Faster-than-Nyquist Signaling: on Linear and Non-Linear Reduced-Complexity Turbo Equalization

In the framework of digital video broadcasting by satellite - second generation (DVB-S2), we analyze a faster-than-Nyquist (FTN) system based on turbo equalization and low-density parity-check (LDPC) codes. Truncated maximum a posteriori (MAP) and minimum mean square error (MMSE) equalizers provide a reduced-complexity implementation of the FTN system. On the other hand, LDPC codes allow us to demonstrate attractive performance results over an additive white Gaussian noise (AWGN) channel while increasing spectral efficiency beyond the Nyquist rate and keeping a complexity comparable to that of a current DVB-S2 mode

Spectrally Efficient FDM over Satellite Systems with Advanced Interference Cancellation

For high data rates satellite systems, where multiple carriers are frequency division multiplexed with a slight overlap, the overall spectral efficiency is limited. This work applies highly overlapped carriers for satellite broadcast and broadband scenarios to achieve higher spectral efficiency. Spectrally efficient frequency division multiplexing (SEFDM) compresses subcarrier spacing to increase the spectral efficiency at the expense of orthogonality violation. SEFDM systems performance degrades compared to orthogonal signals, unless efficient interference cancellation is used. Turbo equalisation with interference cancellation is implemented to improve receiver performance for variable coding, compression and modulation/constellation proposals that may be applied in satellite communications settings. Such parameters may be set to satisfy pre-defined spectral efficiency values for a given quality index (QI) or associated application. Assuming LDPC coded data, the work proposes two approaches to receiver design; a simple matched filter approach and an approach utilising an iterative interference cancellation structure specially designed for SEFDM. Mathematical models and simulations studies are presented indicating promising gains to be achieved for SEFDM transmission with advanced transceiver architectures at the cost of increased complexity at the receiver

Optical Time-Frequency Packing: Principles, Design, Implementation, and Experimental Demonstration

Time-frequency packing (TFP) transmission provides the highest achievable spectral efficiency with a constrained symbol alphabet and detector complexity. In this work, the application of the TFP technique to fiber-optic systems is investigated and experimentally demonstrated. The main theoretical aspects, design guidelines, and implementation issues are discussed, focusing on those aspects which are peculiar to TFP systems. In particular, adaptive compensation of propagation impairments, matched filtering, and maximum a posteriori probability detection are obtained by a combination of a butterfly equalizer and four 8-state parallel Bahl-Cocke-Jelinek-Raviv (BCJR) detectors. A novel algorithm that ensures adaptive equalization, channel estimation, and a proper distribution of tasks between the equalizer and BCJR detectors is proposed. A set of irregular low-density parity-check codes with different rates is designed to operate at low error rates and approach the spectral efficiency limit achievable by TFP at different signal-to-noise ratios. An experimental demonstration of the designed system is finally provided with five dual-polarization QPSK-modulated optical carriers, densely packed in a 100 GHz bandwidth, employing a recirculating loop to test the performance of the system at different transmission distances.Comment: This paper has been accepted for publication in the IEEE/OSA Journal of Lightwave Technolog

Performance Evaluation of a Faster-than-Nyquist System Based on Turbo Equalization and LDPC Codes

In the frame of digital video broadcasting by satellite - second generation (DVB-S2), a faster-than-Nyquist (FTN) system based on turbo equalization and low-density parity-check (LDPC) codes is proposed. Truncated maximum a posteriori (MAP) and minimum mean square error (MMSE) equalizers provide a reduced complexity implementation of the FTN system. On the other hand, LDPC codes allow us to demonstrate attractive performance results over an additive white Gaussian noise (AWGN) channel while increasing spectral efficiency beyond the Nyquist rate up to 60 % and keeping a complexity comparable to a current DVB-S2 modem

Rateless Coding for Gaussian Channels

A rateless code-i.e., a rate-compatible family of codes-has the property that codewords of the higher rate codes are prefixes of those of the lower rate ones. A perfect family of such codes is one in which each of the codes in the family is capacity-achieving. We show by construction that perfect rateless codes with low-complexity decoding algorithms exist for additive white Gaussian noise channels. Our construction involves the use of layered encoding and successive decoding, together with repetition using time-varying layer weights. As an illustration of our framework, we design a practical three-rate code family. We further construct rich sets of near-perfect rateless codes within our architecture that require either significantly fewer layers or lower complexity than their perfect counterparts. Variations of the basic construction are also developed, including one for time-varying channels in which there is no a priori stochastic model.Comment: 18 page

Constellation design for future communication systems: a comprehensive survey

[EN] The choice of modulation schemes is a fundamental building block of wireless communication systems. As a key component of physical layer design, they critically impact the expected communication capacity and wireless signal robustness. Their design is also critical for the successful roll-out of wireless standards that require a compromise between performance, efficiency, latency, and hardware requirements. This paper presents a survey of constellation design strategies and associated outcomes for wireless communication systems. The survey discusses their performance and complexity to address the need for some desirable properties, including consistency, channel capacity, system performance, required demapping architecture, flexibility, and independence. Existing approaches for constellation designs are investigated using appropriate metrics and categorized based on their theoretical algorithm design. Next, their application to different communication standards is analyzed in context, aiming at distilling general guidelines applicable to the wireless building block design. Finally, the survey provides a discussion on design directions for future communication system standardization processes.This work was supported in part by the Basque Government under Grant IT1234-19, in part by the PREDOC under Program PRE_2020_2_0105, and in part by the Spanish Government through the Project PHANTOM (MCIU/AEI/FEDER, UE) under Gran

An Iterative Coded Turbo Equalization Model in High Data Rate Wireless Application System

In next-generation wireless communication and 5G-based mobile communication, error-free communication with high transmission efficiency and reliability in a limited bandwidth is required along with diverse services. Highly reliable communication is difficult with wireless communication systems due to surrounding environment, movement of transmitters and receivers, and various noises. Channel coding technology should be applied to overcome these problems. In addition, an algorithm that can overcome the loss of transmission efficiency caused by the application of channel coding technology should be applied. However, since there is a trade-off relationship between improved transmission rates and performance, it is difficult to satisfy both. Thus, recently, methods to improve both transmission rates and performance simultaneously are being studied. Accordingly, this dissertation proposes a channel coded turbo equalization model that enables improved performance in a high transmission wireless communication system with improved transmission efficiency. The topic of this dissertation can be largely divided into two aspects: performance improvement and high transmission efficiency. First, a turbo equalization model combined with iterative codes for performance improvement in a wireless communication system was investigated, and a soft decision-based iterative coding schemes such as the convolutional code-based BCJR, turbo codes and LDPC codes were introduced. Subsequently, the performance of these coding schemes was comparatively analyzed. The BER performance analysis through the simulation showed that the LDPC code was approximately 1.2 [dB] at BER , which was the closest to the Shannon's channel capacity limit. In addition, the LDPC coding method was suggested as a channel coding scheme suitable for high-speed wireless communication by comparatively analyzing the characteristics of each coding scheme for complexity, decoding speed and performance. Second, the algorithm that achieved high transmission efficiency was investigated. Conventional high-transmission efficiency algorithms such as punctured, FTN and MIMO algorithms were introduced, and these three were comparatively analyzed from the perspective of the same transmission rate. In addition, MIMO-FTN and P-FTN algorithms, which combined each of the punctured and MIMO algorithms with the FTN algorithm to maximize the transmission efficiency, were proposed. The performances of the proposed algorithms were analyzed through the simulation from the perspective of the same transmission rate, and the W-ZF based MIMO-FTN algorithm was found to be the best. However, the performance degradation due to the application of FTN occurred, and subsequently, a turbo equalization model of FTN signals based UEP was proposed to overcome this problem. The UEP scheme was applied to the MIMO-FTN algorithm to maximize the improvement in transmission rates, and the UEP-FTN transmission scheme applying the OFDM scheme in multi-path channels was proposed. The performance of the proposed UEP-based FTN transmission scheme was analyzed through simulation, which showed that the application of the UEP scheme led to the improved performance. Based on this study, a turbo equalization model to achieve the performance improvement and high transmission efficiency was proposed. In addition, not limiting its usage only in the surface wireless communication but expanding its scope to underwater acoustic communication, the way to apply the model to underwater acoustic communication was investigated. Based on the decoded data and the turbo equalization-based UEP-FTN model that improved the transmission efficiency and performance in underwater acoustic communication, a method to calibrate the frequency and phase of the following packet was proposed. Its efficiency was verified through the actual underwater experiment at Gyeongcheon Lake in Mungyeong-si, Geyongsangbuk-do. The results of the experiment showed that the proposed method worked efficiently.제 1 장 서론 1 제 2 장 직렬 연접된 반복 부호화 결합 된 터보 등화 모델 5 2.1 터보 등화 모델 5 2.2 터보 등화 모델과 결합된 반복 부호화 기법 11 2.2.1 BCJR 13 2.2.2 터보 부호 16 2.2.3 LDPC 부호 22 2.2.3.1 DVB-S2 기반 LDPC 부호(Long size) 23 2.2.3.2 IEEE 802.11n 기반 LDPC 부호(Short size) 29 2.2.4 고속 무선 통신을 위한 최적 부호화 기법 34 제 3 장 고전송 효율 알고리즘 37 3.1 기존 고전송 효율 알고리즘 38 3.1.1 Punctured 알고리즘 38 3.1.2 FTN 알고리즘 41 3.1.3 MIMO 알고리즘 48 3.1.3.1 시공간 부호화 기반 MIMO 알고리즘 50 3.1.3.2 ZF 기반 MIMO 알고리즘 54 3.1.4 기존 고전송 효율 알고리즘 전송률 분석 56 3.2 FTN과 결합한 고전송 효율 알고리즘 및 터보 등화 모델 제안 58 3.2.1 FTN 신호에 대한 터보 등화 모델 58 3.2.2 P-FTN 터보 등화 모델 59 3.2.3 MIMO-FTN 터보 등화 모델 62 3.2.3.1 W-ZF를 이용한 채널 분리 알고리즘 63 3.3 FTN과 결합한 고전송 효율 알고리즘 성능 분석 66 제 4 장 비균일 오류 확률 기반 FTN 신호의 터보 등화 모델 제안 71 4.1 비균일 오류 확률 기반 FTN 신호의 터보 등화 모델 71 4.1.1 비균일 오류 확률 기반 우선 순위 설정 방법 74 4.1.2 우선 순위에 따른 부호어 배치 방법 77 4.2 UEP 기법이 적용된 MIMO-FTN 터보 등화 모델 79 4.3 OFDM 기법이 적용된 UEP-FTN 터보 등화 모델 80 4.4 비균일 오류 확률 기반 FTN 신호의 성능 분석 85 4.4.1 UEP-FTN 신호의 성능 분석 85 4.4.2 UEP 기법이 적용된 MIMO-FTN 신호의 성능 분석 90 4.4.3 OFDM 기법이 적용된 UEP-FTN 신호의 성능 분석 93 제 5 장 수중 무선 통신에서의 응용 96 5.1 UEP-FTN 방식의 수중 통신 적용 96 5.2 복호된 데이터를 이용한 연속적인 주파수 보정 방식 98 5.3 실험 환경 100 5.4 실험 결과 105 5.4.1 UEP-FTN 신호의 실험 결과 105 5.4.2 복호된 데이터를 이용한 주파수 보정 방식 실험 결과 107 제 6 장 결 론 110 참고문헌 113Docto

Design tradeoffs and challenges in practical coherent optical transceiver implementations

This tutorial discusses the design and ASIC implementation of coherent optical transceivers. Algorithmic and architectural options and tradeoffs between performance and complexity/power dissipation are presented. Particular emphasis is placed on flexible (or reconfigurable) transceivers because of their importance as building blocks of software-defined optical networks. The paper elaborates on some advanced digital signal processing (DSP) techniques such as iterative decoding, which are likely to be applied in future coherent transceivers based on higher order modulations. Complexity and performance of critical DSP blocks such as the forward error correction decoder and the frequency-domain bulk chromatic dispersion equalizer are analyzed in detail. Other important ASIC implementation aspects including physical design, signal and power integrity, and design for testability, are also discussed.Fil: Morero, Damián Alfonso. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. ClariPhy Argentina S.A.; ArgentinaFil: Castrillon, Alejandro. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Aguirre, Alejandro. ClariPhy Argentina S.A.; ArgentinaFil: Hueda, Mario Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Agazzi, Oscar Ernesto. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. ClariPhy Argentina S.A.; Argentin

Reduced Receivers for Faster-than-Nyquist Signaling and General Linear Channels

Fast and reliable data transmission together with high bandwidth efficiency are important design aspects in a modern digital communication system. Many different approaches exist but in this thesis bandwidth efficiency is obtained by increasing the data transmission rate with the faster-than-Nyquist (FTN) framework while keeping a fixed power spectral density (PSD). In FTN consecutive information carrying symbols can overlap in time and in that way introduce a controlled amount of intentional intersymbol interference (ISI). This technique was introduced already in 1975 by Mazo and has since then been extended in many directions. Since the ISI stemming from practical FTN signaling can be of significant duration, optimum detection with traditional methods is often prohibitively complex, and alternative equalization methods with acceptable complexity-performance tradeoffs are needed. The key objective of this thesis is therefore to design reduced-complexity receivers for FTN and general linear channels that achieve optimal or near-optimal performance. Although the performance of a detector can be measured by several means, this thesis is restricted to bit error rate (BER) and mutual information results. FTN signaling is applied in two ways: As a separate uncoded narrowband communication system or in a coded scenario consisting of a convolutional encoder, interleaver and the inner ISI mechanism in serial concatenation. Turbo equalization where soft information in the form of log likelihood ratios (LLRs) is exchanged between the equalizer and the decoder is a commonly used decoding technique for coded FTN signals. The first part of the thesis considers receivers and arising stability problems when working within the white noise constraint. New M-BCJR algorithms for turbo equalization are proposed and compared to reduced-trellis VA and BCJR benchmarks based on an offset label idea. By adding a third low-complexity M-BCJR recursion, LLR quality is improved for practical values of M. M here measures the reduced number of BCJR computations for each data symbol. An improvement of the minimum phase conversion that sharpens the focus of the ISI model energy is proposed. When combined with a delayed and slightly mismatched receiver, the decoding allows a smaller M without significant loss in BER. The second part analyzes the effect of the internal metric calculations on the performance of Forney- and Ungerboeck-based reduced-complexity equalizers of the M-algorithm type for both ISI and multiple-input multiple-output (MIMO) channels. Even though the final output of a full-complexity equalizer is identical for both models, the internal metric calculations are in general different. Hence, suboptimum methods need not produce the same final output. Additionally, new models working in between the two extremes are proposed and evaluated. Note that the choice of observation model does not impact the detection complexity as the underlying algorithm is unaltered. The last part of the thesis is devoted to a different complexity reducing approach. Optimal channel shortening detectors for linear channels are optimized from an information theoretical perspective. The achievable information rates of the shortened models as well as closed form expressions for all components of the optimal detector of the class are derived. The framework used in this thesis is more general than what has been previously used within the area