Frequency shift based multiple access interference canceller for multirate UMTS-TDD systems

Direct Sequence Spread Spectrum (DS-SS) signals exhibit cyclostationary properties which imply a redundancy between frequency components separated by multiples of the symbol rate. In this paper we present a Multiple Access Interference Canceller that explores this property and applies to UMTS-TDD. This frequency domain canceller operates in the spreaded signal in such way that the interference and noise at its output is minimized (Minimum Mean Squared Error Criterium). The performance is evaluated in two con gurations: one including the Frequency Shift Canceller (FSC) and the other concatenated with Parallel Interference Canceller(PIC). The results are benchmarked against the performance of the conventional RAKE detector and the conventional PIC detector

Multi-sensor frequency domain multiple access interference canceller for DS-CDMA systems

Direct sequence code division multiple access (DS-CDMA) signals exhibit cyclostationary properties which imply a redundancy between frequency components separated by multiples of the symbol rate. In this paper a multiple access interference canceller (frequency shift canceller) that explores this property is presented. This linear frequency domain canceller operates on the spread signal in such way that the interference and noise at its output is minimized (minimum mean squared error criterion). The frequency shift canceller (FSC) performance was evaluated for a UMTS-TDD scenario and multi-sensor configurations, where the cases of diversity and beamforming were considered. All these configurations are evaluated concatenated with a parallel interference canceller (PIC-2D). The results are benchmarked against the performance of the conventional RAKE-2D detector, the conventional PIC-2D detector and single user scenario, and we observe considerable performance gains with the FSC especially for the diversity case and a performance close to the single user case when it was evaluated jointly with PIC-2D

Frequency domain equalizer for multirate UMTS-TDD systems

Direct-sequence spread spectrum (DS-SS) signals exhibit cyclostationary properties which imply a redundancy between frequency components separated by multiples of the symbol rate. In this paper we present a multiple access interference canceller that explores this property and applies to UMTS-TDD. This linear frequency domain canceller operates in the spreaded signal in such a way that the interference and noise at its output is minimized (minimum mean squared error criterium). The performance is evaluated in two configurations: one including the frequency shift canceller (FSC) and the other concatenated with parallel interference canceller (PIC). The results are benchmarked against the performance of the conventional RAKE detector and the conventional PIC detector

Técnicas de cancelamento PIC para o sistema UMTS-TDD

Mestrado em Engenharia Electrónica e TelecomunicaçõesO objectivo desta dissertação é estender o conceito das técnicas PIC (Parallel Interference Cancellation) a receptores com agregados de antenas e avaliar o desempenho das diferentes estruturas PIC em vários cenários no sistema UMTS-TDD (Universal Mobile Telecommunication System). Para tal, a dissertação inclui secções de preparação, onde é efectuado uma revisão da evolução das comunicações móveis celulares, de alguns aspectos fundamentais das técnicas de espalhamento de espectro, das especificações do sistema UMTS-TDD relevantes para o trabalho e a nível mais avançado uma síntese das principais técnicas MUD (Multiuser Detection) propostas na literatura. Após a apresentação deste material preparatório necessário para compreender o trabalho realizado, são descritos, caracterizados, avaliados e comparados os vários algoritmos. Foram implementadas numa cadeia de simulação vários tipos de estruturas PIC, designadamente, com um e dois estágios, com cancelamento parcial e completo, com estimativas hard e soft, com uma antena e com um agregado circular uniforme de M elementos. De forma a avaliar o desempenho destas estruturas PIC foram obtidos resultados em vários cenários, nomeadamente, com estimativas perfeitas dos parâmetros do canal e controlo de potência perfeito; com estimativas imperfeitas dos parâmetros do canal e controlo de potência perfeito; com factores de espalhamento variáveis e estimativas perfeitas dos parâmetros do canal. Os parâmetros necessários para efectuar simulações ao nível do sistema foram, também, calculados. Como conclusão principal deste trabalho, ressalta que a estrutura HD_PIC (hard decision - PIC) com um estágio é a que apresenta a melhor relação desempenho/complexidade, verificando-se que a combinação desta estrutura com um agregado de antenas é uma técnica extremamente promissora para o UMTS_TDD. Palavras Chave: detecção multi-utilizador, cancelamento de interferência, agregados de antenas, filtragem espacio-temporal, DS_CDMA, PIC e UMTSTD

Detecção multiutilizador do domínio da frequência para sistemas DS-CDMA

Doutoramento em Engenharia ElectrotécnicaOs Sinais de Espalhamento de Espectro de Sequência Directa exibem propriedades cicloestacionárias que implicam redundância entre componentes de frequência espaçadas por múltiplos da taxa de símbolo. Nesta tese, é apresentado um cancelador de interferência multiutilizador (Cancelador por translação na frequência - FSC) que tira partido desta propriedade. Este cancelador linear opera no domínio da frequência no sinal espalhado de tal forma que minimiza a interferência e ruído na saída (Critério do Mínimo Erro Quadrado Médio). Além de testado para o caso de antena única, são avaliadas as performances das configurações de antenas múltiplas para o caso de beamforming e canais espacialmente descorrelacionados considerando sistemas síncronos e sistemas com desalinhamento no tempo dos perfis de canais (ambos UMTS-TDD). Essas configurações divergiam na ordem da combinação temporal, combinação espacial e detecção multiutilizador. As configurações FSC foram avaliadas quando concatenadas com o PIC-2D. Os resultados das simulações mostram consideráveis melhorias nos resultados relativamente ao RAKE-2D convencional e PIC-2D. Foi atingida performance próximo ao RAKE de utilizador único quando o FSC foi avaliado concatenado com PIC-2D em quase todas as configurações. Todas as configurações foram avaliadas com modulação QPSK, 8-PSK e 16-QAM. Foi introduzida codificação Turbo e identificou-se as situações da vantagem de utilização do FSC antes do PIC-2D. As modulações 8-PSK e 16-QAM foram igualmente testadas com codificação.Direct Sequence Spread Spectrum signals exhibit cyclostationary properties which imply redundancy between frequency components separated by multiples of the symbol rate. In this thesis a Multiple Access Interference Canceller (Frequency Shift Canceller - FSC) that explores this property is presented. The linear frequency domain canceller operates on the spreaded signal so as to minimize the interference and noise at the output (Minimum Mean Squared Error Criterium). Moreover the FSC was tested with single antenna, the performance of multisensor configurations for the cases of beamforming and uncorrelated spatial channels was evaluated considering both synchronous and time misalignment systems (both UMTS-TDD). Those configurations diverge in temporal combining, spatial combining and multiuser detection order. The FSC configurations were concatenated with PIC-2D structure and evaluated. The simulation results show considerable improvement relative to the conventional RAKE-2D and PIC-2D receiver. A performance close to the single user RAKE case was a achieved when it (FSC) was evaluated jointly with PIC-2D. All the configurations with modulation QPSK, 8-PSK and 16-QAM were evaluated. Turbo Codes were introduced and it was identified the situations which it is advantageous to use the FSC before the PIC-2D. The 8-PSK and 16-QAM modulations were equally tested with coding

Software Defined Radio Solutions for Wireless Communications Systems

Wireless technologies have been advancing rapidly, especially in the recent years. Design, implementation, and manufacturing of devices supporting the continuously evolving technologies require great efforts. Thus, building platforms compatible with different generations of standards and technologies has gained a lot of interest. As a result, software defined radios (SDRs) are investigated to offer more flexibility and scalability, and reduce the design efforts, compared to the conventional fixed-function hardware-based solutions.This thesis mainly addresses the challenges related to SDR-based implementation of today’s wireless devices. One of the main targets of most of the wireless standards has been to improve the achievable data rates, which imposes strict requirements on the processing platforms. Realizing real-time processing of high throughput signal processing algorithms using SDR-based platforms while maintaining energy consumption close to conventional approaches is a challenging topic that is addressed in this thesis.Firstly, this thesis concentrates on the challenges of a real-time software-based implementation for the very high throughput (VHT) Institute of Electrical and Electronics Engineers (IEEE) 802.11ac amendment from the wireless local area networks (WLAN) family, where an SDR-based solution is introduced for the frequency-domain baseband processing of a multiple-input multipleoutput (MIMO) transmitter and receiver. The feasibility of the implementation is evaluated with respect to the number of clock cycles and the consumed power. Furthermore, a digital front-end (DFE) concept is developed for the IEEE 802.11ac receiver, where the 80 MHz waveform is divided to two 40 MHz signals. This is carried out through time-domain digital filtering and decimation, which is challenging due to the latency and cyclic prefix (CP) budget of the receiver. Different multi-rate channelization architectures are developed, and the software implementation is presented and evaluated in terms of execution time, number of clock cycles, power, and energy consumption on different multi-core platforms.Secondly, this thesis addresses selected advanced techniques developed to realize inband fullduplex (IBFD) systems, which aim at improving spectral efficiency in today’s congested radio spectrum. IBFD refers to concurrent transmission and reception on the same frequency band, where the main challenge to combat is the strong self-interference (SI). In this thesis, an SDRbased solution is introduced, which is capable of real-time mitigation of the SI signal. The implementation results show possibility of achieving real-time sufficient SI suppression under time-varying environments using low-power, mobile-scale multi-core processing platforms. To investigate the challenges associated with SDR implementations for mobile-scale devices with limited processing and power resources, processing platforms suitable for hand-held devices are selected in this thesis work. On the baseband processing side, a very long instruction word (VLIW) processor, optimized for wireless communication applications, is utilized. Furthermore, in the solutions presented for the DFE processing and the digital SI canceller, commercial off-the-shelf (COTS) multi-core central processing units (CPUs) and graphics processing units (GPUs) are used with the aim of investigating the performance enhancement achieved by utilizing parallel processing.Overall, this thesis provides solutions to the challenges of low-power, and real-time software-based implementation of computationally intensive signal processing algorithms for the current and future communications systems

Multi-carrier transmission techniques toward flexible and efficient wireless communication systems

制度:新 ; 文部省報告番号:甲2562号 ; 学位の種類:博士(国際情報通信学) ; 授与年月日:2008/3/15 ; 早大学位記番号:新470

Lattice-structure based adaptive MMSE detectors for DS-CDMA systems.

Thesis (M.Sc.Eng.)-University of Natal, Durban, 2001.There has been significant interest in the research community on detectors for DS-CDMA systems. The conventional detector, which detects users ' data bits, by using a filter matched to the users' spreading codes, has two major drawbacks. These drawbacks are (1) its capacity is limited by multiple access interference (MAl) and (2) it suffers from the near-far problem. The remedy to these problems is to use a multiuser detector, which exploits knowledge of users ' transmission and channel parameters to mitigate MAl. Such detectors are called multi user detectors (MUD). A number of these detectors have been proposed in the literature. The first such detector is the optimal detector proposed by Verdu. Following Verdu's work a number of suboptimal detector were proposed. These detectors offer better computational complexity at the expense of the bit error rate performance. Examples of these detectors are the decorrelating detector, the minimum mean squared error detector (MMSE), the successive interference cancellation and parallel interference cancellation. In this thesis, we consider the adaptive DS-CDMA MMSE detector, where lattice-based filter algorithms are employed to suppress MAl. Most of the work in the literature has considered the implementation of this detector using the Least Mean Square (LMS) algorithm. The disadvantage of using the LMS algorithm to implement the MMSE detector is that the LMS algorithm converges very slowly. The main aims of this thesis are as follows. A review of the literature on MUD is presented. A lattice based MUD is then proposed and its performance evaluated using both simulation and analytical methods. The results obtained are compared with those of the LMSMMSE detector. From the results obtained the adaptive Lattice-MMSE detector is shown to offer good performance tradeoff between convergence results and BER results

Spatio-Temporal processing for Optimum Uplink-Downlink WCDMA Systems

The capacity of a cellular system is limited by two different phenomena, namely multipath fading and multiple access interference (MAl). A Two Dimensional (2-D) receiver combats both of these by processing the signal both in the spatial and temporal domain. An ideal 2-D receiver would perform joint space-time processing, but at the price of high computational complexity. In this research we investigate computationally simpler technique termed as a Beamfom1er-Rake. In a Beamformer-Rake, the output of a beamfom1er is fed into a succeeding temporal processor to take advantage of both the beamformer and Rake receiver. Wireless service providers throughout the world are working to introduce the third generation (3G) and beyond (3G) cellular service that will provide higher data rates and better spectral efficiency. Wideband COMA (WCDMA) has been widely accepted as one of the air interfaces for 3G. A Beamformer-Rake receiver can be an effective solution to provide the receivers enhanced capabilities needed to achieve the required performance of a WCDMA system. We consider three different Pilot Symbol Assisted (PSA) beamforming techniques, Direct Matrix Inversion (DMI), Least-Mean Square (LMS) and Recursive Least Square (RLS) adaptive algorithms. Geometrically Based Single Bounce (GBSB) statistical Circular channel model is considered, which is more suitable for array processing, and conductive to RAKE combining. The performances of the Beam former-Rake receiver are evaluated in this channel model as a function of the number of antenna elements and RAKE fingers, in which are evaluated for the uplink WCDMA system. It is shown that, the Beamformer-Rake receiver outperforms the conventional RAKE receiver and the conventional beamformer by a significant margin. Also, we optimize and develop a mathematical formulation for the output Signal to Interference plus Noise Ratio (SINR) of a Beam former-Rake receiver. In this research, also, we develop, simulate and evaluate the SINR and Signal to Noise Ratio (Et!Nol performances of an adaptive beamforming technique in the WCDMA system for downlink. The performance is then compared with an omnidirectional antenna system. Simulation shows that the best perfom1ance can be achieved when all the mobiles with same Angle-of-Arrival (AOA) and different distance from base station are formed in one beam