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Photonic 60 GHz radio-over-fiber (RoF) access link with broadband wireless transmission up to 12.5 Gbps

A key technology trend in wireless communications is the increase in data rate needed to catch up with the expanding broadband requirements. As an example, for bridging a 10 Gb Ethernet (10GbE) link, data rates up to 12.5Gb/s are required. However, no wireless system has yet achieved the transmission of such a high data rate over relevant distances >1m. Usually, multilevel modulation schemes are used in wireless communications to increase the data rate while keeping minimal spectral bandwidth requirements but another practical approach is to extend the carrier frequency into the millimetre-wave band and use a simple modulation scheme. Potential applications for such wireless links include access applications such as enterprise campus connectivity or local area network (LAN) extensions but also short-range in-house applications (WPAN).

To achieve 12.5Gb/s data rate, we have developed a 60GHz wireless photonic link system utilizing advanced mm-wave photonic components and RoF techniques for generating, amplifying and transmitting the mm-wave carrier signal as well as for broadband modulation. The system employs an optical 60GHz generator providing a double-sideband signal with suppressed carrier (DSB-SC) as well as an optical data modulator. For short range applications we have constructed a compact wireless transmitter consisting of a highfrequency photodiode and a simple mm-wave antenna with about 20dBi gain. This system achieved error-free (BER=10-9, 231-1, NRZ) in-door transmission of 12.5Gb/s signals over wireless distances of up to 3.5m with a receiver sensitivity as low as -44.8dBm. In case of
BER of <10-4 required for FWA the maximum transmission distance for 12.5Gb/s is increased up to 7m and can be further extended to >10m by using advanced forward error correction. We even achieved 12.5Gb/s error-free transmission when operating the mm-wave transmitter in passive mode (i.e. without any electrical power supply) with a receiver sensitivity penalty of only ~2dB. This result clearly shows that fully passive mm-wave RoF transmitters for in-house applications are possible.

For access links with longer wireless distances an electrical RF amplifier was employed in the RoF transmitter. Here we achieved 7.5Gb/s error-free transmission in out-door LoS experiments over wireless distances of up to 36m. This result was limited in terms of data rate by the transmitter amplifier’s bandwidth and in terms of wireless distance due to spatial limitations. From calculations based upon the measurement results the maximum wireless distance for 12.5Gb/s transmission increases to about 3000m (without rain) when using Cassegrain antenna with 50dBi gain and a transmitter amplifier with a larger bandwidth.

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