Bidirectional fiber-wireless access technology for 5G mobile spectral aggregation and cell densification

Empowered by spectral aggregation and cell densification, future 5G mobile data networks pose a huge challenge to building next-generation mobile fronthaul systems with higher capacity, scalability, and energy efficiency. Under this circumstance, traditional solutions based on the Common Public Radio Interface or channel aggregation with digital signal processing (DSP) are not sufficient to support heterogeneous ubiquitous wireless access. In this paper, we demonstrate a point-to-multipoint bidirectional mobile fronthaul system. Wavelength division multiplexing plus frequency division multiplexing is applied to support independent asynchronous small cells. Intensity-modulation and direct-detection downlink (DL) as well as field-modulation and heterodyne-detection uplink (UL) are proposed. Combined with efficient virtual tone-based DSP for phase recovery and carrier-frequency-offset estimation, signal degradations from beating among incoherent asynchronous UL signals are mitigated. Proof-of-concept experiments are demonstrated where 20 and 16 80-MHz component carriers are transmitted over 25-km standard single-mode fiber for DL and UL, respectively. Less than 6% error vector magnitudes with 64-, 16-, and 4-ary quadrature amplitude modulation are obtained.