93 research outputs found
Self-interference cancellation for full-duplex MIMO transceivers
PhD ThesisIn recent years, there has been enormous interest in utilizing the full-duplex
(FD) technique with multiple-input multiple-output (MIMO) systems to complement
the evolution of fifth generation technologies. Transmission and reception
using FD-MIMO occur simultaneously over the same frequency band
and multiple antennas are employed in both sides. The motivation for employing
FD-MIMO is the rapidly increasing demand on frequency resources,
and also FD has the ability to improve spectral efficiency and channel capacity
by a factor of two compared to the conventional half-duplex technique.
Additionally, MIMO can enhance the diversity gain and enable FD to acquire
further degrees of freedom in mitigating the self-interference (SI). The
latter is one of the key challenges degrading the performance of systems operating
in FD mode due to local transmission which involves larger power
level than the signals of interest coming from distance sources that are significantly
more attenuated due to path loss propagation phenomena. Various
approaches can be used for self-interference cancellation (SIC) to tackle SI
by combining passive suppression with the analogue and digital cancellation
techniques. Moreover, active SIC techniques using special domain suppression
based on zero-forcing and null-space projection (NSP) can be exploited
for this purpose too. The main contributions of this thesis can be summarized
as follows. Maximum-ratio combining with NSP are jointly exploited in order
to increase the signal-to-noise ratio (SNR) of the desired path and mitigate
the undesired loop path, respectively, for an equalize-and-forward (EF) relay
using FD-MIMO. Additionally, an end-to-end performance analysis of the
proposed system is obtained in the presence of imperfect channel state information
by formulating mathematically the exact closed-form solutions for
the signal-to-interference-plus-noise ratio (SINR) distribution, outage probability,
and average symbol-error rate for uncoded M-ary phase-shift keying
over Rayleigh fading channels and in the presence of additive white Gaussian
noise (AWGN). The coefficients of the EF-relay are designed to attain
the minimum mean-square error (MMSE) between the transmission symbols.
Comparison of the results obtained with relevant state-of-the-art techniques
suggests significant improvements in the SINR figures and system capacity.
Furthermore, iterative detection and decoding (IDD) are proposed to mitigate
the residual self-interference (SI) remaining after applying passive suppression
along with two stages of SI cancellation (SIC) filters in the analogue
and digital domains for coded FD bi-directional transceiver based multiple
antennas. IDD comprises an adaptive MMSE filter with log-likelihood ratio
demapping, while the soft-in soft-out decoder utilizes the maximum a posteriori
(MAP) algorithm. The proposed system’s performance is evaluated in
the presence of AWGN over non-selective (flat) Rayleigh fading single-input
multiple-output (SIMO) and MIMO channels. However, the results of the
analyses can be applied to multi-path channels if orthogonal frequency division
multiplexing is utilised with a proper length of cyclic prefix in order to
tackle the channels’ frequency-selectivity and delay spread. Simulation results
are presented to demonstrate the bit-error rate (BER) performance as a
function of the SNR, revealing a close match to the SI-free case for the proposed
system. Furthermore, the results are validated by deriving a tight upper
bound on the performance of rate-1=2 convolutional codes for FD-SIMO and
FD-MIMO systems for different modulation schemes under the same conditions,
which asymptotically exhibits close agreement with the simulated BER
performance.Ministry of Higher Education and Scientific Research
(MoHESR), and the University of Mosul and to the Iraqi Cultural Attache in
London for providing financial support for my PhD scholarship
Channel estimation and parameters acquisition systems employing cooperative diversity
Doutoramento em Engenharia Eletrotécnica e TelecomunicaçõesThis work investigates new channel estimation schemes for the forthcoming and future generation of cellular systems for which cooperative techniques are regarded.
The studied cooperative systems are designed to re-transmit the received information to the user terminal via the relay nodes, in order to make use of benefits such as high throughput, fairness in access and extra coverage.
The cooperative scenarios rely on OFDM-based systems employing classical and pilot-based channel estimators, which were originally designed to pointto-point links.
The analytical studies consider two relaying protocols, namely, the Amplifyand-Forward and the Equalise-and-Forward, both for the downlink case.
The relaying channels statistics show that such channels entail specific characteristics that comply to a proper filter and equalisation designs.
Therefore, adjustments in the estimation process are needed in order to obtain the relay channel estimates, refine these initial estimates via iterative processing and obtain others system parameters that are required in the
equalisation.
The system performance is evaluated considering standardised specifications and the International Telecommunication Union multipath channel models.Este trabalho tem por objetivo o estudo de novos esquemas de estimação de canal para sistemas de comunicação móvel das próximas gerações, para os quais técnicas cooperativa são consideradas.
Os sistemas cooperativos investigados neste trabalho estão projetados para fazerem uso de terminais adicionais a fim de retransmitir a informação recebida para o utilizador final. Desta forma, pode-se usurfruir de benefÃcios relacionados à s comunicações cooperativas tais como o aumento do rendimento do sistema, fiabilidade e extra cobertura. Os cenários são basedos em sistemas OFDM que empregam estimadores de canal que fazem
uso de sinais piloto e que originalmente foram projetados para ligações ponto a ponto.
Os estudos analÃticos consideram dois protocolos de encaminhamento, nomeadamente, Amplify-and-Forward e Equalise-and-Forward, ambos para o caso downlink. As estatÃsticas dos canais em estudo mostram que tais canais
ocasionam caracterÃsticas especÃficas para as quais o filtro do estimador e a equalisação devem ser apropridamente projetados. Estas caracterÃsticas requerem ajustes que são necessários no processo de estimação a fim
de estimar os canais, refinar as estimativas iniciais através de processos iterativos e ainda obter outros parâmetros do sistema que são necessários na equalização.
O desempenho dos esquemas propostos são avaliados tendo em consideração especificações padronizadas e modelos de canal descritos na International Telecommunication Union
Advanced Trends in Wireless Communications
Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the communication systems requires further investigations to reduce the complexity and the power consumption of the receiver. This book aims to provide highlights of the current research in the field of wireless communications. The subjects discussed are very valuable to communication researchers rather than researchers in the wireless related areas. The book chapters cover a wide range of wireless communication topics
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