Qiuliang Xie

APSK Constellation with Gray Mapping

Amplitude phase shift keying (APSK) constellation is superior to its quadrature amplitude modulation (QAM) counterpart from the mutual information point of view. However, due to the lack of Gray mapping, it introduces high independent demapping loss. In this letter, a special kind of APSK constellations with Gray mapping (Gray-APSK) is proposed, which provides considerable shaping gain compared with the QAM constellations with Gray mapping (Gray-QAM) in both independent and iterative demapping scenarios, as verified by average mutual information analysis and bit error rate simulations.

A Universal Low-Complexity Symbol-to-Bit Soft Demapper

High-order constellations are commonly used for achieving high bandwidth efficiency in most communication systems. However, the complexity of the multiplication operations associated with the standard max-sum approximation of the maximum a posteriori probability in the log-domain (Max-Log-MAP) symbol-to-bit demapper is very high. In this contribution, we conceive a low-complexity universal soft demapper, which reduces the demappers complexity considerably for the binary-reflected Gray-labeled pulse amplitude modulation (PAM), phase shift keying (PSK), quadrature amplitude modulation (QAM), and amplitude phase-shift keying (APSK) relying on product constellation labeling (product-APSK). Our theoretical analysis demonstrates that the proposed demapper has exactly the same performance as the Max-Log-MAP demapper for the Gray-labeled PAM, PSK, and QAM. Our theoretical analysis and simulation results also demonstrate that for the Gray-labeled product-APSK, the performance degradation of the proposed simplified soft demapper is negligible for both 64-ary and 256-ary constellations compared with the Max-Log-MAP demapper.

Simplified Soft Demapper for APSK with Product Constellation Labeling

Amplitude phase shift keying (APSK) constellation is capable of outperforming quadrature amplitude modulation (QAM) in terms of both the mutual information and the error-control performance. However, the lack of simplified demapper prevents its potential applications due to the inherent high computation complexity. In this paper, the concept of APSK using product constellation labeling is introduced, and two simplified demappers are proposed. Theoretical analysis and simulations show that the performance degradation caused by these simplified demappers is negligible, while the complexity is significantly reduced, compared to the traditional Max-Log-MAP demapper.

Coded Modulation with Signal Space Diversity

Signal space diversity (SSD) is a well-known power- and bandwidth-efficient diversity technique with constellation rotation and coordinate interleaving. This paper investigates issues of combining SSD with coded modulation systems (CMSs), e.g., bit-interleaved coded modulation (BICM) and its iterative version, BICM-ID. It demonstrates that the average mutual information (AMI) between the signal after rotated constellation mapping and the signal before or after the soft demapper varies with the rotation angle. A new criterion for determining the optimal rotation angle by maximizing such AMI is therefore proposed. Specific considerations of combining SSD with BICM (BICM-SSD) and BICM-ID (BICM-ID-SSD) are addressed. The demappers extrinsic information transfer (EXIT) curve in traditional BICM-ID systems exhibits different slopes under different channels, which consequently prevents traditional BICM-ID systems from having simultaneously excellent performance under different channels. It is shown that such a different-slope problem can be simply mitigated by a proper use of SSD. Analysis and simulation show that the proposed BICM-ID-SSD systems hold a near-capacity performance under both additive white Gaussian noise (AWGN) and Rayleigh fading channels simultaneously.

Non-Equiprobable APSK Constellation Labeling Design for BICM Systems

The previously proposed amplitude phase shift keying (APSK) with Gray labeling achieves a considerable shaping gain in comparison with conventional square quadrature amplitude modulation. In this letter, by reducing the number of points on the inner rings of Gray-APSK and introducing a non-equiprobable (NE) bit-to-symbol labeling, a novel NE-APSK constellation labeling is proposed. NE-APSK provides additional 0.1 dB shaping gain over Gray-APSK without any complexity increase, as illustrated by the mutual information analysis and verified by the bit error rate simulation.

Bit-Interleaved LDPC-Coded Modulation with Iterative Demapping and Decoding

Bit-interleaved coded modulation (BICM) is a sub- optimal scheme from the average mutual information (AMI) point of view due to independent demapping. However, this AMI loss can be neglected for signal constellations with Gray mapping at high coding rates. AMI of amplitude-phase shift keying (APSK) constrained additive white Gaussian noise (AWGN) channel is provided in this paper, which shows that the BICM scheme has considerable loss with APSK constellations since no Gray mapping exists. Bit-interleaved low-density parity-check (LDPC) coded modulation (BILCM) is an excellent scheme and has been employed in many broadcasting and communication systems, however, such scheme also suffers from the independent demapping loss. Therefore, BILCM with iterative demapping and decoding (BILCM-ID) is proposed in this paper to overcome such loss. Simulation results show that the BILCM-ID scheme outweighs BILCM scheme by about 0.5 and 0.3 dB over AWGN channel for 32-APSK constellation at coding rates 2/3 and 4/5, respectively.

Labeling Optimization for BICM-ID Systems

Labeling is crucial for bit-interleaved coded modulation with iterative demapping and decoding (BICM-ID) systems. Based on extrinsic information transfer (EXIT) charts, a novel adaptive binary switch algorithm (ABSA) in searching for labeling to well match the outer channel code is proposed. ABSA can be applied to arbitrary constellations, meanwhile it makes the proposed BICM-ID systems hold a near-capacity performance.

EXIT-Chart-Matching-Aided Near-Capacity Coded Modulation Design and a BICM-ID Design Example for Both Gaussian and Rayleigh Channels

Bit-interleaved coded modulation with iterative decoding (BICM-ID) is investigated, wherein a novel method of designing amplitude phase-shift keying (APSK) constellations is proposed, which is capable of outperforming both traditional quadrature amplitude modulation (QAM) and nonuniformly spaced QAM (NU-QAM). It is shown that the channel capacity can be approached by the proposed M-APSK constellation as M tends to infinity. Additionally, a new algorithm is introduced for finding the best bit-to-symbol mapping. Furthermore, when signal space diversity is also employed, our extrinsic information transfer (EXIT) chart analysis and Monte Carlo simulations demonstrate that the proposed BICM-ID schemes exhibit a near-Shannon-capacity performance for transmission over both additive white Gaussian noise (AWGN) and Rayleigh fading channels. For a block length of 64 800 bits, the bit-error-rate (BER) curve of the proposed BICM-ID 16/64-APSK scheme is only about 0.8 and 1.0 dB away from the Gaussian-input Shannon limit over AWGN and Rayleigh fading channels, respectively, at the BER of 10-5 and for a code rate of 1/2.

A fast and efficient encoding structure for QC-LDPC codes

Parallel-input parallel-output (PIPO) structure for quasi-cyclic low-density parity-check (QC-LDPC) codes is proposed in this paper to implement a faster and more efficient QC-LDPC encoder than that based on conventional serial-input parallel-output (SIPO) or parallel-input serial-output (PISO) structure. An encoding architecture based on the proposed PIPO structure for multi-rate QC-LDPC codes employed by the Chinese Digital Television Terrestrial Broadcasting (DTTB) standard is also presented and discussed.

Near-capacity BICM-ID for MIMO channels

Bit-interleaved coded modulation with iterative demapping (BICM-ID) is investigated for multiple-input multiple-output (MIMO) channels. Based on the average mutual information (AMI) analysis, vertical Bell-lab layered space-time (V-BLAST) rather than space-time block code (STBC) is chosen to be combined with BICM-ID. Based on the extrinsic information transfer (EXIT) chart analysis, a novel algorithm in searching for a labeling to well match the outer code is proposed for MIMO channels, which facilitates a near-capacity V-BLAST-BICM-ID scheme. Computer simulation confirmed the near-capacity performance.