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config: simplify symbols' constellation

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use rectangular QAM for simplicity
This commit is contained in:
Roman Zeyde
2014-11-11 09:06:15 +02:00
parent da5e971d94
commit f4f742a7a4
1 changed files with 9 additions and 10 deletions
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19
amodem/config.py
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@@ -23,21 +23,20 @@ carrier_index = 0
Fc = frequencies[carrier_index] Fc = frequencies[carrier_index]
Tc = 1.0 / Fc Tc = 1.0 / Fc
# Hexagonal symbol constellation (optimal "sphere packing")
I = np.arange(-Npoints, Npoints+1)
imag_factor = np.exp(1j * np.pi / 3.0)
offset = 0.5
symbols = [(x + y*imag_factor + offset) for x in I for y in I]
symbols.sort(key=lambda z: (z*z.conjugate()).real)
symbols = np.array(symbols[:Npoints])
symbols = symbols / np.max(np.abs(symbols))
Nsym = int(Tsym / Ts) Nsym = int(Tsym / Ts)
baud = int(1/Tsym) baud = int(1 / Tsym)
bits_per_symbol = np.log2(Npoints) bits_per_symbol = np.log2(Npoints)
assert int(bits_per_symbol) == bits_per_symbol
bits_per_baud = bits_per_symbol * Nfreq bits_per_baud = bits_per_symbol * Nfreq
modem_bps = baud * bits_per_baud modem_bps = baud * bits_per_baud
carriers = np.array([ carriers = np.array([
np.exp(2j * np.pi * f * np.arange(0, Nsym) * Ts) for f in frequencies np.exp(2j * np.pi * f * np.arange(0, Nsym) * Ts) for f in frequencies
]) ])
# Hexagonal symbol constellation (optimal "sphere packing")
Nx = 2 ** int(np.ceil(bits_per_symbol / 2))
Ny = Npoints // Nx
symbols = np.array([complex(x, y) for x in range(Nx) for y in range(Ny)])
symbols = symbols - symbols[-1]/2
symbols = symbols / np.max(np.abs(symbols))