Multi-user adaptive orthogonal frequency-division multiplexing system for indoor wireless optical communications

Abstract

An adaptive orthogonal frequency-division multiplexing (OFDM) system is proposed for multi-user communications over indoor wireless optical channels. The designed system uses multi-user least-squares detection techniques applied to space-division multiple access and OFDM schemes, in conjunction with angle-diversity reception. The system, which does not present an excessive increase in complexity with respect to the previous schemes, can support high bit rates for multiple users, beyond 100 Mbits/s. It also mitigates the channel fluctuations induced when either the space distribution or the number of emitters and receivers varies. The performance of the new proposed scheme is compared with that of a non-adaptive multi-user system and an adaptive single-user system, both described in the previous works, when they face similar environmental situations. The obtained results show a significant enhancement with respect to both the previous multi-user system and the adaptive single-user one, since the new scheme allows adaptively managing the system throughput on a multi-user environment.

Indoor visible light communications, networking, and applications

“…Optical OFDM is a candidate modulation scheme often used in RF systems that has attracted attention for VLC systems [44,54,55,98]. Since LEDs can only transmit non-negative and real signals, conventional RF-OFDM schemes cannot be directly adopted.…”

“…Users' different locations result in channel loss differences, which are exploited in spatial division multiple access. OFDM-access is a multiplexing technique based on OFDM that is also used in multiuser VLC systems [54,55].…”

Multi-User Visible Light Communications

“…-QAM (quadrature amplitude modulation) modulator, b p (l) being the number of bits conveyed by the p th subcarrier (1 ≤ p ≤ S I ), according to a rate adaptive algorithm [32] [33]. Then, N -S I zeros are padded to this set of S I symbols generated by the modulators, the first zero being added before, corresponding to the direct-current (DC) value, and the remaining ones after.…”

“…In this chapter, we will apply the rate adaptive algorithm described in [32]. Here, we will only describe it briefly.…”

Digital Modulation Techniques for Optical Asymmetrically-Clipped OFDM

“…Until very recently Orthogonal Frequency Division Multiplexing (OFDM) was not considered suitable for optical fiber or optical wireless systems; however a growing number of papers have shown how OFDM can be applied across the optical domain [1], [2], [3], [4], [5], [6], [7], [8]. One new form of OFDM that is particularly suited to optical wireless communications is asymmetrically clipped optical OFDM (ACO-OFDM) [3].…”