To cope with ever growing mobile data traffic, we recently proposed a concept of cellular ultra-dense radio access network (RAN). In the cellular ultra-dense RAN, a number of distributed antennas are deployed in the base station (BS) coverage area (cell) and user-clusters are formed to perform small-scale distributed multiuser multi-input multi-output (MU-MIMO) transmission and reception in each user-cluster in parallel using the same frequency resource. We also proposed a decentralized interference coordination (IC) framework to effectively mitigate both intra-cell and inter-cell interferences caused in the cellular ultra-dense RAN. The inter-cell IC adopted in this framework is the fractional frequency reuse (FFR), realized by applying the channel segregation (CS) algorithm, and is called CS-FFR in this paper. CS-FFR divides the available bandwidth into several sub-bands and allocates multiple sub-bands to different cells. In this paper, focusing on the optimization of the CS-FFR, we find by computer simulation the optimum bandwidth division number and the sub-band allocation ratio to maximize the link capacity. We also discuss the convergence speed of CS-FFR in a cellular ultra-dense RAN.

It is now becoming important for mobile cellular networks to accommodate all kinds of Internet of Things (IoT) communications. However, the contention-based random access and radio resource allocation used in traditional cellular networks, which are optimized mainly for human communications, cannot efficiently handle large-scale IoT communications. For this reason, standardization activities have emerged to serve IoT devices such as Cellular-IoT (C-IoT). However, few studies have been directed at evaluating the performance of C-IoT communications with periodic data transmissions, despite this being a common characteristic of many IoT communications. In this paper, we give the performance analysis results of mobile cellular networks supporting periodic C-IoT communications, focusing on the performance differences between LTE and Narrowband-IoT (NB-IoT) networks. To achieve this, we first construct an analysis model for end-to-end performance of both the control plane and data plane, including random access procedures, radio resource allocation, establishing bearers in the Evolved Packet Core network, and user-data transmissions. In addition, we include the impact of the immediate release of the radio resources proposed in 3GPP. Numerical evaluations show that NB-IoT can support more IoT devices than LTE, up to 8.7 times more, but imposes a significant delay in data transmissions. We also confirm that the immediate release of radio resources increases the network capacity by up to 17.7 times.

In this paper, we propose new radio access network (RAN) architecture for reliable millimeter-wave (mmWave) communications, which has the flexibility to meet users' diverse and fluctuating requirements in terms of communication quality. This architecture is composed of multiple radio units (RUs) connected to a common distributed unit (DU) via fronthaul links to virtually enlarge its coverage. We further present grant-free non-orthogonal multiple access (GF-NOMA) for low-latency uplink communications with a massive number of users and robust coordinated multi-point (CoMP) transmission using blockage prediction for uplink/downlink communications with a high data rate and a guaranteed minimum data rate as the technical pillars of the proposed RAN. The numerical results indicate that our proposed architecture can meet completely different user requirements and realize a user-centric design of the RAN for beyond 5G/6G.

Deployment of machine-type communications (MTCs) over the current cellular network could lead to severe overloading of the radio access network of Long Term Evolution (LTE)-based systems. This paper proposes a slotted access-based solution, called the Slotted Access For Group Paging (SAFGP), to cope with the paging-induced MTC traffic. The proposed SAFGP splits paged devices into multiple access groups, and each group is then allocated separate radio resources on the LTE's Physical Random Access Channel (PRACH) in a periodic manner during the paging interval. To support the proposed scheme, a new adaptive barring algorithm is proposed to stabilize the number of successful devices in each dedicated access slot. The objective is to let as few devices transmitting preambles in an access slot as possible while ensuring that the number of preambles selected by exactly one device approximates the maximum number of uplink grants that can be allocated by the eNB for an access slot. Analysis and simulation results demonstrate that, given the same amount of time-frequency resources, the proposed method significantly improves the access success and resource utilization rates at the cost of slightly increasing the access delay compared to state-of-the-art methods.

In this paper, a novel method of resource abstraction and an abstracted-resource model for dynamic resource control in optical access networks are proposed. Based on this proposal, an implementation assuming application to 5G mobile fronthaul and backhaul is presented. Finally, an evaluation of the processing time for resource allocation using this method is performed using a software prototype of the control function. From the results of the evaluation, it is confirmed that the proposed method offers better characteristics than former approaches, and is suitable for dynamic resource control in 5G applications.

Ultra-densification of radio access network (RAN) is essential to efficiently handle the ever-increasing mobile data traffic. In this paper, a joint multi-layered user clustering and scheduling is proposed as an inter-cluster interference coordination scheme for ultra-dense RAN using cluster-wise distributed MIMO transmission/reception. The proposed joint multi-layered user clustering and scheduling consists of user clustering using the K-means algorithm, user-cluster layering (called multi-layering) based on the interference-offset-distance (IOD), cluster-antenna association on each layer, and layer-wise round-robin-type scheduling. The user capacity, the sum capacity, and the fairness are evaluated by computer simulations to show the effectiveness of the proposed joint multi-layered user clustering and scheduling. Also shown are uplink and downlink capacity comparisons and optimal IOD setting considering the trade-off between inter-cluster interference mitigation and transmission opportunity.

Communication networks for wide-scale distributed energy resources (DERs) including photovoltaics (PVs), wind, storage and battery systems and electric vehicles (EVs) will be indispensable in future power grids. In this paper, we compare optical fronthaul networks using existing optical ground wires (OPGWs) for centralized radio access network (C-RAN) architecture to realize cost effective wireless communication network expansion including low population area. We investigate the applicability of optical data transport technologies of physical layer split (PLS), analog radio-on-fiber (ARoF), and common public radio interface (CPRI). The deployment costs of them are comparatively analyzed. It was shown that physical layer split and analog radio-on-fiber with subcarrier multiplexing (SCM) result in lower cost than other technologies.

A long-reach coexisting PON system (1G/10G-EPON, video, and TWDM-PON) that uses the Wavelength Selective-Asymmetrical optical SPlitter (WS-ASP) without any active devices like optical amplifiers is proposed. The proposal can take into account the subscriber distribution in an access network and provide specific services in specific areas by varying the splitting ratios and the branch structure in the optical splitter. Simulations confirm the key features of WS-ASP, its novel process for deriving the splitting-ratios and greater transmission distance than possible with symmetrical splitters. Experiments on a prototype system demonstrate how wavelengths can be assigned to specific areas and optical link budget enhancement. For 1G-EPON systems, the prototype system with splitting-ratio of 60% attains the optical link budget enhancement of 4.2dB compared with conventional symmetrical optical splitters. The same prototype offers the optical link budget enhancement of 4.0dB at the bit rate of 10G-EPON systems. The values measured in the experiment agree well with the simulation results with respect to the transmission distance.

This paper presents a water leakage monitoring system that gathers acoustic data of water pipes using wireless communication technology and identifies the sound of water leakage using machine leaning technology. To collect acoustic data effectively, this system combines three types of data-collection methods: drive-by, walk-by, and static. To design this system, it is important to ascertain the wireless communication distance that can be achieved with sensors installed in a basement. This paper also reports on radio propagation from underground manholes made from reinforced concrete and resin concrete in residential and commercial areas using the 920 MHz band. We reveal that it is possible to design a practical system that uses radio communication from underground sensors.

High-performance Network Over Coax, or HINOC for short, is a broadband access technology that can achieve bidirectional transmission for high-speed Internet service through a coaxial medium. In HINOC access networks, buffer management scheme can improve the fairness of buffer usage among different output ports and the overall loss performance. To provide different services to multiple priority classes while reducing the overall packet loss rate and ensuring fairness among the output ports, this study proposes a QoS optimization method for access networks. A backpressure-based queue threshold control scheme is used to minimize the weighted average packet loss rate among multiple priorities. A theoretical analysis is performed to examine the performance of the proposed scheme, and optimal system parameters are provided. Software simulation shows that the proposed method can improve the average packet loss rate by about 20% to 40% compared with existing buffer management schemes. Besides, FPGA evaluation reveals that the proposed method can be implemented in practical hardware and performs well in access networks.

A novel adaptive code division multiplexing system with hybrid electrical and optical codes is proposed for flexible and dynamic resource allocation in next generation asynchronous optical access networks. We analyze the performance of a 10Gbps × 12 optical node unit, using hierarchical 8-level optical and 4-level electrical phase shift keying codes.

The spread of optical access broadband networks using Fiber to the Home (FTTH) has not reached the rural areas of developing countries. The current state of global deployment of ICT indicates that it is difficult to sell network systems as stand-alone products due to prohibitive costs, and the demand is for total services that include construction, maintenance, and operation. Moreover, there is a need to offer proposals that include various solutions utilizing broadband networks, as well as for a business model that takes the sustainability of those solutions into consideration. In this paper, we discuss the issues in constructing broadband networks, introduce case studies of solutions using broadband networks for solving social issues in rural areas of developing countries, and discuss the challenges in the deployment of the solutions.

This paper describes optical access networks focusing on passive optical network (PON) technologies from a technical point of view. Optical access networks have been applied to fiber-to-the-home as a driving force of broadband services and their use will continue growing in the near future. They will be applied as an aggregate component of broadband wireless networks. This paper also addresses solutions for their application.

The cloud radio access network (C-RAN) is embracing unprecedented popularity in the evolution of current RAN towards 5G. One of the essential benefits of C-RAN is facilitating cooperative transmission to enhance capacity and energy performances. In this paper, we argue that the conventional symmetric coordination in which all antennas participate in transmission does not necessarily lead to an energy efficient C-RAN. Further, the current assessments of energy consumption should be modified to match this shifted paradigm in network architecture. Towards this end, this paper proposes an asymmetric coordination scheme to optimize the energy efficiency of C-RAN. Specifically, asymmetric coordination is approximated and formulated as a joint antenna selection and power allocation problem, which is then solved by a proposed sequential-iterative algorithm. A modular power consumption model is also developed to convert the computational complexity of coordination into baseband power consumption. Simulations verify the performance benefits of our proposed asymmetric coordination in effectively enhancing system energy efficiency.

In the near future, many sensors and terminals will be connected to the public network to provide various convenient IoT/M2M services. In order to connect many sensors to the network efficiently, wireless communication systems in the 920MHz band are seen as attractive solutions. We are focusing on the 920MHz band to research and develop high-capacity protocols that can accommodate many terminals, and low power consumption technologies for battery-driven terminals. In this paper, we describe the following three concrete wireless systems that use our proposals. (1) A physical distribution pallet management system that can handle thousands of pallet-embedded sensors and a wireless module with a battery lifetime of about ten years. (2) Water leakage monitoring system for underground pipes by using sensors and a wireless module in each valve box. (3) A wide-area and high-capacity radio relay system for smart metering services like the reading of gas meters. The radio relay system can accommodate various sensors and terminals and has large potential for providing various IoT/M2M services in conjunction with smart metering services.

The widespread use and increasing popularity of broadband service has prompted a focus on the measurement and analysis of its empirical performance in recent studies. The worldwide view of broadband performance has been examined over the short term with Speedtest.net, but research in this area has not yet provided a long-term evolutionary insight on how DSL, Cable, and Fiber access technologies have influenced on user experience. In this study, we present 6 years of measurement results, from 2006 to 2011, of broadband performance with fast developing broadband networks in Korea. With 57% Fiber penetration in 2011, our data consist of a total of 29M test records and 10M subscribers. Over the 6 years, we have observed a 2.9-fold improvement in download speed (57Mbps), 2.8-fold increase in upload speed (38Mbps), and 0.7-fold decrease in latency due to the high penetration rate of Fiber broadband service and the advanced Cable modem technology. In addition, we carried out longitudinal analysis of various aspects of services, providers, regions, and cost-performance. We believe that the evolutionary Korean broadband measurement results can shed light on how high-speed access technologies are substantially enhancing on end-to-end performance.

Ring aggregation networks are widely employed for metro access networks. A layer-2 ring with Ethernet Ring Protection is a popular topology for carrier services. Since frames are forwarded along ring nodes, a fairness scheme is required to achieve throughput fairness. Although per-node fairness algorithms have been developed for the Resilient Packet Ring, the per-node fairness is insufficient if there is bias in a flow distribution. To achieve per-flow fairness, N Rate N+1 Color Marking (NRN+1CM) was proposed. However, NRN+1CM can achieve fairness in case there are sufficient numbers of available bits on a frame header. It cannot be employed if the frame header cannot be overwritten. Therefore, the application range of NRN+1CM is limited. This paper proposes a Signaling based Discard with Flags (SDF) scheme for per-flow fairness. The objective of SDF is to eliminate the drawback of NRN+1CM. The key idea is to attach a flag to frames according to the input rate and to discard them selectively based on the flags and a dropping threshold. The flag is removed before the frame is transmitted to another node. The dropping threshold is cyclically updated by signaling between ring nodes and a master node. The SDF performance was confirmed by employing a theoretical analysis and computer simulations. The performance of SDF was comparable to that of NRN+1CM. It was verified that SDF can achieve per-flow throughput fairness without using a frame header in ring aggregation networks.

This paper studies the impact of integrating pricing with connection admission control (CAC) on the congestion management practices in contention-based wireless random access networks. Notably, when the network is free of charge, each self-interested user tries to occupy the channel as much as possible, resulting in the inefficient utilization of network resources. Pricing is therefore adopted as incentive mechanism to encourage users to choose their access probabilities considering the real-time network congestion level. A Stackelberg leader-follower game is formulated to analyze the competitive interaction between the service provider and the users. In particular, each user chooses the access probability that optimizes its payoff, while the self-interested service provider decides whether to admit or to reject the user's connection request in order to optimize its revenue. The stability of the Stackelberg leader-follower game in terms of convergence to the Nash equilibrium is established. The proposed CAC scheme is completely distributed and can be implemented by individual access points using only local information. Compared to the existing schemes, the proposed scheme achieves higher revenue gain, higher user payoff, and higher QoS performance.

With shortest path bridging MAC (SPBM), shortest path trees are computed based on link metrics from each node to all other participating nodes. When an edge bridge receives a frame, it selects a path along which to forward the frame to its destination node from multiple shortest paths. Blocking ports are eliminated to allow full use of the network links. This approach is expected to use network resources efficiently and to simplify the operating procedure. However, there is only one multipath distribution point in the SPBM network. This type of network can be defined as an end-to-end multipath network. Edge bridges need to split flows to achieve the load balancing of the entire network. This paper proposes a rate-based path selection scheme that can be employed for end-to-end multipath networks including SPBM. The proposed scheme assumes that a path with a low average rate will be congested because the TCP flow rates decrease on a congested path. When a new flow arrives at an edge bridge, it selects the path with the highest average rate since this should provide the new flow with the highest rate. The performance of the proposed scheme is confirmed by computer simulations. The appropriate timeout value is estimated from the expected round trip time (RTT). If an appropriate timeout value is used, the proposed scheme can realize good load balancing. The proposed scheme improves the efficiency of link utilization and throughput fairness. The performance is not affected by differences in the RTT or traffic congestion outside the SPBM network.

High-speed wireless access technologies have evolved over the last years setting new challenges for TCP. That is, to effectively utilize the available network resources and to minimize the effects of wireless channel errors on TCP performance. This paper introduces a new TCP variant, called TCP-BIAD aiming at enhancing TCP performance in broadband wireless access networks. We provide analytical expressions for evaluating the stability, throughput, fairness and friendliness properties of our proposal, and we validate our results by means of computer simulations. Initial results presented in this paper show that this approach achieves high network utilization levels in a wide range of network conditions, while maintaining an adequately fair and friendly behavior with respect to coexisting TCP flows.