Abstract
A novel transmission technique—namely, a DFT-spread spectrally overlapped hybrid OFDM–digital filter multiple access (DFMA) PON based on intensity modulation and direct detection (IMDD)—is here proposed by employing the discrete Fourier transform (DFT)-spread technique in each optical network unit (ONU) and the optical line terminal (OLT). Detailed numerical simulations are carried out to identify optimal ONU transceiver parameters and explore their maximum achievable upstream transmission performances on the IMDD PON systems. The results show that the DFT-spread technique in the proposed PON is effective in enhancing the upstream transmission performance to its maximum potential, whilst still maintaining all of the salient features associated with previously reported PONs. Compared with previously reported PONs excluding DFT-spread, a significant peak-to-average power ratio (PAPR) reduction of over 2 dB is achieved, leading to a 1 dB reduction in the optimal signal clipping ratio (CR). As a direct consequence of the PAPR reduction, the proposed PON has excellent tolerance to reduced digital-to-analogue converter/analogue-to-digital converter (DAC/ADC) bit resolution, and can therefore ensure the utilization of a minimum DAC/ADC resolution of only 6 bits at the forward error correction (FEC) limit (1 × 10−3). In addition, the proposed PON can improve the upstream power budget by >1.4 dB and increase the aggregate upstream signal transmission rate by up to 10% without degrading nonlinearity tolerances.
Highlights
To effectively cope with the current avalanche of mobile traffic, driven by the unprecedented increase in users’ demands for ultrawide bandwidth multimedia and cloud services that have become ubiquitous, fronthauls/backhauls of 5G CRANs capable of converging optical and wireless networks are needed, and require significant changes to network access in order to support the ambitious system requirements [1,2]
To overcome the abovementioned technical challenges, a novel passive optical network (PON) technique termed hybrid orthogonal frequency division multiplexing (OFDM)–digital filter multiple access (DFMA) PON, utilizing spectrally overlapped digital orthogonal filtering, has recently been proposed and extensively investigated [6] where, regardless of the optical network unit (ONU) count, matching filter (MF)-free single fast Fourier transform (FFT) operation and the relevant DSP processes are applied in a pipeline approach
We have applied the discrete Fourier transform (DFT)-spread technique in the hybrid OFDM–DFMA PONs to further improve the flexibility of the system transmission performance [19]
Summary
To effectively cope with the current avalanche of mobile traffic, driven by the unprecedented increase in users’ demands for ultrawide bandwidth multimedia and cloud services that have become ubiquitous, fronthauls/backhauls of 5G CRANs capable of converging optical and wireless networks are needed, and require significant changes to network access in order to support the ambitious system requirements [1,2]. We have applied the DFT-spread technique in the hybrid OFDM–DFMA PONs to further improve the flexibility of the system transmission performance [19] In these PONs, each individual subwavelength spectral region only conveys either a single in-phase (I) or quadrature-phase (Q) channel upstream of the double sideband (DSB) OFDM signal, which halves the spectral efficiency compared with the spectrally overlapped hybrid OFDM–DFMA PONs [6]. PONs [6], in the OLT, without utilizing digital MFs, the single FFT operation followed by summing and subtraction operations of the lower sideband (LSB) and upper sideband (USB), and the corresponding DSP-enabled data recovery processes applied in a pipelined approach, can directly demultiplex and demodulate ONU sub-band signals within the same subwavelength spectral region, while the same OLT receiver can be used to demodulate legacy OFDM signals. PONs utilize only digital filters to multiplex multiple OFDM sub-bands without requiring extra electrical/optical components compared to conventional transceivers in both the ONUs and the OLT
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