Low-complexity iterative receiver algorithms for multiple-input multiple-output underwater wireless communications

This dissertation proposes three low-complexity iterative receiver algorithms for multiple-input multiple-output (MIMO) underwater acoustic (UWA) communications. First is a bidirectional soft-decision feedback Turbo equalizer (Bi-SDFE) which harvests the time-reverse diversity in severe multipath MIMO channels. The Bi-SDFE outperforms the original soft-decision feedback Turbo equalizer (SDFE) while keeping its total computational complexity similar to that of the SDFE. Second, this dissertation proposes an efficient direct adaptation Turbo equalizer for MIMO UWA communications. Benefiting from the usage of soft-decision reference symbols for parameter adaptation as well as the iterative processing inside the adaptive equalizer, the proposed algorithm is efficient in four aspects: robust performance in tough channels, high spectral efficiency with short training overhead, time efficient with fast convergence and low complexity in hardware implementation. Third, a frequency-domain soft-decision block iterative equalizer combined with iterative channel estimation is proposed for the uncoded single carrier MIMO systems with high data efficiency. All the three new algorithms are evaluated by data recorded in real world ocean experiment or pool experiment. Finally, this dissertation also compares several Turbo equalizers in single-input single-output (SISO) UWA channels. Experimental results show that the channel estimation based Turbo equalizers are robust in SISO underwater transmission under harsh channel conditions --Abstract, page iv

Turbo equalization for multiple-input multiple-output (MIMO) wireless communication systems

This dissertation investigates both of the frequency domain and time domain turbo equalization with multiple-input multiple-output (MIMO) fading channels for radio frequency and underwater acoustic communications. First, a low complexity frequency domain turbo equalization (FDTE) is proposed for the MIMO systems with zero padding (ZP) or cyclic prefix (CP) inserted between the transmitted data blocks and its performance is tested on the real-world UWA communications experiments. Second, as high speed communication system requires efficient bandwidth usage and power consumption, CP or ZP is not transmitted as auxiliary information. An inter-block interference cancelation and CP reconstruction algorithm is developed to re-arrange the channel matrix into a block diagonal one. This improvement makes the FDTE effectively detects the continuous data stream from the high speed UWA communications and its performance has been verified by processing data collected from the UWA communications experiment. Finally, a low complexity soft interference cancelation (SIC) time domain turbo equalizer for MIMO systems with high level modulation is proposed. Compared with the conventional linear or nonlinear turbo equalizers, the proposed SIC turbo equalizer can theoretically reach the bound set up by the ideal match filter and its bit error rate (BER) performance from Monte Carlo simulation achieves a lower error floor as well as a more rapid convergence speed. --Abstract, page iv

On implementation aspects of decode and forward and compress and forward relay protocols

In this work, the common relay protocols Decode-and-Forward and Compress-and-Forward (CF) are investigated from a practical point of view: This involves on the one hand the impact of imperfections like channel and carrier phase stimation errors and on the other hand, the question of how to implement relay protocol specific signal processing like quantization for CF which is modeled in information theory simply by additive quantizer noise. To evaluate the performance, achievable rates are determined either numerically with the help of the Max-Flow Min-Cut theorem or by link level simulations.Diese Arbeit untersucht die Relay-Protokolle Decode-and-Forward und Compress-and-Forward (CF) mit dem Fokus auf einer praktischen Umsetzung. Es werden sowohl Störeinflüsse wie Kanal- und Phasenschätzfehler betrachtet als auch spezielle Kompressionsverfahren für das CF Protokoll implementiert. Von großer Bedeutung ist hier die Kompression in Form der Quantisierung, weil diese in der Informationstheorie lediglich durch Quantisierungsrauschen modelliert wird. Zur Auswertung der Leistungsfähigkeit der Protokolle werden die erzielbaren Raten entweder numerisch oder durch Simulation bestimmt

Coded Modulation Assisted Radial Basis Function Aided Turbo Equalisation for Dispersive Rayleigh Fading Channels

In this contribution a range of Coded Modulation (CM) assisted Radial Basis Function (RBF) based Turbo Equalisation (TEQ) schemes are investigated when communicating over dispersive Rayleigh fading channels. Specifically, 16QAM based Trellis Coded Modulation (TCM), Turbo TCM (TTCM), Bit-Interleaved Coded Modulation (BICM) and iteratively decoded BICM (BICM-ID) are evaluated in the context of an RBF based TEQ scheme and a reduced-complexity RBF based In-phase/Quadrature-phase (I/Q) TEQ scheme. The Least Mean Square (LMS) algorithm was employed for channel estimation, where the initial estimation step-size used was 0.05, which was reduced to 0.01 for the second and the subsequent TEQ iterations. The achievable coding gain of the various CM schemes was significantly increased, when employing the proposed RBF-TEQ or RBF-I/Q-TEQ rather than the conventional non-iterative Decision Feedback Equaliser - (DFE). Explicitly, the reduced-complexity RBF-I/Q-TEQ-CM achieved a similar performance to the full-complexity RBF-TEQ-CM, while attaining a significant complexity reduction. The best overall performer was the RBF-I/Q-TEQ-TTCM scheme, requiring only 1.88~dB higher SNR at BER=10-5, than the identical throughput 3~BPS uncoded 8PSK scheme communicating over an AWGN channel. The coding gain of the scheme was 16.78-dB

Burst-by-Burst Adaptive Decision Feedback Equalised TCM, TTCM and BICM for H.263-Assisted Wireless Video Telephony

Decision Feedback Equaliser (DFE) aided wideband Burst-by-Burst (BbB) Adaptive Trellis Coded Modulation (TCM), Turbo Trellis Coded Modulation (TTCM) and Bit-Interleaved Coded Modulation (BICM) assisted H.263-based video transceivers are proposed and characterised in performance terms when communicating over the COST 207 Typical Urban wideband fading channel. Specifically, four different modulation modes, namely 4QAM, 8PSK, 16QAM and 64QAM are invoked and protected by the above-mentioned coded modulation schemes. The TTCM assisted scheme was found to provide the best video performance, although at the cost of the highest complexity. A range of lower-complexity arrangements will also be characterised. Finally, in order to confirm these findings in an important practical environment, we have also investigated the adaptive TTCM scheme in the CDMA-based Universal Mobile Telecommunications System's (UMTS) Terrestrial Radio Access (UTRA) scenario and the good performance of adaptive TTCM scheme recorded when communicating over the COST 207 channels was retained in the UTRA environment

Implementação de códigos LDPC em OFDM e SC-FDE

Os desenvolvimentos dos sistemas de comunicação sem fios apontam para transmissões de alta velocidade e alta qualidade de serviço com um uso eficiente de energia. Eficiência espectral pode ser obtida por modulações multinível, enquanto que melhorias na eficiência de potência podem ser proporcionadas pelo uso de códigos corretores de erros. Os códigos Low-Density Parity-Check (LDPC), devido ao seu desempenho próximo do limite de Shannon e baixa complexidade na implementação e descodificação são apropriados para futuros sistemas de comunicações sem fios. Por outro lado, o uso de modulações multinível acarreta limitações na amplificação. Contudo, uma amplificação eficiente pode ser assegurada por estruturas de transmissão onde as modulações multinível são decompostas em submodulações com envolvente constante que podem ser amplificadas por amplificadores não lineares a operar na zona de saturação. Neste tipo de estruturas surgem desvios de fase e ganho, produzindo distorções na constelação resultante da soma de todos os sinais amplificados. O trabalho foca-se no uso dos códigos LDPC em esquemas multiportadora e monoportadora, com especial ênfase na performance de uma equalização iterativa implementada no domínio da frequência por um Iterative Block-Decision Feedback Equalizer (IB-DFE). São analisados aspectos como o impacto do número de iterações no processo de descodificação dentro das iterações do processo de equalização. Os códigos LDPC também serão utilizados para compensar os desvios de fase em recetores iterativos para sistemas baseados em transmissores com vários ramos de amplificação. É feito um estudo sobre o modo como estes códigos podem aumentar a tolerância a erros de fase que incluí uma análise da complexidade e um algoritmo para estimação dos desequilíbrios de fase

Next generation optical access networks and coexistence with legacy PONs

Nowadays, Fiber-to-the-Home is one of the most promising solutions to provide broadband services in access networks. However, the fiber is inefficiently used as most of the deployed systems are still based on Time Division Multiplexing Passive Optical Networks (TDM-PONs) providing shared transmission capacities up to 2.5 Gb/s down and 1.25 Gb/s up, among multiple users. Research on high-speed electronics and Wavelength Division Multiplexing (WDM) has allowed the emergence of what is known as the second generation PON (NG-PON2), which specify aggregated capacities up to 40 Gb/s, stacking four channels at symmetric data rates of 10 Gb/s each, for residential scenarios. Nevertheless, the capacity per channel is still shared between multiple users due to the use of TDM. Moreover, the optical spectrum efficiency is low because channels are widely spaced (50 to 100 GHz). In addition, the sensitivity, reach and number of users is limited as consequence of using direct detection (DD) systems. In consequence, and due to the increase in bandwidth demands of new multimedia applications, it is necessary to propose solutions that cope with this tendency and, even more important, that can coexist with legacy systems, being one of the major requirements of network operators to guarantee a smooth and non-disruptive technology migration. In this thesis, a breakthrough technology such as Ultra-Dense WDM (UDWDM) that allows to allocate a large number of channels spaced only by a few GHz is used. This approach consent to envision the concept of Wavelength-to-the-User, where each costumer can be served with dedicated bandwidth links. The key technologies are based on coherent systems, with inherent wavelength selectivity and improved sensitivity compared to DD systems, thanks to the booster action of a tunable local oscillator (LO) laser. Because of cost is the main constraint in access networks, especially at the customer premises equipment (Optical Network Unit - ONU), in this thesis, a new class of coherent transceivers, based on low-cost direct modulated lasers and simplified receiver schemes, are proposed and experimentally tested. Moreover, the issue of coexistence is investigated through theoretical studies and real-time implementations, demonstrating full compatibility with legacy systems. Between the proposed solutions, a simple technique to adjust digitally the direct phase modulation of a distributed feedback (DFB) laser is presented to support flexible transmission rates. Next, several multilevel phase modulation formats for achieving higher transmission rates and better spectral efficiency are experimentally compared. Subsequently, the topic of photonic integration is addressed, demonstrating for the first time an 8-ary hybrid amplitude and phase modulated transmitter (Tx), by using a low-cost, small-footprint and energy efficient dual electro-absorption modulated laser (DEML). Finally, two novel proposals, to reduce the complexity of heterodyne and intradyne detection, are provided to face the typical issue of complexity and high-cost of coherent systems. The former explores the possibility of using only one DFB laser as LO and Tx at the ONU. The later demonstrates for the first time, a novel phase time diversity technique alternating phase modulation at each complex component (in-phase - I and quadrature - Q) achieving a 10 Gb/s' transmission with polarization independence.En la actualidad, la Fibra hasta el Hogar es una de las soluciones más prometedoras para proporcionar servicios de banda ancha en las redes de acceso. Sin embargo, la fibra se usa de manera poco eficiente, ya que la mayoría de los sistemas implementados todavía están basados en redes ópticas pasivas de multiplexación por división en el tiempo (TDM-PON) que brindan capacidades de transmisión compartidas entre múltiples usuarios de hasta 2.5 Gb/s y 1.25 Gb/s. La investigación en electrónica de alta velocidad y la multiplexación por división de longitud de onda (WDM) ha permitido el surgimiento de lo hoy se conoce como PON de segunda generación (NG-PON2), que especifica capacidades agregadas de hasta 40 Gb/s, apilando cuatro canales a velocidades de datos simétricas de 10 Gb/s cada uno, para escenarios residenciales. Sin embargo, la capacidad por canal todavía se comparte entre múltiples usuarios debido al uso de TDM. Además, la eficiencia en el uso del espectro óptico es baja porque los canales están muy separados (50 a 100 GHz). Asimismo, la sensibilidad, el alcance y el número de usuarios están limitados debido al uso de sistemas de detección directa. En consecuencia, y debido al aumento de las demandas de ancho de banda de las nuevas aplicaciones multimedia, es necesario proponer soluciones que respondan a esta tendencia y, lo que es más importante, que puedan coexistir con sistemas heredados, siendo uno de los principales requisitos de los operadores de red para garantizar una migración de tecnología fluida y sin interrupciones. En esta tesis, se utiliza una tecnología de vanguardia, como la multiplexación por división ultra densa de longitud de onda (UDWDM) que permite distribuir un gran número de canales espaciados solo por unos pocos GHz. Este enfoque permite vislumbrar el concepto de longitud de onda para el usuario, donde cada cliente puede usar enlaces de ancho de banda dedicados. Las tecnologías clave están basadas en los sistemas coherentes, con selectividad de longitud de onda inherente y sensibilidad mejorada en comparación con los sistemas de detección directa, gracias al efecto de amplificación óptica de un láser oscilador local (LO) sintonizable. Debido a que el costo es la principal restricción en las redes de acceso, especialmente del equipo en las instalaciones del cliente (unidad de red óptica - ONU), en ésta tesis, una nueva clase de transceptores coherentes, basados en láseres de bajo coste modulados directamente y esquemas de recepción simplificados, son propuestos y probados experimentalmente. Además, el problema de la coexistencia es investigado a través de estudios teóricos y experimentos en tiempo real, demostrando compatibilidad total con los sistemas heredados. Entre las soluciones propuestas, se presenta una técnica simple para ajustar digitalmente la modulación de fase directa de un láser de retroalimentación distribuida (DFB), y admitir velocidades de transmisión flexibles. Acto seguido, se comparan experimentalmente varios formatos multinivel de modulación de fase, para lograr tasas de transmisión más altas y una mejor eficiencia espectral. Posteriormente, se aborda el tema de la integración fotónica, demostrando por primera vez un transmisor (Tx) con modulación híbrida de fase y amplitud de ocho puntos, mediante el uso de un dispositivo pequeño, de bajo coste y eficiente energéticamente, como lo es el láser dual de electro-absorción modulada (DEML). Finalmente, se presentan dos propuestas novedosas para reducir la complejidad de la detección heterodina e intradina, afrontando el problema típico de la complejidad y alto coste de los sistemas coherentes. La primera explora la posibilidad de usar solo un láser DFB en la ONU, como LO y Tx. La segunda, demuestra por primera vez, una nueva técnica de diversidad fase en el tiempo, que alterna la modulación de fase en cada componente del plano complejo (fase-I y cuadratura-Q) logrando una transmisión de 10 Gb / s / λ con independencia de polarizació

High Speed Turbo Tcm Ofdm For Uwb And Powerline System

Turbo Trellis-Coded Modulation (TTCM) is an attractive scheme for higher data rate transmission, since it combines the impressive near Shannon limit error correcting ability of turbo codes with the high spectral efficiency property of TCM codes. We build a punctured parity-concatenated trellis codes in which a TCM code is used as the inner code and a simple parity-check code is used as the outer code. It can be constructed by simple repetition, interleavers, and TCM and functions as standard TTCM but with much lower complexity regarding real world implementation. An iterative bit MAP decoding algorithm is associated with the coding scheme. Orthogonal Frequency Division Multiplexing (OFDM) modulation has been a promising solution for efficiently capturing multipath energy in highly dispersive channels and delivering high data rate transmission. One of UWB proposals in IEEE P802.15 WPAN project is to use multi-band OFDM system and punctured convolutional codes for UWB channels supporting data rate up to 480Mb/s. The HomePlug Networking system using the medium of power line wiring also selects OFDM as the modulation scheme due to its inherent adaptability in the presence of frequency selective channels, its resilience to jammer signals, and its robustness to impulsive noise in power line channel. The main idea behind OFDM is to split the transmitted data sequence into N parallel sequences of symbols and transmit on different frequencies. This structure has the particularity to enable a simple equalization scheme and to resist to multipath propagation channel. However, some carriers can be strongly attenuated. It is then necessary to incorporate a powerful channel encoder, combined with frequency and time interleaving. We examine the possibility of improving the proposed OFDM system over UWB channel and HomePlug powerline channel by using our Turbo TCM with QAM constellation for higher data rate transmission. The study shows that the system can offer much higher spectral efficiency, for example, 1.2 Gbps for OFDM/UWB which is 2.5 times higher than the current standard, and 39 Mbps for OFDM/HomePlug1.0 which is 3 times higher than current standard. We show several essential requirements to achieve high rate such as frequency and time diversifications, multi-level error protection. Results have been confirmed by density evolution. The effect of impulsive noise on TTCM coded OFDM system is also evaluated. A modified iterative bit MAP decoder is provided for channels with impulsive noise with different impulsivity