This paper proposes and demonstrates experimentally, for the first time to our knowledge, a software-defined beamforming implementation based on the precise timing control of the samples generated by different digital-to-analog converters (DACs) modulating a single laser light and transmitted over a multicore fiber (MCF) optical fronthaul.
Optical fronthaul systems based on standard single-mode fiber exhibit the problem of coherent signal distribution, as the signals for each antenna element are transmitted in wavelength division multiplexing (WDM), experiencing different delays from different chromatic dispersion (CD) values. Moreover, CD dynamics are different for each WDM signal due to temperature and vibration, making difficult to control the delay of the signals for the different antenna elements. This limitation can be solved using an optical fronthaul based on MCF, where the signals for the different antenna elements are transmitted through the different cores with spatial division multiplexing at the same wavelength from a single laser source.
In this work, the software-defined beamforming functionality over a MCF optical fronthaul is proposed and demonstrated experimentally with the transmission of an LTE-like signal in the 700 MHz frequency band over 1 km of 7-core fiber. The LTE signal is steered ±45° by defining a delay of ±1 digital sample at 2 GS/s (±500 ps), ensuring error vector magnitude (EVM) compliant transmission after 1 km of MCF. This paper also demonstrates that, increasing the DAC sampling frequency to 5 GS/s, a higher density area can be covered.
Proc. SPIE. 10945, Broadband Access Communication Technologies XIII
KEYWORDS: Fiber to the x, Quadrature amplitude modulation, Modulation, Single mode fibers, Field programmable gate arrays, Optical networks, Forward error correction, Orthogonal frequency division multiplexing, Commercial off the shelf technology
This paper proposes and evaluates experimentally the performance of single-carrier QAM (SC-QAM) and OFDM-QAM signals for next-generation backhaul over a deep fiber-to-the-home (FTTH) network comprising up to 50 km SSMF combined with in-building transmission over 150 m of 4-core multi-core fiber in order to reach the cellular transmission equipment usually located in the roof. The data signals are generated with commercial off-the-shelf (COTS) components using QAM modulation orders up to 256QAM. OFDM and SC-QAM transmission after 10-km SSMF PON and 150-m MCF in-building riser employing 256QAM provides 14.22-14.36 Gb/s per channel. 50-km PON is reached employing 128QAM signals. Channel aggregation is also investigated to increase the system capacity. The experimental results point out that aggregation of a second data channel is feasible employing the same components with a 3-dB received power penalty. The minimum received optical power level is evaluated experimentally for each signal. This approach enables operators to select the optimum modulation order depending on the distance and the received power level, providing up to 28.44 Gb/s per user with two 256QAM channels.