Özet:

Quadrature spatial modulation (QSM) is a promising technique for multiple-input-multiple-output (MIMO) systems that completely prevents inter-channel interference (ICI) and provides spatial multiplexing gain greater than spatial modulation (SM). In QSM, the information conveyed by the indices of the transmit antennas doubles thanks to the in-phase and quadrature components. In this regard, the quadrature spatial pulse amplitude modulation (QSPAM), which enables QSM for visible light communication (VLC) with the help of orthogonal pulses, is proposed in this paper. Generalized versions of QSPAM, i.e. generalized QSPAM (GQSPAM) and variable-length generalized QSPAM (VGQSPAM) have also been proposed and a well-known scheme, spatial pulse amplitude modulation (SPAM), is used as a benchmark. The proposed schemes efficiently use the spatial domain and increase spectral efficiency with fewer light-emitting diodes (LEDs). The angular diversity receiver (ADR) proposed for the channel correlation problem of indoor MIMO VLC systems is used as the receiver unit. Although ADR reduces channel correlation, it is not sufficient in the corner of the room. Therefore, a precoding matrix is generated with the help of convex optimization for demanding conditions. The bit error rate (BER) performance of considered modulation schemes is obtained through Monte Carlo simulations and, the upper bound BER performances are also derived analytically to validate these results. Additionally, spectral efficiency (SE) versus signal-to-noise ratio (SNR) graphs are obtained at a fixed symbol error rate (SER) of 10-5. According to the results, VGQSPAM performs better than the other schemes and benchmarks when the channel correlation is low. However, GQSPAM outperforms VGQSPAM for harsh conditions.

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