Simple 2 × 2 MIMO 60-GHz Optical/Wireless System With Extending Fiber Transmission Distance

This paper presents a simple 2 × 2 multiple-input multiple-output (MIMO) 60-GHz radio-over-fiber system. Due to the proposed specific frequency arrangement of driving signals, each optical transmitter requires only a single-drive Mach-Zehnder modulator with 3-dB bandwidth of less than 35 GHz. This arrangement of frequencies can increase the tolerance of optical signals to dispersion-induced RF fading, thereby extending fiber transmission distance. Unfortunately, this scheme leads to signal-to-signal beating interference (SSBI), which can deteriorate system performance. Thus, we employed a 2 × 2 MIMO scheme to enhance data capacity by combining two data streams and two corresponding SSBIs prior to signal demodulation. We also developed a novel iterative equalization technique to mitigate SSBI in the MIMO system. The proposed system achieved a maximum capacity of 55.9-Gb/s in the transmission of 7-GHz orthogonal frequency division multiplexing signals over 12-km fiber and 3.5-m air transmission using a bit-loading algorithm.