This article proposes a novel Airborne Internet of Things Network (AIN) system architecture for monitoring water quality, combining existing wireless technologies with the aid of a low altitude platform (LAP) to relay data over long distances in hilly terrain. The proposed system consists of water quality sensors, smart utility network (SUN) devices, long range (LoRa) wireless devices, an LAP air balloon, and Wi-Fi devices. A measurement campaign was conducted to assess the proposed system, focusing on the communication link reliability and the LAP stability and robustness. Several constraints, such as payload limit and safe weather conditions, were also highlighted for operating the LAP with extensive and reliable coverage. On the other hand, characterizing the wireless channel has become a crucial parameter for planning and deploying Internet of Things (IoT) applications. Accordingly, this work proposes a novel hybrid machine learning (ML)-based semi-empirical path loss (PL) model for LoRa wireless communication. The results validated the proposed system’s effectiveness, unique characteristics, and capability to monitor water quality in a harsh environment. Results also revealed a significant difference in packet delivery rate (PDR) for different gateway height and spreading factor (SF) configurations. For instance, switching SF7 to SF12 increased PDR by 28.7%. Meanwhile, increasing gateway height increased PDR by 29.2% for similar SF configurations. The evaluation also revealed that none of the established PL models are suitable to represent harsh tropical environments. Finally, the proposed model achieved nearly 90% prediction accuracy for testing samples and 95% accuracy for training and overall measurement samples, vastly outperforming conventional models.

Since IEEE 802.11af was standardized in 2013 as one of the standards for TVWS (TV white-spaces) communication, a variety of radio devices such as a high-power radio device al-lowing a transmission power of 1 W and a dongle-type com-pact radio device have been prototyped and demonstrated in field experiments. Meanwhile, since all the reported prototypes were limited to a single channel operation with a channel bandwidth of 6 MHz, achieved throughput was inferior to the commercialized WLAN (Wireless Local Area Network) systems with a channel bandwidth of 20 MHz or more. In this paper, to enhance the throughput of the IEEE 802.11af system, we de-sign and prototype a radio device based on IEEE 802.11af with a channel aggregation function. In addition, we evaluate fun-damental characteristics of the prototype radio device including radio performance and throughput.

It is of great interest to develop larger scale multiple-input multiple-output (MIMO) technology based on frequency division duplexing (FDD) for backward compatibility with existing standards and already deployed cellular networks. One hindrance to the FDD approach is the complexity of the codeword search performed by the receiver, which is known to scale with the number of transmit antennas N in a system. The codeword search complexity does not scale linearly and soon becomes infeasible even for the not-so-massive MIMO systems expected in the very near future. We address this problem by proposing a natural sequence-based orthogonal codebook and an intra-array interference magnitude (IIM) framework for MIMO beamforming based on quantized equal gain transmission that altogether tremendously simplifies the codeword search problem. We also present an assessment on the quality of the codeword selected by the proposed framework that explains it's near optimal performance, and, provide detailed codeword search complexity quantification. Finally, we provide simulation analyses of beamforming gain under time selective fading channels and an FDD MIMO system transmit delay model. Our analyses indicate that despite significantly reducing complexity, the proposed IIM framework executed by already commercialized processors is capable of approaching the ideal performance of an static system even in the presence of time-selectivity inherent to high-speed mobile communications. Our analyses also quantify the impact of feedback delay on average beamforming gain of moderately large transmit arrays.

The IEEE 802.11ad technology, which allows wireless devices to communicate in the unlicensed 60 GHz ISM band, promisingly provides multi-Gbps data rates for bandwidth-intensive applications. After years of research and development, we are now observing an increasing number of commodity IEEE 802.11ad radios that motivate researchers to exploit the IEEE 801.11ad capability for applications. This work first conducts an empirical study on the IEEE 802.11ad performance. In particular, we characterize the performance of IEEE 802.11ad links considering the variation of network parameters and interference. Secondly, we investigate the possibility of introducing IEEE 802.11ad to an evolving Wi-Fi network. The evaluation results show that our off-the-shelf IEEE 802.11ad hardware can achieve the Gbps level throughput of the transmission control protocol (TCP) and user datagram protocol (UDP). However, the evolvement is not trivial since the hardware can not well maintain the 60 GHz link. The main reason is lacking the fast switchover function between an IEEE 802.11ad and a legacy Wi-Fi link. We then seek the potential of multipath TCP (MPTCP) for the expected switchover. The default MPTCP, which enables data transmissions on both the IEEE 802.11ad and Wi-Fi links, is harmful to the IEEE 802.11ad throughput. Meanwhile, the backup mode of MPTCP, in which the Wi-Fi link acts as a backup for IEEE 802.11ad one, can maintain the comparable performance. Therefore, we propose to adopt MPTCP with the backup mode in the evolving Wi-Fi networks. The efficiency of MPTCP-based switchover is confirmed by conducting real experiments.

An important challenge to realize spectrum sharing through dynamic spectrum access in cognitive radio networks based on Orthogonal Frequency Division Multiplexing (OFDM) is to suppress high sidelobes of OFDM signals that interfere with the adjacent bands. Orthogonal precoding is a promising technique for sidelobe suppression where emitted OFDM signals must change their spectrum occupancy adaptively. However, the high computational complexity, quadratic in the number of subcarriers, has seriously prevented its application. To solve the problem, this paper proposes a novel orthogonal precoding with the compact WY representation. Numerical experiments show that the proposed method is significantly promising for implementation of the orthogonal precoding since it can achieve the efficiency of not only the coding operations (e.g., 5.1% of the multiplications in the conventional method) but also the precoder generation with remarkable numerical stability as keeping the attractive performances in the orthogonal precoding.

The 3rd generation partnership project (3GPP) has recently specified the non-standalone 5G New Radio (NR), in which the dual connectivity (DC) feature plays an essential role. A User Equipment (UE) with DC is able to concurrently connect to an evolved NodeB (eNB) (e.g., using LTE in a macro cell) and a next generation NodeB (gNB) (e.g., using 5G NR in a small cell) aiming to satisfy the 5G's required Key Performance Indicators (KPIs). In this work, we focus on the issue of concurrent transmissions on the 5G small cell, which potentially exploit the benefits of DC. With DC, an application is able to spread its traffic over different two paths (via eNB and gNB) between the UE and the LTE core network. The traffic over diverse paths may experience different delay since the conditions are generally different (e.g., due to wireless channel, background traffic). Therefore, one of the most important problems in efficient operation with DC is minimizing the end-to-end delay considering all the connections. To address that problem, we adopt the deterministic network calculus to first characterize the delay experienced by each connection; then to model the overall end-to- end delay in the 5G small cell. We then formulate an optimization problem that attempts to find the optimal traffic splitting over the connections while minimizing the delay. We derive the solution for the problem, as well as, present the numerical results.

The shared resource access wireless communication system is regarded as a paradigm that allows the mobile network operators (MNOs) to have extended coverage and allows them to satisfy their subscribers' high capacity demands while keeping the capital and operational expenditure in check. On the other hand, dual connectivity (DC), a small cell enhancement feature, allows the subscribers to have two simultaneous connections increasing throughput and enhancing mobility robustness. For the DC mechanism, the user needs to be under the coverage of multiple BSs concurrently. Because of random nature of the wireless links and distribution of BSs in a network, the practicability/operability of DC for a typical user under such random operating conditions (both topological and wireless link randomness) needs to be properly evaluated. In this paper, we perform stochastic analysis of DC in shared resource access high capacity wireless networks. We consider a fading-averaged signal propagation loss process, where the selection of the serving BS is perturbed shadowing, not by fading. The DC coverage probability is analyzed in terms of tractable, integral expressions. We have observed that the DC coverage probability is greatly affected by the density of the small cell BSs and the variance of the log-normal shadowing.

To make WiGig/IEEE 802.11ad backward compatible with the legacy Wi-Fi, a multi-band device that is capable of WiGig and Wi-Fi is necessarily equipped a function of fast switchover between the WiGig and Wi-Fi link. It is expected that the switching action is done as quickly as possible in order to minimize negative effects on an ongoing application. The IEEE 802.11ad standard defines the switching operation within the scope of fast session transfer (FST) protocol. To properly run FST, the device needs extra layer-2 entities that simultaneously manage the PHY/MAC states of multiple radios. Although introducing WiGig radios is a trivial task, installing those entities on an existing legacy Wi-Fi network is unfortunately a challenging one. This work presents an experimental feasibility study of achieving the backward compatibility without FST. We initially analyze the feasible capability of multipath transmission control protocol (MPTCP). We then setup a real- world testbed and evaluate different operational modes of MPTCP, aiming to find the most suitable one. Our experimental results show that the fast switchover between a multi-Gigabit WiGig and a legacy Wi-Fi link is achievable with the MPTCP's backup mode.

We investigate an advanced two-phase shared spectrum access communication scheme as an efficient approach to enhance the spectral utilization of a network. In the first phase, we devise a spectrum-sharing policy based on demands, fairness, and so on, which utilizes a priority scheme in fulfilling operators' demands, and envision a secure operator-specific information sharing policy where no critical information is exchanged between the operators. In the second phase, a macro cell network (MCN) benefits through offloading services offered by small cell network (SCN). This allows the MCN to satisfy its users' capacity demands, improve its quality of services and coverage under Nakagami fading channel. As a repayment, the SCN is rewarded with licenses to share and operate on the spectrum originally owned by the MCN. We devise a density division-based shared spectrum access model, where the density of the licensee's SCN deployment is exploited as network resources. A fair division of the densities of the licensee operator's small cell base stations into fractions of licensed small cell base stations serving its own users and offloading small cells is presented. Unlike most of the previous research works that considered Poisson point process (PPP) to model the distribution of the network entities even when PPP modeling is not accurate for the networks, where the number of MCN/SCN base stations is definite and the number of MCN/SCN base stations in disjoint areas is not independent, we employ a more realistic network model known as binomial point process to perform an analytical analysis of the cumulative interference and performance of the system. Furthermore, we analyze the rate coverage and outage performances considering a wide range of values for path-loss exponent and fading severity parameter of Nakagami fading.

In this paper, we conceive an advanced small cells wireless network deployment framework within a managed space under shared spectrum access paradigm. We also conceive a complementary business model, referred to as neutral host micro operator (NH-μO), that leverages a single shared wireless infrastructure to mutually benefit μO (a third party service provider), the owner of the space/facility, and mobile network operators (MNOs). The model is composed of a μO slice, which delivers a venue with customized wireless services tailored to the its local service requirements, and an MNO slice, which facilitates improved wireless coverage to visitors/end-users with subscriptions to several different MNOs. The NH-μO is not biased to favor any specific client, which can be enforced through a concrete commercial agreement. A radio access network slicing concept is exploited to support and optimize both the slice instances (SIs) efficiently in a shared manner on a single physical network infrastructure. In addition, we devise an efficient architecture for the NH-μO small cell base station and dynamic spectrum assignment control unit, and their required functionalities supporting sustainable coexistence of different SIs in shared spectrum. We also devise both interSI and intra-SI dynamic spectrum allocation policies considering time-varying requirements of different SIs. These policies take care of application level priority by providing a proper mixture of users with guaranteed quality of service and best-effort users, while ensuring a healthy SI competition. The advantages of the proposed framework are twofold. It enables the venue owner to manage its wireless networks and consider its very specific requirements while capitalizing from the MNO slice. This, in turn, reduces the need for deployment of new infrastructure while providing improved wireless coverage and savings to MNOs. Finally, our proposed framework leverages efficient utilization of spectrum, physical infrastructure, and computational resources. The simulation results exhibit various important features of the proposed shared spectrum access policies.

We consider a cognitive radio (CR) network consisting of a primary cellular system and a secondary cognitive machine-to-machine (M2M) system, and study the throughput enhancement problem of the latter system employing universal-filtered orthogonal frequency division multiplexing (UF-OFDM) modulation. The downlink transmission capacity of the cognitive M2M system is thereby maximized, while keeping the interference introduced to the primary users (PUs) below the prespecified threshold, under total transmit power budget of the secondary base station (SBS). The performance of UF-OFDM-based CR system is compared to the performances of OFDM-based and filter bank multicarrier (FBMC)-based CR systems. We also propose a near-optimal resource allocation method separating the sub-band and power allocation. The solution is less complex compared to optimization of the original combinatorial problem. We present numerical results that show that for given interference thresholds of the PUs and maximum transmit power limit of the SBS, the UF-OFDM-based CR system exhibits intermediary performance in terms of achievable capacity compared to OFDM- and FBMC-based CR systems. Interestingly, for a certain degree of robustness of the PUs, the UF-OFDM performs equally well as FBMC. Furthermore, the percentage rate-gain of UF-OFDM-based CR system increases by a large amount when UF-OFDM modulation with lower sidelobes ripple is employed. Numerical results also show that the proposed throughput enhancing method despite having lower computational complexity compared to the optimal solution achieves near-optimal performance.

TV White Spaces (TVWS) technology allows wireless devices to opportunistically use locally-available TV channels enabled by a geolocation database. The UK regulator Ofcom has initiated a pilot of TVWS technology in the UK. This paper concerns a large- scale series of trials under that pilot. The purposes are to test aspects of white space technology, including the white space device and geolocation database interactions, the validity of the channel availability/powers calculations by the database and associated interference effects on primary services, and the performances of the white space devices, among others. An additional key purpose is to perform research investigations such as on aggregation of TVWS resources with conventional resources and also aggregation solely within TVWS, secondary coexistence issues and means to mitigate such issues, and primary coexistence issues under challenging deployment geometries, among others. This paper provides an update on the trials, giving an overview of their objectives and characteristics, some aspects that have been covered, and some early results and observations.

Utilization of the TV white-spaces (TVWS), which are spatially or temporally unused frequency in TV bands, is promising technology to alleviate spectrum resource shortage. Services using the TVWS have been already started in the U.S.A., and the TVWS pilot program has been performed and test operation of qualified white-spaces database (WSDB) has been started by the Ofcom in the U.K. Authors have developed TVWS LTE (Long Term Evolution) system with white-space devices (WSDs) licensed by the Ofcom and WSDB qualified by also the Ofcom, and participated in the pilot program performed in the U.K. In this paper, developed TVWS LTE system is summarized and field experiment of throughput measurement is performed in the London urban area is described. As a result of the field experiment, maximum downlink throughput of 45.4 Mbps in the FDD mode and 19.5 Mbps in the TDD mode were obtained under the condition of SISO with a signal bandwidth of 20 MHz. This is the first report on the field experiment of the TVWS LTE system aiming for practical use.

This paper performs the world's first IEEE 802.11af based Wireless Local Area Networks (WLAN) operating in TV White Space (TVWS) indoor experiment in the Ofcom TVWS pilot program of the UK. The prototype system consists of TVWS Database (WSDB), Registered Location Secure Server (RLSS), and two prototype hardware for an Access Point (AP) and a Station (STA). The developed WSDB qualified by Ofcom TVWS pilot program of the UK. The prototype hardware meets to the transmission spectrum regulation of the European Telecommunication Standards Institute (ETSI). By using the developed system, a trial indoor experiment performed in the building of the King's College London (KCL), Denmark Hill Campus in London, UK. The prototype system and the experiment results show an effectiveness of the IEEE 802.11af and indicate the way to the practical application.

In recent years, there has been an increasing number of Software Defined Wireless Access Network (SDWAN) proposals aiming to cope with the proliferation of mobile devices, as well as, the novel Quality of Service (QoS) demands. One of the most important issues in the SDWANs is to maintain a scalable and robust OpenFlow channel through which the network control and update information (i.e., OpenFlow traffic) are exchanged. However, the standard channel does not well support those characteristics nor does it properly conform to the SDWAN environment. This paper seeks to remedy these problems by analyzing the requirements of SDWAN's OpenFlow channel. We then propose a novel OpenFlow channel named mOpenFlow, which is not only compatible with the SDWANs but also evolved with the OpenFlow standard. The advantage of mOpenFlow is using multipath communication for conveying OpenFlow traffic. Hence, both the robustness and the achievable throughput of the OpenFlow channel is significantly enhanced (i.e., scalable). Combining with the compatibility requirement, the multipath TCP is adopted in the mOpenFlow's design. We extensively evaluate the channel's performance in SDWANs including emulated SDN devices and a real controller. The results show that mOpenFlow outperforms the standard channel both in terms of robustness and scalability.

An IEEE 802.11af indoor trial experiment has been conducted in the Ofcom pilot program of the United Kingdom. This paper describes an indoor propagation characterization and throughput estimation method using prototype devices based on the IEEE 802.11af standard. Since the IEEE 802.11af is recent technology for TV white space (TVWS) spectrum sharing, indoor propagation measurements at TVWS band for WLAN usage are very seldom in the previous researches. Path loss model parameters has been extracted for each line-of-sight (LoS) and non-LoS (NLoS) situation on the same floor. Also a fluctuation of measured path loss is analyzed using the log-normal and the extreme value distributions. A developed path loss model is useful for the location design of access points and the interference risk estimation for IEEE 802.11af devices. As another modeling, a throughput estimation model has been developed using the exponential distribution derived from the cumulative probability distribution (CDF) of measured throughputs. By combination of the developed path loss model and the throughput estimation model, throughput can be estimated as a function in each LoS and NLoS situation.

In a white space communication system the database calculates and provides operational parameters to the device based on the device's specifications and geo-location. There is an option for the mobile device to submit an area where it may be located, then obtain the list of parameters that can be used anywhere within the submitted area. This paper addresses the effects of the area's size to the available channels and maximum transmission power. By using a database which passed the qualification tests for the Ofcom TV white space pilot, this paper shows the numerical results of spectrum availability in several locations in London corresponding to different area's sizes which are determined by the geo-location uncertainty.

Some important issues remain to be better resolved before sensing technologies can be widely used in applications. For the reason, spectrum sensing is not selected as the mandatory solution for protection of primary users in current FCC regulations on usage of TV white space (TVWS). In this work, we introduce a sensing prototype for detection of Japanese digital TV signals. The prototype targets at fulfilling the strict FCC sensing requirement under reasonable interference. Moreover, efforts are made to improve physical features and cost-performance ratio. Computer simulation and hardware tests are conducted to evaluate performance of the sensing prototype under adjacent channel interference and co-channel interference. The results verify that the prototype has improved robustness for sensing under interference.

By increase of various radio access network (RAN) services, available spectrum resources for mobile communications get decrease, and efficient use of the radio resource is becoming a very important issue. In order to optimize the radio resource usage and maxmize the throughput and quality of service (QoS), the link aggregation technologies to utilize multiple different available RANs have been studied. However, in such heterogeneous wireless networks, it is difficult to improve the throughput by their aggregation because of the differences among the QoSs of the different RANs. In this paper, we propose an autonomous parameter optimization scheme using a machine learning algorithm, which maximize the throughput of the heterogeneous RAN aggregation system. We evaluate the performance of the proposed scheme implemented on a cognitive wireless network system called Cognitive Wireless Cloud (CWC) system, connected to real wireless network services, such as HSDPA, WiMAX and W-CDMA. Our experimental results of the proposed system show that the aggregation throughput can be improved with increase of the training samples, which are collected autonomously.

AMPHIBIA is a framework which enables dynamic virtual network provisioning over wired and wireless networks for providing diverse services by coordinated reconfiguration in both sides of wired and wireless networks, exploiting the emerging network virtualization and cognitive radio technologies. AMPHIBIA introduces a new concept of a virtual cognitive base station (vCBS), a cognitive base station built on the virtualized infrastructure. The target applications of AMPHIBIA include flexible and rapid deployment of mobile services, end-to-end QoS, efficient wireless and wired resource utilization, and green networking. In prior work, we proposed a basic framework design of AMPHIBIA and a service model. In this paper, we show the implementation and prototype system of AMPHIBIA including the implementation of a cognitive virtualization manager (CVM), which is responsible for coordinated reconfiguration. We implement the AMPHIBIA prototype as an extension of CoreLab, a flexible software-based virtual router platform. Specifically, we develop vCBS by incorporating cognitive radio functionalities into a CoreLab virtual machine (VM). We also implement CVM and a reconfiguration manager of cognitive radio as external entities to enhance CoreLab. We confirm the basic behavior of the prototype and demonstrate with a set of simple typical scenarios that a VM-based virtual network including vCBS can be dynamically created, expanded, and deleted, and mobile streaming services can be flexibly deployed on the virtual network on an on-demand basis. We also demonstrate that AMPHIBIA can create and reconfigure a vCBS in about 51 seconds, and can timely operate the successive handover of a mobile terminal.

In heterogeneous wireless network environment, various radio access networks (RANs) are available for mobile terminals which have multiple wireless network interfaces to connect to each different RAN. However, it is very difficult to improve the throughput by aggregating different RANs, which have different quality of service (QoS) in the throughput, the delay, the packet loss, and so on. In this paper, we propose a traffic allocation control scheme using a machine learning algorithm to improve the link aggregation throughput in such heterogeneous wireless networks. We introduce the support vector machine, which has an advantage on generalization to have good performance for unknown input patterns. By our experiments using a cognitive wireless network system, called Cognitive Wireless Clouds, it is clarified that our proposed scheme improves the throughput higher than the conventional methods based on the throughput of each RAN.

To cope with the increasingly diversifying services, QoS, and network architectures, network virtualization is a promising technology that enables the concurrent deployment of multiple network technologies on a shared network. However, traditional research on network virtualization preliminarily focuses on a wired environment and network virtualization for a wireless environment is not well studied. Considering that in near-future, various wireless technologies will play the most important role in access networks and multi-mode wireless terminals will become more popular, it is crucial to extend the concept of network virtualization to wireless networks. We refer to building such extended virtual networks as "end-to-end slicing". The key technical challenges for such extension are (1) abstraction of heterogeneous wireless access networks for maximizing radio frequency utilization and (2) isolation of wireless resources such as radio frequencies, throughput, or name spaces for accommodating multiple virtual networks on a single wireless access network. In this paper, we tackle the first challenge and propose a Cognitive Virtualization Platform, called AMPHIBIA, which enables end-to-end slicing over heterogeneous wired and wireless networks. AMPHIBIA is a platform to provide independent virtual networks each of which can be configured for the corresponding service and to coordinate the resource management in both sides of wired and wireless networks, exploiting the network virtualization and cognitive radio technology. AMPHIBIA is motivated by the shared property of "reconfigurability" of network virtualization and cognitive radio, and provides network operators with the capability of cooperative resource allocation over wired and wireless networks. In other words, AMPHIBIA virtualizes a cognitive base station to dynamically configure a wireless access network for each virtual network. In this paper, we first show the basic architecture of AMPHIBIA from the perspective of network virtualization. Then we show the hardware and software design of prototype system.

This paper investigates effectiveness of distributed radio access network (RAN) selection schemes to optimize radio resource usage, for the realistic heterogeneous wireless networks, in which the distribution of the base stations are non-uniform and the non-cognitive legacy terminals also connect to the same RANs. Our proposed algorithm is based on mutually-connected and higher-order neural networks, which can directly optimize any objective functions of entire heterogeneous wireless networks, by completely distributed procedure. Our simulation results show that the proposed scheme is effective even for non-uniform heterogeneous wireless network environments, especially for higher-order and complex optimization problems. Such improvements in the proposed method also can be seen also for the cases that the legacy non-cognitive terminals co-exist in the same heterogeneous wireless networks.

The current radio operational environment is characterized by its heterogeneity, which includes multiple operators, services, radio access technologies, network topologies, radio equipment, and frequency bands. While each radio access technology has mechanisms for efficient usage of the assigned spectrum, there is a need for the new intelligent management system, which can have capability to optimize spectrum usage across different radio access technologies and operators. In IEEE the standardization of such new management system has been performed under the Working Group 1900.4 of the Standards Coordinating Committee 41. The IEEE standard 1900.4 "Architectural Building Blocks Enabling Network-Device Distributed Decision Making for Optimized Radio Resource Usage in Heterogeneous Wireless Access Networks" was published in February 2009. Currently, two more projects are active in Working Group 1900.4. The first project is P1900.4.1 "Interfaces and Protocols Enabling Distributed Decision Making for Optimized Radio Resource Usage in Heterogeneous Wireless Networks." The second project is P1900.4a "Architecture and Interfaces for Dynamic Spectrum Access Networks in White Space Frequency Bands." The purpose of this paper is to give overview of the current status of the IEEE projects P1900.4.1 and P1900.4a.1

This paper proposes a method to estimate locations of neighboring APs near a specified AP without using absolute location measured by the GPS. This estimation contributes to reduce handover latency between APs and improve communication quality. The method does not require terminals to have the GPS because it's not supported by all existing terminals. The estimation utilizes relative location of APs calculated using the spring model where RSSI and detection probability of APs are applied. Simulation results show that the nearest three APs can be estimated with probability of around 30%. The relative location is expected to be applied to enhance communication quality on mobile terminals.

We have designed and implemented a radio access network selection algorithm for heterogeneous wireless network environment, in which mobile terminals can adaptively and seamlessly handover among different radio access technologies. We propose a radio resource usage optimization algorithm without centralized computation on the network side, which is based on the Hopfield neural network dynamics whose energy function autonomously minimizes by distributed update of each neuron. We have implemented the proposed algorithm on an experimental heterogeneous wireless network system, which includes functionalities defined in IEEE 1900.4. First, we show that the proposed algorithm can optimize fairness of the throughput by numerical simulation. Then, we show that our algorithm works correctly and optimizes radio resource usage also on the experimental wireless network by distributed handover decisions on the terminal side.

In this paper, we propose a method to reduce the scan time using detection probability calculated from reports from multiple terminals. The detection probability is a probability that any of two APs (APiand APj) are found at the same time under the condition when APiis found. By using this method, terminals can omit to scan some of channels which are apparently lower in probability that available APs are found. Our simulation results show that the scan time has been reduced by more than 40% compared with a RSSI based AP selection method. The proposed method is expected to improve the quality of service of real-time applications on mobile terminals.

This paper proposes a framework to collect bandwidth information from terminals, analyze them statistically, and feed back to terminals in order to increase usable bandwidth in terminals keeping coexistence with legacy WiFi systems. This coexistence feature enables practical integration of the proposed framework with the legacy WiFi systems including Internet. By introducing two-level transmission via components categorized into radio access network side and core network side, replacement or modification on existing systems is not required for deployment of the proposed framework. The feedback is transmitted using multicast from APs to terminals in order to reduce message traffic, but the transmission from the server to APs is unicast because the current Internet does not fully support the IP multicasting. The proposed algorithm increases minimum throughput among all terminals by more than twice at maximum per terminal as well as total network throughput by 30% on average, compared with random selection method.

This paper proposes a user-centric access point selection scheme to minimize the number of unnecessary reconfigurations of cognitive terminal. In this scheme, number of terminal reconfigurations is defined based on the dwell-time of terminal which is estimated from user’s mobility and coverage area of the access point (AP). Each terminal selects one AP from a candidate list that is generated based on user’s preferences. Information needed for the selection scheme is obtained from both network-side and terminal-side entities. Four different algorithms are investigated in order to find the best combination of dwell-time and other parameter such as load of APs, to minimize the number of reconfigurations and to achieve load balancing for Radio Access Networks simultaneously.

This paper introduces the concept, features and architecture of a software defined cognitive radio system: Cognitive Wireless Clouds (CWC) that can realize user-centric and scalable network based on unique cognitive spectrum access, cross-network signaling, network optimization, and fast reconfiguration methods. Then, this paper shows results of feasibility studies on a software defined cognitive radio (SDCR) terminal that can access to the CWC. This includes the configuration of the SDCR terminal and a measurement data for spectrum sensing period and reconfiguration period by using software packages of W-CDMA and IEEE802.11a.

New services on trains are attracting a great deal of attention throughout Europe and Asia where trains are one of the most important forms of transportation. We introduced two information services on bullet-trains; Internet access and video. There are three technical challenges posed by seamless handover at 300 hn/h, aggregation of multiple access, and attack-tolerant communications. We proposed a network architecture to solve them based on the requirements of these services. Due to its extendibility and flexibility, new services that will be introduced in the future can be integrated easily. We are currently developing a tested for experimental evaluations.

Requirements for broadband mobile communications suggest the importance of the metropolitan area network (MAN) in beyond 3G integration. Beyond 3G accommodates radio systems including 3G, 4G and wireless LANs, and operates all-IP networks. Ethernet technology has become a suitable solution to cover all access points of various radio systems because of its simplicity and flexibility. A MAN by Ethernet, however, still has issues of scalability. The spanning tree protocol requires so much time to rebuild the tree in a change of topology, especially in a large MAN, and eventually causes much packet loss, which is intolerable to real time applications, such as voice and video, during reconfiguration. We propose a scalable spanning tree protocol (SSTP) to realize fast rebuilding of a spanning tree by applying a concept of regions and configure its parameters automatically. Our evaluation shows that SSTP is a solution for future mobile communication networks consisting of thousands of bridges.