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This paper summarizes our studies on the software implementation of passive optical network (PON) physical-layer (PHY) processing to maximize the flexibility of the optical line terminal in access systems and demonstrates the softwarization of complete 10G-EPON upstream PHY of an optical system for the first time. Softwarization based on general-purpose hardware is more difficult to implement successfully than the application-specific integrated circuits used by dedicated hardware due to the marginal performance. Our work utilizes general-purpose graphic processing units (GPUs) as the implementation device as they offer significant computation performance. Our key advances that yield the softwarization of PON PHY processing, the GPU direct transfer technique, and a low-complexity algorithm are described. In addition, this paper describes the parallel implementation method of PON PHY decoding for upstream transmission. Demonstration results show that the proposed algorithm together with implementation satisfy the 10G-EPON standard by achieving 10.3125 Gb/s real-time processing.

In this paper, we evaluate the wireless uplink performance and the mobile fronthaul (MFH) bandwidth of split-physical layer (PHY) processing (SPP), which is a base station (BS) functional split scheme used to link baseband units (BBUs) and remote radio heads (RRHs) in a centralized/cloud — radio access network (C-RAN). SPP enables MFH bandwidth reduction by splitting the BS functions between channel coding/decoding and modulation/demodulation within the PHY layer functions. SPP also enables high coordinated multipoint (CoMP) transmission and reception performance by employing uplink joint reception (JR) with log likelihood ratio (LLR) combining. Link level simulation results show that SPP with LLR combining achieves a block error rate (BLER) performance of 10% with a signal to noise ratio (SNR) penalty of less than 1 dB compared with that of conventional CRAN, which centralizes PHY layer functions in BBU. In addition, SPP has an SNR gain of more than 3 dB over medium access control (MAC)-PHY split, which splits the BS functions between the MAC and PHY layer functions. System level simulation results show that SPP with LLR combining improves the cell-edge user throughput by more than 33% over MAC-PHY split with selection combining and reduces the MFH bandwidth by 91% when compared with conventional C-RAN. Moreover, link and system level simulation results above are also observed when the channel estimation is non-ideal.

We propose and demonstrate a beyond-5G x-haul platform with autonomous time aware shaper and adaptive mobile fronthaul compression, which simultaneously accommodates real-time 5G NR-class fronthauls (2*29.49-Gbps CPRI-equivalent-rate) and 1,000+ massive IoT live backhaul traffic through a 10GbE interface while keeping $ end-to-end fronthaul latency.

We propose autonomous dynamic gate shaping and rerouting according to real-time traffic-state for enhancing IoT-traffic throughput on deterministic Layer-2 network that also accommodates latency-sensitive mobile front-haul. System-level demonstrations show throughput improvement from 3.9Gbps to 7.9Gbps.

We propose a long-reach bus-type optical access system by using distributed Raman amplification and asymmetric power splitters. The feasibility is experimentally verified by using 10G-EPON and its scale is estimated by bit error rate measurements.

Real-time motion control of Internet of Things (IoT) devices over the network has been studied with the emergence of advanced applications such as drones and industrial robots. However, delay fluctuation is caused by the network, which leads to the deterioration of control performance. This study introduces the concept of access edge that performs real-time motion control on an edge server located in the central office. To reduce the effect of delay in the access network on control performance, we propose and evaluate the control method that uses the delay information. In the proposed method, the delay information is actively obtained and sent to the controller for delay compensation. We construct an experimental system that simulates peer to peer communication in the access network, and evaluate the real-time control performance. We confirm that the settling time is improved by the proposed method in motor and drone experiments.

In future radio access systems, since the number of mobile base stations will increase to cope with the increasing mobile traffic, the number of mobile fronthaul (MFH) links will also have to increase. To reduce the MFH link cost, MFH networking has been attracting attention. In particular, the use of a time-division multiplexed passive optical network (TDM-PON) makes the MFH link cost effective. On the other hand, a TDM-PON has a huge latency when forwarding uplink traffic. In a typical dynamic bandwidth allocation (DBA) scheme, an optical network unit (ONU) has a very long transmission waiting time, e.g., several milliseconds. This transmission waiting time in the ONU is a critical problem since the latency requirement for the MFH link is very strict, e.g., less than 250 μs defined by the Third Generation Partnership Project. In this paper, we propose a novel statistical DBA scheme taking high-speed traffic fluctuation to reduce the transmission waiting time. Our proposed scheme allocates bandwidth based on the only ratio of the data amount of each distributed unit and detects the pattern of the transmission interval of the burst signal. We show the feasibility with a numerical simulation and experiments.

Fronthaul bridged network has been a hot research topic in recent years. A challenge for existing path-control protocols for bridged networks is that the route computation is executed after the advertisement of the link fault based on the updated link state information. To address this issue, this letter proposes a novel fault detection and recovery scheme for fronthaul bridged networks. With the proposed scheme, bridges estimate the fault location utilizing the time-division duplex configuration of fronthaul streams and immediately switch the forwarding paths for the affected flows to backup paths. Consequently, the end-to-end communication of fronthaul streams is rapidly recovered compared with the existing protocols.

A time division multiplexing-passive optical network (TDM-PON) has been attracting attention with a view to realizing the cost-effective mobile fronthaul (MFH) of a mobile base station (BS). A cost-effective MFH is needed because a lot of BSs will be densely deployed in fifth generation mobile networks (5G). A TDM-PON is capable of reducing the network cost as the number of subscribers increases. However, the number of remote radio heads that can be accommodated in a TDM-PON is limited since a 5G MFH has a throughput of more than 1 Gbps. The accommodation of not only the MFH but also multiple services will enable us to construct a more cost-effective network that will in turn achieve cost-effective 5G MFH. Therefore, we propose the accommodation of the fronthaul and secondary services in a TDM-PON. Our proposed TDM-PON allows us to increase the number of accommodated ONUs. We use a traffic monitor to capture the MFH signal and then estimate the unallocated interval in the PON domain by using the characteristics of the MFH signal. The signals of the secondary services are inserted in the unallocated interval of the MFH signal. We estimate the unallocated interval by using this characteristic. In this paper, we report experimental and the theoretical results for our proposed technique obtained with a 10 Gigabit-Ethernet PON prototype. Moreover, we also discuss the variation in throughput when we increase the number of ONUs.

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.

We experimentally demonstrate 10.3125 Gbit/s upstream transmission with loss budget of 42.5 dB by using DRA combined with pre-amplifiers, where DRA is avoided in the access span due to its many optical connection points.

This paper describes optical network technologies to accommodate various types of base stations for 5G and beyond. AMCC technique for WDM-PON suitable for constant bit rate stream and cooperative I/F and DBA to achieve low-latency transmission with TDM-PON are introduced.

This paper overviews flexible management functions of WDM-PON using an auxiliary management and control channel and introduces wavelength allocation, adjustment as use-cases.

In this paper, we summarize our 5G RaD achievements for "High-Data-Rate and Low-Power-Consumption Radio Access Technologies with Ultra Higher-Frequency-Band and Wider-Bandwidth Massive MIMO", funded by the Ministry of Internal Affairs and Communications (MIC), Japan. This Japanese national project consists of three research subjects: "Massive MIMO (massive-element antenna) and beam control technologies for low SHF bands", "Wideband Massive MIMO and beam control technologies for high SHF bands" and "Discovery technologies for terminals with ultra-low power consumption". We describe detailed research contents and achievements of our promoting 5G RaD project.

In this paper, we make a summary report of our 5G RaD activities for "High Capacity Technologies with Ultra High-Density Multi-Band and Multi-Access Layered Cells", funded by the Ministry of Internal Affairs and Communications (MIC) in Japan. This national project consists of three research subjects: "Ultra high-density distributed antenna systems", "Optical access technologies accommodating highly densified small cells" and "Multi-RAT system technologies for multi-band and multi-access layered cells". We describe the research and development result for each subject.

Given the paradigm shift demanded by the widening variation in service requirements, we introduce an edge-server architecture that utilizes commodity hardware to create especially advanced DSP-oriented optical access with maximized system flexibility and server utilization.

We propose an in-service software updating method for optical access network equipment. The method is implemented and confirmed to update OLT software within 15 microseconds without packet loss.

This paper describes optical network technologies to accommodate various types of 5G base stations.

This paper presents a clock conversion scheme for burst-mode digital coherent QPSK receivers in an asynchronous PON upstream and confirms its validity. The scheme converts the number of samplings of transmitted signal based on the clock at Rx. We demonstrate the proposed scheme in a realistic environment that emulates a fixed clock difference by two independent synthesizers at Tx and Rx mixed together with clock jitter induced by 20-km fiber transmission. In the real-time demonstration, a digital coherent receiver employing the proposed clock conversion successfully receives 330-µs burst QPSK frames over 20-km transmission in the presence of a 100-ppm clock mismatch.

InP-based high electron mobility transistors (InP-HEMTs) and graphene-channel FETs (G-FETs) are experimentally examined as photonic frequency converters for future broadband optical and wireless communication systems. Optoelectronic properties and three-terminal functionalities of the InP-HEMTs and G-FETs are exploited to perform single-chip photonic double-mixing operation over the 120 GHz wireless communication band. A 10 Gbit/s-class data signal on a 112.5 GHz carrier is mixed down to a 25 GHz IF band with an 87.5 GHz LO signal that is simultaneously self-generated from an optically injected photomixed beat note. The results suggest that the intrinsic channel of the G-FET can achieve a speed performance that is superior to that of an InP-HEMT having an equivalent device feature size. The reduction of the extrinsic parasitic resistances and the implementation of an efficient photo-absorption structure in the G-FET may allow a millimeter-wave and sub-THz photonic frequency conversion with a sufficiently high conversion gain for practical purposes.

This paper describes continuous millimeter-wave and terahertz (THz)-wave applications, where telecom-based photonics technologies are efficiently employed to enhance their performance. First, 300-GHz-band wireless communications are described toward real-time error-free transmissions at 50 Gbit/s and beyond. Next, a novel approach to increase a phase measurement sensitivity in THz frequency-domain spectroscopy systems is explained, and a similar technique is successfully applied to the visualization of electric-field radiation and propagation. Finally, as a futuristic study, the manipulation of THz waves with a concept of photonic crystals and its possible applications to platforms in THz integrated systems are presented.

The dis-aggregated passive optical network (PON) optical line terminal (OLT) architecture is attracting attention in academia and industry. This paper first reviews the evolution in dynamic bandwidth allocation (DBA) dis-aggregation. We further enhance the scalability of the dis-aggregated PON-OLT by reducing the bandwidth overhead of REPORT/GATE, the time division multiplexing (TDM) control information transferred between dis-aggregated DBA and the hardware platform. Our experiment verifies that the data compression based on basic integer coding can improve the scalability by 27% with acceptable processing time.

We propose a new automation concept for access network equipment called “Plug & Provision.” This concept aims at reducing the workload in provisioning passive optical network (PON) service by utilizing a modular optical line terminal (OLT) and automating the setup sequence. To realize this concept, the automation platform must automatically detect the modular OLT plugged into a switch port and execute the configuration sequence that it triggered. We utilize open-source software in the control/management layer, especially focusing on OpenFlow as a control protocol. We present the overall architecture including a newly proposed PON abstraction and in-band control method for deeply disaggregated modular OLTs, and we demonstrate the feasibility of the architecture.

This paper investigates the uplink coordinated multiple point (CoMP) reception with quantize-and-forward (QF) relaying. In this relaying system, two relay nodes directly quantize the received symbols to integer numbers based on modulo-lattice and parallelly forward these numbers to the destination via optical fiber. In order to reduce the traffic load of optical fiber without sacrificing CoMP gain, we propose an optimization strategy from the viewpoint of mutual information which adaptively controls the quantization level at the relay nodes. We have demonstrated that the proposed optimization is capable of helping the system achieve high throughput and low traffic load of optical fiber at the same time by computer simulations.

Time- and wavelength- division multiplexed passive optical network (TWDM-PON) have attracted attention as the next step in relation to optical access systems. A major application of TWDM-PON is expected to be fronthaul streams in the centralized radio access network (C-RAN) architecture of mobile networks. In the 5G era, the upstream traffic that OLT receives becomes highly bursty, because of the variable data rate generated by the functional split between baseband unit and remote radio heads, and the global synchronization of data transmission with time-division duplex (TDD). To flexibly allocate upstream bandwidth via the dynamic wavelength and bandwidth allocation (DWBA) scheme has been a hot research topic for TWDM-PON. However, there is no existing DWBA scheme for TWDM-PON that is designed to satisfy the strict delay requirement for fronthaul with minimum number of active wavelength channels. Therefore, in this paper we propose a novel efficient DWBA algorithm that minimizes active wavelength channels considering the high burstiness of fronthaul data transmission. With the proposed algorithm, the allowable delay and constraint for allocation timing for each ONU is formulated based on the different propagation delay between the OLT and ONUs. Then, the wavelength channel and bandwidth is allocated with the simple allocation algorithm based on the descending sort by propagation delay. It was confirmed through computer simulations that the proposed algorithm can reduce the number of active wavelength by 50% by considering propagation delay.

A time sensitive converged network that can aggregate fronthaul and machine-to-machine (M2M) streams is required for the fifth generation mobile communication system (5G) era. Recently, a time sensitive network (TSN) for fronthaul in IEEE 802.1CM has been attracting attention. A time aware shaper (TAS), which is a component technology of a TSN, is an effective way to realize a converged network. However, lower priority streams suffer from a lack of usable bandwidth and a huge latency when employing a TAS because the broad bandwidth is reserved for high priority streams in TAS schemes. In this paper, we propose a gate shrunk (GS-)TAS, where a GS-frame is added at the end of high priority streams. We evaluate bandwidth use efficiency by using a numerical simulation. We also simulate the cumulative distribution function (CDF) for the latency performance in a bridged node. We report that the latency reduction rate for the M2M stream is 55.2% for a CDF of 99.7%. In addition, the GS-TAS use does not affect the fronthaul streams.

We propose a low latency transmission scheme for mobile fronthaul with intra PHY split RAN architecture. It forwards short segments of encoded bit data corresponding to modulation symbols of wireless signals. Evaluation results confirm the latency reduction of 140 μs.

For mobile fronthaul with TDM-PON, we propose a practical DBA scheme that allocates proper time slots by estimating the data-arrival period from mobile scheduling information. Experiments show that the scheme actually satisfies the fronthaul latency requirement for the first time.

We propose a novel automatic detection and recovery scheme for estimation error when accommodating TDD-based fronthaul and secondary services in a TDM-PON. We demonstrate experimentally that normal operation is restored in less than 14 ms.

We demonstrate NG-PON2 with small delay variation and low latency for 5G mobile fronthaul for the first time. We experimentally confirm the proposed fixed delay function and the implemented mobile DBA are greatly effective to delay performances.

This paper proposes a unified design of log likelihood ratio (LLR) quantization and joint reception (JR) to reduce the mobile fronthaul (MFH) bandwidth in the split-physical (PHY) processing (SPP). SPP is one of the schemes that redefine the base station (BS) functional split between a baseband unit (BBU) and a remote radio head (RRH) in cloud radio access network (C-RAN). SPP splits the BS functions between the channel encoder/decoder and the modulator/demodulator of the PHY layer functions. In the uplink scenarios, the RRH forwards demodulator output LLR to the channel decoder at the BBU through the MFH. To reduce the MFH bandwidth, the number of LLR quantization bits must be minimized while maintaining the requested quality after JR, for example in terms of bit error rate (BER) requirement. To deal with the minimization, the proposed scheme adaptively controls the LLR quantization threshold according to the received signal to noise ratio (SNR) as well as the capability of source coding for data compression of the quantized LLR. Numerical simulations show that the proposed scheme is capable of reducing the average number of LLR quantization bits to fewer than 2 bits and 1.1 bits at the minimum with a JR block error rate (BLER) performance superior to that of selection combining.

A fronthaul bridged network has attracted attention as a way of efficiently constructing the centralized radio access network (C-RAN) architecture. If we change the functional split of C-RAN and employ time-division duplex (TDD), the data rate in fronthaul will become variable and the global synchronization of fronthaul streams will occur. This feature results in an increase in the queuing delay in fronthaul bridges among fronthaul flows. This paper proposes a novel low-latency routing scheme designed to satisfy the latency requirements in fronthaul networks with path-control protocols. The proposed scheme formulates the maximum queuing delay by defining competitive links and flows. It selects the set of paths that satisfy the latency requirements with the Markov chain Monte Carlo method using machine learning (MCMC-ML). The initial paths are selected from candidate paths using the learned solutions, and path-reselection is performed with the MCMC method. We confirmed with computer simulations that the proposed scheme can compute routes for all flows that satisfy the delay requirements. We also confirmed that the route computation is accelerated with the learned solutions, even if the flow distribution changes.

Mobile fronthaul (MFH) networking has been widely studied to construct the MFH link cost-effectively. However, the MFH link has a strict latency requirement. Moreover, the burst signals are simultaneously generated since the mobile base stations (MBSs) are time-synchronized among the neighboring MBSs. That is, the number of accommodatable MBSs will be limited even though the MFH link will be networked. To increase the MBSs in the MFH network, the latency requirement needs to be relaxed. The latency requirement is determined by a hybrid automatic repeat request (HARQ) process. In the HARQ process, an acknowledge (ACK) or negative-ACK signal must be forwarded through the MFH link with low latency. A main user data signal does not need to be forwarded with low latency when a time-division duplex scheme is applied to the MBS. Therefore, this paper proposes a signal-forwarding scheme for decoupling the uplink user and HARQ response signals. The proposed scheme can be applied to a system in which HARQ is used—for example, 4G [long-term-evolution (LTE), LTE-Advanced], or next-generation 5G mobile communication systems. The decoupled HARQ response signal is forwarded as the highest priority. Numerical simulation shows the feasibility of the proposed scheme.

We propose the use of Small Cell Forum application program interface mapped over Radio over Ethernet frames to realize a transport interface for mobile fronthaul where the function of the base stations is split between MAC and PHY layers for 5G mobile with a centralized radio access network configuration. We confirmed that this approach successfully reduced the bandwidth required for the fronthaul to less than 10 Gbit/s by numerical simulation when the wireless system bandwidth was 600 Mbit/s for 16 streams per access point, owing to the statistical multiplexing effect described in our proposal.

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.

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.

This paper reviews advances in sub-THz photonic frequency conversion using optoelectronic transistors for future fully coherent access network systems. Graphene-channel field effect transistors (G-FETs) and InP-based high electron mobility transistors (inP-HEMT) are experimentally examined as photonic frequency converters. Optoelectronic properties and three-terminal functionalities of the G-FETs and InP-HEMTs are exploited to perform single-chip photonic double-mixing operation over the 120 GHz wireless communication band. A single transistor can photomix the optical subcarriers to generate LO and mix down the RF data on the sub-THz carrier to the IF band.

We analyze the mobile fronthaul (MFH) bandwidth and the wireless transmission performance in the split-PHY processing (SPP) architecture, which redefines the functional split of centralized/cloud RAN (C-RAN) while preserving high wireless coordinated multi-point (CoMP) transmission/reception performance. The SPP architecture splits the base stations (BS) functions between wireless channel coding/decoding and wireless modulation/demodulation, and employs its own CoMP joint transmission and reception schemes. Simulation results show that the SPP architecture reduces the MFH bandwidth by up to 97% from conventional C-RAN while matching the wireless bit error rate (BER) performance of conventional C-RAN in uplink joint reception with only 2-dB signal to noise ratio (SNR) penalty.

The RAN architecture splitting BS functions within PHY layer is prototyped and evaluated to confirm its validity. Experiments show that mobile fronthaul optical bandwidth is reduced by 90% compared to conventional C-RAN maintaining wireless performance.

To quickly meet the diverse requirements imposed by emerging new services on optical access networks, we recently proposed the new concept of "flexible access system architecture" (FASA), which features the disaggregation of time-critical applications. This paper introduces our activities on FASA along with related technical trends. As our key ongoing challenge, the modularization of the dynamic bandwidth assignment function in a passive optical network is reviewed, and information on its use cases, approach, and sequences is given. Furthermore, a reference hardware implementation of FASA for mobile service is described.

Time division multiplexing passive optical networks (TDM-PONs) are attracting attention as a cost-effective way of realizing mobile fronthaul (MFH), which is an optical link between a central unit (CU) and a distributed unit (DU) in a centralized radio access network (C-RAN). To realize an even more cost-effective network, we have studied the accommodation of MFH and secondary services in a single TDM-PON. We focus on the fact that a time division duplex (TDD) scheme will be applied to future radio access (FRA). Since a PON link is a wavelength division multiplexing (WDM) scheme, whereas a radio propagation link is a TDD scheme, unallocated intervals occur periodically in the PON link. For the above reason, we have already proposed a technique for estimating unallocated intervals in a TDD-based MFH link that involves prelearning based on a test signal transmission, and the signal of the secondary service is accommodated in the unallocated intervals. However, a scheme for recovering from an error when the estimation is wrong and the test signal is not transmitted has yet to be studied. This paper proposes an estimation technique without a test signal transmission and an estimation-error recovery scheme. The proposed estimator calculates the correlation coefficient between captured uplink traffic and the seven types of uplink and downlink ratio patterns standardized by the third generation partnership project (3GPP: http://www.3gpp.org/). We evaluate the effectiveness of the proposed estimation technique by using a numerical simulation. The recovery scheme detects the estimation error and re-allocates the bandwidth. We implement the estimator and the recovery scheme in a 10 Gigabit Ethernet PON (10G-EPON) prototype. We report the feasibility of the proposed scheme along with experimental results.

A fronthaul bridged network has attracted attention as a means of efficiently constructing the centralized radio access network (C-RAN) architecture. If we change the functional split of C-RAN and employ timedivision duplex (TDD), the data rate in fronthaul will become variable, and the global synchronization of front-haul streams will occur. This feature results in an increase in the queuing delay in fronthaul bridges among fronthaul flows. To address this problem, this paper proposes a novel low-latency routing scheme designed to minimize the worst-case delay in fronthaul networks with path-control protocols. The proposed scheme formulates the worst-case delay of each fronthaul stream based on the distribution of nodes, the propagation delay, and metric of the links. It selects the set of paths that minimizes the maximum value of the worst-case delay from the candidate path sets for fronthaul flows generated with the k-th shortest path algorithm. We confirmed with computer simulations that the proposed scheme can adequately minimize the worst-case delay, irrespective of the network topology. The maximum queuing delay is minimized by considering the time synchronization between fronthaul flows and the burst size determined by the TDD subframe length.

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.

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.

We experimentally evaluate the mobile fronthaul (MFH) optical bandwidth and wireless coordinated multipoint (CoMP) transmission and reception performance in Ethernet-based MFH with our proposed split-physical (PHY) processing (SPP). To reduce the MFH optical bandwidth, SPP redefines the base station (BS) functional split between the baseband unit (BBU) and the remote radio head (RRH) in a centralized/cloud radio access network (C-RAN) with a common public radio interface. The functional split point of SPP is between wireless channel coding and wireless modulation within the PHY layer functions. SPP employs its own CoMP joint transmission and reception schemes to achieve high wireless CoMP performance comparable to that in a conventional C-RAN while reducing the MFH optical bandwidth. Experimental results in the uplink and downlink show that SPP reduces the MFH optical bandwidth by over 90% compared to the conventional C-RAN. At the same time, SPP achieves wireless performance with a signal-to-noise ratio penalty of less than 2 dB compared to the conventional C-RAN in the uplink and outputs wireless signals identical to the wireless signal output in the conventional C-RAN in the downlink.

The trend in broadband access services is shifting from the fixed to the mobile. Accordingly, the role of the optical access network systems is changing from the fiber-to-the-home/fiber-to-the-building infrastructure to a common access platform that supports both the fixed and mobile broadband services. It is expected that various virtual network operators will provide a variety of services on the common platform. In particular, the mobile fronthaul (MFH) using optical access is becoming more important in terms of supporting the massive deployment of small cells given the continuous speed increase in mobile access. This paper first reviews and discusses solutions for future MFH networks to address several issues in the evolution of the radio access network. It next discusses access-network convergence for the fixed and mobile services, and describes technologies and an architecture to realize this convergence. The overall motivation of these works is to reduce the total cost of access network ownership.

We propose the wavelength adjustment method of the upstream signal using the AMCC complied with G.989.3 against the wavelength drift in WDM-PON and demonstrate it in the evaluation platform implementing the AMCC processor.

This paper proposes a novel rank-based queue scheduling method for achieving low latency in a fronthaul bridged network. We confirmed with computer simulations the proposed scheme increased the number of accommodated fronthaul streams by 40%.

Recently, many telecom carriers are promoting the re-architecture of access networks and COs by utilizing SDN/NFV and OSS. We present our research relevant to the software PON-OLT architecture that we proposed for further flexibility.

We implement our abstraction method for provisioning and controlling, via OpenFlow, the disaggregated PON-OLT that features separation of hardware module and softwarized OLT functions, and demonstrate its operation by utilizing open source controllers ONOS / VOLTHA.