This work focuses on the study of a heterogeneous wireless-powered communication (H-WPCN) system, where a device-to-device (D2D) communication pair is overlaid with a downlink (DL) communication pair. In DL communications, the access point keeps spreading radio frequency (RF) signals to serve the DL user equipment (UE). In addition to being the data source of the UE, DL RF signals are also utilized by the D2D transmitter as the only energy source supporting D2D communications. To capture the impact of limited spectrum resource on the proposed H-WPCN system, co-channel interference is considered. Assuming the Rayleigh block fading channel for signal propagation, a tight lower bound as well as its closed-form approximation are provided for the outage probability of the DL communication link, and an exact expression is derived for the outage probability of the D2D communication link. After that, the throughput of the H-WPCN system is optimized via joint power control and time allocation, where the throughput of the D2D communication link is maximized subject to a required throughput for DL communications. Finally, our theoretical analysis is verified by numerical simulations. The simulation results show that the throughput of the H-WPCN system may not benefit from a high energy conversion efficiency.

Compared to the successive cancellation (SC)-based decoding algorithms, the sphere decoding (SD) algorithm can achieve better performance with reduced computational complexity, especially for short polar codes. In this paper, we propose a new method to construct the binary polar codes with the modified multiplicative repetition (MR)-based matrix. Different from the original construction, we first design a $2\times 2q$-ary kernel to guarantee the single-level polarization effect. Then, by replacing the new-designed binary companion matrix, a novel strategy is further developed to enhance the polarization in the bit level, resulting in a better distance property. Finally, the SD-based Monte-Carlo (SDMC) method is used to construct MR-based binary polar codes, while the resulting codes without the butterfly pattern are decoded by the SD algorithm. Simulation results show that the proposed method with the SD algorithm can achieve a maximum performance gain of 0.27 dB compared to the original method with slightly lower complexity.

Polar codes are considered as one of the most competitive channel coding schemes for the future wireless communication system. To improve the performance of polar codes with short code-length for control channels, a sphere decoding algorithm based on received value flipping is proposed in this paper. When a codeword fails the cyclic redundancy check, the algorithm flips the received value with low reliability and forms a new received sequence. Then, this new sequence is sent to the decoder for another decoding attempt. In addition, we also compare the performance of different flipping sets and evaluate the influence of the associated flipping set sizes. Simulation results show that, the proposed algorithm can achieve performance improvement over additive white Gaussian noise channel with acceptable complexity. For the (64, 16) polar code, the proposed algorithm can achieve about 0.23 dB performance gain at frame error rate = ${10}^{-3}$, compared to the conventional sphere decoding algorithm. Finally, we also verify the applicability of the proposed algorithm over Rayleigh fading channel and observe similar results.

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.