Contents I. Introduction
Today, wireline and wireless technologies are competing strongly in the access network segment, yet none of them seems to offer disruptive advantages in all scenarios. Scenario for the proposed transmission technique: A hybrid multiservice BS supporting both wireless and wireline accesses is fed by a single CS A shared infrastructure that ensures coexistence of both wireline and wireless accesses seems to be a key requirement to ensure transparency and interoperability at the access node (AN). Future bandwidth requirements of access networks demanded by the expected traffic growth (in the gigabits per second range) impose the use of optical fiber to feed a number of remote wireline or wireless ANs or base stations (BSs) from a central station (CS). This centralized scheme allows a reduction of capital and operational expenditures for installation and maintenance as all the remote ANs (wireless and wireline) share the cost of the unique CS. Hybrid radio-fiber techniques have been proposed as promising technologies to achieve that goal, using a variety of approaches [1]–[4] coping with the carrier suppression effect induced by the fiber chromatic dispersion [5]. The possibility of transmitting simultaneously at different frequency bands has been proposed recently as a cost-effective and flexible way for feeding heterogeneous and multiservice ANs [6]–[9]. In this letter, the transmission of quadrature-phase-shift keying (QPSK) and -quadrature amplitude modulation (-QAM) signals with different bit rates modulated simultaneously onto 1- and 38-GHz carriers using a dispersion-tolerant harmonic optical modulation scheme based on a single dual-drive Mach–Zehnder modulator (DD-MZM) is demonstrated experimentally. Previously, the technique was demonstrated for baseband signals [8], [9]. The modulated data can be error-free recovered at both frequency bands after transmission over a 50-km fiber link and at 38 GHz after including a 2-m length radio path. In addition, the obtained results show that the proposed technique is highly tolerant to deviations on the bias point of the DD-MZM. Experimental setup used in the measurements including the single CS, the wireless AN, and the wireline AN. Inset: measured optical spectrum at the DD-MZM output
