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.

Network requirements in optical access networks continue to expand, and softwarization of transmission function has been studied for complete virtualization of access systems. In order to meet the requirements posed by Internet of Things (IoT) applications, SDN/NFV-based access network is an excellent candidate for the edge computing platform needed. However, using a common transmission method is inefficient and will increase the computational loads placed on edge servers. We are aiming to maximize the benefits of SDN/NFV by realizing transmission that can respond to individual IoT application requests. This paper proposes novel application-oriented optical transmission control to enhance computational efficiency, especially for image processing applications. Our proposal is implemented on a general-purpose server and we demonstrate its performance on a 10-Gbps optical transmission system. The results show that the proposal does achieve transmission control to suit application requests.

This paper describes a novel wavelength aggregation scheme that we propose. The scheme aims to incrementally upgrade time and wavelength division multiplexing passive optical networks (TWDM-PONs), with the aim of enabling future networks to function effectively. Mobile base stations are split into central units/distributed units (CU/DUs) and remote units (RUs). The optical link between the CU/DUs and the RUs is known as mobile fronthaul (MFH). Future networks that rise above fifth generation networks will need to deploy a huge number of RUs. Thus, quite a few optical fibers will be needed. Accordingly, TWDM-PONs enable MFH to be constructed cost effectively. However, mobile systems tend to upgrade their data rate incrementally up to the standardized maximum data rate in response to user traffic demand. Thus, both upgraded and non-upgraded CU/DUs co-exist in a mobile system at the same time. Therefore, TWDM-PONs have to upgrade their maximum data rates to enable the CU/DUs to be upgraded without stopping any transmission from other CU/DUs that were not upgraded in the PON branch. For this purpose, we propose a wavelength-aggregation scheme with a delay-based frame distribution technique that satisfies the MFH latency requirement. Unlike other schemes, this scheme can upgrade TWDM-PON data rates without stopping any other traffic. Numerical simulations demonstrated that the scheme can provide seamless upgrading that satisfies the MFH latency requirement with a minimized number of wavelengths, one that is less than the upper limit defined in the TWDM-PON specification.

In this paper, we make a summary report of our 5G R&D 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.

In this paper, we summarize our 5G R&D 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 R&D project.

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.

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.

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 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.

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.

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.

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.

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.

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.

We propose an uplink joint reception method for coordinated multi-point transmission and reception (CoMP) where the quantized log likelihood ratio (LLR) is forwarded by an optical interface different from the common public radio interface (CPRI), to suppress the explosive increase in the optical transmission bandwidth in the mobile fronthaul (MFH) of the centralized/cloud radio access network (C-RAN) and thus reduce the MFH optical transmission cost of future radio access. To exploit the proposed method, we focus on the split-PHY processing (SPP) architecture for MFH redefinition where the base station (BS) functions are split between modulation and channel coding functions within the PHY (Physical) layer. Numerical simulations of block error rate (BLER) performance confirm a signal to noise ratio (SNR) degradation due to the proposed method in the SPP architecture of less than 3 dB compared with the conventional C-RAN, and an SNR improvement compared to the performance without joint reception of more than 5 dB. Meanwhile, numerical calculations that assume future radio access show that the SPP architecture with the proposed method reduces MFH optical transmission bandwidth by at least 85 % compared to the conventional C-RAN. These results show that the SPP architecture with the proposed method will enable cost-effective MFH deployment.

Simple Serial Synchronized (SSS) Multistage Interconnection Network (MIN) is a novel MIN architecture for connecting processors and memory modules in multiprocessors. Synchronized bit-serial communication simplifies the structure/control, and also solves the pin-limitation problem. Here, design, implementation, and evaluation of a multiprocessor prototype called SNAIL with the SSS-MIN are presented. The heart of SNAIL is the prototype 1 /mu CMOS SSS-MIN gate array chip which exchanges packets from 16 inputs with 50MHz clock. The message combining is implemented only with 20% increases of the hardware. From the empirical evaluation with some application programs, it appears that the latency and synchronization overhead of the SSSMIN are tolerable, and the bandwidth of the SSS-MIN is sufficient. Although the performance improvement with the bit serial message combine is not so large (1%) when instructions are stored in the local memory, it becomes up to 400% when instructions are stored in the shared memory.