All-Digital, Radio-Over-Fiber, Communication Link Architecture for Time-Division Duplex Distributed Antenna Systems

Radio-over-fiber is a popular technique to establish communication links between a central location and many remote antenna units. Many different architectures are available for the downlink, i.e., for the communication link from the central unit to the remote antennas. On the contrary, the low-cost and low-complexity requirement of the remote units makes it difficult to devise architectures suitable for the uplink, i.e., for the communication link from the remote antennas to the central unit. In this article, we address this and propose a low-complexity, all-digital, time-division-duplex communication architecture. For the downlink, a band-pass sigma-delta-over-fiber is employed. In the receive mode, the uplink includes an all-digital pulse-width-modulation technique. The received radio frequency (RF) signal is quantized into a binary stream through comparison with a tailored reference signal provided by the central unit. The direct quantization of the RF signal eliminates any need for local-oscillator and mixer stages at the remote units. The performance of the proposed architecture is investigated through extensive simulations and measurements. For instance, the all-digital, time-division duplex communication link provides -30.0 dB and -25.5 dB normalized mean square error signal quality through downlink and uplink communication with 20-MHz, 64-quadrature amplitude modulation signals centered at 2.365-GHz, respectively.