Naotaka Shibata

Performance evaluation of mobile front-haul employing ethernet- based TDM-PON with IQ data compression [Invited]

In this paper, we experimentally and numerically evaluate the performance of a common public radio interface (CPRI) over a time division multiplexed passive optical network (TDM-PON) system for accommodating densely deployed small cells in centralized-radio-accessnetwork- based future radio access. A prototype of the CPRI over TDM-PON is developed by using Ethernet-based TDM-PON. Experimental results showed that its synchronization accuracy and latency meet the requirements of a mobile front-haul using CPRI by the implemented delay jitter reduction and low-latency bandwidth allocation techniques. An in-phase and quadrature (IQ) data compression technique is also implemented on the system to enable a higher accommodation of remote radio heads. Experiments confirmed that the compression technique meets open radio equipment interface standards in terms of latency and signal quality degradation. Numerical results showed that the technique with a 0.45 compression ratio increases the number of supportable remote radio heads from 3 to 7 for a mobile front-haul with a 100 μs latency limitation.

Mobile front-haul employing ethernet-based TDM-PON system for small cells

We develop a mobile front-haul prototype based on TDM-PON (10G-EPON). The system can accommodate 3 CPRI option-3 links and 7 compressed CPRI option-3 links with reasonable latency under 100 μs.

Dynamic IQ data compression using wireless resource allocation for mobile front-haul with TDM-PON [invited]

The time-division multiplexed-passive optical network (TDM-PON) architecture can efficiently accommodate densely deployed small cells in a centralized radio access network (C-RAN)-based future radio access (FRA). C-RAN is a type of mobile front-haul network, which connects multiple remote radio heads to a baseband unit pool by optical links. The required optical bandwidth in the mobile front-haul of FRA is very large, so it is necessary to efficiently use the optical bandwidth by using in-phase and quadrature-phase (IQ) data compression techniques. This paper proposes an IQ data compression technique that dynamically reduces the required optical bandwidth based on wireless resource allocation, and provides TDM-PON with statistical multiplexing gain. Simulation results showed the achievable compression ratio of the proposed IQ data compression technique. The feasibility of our technique was confirmed by experiments. The reduction in the average TDM-PON bandwidth was 50% when there were 60 mobile terminals, all of which required 0.18 Mbps bandwidth.

System level performance of uplink transmission in split-PHY processing architecture with joint reception for future radio access

In this paper, the system level performance of uplink transmission in the split-PHY processing (SPP) architecture is evaluated. The SPP architecture splits the PHY functions of the base station so that some PHY functions are implemented on the remote radio head (RRH). Compared to the centralized radio access network (C-RAN) architecture with common public radio interface (CPRI), the SPP architecture significantly reduces the required optical bandwidth in the mobile front-haul. Moreover, by implementing the FEC processing in the baseband unit (BBU), joint reception can be realized in uplink transmissions by forwarding the quantized log likelihood ratio (LLR) from RRHs to the BBU. System level evaluations show that the SPP architecture improves the cell-edge user throughput by 116 % compared with the MAC-PHY split architecture without coordinated operations while reducing the required optical bandwidth by 92 % compared with the C-RAN architecture.

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.

Dynamic IQ compression technique in mobile front-haul for mobile optical network

Dynamic IQ-data compression is essential in the mobile front-haul for cost-effective mobile optical network. We briefly introduce the compression technique, and show our recent research results.