Experimental Demonstration of a Real-Time Digital Filter Multiple Access PON With Low Complexity DSP-Based Interference Cancellation

Abstract

A 4-channel, upstream, digital filter multiple access (DFMA) passive optical network (PON) is experimentally demonstrated for the first time in a 26km SMF IMDD system employing real-time ONUs and OLT, which are dynamically reconfigurable in terms of channel spectral allocation and signal modulation parameters. To combat physical channel frequency response-induced cross channel interference (CCI) between spectrally-overlaid orthogonal channels, a real-time, reconfigurable CCI cancellation (CCIC) function implemented in the OLT receiver DSP, is demonstrated to significantly improve the DFMA PON performance and robustness in terms of; significant reductions in total channel BERs and individual subcarrier BERs, substantial increases in channel capacities, considerably reduced sensitivity to ONU synchronisation and excellent transparency to the interfering channel's signal modulation format. The trade-off between the complexity of the CCIC function's filter, in terms of tap count (multiplier elements) and the DFMA PONs performance is optimised to determine the optimum trade-off. It is shown that the CCIC filter only requires as few as 42 taps to achieve excellent CCIC performance. We also fully analyse the DSP complexity of the transmit and receive DFMA filters and the CCIC filters for varying DFMA channel counts and varying ratios of AD/DA converter sample rate to digital logic clock rate (parallelisation factor). It is shown that DFMA filter complexity is independent of channel count and furthermore that for channel counts ≥4 the CCIC filter only needs to process ~10 interference-inducing samples per wanted signal sample, resulting in only ~10 multipliers per parallel filter in the CCIC filter. We have therefore successfully demonstrated an ultra-low complexity, real-time CCIC function, which considerably enhances the performance and robustness of DFMA PONs.

Hybrid SSB OFDM-Digital Filter Multiple Access PONs

“…12 that for digital filter lengths of > L=>64, the power penalty curves become flattened, indicating that L=64 is indeed the minimum digital filter lengths for all the considered cases. Since the minimum digital filter length is independent of ONU count [13], it is therefore easy to understand that the digital filter length-dependent power penalty behaviours presented in Fig. 12 are applicable regardless of ONU counts.…”

Hybrid OFDM-Digital Filter Multiple Access PONs Utilizing Spectrally Overlapped Digital Orthogonal Filtering

“…5(b) and 5(c) also show that in comparison to Hybrid Case-I, relatively large receiver sensitivity variations are observed among different sub-bands for both Hybrid Case-II(A) and Hybrid Case-II(B). This is a result of channel fading which leads to undesirable power leakage between orthogonal sub-bands sharing a sub-wavelength spectral region [13], [18], [19]. However, no such power leakage occurs for Hybrid Case-I, as only an I-phase sub-band exists within each individual sub-wavelength spectral region, as shown in Fig.3(a).…”

“…These receiver sensitivity variations are not observed in the B2B transmission systems where the lowest frequency channel and highest frequency channel have almost identical BER performances for all three cases. It should be noted that the abovementioned imperfect orthogonality-induced power leakage between different channels can be significantly reduced when the cross-channel interference cancellation technique reported in [13], [18], [19] is used.…”

“…This does not require extra analogue hardware compared to conventional PON transceivers. Extensive numerical investigations and experimental demonstrations of the IMDD DFMA PONs have been reported in [9]- [13]. However, as the number of required digital matching filters embedded in the OLT is proportional to the overall channel count, for a large number of ONUs, the OLT digital signal processing (DSP) complexity grows uncomfortably large for cost-sensitive mobile applications.…”

Time Domain Equalization and Digital Back-Propagation Method-Based Receiver for Fiber Optic Communication Systems

“…A demonstration of higher order modulation format data transmission with Raman amplifiers is performed with DSP techniques in [20]. In [21], authors have discussed a 4-channel FOCS over 26 km SMF in terms of DSP and digital filters, but the implementation cost of such filters is a real issue. Similarly, in [22], researchers used methodologies such as coherent optical orthogonal frequency multiplexing (COOFDM) for FOCS, where they successfully addressed the nonlinear issues, but the transmission distance for an order of 100 km still needs to be investigated to analyze the cumulative channel effects for long-haul FOCS.…”