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.

Virtualization of optical access systems is being pursued to speedup service deployment and reduce CAPEX/OPEX. Several passive optical network (PON) specifications have been standardized and the applicability of virtualization to access networks is being considered. We have proposed a programmable optical line terminal (OLT) that performs OLT functions by software processing on general-purpose hardware.Unfortunately, general-purpose hardware struggles to achieve the 10-Gbps throughput demanded of access systems. Our work solves this problem by introducing software implementation techniques for PHY processing, a key component of computation complexity. This paper proposes a 2-stage parallel pipeline based on data-parallelism, and details its implementation with the use of look up table (LUT) for the Galois-field multiplier for implementing the standard OLT functions of forward error correction (FEC) and encryption. We implement our proposals on a general-purpose server with optical transmitter. Evaluation results show that proposals drastically accelerate algorithm performance and attain the throughputs of 10 Gbps with RS(255,239), 5.1 Gbps with RS(255,223), 2.5 Gbps with CTR-AES-128 and 1.2 Gbps with GCM-AES-128.

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.

Both the variety of communication devices and their options in connecting to the Internet are continuously increasing due to the advances in numerous attractive network applications. These trends make designing the network much more complex. Legacy network design only had to consider predefined applications using common end-point devices such as plain old telephone system. On the other hand, the current and future network, especially in the access part, is expected to be universal so as to cover not only residential users, but also mobile users, and the huge number Internet of Things devices for the sake of cost efficiency. The key issue is the difficulty of designing a complex network that is also extremely energy efficient, particularly the future access system. Although many studies have attempted to improve the bandwidth utilization or energy efficiency in multiple-wavelength systems, little is known about how it will be impacted by the divergence among these multiple concrete services. In order to solve this energy issue, we propose a service multiplexing method with a profile-based network architecture, where each device declares its traffic profile. Our concept provides the feasible and practical control of complex network. It differs markedly from the methods that control the traffic at the packet or session level as it is easy to apply in actual networks.

In the era of the Internet of Things (IoT), the access network should provide Internet connectivity to huge numbers of wireless sensor nodes that are collecting data. For most sensor nodes, the macro cells of cellular networks provide cost-effective connectivity. However, covering the remaining nodes, which are either in the out-of-service state or have short-range wireless interfaces only, is a difficult issue. For example, when deploying small cells densely to provide fuller node coverage, the cost of the small cells should be well considered. From the perspective of economy, small cells that use the passive optical network (PON) and moderately priced wireless interfaces, called fiber-wireless (Fi-Wi) in this paper, seem the most promising candidates. However, the flexibility in Fi-Wi system deployment is strictly constrained by the need for a stable power source. Because most of the PON systems have been developed for fiber to the home (FTTH), the gateway node on the customer premise continuously consumes power and thus requires a stable power source. Therefore, the key issue is how to reduce the power consumption of the Fi-Wi gateway node drastically enough to run continuously with only battery and/or solar power. Additionally, the power-saving approach must meet the requirements of the IoT applications at the same time. We focus on the deep sleep approach, which turns OFF almost all the components, with significant power savings at the cost of a drop in quality of service (QoS). This paper proposes methods to control the deep sleep while assuring successful packet reception.

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.