In Chapter 3, the power budget and cumulating SNR issues of a Fi-Wi system with a single RF carrier were studied. However, often multiple RF signals need to be transmitted over a Fi-Wi channel in a subcarrier-multiplexed manner. When two or more RF signals propagate over fiber, the performance analysis is complicated because the ROF link is a nonlinear medium. Study of such a dual-subcarrier system is the objective of this and the next chapter. This chapter investigates the performance in the downlink direction while the next chapter studies the performance in the uplink direction.
In this chapter, SCM transmission of IEEE 802.11b wireless local area network (WLAN) and cellular radio WCDMA signals is considered. These two systems are of particular interest. First, numerous wireless hot-spots are deployed these days. These hot-spot antennas can easily be fed by ROF links. Since most smart cellular phones have Wi-Fi capability, the ability to provide both Wi-Fi and cellular radio access from a single access point is of practical interest. This arrangement also benefits the end users, because Wi-Fi supports high bandwidth and the spectrum is usually free. Figure 5.1 illustrates such an interesting architecture, where the central node is linked to multiple radio access points via ROF links. Each RAP covers a relatively large WCDMA microcell and a relatively small Wi-Fi hot-spot.