Jun Terada

Terahertz wireless communications based on photonics technologies

There has been an increasing interest in the application of terahertz (THz) waves to broadband wireless communications. In particular, use of frequencies above 275 GHz is one of the strong concerns among radio scientists and engineers, because these frequency bands have not yet been allocated at specific active services, and there is a possibility to employ extremely large bandwidths for ultra-broadband wireless communications. Introduction of photonics technologies for signal generation, modulation and detection is effective not only to enhance the bandwidth and/or the data rate, but also to combine fiber-optic (wired) and wireless networks. This paper reviews recent progress in THz wireless communications using telecom-based photonics technologies towards 100 Gbit/s.

A Burst-Mode 3R Receiver for 10-Gbit/s PON Systems With High Sensitivity, Wide Dynamic Range, and Fast Response

The burst-mode 3R receiver using monolithic ICs for 10-Gbit/s-class optical access networks is reported. In a point-to-multipoint access system like a passive optical network (PON), the receiver at the optical line terminal (OLT) must be able to handle burst-mode optical packets with significantly different powers and phases. An OLT receiver with high sensitivity with instantaneous response to burst inputs is desired for widening the accommodation area and for high efficiency in PON uplinks. Currently, the diffusion of high-speed Internet connection services represented by fiber to the home services at 1.25 Gbit/s is remarkable and the standardization of the next-generation system operating at 10 Gbit/s has started in IEEE. We first discuss the issues in the implementation of 10-Gbit/s-class PON systems, focusing on securing the accommodation area and the quality of the service comparable with those of the deployed system. Against that background, we propose target specifications for sensitivity, a dynamic range and response speed of the 10-Gbit/s-class burst-mode receiver so as to secure the power budget and the upstream efficiency comparable with those of the already-installed systems. Our burst-mode 3R receiver was designed to meet the above requirements and developed using monolithic ICs of transimpedance amplifier, limiting amplifier, and clock and data recovery circuit fabricated by using SiGe BiCMOS technologies along with a p-i-n photodiode. High sensitivity of , a wide dynamic range of over 16.5 dB, and quick response time of 75 ns were confirmed for burst inputs with extremely different powers.

Dynamic TWDM-PON for Mobile Radio Access Networks

In recent years, the diffusion of mobile terminals has brought about an explosive increase in communication traffic of mobile RANs. The number of radio base stations and optical fiber lines between them is becoming larger. For this reason, we studied effective optical network technologies for mobile RANs and propose the use of TWDM-PON as a means of enabling RANs to be operated flexibly and have wideband communication capability. We confirmed the feasibility of TWDM-PON for this application by numerical simulation. The results show that TWDM-PON can accommodate the bandwidth more than TDM-PON and completely eliminate unused bandwidth in TDM-PON.

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.

A 10.3 Gb/s Burst-Mode CDR Using a ΔΣ DAC

A burst-mode clock and data recovery circuit (CDR) for 10 G-EPON systems is described. We propose a new architecture with a single gated voltage-controlled oscillator (GVCO), a digital frequency detector, and a ΔΣ digital-to-analog converter (DAC). The single GVCO and detector reduce frequency error to less than 2 MHz. The ΔΣ DAC eliminates external devices. Moreover, the simulation results show the DAC is more tolerant to process, voltage, and temperature (PVT) variations than a conventional charge pump. We fabricated a test CDR with this architecture using the 0.25 μm SiGe BiCMOS process. The measurement results show root-mean-square (rms) and total jitter of the recovered data of 2.4 and 14.7 ps, respectively, instantaneous locking in 1 bit, tolerance to a 160-bit sequence without transition in the data, and jitter tolerance of over 0.27 UIpp.

Split-PHY processing architecture to realize base station coordination and transmission bandwidth reduction in mobile fronthaul

We propose a new RAN architecture splitting BS functions within PHY layer. It reduces mobile fronthaul transmission bandwidth by 90 % and achieves BS coordination performance with 0.5 dB SNR degradation compared to conventional C-RAN.

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.

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.

A 10.3125Gb/s Burst-Mode CDR Circuit using a δσ DAC

The CDR circuit is fabricated in 0.25 mum SiGe BiCMOS technology. The low-speed digital blocks, such as the frequency detector, the up/down counter, the modulator, and the dither generator, are developed using CMOS transistors. The LPF used in the DAC is integrated in the chip. Two power supplies, 3.3 V for bipolar transistors and 1.8 V for CMOS, are used. PONs such as 10G-EPON systems require a burst-mode CDR circuit for upstream transmission that has an instantaneous response, tolerance to long consecutive-identical digits (CIDs), and high jitter tolerance. In this paper, a burst-mode CDR circuit achieves instantaneous locking of 1b, CID tolerance of 160b, and jitter tolerance of 0.27UIpp at 10.3125Gb/s operation. These characteristics are provided by a CDR architecture using a single gated VCO (GVCO) and DeltaSigma DAC.The simple architecture of the GVCO-based bust-mode CDR circuit provides instantaneous phase locking, which reduces the overhead time and increases the transmission efficiency.

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.