In this paper, we present a new class of spatially coupled codes obtained by using both non-recursive and recursive block-oriented superposition. The resulting codes are termed as bidirectional block Markov superposition transmission (BiBMST) codes. Firstly, we perform an iterative decoding threshold analysis according to protograph-based extrinsic information transfer (PEXIT) charts for the BiBMST codes over the binary erasure channels (BECs). Secondly, we derive the generator and parity-check matrices of the BiBMST codes. Thirdly, extensive numerical results are presented to show the advantages of the proposed BiBMST codes. Particularly, our numerical results show that, under the constraint of an equal decoding latency, the BiBMST codes perform better than the recursive BMST (rBMST) codes. However, the simulation results show that, in finite-length regime, negligible performance gain is obtained by increasing the encoding memory. We solve this limitation by introducing partial superposition, and the resulting codes are termed as partially-connected BiBMST (PC-BiBMST) code. Analytical results have confirmed the advantages of the PC-BiBMST codes over the original BiBMST codes. We also present extensive simulation results to show the performance advantages of the PC-BiBMST codes over the spatially coupled low-density parity-check (SC-LDPC) codes, spatially coupled generalized LDPC (SC-GLDPC) codes, and the original BiBMST codes in the finite-length regime.

In this paper, we propose the two-stage constructions for the rate-compatible shortened polar (RCSP) codes. For the Stage-I construction, the shortening pattern and the frozen bit are jointly designed to make the shortened bits be completely known by the decoder. Besides, a distance-greedy algorithm is presented to improve the minimum Hamming distance of the codes. To design the remaining Stage-II frozen bits, three different construction algorithms are further presented, called the Reed-Muller (RM) construction, the Gaussian Approximation (GA) construction, and the RM-GA construction. Then we give the row weight distribution numerical results of the generator matrix after the Stage-I and Stage-II constructions, which shows that the proposed constructions can efficiently increase the minimum Hamming distance. Simulation results show that the proposed RCSP codes have excellent frame error rate (FER) performances at different code lengths and code rates. More specifically, the RM-GA construction performs best and can achieve at most 0.8 dB gain compared to the Wang14 and the quasi-uniform puncturing (QUP) schemes. The RM construction is designed completely by the distance-constraint without channel evaluation thus has the simplest structure. Interestingly, it still has better FER performance than the existing shortening/puncturing schemes, especially at high signal noise ratio (SNR) region.

Polar coding are the first class of provable capacity-achieving coding techniques for a wide range of channels. With an ideal recursive structure and many elegant mathematical properties, polar codes are inherently implemented with low complexity encoding and decoding algorithms. Since the block length of the original polar construction is limited to powers of two, rate-compatible polar codes (RCPC) are presented to meet the flexible length/rate transmission requirements in practice. The RCPC codes are well-conditioned to combine with the hybrid automatic repeat request (HARQ) system, providing high throughput efficiency and such RCPC-HAPQ scheme is commonly used in delay-insensitive communication system. This paper first gives a survey of both the classical and state-of-the-art encoding/decoding algorithms for polar codes. Then the RCPC construction methods are discussed, including the puncturing, shortening, multi-kernel construction, etc. Finally, we investigate several RCPC-HARQ jointly design systems and discuss their encoding gain and re-transmission diversity gain.