Ricerc@Sapienza

Spectral efficiency of low-density spreading nonorthogonal multiple access channels in the presence of fading is derived for linear detection with independent decoding as well as optimum decoding. The large system limit, where both the number of users and number of signal dimensions grow with fixed ratio, called load, is considered. In the case of optimum decoding, it is found that low-density spreading underperforms dense spreading for all loads. Conversely, linear detection is characterized by different behaviors in the underloaded vs. overloaded regimes.

This letter proposes a modulation scheme that combines both pulse slots and amplitudes in a flexible manner to obtain a desired level of flicker-free dimming while efficiently conveying information for visible light communication. The scheme is referred to as energy-constrained slot-amplitude modulation (ECSAM). Specifically, the total energy for every macro-symbol, containing multiple pulse slots, is fixed at a level that depends on the requested dimming target by adjusting the number of active slots and their amplitude levels.

In this paper, we propose a modified generalized spatial modulation (MGSM) scheme with dimming support for indoor optical wireless communication (OWC) systems. The spatial indices of the active LEDs and their transmitted optical power levels are utilized to modulate data in MGSM. The key property of the signal waveforms in MGSM is that it provides the same amount of optical power emitted at any time instant that corresponds to the dimming level requested.

This paper proposes an advanced multi-pulse multi-light emitting diodes (LEDs) modulation technique to improve the efficiency for indoor visible light communication systems. The technique is referred to as spatial multiple pulse position modulation (SMPPM), and it is developed by combining a high spectral efficiency space shift keying (SSK) with a high energy efficiency multiple pulse position modulation (MPPM).