67 research outputs found
LTE SFBC MIMO Transmitter Modelling and Performance Evaluation
High data rates are one of the most prevalent requirements in current mobile
communications. To cover this and other high standards regarding performance,
increasing coverage, capacity, and reliability, numerous works have proposed
the development of systems employing the combination of several techniques such
as Multiple Input Multiple Output (MIMO) wireless technologies with Orthogonal
Frequency Division Multiplexing (OFDM) in the evolving 4G wireless
communications. Our proposed system is based on the 2x2 MIMO antenna technique,
which is defined to enhance the performance of radio communication systems in
terms of capacity and spectral efficiency, and the OFDM technique, which can be
implemented using two types of sub-carrier mapping modes: Space-Time Block
Coding and Space Frequency Block Code. SFBC has been considered in our
developed model. The main advantage of SFBC over STBC is that SFBC encodes two
modulated symbols over two subcarriers of the same OFDM symbol, whereas STBC
encodes two modulated symbols over two subcarriers of the same OFDM symbol;
thus, the coding is performed in the frequency domain. Our solution aims to
demonstrate the performance analysis of the Space Frequency Block Codes scheme,
increasing the Signal Noise Ratio (SNR) at the receiver and decreasing the Bit
Error Rate (BER) through the use of 4 QAM, 16 QAM and 64QAM modulation over a
2x2 MIMO channel for an LTE downlink transmission, in different channel radio
environments. In this work, an analytical tool to evaluate the performance of
SFBC - Orthogonal Frequency Division Multiplexing, using two transmit antennas
and two receive antennas has been implemented, and the analysis using the
average SNR has been considered as a sufficient statistic to describe the
performance of SFBC in the 3GPP Long Term Evolution system over Multiple Input
Multiple Output channels.Comment: 11 pages, 20 figures, 5 table
Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 Years
Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last 5 years (2010–2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input single-output (SISO), multiple-input multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorize the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions
Performance Analysis and Mitigation Techniques for I/Q-Corrupted OFDM Systems
Orthogonal Frequency Division Multiplexing (OFDM) has become a widely adopted modulation technique in modern communications systems due to its multipath resilience and low implementation complexity. The direct conversion architecture is a popular candidate for low-cost, low-power, fully integrated transceiver designs. One of the inevitable problems associated with analog signal processing in direct conversion involves the mismatches in the gain and phases of In-phase (I) and Quadrature-phase (Q) branches. Ideally, the I and Q branches of the quadrature mixer will have perfectly matched gains and are orthogonal in phase. Due to imperfect implementation of the electronics, so called I/Q imbalance emerges and creates interference between subcarriers which are symmetrically apart from the central subcarrier. With practical imbalance levels, basic transceivers fail to maintain the sufficient image rejection, which in turn can cause interference with the desired transmission. Such an I/Q distortion degrades the systems performance if left uncompensated.
Moreover, the coexistence of I/Q imbalance and other analog RF imperfections with digital baseband and higher layer functionalities such as multiantenna transmission and radio resource management, reduce the probability of successful transmission. Therefore, mitigation of I/Q imbalance is an essential substance in designing and implementing modern communications systems, while meeting required performance targets and quality of service. This thesis considers techniques to compensate and mitigate I/Q imbalance, when combined with channel estimation, multiantenna transmission, transmission power control, adaptive modulation and multiuser scheduling. The awareness of the quantitative relationship between transceiver parameters and system parameters is crucial in designing and dimensioning of modern communications systems. For this purpose, analytical models to evaluate the performance of an I/Q distorted system are considered
Uplink MIMO schemes in local area time division duplex system
One of 3rd Generation Partnership Projects's release 9 research areas is deployment and improvement of Long Term Evolutions's Evolved Universal Terrestrial Radio Access interface in local area cells, using time division duplex and 100MHz available bandwidth. For uplink part of this system, we revise and study MIMO algorithms considered in release 8's downlink (Cyclic Delay Diversity and Space-Frequency Block Codes open-loop schemes, Singular Value Decomposition and codebook-based closed-loop schemes), look for new alternatives, and simulate impacts of given scenario - reciprocity, correlated MIMO channels, slow fading etc. As a result, we draw conclusions about advantages of having multiple transmit antennas in User Equipment in contrast with higher price and power consumption
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
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