[SciPy-user] Cookbook addition?

Ivo Maljevic ivo.maljevic@gmail....
Sat Jun 6 14:42:50 CDT 2009


Hi,
I wanted to add something to cookbook, but I'm not quite familiar with
this tool. I can edit the main page, but I do not dare save changes in
fear of overwritting the main page, and I don't see how to create
"child" pages.

Anyway, if you guys think this would be useful, you can either post
it, or tell me how to do it.

Here is what I generated:

----------------------------
Raw text is bellow
---------------------------

These two examples illustrate simple simulation of a digital BPSK
modulated communication system where only one sample per symbol is
used, and signal is affected only by AWGN noise.

In the first example, we cycle through different signal to noise
values, and the signal length is a function of theoretical probability
of error. As a rule of thumb, we want to count about 100 errors for
each SNR value, which determines the length of the signal (and noise)
vector(s).

{{{
#!python numbers=disable
#!/usr/bin/python
# BPSK digital modulation example
# by Ivo Maljevic
from numpy import *
from scipy.special import erfc
import matplotlib.pyplot as plt
SNR_MIN     = 0
SNR_MAX     = 9
Eb_No_dB    = arange(SNR_MIN,SNR_MAX+1)
SNR         = 10**(Eb_No_dB/10.0)  # linear SNR
Pe          = empty(shape(SNR))
BER         = empty(shape(SNR))
loop = 0
for snr in SNR:      # SNR loop
  Pe[loop] = 0.5*erfc(sqrt(snr))
  VEC_SIZE = ceil(100/Pe[loop])  # vector length is a function of Pe
  # signal vector, new vector for each SNR value
  s = 2*random.randint(0,high=2,size=VEC_SIZE)-1
  # linear power of the noise; average signal power = 1
  No = 1.0/snr
  # noise
  n = sqrt(No/2)*random.randn(VEC_SIZE)
  # signal + noise
  x = s + n
  # decode received signal + noise
  y = sign(x)
  # find erroneous symbols
  err = where(y != s)
  error_sum = float(len(err[0]))
  BER[loop] = error_sum/VEC_SIZE
  print 'Eb_No_dB=%4.2f, BER=%10.4e, Pe=%10.4e' % \
         (Eb_No_dB[loop], BER[loop], Pe[loop])
  loop += 1
#plt.semilogy(Eb_No_dB, Pe,'r',Eb_No_dB, BER,'s')
plt.semilogy(Eb_No_dB, Pe,'r',linewidth=2)
plt.semilogy(Eb_No_dB, BER,'-s')
plt.grid(True)
plt.legend(('analytical','simulation'))
plt.xlabel('Eb/No (dB)')
plt.ylabel('BER')
plt.show()
}}}
In the second, slightly modified example, the problem of signal length
growth is solved by braking a signal into frames.



{{{
#!python numbers=disable
#!/usr/bin/python
# BPSK digital modulation: modified example
# by Ivo Maljevic
from scipy import *
from math import sqrt, ceil  # scalar calls are faster
from scipy.special import erfc
import matplotlib.pyplot as plt
rand   = random.rand
normal = random.normal
SNR_MIN   = 0
SNR_MAX   = 10
FrameSize = 10000
Eb_No_dB  = arange(SNR_MIN,SNR_MAX+1)
Eb_No_lin = 10**(Eb_No_dB/10.0)  # linear SNR
# Allocate memory
Pe        = empty(shape(Eb_No_lin))
BER       = empty(shape(Eb_No_lin))
# signal vector (for faster exec we can repeat the same frame)
s = 2*random.randint(0,high=2,size=FrameSize)-1
loop = 0
for snr in Eb_No_lin:
  No        = 1.0/snr
  Pe[loop]  = 0.5*erfc(sqrt(snr))
  nFrames   = ceil(100.0/FrameSize/Pe[loop])
  error_sum = 0
  scale = sqrt(No/2)
  for frame in arange(nFrames):
    # noise
    n = normal(scale=scale, size=FrameSize)
    # received signal + noise
    x = s + n
    # detection (information is encoded in signal phase)
    y = sign(x)
    # error counting
    err = where (y != s)
    error_sum += len(err[0])
    # end of frame loop
    ##################################################
  BER[loop] = error_sum/(FrameSize*nFrames)  # SNR loop level
  print 'Eb_No_dB=%2d, BER=%10.4e, Pe[loop]=%10.4e' % \
         (Eb_No_dB[loop], BER[loop], Pe[loop])
  loop += 1
plt.semilogy(Eb_No_dB, Pe,'r',linewidth=2)
plt.semilogy(Eb_No_dB, BER,'-s')
plt.grid(True)
plt.legend(('analytical','simulation'))
plt.xlabel('Eb/No (dB)')
plt.ylabel('BER')
plt.show()
}}}
----
 . CategoryCookbook
----
 CategoryCookbook
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