Detailed Decoding Trace Information

The -T option to decode causes a detailed trace of information on the process of decoding to be written to standard output, in a multi-column format, with the first line containing the headers for each column. This format is suitable for reading into S-Plus or R. The first column is always the number of the block being decoded; several lines may be output for each block. The other columns vary with the decoding method used, as described below.

Enum-bit and Enum-block decoding methods

For source messages with K bits, 2^K lines are output for each block, containing the following information:

block The number of the block, from zero

decoding A possible decoding for the message bits, expressed as a hexadecimal number. The other bits are determined by the message bits.

likelihood The likelihood for this decoding (ie, the probability of obtaining the data received if this was the message sent).

For these methods, the number of "iterations" (output with the -t option) is always 2^K.

Prprp decoding method

Each block results in one line of output for the initial state (based on individual likelihood ratios), and one line for each subsequent iteration, containing the following information:

block The number of the block, from zero

iter The number of an iteration, zero for the initial state.

changed The number of bits in the decoding that differ from the bit that would be chosen based just on the likelihood ratio for that bit. Bits whose likelihood ratios are exactly one contribute 0.5 to this count. (Likelihood ratios of exactly one can arise when the output of an AWGN channel rounds to exactly 0.00.)

perrs The number of parity check errors in the current tentative decoding.

loglik The log likelihood of the current tentative decoding.

Eperrs The expected number of parity check errors in a decoding found by randomly picking a value for each bit, independently, according to the current bit probabilities.

Eloglik The expected log likelihood of a decoding found by randomly picking a value for each bit, independently, according to the current bit probabilities.

entropy The entropy (in bits) of the distribution defined by the current bit probablities, assumed to apply to bits independently.

The number of "iterations" (output with the -t option) is the obvious count of probability propagation iterations. The initial state does not count as an iteration.

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block	The number of the block, from zero
decoding	A possible decoding for the message bits, expressed as a hexadecimal number. The other bits are determined by the message bits.
likelihood	The likelihood for this decoding (ie, the probability of obtaining the data received if this was the message sent).

block	The number of the block, from zero
iter	The number of an iteration, zero for the initial state.
changed	The number of bits in the decoding that differ from the bit that would be chosen based just on the likelihood ratio for that bit. Bits whose likelihood ratios are exactly one contribute 0.5 to this count. (Likelihood ratios of exactly one can arise when the output of an AWGN channel rounds to exactly 0.00.)
perrs	The number of parity check errors in the current tentative decoding.
loglik	The log likelihood of the current tentative decoding.
Eperrs	The expected number of parity check errors in a decoding found by randomly picking a value for each bit, independently, according to the current bit probabilities.
Eloglik	The expected log likelihood of a decoding found by randomly picking a value for each bit, independently, according to the current bit probabilities.
entropy	The entropy (in bits) of the distribution defined by the current bit probablities, assumed to apply to bits independently.