5
0
50
100
150
200
250
300
350
Then we can see the com bined effect of sco and ceo
3
2
0
2
0
50
100
150
200
250
300
350
From the analysis of above, we can use value of asco k=-21 pilots phase to see indicate the FFt
Window shift
2π·N。
M
A·k==-3.9272*10-4*21*M=8.2471*10-3*M
And we know if we shift one sample of 20Mhz in time domain it will introduce the phase error on
the subcarrier of pilot -21 be the expression:
21
error,-21=phase le
2
=2.0617
64
We can see that, one FFt Window operation will cause subcarrier of pilot- 21 phase change value
2.0617
the scheme of fft window shift
Then the scheme of start on FFT Window shift can be following
(1)Observe the accumulate Sco phase of subcarrier -21
(2) If it larger than 2.0617, we can shift on sample of FFT Windows
(3 And in phase tracking module we will count in these phase error in different subcarrier by the
following expression
2*丌
日
*k,k=-26,-25,…,1,2,…26
64
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