Contents I. Introduction
Millimeter-Wave (mm-wave) fiber-radio access technology is being proposed for the future distribution of broadband services [1]. The mm-wave frequency band offers a large transmission bandwidth and overcomes spectral congestion in the lower microwave frequency regions. Optical fiber, with its inherent properties of low loss and large bandwidth, is an ideal medium to distribute broadband mm-wave radio signals to the base stations (BSs) [1]–[4]. The proposed architecture of such a hybrid network comprises a central office (CO), where all switching, routing, and frequency management functions are performed, and an optical fiber network, which interconnects a large number of functionally simple and compact antenna BSs for wireless distribution. The distribution of radio signals to and from BSs can be either as mm-wave modulated optical signals (RF-over-fiber) [5], [6] or as lower frequency subcarriers (IF-over-fiber) [7]. Signal distribution as RF-over-fiber has the advantage of a simplified BS design but is susceptible to fiber chromatic dispersion that severely limits the transmission distance [8], [9]. The impact of fiber dispersion, however, can be mitigated by using an optical single sideband with carrier (OSSB+C) modulation scheme [10]. In contrast, the effect of fiber chromatic dispersion on the distribution of intermediate-frequency (IF) signals is much less pronounced, although antenna BSs implemented for fiber-radio systems incorporating IF-over-fiber transport require additional electronic hardware such as a mm-wave frequency local oscillator (LO) for frequency up- and downconversion, which complicates the BS design. This requirement can be relaxed by remote delivery of the LO signal [7], [11].
