Abstract

I. INTRODUCTION In recent years radio over fiber (RoF) technology has been extensively studied due to its numerous advantages such as broad bandwidth low attenuation and flexibility for wireless links. RoF combined with optical remote heterodyne technology [1-3] where the modulated signal light is coupled with an optical local oscillator (LO) at the central station (CS) and the base stations (BSs) do not need LO any more can further simplifies the BS and greatly reduces the overall system cost. In addition orthogonal frequency division multiplexing (OFDM) has been introduced in RoF system and attracted much attention due to its good tolerance to dispersion effects and multipath fading [4,5]. As is well known the single sideband OFDM (SSBOFDM) has higher spectral efficiency and robustness against chromatic dispersion-induced power fading in contrast to double sideband OFDM (DSB-OFDM). In optical remote heterodyne RoF system a single photo-detector (PD) can be used for RF signal recovery from the optical SSB signal which provides a cost-effective solution to the system. However the signal-to-signal beating interference (SSBI) is introduced by square-law detection of the photodiode [6]. Without extra SSBI cancellation processing the SSBI may deteriorate the system performance considerably. Generally there are two common methods to recover baseband signal from RF signal one is using power detector such as Schottky diode and the other is employing mixer for down conversion [7]. For the former one, an electric carrier along with the RF signal is needed which increases the transmitter complexity and decreases the power efficiency. For the latter one an extra microware LO is necessary for the mixer with high complexity and cost. Furthermore none of the two methods can mitigate the SSBI term if no additional SSBI elimination techniques are used [6]. Instead of depending extra SSBI cancellation processing the recently proposed approach named Kramers–Kronig (KK) algorithm can fully reconstruct the complex field baseband signal from the RF signal and is able to alleviate the SSBI very well with a low digital signal processing (DSP) complexity [8- 11]. Further signal processing like electrical chromatic dispersion compensation (CDC) can be performed together with OFDM demodulation. In this paper, we propose and demonstrate a SSB-OFDM-RoF system employing optical remote heterodyne technique with KK receiver. At the CS, the SSB-OFDM signal is generated by an IQ modulator coupled with a LO light. At each BS, the specified RF signal is obtained by heterodyne detection and transmitted to the user terminal where the original signal is reconstructed utilizing the KK-based approach. The key advantages of the proposed KK receiver-based SSB-OFDM-RoF scheme are listed in the following: 1) simplified system architecture and reduced complexity by employing optical remote heterodyne technology; 2) significantly reduced system cost without RF power detector, RF mixer, and microware LO as usual; 3) effectively mitigate the SSBI introduced by square-law detection of PD.

© 2018 The Author(s)