AbslmclWe propose the dual-band wireless LAN ryslem based on Radio-over-Fiber technique. A demonsvation of optical transmission of 5-GHm OFDM signal specified in IEEE802.11a and a feasibility of 2.4iS-GHz dual-band transmission will be reponed.
InlmduclionRadio-over-Fiber (RoF) is vely a11racLivs lcchnique for wirele~5 access network infrzstmchlre, because it can transmit microwaves and millimelcr-waves through optical fibers for a long distance [I], [2]. Actually, RoF has been already introduced in 2"d and 3d generation csI1ular syslsms 80 overcome a blind area issue [31-(61. Moreover, 5-GHz RoF link using a direct modulation scheme [7], [8] has k e n devcloped to support some impnanl furure wireless systems, such as wirel~ss l o c i area networks (WLANrj, intelligent transport syslems (ITS$), and the 4Ib generation ~ellular systems.In panicular, RoF is promising technique for WLAN infraslrustures because RoF technique can manage WLAN modems at a bass station (BS) and can solve wnour interference problem between wircIess signals caused by proliferated WLAN access points (APs). In addition, ii is expected lhat RoF technique is applied to dual-band WLAN specified in IEEE802.1 Ib and IEEE8OZ.I la, which provide data rafss of I 1 and 54 MbiWs.HOWCYCC, there are few reports on bi-directional RoF transmission of WLAN signal, espcially on RoF transmission of dual-band WLAN signal.In this paper, wc pmpere lhe dual-band WLAN syrlcm bared on RoF technique. In the proposed system, the functions of conventional WLAN APs can be ret at a BS. So, the system can accommodates both 2.4-GHz and 5-CHz WLAN mobile terminals by using simple remote anlenna stations. Moreover, upgraded WLAN standards can be established by simply rcplacing the cenlral WLAN AP funclions.And UIc system can accommodate not only lEEE802.1 I but also HiperLAN2 and HiSWANa. This paper describes a demonstration of the bi-directional op~icsl transmission of 5-GHz onhoganal frequency division mulliplencd (OFDM) signal specified in IEEESOZ. I l a for the first time, and discusses Ihe feasibility of 2.4 and 5-GHz dual-band transmission.
Conjiguralion ef WDINsysIem based on RoFFigure I shows a configuration of Ihe proposed WLAN System based on RoF technique. In a BS, some modems C O~V C~ Ethcmet signal Io 2.4-CHI radio frequency ( W j signals specified in IEEE802.llb or to 5-GHz RF signals specified in IEEES02.lla. Then, lhese RF signals are frequency-multiplexed and convened to an optical signal by udng a 1.55 pm DFB-LD m an ~lectrical-to-oplical convener (EIO), directly. The optical signal is transmined to remote antenna sfations (RASs) through a single mode optical fiber In the RASs, Ihe received optical signal is re-converted lo the RF signals by using a photo diode in an optical-to-electtiicd convs~ei (OiEj. The W signals are amplified by the RF 'amplifier$ (Amps) and radiated by an antenna. Conversely, Ihe RF signals 139
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