Noriko Iiyama

DSP-based optical access approaches for enhancing NG-PON2 systems

Motivated by recent progress in next-generation PON2, or NG-PON2, standardization, this article reviews digital signal processing technologies to further enhance NG-PON2 systems by realizing flexible and cost-effective optical access network deployments. First, flexible speed upgrades by DSP-enabled advanced modulation and multiplexing approaches are described, followed by a consideration of cost-performance trade-offs. Next, reach extension using DSP-based digital coherent reception and impairment compensation is overviewed. Finally, as a future goal, access network virtualization with reconfigurable optical line terminals and optical network units is discussed.

Feasibility Study on a Scheme for Coexistence of DSP-Based PON and 10-Gbps/λ PON Using Hierarchical Star QAM Format

This paper presents a downlink scheme that permits the coexistence, on a passive optical network branch, of future DSP-based optical network units (ONUs) that can receive advanced modulation signals and legacy ONUs that can receive only on-off keying (OOK) signals. In the proposed scheme, the two types of signals, advanced modulation signals and OOK signals, are multiplexed by using a hierarchical star quadrature amplitude modulation (QAM) format and transmitted simultaneously on a single carrier. The design criteria and the feasibility of the proposal are discussed. The coexistence of 10G-class ONUs and DSP-based ONUs using hierarchical star 8-QAM format is numerically analyzed and experimentally evaluated. The results confirm that a 10-Gbps OOK signal and 30-Gbps star 8-QAM signal can be received with 30.5-dB loss budget by an APD and intradyne detector with DSP, respectively. The ability of the proposed approach to expand the coverage area is also introduced.

Two-phased capacity upgrade method for NG-PON2 with hierarchical star 8-QAM and square 16-QAM

We propose a two-phased upgrade method of capacity per wavelength in NG-PON2. Coexistence with conventional NG-PON2 ONUs and a higher capacity are realized using star 8-QAM and square 16-QAM in phases 1 and 2, respectively.

Advanced DSP for optical access networks: Challenges and opportunities

Employing DSP technology is an attractive way to enhance standardized 10-Gbps per wavelength PONs toward the converged optical-wireless network. For TDM-based co-existence of digital coherent PON and existing PONs, burst mode coherent receivers for uplink and hierarchical modulation for downlink are introduced.

Constellation design for next-generation hierarchically-modulated PON systems

In this paper, we study the performance of star quadrature amplitude modulation (QAM) signals with various constellations for hierarchically-modulated PON systems that overlay an over 20-Gbps PSK signal on a 10-Gbps on-off keying (OOK) signal; previous work examined only the performance of an 8-star QAM signal. A star QAM signal consists of a PSK signal with lower amplitude (inner-PSK signal) and a PSK signal with higher amplitude (outer-PSK signal). We propose to decrease the modulation level of the inner-PSK signal and increase that of the outer-PSK signal with the goal of improving the bit error rate performance in some conditions. Simulations indicate the minimum required received power for the various constellations examined: it is shown that effective design depends on the extinction ratio. For example, 10-star QAM improves the minimum required received power by 3 dB compared to 8-star QAM when the extinction ratio is 12 dB.

Application of hierarchical modulation to optical access network

Hierarchical modulation is a technology for point-to-multipoint architectures that can simultaneously transmit multiple independent signals using a single wavelength/frequency. This paper reviews the principle of hierarchical modulation and introduces some application examples. For this interesting technology, we have proposed its use for coexistence of different generation passive optical networks (PONs). The validity of combining hierarchical modulation with star quadrature amplitude modulation (QAM) format in migrating the conventional 10G/channel class PON to the future digital coherent PON is shown.

Star-QAM Constellation Design for Hierarchically Modulated PON Systems With 20-Gbps PSK and 10-Gbps OOK Signals

In this paper, we show an effective star-QAM constellation in terms of the allowable range of the extinction ratio for hierarchically modulated PON systems that overlay a 20-Gbps PSK signal on a 10-Gbps OOK signal. In ten-star and 17-star QAM signals, the modulation level of the PSK signal is dynamically changed based on the amplitude of the OOK signal while the modulation level of the PSK signal is constant in the fundamental eight-star QAM signal. Numerical results studied the performance of these constellations, and indicated the effective constellation to achieve the lowest power penalty depends on the extinction ratio. Simulation results showed that by using eight-star QAM or ten-star QAM signals, new ONUs satisfied the required receiver sensitivity in 10G-EPON and XG-PON. Experimental results showed that, compared to the eight-star QAM signal, the ten-star QAM signal enhanced the range of the extinction ratio wherein ONUs of legacy and new systems satisfied the required sensitivity for 10G-EPON and XG-PON. The range was from 7.4 -9.7 dB. The ten-star QAM signal also improved the required received power by 7.7 dB compared to the required sensitivity in 10G-EPON when the extinction ratio was 8.2 dB.