10 research outputs found
Iterative signal detection for large scale GSM-MIMO systems
Generalized spatial modulations (GSM) represent a novel multiple input multiple output (MIMO) scheme which can be regarded as a compromise between spatial multiplexing MIMO and conventional spatial modulations (SM), achieving both spectral efficiency (SE) and energy efficiency (EE). Due to the high computational complexity of the maximum likelihood detector (MLD) in large antenna settings and symbol constellations, in this paper we propose a lower complexity iterative suboptimal detector. The derived algorithm comprises a sequence of simple processing steps, namely an unconstrained Euclidean distance minimization problem, an element wise projection over the signal constellation and a projection over the set of valid active antenna combinations. To deal with scenarios where the number of possible active antenna combinations is large, an alternative version of the algorithm which adopts a simpler cardinality projection is also presented. Simulation results show that, compared with other existing approaches, both versions of the proposed algorithm are effective in challenging underdetermined scenarios where the number of receiver antennas is lower than the number of transmitter antennas.info:eu-repo/semantics/acceptedVersio
Sparse Bayesian Learning Approach for Discrete Signal Reconstruction
This study addresses the problem of discrete signal reconstruction from the
perspective of sparse Bayesian learning (SBL). Generally, it is intractable to
perform the Bayesian inference with the ideal discretization prior under the
SBL framework. To overcome this challenge, we introduce a novel discretization
enforcing prior to exploit the knowledge of the discrete nature of the
signal-of-interest. By integrating the discretization enforcing prior into the
SBL framework and applying the variational Bayesian inference (VBI)
methodology, we devise an alternating update algorithm to jointly characterize
the finite alphabet feature and reconstruct the unknown signal. When the
measurement matrix is i.i.d. Gaussian per component, we further embed the
generalized approximate message passing (GAMP) into the VBI-based method, so as
to directly adopt the ideal prior and significantly reduce the computational
burden. Simulation results demonstrate substantial performance improvement of
the two proposed methods over existing schemes. Moreover, the GAMP-based
variant outperforms the VBI-based method with an i.i.d. Gaussian measurement
matrix but it fails to work for non i.i.d. Gaussian matrices.Comment: 13 pages, 7 figure
New challenges in wireless and free space optical communications
AbstractThis manuscript presents a survey on new challenges in wireless communication systems and discusses recent approaches to address some recently raised problems by the wireless community. At first a historical background is briefly introduced. Challenges based on modern and real life applications are then described. Up to date research fields to solve limitations of existing systems and emerging new technologies are discussed. Theoretical and experimental results based on several research projects or studies are briefly provided. Essential, basic and many self references are cited. Future researcher axes are briefly introduced
Low complexity receivers for single carrier large-scale spatial modulation systems
The dissertation aims to study the low-complexity receivers for Single Carrier (SC)
systems and generalized spatial modulation (GSM) in order to reduce the number of radio
frequency (RF) chains used in the emitter and making the system more efficient
energetically. In the first instance, the study addressed the use of multiple-Input multipleOutput (MIMO) schemes in conjunction with GSM in SC systemsin order to increase the
throughput of a telecommunications network without diminishing energy efficiency. This
study was followed by the development of an algorithm based on the alternating Direction
method of Multipliers (ADMM) as a low-complexity receiver intending to achieve
performances close to the optimal Maximum Likelihood Detector (MLD).
The study of the ADMM receptor was done in two stages, the first step consists of the
exclusive study of the ADMM receptor is SC systems where the main parameters of the
receiver are tested. The second step compared the ADMM receiver with other receivers,
namely the MMSE and the Zero Forcing in severe time dispersive environments.
The realization of the various simulations with various receivers and scenarios allows to
demonstrate that the ADMM can be an efficient and robust alternative. The referred
technologies promote the reduction of the ecological footprint and the development of the
technologies.A dissertação visa estudar os receptores de baixa complexidade para sistemas "Single
Carrier" (SC) e modulações espaciais generalizadas (GSM) de modo a reduzir o número
de cadeias radio frequência (RF) utilizadas no emissor e tornando o sistema mais eficiente
energeticamente. Em primeira instância o estudo apresentado abordou a utilização de
esquemas "Multiple-Input Multiple-Output" (MIMO) em conjunto com o GSM em sistemas
SC de forma a aumentar o "throughput" de uma rede de telecomunicações sem que a
eficiência energética diminua. De seguida foi realizado o estudo de um algoritmo baseado
no método "Alternating Direction Method of Multipliers" (ADMM) como um receptor de
baixa complexidade, pretendendo-se obter desempenhos próximos do receptor ótimo
"Maximum Likelihood Detector" (MLD).
O estudo do receptor ADMM foi feito em duas etapas. A primeira etapa consistiu no
estudo exclusivo do receptor ADMM onde foram testados os parâmetros principais do
receptor. A segunda etapa consistiu em comparar o receptor ADMM com outros
receptores, nomeadamente o MMSE e o Zero Forcing em ambiente altamente dispersivo
no tempo.
A realização das diversas simulações com vários receptores e cenários, permitiu
demonstrar que o ADMM pode ser uma alternativa bastante eficiente e robusta. As
tecnologias referidas promovem a diminuição da pegada ecológica e o desenvolvimento
das mesmas
Spatial modulations for green heterogeneous networks
A rápida evolução dos sistemas de telecomunicações culminou numa necessidade cada vez mais
crescente por redes que permitam elevados débitos. Associado a esse throughput elevado está
o custo energético que gradualmente torna os sistemas pouco eficientes energeticamente. As
modulações espaciais generalizadas (Generalized Spatial Modulation -GSM) surgem da
necessidade de criar comunicações mais “verdes”, permitindo obter melhores eficiências
energéticas através da redução do número de cadeias de blocos radio-frequência (RF) utilizadas
no emissor.
O estudo apresentado neste trabalho pretende realçar, num primeiro ponto, a importância da
evolução dos sistemas de transmissão MIMO (Multiple-Input Multiple-Output) como forma de
aumento do throughput global de uma rede de telecomunicações mantendo uma eficiência
energética alta, com foco em GSM. O segundo ponto consiste no estudo de um algoritmo
baseado no método ADMM (Alternating Direction Method of Multipliers), como recetor de
baixa complexidade para esquemas GSM com desempenho próximo do ótimo, o detetor de
máxima verosimilhança (MLD).
O estudo do recetor ADMM foi efetuado em duas fases, sendo que a primeira é referente ao
estudo extensivo e exclusivo do recetor ADMM, com principal enfoque nos vários parâmetros
que o definem. Na segunda fase é feita uma comparação para vários cenários entre o recetor
ADMM e alguns dos recetores de baixa complexidade mais conhecidos, entre eles o OB-MMSE
(Ordered Block MMSE) e o BPDN (Basis Pursuit De-Noising), por exemplo.
A realização de simulações, com os vários recetores, em vários cenários permitiu concluir que
o ADMM, com recurso às suas técnicas de refinamento, representa uma alternativa eficiente, e
em certos casos superior, ao OB-MMSE principalmente para cenários com um elevado número
de bits por símbolo espacial.The fast evolution of telecommunications systems resulted in a growing need for networks that
support high transmission rates. Associated with this high throughput is the energy cost that
gradually makes this systems less energy-efficient . The Generalized Spatial Modulation
(GSM) arises from the need to create more "green" communication, allowing best energy
efficiencies.
The study presented in this thesis aims to highlight firstly, the importance of the development
of MIMO (Multiple-Input Multiple-Output) transmission systems capable of increasing the
overall throughput of a telecommunications network while maintaining high energy efficiency,
focusing on GSM. The second relevant aspect is the study of an algorithm based on the ADMM
(Alternating Direction Method of Multipliers) method, as a solution for a low complexity
receiver for GSM schemes with a performance close to the optimal one, the maximum
likelihood detector (MLD).
The ADMM receiver study was conducted in two phases, the first of which refers to the
extensive and unique study of the ADMM receiver, with main focus on the various parameters
that define it. In the second stage a comparison is made between the settings for various ADMM
receivers and some of the known low-complexity receivers, including OB-MMSE (Ordered
Block MMSE) and BPDN (Basis Pursuit De-noising), for example.
The results obtained from the evaluations performed several scenarios allow us to conclude that
the ADMM based receiver combined with refinement techniques, is an efficient alternative and
in some cases with better performance than the OB-MMSE receiver, especially for scenarios
with a large number of bits per spatial symbol
Spatial Coded Modulation
In this paper, we propose a spatial coded modulation (SCM) scheme, which
improves the accuracy of the active antenna detection by coding over the
transmit antennas. Specifically, the antenna activation pattern in the SCM
corresponds to a codeword in a properly designed codebook with a larger minimum
Hamming distance than its counterpart conventional spatial modulation. As the
minimum Hamming distance increases, the reliability of the active antenna
detection is directly enhanced, which in turn improves the demodulation of the
modulated symbols and yields a better system reliability. In addition to the
reliability, the proposed SCM scheme also achieves a higher capacity with the
identical antenna configuration compared to the conventional spatial modulation
technique. Moreover, the proposed SCM scheme strikes a balance between spectral
efficiency and reliability by trading off the minimum Hamming distance with the
number of available codewords. The optimal maximum likelihood detector is first
formulated. Then, a low-complexity suboptimal detector is proposed to reduce
the computational complexity, which has a two-step detection. Theoretical
derivations of the channel capacity and the bit error rate are presented in
various channel scenarios, i.e., Rayleigh, Rician, Nakagami-m, imperfect
channel state information, and spatial correlation. Further derivation on
performance bounding is also provided to reveal the insight of the benefit of
increasing the minimum Hamming distance. Numerical results validate the
analysis and demonstrate that the proposed SCM outperforms the conventional
spatial modulation techniques in both channel capacity and system reliability.Comment: 30 pages, 17 figure