diff options
Diffstat (limited to 'gr-digital/python/psk.py')
| -rw-r--r-- | gr-digital/python/psk.py | 174 |
1 files changed, 101 insertions, 73 deletions
diff --git a/gr-digital/python/psk.py b/gr-digital/python/psk.py index acedf3b69..58f6787f0 100644 --- a/gr-digital/python/psk.py +++ b/gr-digital/python/psk.py @@ -1,5 +1,5 @@ # -# Copyright 2005,2006 Free Software Foundation, Inc. +# Copyright 2005,2006,2011 Free Software Foundation, Inc. # # This file is part of GNU Radio # @@ -19,76 +19,104 @@ # Boston, MA 02110-1301, USA. # -from math import pi, sqrt, log10 -import math, cmath - -# The following algorithm generates Gray coded constellations for M-PSK for M=[2,4,8] -def make_gray_constellation(m): - # number of bits/symbol (log2(M)) - k = int(log10(m) / log10(2.0)) - - coeff = 1 - const_map = [] - bits = [0]*3 - for i in range(m): - # get a vector of the k bits to use in this mapping - bits[3-k:3] = [((i&(0x01 << k-j-1)) >> k-j-1) for j in range(k)] - - theta = -(2*bits[0]-1)*(2*pi/m)*(bits[0]+abs(bits[1]-bits[2])+2*bits[1]) - re = math.cos(theta) - im = math.sin(theta) - const_map.append(complex(re, im)) # plug it into the constellation +""" +PSK modulation and demodulation. +""" + +from math import pi, log +from cmath import exp + +import digital_swig +import modulation_utils +from utils import mod_codes, gray_code +from generic_mod_demod import generic_mod, generic_demod + +# Default number of points in constellation. +_def_constellation_points = 4 +# The default encoding (e.g. gray-code, set-partition) +_def_mod_code = mod_codes.GRAY_CODE + +def create_encodings(mod_code, arity): + post_diff_code = None + if mod_code not in mod_codes.codes: + raise ValueError('That modulation code does not exist.') + if mod_code == mod_codes.GRAY_CODE: + pre_diff_code = gray_code.gray_code(arity) + elif mod_code == mod_codes.SET_PARTITION_CODE: + pre_diff_code = set_partition_code.set_partition_code(arity) + elif mod_code == mod_codes.NO_CODE: + pre_diff_code = [] + else: + raise ValueError('That modulation code is not implemented for this constellation.') + return (pre_diff_code, post_diff_code) - # return the constellation; by default, it is normalized - return const_map - -# This makes a constellation that increments around the unit circle -def make_constellation(m): - return [cmath.exp(i * 2 * pi / m * 1j) for i in range(m)] - -# Common definition of constellations for Tx and Rx -constellation = { - 2 : make_constellation(2), # BPSK - 4 : make_constellation(4), # QPSK - 8 : make_constellation(8) # 8PSK - } - -gray_constellation = { - 2 : make_gray_constellation(2), # BPSK - 4 : make_gray_constellation(4), # QPSK - 8 : make_gray_constellation(8) # 8PSK - } - -# ----------------------- -# Do Gray code -# ----------------------- -# binary to gray coding -- constellation does Gray coding -binary_to_gray = { - 2 : range(2), - 4 : [0,1,3,2], - 8 : [0, 1, 3, 2, 7, 6, 4, 5] - } - -# gray to binary -gray_to_binary = { - 2 : range(2), - 4 : [0,1,3,2], - 8 : [0, 1, 3, 2, 6, 7, 5, 4] - } - -# ----------------------- -# Don't Gray code -# ----------------------- -# identity mapping -binary_to_ungray = { - 2 : range(2), - 4 : range(4), - 8 : range(8) - } - -# identity mapping -ungray_to_binary = { - 2 : range(2), - 4 : range(4), - 8 : range(8) - } +# ///////////////////////////////////////////////////////////////////////////// +# PSK constellation +# ///////////////////////////////////////////////////////////////////////////// + +def psk_constellation(m=_def_constellation_points, mod_code=_def_mod_code): + """ + Creates a PSK constellation object. + """ + k = log(m) / log(2.0) + if (k != int(k)): + raise StandardError('Number of constellation points must be a power of two.') + points = [exp(2*pi*(0+1j)*i/m) for i in range(0,m)] + pre_diff_code, post_diff_code = create_encodings(mod_code, m) + if post_diff_code is not None: + inverse_post_diff_code = mod_codes.invert_code(post_diff_code) + points = [points[x] for x in inverse_post_diff_code] + constellation = digital_swig.constellation_psk(points, pre_diff_code, m) + return constellation + +# ///////////////////////////////////////////////////////////////////////////// +# PSK modulator +# ///////////////////////////////////////////////////////////////////////////// + +class psk_mod(generic_mod): + + def __init__(self, constellation_points=_def_constellation_points, + mod_code=_def_mod_code, + *args, **kwargs): + + """ + Hierarchical block for RRC-filtered PSK modulation. + + The input is a byte stream (unsigned char) and the + output is the complex modulated signal at baseband. + + See generic_mod block for list of parameters. + """ + + constellation = psk_constellation(constellation_points, mod_code) + super(psk_mod, self).__init__(constellation, *args, **kwargs) + +# ///////////////////////////////////////////////////////////////////////////// +# PSK demodulator +# +# ///////////////////////////////////////////////////////////////////////////// + +class psk_demod(generic_demod): + + def __init__(self, constellation_points=_def_constellation_points, + mod_code=_def_mod_code, + *args, **kwargs): + + """ + Hierarchical block for RRC-filtered PSK modulation. + + The input is a byte stream (unsigned char) and the + output is the complex modulated signal at baseband. + + See generic_demod block for list of parameters. + """ + + constellation = psk_constellation(constellation_points, mod_code) + super(psk_demod, self).__init__(constellation, *args, **kwargs) + +# +# Add these to the mod/demod registry +# +modulation_utils.add_type_1_mod('psk', psk_mod) +modulation_utils.add_type_1_demod('psk', psk_demod) +modulation_utils.add_type_1_constellation('psk', psk_constellation) |