Optical Wireless Communications Using Signal Space Diversity with Spatial Modulation

A signal space diversity (SSD) scheme was proposed to be incorporated with spatial modulation (SM) in an intensity-modulation/direct-detection-based multiple-input-single-output (MISO) indoor optical wireless communication (OWC) system to improve bit-error-rate (BER) performance and system throughput. SSD was realized via signal constellation rotation and diversity interleaving using different channel gains to improve the BER. With SM incorporated, the MISO-OWC system throughput increased. Theoretical BER expressions of the SSD scheme were established for the first time by investigating the distance of neighboring constellation symbols upon maximum-likelihood detection. Such BER expressions were further verified by numerical results. The results showed that, except for the slightly-lower-accuracy performance brought by comparable distances of neighboring constellation symbols in cases of low signal-to-noise ratios, these BER expressions were accurate in most scenarios. Moreover, theoretical investigations of channel gain distributions were performed at different signal constellation rotation angles to show the capability of the SSD scheme to improve the BER. The results showed that a significantly improved BER by two orders of magnitude could be achieved using a reasonably high channel-gain ratio and a larger constellation rotation angle. The SSD-SM scheme provides a promising option to achieve transmitter diversity with an enhanced throughput in high-speed indoor OWC systems.

Analysis and FPGA Implementation of Zero-Forcing Receive Beamforming with Signal Space Diversity under Different Interleaving Techniques

We combine multiple-input multiple-output zero-forcing receive beamforming (ZFRBF) with time and spatial component interleaved signal space diversity (SSD) and analyze the system’s error performance and implementation complexity. A transreceiver system with two transmit and [Formula: see text] ([Formula: see text]) receive antennas is considered where the number of simultaneous substreams equals two. The error performance of the proposed scheme with binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulations is studied. Under the time component interleaved SSD case, we derive an exact average bit error probability expression for BPSK and a tight approximation on the average symbol error probability for QPSK. The signal constellation rotation angles are accordingly computed. Using a similar approach, the signal constellation rotation angles are also determined for the scenario of spatial component interleaved SSD. It is demonstrated that the performance of the original ZFRBF model can be improved significantly by utilizing SSD especially with the time interleaving method. Another contribution to the literature is to study hardware complexity of the proposed scheme on FPGA. It is shown that while achieving considerable performance gain, SSD introduces only an insignificant increase to the system complexity without any extra bandwidth or time slot usage.