Tatsuya Shimada

WDM access system based on shared demultiplexer and MMF links

A wavelength-division-multiplexing (WDM) access system can be used in two basic ways: user multiplexing, which assigns a wavelength to each user, and service multiplexing, which assigns a wavelength to each service. In current designs for service multiplexing, each optical network unit (ONU) must have a demultiplexer that can select any wavelength. This paper proposes a new WDM access system that uses one demultiplexer shared by many ONUs to offer optical-distribution access services. This system realizes significant cost reductions due to its passive optical network (PON) architecture, high capacity due to its WDM technology, and easy wiring through the use of multimode fiber (MMF). As one of the realization approaches of the shared demultiplexer, we explain the principle and configuration of a shared demultiplexer based on diffraction theory, and present theoretical and experimental analyses of a prototype 4/spl times/(4/spl times/4) shared demultiplexer whose configuration is based on Littrow mounting. Experimental transmission performances demonstrate the feasibility of the proposed WDM access system.

Bandwidth allocation scheme based on simple statistical traffic analysis for TDM-PON based mobile fronthaul

We propose a bandwidth allocation scheme utilizing simple statistical traffic analysis for TDM-PON based mobile fronthaul. Experiments show that excess bandwidth allocation can be reduced while achieving latency under 50 μs.

WDM passive optical network managed with embedded pilot tone for mobile fronthaul

A WDM-PON system managed with an electrically embedded pilot tone to accommodate mobile fronthaul is proposed. Experimental results show a 128 kb/s pilot tone can be inserted into the low frequency area of CPRI signals with negligible insertion penalty.

Dynamic SNR management using variable precision DSP for energy efficient OFDM-PON

We propose a novel energy-saving technique using variable precision DSP for OFDM-PON. This technique dynamically manages the minimum SNR satisfying the required transmission conditions. We clarify the feasibility of our proposed technique.

Utilization comparison of small-cell accommodation with PON-based mobile fronthaul

The network between the baseband units (BBUs) and the remote radio heads (RRHs) in a centralized radio access network (C-RAN) architecture is called the mobile fronthaul (MFH). A passive optical network (PON) is expected to reduce the deployment cost of MFH by sharing the optical fibers. Using system-level simulation results as a basis, we report that MFH downlink utilization can be improved with PON, regardless of the functional splitting point between BBUs and RRHs. We then clarify the application range of PON-based architectures, which represents the number of small cells that a PON system can accommodate with a certain amount of user equipment and certain data rates.

Efficient accommodation of mobile fronthaul and secondary services in a TDM-PON system with wireless TDD frame monitor

We propose a novel technique for the accommodation of mobile base stations (BSs) and a secondary system with a time division duplex (TDD) frame monitor. By increasing the number of BSs accommodated in a passive optical network (PON), the cost of mobile fronthaul (MFH) can be reduced. To realize even further cost reduction, a secondary system is accommodated in the PON with the MFH while the mobile signal is transferred with low latency. We propose a technique for overlapping the signal of the secondary system on the signals of the TDD mobile BSs by using a function for distinguishing the unallocated interval of TDD uplink signals. We evaluate the improvement in the optical uplink bandwidth efficiency with a numerical calculation. By employing the proposed technique, in a numerical simulation we greatly increase the optical bandwidth of the secondary system compared with that without a TDD frame monitor. For the uplink of the mobile system, the MFH latency is kept at a low value regardless of TDD frame monitoring.

Passive optical network range applicable to cost-effective mobile fronthaul

In 5th generation mobile communications systems (5G), the number of small cells with centralized-radio access network (C-RAN) architecture is expected to increase greatly. Time division multiplexing-passive optical networks (TDM-PON) are promising transmission systems for networks between a baseband unit (BBU) and a remote radio head (RRH). However, there is a challenge as regards the ultra-low latency requirements of 5G including less than 1 ms for end-to-end communication, because a TDM-PON generally transmits using time division multiple access (TDMA) as a basis. In this paper, we derive the achievable latency and the number of RRHs accommodable by TDM-PON, and analyze the applicable range of a TDM-PON for mobile use. Our analysis shows that it is possible to design a PON application in accordance with the latency requirements of mobile systems.

Effective utilization of unallocated intervals in TDD-based fronthaul employing TDM-PON

A time-division-multiplexing passive optical network (TDM-PON) accommodating a time-division duplex (TDD)-based mobile fronthaul (MFH) contributes to the realization of a low-cost network. However, there are two issues with the TDM-PON. The first is the limited number of optical network units (ONUs) that can be accommodated because the statistical multiplexing effect is weaker than with the accommodation of a conventional MFH. The other issue is the discovery process for registering new ONUs. While operating the discovery process, the signals of the registered ONUs cannot be forwarded in the optical link, and a huge latency is added to the registered ONUs. We have proposed a technique for the effective utilization of unallocated intervals, which certainly occur in optical links. Secondary service signals are forwarded in the unallocated intervals to increase the number of ONUs. The discovery process also operates in the unallocated intervals to avoid any latency increase. In this paper, we report evaluation results obtained using the numerical simulations.

Experimental Analysis of LTE Signals in WDM-PON Managed by Embedded Pilot Tone

Dense deployment of many small cells is one promising solution to cope with mobile traffic increases. However, the deployment needs many optical fibers and network operators require efficient management for these cells. To overcome these issues, we have proposed a WDM-PON system managed by an electrically embedded pilot tone and confirmed its feasibility. In this letter, we compare management methods and clarify 128-kb/s pilot tone parameters that negligibly affect LTE signals transported by CPRI option seven experimentally. The results show that the modulation index as high as 20% and carrier frequency as high as 5 MHz are suitable under 1.0-dB optical power penalty.

Multi-Stage Access Network Based on SOA With/Without OEO for Low Delay Performance

Recently, various architectures for future networks have been researched and discussed. In one of these approaches, we assume the deployment of an access network in which wavelength division multiplexing (WDM) and time division multiplexing (TDM) techniques will be applied to user and service multiplexing, respectively. In line with the envisioned scenario, we are studying a new access network based on a multi-stage semiconductor optical amplifier (SOA), which has a flexible transmission distance, low delay performance and low power consumption for each service. It has multi-access points supporting the dropping/adding/regenerating of signals with/without optical-electrical-optical (OEO) conversion. In this paper, we describe the configuration of this new access network. Moreover, we propose a priority control method for adding/regenerating signals designed to realize a low delay, and describe simulation results related to the number of OEO conversions. Moreover, we clarify a multi-access point traffic design for low delay performance.