Performance Analysis of Multicarrier Code Division Multiple Access (MC-CDMA) Systems

A thesis presented to the faculty of the College of Science and Technology at Morehead State University in partial fulfillment of the requirements for the Degree of Master of Science by Pravinkumar Patil on August 11, 2008

Performance of extended space-time coding techniques for MIMO MC-CDMA systems

In this paper we consider a transmission system based on MC-CDMA, where signal spreading is performed entirely in the frequency domain. An extended spacetime coding technique, the Double Alamouti, is evaluated considering a MIMO channel. This assessment is made against standard Alamouti coding, for two different Tx/Rx antenna schemes (2x1 and 2x2). Numerical results, attained through system model simulations, are presented for performance evaluation under realistic scenarios considering some typical system impairments. These results show that in practical systems significant improvements can be achieved by using the Double Alamouti coding scheme

Multicarrier communication systems with low sensibility to nonlinear amplification

Actualment estem entrant a una nova era de la informació amb gran demanda de sistemes de comunicació sense fils. Nous serveis com dades i video requereixen transmissions fiables d'alta velocitat, fins i tot en escenaris d'alta mobilitat. A més a més, la dificultat d'assignar el limitat espectre radioelèctric juntament amb la necessitat d'incrementar el temps de vida de les bateries dels terminals mòbils, requereix el diseny de transceptors que usin la potència i l'ampla de banda disponibles de manera eficient. Les comunicacions multiportadora basades en OFDM són capaces de satisfer la majoria d'aquests requeriments. Però, entre altres reptes, reduir la sensibilitat a la amplificació no-lineal és un factor clau durant el diseny. En aquesta tesi doctoral s'analitza la sensibilitat dels sistemes multiportadora basats en OFDM a l'amplificació no-lineal i es consideren formes eficients per superar aquest problema. La tesi s'enfoca principalment al problema de reduir les fluctuacions de l'envolupant del senyal transmès. En aquest sentit es presenta també un estudi de les mètriques de l'envolupant del senyal, PAPR i CM. A més a més, basant-nos en l'anàlisis presentat es proposen noves tècniques per sistemes OFDM i MC-SS. Per MC-SS, també es tracta el diseny d'una tècnica de postprocessament en forma de detector multiusuari per canals no-lineals.Actualmente estamos entrando en una nueva era de la información donde se da una gran demanda de sistemas de comunicación inalámbricos. Nuevos servicios como datos y vídeo requieren transmisiones fiables de alta velocidad, incluso en escenarios de alta movilidad. Además, la dificultad de asignar el limitado espectro radioeléctrico junto con la necesidad de incrementar el tiempo de vida de las baterías de los terminales móviles, requiere el diseño de transceptores que usen eficientemente la potencia y el ancho de banda disponibles. Las comunicaciones multiportadora basadas en OFDM son capaces de satisfacer la mayoría de dichos requerimientos. Sin embargo, entre otros retos, reducir su sensibilidad a la amplificación no-lineal es un factor clave durante el diseño. En esta tesis se analiza la sensibilidad de los sistemas multiportadora basados en OFDM a la amplificación no-lineal y se consideran formas eficientes para superar dicho problema. La tesis se enfoca principalmente al problema de reducir las fluctuaciones de la envolvente. En este sentido también se presenta un estudio de las métricas de la señal, PAPR y CM. Además, basándonos en el análisis presentado se proponen nuevas técnicas para OFDM y MC-SS. Para MC-SS, también se trata el diseño de un detector multiusuario para canales no-lineales.We are now facing a new information age with high demand of wireless communication systems. New services such as data and video require achieving reliable high-speed transmissions even in high mobility scenarios. Moreover, the difficulty to allocate so many wireless communication systems in the limited frequency band in addition to the demand for long battery life requires designing spectrum and power efficient transceivers. Multicarrier communications based on OFDM are known to fulfill most of the requirements of such systems. However, among other challenges, reducing the sensitivity to nonlinear amplification has become a design key. In this thesis the sensitivity of OFDM-based multicarrier systems to nonlinear amplification is analyzed and efficient ways to overcome this problem are considered. The focus is mainly on the problem of reducing the envelope fluctuations. Therefore, a study of the signal metrics, namely PAPR and CM, is also presented. From the presented analysis, several new techniques for OFDM and MC-SS are proposed. For MC-SS, the design of a post-processing technique in the form of a multiuser detector for nonlinearly distorted MC-SS symbols is also addressed

Identification of Technologies for Provision of Future Aeronautical Communications

This report describes the process, findings, and recommendations of the second of three phases of the Future Communications Study (FCS) technology investigation conducted by NASA Glenn Research Center and ITT Advanced Engineering & Sciences Division for the Federal Aviation Administration (FAA). The FCS is a collaborative research effort between the FAA and Eurocontrol to address frequency congestion and spectrum depletion for safety critical airground communications. The goal of the technology investigation is to identify technologies that can support the longterm aeronautical mobile communication operating concept. A derived set of evaluation criteria traceable to the operating concept document is presented. An adaptation of the analytical hierarchy process is described and recommended for selecting candidates for detailed evaluation. Evaluations of a subset of technologies brought forward from the prescreening process are provided. Five of those are identified as candidates with the highest potential for continental airspace solutions in L-band (P-34, W-CDMA, LDL, B-VHF, and E-TDMA). Additional technologies are identified as best performers in the unique environments of remote/oceanic airspace in the satellite bands (Inmarsat SBB and a custom satellite solution) and the airport flight domain in C-band (802.16e). Details of the evaluation criteria, channel models, and the technology evaluations are provided in appendixes

Effect of amplifier non-linearity on the performance of CDMA communication systems in a Rayleigh fading environment

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.The effect of amplifier non-linearity on the performance of a CDMA communications syste

Pré-codificação e equalização para sistemas SC-FDMA heterogéneos

Mestrado em Engenharia Electrónica e TelecomunicaçõesMobile traffic in cellular networks is increasing exponentially. Small-cells are considered as a key solution to meet these requirements. Under the same spectrum the small-cells and the associated macro-cell (forming the so called heterogeneous systems) must cooperate so that one system can adapt to the other. If no cooperation is considered then the small-cells will generate harmful interference at the macro-cell. Interference alignment (IA) is a precoding technique that is able to achieve the maximum degrees of freedom of the interference channel, and can efficiently deal with inter-systems interference. Single carrier frequency division multiple access (SC-FDMA) is a promising solution technique for high data rate uplink communications in future cellular systems. Conventional linear equalizers are not efficient to remove the residual inter-carrier interference of the SC-FDMA systems. For this reason, there has been significant interest in the design of nonlinear frequency domain equalizers in general and decision feedback equalizers in particular, with the iterative block decision feedback equalizer (IB-DFE) being the most promising nonlinear equalizer. In this dissertation we propose and evaluate joint interference alignment precoding at the small cell user terminals with iterative non-linear frequency domain equalizer at the receivers (macro base station and central unit) for SC-FDMA based heterogeneous networks. The small-cell precoders are designed by enforcing that all generated interference at the macro-cell is aligned in an orthogonal subspace to the macro-cell received signal subspace. This enforces that no performance degradation is observed at the macro cell. Then, we design an iterative nonlinear frequency domain equalizer at the macro-cell receiver that is able to recover the macro-cell spatial streams, in the presence of both small-cell and inter-carrier interferences. The results show that the proposed transmitter and receiver structures are robust to the inter-system interferences and at the same time are able to efficient separate the macro and small cells spatial streams.O trafego móvel nas redes celulares tem aumentado exponencialmente. As pico- células são consideradas como a solução chave para cumprir estes requisitos. Dentro do mesmo espectro, as pico-células e as macro-células (formando os chamados sistemas heterogéneos) precisam de colaborar de modo a que um sistema possa adaptar-se ao outro. Se não for considerada a cooperação, então as pico-células irão gerar interferência prejudicial na macro-célula. Interference alignment (IA) é uma técnica de précodificação que é capaz de atingir o grau máximo de liberdade do canal de interferência, e consegue lidar eficazmente com interferência entre sistemas. Single carrier frequency division multiple access (SC-FDMA) é uma solução técnica promissora para transmissão de dados em uplink, para sistemas celulares futuros. Equalizadores lineares convencionais não são eficientes a remover a interferência residual entre portadoras dos sistemas SC-FDMA. Por este motivo, tem havido interesse significativo no desenho de equalizadores não lineares no domínio da frequência em geral e em equalizadores baseados em decisão por feedback em particular, tendo o iterative block decision feedback equalizer (IB-DFE) como o equalizador não linear mais promissor. Nesta dissertação propomos e avaliamos précodificação de alinhamento de interferência nos terminais das pico-células em conjunto com equalizadores não lineares no domínio da frequência nos recetores (estação base da macro-célula e unidade central de processamento) para redes heterogéneas baseadas em SC-FDMA. Os précodificadores das pico-células são desenhados de maneira a obrigar a que toda a interferência gerada na macro-célula esteja alinhada num subespaço ortogonal em relação ao subespaço do sinal recebido na macro- célula. Isto obriga a que não seja observada degradação de desempenho na macro-célula. Em seguida, desenhamos um equalizador não linear no domínio da frequência no recetor da macro-célula capaz de recuperar os fluxos de dados da macro-célula, na presença de interferência tanto entre portadoras como das pico-células. Os resultados mostram que as estruturas de transmissão e receção propostas são robustas contra a interferência entre sistemas e ao mesmo tempo capaz de separar eficientemente os dados da macro e das pico células

Time diversity solutions to cope with lost packets

A dissertation submitted to Departamento de Engenharia Electrotécnica of Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engenharia Electrotécnica e de ComputadoresModern broadband wireless systems require high throughputs and can also have very high Quality-of-Service (QoS) requirements, namely small error rates and short delays. A high spectral efficiency is needed to meet these requirements. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation. An alternative to simple retransmission that can improve both power and spectral efficiency is to combine the signals associated to different transmission attempts. This thesis analyses two time diversity approaches to cope with lost packets that are relatively similar at physical layer but handle different packet loss causes. The first is a lowcomplexity Diversity-Combining (DC) Automatic Repeat reQuest (ARQ) scheme employed in a Time Division Multiple Access (TDMA) architecture, adapted for channels dedicated to a single user. The second is a Network-assisted Diversity Multiple Access (NDMA) scheme, which is a multi-packet detection approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This thesis combines these techniques with Single Carrier with Frequency Division Equalizer (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems. It proposes a new NDMA scheme capable of handling more Mobile Terminals (MTs) than the user separation capacity of the receiver. This thesis also proposes a set of analytical tools that can be used to analyse and optimize the use of these two systems. These tools are then employed to compare both approaches in terms of error rate, throughput and delay performances, and taking the implementation complexity into consideration. Finally, it is shown that both approaches represent viable solutions for future broadband wireless communications complementing each other.Fundação para a Ciência e Tecnologia - PhD grant(SFRH/BD/41515/2007); CTS multi-annual funding project PEst-OE/EEI/UI0066/2011, IT pluri-annual funding project PEst-OE/EEI/LA0008/2011, U-BOAT project PTDC/EEATEL/ 67066/2006, MPSat project PTDC/EEA-TEL/099074/2008 and OPPORTUNISTICCR project PTDC/EEA-TEL/115981/200

Approaching universal frequency reuse through base station cooperation

Base Station (BS) architectures are a promising cellular wireless solution to mitigate the interference issues and to avoid the high frequency reuse factors implemented in conventional systems. Combined with block transmission techniques, such as Orthogonal Frequency-Division Multiplexing (OFDM) for the downlink and Single-Carrier with Frequency-Domain Equalization (SC-FDE) for the uplink, these systems provide a significant performance improvement to the overall system. Block transmission techniques are suitable for broadband wireless communication systems, which have to deal with strongly frequency-selective fading channels and are able to provide high bit rates despite the channel adversities. In BS cooperation schemes users in adjacent cells share the same physical channel and the signals received by each BS are sent to a Central Processing Unit (CPU) that combines the different signals and performs the user detections and/or separation, which can be regarded as a Multi-User Detection (MUD) technique. The work presented in this thesis is focused on the study of uplink transmissions in BS cooperations systems, considering single carrier block transmission schemes and iterative receivers based on the Iterative-Block Decision Feedback Equalization (IB-DFE) concept, which combined with the employment of Cyclic Prefix (CP)-assisted block transmission techniques are appropriate to scenarios with strongly time-dispersive channels. Furthermore, the impact of the sampling and quantization applied to the received signals from each Mobile Terminal (MT) to the corresponding BS is studied, with the achievement of the spectral characterization of the quantization noise. This thesis also provides a conventional analytical model for the BER (Bit Error Rate) performance complemented with an approach to improve its results. Finally, this thesis addresses the contextualization of BS cooperation schemes in clustered C-RAN (Centralized-Radio Access Network)-type solutions.As arquitecturas BS cooperation são uma solução promissora de redes celulares sem fios para atenuar o problema da interferência e evitar os factores de reuso elevados, que se encontram implementados nos sistemas convencionais. Combinadas com técnicas de transmissão por blocos, como o OFDM para o downlink e o SC-FDE no uplink, estes sistemas fornecem uma melhoria significativa no desempenho geral do sistema. Técnicas de transmissão por blocos são adequadas para sistemas de comunicações de banda larga sem fios, que têm que lidar com canais que possuem um forte desvanescimento selectivo na frequência e são capazes de fornecer ligações com taxas de transmissão altas apesar das adversidades do canal. Em esquemas BS cooperation os terminais móveis situados em células adjacentes partilham o mesmo canal físico e os sinais recebidos em cada estação de base são enviados para uma Unidade Central de Processamento (CPU) que combina os diferentes sinais recebidos associados a um dado utilizador e realiza a detecção e/ou separação do mesmo, sendo esta considerada uma técnica de Detecção Multi-Utilizador (MUD). O trabalho apresentado nesta tese concentra o seu estudo no uplink de transmissões em sistemas BS cooperation, considerando transmissões em bloco de esquemas monoportadoras e receptores iterativos baseados no conceito B-DFE, em que quando combinados com a implementação de técnicas de transmissao por blocos assistidas por prefixos cíclicos (CP) são apropriados a cenários com canais fortemente dispersivos no tempo. Além disso, é estudado o impacto do processo de amostragem e quantização aplicados aos sinais recebidos de cada terminal móvel para a estação de base, com a obtenção da caracterização espectral do ruído de quantização. Esta tese também fornece um modelo analítico convencional para a computação do desempenho da taxa de erros de bit (BER), com um método melhorado para o mesmo. Por último, esta tese visa a contextualização dos sistemas BS cooperation em soluções do tipo C-RAN