Soft-In Soft-Out Polar Decoding Aided Three-Stage Concatenated Iterative MIMO-Turbo Transceivers

A novel Soft-Input Soft-Output (SISO) polar decoding algorithm is proposed, which is capable of iterating between an inner and outer decoder in a three-stage serial concatenated iterative receiver. The proposed polar decoding algorithm leverages a hybrid of Soft Cancellation (SCAN) and g-function aided-SCAN (G-SCAN) decoding. The SCAN decoder enables iterative soft-information exchange with the outer decoders and the G-SCAN decoder facilitates iterative soft-information exchange with the inner decoders while exploiting the error correction capability of the classic Successive Cancellation List (SCL) decoder. Furthermore, we present the Three-Dimensional (3D) Extrinsic Information Transfer (EXIT) chart analysis of polar codes for the first time, in order to characterise the iterative exchange of extrinsic information between these three concatenated stages. This offers an insight into the interactions of these three decoders and characterises their iterative convergence. In this three-stage serial concatenated scheme the first stage is a Joint Source Channel Coding (JSCC) decoder, the second stage is a 5th Generation (5G) 3rd Generation Partnership Project (3GPP) New Radio (NR) polar decoder based on our novel hybrid SISO polar algorithm, and the third stage is a 2 × 2 Multiple Input Multiple Output (MIMO) detector. We characterized the Symbol Error Rate (SER) vs. complexity of the proposed scheme, and compare it to various soft- and hard-decision benchmarkers, as well as to the relevant JSCC and Separate Source Channel Coding (SSCC) schemes. In comparison to a three-stage serial concatenated JSCC benchmarker, the proposed SISO scheme offers 11${\%}$ complexity reduction over to the state-of-the-art SISO SCAN polar decoder at a similar SER performance. Additionally, the proposed SISO scheme achieves a 0.75 dB SNR gain over the SCAN polar decoder of a two-stage serial concatenated SSCC benchmarker.