Radio-Over-Fiber System for TDD-Based OFDMA Wireless Communication Systems

• Published in: Journal of lightwave technology Vol. 25; no. 11; pp. 3419 - 3427
• Main Authors: Hoon Kim, Hoon Kim, Jae Hun Cho, Jae Hun Cho, Sangho Kim, Sangho Kim, Ki-Uk Song, Ki-Uk Song, Hanlim Lee, Hanlim Lee, Jaehoon Lee, Jaehoon Lee, Byungjik Kim, Byungjik Kim, Yunje Oh, Yunje Oh, Jaekon Lee, Jaekon Lee, Seongtaek Hwang, Seongtaek Hwang
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-11-2007; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antenna measurements; Antennas; Channels; Control systems; Crosstalk; Delay; Distortion measurement; Electric power generation; Links; MIMO; Noise levels; Optical communication; Optical fibers; orthogonal frequency division multiple access (OFDMA); Propagation delay; Radios; subcarrier multiplexing; time division duplex (TDD); Transmitting antennas; Wavelength measurement; Wireless communication; Wireless communications; Optical communication; orthogonal frequency division multiple access (OFDMA); time division duplex (TDD); subcarrier multiplexing
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2007.906807

We report on a fiber-optic transport system for next-generation wireless-communication systems utilizing 4 times 4 multiple-input multiple-output (MIMO) orthogonal-frequency-division-multiple-access (OFDMA) technology. Our system supports time-division-duplex (TDD)-based wireless signals operating at 3.775 GHz. To accommodate the TDD-based MIMO signals over a single strand of optical fiber, we utilize nine-channel coarse wavelength-division-multiplexed optical channels: one for link delay measurement and TDD control signal transmission, four for downlink, and the others for uplink. The system first measures the propagation delay between the central base station (CBS) and the remote antenna (RA) and sends the result to delay modules to compensate for the delay added by the transmission link. This procedure makes the CBS and RA emit the downstream signals simultaneously into the air and, consequently, helps avoid the performance degradation caused by the propagation delay of the radio-over-fiber system. The system then sends the MIMO signals together with TDD control signals to the RA. Our experimental demonstration is carried out with 1-Gb/s OFDMA signals having pilot, control, and data channels. For downstream, the error vector magnitudes (EVMs) are measured to be < -30 dB after a 3.9-km transmission over conventional single-mode fiber when the antenna output power is set to be 24 dBm. For upstream, the best EVMs are measured to be < -35 dB. Both the downstream and upstream performance is limited by the shot and thermal noise of the receiver when the signal power is low, whereas nonlinear distortions of electrical amplifiers start to degrade the system performance as the signal power increases. We also measure the crosstalk between channels. It is measured to be less than -42 dB for all channels, which is found to be caused by board-to-board interference at the RA.