Flexible Channel Decoder

A Soft-Input-Soft-Output Turbo- and LDPC-decoding unit (DPi) having:

• a first input port (I1i) for input reliabilities (λ) used in Turbo-decoding, and for check-to-variable metrics (c2v) used in LDPC-decoding;
• a second input port (I2i) for extrinsic reliabilities (Δ, Λ) used in Turbo-decoding and for intermediate soft outputs SO used for LDPC-decoding;
• a first output port (O1i) for check-to-variable metrics updated during LDPC-decoding;
• and
• a second output port (O2i) for extrinsic reliabilities obtained as intermediate or final results of Turbo-decoding, and for soft outputs obtained as intermediate or final results of LDPC-decoding;
• said decoding unit comprising the following functional blocks:
• A by-passable channel cumulative computation unit (CCC) for computing channel cumulative messages by adding-up input reliabilities;
• A state-metric recursive unit (SMRU) for successively performing recursive computation of forward- and backward metrics, taking said channel cumulative messages as inputs;
• A state-metric memory (SMM) for storing already-computed forward metrics while the state-metric recursive unit is computing backward metrics, or vice-versa;
• and
• An extrinsic reliabilities processor (EP) for computing extrinsic reliabilities, for Turbo-decoding, and soft outputs and check-to-variable metrics, for LDPC decoding, taking said forward metrics, backward metrics and channel cumulative messages as its inputs.

An extrinsic reliability processor for computing extrinsic reliabilities in Turbo-decoding, and soft outputs and check-to-variable metrics, in LDPC decoding, having input ports for forward metrics, backward metrics and channel cumulative messages corresponding to different trellis edges:

• a first stage of adders, for adding forward, backward and channel cumulative messages corresponding to a same trellis edge;
• a number 2M of max* or max trees equal to the number of said alphabet symbols;
• a number K of 2M×2M permutation networks equal to the number of said trellis states, connecting output ports of said adders to input ports of said max* or max trees, wherein each of said max* or max trees has K input ports, each one being connected to a different one of said permutation networks;
• a third stage of adders for computing extrinsic reliabilities as sums of outputs of said max* or max trees;
• and
• fourth and fifth stages of adders for computing updated check-to-variable metrics and LDPC-soft outputs by combining input and outputs of first stages of said max* or max trees.

A state-metric recursive unit (SMRU) for performing recursive computation of forward- and backward metrics according to the BCJR algorithm, comprising a plurality of state metric processors (SMPi) for computing forward and backward metrics of respective states of a code trellis, interconnected by a configurable recursion network (RN), wherein each said state metric processor comprises

• first input ports for receiving, through said recursion network, forward (α)/backward (β) metrics;
• second input ports for receiving channel cumulative messages (γ) corresponding to different edges reaching a same state of a code trellis;
• a first stage of adders, for adding forward, backward and channel cumulative messages corresponding to a same code symbol;
• third input ports for receiving a posteriori reliabilities (Λ)/Soft-outputs (SO);
• a second stage of adders, for adding said a posteriori reliabilities to the sums performed by the adders of said first stages;
• a max* or max tree taking as inputs the sums computed by the adders of said second stage;
• and
• first output ports for updated values of said forward/backward metrics.