Channel estimation techniques for filter bank multicarrier based transceivers for next generation of wireless networks

A dissertation submitted to Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering (Electrical and Information Engineering), August 2017The fourth generation (4G) of wireless communication system is designed based on the principles of cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) where the cyclic prefix (CP) is used to combat inter-symbol interference (ISI) and inter-carrier interference (ICI) in order to achieve higher data rates in comparison to the previous generations of wireless networks. Various filter bank multicarrier systems have been considered as potential waveforms for the fast emerging next generation (xG) of wireless networks (especially the fifth generation (5G) networks). Some examples of the considered waveforms are orthogonal frequency division multiplexing with offset quadrature amplitude modulation based filter bank, universal filtered multicarrier (UFMC), bi-orthogonal frequency division multiplexing (BFDM) and generalized frequency division multiplexing (GFDM). In perfect reconstruction (PR) or near perfect reconstruction (NPR) filter bank designs, these aforementioned FBMC waveforms adopt the use of well-designed prototype filters (which are used for designing the synthesis and analysis filter banks) so as to either replace or minimize the CP usage of the 4G networks in order to provide higher spectral efficiencies for the overall increment in data rates. The accurate designing of the FIR low-pass prototype filter in NPR filter banks results in minimal signal distortions thus, making the analysis filter bank a time-reversed version of the corresponding synthesis filter bank. However, in non-perfect reconstruction (Non-PR) the analysis filter bank is not directly a time-reversed version of the corresponding synthesis filter bank as the prototype filter impulse response for this system is formulated (in this dissertation) by the introduction of randomly generated errors. Hence, aliasing and amplitude distortions are more prominent for Non-PR. Channel estimation (CE) is used to predict the behaviour of the frequency selective channel and is usually adopted to ensure excellent reconstruction of the transmitted symbols. These techniques can be broadly classified as pilot based, semi-blind and blind channel estimation schemes. In this dissertation, two linear pilot based CE techniques namely the least square (LS) and linear minimum mean square error (LMMSE), and three adaptive channel estimation schemes namely least mean square (LMS), normalized least mean square (NLMS) and recursive least square (RLS) are presented, analyzed and documented. These are implemented while exploiting the near orthogonality properties of offset quadrature amplitude modulation (OQAM) to mitigate the effects of interference for two filter bank waveforms (i.e. OFDM/OQAM and GFDM/OQAM) for the next generation of wireless networks assuming conditions of both NPR and Non-PR in slow and fast frequency selective Rayleigh fading channel. Results obtained from the computer simulations carried out showed that the channel estimation schemes performed better in an NPR filter bank system as compared with Non-PR filter banks. The low performance of Non-PR system is due to the amplitude distortion and aliasing introduced from the random errors generated in the system that is used to design its prototype filters. It can be concluded that RLS, NLMS, LMS, LMMSE and LS channel estimation schemes offered the best normalized mean square error (NMSE) and bit error rate (BER) performances (in decreasing order) for both waveforms assuming both NPR and Non-PR filter banks. Keywords: Channel estimation, Filter bank, OFDM/OQAM, GFDM/OQAM, NPR, Non-PR, 5G, Frequency selective channel.CK201

Waveform Design for 5G and beyond Systems

5G traffic has very diverse requirements with respect to data rate, delay, and reliability. The concept of using multiple OFDM numerologies adopted in the 5G NR standard will likely meet these multiple requirements to some extent. However, the traffic is radically accruing different characteristics and requirements when compared with the initial stage of 5G, which focused mainly on high-speed multimedia data applications. For instance, applications such as vehicular communications and robotics control require a highly reliable and ultra-low delay. In addition, various emerging M2M applications have sparse traffic with a small amount of data to be delivered. The state-of-the-art OFDM technique has some limitations when addressing the aforementioned requirements at the same time. Meanwhile, numerous waveform alternatives, such as FBMC, GFDM, and UFMC, have been explored. They also have their own pros and cons due to their intrinsic waveform properties. Hence, it is the opportune moment to come up with modification/variations/combinations to the aforementioned techniques or a new waveform design for 5G systems and beyond. The aim of this Special Issue is to provide the latest research and advances in the field of waveform design for 5G systems and beyond

Spectrum Optimisation in Wireless Communication Systems: Technology Evaluation, System Design and Practical Implementation

Two key technology enablers for next generation networks are examined in this thesis, namely Cognitive Radio (CR) and Spectrally Efficient Frequency Division Multiplexing (SEFDM). The first part proposes the use of traffic prediction in CR systems to improve the Quality of Service (QoS) for CR users. A framework is presented which allows CR users to capture a frequency slot in an idle licensed channel occupied by primary users. This is achieved by using CR to sense and select target spectrum bands combined with traffic prediction to determine the optimum channel-sensing order. The latter part of this thesis considers the design, practical implementation and performance evaluation of SEFDM. The key challenge that arises in SEFDM is the self-created interference which complicates the design of receiver architectures. Previous work has focused on the development of sophisticated detection algorithms, however, these suffer from an impractical computational complexity. Consequently, the aim of this work is two-fold; first, to reduce the complexity of existing algorithms to make them better-suited for application in the real world; second, to develop hardware prototypes to assess the feasibility of employing SEFDM in practical systems. The impact of oversampling and fixed-point effects on the performance of SEFDM is initially determined, followed by the design and implementation of linear detection techniques using Field Programmable Gate Arrays (FPGAs). The performance of these FPGA based linear receivers is evaluated in terms of throughput, resource utilisation and Bit Error Rate (BER). Finally, variants of the Sphere Decoding (SD) algorithm are investigated to ameliorate the error performance of SEFDM systems with targeted reduction in complexity. The Fixed SD (FSD) algorithm is implemented on a Digital Signal Processor (DSP) to measure its computational complexity. Modified sorting and decomposition strategies are then applied to this FSD algorithm offering trade-offs between execution speed and BER

Diseño de arquitecturas eficientes basadas en dispositivos lógicos programables para técnicas de acceso al medio en comunicaciones PLC

En el trabajo propuesto en esta tesis se han estudiado, analizado y desarrollado nuevas arquitecturas para la implementación de técnicas de acceso al medio en comunicaciones PLC de banda ancha. Estas arquitecturas se han incluido como periféricos avanzados en un sistema SoC general basado en FPGAs que integra un microprocesador soft encargado de realizar la supervisión del sistema y la gestión de las transferencias de datos. Además, la arquitectura SoC general dispone de un módulo DMA que asegura el flujo de datos necesario para cada técnica de acceso al medio, permitiendo que todo el sistema opere en tiempo real, atendiendo a los requisitos del estándar de PLC de banda ancha. Para la definición de las distintas arquitecturas, se ha realizado un exhaustivo estudio de las técnicas de acceso al medio consideradas. Dentro de este estudio se ha efectuado un análisis de distintos algoritmos para su implementación, evaluándose las opciones más idóneas en cada caso. El análisis de distintas alternativas ha permitido obtener una arquitectura con un bajo consumo de recursos y que a su vez disponga de un tiempo de cómputo que permita la implementación en tiempo real. Esto se ha conseguido con el ratio de paralelismo, el cual ha permitido una reutilización a lo largo del tiempo de los recursos implicados, obteniéndose un compromiso entre tiempo de procesamiento y recursos empleados. Asimismo, dado que las arquitecturas se van a implantar sobre un dispositivo FPGA, es necesario considerar en todo este estudio el efecto de la precisión finita, ya que es determinante a la hora de obtener unas prestaciones adecuadas. Para ello, se ha tenido en especial consideración el dispositivo en el que se iba a realizar la implementación, utilizando el ancho de palabra máximo de las celdas aritméticas y de las memorias disponibles. Para la comprobación de la calidad de las arquitecturas diseñadas se han desarrollado modelos de simulación en coma flotante y en coma fija. La utilización de modelos de simulación permite realizar análisis cuantitativo del efecto de la precisión finita y a su vez comprobar que la implementación desarrollada es correcta. Tanto los modelos de simulación, como las posteriores pruebas experimentales, han sido evaluados en distintas escenarios prácticos, permitiendo una verificación precisa de los datos obtenidos y su corroboración con los resultados simulados. Los escenarios considerados han tenido en cuenta distintos tipos de canales de transmisión, incrementando el nivel de ruido y atenuación gradualmente. En el primer caso se ha empleado un canal ideal, que ha permitido realizar un estudio del efecto de la precisión finita sobre las arquitecturas propuestas. En el segundo caso se ha empleado un cable SMA como canal de transmisión. El cable SMA presenta una buena respuesta en frecuencia y por tanto se puede comparar la calidad de las arquitecturas en un sistema de transmisión completo, cuyo canal se aproxima al ideal. Por último, el tercer caso introduce un canal más agresivo formado por un cable eléctrico de doce metros. Con este canal se ha realizado una estimación del comportamiento de la técnica de acceso al medio en un canal similar al real sin el empleo de ningún módulo de estimación e igualación de canal