Takeshi Kitahara

An adaptive load balancing in multi-hop mesh networks for broadband fixed wireless access systems

Broadband fixed wireless access (BFWA) systems with multi-hop mesh topologies operating at millimeter-wave bands have attracted considerable attention as a promising technology for high capacity access infrastructures. The primary advantage of the mesh network is an improvement of capacity by means of traffic engineering throughout the network. This work discusses an adaptive load balancing method that enables us to maximize the capacity for the mesh BFWA networks by transferring traffic using multiple routes. Considering wireless link qualities, the adaptive traffic load balancing method attempts to equalize each wireless links utilization. The proposed method implements flow-based traffic load balancing in order to avoid deteriorating the performance of TCP communications. The performance of the proposed adaptive traffic load balancing method is evaluated on experimental mesh network environments.

Implementation of the integrated network and link control functions for multi-hop mesh networks in broadband fixed wireless access systems

Broadband fixed wireless access (BFWA) systems with multi-hop mesh topologies have attracted considerable attention as a promising technology for next generation, high quality, high capacity, and high density access infrastructures. The primary advantages of mesh network topologies are an improvement of availability in connectivity between pairs of nodes by means of diversity routes. The paper discusses a wireless node architecture that enables the integrated control of route diversity and traffic engineering together with the control of wireless links whose quality and performance could be affected by radio propagation conditions. Taking into account the functional requirements for multi-hop mesh BFWA networks, such as adaptive link configuration with multiple channels, distributed network management, and traffic engineering in mesh networks, the entity called network control unit (NCU) is designed and developed on a common UNIX based server computer. Implemented functions and their performance are demonstrated using experimental environments with wired networks.

A Data Transmission Control to Maximize Discharge Capacity of Battery

In machine-to-machine communications, battery life is so critical that many researchers make efforts in the areas of system configurations, network topology, protocols and so forth. This paper proposes a data transmission control method that focuses on well-known electrochemical characteristics of batteries. An objective of the proposed method is to increase the discharge capacity as the total amount of available current from a fully charged battery. From Peukerts law, it is known that increasing the average level of current extracted from the battery decreases the discharge capacity. Pulse discharge by insertion of rest time periods, however, has an effect equivalent to that the average level of current decreases. Furthermore, since such pulse discharge needs to be managed in consideration of the status of data transmission and network congestion, we suggest a novel data transmission control method aiming at an effective pulse discharge to maximize the discharge capacity with sufficient quality of data transmission. The proposed method can be implemented as a function to manage the size of data and the timing of data transmissions. A prototype terminal that employs the proposed method was developed with a small-capacity lithium-ion secondary battery. Experimental results show the effectiveness of pulse discharge in the application of the proposed method to the prototype terminal. Furthermore, an analytical investigation provides appropriate operational parameters to enhance the effectiveness.

Autonomous Data Transmission Using Off-Peak Hours for Cellular-Based M2M Communications

This paper proposes autonomous data transmission using off-peak hours for cellular-based machine-to-machine (M2M) communications. In the near future, there will be an enormous number of machine type terminals (MTs) capable of connecting to cellular networks. Thus, an efficient scheme for accommodating M2M traffic in existing cellular networks is required. To tackle this challenge, we focus on the fact that there are a lot of delay-insensitive services in M2M communications. The goal of the proposed method is to shift such traffic to off-peak hours in a scalable, flexible and simple manner. We evaluate the proposed method through a field experiment and a computer simulation using traffic data obtained from a commercial cellular network.

Experimental Evaluation of Adaptive SR-SW-ARQ/FEC Scheme for Ultra Low-Latency Mobile Networks

In order to realize ultra low-latency mobile networks whose target is a unidirectional end-to-end latency of 10 milliseconds per IP packet, we proposed an adaptive error recovery scheme. The simulation results, which verified the effectiveness of the proposed scheme, need to be complemented by more realistic testing. Hence, we have implemented the proposed scheme using field programmable gate array (FPGA) and developed a testbed. The experimental evaluation results obtained using the testbed show similar IP packet error rate (IP PER) performances to those of the simulation results. Moreover, the IP PER performances with an end-to-end latency limitation (including transmission latency and processing latency) are firstly evaluated using the testbed. The experimental results verify the effectiveness of the proposed adaptive error recovery scheme using the testbed and indicate the possibility of realizing ultra low-latency mobile networks using the proposed error recovery scheme.

A Novel Adaptive SR-SW-ARQ/FEC Scheme for an Ultra Low-Latency Mobile Network

To realize an ultra low-latency mobile network that has a quite short end-to-end latency, we present an adaptive error recovery scheme. In the proposed scheme, a combination of selective repeat (SR) and stop-and-wait (SW) ARQ (automatic repeat request), is adopted at the link layer. In addition, an adaptive FEC (forward error correction) scheme that has a different redundancy rate depending on the number of retransmissions is adopted at the physical layer. Theoretic analyses show that the proposed SR-SW-ARQ has a shorter transmission latency than that of the conventional SW-ARQ protocol when the error rate is sufficiently low. Simulations of the proposed adaptive SR-SW-ARQ/FEC scheme were conducted based on the flat Rayleigh channel. The simulation results verify that the proposed scheme provides better performance in terms of a normalized throughput at the link layer and less transmission latency compared to a scheme that has a static redundancy FEC scheme and SR-SW-ARQ protocol

An experimental study on switching threshold for adaptive modulation in broadband FWA systems

A number of wireless systems have recently adopted an adaptive modulation scheme to improve frequency efficiency. Unlike mobile systems, FWA (fixed wireless access) systems including IEEE 802.16 systems used for MAN (metropolitan area network) are allowed to use quasi-millimeter and millimeter bands, but those are vulnerable to rain attenuation. Adaptive modulation scheme is effective in those systems to improve the availability of wireless links. A 26 GHz-band broadband FWA system with a five-level (1024 QAM to BPSK) adaptive modulation scheme was proposed and developed by the authors for field experiments. This paper introduces field experimental results concerning switching thresholds for adaptive modulation controls using the developed FWA system. The numerical results reveal that conventional ideas, in which identical switching thresholds in terms of BER (bit error rate) apply to all modulation methods and switching thresholds maximizing Layer-2 throughput, can neither obtain the maximum TCP (transmission control protocol) throughput nor satisfy the upper limit of the UDP (user datagram protocol) packet loss rate

Unsupervised multi scale anomaly detection in streams of events

Automatically detecting anomalies in streams of events is crucial for many applications in communications, security, healthcare, finance and real-time systems. In communication systems, it can be used to forecast equipment breakdowns or to detect unprecedented issues that do not trigger any alarms. Several methods have been proposed to detect anomalies in streams of events but they are not suited to detect large-scale anomalies with different durations and features. In this paper, we first propose a new data structure called s-digest to learn the distributions of values originating from streams of events for multiple time-scales. The structure is then used to conceive an unsupervised multi-scale method able to detect anomalies with different durations and characteristics. The method withstands high-throughput streams of events, is highly scalable and memory efficient. We then simulate a mobile network based on actual data from a commercial LTE network and apply our method to detect various anomalies and prove its accuracy and practicability.

Group Mobility in Mobile Networks: Signaling Based Detection and Network Utilization Modeling

Group mobility in mobile networks is responsible for dynamic changes of network utilization as well as concentrated accesses to base stations that eventually lead to a degradation of network quality. In particular, a fast-moving group of users intensively accessing the network, such as passengers on a train running in a densely populated area, affects the perceived network quality. Efficiently evaluating and monitoring the performance of the network for these specific users is thus crucial. In this paper, we focus on the analysis of network signaling data, which contains information related to mobility and connectivity. We propose a practical and automated group movement detection method to detect train passengers without relying on the location of users and build network utilization models for train users and non-train users. The models reveal that train users consume 3.5 times more resources than non-train users, which proves that group mobility has a significant influence on mobile networks.

An Adaptive Traffic Load Balancing Method for Multi-Hop Mesh Networks in Broadband Fixed Wireless Access Systems

Broadband fixed wireless access (BFWA) systems with multi-hop mesh topologies have attracted considerable attention as a promising technology for next generation, high quality, high capacity, and high density access infrastructures. The primary advantages of mesh network topologies are an improvement of capacity by means of traffic engineering throughout the networks. This paper discusses an adaptive traffic load balancing method that maximizes the capacity for the mesh BFWA networks. Taking into account the variation of network conditions such as traffic demand distributions and qualities of wireless links, the adaptive traffic load balancing method attempts to equalize the utilization of capacity for each wireless link. To avoid deteriorating the performance of TCP communications, the proposed method implements flow-based traffic load balancing. Performance of the proposed adaptive traffic load balancing method is demonstrated and validated using the experimental mesh network environments with wired networks with up to sixteen nodes that emulates the variation of the wireless link capacity.