Esquemas de pré-codificação IA com IB-DFE para sistemas MC-CDMA

Mestrado em Engenharia Eletrónica e TelecomunicaçõesTo achieve high bit rates, needed to meet the quality of service requirements of future multimedia applications, multi-carrier code division multiple access (MC-CDMA) has been considered as a candidate air-interface. Interference alignment (IA) is a promising technique that allows high capacity gains in interfering channels. On the other hand, iterative block decision feedback equalization (IB-DFE) based receivers can efficiently exploit the inherent space-frequency diversity of the MIMO MC-CDMA systems. In this thesis we proposed an IA precoding at the transmitter with IB-DFE based processing at the receiver for MC-CDMA systems. The IA precoding is applied at chip level instead of the data symbols level, as in the conventional IA based systems. The receiver is designed in two steps: first the equalizers based on zero forcing (ZF) or minimum mean square error (MMSE) are used to remove the aligned users´ interference. Then and after a whitening noise process, an IB-DFE based equalizer is designed to remove both the residual inter-user aligned and inter-carrier interferences. The results have shown that the obtained performance is very close to the one obtained by the optimal matched filter, with few iterations at the receiver side.Para atingir maiores ritmos de transmissão, as futures aplicações multimédia necessitam de atingir a qualidade de serviço necessária. Para isso, o multi-carrier code division multiple access (MC-CDMA) tem sido apontado como um forte candidato para interface ar dos futuros sistemas celulares. O Interference Alignment (IA) ou alinhamento de interferência é uma técnica promissora que permite ter altos ganhos de capacidade em canais com interferência. Por outro lado, temos receptores baseados no conceito iterative block decision feedback equalization(IB-DFE) que conseguem tirar partido, de uma forma eficiente, da inerente diversidade espaço-frequência dos sistemas MIMO MC-CDMA. Nesta dissertação é implementada uma pré-codificação baseada no conceito de IA considerando três transmissores (ou estações base) juntamente, com um processamento IB-DFE no receptor para sistemas MC-CDMA.A pré-codificação é aplicada ao nível de chip em vez de ser aplicado ao nível dos dados. O receptor é projectado em dois passos: em primeiro lugar equalizadores baseados em ZF ou em MMSE são utilizados para remover a interferência alinhada dos restantes utilizadores. De seguida, e após aplicar um processo de branqueamento do ruído ao sinal à saída do primeiro equalizador, um segundo equalizador baseado em IB-DFE é projectado para remover a interferência inter-utilizador residual e também a interferência residual entre portadoras. Os resultados obtidos mostraram-se satisfatórios na remoção da interferência obtendo-se um desempenho muito próximo do obtido considerando um filtro adaptado

Implementação de um sistema de comunicações móveis para o Uplink

Mestrado em Engenharia Electrónica e TelecomunicaçõesÉ evidente que actualmente cada vez mais a internet móvel está presente na vida das sociedades. Hoje em dia é relativamente fácil estar ligado à internet sempre que se quiser, independentemente do lugar onde se encontra (conceito: anytime and anywhere). Desta forma existe um número crescente de utilizadores que acedem a serviços e aplicações interactivas a partir dos seus terminais móveis. Há, portanto, uma necessidade de adaptar o mundo das telecomunicações a esta nova realidade, para isso é necessário implementar novas arquitecturas que sejam capazes de fornecer maior largura de banda e reduzir os atrasos das comunicações, maximizando a utilização dos recursos disponíveis do meio/rede e melhorando assim a experiência do utilizador final. O LTE representa uma das tecnologias mais avançadas e de maior relevância para o acesso sem fios em banda larga de redes celulares. OFDM é a tecnologia base que está por traz da técnica de modulação, bem como as tecnologias adjacentes, OFDMA e SC-FDMA, usadas especificamente no LTE para a comunicação de dados descendente (downlink) ou ascendente (uplink), respectivamente. A implementação de múltiplas antenas em ambos os terminais, potenciam ainda mais o aumento da eficiência espectral do meio rádio permitindo atingir grandes taxas de transmissão de dados. Nesta dissertação é feito o estudo, implementação e avaliação do desempenho da camada física (camada 1 do modelo OSI) do LTE, no entanto o foco será a comunicação de dados ascendente e a respectiva técnica de modelação, SC-FDMA. Foi implementada uma plataforma de simulação baseada nas especificações do LTE UL onde foram considerandos diferentes esquemas de antenas. Particularmente para o esquema MIMO, usou-se a técnica de codificação no espaço-frequência proposta por Alamouti. Foram também implementados vários equalizadores. Os resultados provenientes da simulação demonstram tanto a eficiência dos diversos modos de operação em termos da taxa de erro, como o excelente funcionamento de processos de mapeamento e equalização, que visam melhorar a taxa de recepção de dados.It is clear that mobile Internet is present in the life of societies. Nowadays it is relatively easy to be connected to the internet whenever you want, no matter where you are (concept: anytime and anywhere). Thus, there are a growing number of users accessing interactive services and applications from their handsets. Therefore, there is a need to adapt the world of telecommunications to this new reality, for that it is necessary to implement new architectures that are able to provide higher bandwidth and reduce communication delays, maximizing use of available resources in the medium/network and thereby improving end-user experience. LTE represents one of the most advanced architectures and most relevant to wireless broadband cellular networks. OFDM is the technology that is behind the modulation technique and the underlying technologies, OFDMA and SCFDMA, used specifically in LTE for data communication downward (downlink) or upward (uplink), respectively. The implementation of multiple antennas at both ends further potentiate the increase of spectral efficiency allowing to achieve high rates of data transmission. In this dissertation is done the study, implementation and performance evaluation of the physical layer (OSI Layer 1) of the LTE, but the focus will be communication and its upstream data modeling technique, SC-FDMA. We implemented a simulation platform based on LTE UL specifications where were considered different antenna schemes. Particularly for the MIMO scheme, we used the technique of space-frequency coding proposed by Alamouti. We also implemented several equalizers. The results from the simulation demonstrate both the efficiency of different modes of operation in terms of error rate, as the excellent operation of mapping processes and equalization, designed to improve the rate of receiving data

LTE-verkon suorituskyvyn parantaminen CDMA2000:sta LTE:hen tehdyn muutoksen jälkeen

CDMA2000 technology has been widely used on 450 MHz band. Recently the equipment availability and improved performance offered by LTE has started driving the operators to migrate their networks from CDMA2000 to LTE. The migration may cause the network performance to be in suboptimal state. This thesis presents four methods to positively influence LTE network performance after CDMA2000 to LTE migration, especially on 450 MHz band. Furthermore, three of the four presented methods are evaluated in a live network. The measured three methods were cyclic prefix length, handover parameter optimization and uplink coordinated multipoint (CoMP) transmission. The objective was to determine the effectiveness of each method. The research methods included field measurements and network KPI collection. The results show that normal cyclic prefix length is enough for LTE450 although the cell radius may be up to 50km. Only special cases exist where cyclic prefix should be extended. Operators should consider solving such problems individually instead of widely implementing extended cyclic prefix. Handover parameter optimization turned out to be an important point of attention after CDMA2000 to LTE migration. It was observed that if the handover parameters are not concerned, significant amount of unnecessary handovers may happen. It was evaluated that about 50% of the handovers in the network were unnecessary in the initial situation. By adjusting the handover parameter values 47,28 % of the handovers per user were removed and no negative effects were detected. Coordinated multipoint transmission has been widely discussed to be an effective way to improve LTE network performance, especially at the cell edges. Many challenges must be overcome before it can be applied to downlink. Also, implementing it to function between cells in different eNBs involve challenges. Thus, only intra-site uplink CoMP transmission was tested. The results show that the performance improvements were significant at the cell edges as theory predicted.CDMA2000 teknologiaa on laajalti käytetty 450 MHz:n taajuusalueella. Viime aikoina LTE:n tarjoamat halvemmat laitteistot ja parempi suorituskyky ovat kannustaneet operaattoreita muuttamaan verkkoaan CDMA2000:sta LTE:hen. Kyseinen muutos saattaa johtaa epäoptimaaliseen tilaan verkon suorituskyvyn kannalta. Tämä työ esittelee neljä menetelmää, joilla voidaan positiivisesti vaikuttaa LTE-verkon suorituskykyyn CDMA2000:ste LTE:hen tehdyn muutoksen jälkeen erityisesti 450 MHz:n taajuusalueella. Kolmea näistä menetelmistä arvioidaan tuotantoverkossa. Nämä kolme menetelmää ovat suojavälin pituus, solunvaihtoparametrien optimointi ja ylälinkin koordinoitu monipistetiedonsiirto. Tavoite oli määrittää kunkin menetelmän vaikutus. Tutkimusmenetelmiin kuului kenttämittaukset ja verkon suorituskykymittareiden analyysi. Tutkimustulosten perusteella voidaan sanoa, että normaali suojaväli on riittävän pitkä LTE450:lle vaikka solujen säde on jopa 50km. Vain erikoistapauksissa tarvitaan pidennettyä suojaväliä. Operaattoreiden tulisi ratkaista tällaiset tapaukset yksilöllisesti sen sijaan, että koko verkossa käytettäisiin pidennettyä suojaväliä. Solunvaihtoparametrien optimointi osoittautui tärkeäksi huomion aiheeksi CDMA2000:sta LTE:hen tehdyn muutoksen jälkeen. Turhia solunvaihtoja saattaa tapahtua merkittäviä määriä, mikäli parametreihin ei kiinnitetä huomiota. Lähtötilanteessa noin 50 % testiverkon solunvaihdoista arvioitiin olevan turhia. Solunvaihtoparametreja muuttamalla 47,28 % solunvaihdoista per käyttäjä saatiin poistettua ilman, että mitään haittavaikutuksia olisi huomattu. Koordinoidun monipistetiedonsiirron on laajalti sanottu olevan tehokas tapa parantaa LTE-verkon suorituskykyä, etenkin solujen reunoilla. Monia haasteita pitää ratkaista, enne kuin sitä voidaan käyttää alalinkin tiedonsiirtoon. Lisäksi sen käyttöön eri tukiasemien solujen välillä liittyy haasteita. Tästä syystä monipistetiedonsiirtoa voitiin testata vain ylälinkin suuntaan ja vain yhden tukiaseman välisten solujen kesken. Tulokset osoittivat, että suorituskyky parani merkittävästi solun reunalla

A General Framework for Analyzing, Characterizing, and Implementing Spectrally Modulated, Spectrally Encoded Signals

Fourth generation (4G) communications will support many capabilities while providing universal, high speed access. One potential enabler for these capabilities is software defined radio (SDR). When controlled by cognitive radio (CR) principles, the required waveform diversity is achieved via a synergistic union called CR-based SDR. Research is rapidly progressing in SDR hardware and software venues, but current CR-based SDR research lacks the theoretical foundation and analytic framework to permit efficient implementation. This limitation is addressed here by introducing a general framework for analyzing, characterizing, and implementing spectrally modulated, spectrally encoded (SMSE) signals within CR-based SDR architectures. Given orthogonal frequency division multiplexing (OFDM) is a 4G candidate signal, OFDM-based signals are collectively classified as SMSE since modulation and encoding are spectrally applied. The proposed framework provides analytic commonality and unification of SMSE signals. Applicability is first shown for candidate 4G signals, and resultant analytic expressions agree with published results. Implementability is then demonstrated in multiple coexistence scenarios via modeling and simulation to reinforce practical utility

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

Evaluation of fourth generation air-interfaces for mobile communications

Abstract Development of the Fourth Generation of mobile communication systems, or 4G, has already begun in various organizations and research institutions worldwide. There is currently no single conclusive definition for 4G systems, and the process of 4G standardization will only begin after the World Radiocommunication Conference in 2007. The purpose of this report is to provide an objective definition of 4G systems based on user requirements, and to use this definition to determine an appropriate 4G access network architecture. By examining the current trends in user requirements, and the methodologies proposed by different researchers, an objective definition of 4G systems was developed. The definition states that the purpose of 4G systems is to provide users with the capacity to access any service at any time at a reasonable cost and at the required levels of quality. There are two developmental methodologies which are currently being considered to achieve this objective: first the evolution and convergence of existing systems, including cellular, IT and broadcasting communication systems, and second, the development of a new 4G access network capable of providing users with access to advanced services. The primary specification for this new access network is that it must provide a throughput of 1 Mbps for mobile users and 1 Gbps for users that are stationary. Other requirements include high spectral efficiency and high capacity and coverage. The primary focus of this report is the examination of the second of the above methodologies by evaluating the performance of candidate 4G air-interface architectures so that a recommendation could be made as to which of the architectures is the preferred choice as the core component in a new 4G access network. Orthogonal Frequency Division Multiplexing (OFDM) modulation is a high performance modulation technique capable of achieving high levels of spectral efficiency and is widely accepted as the technique most capable of meeting 4G access network requirements. There are two primary access network architectures that make use of OFDM modulation and could form the core components of a 4G air-interface, the physical component of a 4G access network. To determine which architecture is the appropriate choice for 4G systems, a series of simulations were run using realistic models of a wireless environment. The results of those simulations were analyzed, and it was determined that, due to the absence of multiple access interference found in MC-CDMA, OFDMA systems better met the defined requirements for a 4G air-interface. The use of additional techniques such as radio resource management, multi-antennae technologies and software defined radios are cited as potential methods for improving both OFDMA and MC-CDMA performance

Performance study of air interface for broadband wireless packet access

Ph.DDOCTOR OF PHILOSOPH

Power control for WCDMA

This project tries to introduce itself in the physical implementations that make possible the denominated third generation mobile technology. As well as to know the technology kind that makes possible, for example, a video-call in real time. During this project, the different phases passed from the election of WCDMA like the access method for UMTS will appear. Its coexistence with previous network GSM will be analyzed, where the compatibility between systems has been one of the most important aspects in the development of WCDMA, the involved standardization organisms in the process, as well as the different protocols that make the mobile communications within a network UTRAN possible. Special emphasis during the study of the great contribution that has offered WCDMA with respect to the control of power of the existing signals will be made. The future lines that are considered in the present, and other comment that already are in their last phase of development in the field of the mobile technology. UMTS through WCDMA can be summarized like a revolution of the air interface accompanied by a revolution in the network of their architecture

Técnicas de processamento com múltiplas antenas para o sistema LTE

Mestrado em Engenharia Electrónica e TelecomunicaçõesPerformance, mobilidade e partilha podem ser consideras como as três palavras-chave nas comunicações móveis de hoje em dia. Uma das necessidades fundamentais do ser humano é a partilha de experiencias e informação. Com a evolução ao nível do hardware móvel, a crescente popularidade de smartphones, tablets e outros dispositivos moveis, fez com que a exigência em termos de capacidade e taxa de transferência por parte das redes móveis não parasse de crescer. As limitações das redes 3G fizeram com que não conseguissem corresponder a tais exigências e como tal, a transição para uma tecnologia mais robusta e eficiente passou a ser inevitável. A resposta escolhida como solução a longo prazo é a rede designada por LTE, desenvolvida pela organização 3GPP é assumido que será a rede de telecomunicações predominante no futuro. As vantagens mais sonantes são, naturalmente, elevadas taxas de transmissão, maior eficiência espectral, redução da latência e de custos de operação. As principais tecnologias em que o LTE se baseia, são o OFDM e sua variante para múltiplo acesso, OFDMA, usado para o downlink e o SC-FDMA para o uplink. Além disso, usa sistemas com múltiplas antenas para impulsionar a eficiência espectral. Apesar de já implementado em alguns países por diversas operadoras, constantes pesquisas continuam a ser realizadas com o intuito de melhorar a sua performance. Nesta dissertação é proposto um esquema duplo de codificação na frequência e no espaço (D-SFBC) para um cenário baseado em OFDM com 4 antenas de transmissão e duas antenas de recepção (4 × 2 D-SFBC) para o downlink. No cenário considerado, 4 símbolos de dados são transmitidos utilizando unicamente 2 sub-portadoras, fazendo com que, este sistema seja limitado pela interferência. Para de forma eficiente descodificar os símbolos de dados transmitidos, foi desenvolvido um equalizador iterativo no domínio da frequência. Duas abordagens são consideradas: cancelamento da interferência em paralelo (PIC) e sucessivo cancelamento de interferência (SIC). Uma vez que apenas 2 sub-portadoras são usadas para transmitir quatro símbolos de dados em paralelo, o esquema desenvolvido duplica a taxa de dados quando comparado com o esquema 2 × 2 SFBC, especificado no standard do LTE. Os esquemas desenvolvidos foram avaliados sob as especificações para LTE e usando codificação de canal. Os resultados mostram que os esquemas implementados neste trabalho utilizando um equalizador iterativo supera os convencionais equalizadores lineares na eliminação da interferência adicional introduzida, em apenas 2 ou 3 iterações.Performance, mobility and sharing can be assumed as the three keywords in the mobile communications nowadays. One of the fundamental needs of human beings is to share experiences and information. With the evolution of mobile hardware level, the growing popularity of smartphones, tablets and other mobile devices, has made that the demand in terms of capacity and throughput by mobile networks did not stop growing. Thus, the limitations of 3G stops it of being the answer of such demand, and a transition to a powerful technology has become unavoidable. The answer chosen is LTE, developed by the 3GPP organization is assumed to be the predominant telecommunications network in the future. The most relevant advantages are high transmission rates, higher spectral efficiency, reducing latency and operating costs. The key technologies in which LTE is based, are OFDM and its variant schemes for multiple access, OFDMA, used for downlink, and SC-FDMA for the uplink. It also uses multiple antennas systems in order to improve spectral efficiency. Although already implemented in some countries by several operators, continuous research is conducted in order to improve their performance. In this dissertation it is proposed a double space-frequency block coding (D-SFBC) scheme for an OFDM based scenario with 4 transmit antennas and 2 receive antennas (4×2 D-SFBC) for the downlink. In the considered scenario, 4 data symbols are transmitted by using only 2 subcarriers and thus the system is interference limited. To efficiently decode the transmitted data symbols an iterative equalizer designed in frequency domain is developed. Two approaches are considered: parallel interference cancellation (PIC) and successive interference cancellation (SIC). Since only 2 subcarriers are used to transmit 4 data symbols in parallel the developed scheme achieve the double data rate when compared with the 2×2 SFBC, specified in the LTE standard. The developed schemes were evaluated under the main LTE specifications and using channel coding. The results have show that the schemes implemented in this work using an interactive equalizer outperforms the conventional linear equalizers in the interference removal, just by using 2 or 3 iterations