JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 26, NO. 16, AUGUST 15, 2008 2857 Multifunctional Optical Interface for Fiber-Radio Systems in Heterogeneous Access Networks Christina Lim, Senior Member, IEEE, Ka-Lun (Alan) Lee, Member, IEEE, (Thas) Ampalavanapillai Nirmalathas, Senior Member, IEEE, Dalma Novak, Fellow, IEEE, and Rod Waterhouse, Senior Member, IEEE Abstract—In this paper, we investigate through simulation a proposed multi-functional optical interface incorporating an arrayed waveguide grating (AWG) that multiplexes multiple wavelength-interleaved dense-wavelength-division-multiplexed (DWDM) optical RF channels while simultaneously reducing inter- modulation distortion (IMD) in fiber-radio systems incorporating optical single sideband with carrier (OSSB+C) modulation. The proposed optical interface is also able to simultaneously support multiple baseband transmission in an integrated wireless/wired heterogeneous access environment. We derive an analytical model and present a detailed analysis of the proposed interface to es- tablish the viability of its operation and quantify performance limitations. Our results show that the proposed scheme is not dependent on the inherent characteristics of the optical carrier and a maximum IMD suppression of can be achieved. The proposed interface was also investigated via simulation for a larger number of DWDM channels to establish the viability and subsequently quantify the overall performance of a heterogeneous millimeter-wave fiber-radio system with other wired-access infra- structure. Index Terms—Fiber-wireless, linearization schemes, microwave photonics, optical-wireless integration, radio-over-fiber. I. INTRODUCTION H YBRID fixed wireless access at submillimeter-wave or millimeter-wave (mm-wave) radio frequencies inte- grated with optical fiber backbone networks has the capacity to deliver future broadband services [1]–[3]. In general, such an architecture comprises a central office (CO) incorporating a wide range of functions including switching, routing, pro- cessing and management that distributes the radio signals via an optical backbone to a large number of functionally simple antenna base stations (BSs) for wireless distribution. The use of fiber distribution schemes simplifies the overall wireless access network, enabling the sharing of resources among a large number of BSs. However, the optical distribution of Manuscript received July 16, 2007; revised November 11, 2007. Current ver- sion published October 24, 2008. This work was supported by the Australian Research Council Discovery Grant DP0452223. C. Lim and K.-L. Lee are with the ARC Special Research Centre on Ultra Broadband Information Networks, Department of Electrical and Electronic Engineering, The University of Melbourne, VIC 3010, Australia (e-mail: c.lim@ee.unimelb.edu.au; a.lee@ee.unimelb.edu.au). A. (Thas) Nirmalathas is with the National ICT Australia, Victoria Research Laboratory, Department of Electrical and Electronic Engineering, The Univer- sity of Melbourne, VIC 3010, Australia (e-mail: a.nirmalathas@ee.unimelb. edu.au). D. Novak and R. Waterhouse are with the Pharad, LLC, Glen Burnie, MD 21061 USA (e-mail: dnovak@pharad.com; rwaterhouse@pharad.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2007.914530 Fig. 1. Schematic of proposed linearization technique with simultaneous base- band transmission. submillimeter-wave and millimeter-wave signals is susceptible to the effects of fiber chromatic dispersion which can severely limit the fiber transmission distance [4], [5]. It is well estab- lished that this shortcoming can be overcome using optical single sideband with carrier (OSSB+C) modulation [6], [7]. There are also other methods to mitigate this penalty which are well documented in [8]–[10] using filtering techniques, phase diversity, and specialized electrooptic modulators. In a wireless access network with a multicarrier environment, linearity plays an important role in the improvement of the system dynamic range. It has been shown that the nonlinearity of the optical frontend in a fiber distributed wireless network limits the overall system dynamic range [11] and this con- dition worsens due to other fiber nonlinearities as the radio signals propagate through the fiber link [12]. A number of linearization techniques have been demonstrated to combat IMD products and improve the dynamic range of optical analog links including: optical feedforward [13], gain modulation [14], predistortion [15], [16], and parallel modulator configurations [17]–[19]. However, to date, there has been limited work undertaken to cancel IMD for OSSB+C modulated optical signals in fiber-radio applications. Recently, we have proposed a linearization technique based on the removal of the dominant sources of IMD in the optical domain that were generated due to the OSSB+C nonlinear characteristics with improvement achieved in the carrier-to-interference ratio (CIR) [20], [21]. We have also previously demonstrated an optical interface based on arrayed-waveguide-gratings (AWGs) that support multiple dense-WDM (DWDM) optical fiber-radio 0733-8724/$25.00 © 2008 IEEE