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An electro-absorption transceiver has been evaluated for use as a remote antenna unit in a WCDMA in-building distributed antenna system. The experiment showed penalty-free transmission over a wide range of input and output RF powers. The ACLR limited the downlink output power to less than -28 dBm.
Introduction: Dedicated indoor radio systems can provide better coverage and capacity in public areas such as airports, hotels, and shopping malls, in addition to office buildings. The importance of indoor cellular networks increases when third generation (3G) radio systems are introduced, which give users higher bit rates with multimedia services. For example, wideband code division multiple access (WCDMA) provides data rates up to 2 Mbit=s, but at the expense of a decreased cell radius. Distributed antenna systems (DASs), where radio base stations feed remote antenna units (RAUs) from a centralised location, have the advantage of decoupling coverage from capacity. Today 80-90% of all in-building DAS installations for cellular radio systems use passive coaxial cable distribution networks. The main reason for this is the cost of fibre optics, which is in general cost-effective only for link spans longer than 100-200 m. Cost is a major obstacle to a more widespread implementation of fibre-optic DAS. The requirements on these RAUs are that they should be small, light, inexpensive, and flexible enough to act as a transceiver for all today's wireless communications systems, and those of the future. Low-cost technologies that can be used include VCSELs and multimode fibres [1]. However, one promising candidate providing these features is the electro-absorption transceiver (EAT). This concept takes RAU simplification to the limit since only two components are required, an EAT and an antenna. The EAT is a single device which is capable of functioning as a passive transceiver, requiring no amplifiers or power supply [2-4]. It acts as a photodetector for the downlink path and as an optical modulator for the uplink path. The lack of amplification necessarily places strict limits on the radio coverage. The purpose of this Letter is to investigate the feasibility of using an EAT as a transceiver in a WCDMA antenna system.
Experimental setup: Fig. 1 shows the experimental setup used for measuring the radio signal quality after transmission over the fibre opticallink.For thedownlinkpath,theRFoutputfromeitheranetwork analyser, one...