commpy.channelcoding.map_decode

map_decode(sys_symbols, non_sys_symbols, trellis, noise_variance, L_int, mode='decode')

Maximum a-posteriori probability (MAP) decoder.

Decodes a stream of convolutionally encoded (rate 1/2) bits using the MAP algorithm.

Parameters :

sys_symbols : 1D ndarray

Received symbols corresponding to the systematic (first output) bits in the codeword.

non_sys_symbols : 1D ndarray

Received symbols corresponding to the non-systematic (second output) bits in the codeword.

trellis : Trellis object

Trellis representation of the convolutional code.

noise_variance : float

Variance (power) of the AWGN channel.

L_int : 1D ndarray

Array representing the initial intrinsic information for all received symbols.

Typically all zeros, corresponding to equal prior probabilities of bits 0 and 1.

mode : str{‘decode’, ‘compute’}, optional

The mode in which the MAP decoder is used. ‘decode’ mode returns the decoded bits

along with the extrinsic information. ‘compute’ mode returns only the extrinsic information.

Returns :

[L_ext, decoded_bits] : list of two 1D ndarrays

The first element of the list is the extrinsic information. The second element of the list is the decoded bits.