Image Processing Reference
In-Depth Information
The comparison of time-delay is shown in Table 2. Frequency resolution is adjusted by
parameter of each system in accordance with the target performance of Table 1. Since the
signal-processing inputs are sampled by
fs
, time-delay will become large if
fs
becomes
low. Table 2 is calculated by
fs
=4kHz condition. Incidentally by
fs
=1kHz, time-delay
increases 4 times. The time-delay caused by operation is assumed zero, and estimated
only the delay caused by sampling simply. Moreover, the influence of the transient
response of the complex IIR system and the phase-shift system is not taking into
consideration here.
I-channel
Q-channel
Amp litud e
Time (ck)
(a) input si
gn
al
Amplitude
forward
reverse
Time (ck)
(b) output signal of the complex FIR system
Amplitud e
forward
reverse
Time (ck)
(c) output signal of the complex IIR system
Fig. 8. Comparison of response between complex FIR method and complex IIR method
method estimation time-delay (ms)
Hilbert transform
tap/fs
32 (
tap
=128)
Complex FIR
tap/fs
32 (
tap
=128)
Complex IIR
order/fs
(*1) 2 (
order
=8)
FFT/IFFT
1.5*N/fs
(*2) 48 (
N
=128)
Moduration/Demoduration
tap/fs
32 (
tap
=128)
Phase shift
max(2,order/N)/fs
(*1) 1 (
order
=4,
N
=1)
Estimated at
fs
=4kHz, (*1) not including transient response, (*2) IFFT shift addition pitch is
N/4
Table 2. Comparison of time-delay
As calculation load depends on the hardware architecture, the multiplication and addition
times per 1 second (floating point single precision) is used for this estimation. Moreover, the
complex-multiplication is considered as 4 times, and complex-addition is considered as
twice. The overhead of the processing which requires a lot of memory buffers is assumed to
be 20%. The other overhead is assumed to be 10%. The calculation elements, estimation
formula and calculation load for each signal-processing systems are shown in Table 3.
Incidentally, at
fs
=52 kHz (maximum PRF in actual system), calculation load increases 13
times. The result of Table 2 and Table 3 shows that the complex IIR system and the phase-
