115 research outputs found
Channel Coding in Molecular Communication
This dissertation establishes and analyzes a complete molecular transmission system from
a communication engineering perspective. Its focus is on diffusion-based molecular communication
in an unbounded three-dimensional fluid medium. As a basis for the investigation
of transmission algorithms, an equivalent discrete-time channel model (EDTCM) is developed
and the characterization of the channel is described by an analytical derivation, a
random walk based simulation, a trained artificial neural network (ANN), and a proof of
concept testbed setup. The investigated transmission algorithms cover modulation schemes
at the transmitter side, as well as channel equalizers and detectors at the receiver side.
In addition to the evaluation of state-of-the-art techniques and the introduction of orthogonal
frequency-division multiplexing (OFDM), the novel variable concentration shift
keying (VCSK) modulation adapted to the diffusion-based transmission channel, the lowcomplex
adaptive threshold detector (ATD) working without explicit channel knowledge,
the low-complex soft-output piecewise linear detector (PLD), and the optimal a posteriori
probability (APP) detector are of particular importance and treated. To improve the
error-prone information transmission, block codes, convolutional codes, line codes, spreading
codes and spatial codes are investigated. The analysis is carried out under various
approaches of normalization and gains or losses compared to the uncoded transmission are
highlighted. In addition to state-of-the-art forward error correction (FEC) codes, novel line
codes adapted to the error statistics of the diffusion-based channel are proposed. Moreover,
the turbo principle is introduced into the field of molecular communication, where extrinsic
information is exchanged iteratively between detector and decoder. By means of an extrinsic
information transfer (EXIT) chart analysis, the potential of the iterative processing is
shown and the communication channel capacity is computed, which represents the theoretical
performance limit for the system under investigation. In addition, the construction of an
irregular convolutional code (IRCC) using the EXIT chart is presented and its performance
capability is demonstrated. For the evaluation of all considered transmission algorithms the
bit error rate (BER) performance is chosen. The BER is determined by means of Monte
Carlo simulations and for some algorithms by theoretical derivation
Transceiver Design for MIMO DCO-OFDM in Visible Light Communication
Direct current-biased optical-orthogonal frequency-division multiplexing (DCO-OFDM) is a simple yet spectrally efficient multicarrier modulation scheme for visible light communication (VLC). But in multiple-input multiple-output (MIMO) scenario, which is more practical for VLC due to the LED deployment, the research on DCO-OFDM is still limited and calls for in-depth investigation. In this chapter, we first study the basic modulation scheme of DCO-OFDM, including the design of conventional receiver without considering the clipping noise. Secondly, we present a novel receiver for combating clipping distortion in the DCO-OFDM system, which can reconstruct the clipping noise and subtract it from the received signal. Thirdly, we generalize the results to MIMO scenario and investigate the preliminary transceiver design, which is based on the minimum mean-square error (MMSE) criteria. Based on this, we propose a precoding algorithm to further enhance the performance. Finally, the symbol error rate performance is compared through computer simulations to give the reader a whole picture of the performance of MIMO VLC system
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
Performance analysis of OFDM technology on radio-over-fiber systems
Dissertação de mest., Engenharia Eletrónica e Telecomunicações, Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2011Nowadays, the demand for high speed, high quality and diversity in distributed services presents a challenge for telecommunication technology. Wireless systems provide the accessibility to end-user, but are not the solution for long distance links. Currently, the ideal technology for long-range transmissions at high data rates is optical fiber. Hence, a new concept for high capacity networks emerges, with centralized services into Base Stations (BS) engineered to provide flexibility and control over the system, and to perform operations such as electrical to optical domain conversion and modulation. Such Radio-over-Fiber (RoF) networks also appear as an attractive technology because they are efficient and cost effective.
Orthogonal Frequency Division Multiplexing (OFDM) technology is widely used in a number of standards. For instance, it is actually the Multi-Carrier Modulation (MCM) technique applied in 802.11a/g/n wireless standards and in Digital Video Broadcasting-Terrestrial (DVB-T), among other prevailing systems, which makes this subject one particularly pertinent to study. OFDM systems are an appealing choice for waveform modulation, as they are very bandwidth efficient comparing to others MCM, and provide flexibility in data transmission rates. Additionally, an important advantage dwells in its natural robustness against severely interfering environments.
In this thesis, fundamentals on OFDM technology are extensively described, and its application to wireless and optical fiber networks is introduced. The combined channel effects of these technologies on OFDM signals are investigated. In terms of performance analysis, this exposition focuses on understanding the importance of OFDM modulation parameters, and explores some OFDM signal properties. To achieve this, a simulator was implemented with Matlab to create arbitrary OFDM waveforms and emulate channel effects. This study also investigates the efficiency of OFDM technology over a real Radio Frequency (RF) system with an ideal communication channel. Finally, an experimental RoF configuration is implemented and its performance is assessed
Advanced Digital Signal Processing Techniques for High-Speed Optical Links
L'abstract è presente nell'allegato / the abstract is in the attachmen
Advanced Technique and Future Perspective for Next Generation Optical Fiber Communications
Optical fiber communication industry has gained unprecedented opportunities and achieved rapid progress in recent years. However, with the increase of data transmission volume and the enhancement of transmission demand, the optical communication field still needs to be upgraded to better meet the challenges in the future development. Artificial intelligence technology in optical communication and optical network is still in its infancy, but the existing achievements show great application potential. In the future, with the further development of artificial intelligence technology, AI algorithms combining channel characteristics and physical properties will shine in optical communication. This reprint introduces some recent advances in optical fiber communication and optical network, and provides alternative directions for the development of the next generation optical fiber communication technology
Spectrally Efficient WDM Nyquist Pulse-Shaped 16-QAM Subcarrier Modulation Transmission With Direct Detection
The ability to transmit signals with high information spectral density (ISD) using low-complexity and cost-effective transceivers is essential for short- and medium-haul optical communication systems. Consequently, spectrally efficient direct detection transceiver-based solutions are attractive for such applications. In this paper, we experimentally demonstrate the wavelength-division multiplexed (WDM) transmission of 7×12 GHz-spaced dispersion pre-compensated Nyquist pulse-shaped 16-QAM subcarrier modulated channels operating at a net bit rate of 24 Gb/s per channel, and achieving a net optical ISD of 2.0 b/s/Hz. The direct detection receiver used in our experiment consisted of a single-ended photodiode and a single analog-to-digital converter. The carrier-to-signal power ratio at different values of optical signal-to-noise ratio was optimized to maximize the receiver sensitivity performance. The transmission experiments were carried out using a recirculating fiber loop with uncompensated standard single-mode fiber and EDFA-only amplification. The maximum achieved transmission distances for single channel and WDM signals were 727 and 323 km below the bit-error ratio of 3.8 × 10-3, respectively. To the best of our knowledge, this is the highest achieved ISD for WDM transmission in direct detection links over such distances
Visible Light Communication (VLC)
Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, “Visible Light Communication (VLC)”, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC
Nonlinear effects in OFDM signal transmission over radio over fibre links
The dynamic range limitations that arise from nonlinearity in low-cost and low complexity directly modulated radio over fibre (RoF) links are examined. Statistical non linear models are presented and applied to the case of a RoF link with a low biased laser diode. The effects of distortion on the Error Vector Magnitude (EVM) performance of Orthogonal Frequency-Division Multiplexing (OFDM) signals with different numbers of subcarriers and the connection to the Peak-ta-Average Power Ratio (PAPR) of the signals are investigated. Statistical distributions of the EVM over a large number of transmitted OFDM frames are gained from experimental measurements and analyses of idealized processes. The measurement results show that as the number of subcarriers is reduced the distribution means are not dependent in the expected way on the statistical PAPR of the transmitted OFDM signals. Instead, it is shown that in regions of moderate distortion the median of the EVM is more closely related to the statistical PAPR and to the required back-off for signals with different numbers of subcarriers. Through the employed statistical analysis, the asymptotic convergence of the EVM result to that expected in the idealized case is observed. The results of this analysis also show, how, including the EVM variance in estimations for back-off might be useful, how, in a measurement, the number of transmitted OFDM frames affects the estimated mean EVM. Differing EVM results for subcarriers at the edge and middle of the signal band show that distortion affects the subcarriers at the middle of the band to a stronger degree and that their behaviour is correlated "to the statistical PAPR of the individual signals. Then, a laser model validated against measured performance is designed arid used for simulating the performance of a subcarrier multiplexed 4th generation mobile/wireless RoF transmission system. Predictions indicate that the architecture provides adequate performance in terms of EVM, for different IFFT sizes and modulation levels of up to 256 QAM (at leastL and a combined raw data rate of up to 3.2 Gbps. Based on a 1.5% EVM transmitter requirement with 256 QAM, a system dynamic range of approximately 5.1 dB is predicted. Finally, the use of companding in a directly modulated RaF link, with the aim of reducing the amplification (and isolation) requirements in the remote antenna unit, is demonstrated, quantified through EVM measurements. The resulting improvements in output power are approximately 4.7 dB at an EVM transmitter requirement of 5.6 %, while in terms of the point of onset of distortion-induced EVM increase, the improvement is approximately 7.6 dB
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