361 research outputs found
Mobile Speed Classification for Cellular Systems Over Frequency Selective Rician Fading Channels
In this paper, a new algorithm is proposed for estimating mobile speed of cellular systems over frequency selective Rician fading channels. Theoretical analysis is first derived and practical algorithm is proposed based on the analytical results. The algorithm employs a modified auto-covariance of received signal power to estimate the speed of mobiles. The algorithm is based on the received signals which contain unknown transmitted data, unknown frequency selective multipaths including line-of-sight(LOS) component, and random receiver noise. The algorithm works very well for frequency selective Rician fading channels with large ranges of Rice factor and angle of arrival of the LOS component. Simulation results indicate that the new algorithm is very reliable and effective to distinguish slow speed and fast speed mobiles. The algorithm is computationally efficient. It only requires simple arithmetic operations such as multiplications, additions and subtractions
Equalizador hĂbrido na banda das ondas milimĂ©tricas para sistemas GFDM
Wireless communication using very-large multiple-input multiple-output
(MIMO) antennas has been regarded as one of the enabling technologies
for the future mobile communication. It refers to the idea of equipping
cellular base stations (BSs) with a very large number of antennas giving the
possibility to focusing the transmitted signal energy into very short-range
areas, which will provide huge improvements in the capacity, in addition
to the spectral and energy efficiency. Concurrently, this demand for high
data rates and capacity led to the necessity of exploiting the enormous
amount of spectrum in the millimeter wave (mmWave) bands. However,
the combination of millimeter-wave communications arrays with a massive
number of antennas has the potential to dramatically enhance the features
of wireless communication. This combination implies high cost and power
consumption in the conventional full digital architecture, where each RF chain
is dedicated to one antenna. The solution is the use of a hybrid architecture,
where a small number of RF chains are connected to a large number of
antennas through a network of phase shifters.
On the other hand, another important factor that affect the transmission
quality is the modulation technique, which plays an important role in the
performance of the transmission process, for instance, GFDM is a flexible
non-orthogonal multicarrier modulation concept, that introduces additional
degrees of freedom when compared to other multicarrier techniques. This
flexibility makes GFDM a promising solution for the future cellular generations,
because it can achieve different requirements, such as higher spectrum
efficiency, better control of out-of-band (OOB) emissions, as well as achieving
low peak to average power ratio (PAPR).
In this work, we present an analog-digital transmitter and receiver structures.
Considering a GFDM modulation technique to be implemented in the digital
part, while in the analog part, we propose a full connected hybrid multiuser
linear equalizer, combined with low complexity hybrid precoder for wideband
millimeter-wave massive MIMO systems. The hybrid equalizer is optimized by
minimizing the mean square error between the hybrid approach and the full
digital counterpart.
The results show that the performance of the proposed hybrid scheme is very
close to the full digital counterpart and the gap reduces as the number of RF
chains increases.O uso de um nĂșmero elevado de antenas, tambĂ©m designado por MIMO
massivo, tem sido considerada uma das tecnologias mais promissoras para
os futuros sistemas de comunicação sem fios. Esta tecnologia, refere-se Ă
ideia de equipar as estaçÔes base (BSs) com um nĂșmero muito grande de
antenas, dando a possibilidade de focar a energia do sinal transmitido em
ĂĄreas de alcance muito restritas, o que proporcionarĂĄ grandes melhorias na
capacidade, alĂ©m das espectrais e eficiĂȘncia energĂ©tica. Simultaneamente,
a exigĂȘncia por taxas de dados elevadas e capacidade levou Ă necessidade
de explorar uma enorme quantidade de espectro nas bandas de ondas
milimétricas (mmWave). A combinação de comunicação na banda das ondas
milimĂ©tricas com terminais equipados com um grande nĂșmero de antenas
tem o potencial de melhorar drasticamente os recursos da comunicação sem
fios. Considerando no entanto uma arquitetura digital, usada em sistemas
MIMO convencionais, em que cada cadeia de RF Ă© dedicada a uma antena,
implica um custo e um consumo de energia elevados. A solução é o uso
de uma arquitetura hĂbrida, na qual um pequeno nĂșmero de cadeias de
RF Ă© conectado a um grande nĂșmero de antenas atravĂ©s de um conjunto
de deslocadores de fase. Outro fator importante que afeta a qualidade da
transmissão é a técnica de modulação usada, que desempenha um papel
importante no desempenho do processo de transmissĂŁo. O GFDM Ă© um
conceito de modulação de portadora mĂșltipla, nĂŁo ortogonal e flexĂvel, que
introduz graus de liberdade adicionais, quando comparado a outras técnicas
de portadora mĂșltipla, como o OFDM. Essa flexibilidade faz do GFDM uma
solução promissora para as futuras geraçÔes celulares, pois pode atender
a diferentes requisitos, como maior eficiĂȘncia de espectro, melhor controle
das emissĂ”es fora de banda (OOB), alĂ©m de atingir baixo rĂĄcio de potĂȘncia
média / pico ( PAPR).
Neste trabalho, Ă© assumido uma arquitetura hibrida no transmissor e
recetor. Considera-se uma técnica de modulação GFDM a ser implementada
na parte digital, enquanto na parte analĂłgica, Ă© proposto um equalizador
linear hĂbrido multiutilizador totalmente conectado, i.e., cada cadeia RF
estĂĄ ligada a todas as antenas, combinado com um prĂ©-codificador hĂbrido,
de baixa complexidade para sistemas MIMO massivo de banda larga. O
equalizador hĂbrido Ă© otimizado, minimizando o erro quadrĂĄtico mĂ©dio entre a
abordagem hĂbrida e a contraparte totalmente digital. Os resultados mostram
que o desempenho do esquema hĂbrido proposto estĂĄ muito prĂłximo do
equivalente digital, Ă medida que o nĂșmero de cadeias de RF aumenta.Mestrado em Engenharia EletrĂłnica e TelecomunicaçÔe
Bit error rate estimation in WiMAX communications at vehicular speeds using Nakagami-m fading model
The wireless communication industry has experienced a rapid technological evolution from its basic first generation (1G) wireless systems to the latest fourth generation (4G) wireless broadband systems. Wireless broadband systems are becoming increasingly popular with consumers and the technological strength of 4G has played a major role behind the success of wireless broadband systems. The IEEE 802.16m standard of the Worldwide Interoperability for Microwave Access (WiMAX) has been accepted as a 4G standard by the Institute of Electrical and Electronics Engineers in 2011. The IEEE 802.16m is fully optimised for wireless communications in fixed environments and can deliver very high throughput and excellent quality of service. In mobile communication environments however, WiMAX consumers experience a graceful degradation of service as a direct function of vehicular speeds. At high vehicular speeds, the throughput drops in WiMAX systems and unless proactive measures such as forward error control and packet size optimisation are adopted and properly adjusted, many applications cannot be facilitated at high vehicular speeds in WiMAX communications. For any proactive measure, bit error rate estimation as a function of vehicular speed, serves as a useful tool. In this thesis, we present an analytical model for bit error rate estimation in WiMAX communications using the Nakagami-m fading model. We also show, through an analysis of the data collected from a practical WiMAX system, that the Nakagami-m model can be made adaptive as a function of speed, to represent fading in fixed environments as well as mobile environments
Design and development of mobile channel simulators using digital signal processing techniques
A mobile channel simulator can be constructed either in the time domain using a tapped delay line filter or in the frequency domain using the time variant transfer function of the channel. Transfer function modelling has many advantages over impulse response modelling. Although the transfer function channel model has been envisaged by several researchers as an alternative to the commonly employed tapped delay line model, so far it has not been implemented. In this work, channel simulators for single carrier and multicarrier OFDM system based on time variant transfer function of the channel have been designed and implemented using DSP techniques in SIMULINK. For a single carrier system, the simulator was based on Bello's transfer function channel model. Bello speculated that about 10ÎÏ(_MAX) frequency domain branches might result in a very good approximation of the channel (where ĐČ is the signal bandwidth and Ï(_MAX) is the maximum excess delay of the multi-path channel). The simulation results showed that 10BÏ(_MAX) branches gave close agreement with the tapped delay line model(where Be is the coherence bandwidth). This number is Ï times higher than the previously speculated 10BÏ(_MAX).For multicarrier OFDM system, the simulator was based on the physical (PHY) layer standard for IEEE 802.16-2004 Wireless Metropolitan Area Network (WirelessMAN) and employed measured channel transfer functions at the 2.5 GHz and 3.5 GHz bands in the simulations. The channel was implemented in the frequency domain by carrying out point wise multiplication of the spectrum of OFDM time The simulator was employed to study BER performance of rate 1/2 and rate 3/4 coded systems with QPSK and 16-QAM constellations under a variety of measured channel transfer functions. The performance over the frequency selective channel mainly depended upon the frequency domain fading and the channel coding rate
Recommended from our members
Performance evaluation of fixed WiMax physical layer under high fading channels
This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.A radio channel characteristic modelling is essential in every network planning. This project deals with the performance of WiMax networks in an outdoor environment while using fading channel models. The radio channels characteristics are analyzed by simulations have been done using Matlab programming. Stanford University Interim(SUI) Channels set was proposed to simulate the fixed broadband wireless access channel environments where IEEE 802.16d is to be deployed. It has six channel models that are grouped into three categories according to three typical different outdoor Terrains, in order to give a comprehensive study of fading channels on the overall performance of the system, WiMax system has been tested under SUI channels that modified into account for 30o directional antennas, with 90% cell coverage and with 99.9% reliability in its geographical covered area. Furthermore, in order to combat the fading which occurs in urban areas and improve the capacity and the throughput of the system, multiples antennas at both ends of communication link are used, the transmission gain obtained when using multiple antennas instead of only a single antenna. Space-time coding and maximum ratio combining for more than one transmit and receive antenna is implemented to allow performance investigations in various MIMO scenarios. It has been concluded that uses multiple antennas at the receiver offers a significant improvement of 3 dB of gain in the channel SNR. This thesis also contain implementation of all compulsory features of the WiMax OFDM physical layer specified in IEEE 802.16-2004 using Matlab coding. In order to combat the temporal variations in quality on a multipath fading channel, an adaptive modulation technique is used. This technique employs multiple modulation schemes to instantaneously adapt to the variations in the channel SNR, thus maximizing the system throughput and improving BER performance. WiMax transceiver has been tested with and without encoding and studied the effect of encoding on multipath channel. Testing the system with flexible channel bandwidth has been part of this thesis. Finally it has been explained in this thesis the affect of increasing the size of cyclic prefix on overall performance of WiMax system
The Multi-Input Multi-Output (MIMO) Channel Modeling, Simulation and Applications
This thesis mainly focus on the Multi-Input Multi-Output (MIMO) channel modeling, simulation and applications. There are several ways to design a MIMO channel. Most of the examples are given in Chapter 2, where we can design channels based on the environments and also based on other conditions. One of the new MIMO channel designs based on physical and virtual channel design is discussed in Unitary-Independent- Unitary (UIU) channel modeling. For completeness, the different types of capacity are discussed in details. The capacity is very important in wireless communication. By understanding the details behind different capacity, we can improve our transmission efficiently and effectively. The level crossing rate and average duration are discussed.One of the most important topics in MIMO wireless communication is estimation. Without having the right estimation in channel prediction, the performance will not be correct. The channel estimation error on the performance of the Alamouti code was discussed. The design of the transmitter, the channel and the receiver for this system model is shown. The two different types of decoding scheme were shown - the linear combining scheme and the Maximum likelihood (ML) decoder. Once the reader understands the estimation of the MIMO channel, the estimation based on different antenna correlation is discussed. Next, the model for Mobile-to-Mobile (M2M) MIMO communication link is proposed. The old M2M Sum-of-Sinusoids simulation model and the new two ring models are discussed. As the last step, the fading channel modeling using AR model is derived and the effect of ill-conditioning of the Yule-Walker equation is also shown. A number of applications is presented to show how the performance can be evaluated using the proposed model and techniques
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