An efficient multi-channel hybrid fiber-radio scheme for both down and up-link paths is demonstrated based on digitized RF-over-fiber technique, where the frequency translation stages are implemented using a single analog-to-digital converter (ADC) and digital-to-analog converter (DAC) instead of mixers and local oscillators. The simultaneous transmission of GSM, UMTS and WiMAX services is demonstrated with error-free reception. With a minimum sampling rate of 50 MHz and an overall optical data rate of 400 Mb/s, all the three wireless services can be successfully recovered in a full-duplex transmission. In the downlink direction, the performance is dependent on the amount of amplification required for the wireless signal at the desired carrier frequency. The amount of amplification on the other hand is dependent on the location of the wireless signal within the Nyquist zone which increases significantly with the order of the Nyquist zone. In the uplink direction, the performance is limited by inter-channel interference as a result of spectra aliasing of the regenerated IF signals which limits the signal-to-noise-ratio. With proper system design that optimizes downlink amplification and minimizes inter-channel interference, simultaneous multi-service transmission using digitized RF-over-fiber technique is able to improve spectral efficiency and minimize hardware count.
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