245Gb/s P2MP Mobile Fronthaul Downstream Transmission Using Code-Division Multiplexing and Self-Homodyne Coherent Technologies

We have proposed and experimentally demonstrated a high-speed and point-to-multipoint (P2MP) mobile fronthaul (MFH) downstream system based on the code-division multiplexing (CDM) and self-homodyne coherent (SHC) technologies. We find that compared with the traditional 16-ary quadrature amplitude modulation (16-QAM) signal transmission, the change of phase noise between two demultiplexed symbols is much larger in the CDM-16QAM signal transmission because it is the accumulation of phase noise change of n multiplexed symbols. Therefore, a low-complexity pilot sequence-assisted phase noise estimation algorithm is proposed and designed to compensate for the phase noise caused by fiber mismatch length, which makes it possible to use a low-cost distributed feedback (DFB) laser. Besides, the spread signal's distribution in the frequency domain of each code sequence is different, leading to different transmission performances between different remote radio units (RRUs). A power optimization scheme is proposed to balance the transmission performances of different RRUs by multiplying each channel's signal by a normalized weight factor at the transmitter. The experimental results show that the proposed system could successfully support the transmission of 245 Gb/s 16QAM signal from baseband unit (BBU) to 7 RRUs (each RRU could have 2 antennas to transmit signals at 2 polarizations) over 10 km standard single-mode fiber (SSMF). The measured worst bit error rate (BER) value of 14 channels is 1.77e-3 which is below the hard-decision forward error correction (HD-FEC) threshold (3.8e-3).