Performance analysis of modified asymmetrically-clipped optical orthogonal frequency-division multiplexing systems

A modification to the Asymmetrically-Clipped Optical Orthogonal Frequency-Division Multiplexing (ACO-OFDM) technique is proposed through unipolar encoding. A performance analysis of the Bit Error Rate (BER) is developed and Monte Carlo simulations are carried out to verify the analysis. Results are compared to that of the corresponding ACO-OFDM system under the same bit energy and transmission rate; an improvement of 1 dB is obtained at a BER of 10-4. In addition, the performance of the proposed system in the presence of atmospheric turbulence is investigated using single-input multiple-output (SIMO) configuration and its performance under that environment is compared to that of ACO-OFDM. Energy improvements of 4 dB and 2.2 dB are obtained at a BER of 10-4 for SIMO systems of 1 and 2 photodetectors at the receiver for the case of strong turbulence, respectively

Suitability of variance shift keying for real conditions

This paper investigates the possibility of real-life using the brand new type of digital modulation, which implies the transmission of white Gaussian noise whose variance changes in time. That modulation has been entitled as variance shift keying. The signals obtained on its basis have a high level of transmission security, and they even cannot be detected by standard means of matched filtering. However, the paper suggests the decision on how to process these signals at the receiver site. It is proposed to use a specially developed optimal receiver, whose restoration quality appears to be better in comparison with the conventional cumulative receiver. The digital simulation of propagation in frequency selective media has shown the signal with variance shift keying is possible to be used in real conditions since its distribution of instantaneous amplitudes remains Gaussian. © 2018 Academic Mind.The work was supported by Act 211 Government of the Russian Federation, contract № 02.A03.21.0006. The research was executed by the grant of the Ministry of education and science of the Russian Federation (project № 8.2538.2017/4.6)

Introduction to Random Signals and Noise

Random signals and noise are present in many engineering systems and networks. Signal processing techniques allow engineers to distinguish between useful signals in audio, video or communication equipment, and interference, which disturbs the desired signal. With a strong mathematical grounding, this text provides a clear introduction to the fundamentals of stochastic processes and their practical applications to random signals and noise. With worked examples, problems, and detailed appendices, Introduction to Random Signals and Noise gives the reader the knowledge to design optimum systems for effectively coping with unwanted signals.\ud \ud Key features:\ud • Considers a wide range of signals and noise, including analogue, discrete-time and bandpass signals in both time and frequency domains.\ud • Analyses the basics of digital signal detection using matched filtering, signal space representation and correlation receiver.\ud • Examines optimal filtering methods and their consequences.\ud • Presents a detailed discussion of the topic of Poisson processed and shot noise.\u

A study of the minimum shift keying modulation scheme

This thesis concerns itself with the study of the Minimum Shift Keying (MSK) modulation scheme. The aspects considered are its operation under non-linear conditions as well as an investigation into the hardware implementation of both coherent and non-coherent MSK modems. The literature on digital data transmission and MSK in particular is surveyed, and a comprehensive theoretical description of MSK is given. In addition, papers on the operation of MSK under non-linear conditions were studied, and their major findings are presented. Due to the lack of theory on the effects of incorrect modulation index on the error performance of MSK, an investigation into this avenue was performed. The design of a correction mechanism for maintaining the modulation index at its correct value is described, and aspects of its implementation are considered. Using the available literature, various modules of which a coherent MSK modem is comprised were developed, and their design is discussed. The design of a non-coherent MSK demodulator is also described

A review of gallium nitride LEDs for multi-gigabit-per-second visible light data communications

The field of visible light communications (VLC) has gained significant interest over the last decade, in both fibre and free-space embodiments. In fibre systems, the availability of low cost plastic optical fibre (POF) that is compatible with visible data communications has been a key enabler. In free-space applications, the availability of hundreds of THz of the unregulated spectrum makes VLC attractive for wireless communications. This paper provides an overview of the recent developments in VLC systems based on gallium nitride (GaN) light-emitting diodes (LEDs), covering aspects from sources to systems. The state-of-the-art technology enabling bandwidth of GaN LEDs in the range of >400 MHz is explored. Furthermore, advances in key technologies, including advanced modulation, equalisation, and multiplexing that have enabled free-space VLC data rates beyond 10 Gb/s are also outlined

Investigation and analysis of time codes Quarterly report

Optimum time code system analysis including characterization of transmission channels, and signal desig

Design And Realization Of Gmsk Modem

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2006Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2006Bu çalısmada, GMSK modülatörü ve demodülatörünün tasarımı yapılmıstır.Genel sayısal haberlesme teknikleri anlatılmıstır. Bazı modülasyon türleri ele alınmıstır. GMSK modülasyonu detaylı olarak anlatılmıstır. Sistem, modülatör ve demodülatör, MATLAB de modellenmistir. Haberlesme sistemlerinde önemli olan, gürültü, çok yollu sönme, kanallar arası girisim olguları MATLAB de modellenip simule edilmistir. Tüm sistemin performansı simule edilmistir. Haberlesme asenkron olarak gerçeklestiğinden dolayı, örnekleme zaman hataları ve frekans hatalarını karsılamak için senkronizasyon yapılmıstır. Tasarlanan modem TI 5509 sayısal isaret islemcisinde kodlanmıstır.In this study design of a GMSK modulator and demodulator is done. General digital communication techniques are described. Some modulation schemes are explained. The GMSK modulation is explained in detail. The system, modulator and demodulator, is modelled by MATLAB. The tasks concerning communication systems such as noise, multipath fading and co-channel interference is modelled and simulated by MATLAB. Overall system performance of the modem is evaluated. As the communication is done in an asynchronous manner, synchronization is utilized in order to compansate for sampling timing errors and frequency offsets. The designed modem is coded on a TI 5509 DSP chipset.Yüksek LisansM.Sc

Improvements to Optical Communication Capabilities Achieved through the Optical Injection of Semiconductor Lasers

Optically injection locked lasers have shown significant improvement in the modulation capabilities of directly modulated lasers. This research creates a direct-modulated optical communications system to investigate the bit-rate distance improvements achievable using optically injected Fabry-Pérot laser diodes. The injection strength and detuning frequency of the injection signal was varied to determine their impact on the optical communication link\u27s characteristics. This research measured a 25 fold increase in bit-rate distance product using optical injection locking as compared to the injected laser\u27s free-running capability. A 57 fold increase was measured in the bit-rate distance product when signal power is considered in a power-penalty measurement. This increased performance is attributed to the injected signals tolerance to dispersion given its reduced linewidth and chirp. This work also investigates the suitability of optical injection for radio over fiber applications using the period-one dynamic of optical injection. The all-optically generated, widely tunable microwave subcarrier frequency, well above the 3-dB cutoff frequency of the laser\u27s packaging electronics, was modulated with the same baseband electronics. This optically carried, ultra-wide spread spectrum signal was transported over 50km of standard-single-mode fiber. After detection at a high-speed photo- detector and the baseband modulation component was removed, the resultant signal was found to be suitable for broadcasting with an antenna or added to a frequency division multiplexed channel

CMOS-integrated GaN LED array for discrete power level stepping in visible light communications

We report a CMOS integrated micro-LED array capable of generating discrete optical output power levels. A 16 x 16 array of individually addressable pixels are on-off controlled through parallel logic signals. With carefully selected groups of LEDs driven together, signals suitable for discrete transmission schemes are produced. The linearity of the device is assessed, and data transmission using pulse amplitude modulation (PAM) and orthogonal frequency division multiplexing (OFDM) is performed. Error-free transmission at a symbol rate of 100 MSamples/s is demonstrated with 4-PAM, yielding a data rate of 200 Mb/s. For 8-PAM, encoding is required to overcome the baseline wander from the receiver, reducing the data rate to 150 Mb/s. We also present an experimental proof-of-concept demonstration of discrete-level OFDM, achieving a spectral efficiency of 3.96 bits/s/Hz