Low-latency synchronous clock distribution and recovery for high-speed OFMDA-based mobile backhaul

A method for clock distribution and recovery for an optical mobile backhaul, comprising:

• generating an Orthogonal Frequency-Division Multiple Access (OFDMA) signal with a transmitter (Tx) at an optical line terminal (OLT), the OFDMA signal generated by assigning orthogonal subcarriers to different cell sites through digital signal processing;
• generating two electrical clock signals:
• a baseband square wave clock, Csquare, that controls Tx-side digital logic and a sine wave clock Csine, that controls a digital to analog converter (DAC);
• combining the OFDMA signal and clock signals;
• intensity-modulating the resulting joint OFDMA signal+clock signal;
• optically multiplexing aggregate OFDMA signal+clock signals on multiple wavelengths with a dense wavelength division multiplexing DWDM λ-spacing;
• distributing at a remote node (RN) each wavelength by a de-multiplexer (Demux) to a designated general small cell area to which cell sites are connected by optical splitters;
• and
• photodetecting and digitizing received OFDMA signal and clock signals at each optical network unit (ONU), wherein downstream (DS) information for each cell is then digitally extracted and prepared for wireless radio frequency (RF) transmission over an air interface:
• providing a band-pass filter (BPF) and a lowpass filter (LPF) with passbands to filter out the Csine and the Csquare, respectively, for DSP-free clock recovery.

A communication system, comprising:

• an OFDMA transmitter (Tx) at an optical line terminal (OLT) generating an orthogonal frequency division multiple access OFDMA signal by assigning orthogonal subcarriers to different cell sites through digital logic and then intensity-modulating the resulting electrical OFDMA signal;
• an electrical multiplexer combining the electrical OFDMA signal with two electrical clock signals;
• an optical intensity modulator intensity-modulating the resulting joint electrical signal OFDMA+clock signals;
• an optical multiplexer aggregate OFDMA signals on multiple wavelengths with tight Dense Wavelength Division Multiplexing DWDM λ-spacing;
• a remote node (RN) receiving the OFDMA signals, each wavelength is distributed by a de-multiplexer (Demux) to designated general small cell area, to which cell sites are connected by optical splatters;
• and an optical network unit (ONU) to directly photodetect and digitize received OFDMA signal, wherein downstream (DS) information for each cell is digitally extracted and prepared for wireless radio frequency (RF) transmission over an air interface;
• an electrical splitter, a bandpass filter (BPF) and a low pass filter (LPF) to separate
• the received OFDMA signals and the clock signals;
• wherein at the ONU, a joint data and clock signal is directly detected by a photo detector (PD) and is electrically split into three parts.