Offset value determination in a check node processing unit for message-passing decoding of non-binary codes

A check node processing unit implemented in a non-binary error correcting code decoder, the check node processing unit comprising:

• a plurality of elementary check node processing units, the check node processing unit being configured to compute check node messages, an elementary check node processing unit being configured to receive a first message and a second message derived from variable node messages received by the check node processing unit from one or more variable node processing units in the decoder, each of the first message and the second message comprising at least two components, each component of the first message and of the second message comprising a symbol and a reliability metrics associated with the symbol, the elementary check node processing unit being configured to determine an elementary check node message from the first message and the second message, wherein the elementary check node processing unit comprises:
• a calculation unit being configured, based on multiple elementary calculations, to:
• determine two or more auxiliary components, comprising nB auxiliary components, from the components comprised in said first message and the components comprised in the second message, an auxiliary component comprising an auxiliary reliability metrics determined by applying addition operations to symbols and reliability metrics comprised in the components of the first and the second messages;
• and
• determine decoding performance values, in association with each of said two or more auxiliary components;
• a selection unit configured to select, among said two or more auxiliary components, the auxiliary component that is associated with optimal decoding performance values, and determine an offset value from the auxiliary reliability metrics comprised in the selected auxiliary component,
• the elementary check node processing unit being further configured to transmit said offset value and an elementary check node message to a variable node processing unit, the transmitted elementary check node message comprising a number ny of auxiliary components among said two or more nB determined auxiliary components to said variable node processing unit, wherein the offset value is used as a default reliability metrics value at said variable node for the symbols that are not included in the transmitted check node message to determine at least one variable node message, and
• wherein an estimate of a codeword from a sequence received from a transmitter is determined and output by the decoder using the messages exchanged between the one or more variable node processing units and the one or more check node processing units.