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Spectral efficiency improvement is a key focus in most wireless communication systems and achieved by various means such as using large antenna arrays and/or advanced modulation schemes and signal formats. This work proposes to further improve spectral efficiency through combining non-orthogonal spectrally efficient frequency division multiplexing (SEFDM) systems with index modulation (IM), which can efficiently make use of the indices of activated subcarriers as communication information. Recent research has verified that IM may be used with SEFDM to alleviate inter-carrier interference (ICI) and improve error performance. This work proposes new SEFDM signal formats based on novel activation pattern designs, which limit the locations of activated subcarriers and enable a variable number of activated subcarriers in each SEFDM subblock. SEFDM-IM system designs are developed by jointly considering activation patterns, modulation schemes and signal waveform formats, with a set of solutions evaluated under different spectral efficiency scenarios. Detailed modelling of coded systems and simulation studies reveal that the proposed designs not only lead to better bit error rate (BER) but also lower peak-to-average power ratio (PAPR) and reduced computational complexity relative to other reported index-modulated systems. [ABSTRACT FROM AUTHOR]

The ever-growing machine-to-machine traffic in data centers has stimulated the increase of transceiver data rate from 25 Gb/s/λ to 100 Gb/s/λ and beyond. It is believed that advanced modulation formats and digital-to-analog converters (DACs) will be employed in next generation short-reach transceivers. Digital pre-emphasis techniques are widely employed in DAC-based transceivers to compensate for the high frequency roll-off due to the RF and optoelectronics components in optical transceivers. However, digital pre-emphasis essentially reduces the magnitude of the signal low frequency components for a flat frequency response, which unavoidably increases quantization error, reducing the overall signal-to-noise ratio. This trade-off between SNR and bandwidth conflicts with the high SNR requirement of advanced modulation formats such as the Nyquist-shaped pulse amplitude modulation (PAM). To mitigate the quantization error induced SNR degradation, we show that analog pre-emphasis filters can be used in conjunction with digital pre-emphasis for improved system performance. To understand the impact of the analog pre-emphasis filter on system performance, we analyze the relationship between the flatness of the system frequency response and the SNR degradation due to digital pre-emphasis, and demonstrate 1.1-dB increase of receiver sensitivities, for both 64-Gb/s and 128-Gb/s intensity-modulation direct detection (IM-DD) PAM4 signals, respectively employing a directly modulated laser (DML) and an electroabsorption modulator (EAM). [ABSTRACT FROM AUTHOR]

In this letter we experimentally verify a real-time implementation of the ‘better-than-Nyquist’ pulse shape in carrier-less amplitude and phase (CAP) modulation in the context of a visible light communications system. We use two National Instruments universal software radio peripherals (USRPs) as a transmitter and receiver working independently. Previously reported experimental work on pulse shaping in CAP is also verified in real time, showing lower error vector magnitudes (EVM) can be obtained at shorter filter lengths using the better-than-Nyquist pulses in place of the conventionally used square-root raised cosine as the basis function of the signal. We show that a real time EVM penalty is an additional 3% EVM in the worst case and is a result of synchronisation offset at the receiver. [ABSTRACT FROM AUTHOR]

Visible light communications is a technology with enormous potential for a wide range of applications within next generation transmission and broadcasting technologies. VLC offers simultaneous illumination and data communications by intensity modulating the optical power emitted by LEDs operating in the visible range of the electromagnetic spectrum (~370?780 nm). The major challenge in VLC systems to date has been in improving transmission speeds, considering the low bandwidths available with commercial LED devices. Thus, to improve the spectral usage, the research community has increasingly turned to advanced modulation formats such as orthogonal frequency-division multiplexing. In this article we introduce a new modulation scheme into the VLC domain; multiband carrier-less amplitude and phase modulation (m-CAP) and describe in detail its performance within the context of bandlimited systems. [ABSTRACT FROM PUBLISHER]

We investigate the radiation hardness of Reflective Electroabsorption Modulators (REAMs) for fluence levels up to 14 \times 10^15 24 GeV p/cm^2 to explore the possibility of utilising REAMs for data readout at the High-Luminosity Large Hadron Collider (HL-LHC). The high fluence levels used in the experiment and the online spectral measurements carried out provide significant insight into the radiation damage mechanism. The radiation limits of an architecture based on REAMs are established and compared to LHC and HL-LHC fluence levels. [ABSTRACT FROM PUBLISHER]