Class-O base station system with RF pulse-width-modulation in downlink and uplink

In this paper, we present a novel so-called class-O distributed base station system where the remote unit and the central unit are connected via an optical link. In contrast to existing systems, we transmit a binary RF signal over the optical link which significantly reduces the complexity of the remote unit. The conversion from an analog to a binary signal is implemented using a fast pulse-width-modulator in the RF domain. For downlink this pulse-width-modulator is combined with a class-S amplifier, meeting the 3GPP ACLR requirements within an excellent 10 dB electrical output power range. The uplink shows a dynamic range of 65 dB for a 5 MHz LTE signal. Lab measurements show robust optical transmission of the RF signals over up to 40 km fiber. It is shown that both downlink and uplink are capable of supporting simultaneous transmission and reception, respectively, of non-contiguous frequency bands.