Low Earth Orbit (LEO) satellite networks, such as Starlink, are undergoing remarkable development. However, related research has reported that communication in these networks suffers from link quality fluctuations and performance degradation due to frequent handovers. These frequent handovers stem from the limited communication range in conventional bent-pipe environments. Consequently, Inter-Satellite Links (ISLs) are being explored to expand this range. However, a practical route selection method for ISL-enabled environments has not yet been established, and protocols like AODV result in massive control overhead. To address this issue, this paper proposes a new route selection method. We extend a technique from our previous work, which predicted the trajectories of individual satellites, to a new approach that first predicts the trajectory of individual satellites on the same orbit and then selects the optimal satellites for the ISLs route. This method is designed to provide long communication durations in ISL-enabled environments. We validated its effectiveness on the ns-3 LEO module to simulate a future satellite constellation. The results demonstrate that, compared to AODV, proposed method significantly increases communication duration by 222.6% and dramatically reduces control overhead, although this comes at the cost of reduced route diversity.

In 5G networks, users require high-quality services for a wide range of applications. However, conventional QoS control mechanisms do not reflect the quality actually experienced by end users in network management. This study proposes a stress-aware networking system for Beyond 5G environment utilizing user’s stress level data collected from wearable devices. This paper evaluates the effectiveness of the proposed system using free5GC. The evaluation demonstrated that performance variations among network slices influence video quality. These results indicate that dynamic network slice switching based on user stress levels has the potential to achieve QoE enhancement for users.

Recent developments in IoT technology are expected to enable the realization of systems that collect and process physical-space data at the edge for each region and provide it in real time. However, if large volumes of raw data are transmitted without considering the recipient’s location or requirements, network traffic increases and the risk of private information leakage beyond the region also rises. Therefore, regional data must be abstracted according to the user context before delivery. To address these challenges, this study proposes a content delivery method based on semantic communication, which extracts only the semantic information from the data, transmits it, and reconstructs it on the receiver side. Through image transmission experiments, we confirmed that the proposed method reduces communication traffic by approximately 40 percent while maintaining image quality (SSIM of at least 0.9), demonstrating both the potential and the challenges of user-context-adaptive content delivery.

Cyber Physical System (CPS) is a system that accumulates information from physical space, analyzes them in cyberspace, and then feeds back the results. We aim to realize a Floating Cyber Physical System (F-CPS), a regionally distributed CPS. We have proposed a large-capacity spatio-temporal data retention system for delivering data and function (application) in the F-CPS. In a previous work, we proposed a data completeness-aware transmission control and evaluated it by simulation. However, considering the movement of obstacles and fluctuation of radio waves in the real environment, packet loss occurs frequently. Thereby, the system may not be able to have complete data and may not function. In this paper, we proposed a method to recover missing data using redundant packets and evaluated its impact on the entire system by testing it with actual equipment.

LPWA (Low Power Wide Area) is expected to be a communication technology suitable for the Internet of Things (loT) because of its features. Since LoRa communication has a trade-off between communication range and transmission rate, performance is inherently varied depending on the surrounding environment. Therefore, to achieve stable and efficient communication performance, it is necessary to set appropriate parameters for LoRa depending on the communication environment between the base station and the terminal. We here propose a method for dynamic control of parameter settings based on reception statistics of beacons. The effectiveness of the proposed method is evaluated from the real experiments.

Long-range wide area network (LoRaWAN) has been newly designed to exploit the 2.4 GHz unlicensed band instead of the traditional sub-GHz bands. However, this makes LoRaWAN frequently suffer from wireless communication failures caused by the cross-technology interference (CTI) from coexisting Wi-Fi networks using the same 2.4 GHz band. As a physical-layer solution to this problem, this paper presents CoWiL to combat the CTI from Wi-Fi to LoRa (the physical layer of LoRaWAN) in the 2.4 GHz band for better coexistence between LoRaWAN and Wi-Fi networks. Existing approaches address this problem by sacrificing Wi-Fi transmission performance or assuming that Wi-Fi interferes with only a small portion of LoRa signals. Unlike them, CoWiL does not affect normal Wi-Fi communications and is workable regardless of the degree of the CTI. This is achieved by implementing CoWiL at a LoRa receiver to directly extract LoRa data out of the CTI from Wi-Fi. Specifically, CoWiL exploits the correlation of the signal demodulation results between the preamble and the payload of a LoRa signal. A novel frequency bin mask is generated based on the demodulated preamble and then applied to the following payload for data decoding. Experimental results in various real-world environments show that in comparison with the existing solutions, CoWiL can reduce the packet error rate of LoRa transmissions by up to 96% under the CTI from Wi-Fi.

Low-power wide-area (LPWA) is a major communicaiton technology used in the Internet of Things (Io‘I’), Major sensor networks are constructed using original protocols specific to each LPWA standard and cannot communicate directly with devices connected to the Internet. To enhance the convenience of devices using LPWA, it is necessary to improve their interop-erability with Internet applications with TCP/IP. Previous study have enabled Single-hop TCP/IP communication over Private LoRa. In this study, we construct a multi-hop environment for TCP/IP communication over Private LoRa, and evaluate its performance using both UDP and TCP communication. Previous research has enabled one-to-one communication using UDP and TCP over a Private LoRa interface, an LPWA technology. This study leverages the characteristics of LPWA for ultra-Iong-distance transmission and implements TCP/IP communication in a multi-hop environment. This paper evaluates the performance of UDP and TCP on actual devices.

This paper presents a novel model-free resource allocation framework for the downlink of 5G cellular networks to guarantee stringent QoS requirements in wireless applications. A Deep deterministic policy gradient (DDPG) agent with a modified Genetic Algorithm (GA) based resource allocation framework is proposed to balance the tradeoffs between reliability, latency, and data rate. Any feasible point in the rate-latency-reliability domain can be achieved with this approach. Compared to state-of-the-art approaches DDPG-Dual and DDPG-PSO, the proposed model achieves higher reliability and scalability in joint optimization with QoS constraints. Specifically, the proposed model guarantees the expected reliability with 25 % and 42.86 % improvement respectively over the compared models. In terms of conventional effective bandwidth approach, the proposed model achieves 30.82 % improvement of energy efficiency under the same QoS constraints. Moreover, the proposed model offers a practical solution, namely, three times faster convergence and only 6.7% of the scheduling time compared to the ground truth Dual decomposition optimization.

This paper proposes a heterogeneous carrier-sense multiple access (CSMA) protocol named LoHEC as the first research attempt to improve energy fairness when applying CSMA to long-range wide area network (LoRaWAN). LoHEC is enabled by Channel Activity Detection (CAD), a recently introduced carrier-sensing technique to detect LoRaWAN signals even below the noise floor. The design of LoHEC is inspired by the fact that existing CAD-based CSMA proposals are in a homogeneous manner. In other words, they require LoRaWAN end devices to perform identical CAD regardless of the differences of their used network parameter – spreading factor (SF). This causes energy consumption imbalance among end devices since the consumed energy during CAD is significantly affected by SF. By considering the heterogeneity of LoRaWAN in terms of SF, LoHEC requires end devices to perform different numbers of CAD operations with different CAD intervals during channel access. Particularly, the number of needed CADs and CAD interval are determined based on the CAD energy consumption under different SFs. We conduct extensive experiments regarding LoHEC with a practical LoRaWAN testbed including 60 commercial off-the-shelf end devices. Experimental results show that in comparison with the existing solutions, LoHEC can achieve up to$0.85\times $improvement of the energy fairness on average.

Spatio-temporal aware IoT applications need to deliver the Spatio-Temporal Data (STD), which depends on geographic location and time, to the users in real-time. We have proposed the STD retention system using crowds of vehicles to promote the immediate distribution and utilization of STDs in geographical proximity to the user. However, when the system retains a Large-size STD (LSTD) consisting of multiple packets such as videos and photos, the packet loss due to channel collisions should be suppressed for effective retention of an LSTD. In this paper, we propose a complementary data transmission control method with collision avoidance for LSTD retention and clarify the effectiveness of our proposed method by simulation.

IoT data includes Spatio-temporal data (STD) that is needed only at a specific time and place. In our previous research, we have proposed the STD data retention system (STD-RS), aiming to construct a novel architecture for STD distributing in a retention area by vehicles. However, since vehicles may distribute the STD in unexpected locations due to GPS errors or malicious behavior in a real environment. Therefore, we propose a reliability audit mechanism based on multi-layered blockchain managing and analyzing the history of STD distribution and vehicles' behavior in each retention area. Through simulation experiment, we demonstrated that our mechanism detects the malfunction of STD-RS effectively.

With the development and spread of IoT technology, the number of devices connected to the Internet is increasing. Some data generated by IoT devices include spatio-temporal data (STD) that depends on the location and time of data generation. Therefore, we have proposed the STD retention system (STD-RS) using vehicles as a network infrastructure for local production and consumption of STD. This paper proposes a transmission control method that can mitigate the fluctuation of RSS due to the influence of obstacles in the real environment and evaluates its effectiveness through experiments on actual devices.

Low-power wide-area (LPWA) is a major communication technology used in the Internet of Things (IoT). However, since LPWA does not conform to the TCP/IP protocol stack and employs its own unique protocol, sensors equipped with LPWA I/F face difficulty when connecting directly to the Internet. In a previous study, to extend general TCP/IP communication on LPWA networks, we constructed a TCP/IP network over Private LoRa, but it was found that TCP communication performance using LoRa devices was significantly degraded due to the characteristics of LPWA such as the low transmission rate. In the present study, to improve the performance of TCP communication using the Private LoRa interface, we propose a transmission control method that avoids collisions by modifying the advertised window size on IP2LoRa and demonstrate the effectiveness of the proposed method using TCP flow analysis.

Low-power wide-area (LPWA) is a major communication technology used in the Internet of Things (IoT). However, since LPWA does not conform to the TCP/IP protocol stack and employs its own unique protocol, it is difficult for sensors equipped with LPWA I/F to connect to the Internet directly. In the present study, to realize general TCP/IP communication on LPWA networks, we construct a TCP/IP network over Private LoRa, and evaluate its communication performance. Moreover, we verify the feasibility of TCP/IP communication over LoRa by using a popular Internet application.

Some specific services for Internet of Things, such as real-time map and providing local weather information, depend strongly on geographical time and location. We refer to the data for such service as spatio-temporal data (STD). When STD is used in a query response system similar to conventional Internet services, users not only need to acquire data actively as required, they must also have functions for retrieving data available STD. Therefore, we propose an STD retention system that uses vehicles as information hubs (InfoHubs) for disseminating and retaining the data in a specific area. In our system, InfoHubs diffuse, maintain, and advertise STD over places and times where the STD are strongly dependent, thereby allowing users to receive such data passively within the specific area. Additionally, because STD are associated with a particular space, the system can reduce search costs. We also propose an adaptive transmission control method that each vehicle effectively operates its wireless resources autonomously and STD are retained and distributed efficiently. Finally, we evaluated our proposed method using simulations and clarified that our proposed system is capable of achieving a coverage rate of nearly 100% for STD while reducing the number of data transmissions compared to existing systems.

Wireless LAN access points (APs) and stations (STAs) are widespread. In such an environment, APs with different specifications, such as IEEE 802.11a and 802.11ac, or different settings, such as very high throughput technology, are simultaneously operated in proximity. In this paper, we propose a new STA-centric AP selection method that maximizes the throughput performance while achieving “airtime fairness” on all channels. In our proposed method, each STA dynamically adjusts the frame size based on its own transmission rate for achieving airtime fairness. Furthermore, the STA calculates the predicted throughput of all of available APs, and then selects the AP with the highest predicted throughput for improving the throughput performance. Through simulations, we demonstrated that each STA reliably connects to an AP with better throughput performance, thereby increasing the total throughput performance in a heterogeneous Wi-Fi environment.

To facilitate local production and consumption (LPAC) of spatio-temporal data (STD) generated by Internet of Things (IoT) devices, we propose a STD retention system that works in collaboration with Mobile Edge Computing (MEC) infrastructure. In this paper, we will introduce the architecture of our proposed system and discuss its contributions and challenges.

Transmission Control Protocol (TCP) with Network Coding (TCP/NC) was designed to recover the lost packets without TCP retransmission to improve the goodput performance in lossy networks. However, TCP/NC is too costly to be implemented in some types of end devices, e.g., with less memory and power. In addition, TCP/NC across loss-free but thin networks may waste scarce link bandwidth due to the redundant combination packets sacrificed for the lossy network. In this paper, we propose the TCP/NC tunnel to convey end-to-end TCP sessions on a single TCP/NC flow traversing a lossy network between two special gateways without per-flow management. We implemented and validated our proposal in Network Simulator 3, in which each gateway runs a reinforced version of TCP/NC that we previously developed. The results show that the proposed TCP/NC tunnel can mitigate the goodput degradation of end-to-end TCP sessions traversing a lossy network without any change in TCP on each end host.

Summary With the recent advances in machine‐to‐machine communications, huge numbers of devices have become connected and massive amounts of traffic are exchanged. Machine‐to‐machine applications typically generate small packets, which can profoundly affect the network performance. Namely, even if the packet arrival rate at the router is lower than the link bandwidth, bits per second, it can exceed the router forwarding capacity, which indicates the maximum number of forwarded packets per second. This will cause the decrease in the network throughput. Therefore, eliminating the packets per second limitation by chunking small packets will enable machine‐to‐machine cloud services to spread further. This paper proposes new packet‐chunking schemes aimed at meeting both application requirements and improving achievable router throughput. In our schemes, multiple buffers, each of which accommodates packets classified based on their delay requirement, are installed in parallel. Herein, we report on analysis of the theoretically performance of these schemes, which enabled us to derive some important features. We also propose a scheme whereby a single chunking buffer and parallel multiple buffers were arranged in tandem. Through our simulation and numerical results, we determined that these schemes provide excellent performance in reducing the number of outgoing packets from the router while meeting various delay requirements.

We propose a method for regulating wireless access points (APs) that is based on mechanisms of biological development and evolution. The purpose of the proposed regulation is to simultaneously achieve power savings in the APs and achieve reliable connection services through the APs better, which is shown to be a trade-off relationship in this study. The regulation target is the cycle time at which each AP enters the power-off state, which is referred to as the sleep cycle time. Biological development mechanisms form bodies of a variety of shapes using different genomes as design information, and these genomes are modified evolutionarily. Similarly, in the present study, a method inspired by biological development forms a variety of the sleep cycle times of APs, and an evolutionary method modifies the parameter values of the method inspired by the biological development in order to obtain better configurations of the APs. In addition, the regulation method is able to configure APs in a distributed manner without knowing global information; the total number of APs, their locations, or their identifiers, which is actually suitable for the situation assumed in the present study, in which APs are established and removed freely by their owners and AP users freely appear. Simulation results show that the proposed method is capable of exploring the tradeoff relationship between the amount of consumed power of the APs and the reliability of connection services in terms of momentary achievement by regulating APs, but yields highly varying regulation results along time.

This paper examines our previously proposed mutation-based search method for temporary information sharing in a wireless mesh network. The temporary information sharing indicates that for the case in which information senders and receivers freely appear in the network, information is forwarded from an information sender to a receiver. The mutation-based search method determines a unique route to find receivers who want the forwarded information by operations among numerical values assigned to each node and probabilistically changes the assigned numerical values according to the search results, which can be regarded as a sort of mutation in evolutionary computation. A variety of types of operations and numerical values can be used for this search method. In simulations, the method is evaluated in terms of search reliability under two appearance patterns of an information sender-receiver pair. One is the appearance pattern that locations of the receiver and the receiver are randomly determined. The other is that only a location of the receiver is fixed. Simulation results reveal that search reliability depends on the types of operations and numerical values and is related to how frequently a closed path is generated in the search. The results also suggest that the degree of randomness in search is important for reliable search and varies with the types of operations and numerical values.

This paper presents design and experimental evaluation of a distributed autonomous multi-hop vehicle-to-vehicle (V2V) communication system over TV white space performed in Japan. We propose the two-layer control channel model, which consists of the Zone Aware Control Channel (ZACC) and the Swarm Aware Control Channel (SACC), to establish the multi-hop network. Several vehicles construct a swarm using location information shared through ZACC, and share route and channel information, and available white space information through SACC. To evaluate the system we carried out field experiments with swarm made of three vehicles in a convoy. The vehicles observe channel occupancy via energy detection and agree on the control and the data channels autonomously. For coarse synchronization of quiet periods for sensing we use GPS driven oscillators, and introduce a time margin to accommodate for remaining drift. When a primary user is detected in any of the borrowed channels, the vehicles switch to a vacant channel without disrupting the ongoing multi-hop communication. We present the experimental results in terms of the time to establish control channel, channel switching time, delivery ratio of control message exchange, and throughput. As a result, we showed that our implementation can provide efficient and stable multi-hop V2V communication by using dynamic spectrum access (DSA) techniques.

With the proliferation of new wireless service, scarce wireless resources is expected to become a critical issue. For this reason, cognitive radio mobile ad hoc networks (CogMANET) are being developed as a promising solution to this problem. However, in CogMANET, channel switching is inherently necessary whenever a primary user with a license appears on the channel. Allowing secondary users to choose an available channel from among a wide spectrum range thus enables reliable communication in this context, but communication characteristics such as bottleneck bandwidth and RTT will change with channel switch. In response to this change, TCP has to adaptively update its congestion window (cwnd) to make an efficient use of the available resources. For this purpose, TCP CRAHN was proposed for CogMANET. In this paper, TCP CRAHN is first evaluated in cases where bottleneck bandwidth and RTT drastically change. Based on these results, TCP CoBA is proposed to further improve the throughput of the above use cases. TCP CoBA updates the cwnd based upon the available buffer space in the relay node upon channel switch, as well as other communication characteristics. Through simulations, we show that compared with TCP CRAHN, TCP CoBA improves the throughput by up to 200 percent.

This study presents new channel utilization methods for a multi-channel wireless backbone network (WBN). To flexibly and efficiently use multiple channels, we exploit OpenFlow as a baseline function. In this paper, we propose a new framework to build an OpenFlow-based multi-channel WBN and then implement two new channel utilization methods: (i) a flow direction aware channel assignment method (DCA) and (ii) a flow balance aware channel assignment method (BCA). BCA is classified into two simple multi-hop transmission procedures: (ii-1) each flow is transmitted on a persistent channel (BCA-PC), while (ii-2) being transmitted on a different channel for each hop (BCA-DC). Finally, we evaluate the proposed channel utilization methods in a real testbed. As a result, our methods can obtain approximately three times as much network capacity as the conventional WBN. In addition, BCA-DC can avoid the radio interference with neighbor hops effectively, thereby not only achieving efficient channel utilization but also expanding network capacity significantly.

This paper presents design and experimental evaluation of a distributed autonomous multi-hop vehicle-to-vehicle (V2V) communication system over TV white space performed in Japan. We propose the two-layer control channel model, which consists of the Zone Aware Control Channel (ZACC) and the Swarm Aware Control Channel (SACC), to establish the multi-hop network. Several vehicles construct a swarm using location and direction information shared through ZACC, and share route and channel information, and available white space information through SACC. To evaluate the system we carried out field experiments with swarm made of three vehicles in a convoy. As the test case application, the leading vehicle sends real-time speed and sudden break information to the rear vehicle, while the vehicle in between acts as the relay. The vehicles observe channel occupancy via energy detection and agree on the control and the data channels autonomously. For coarse synchronization of quiet periods for sensing we use GPS driven oscillators, and introduce a time margin to accommodate for remaining drift. When a primary user is detected in any of the borrowed channels, the vehicles switch to a vacant channel without disrupting the ongoing multi-hop communication. We present results of the experiments in terms of the time to establish control channel, channel switching time, and throughput.

Vehicular networking has significant potential to enable diverse range of applications, including safety and convenience. As the number of vehicles and applications using the specially designated wireless spectrum grow, one can expect substantial increase in the bandwidth requirements. In this paper and demonstration, we advocate that dynamic spectrum access techniques facilitating the utilization of white spaces for vehicles will be the first step towards solving the expected spectrum shortage. In the demonstration, we will introduce field tests of a multi-hop inter-vehicle communication system with distributed and autonomous TV white space channel selection, performed in Japan from January to February 2012. Furthermore, in addition to the field test videos, we will show an indoor emulation of the entire system used during the field tests in the vehicles.

The present paper proposes a self-adaptive routing method for temporary information sharing in a wireless mesh network without a global connection that is deployed in a geographically limited area. The temporary information sharing indicates that for the case in which information senders and receivers freely appear in the network, information is forwarded from an information sender to a receiver. The self-adaptive routing method determines a unique route by operations among numerical values assigned to each node and adaptively changes the assigned numerical values according to the routing results. A variety of types of operations and numerical values can be used for this routing method. In simulations, the method is evaluated in terms of routing reliability under an appearance pattern of an information sender-receiver pair in which a location of the receiver is fixed. Simulation results reveal that routing reliability depends on the types of operations and numerical values and is related to how frequently a closed route is generated in the routing. The results also suggest that the degree of randomness in routing is important for reliable routing and varies with the types of operations and numerical values.

Future vehicular communications systems are expected to utilize the vacant channels (white spaces) of the spectrum, otherwise allocated for specific designated use. One such candidate of white space comes from the TV broadcast band. In this demonstration, we will first present animated results of a TV spectrum measurement campaign along the entire portion of Interstate I-90 located in the US state of Massachusetts. Next, we will demonstrate a cyber-physical proof-of-concept lab implementation of our previously developed control and data channel assignment schemes for vehicle-to-vehicle communications over (TV) white space. Finally we will show a video of actual vehicle to vehicle communications field tests conducted in Japan using TV white space.

In ubiquitous Wireless LANs (WLANs), Mobile Nodes (MNs) are likely to experience many and frequent handovers between WLANs managed by different organizations/ISPs during TCP communication. Although we proposed a WLAN handover management scheme based on the number of frame retransmissions, the proposed scheme cannot adapt to multirate WLAN used in a more realistic environment. Furthermore, the handover is controlled based on only a predetermined threshold of the number of frame retransmissions, thereby degrading the performance drastically when the inappropriate threshold is employed. Therefore, in this paper, to enhance the practicality of handover scheme in a realistic environment where WLAN supports multiple data rates and automatically changes the rate in response to wireless link condition, we propose a handover management scheme adaptable to multi-rate WLANs. Our scheme exploits two sorts of information to recognize the wireless condition appropriately: (1) data rate used most frequently (DRMF) by each interface and (2) frame retransmission ratio (FRR) on each interface for some duration. The former of two criteria first enables us to estimate an area where we should start handover, and if DRMFs of two interfaces are same in the area, the latter then allows us to compare wireless condition on two interfaces precisely, thereby giving an optimal handover point. The simulation results demonstrate the advantages of the proposed method, especially in the multi-rate WLAN environment.

In this paper, we focus on the problem of tracking a moving target in a wireless sensor network (WSN) in which the capability of each sensor is relatively limited in order to construct large-scale WSNs at a reasonable price. In our prior study, we proposed a simple multi-point surveillance scheme for a moving target in a WSN and demonstrated that the scheme achieved high tracking probability with low power consumption. However, we have not suggested guidelines for designing the WSN to completely satisfy the wide range of user requirements. Therefore, in this study, we examine the relationship between tracking probability and sensor density through simulations, and then derive an approximate expression representing the relationship. As a result, we show guidelines for sensor density, tracking probability, and the number of monitoring sensors that satisfy a variety of application demands.

The use of dynamic spectrum access techniques has a great potential in future inter-vehicle communications, while it must cope with (i) temporal and spatial spectrum utilization changes introduced by the primary and secondary users (environmental changes); and (ii) topology changes due to movement of vehicles (spatial movement). In the present paper, along this line, dynamic per-hop channel switching in multi-hop vehicular ad hoc networking is investigated. After defining a set of simple metric-based dynamic channel selection schemes with/without spatial-awareness, the basic performance (the total communication duration and the amount of transmitted data) are evaluated. These spatially-aware schemes estimate the maximum communication period, and tend to select a channel with a large amount of possible data transmission within the period. The simulation results demonstrate the advantages of the proposed spatial-awareness, especially in the multi-hop and highly congested environments with high-speed mobility.

In the near future, mobile nodes (MNs) need to automatically select an optimal interface based on communication quality in a multimodal environment, that is, multimodal communication. While the existing handover management schemes avoid the communication termination, they can not satisfy (1) seamless communication and (2) selection of an optimal wireless network based on communication quality, and thus its performance during handover is drastically decreased. In our previous work, we proposed a new handover management scheme that employs (a) cross-layer approach and (b) multiple TCP connections to satisfy (1) and (2), and showed its effectiveness through simulation experiments. However, any other existing studies have not yet proposed a handover management scheme that employs both (a) cross-layer approach by exploiting beacon messages and (b) multiple TCP connections, and demonstrated the effectiveness of them on a real system. Thus, in this paper, we describe the implementation design of our proposed scheme in detail, and then show preliminary results for the fundamental performance of the proposed prototype system in a real wireless environment.

In ubiquitous networks based on Wireless Local Area Networks (WLANs), mobile nodes (MNs) will experience performance degradation at the handover. To achieve seamless and efficient communication, it is necessary for the MNs to satisfy the following three requirements: (I) initiation of han- dover processes based upon quick perception of the change in the wireless link quality, (II) elimination of a communication interruption due to handover processes, (III) selection of an optimal WLAN. In this paper, we propose a unified handover management scheme for TCP communication that can satisfy all of the above three requirements. Our proposed scheme employs both a cross-layer approach for obtaining the number of frame retransmissions to satisfy (I) and (III) and multi-homing to satisfy (II). Through simulation experiments, we demonstrate that our proposed scheme can quickly and reliably perceive the deterioration of the wireless link quality and select the optimal WLAN without communication interruption due to the handover process, thereby maintaining the best TCP performance at the handover. Index Terms— Seamless Handover, Cross-Layer, Multi- Homing, Frame Retransmission, TCP

In the near future, wireless local area networks (WLANs) will overlap to provide continuous coverage over a wide area. In such ubiquitous WLANs, a mobile node (MN) freely moves between WLANs with different IP subnets during VoIP communication. In such situations, since an MN experiences several handovers, the communication quality is degraded. In previous studies, in order to solve this problem, we proposed a seamless handover scheme based on frame retransmissions and demonstrated its effectiveness through simulation experiments. However, no existing scheme has demonstrated the effectiveness of cross-layer architecture exploiting the number of frame retransmissions on a real system. In the present paper, therefore, we design and implement a handover scheme based on the number of frame retransmissions. In our implementation, we propose a cross-layer architecture using a shared memory to pass the information, i.e., the number of frame retransmissions, from MAC layer to Transport layer. Finally, we show preliminary results in a real wireless environment and evaluate the performance of the proposed prototype system in a simple topology.