306 research outputs found
Timing Jitter Analysis and Mitigation in Hybrid OFDM-DFMA PONs
Hybrid orthogonal frequency division multiplexing-digital filter multiple access passive optical networks (OFDM-DFMA PONs) offer a cost-effective solution to the challenging requirements of next-generation optical access networks and 5G and beyond radio access networks. It is crucial to consider the impact of timing jitter in any ADC/DAC-based system, therefore this paper presents an in-depth investigation into the impacts of DAC/ADC timing jitter on the hybrid OFDM-DFMA PON's performance. We introduce improved accuracy white and coloured, DAC and ADC timing jitter models, applicable to any DSP-based transmission system. We prove that DAC and ADC timing jitter effects are virtually identical and investigate the effects of white/coloured timing jitter on upstream performance in hybrid OFDM-DFMA PONs and determine the associated jitter-induced optical power penalties. To mitigate against the timing jitter-induced performance degradations, a simple, but highly effective DSP-based technique is implemented which increases robustness against the timing jitter effects and significantly reduces timing jitter-induced optical power penalties. This consequently relaxes DAC/ADC sampling clock jitter requirements and so reduces implementation costs. White (coloured) timing jitter effects are shown to be independent of (dependent on) ONU operating frequency band and a trade-off between DAC and ADC jitter levels can be exploited to reduce ONU costs
OFDM systems design using harmonic wavelets
Orthogonal frequency-division multiplexing
(OFDM) is a popular multi-carrier technique used in many
digital communication systems such as wireless fidelity (Wi-Fi),
long term evolution (LTE) and power line communication
systems. It can be designed using fast Fourier transform (FFT)
or wavelet transform (WT). The major drawback in using
WT is that it is computationally inefficient. In this study, we
introduce a simple and computationally efficient WT, harmonic
wavelet transform, for OFDM signal processing. The new WT
uses the orthogonal basis functions of conventional FFT-OFDM
except that it involves translation and dilation of the input
signal; the new wavelets is referred to as harmonic wavelets
(HW). When compared with pilot-assisted OFDM system in
terms of reduction in the peak-to-average power ratio, the
results show that HW-OFDM outperforms FFT-OFDM by 3
dB at 10−4 CCDF (complementary cumulative distribution
function). Over Rayleigh fading channel with additive white
Gaussian noise (AWGN), the bit error ratio of both FFT-OFDM
and HW-OFDM perfectly matched, showing that the proposed
HW-OFDM is better in terms of peak-to-average power ratio
reduction
Convergence of millimeter-wave and photonic interconnect systems for very-high-throughput digital communication applications
In the past, radio-frequency signals were commonly used for low-speed wireless electronic systems, and optical signals were used for multi-gigabit wired communication systems. However, as the emergence of new millimeter-wave technology introduces multi-gigabit transmission over a wireless radio-frequency channel, the borderline between radio-frequency and optical systems becomes blurred. As a result, there come ample opportunities to design and develop next-generation broadband systems to combine the advantages of these two technologies to overcome inherent limitations of various broadband end-to-end interconnect systems in signal generation, recovery, synchronization, and so on. For the transmission distances of a few centimeters to thousands of kilometers, the convergence of radio-frequency electronics and optics to build radio-over-fiber systems ushers in a new era of research for the upcoming very-high-throughput broadband services.
Radio-over-fiber systems are believed to be the most promising solution to the backhaul transmission of the millimeter-wave wireless access networks, especially for the license-free, very-high-throughput 60-GHz band. Adopting radio-over-fiber systems in access or in-building networks can greatly extend the 60-GHz signal reach by using ultra-low loss optical fibers. However, such high frequency is difficult to generate in a straightforward way. In this dissertation, the novel techniques of homodyne and heterodyne optical-carrier suppressions for radio-over-fiber systems are investigated and various system architectures are designed to overcome these limitations of 60-GHz wireless access networks, bringing the popularization of multi-gigabit wireless networks to become closer to the reality.
In addition to the advantages for the access networks, extremely high spectral efficiency, which is the most important parameter for long-haul networks, can be achieved by radio-over-fiber signal generation. As a result, the transmission performance of spectrally efficient radio-over-fiber signaling, including orthogonal frequency division multiplexing and orthogonal wavelength division multiplexing, is broadly and deeply investigated. On the other hand, radio-over-fiber is also used for the frequency synchronization that can resolve the performance limitation of wireless interconnect systems. A novel wireless interconnects assisted by radio-over-fiber subsystems is proposed in this dissertation.
In conclusion, multiple advantageous facets of radio-over-fiber systems can be found in various levels of end-to-end interconnect systems. The rapid development of radio-over-fiber systems will quickly change the conventional appearance of modern communications.PhDCommittee Chair: Gee-Kung Chang; Committee Member: Bernard Kippelen; Committee Member: Shyh-Chiang Shen; Committee Member: Thomas K. Gaylord; Committee Member: Umakishore Ramachandra
FPGA implementation of OFDM signals for application to radio-over-fiber systems
Foi Implementado a geração de sinais OFDM em Matlab/System Generator e feita a validação funcional do hardware bem como a verificação em FPGA do sistema implementado. Validação do sistema em laboratório usando o spectrum analyzer
Effects of Fixed Point FFT Implementation of Wireless LAN
With the rapid growth of digital wireless communication in recent years, the need for high
speed mobile data transmission has increased. New modulation techniques are being
implemented to keep with the desire more communication capacity. Processing power has
increased to a point where orthogonal frequency division multiplexing (OFDM) has become
feasible and economical. Since many wireless communication systems being developed use
OFDM, it is a worthwhile research topic. Some examples of applications using OFDM
include Digital subscriber line (DSL), Digital Audio Broadcasting (DAB), High definition
television (HDTV) broadcasting, IEEE 802.11 (wireless networking standard).OFDM is a
strong candidate and has been suggested or standardized in high speed communication
systems.
This thesis analyzes the factor that affects the OFDM performance. The performance
of OFDM was assessed by using computer simulations performed using Matlab.it was
simulated under Additive white Gaussian noise (AWGN) channel conditions for different
modulation schemes like binary phase shift keying (BPSK), Quadrature phase shift keying
(QPSK), 16-Quadrature amplitude modulation (16-QAM), 64-Quadrature amplitude
modulation (64-QAM) which are used in wireless LAN for achieving high data rates.
One key component in OFDM based systems is inverse fast Fourier transform/fast
Fourier transform (IFFT/FFT) computation, which performs the efficient
modulation/demodulation. This block consumes large resources in terms of computational
power.this thesis analyzes, different IFFT/FFT implementation on performance of OFDM
communication system. Here 64-point IFFT/ FFT is used. FFT is a complex function whose
computational accuracy, hardware size and processing speed depend on the type of arithmetic
format used to implement it. Due to non-linearity of FFT its computational accuracy is not
easy to calculate theoretically. The simulation carried out here, measure the effects of fixed
point FFT on the performance of OFDM. Comparison has been made between bit error rate
of OFDM using fixed point IFFT/FFT and a floating point IFFT/FFT. Simulation tests were
made for different integer part lengths, fractional part lengths by limiting the input word
lengths to 16 bits and found the suitable combination of integer part lengths and fractional
part lengths which can achieve the best bit error rate (BER) performance with respect to
floating point performance. Extensive computer simulations show that fixed point
computation provides very near result as floating point if the delay parameter is suitably
selected
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