Peer-to-Peer (P2P) communication emerges as a potent paradigm in distributed processing models. However, network accessibility challenges and inherent limitations in ex-isting solutions have impeded the full realization of P2P's poten-tial. To address these issues, we've developed CYber PHysical Overlay Network over Internet Communication (CYPHONIC), an innovative solution enabling P2P-based direct device-to-device communication while ensuring robust zero-trust security. Additionally, we introduce the concept of a gateway device equipped with a CYPHONIC adapter to cater to conventional devices, often referred to as general nodes. Our paper focuses on implementing a remote camera monitoring solution, providing secure access to surveillance cameras. We aim to demonstrate that our overlay network seamlessly connects all CYPHONIC clients, including general nodes. We also present a comprehensive case study centered on remote camera monitoring. This case study showcases the effortless connectivity enabled by our overlay network, highlighting how CYPHONIC clients, including general nodes, can efficiently interconnect.

This paper reports an extension of the private 5G service area to the outside of the licensed area by integrating visible light communication (VLC). As VLC is license-free, integrating the VLC function into the private 5G networks gives a more flexible system design. For example, it will be possible to provide services to mobile vehicles and robots working outside the service area of a private 5G network. Alternatively, private 5G networks in different locations can be connected. A challenge is integrating the VLC function into a 5G core network. We successfully designed a testbed and an experiment using open-source 5G projects to evaluate and compare methods to integrate VLC and private 5G, including the simulation of poor network environments. Experimental results demonstrate the availability of integrating private 5G with VLC, which are compared with image-based methods and show better latency performance.

Predicting trajectories of neighboring vehicles accurately is essential for safe driving in Advanced Driving Assistance Systems (ADAS). Conventional approaches for predicting trajectory rely upon an expensive image sensor (i.e., lidar). However, high cost but limited sensing range of lidar makes installing a trajectory prediction system on existing vehicles impractical. Using two functionalities provided by a smartphone, i.e., periodic beaconing and GPS positioning could address issues of conventional approaches. However, modules for wireless communications and GPS are limited in achieving accurate prediction in their current form: transmission error and inaccurate GPS data. In this paper, we propose a novel scheme for predicting neighbors’ trajectories using periodic beaconing and GPS, and show that our scheme is feasible to trajectory prediction. To address the limitations of the wireless and GPS modules, our scheme integrates Long Short-Term Memory (LSTM) with two strategies: 1) Tailoring Multi-band Transmission to Prediction (TMTP) and 2) Environment-Aware Positioning (EAP). To improve prediction accuracy even with the imperfect input, our scheme employs interactive LSTM model. To our knowledge, this is the first to enable predicting the neighbors’ trajectories using periodic beaconing with inaccurate GPS data. Experimental results using real traces demonstrate that our scheme is accurate in predicting neighbors’ trajectories.

Since the current Internet has accessibility issues due to Network Address Port Translation (NAPT) and different IP protocol versions, recent service such as video conferencing also uses a client-server model even if the service model is peer-to-peer. The authors have developed an overlay network protocol to realize peer-to-peer communication because of the lack of the enough implementation for peer-to-peer protocol tackling the accessibility issues. This paper have updated the implementation to support scalability and performance of the proposed protocol. The feature of the proposed protocol provides seamless connectivity over the Internet for any applications. This paper demonstrates the multi-point video conferencing service with the proposed protocol. The service can be available on the Internet even if it only supports local area communication because the proposed protocol virtually connects the conference service. The demonstration also shows the actual signaling process of the proposed protocol to realize the overlay network. Since the proposed system does not relay the communication data at the cloud, the service has high scalability with distributed peer-to-peer communication.

Current IoT systems use the cloud to process data. However, this places a heavy load on the cloud. Fog computing and edge computing are the new trends to avoid centralized cloud processing. They both have in common that they distribute computing resources closer to the edge. In addition, both send the data to the cloud ultimately. Therefore, if numbers of IoT or the data transmitted to the cloud become more frequent, there will be the same issues. Information flow has been proposed to solve the issues by processing the information as distributed flow. The concept of information flow processes the data immediately without storing data in one place. However, the usefulness of information flow in services and platforms is still unclear. This paper proposes an IoT platform prototype implementation to utilize and combine information flow. We name it InfoFlow System as the new distributed processing platform. Using the platform enables IoT devices to utilize information flow. We aim to prove the effectiveness of the information flow during the implementation of this platform. The evaluation results show that the implemented prototype is an appropriate framework for information flow utilization.

As the capabilities for vehicular communications have become widespread, periodic beaconing is becoming fundamental to tracking neighbors. Specifically, a vehicle periodically broadcasts its kinematic data and receivers estimate the sender’s evolving position. To ensure safety, tracking neighbors via beaconing requires position errors and transmission delay to be small. To satisfy stringent requirements, previous proposals have employed multiple RF devices based on the unrealistic assumption that vehicles have the same type of RF devices. In reality, vehicles possess different RF devices (heterogeneous vehicle conditions). Satisfying the requirements under heterogeneous conditions is challenging because network connectivity is low and multi-hop transmissions to improve the connectivity aggravate network congestion. To address this challenge, we propose a novel scheme using a model-based trajectory prediction and multi-hop transmissions adaptively. To maintain accuracy of the model, each vehicle creates a model for predicting its own trajectory and distributes the model. For reliable multihop transmissions, our scheme employs periodic scan for translator and disconnected neighbors (PSTN) and probabilistic relay (PR). To our knowledge, this is the first to consider heterogeneous vehicle conditions for tracking neighbors via beaconing. Evaluation confirms that our scheme tracks neighbors more accurately than previous work.

The authors have developed CYber PHysical Overlay Network over Internet Communication (CYPHONIC) that supports accessibility and seamless mobility over the Internet. This paper introduces the detailed implementation of the simple prototype system that supports a basic communication mechanism of CYPHONIC. The developed prototype system consists of cloud service for authentification, end-node management, and a packet relay among end-nodes, and client service for end-nodes. The evaluation result confirmed that the cloud service and the end node operate normally.

This paper proposes a service framework to realize a wide area information-sharing system based on a delay-tolerant network. The proposed system consists of gateway nodes, relay nodes, and application services. The application services push the data to the nearest gateway node. The relay nodes copy the data from the gateway and carry them to another gateway. The proposed system serves an end-to-end data delivery service for application services over DTN. We have implemented a prototype of the proposed system. The prototype system uses Raspberry Pis 3 as the gateway nodes and relay nodes. We have implemented some application services as an iOS application that can send and receive media files using HTTP communication, an iOS message application that uses BLE communication, and a Bulletin Board System that uses HTTP communication. This paper demonstrates a prototype implementation of end-to-end data delivery service based on the proposed service framework.

This paper develops a prototype chat application that employs an automated communication scheme among smart-phones based on Bluetooth Low Energy (BLE) technology. Conventional smartphone applications use a cellular network to communicate with each other even when they can communicate directly. The proposed scheme realizes a direct data transfer over long distances by designing multi-hop communication technology. As communication technology, we employ BLE that is the latest standard of Bluetooth with low-rate communication capability and low-power consumption. We demonstrate the prototype chat application based on the proposed method to confirm the feasibility of the proposed multi-hop communication.

Some Internet of Things (IoT) devices for smart lock systems, home management systems have been released in recent years. Almost all services employ a client-server model because direct communication among these devices is difficult due to the Network Address Port Translation (NAPT) mechanism. Recently, some new ideas such as a fog computing and an edge computing have been proposed to create a distributed service. A direct communication is suitable for these ideas because each service devices should communicate with each other to realize a distributed processing. The authors have been developed Network Traversal with Mobility (NTMobile) which is a protocol for realizing a direct communication between devices and a secure communication. This paper extends the secure communication mechanism of NTMobile to realize a direct encryption key exchange mechanism between devices by employing the technology of Public Key Infrastructure (PKI). The developed protocol can provide a mutual authentication mechanism and secure encryption key exchange mechanism among devices. The evaluation results show that the overhead of the developed implementation is not large in practical services comparing to the conventional key exchange mechanism of NTMobile.

Local governmental units in Japan have stepped up contingency planning after the great East Japan earthquake in 2011. Due to expensive update cost and operation cost of special community wireless systems for disasters, more reasonable disaster support systems are required in many local governmental units. A management of staff during disaster-relief activities is strictly important to quick rescue and recovery. On the contrary, it is typically difficult in practical situations because many staffs should go on patrol to check on damages of a disaster. As a result, local governmental units cannot optimize disaster-relief activities according to the latest situation of staffs. This paper develops a human management system with BLE beacon devices in natural disasters. A location of each staff is very important information to optimize disaster-relief activities. The developed system consists of BLE beacon devices, a special smartphone application, and a management cloud. Each staff can control the operation of their BLE beacon device to protect their privacy by turning off the device. The smartphone application can collect a beacon from BLE beacon devices around the smartphone, and can upload their location information to the management cloud automatically. Emergency Management headquarters can optimize their operations according to the location information on the management cloud.

Field sensing systems for agricultural usages are a new trend to increase agricultural production due to the downward price trend of sensor devices. Recent systems employ short range wireless communication technologies such as WiFi, IEEE 802.15.4, Bluetooth etc. WiFi is a suitable solution when an existing network is available in a field, and IEEE 802.15.4 is employed in mesh networks. Bluetooth attracts attention in smartphone sensing because it is suitable to reduce power consumption in mobile devices. Smartphone sensing is a new data collection scheme. Smartphone sensing application usually consumes energy to collect data continuously because it runs as a background process. Therefore, users request smart data collection scheme to reduce excessive consumption of energy and to avoid the conscious operation of the application. This paper develops Bluetooth Low Energy (BLE) based automated data collection scheme in agricultural measurement system. The developed scheme utilizes a smartphone to realize automated measurement information collection from sensor devices. The demonstrations show the special BLE based sensor device, a data collection application, and a browsing application.

This paper demonstrates a new RFID based health management system with a low-power ARM microcomputer. RFID cards are usually used as identification in many companies. The developed RFID cards can measure exercise quantity of office workers by deploying a low-power microcomputer and sensors. It is well known that a quantity of exercise has a strong relation with a health condition. Therefore, a quantity of exercise is a key indicator to prevent chronic diseases. The developed system employs a standardized RFID system to communicate with RFID reader/writers. Therefore, it is easy to install the developed system by updating software for RFID reader/writers in entrance gates, doors, etc. This paper demonstrates the prototype system for health management system built on a low-power ARM microcomputer.

Reliable safety message dissemination is a fundamental primitive for constructing intersection safety systems. Normally, the dissemination is based on vehicular communications, of which the de-facto standard is Dedicated Short Range Communications (DSRC). However, due to high frequency operations, a DSRC signal is seriously attenuated when being propagated in Non Line-Of-Sight (NLOS) conditions. Previous schemes leveraged the use of centralized infrastructures or relay vehicles enabling a safety message to bypass large obstacles. However, implementing the infrastructures in all intersections would be very costly; one may not find proper relay vehicles in low density, and frequent rebroadcasts cause serious network congestion in high density. To address this challenge, we propose a novel scheme that exploits excellent propagation characteristics of a TV White Space (TVWS) band (in addition to a DSRC band) for reliable dissemination in NLOS intersections. To ensure reliable dissemination throughout a broad range of densities without infrastructures, our scheme employs two innovative mechanisms: a collaborative procedure and a Dynamic optimal Configuration (DoC). To our knowledge, this is the first that simultaneously satisfies two vital demands for intersection safety system: 1) lacking infrastructures and 2) working well in all densities. Simulation studies show that the proposed scheme outperforms previous infrastructure-based schemes.

This paper demonstrates a new cooperative bus location system with BLE (Bluetooth Low Energy) devices and smartphones. Our idea has extended common participatory sensing systems to realize more practical sensing systems because common participatory sensing mechanisms require a participants' operation to measure some values. Our proposed system consists of a BLE devices on a bus, smartphone applications on a participants' smartphone, and a cloud service. The BLE device has a GPS (Global Positioning System) receiver and a communication function based on the BLE specification. The BLE device also activates a neighbor smartphone application by transmitting a special beacon message. Hence, the smartphone application can work and obtain the bus location from BLE device even if it was a suspended status. Additionally, it also uploads the bus location to the cloud service automatically. As a result, the proposed system can collect a bus location from BLE devices through smartphones automatically. The demonstration shows a prototype system based on the proposed idea for a bus location system.

This paper demonstrates a new ID card based momentum measurement system for office workers' health managements in companies. Our system can measure office workers' momentum with a new ID card that implements a microprocessor, sensors and a RFID tag because an amount of momentum has a relation with a health condition and it is an important indicator to prevent chronic diseases. RFID based ID cards are widely used in office buildings to manage a security control and to record working hours. Therefore, companies can install the proposed system by updating software for a RFID reader/writer in entrance gates, doors, etc. The demonstration shows a prototype system for health management system with ID card based measurement devices of momentum.

Wireless multi-hop networks are candidate communication infrastructures in developing regions because their installation cost is quite low comparing to that for conventional wired networks. Reliable and scalable dissemination mechanism is required in practical multi-hop networks. Cooperative communication is a new scheme to improve communication performance to realize a reliable dissemination mechanism. However, high mobility networks have a big issue for autonomous control for cooperative communication. Additionally, conventional cooperative schemes cannot reduce packet collisions even if packet collisions are a big degradation factor of performance in dense multi-hop networks. We have discussed a new cooperative communication scheme that employs Orthogonal Frequency-Division Multiplexing (OFDM). Our scheme can improve communication performance and reduce packet collisions based on distributed control matter. Our advance evaluation has shown a good potential of the proposed scheme to improve communication performance in multi-hop network simulations. On the contrary, the feasibility of the proposed scheme with a real hardware device was not shown. This paper evaluates the feasibility of our original cooperative communication scheme on IEEE 802.11a standard devices. Almost all conventional cooperative communication schemes require a special physical layer and a media access control mechanism. We have focused on a characteristic of OFDM, where a receiver can demodulate multiple signals within a guard interval period. The experimental evaluation has been performed with software defined radio devices (USRP B200). We have implemented multiple transmitters, a receiver and a fading simulator for each transmitter with two USRP B200 devices. The results can show that the proposed scheme works well on IEEE 802.11a standard devices and improves communication performance in practical situations. Hence, the proposed scheme will be a new candidate of cooperative communication mechanisms that can employ general consumer devices and can realize effective dissemination mechanism for multi-hop networks.

This paper demonstrates a new unconscious sensing system for bus location. Our system is a new type of application based on participatory sensing systems. However, it can perform sensing operation without users' operation. Therefore, we can employ the mechanism to realize practical application such as bus location systems. Our sensing system consists of a beacon device, a smartphone application and a cloud service. The beacon device is installed on a bus to activate the smartphone application. The smartphone application can upload a bus location to the cloud service when the smartphone application detects the beacon device. The cloud service manages the bus location and distributes them for smartphone applications. The demonstration shows a prototype system for a bus location system based on the new participatory sensing mechanism.

In wireless networks, broadcasting is a fundamental communication primitive for network management and information sharing. However, in multi-channel networks, the broadcast efficiency is very poor as devices are distributed across various channels. Thus, a sender tries all channels for broadcasting a single message, which causes large overhead. In this paper, we propose a novel scheme for efficient broadcast in multichannel networks. Our scheme leverages the overlapped band, which is the frequency range that partially overlapped channels (i.e., adjacent channels) share within their channel boundaries. Specifically, a sender advertises the rendezvous channel through the overlapped band of adjacent channels; the message sharing via broadcast is done on the rendezvous channel. Our scheme employs Signaling via Overlapped Band (SOB), which defines a new signal processing mechanism for communication via the overlapped band. SOB is integrated with MAC layer mechanisms: 1) Reserve Idle Spectrum Fragment (RISF) to reduce waiting time, 2) Reinforce Switch Notification (RSN) to reduce the residing time at a wrong channel, and 3) Multi-sender Agreement on Rendezvous CHannel (MARCH) to support multisender broadcasts. We implemented our scheme on the SORA platform. Experiment results validated communication through the overlapped band. Intensive simulation studies showed that our scheme drastically outperformed previous approach.

Smartphones are a new type of mobile devices that users can install additional mobile software easily. In the almost all smartphone applications, client-server model is used because end-to-end communication is prevented by NAT routers. Recently, some smartphone applications provide real time services such as voice and video communication, online games etc. In these applications, end-to-end communication is suitable to reduce transmission delay and achieve efficient network usage. Also, IP mobility and security are important matters. However, the conventional IP mobility mechanisms are not suitable for these applications because most mechanisms are assumed to be installed in OS kernel. We have developed a novel IP mobility mechanism called NTMobile (Network Traversal with Mobility). NTMobile supports end-to-end IP mobility in IPv4 and IPv6 networks, however, it is assumed to be installed in Linux kernel as with other technologies. In this paper, we propose a new type of end-to-end mobility platform that provides end-to-end communication, mobility, and also secure data exchange functions in the application layer for smartphone applications. In the platform, we use NTMobile, which is ported as the application program. Then, we extend NTMobile to be suitable for smartphone devices and to provide secure data exchange. Client applications can achieve secure end-to-end communication and secure data exchange by sharing an encryption key between clients. Users also enjoy IP mobility which is the main function of NTMobile in each application. Finally, we confirmed that the developed module can work on Android system and iOS system.

This paper proposes a new application-based end-to-end communication platform for smartphones. We have implemented a “Network Traversal with Mobility” (NTMobile) function, which is an IP mobility protocol developed by the authors, as an application library, and extended it suitable for smartphone

Broadband Analog Network Coding (ANC) based on OFDM has been widely investigated to increase capacity of bi-directional relay communications. The broadband ANC based on OFDM technique is required to estimate channel frequency responses (CFRs) between both user terminals (UTs) and a relay station (RS) precisely so as to remove the self-information data from the received signal and to demodulate the other user's information data with frequency equalization. Many channel estimation methods have been proposed for the OFDM based broadband ANC. However bit error rate (BER) performance of these methods would be degraded relatively in higher time- varying fading channels due to the inaccurate estimation of CFR. To solve this problem, this paper proposes a CFR estimation method which can achieve better BER performance with keeping higher transmission efficiency even in higher time-varying fading channels. The salient features of proposed CFR estimation method are to enable the estimation of combined CFR at the UT for both channels between the UTs and RS by using scattered pilot subcarriers and to enable the demodulation of information data without feedback information of CFR estimated at the RS. This paper presents various simulation results in the higher time-varying fading channels to demonstrate the effectiveness of proposed CFR estimation method for the bi-directional OFDM based ANC.

This paper aims to provide performance enhancement to our previously proposed simple autonomous active period selection scheme for cluster-tree based IEEE 802.15.4 beacon enabled WSNs under cluster mobility environments. The cluster mobility causes severe beacon collisions and greatly degrades the system performance. To enhance the system performance of WSNs with cluster mobility, this paper proposes an active period reuse mechanism to the active period selection scheme, and investigates its system performance. The results evaluated by computer simulation demonstrate the proposed mechanism can improve the system in cluster-tree based WSNs under cluster mobility environments.

In vehicular safety systems, two types of safety messages are required: Emergency Safety Message (ESM) and Periodic Beacon Message (PBM). The ESM has to be disseminated within a specified area with stringent delay and delivery ratio requirements, while the PBM does not need to meet these requirements. For exchanging the safety messages in Vehicular Ad-hoc NETwork (VANET), Inter-Vehicle Communication (IVC) is necessary whose de facto standard is Dedicated Short-Range Communications (DSRC). However, the effective transmission range in the DSRC-based IVC is short since a signal can be attenuated due to blocking by obstacles. In order to cover a large dissemination area in the DSRC-based IVC, multi-hop dissemination is required, which however causes channel collision and network congestion. Moreover, the coexistence with PBMs aggravates the collision and the congestion, which make it hard to satisfy the requirements of the ESM dissemination. To overcome the limitation of the DSRC, we utilize an extra TV White Space (TVWS) band that has a large communication range for ESM disseminations, and exploit a DSRC band for 1) the exchange of control data and 2) the compensation of ESM reception errors. In this paper, we propose and analyze a distributed channel usage framework that exploits advantages of DSRC and TVWS bands for ESM dissemination under the existence of PBMs. Our scheme employs TVWS Channel Rendezvous Algorithm (TCRA), ensuring that vehicles within a dissemination area select the same channel with the ESM sender. To compensate ESM reception failures in a TVWS band, our scheme adopts Two-Way Recovery Algorithm (TWRA) that uses DSRC and TVWS bands for ESM retransmission. Further, we establish an analytical delivery ratio model that considers a delay bound of an ESM for optimal parameter selections. To the best of our knowledge, this is the first attempt to propose a distributed channel usage scheme that leverages the strengths of TVWS and DSRC bands for safety message dissemination. Through an in-depth simulation study, we show that the proposed scheme satisfies ESM requirements for latency and packet delivery ratio, and outperforms previous approaches in various vehicular scenarios.

One of the major disadvantages of OFDM technique is the high PAPR in the time domain signal. The larger PAPR signal would cause the fatal degradation of BER performance and un-desirable spectrum regrowth in the nonlinear channel. One of the promising PAPR reduction methods is the Partial Transmit Sequence (PTS) method which can achieve better PAPR performance with reasonable computation complexity. But the PTS method is required to inform the side information to the receiver for the correct demodulation of data information by using the separate channel. To solve the above problem, this paper proposes a new PAPR reduction method without requiring the separate channel. The salient feature of the proposed method is to reduce the PAPR performance by reordering of clusters in the frequency domain at the transmitter and reconstructing the clusters by using the cluster ID under embedded in the data information at the receiver. The proposed method can achieve almost the same PAPR performance and computation complexity as those for the PTS method without requiring the transmission of side information. This paper presents various computer simulation results to verify the effectiveness of the proposed method.

With the spread of mobile devices, there is a growing demand for direct communication between users. However, under recent complex IP networks, it is extremely hard to establish a direct connection between devices. In order to solve the problem, authors have been proposing a new end-to-end communication architecture called "Network Traversal with Mobility" (NTMobile). In NTMobile, applications in the mobile device establish an end-to-end connection by using virtual IPv4/IPv6 addresses in the NTMobile network independent from real IP networks. In this demo, we will show that Android smartphones can make free communication with each other without any constraint such as an NAT traversal problem in IPv4 networks and incompatibility between IPv4 and IPv6 architectures.

This paper investigates simple active period selection mechanism for the cluster based WSNs employing traffic adaptive IEEE 802.15.4 beacon enabled mode, and proposes an autonomous distributed superframe duration (SD) selection scheme to reduce beacon collisions by using simple control mechanism. The proposed scheme autonomously selects an active SD by using beacon reception power monitoring with distributed fashion and also introduces a beacon status notice from sensor nodes (SNs) to their parent cluster heads (CHs) in order to prevent unnecessary SD selection at CHs. The results evaluated by computer simulation show that the proposed scheme can improve the tars mission performance while keeping the better power consumption performance in cluster-based WSNs under cluster mobility environments.

IP mobility is the technology that realizes a continuous communication even when communicating wireless nodes switch access networks. NTMobile (Network Traversal with Mobility) is a new type of IP mobility technology for the IPv4 and IPv6 networks. NTMobile nodes can also achieve IP mobility in global IP networks as well as in private IP networks by creating a tunnel route between a pair of NTMobile nodes. In NTMobile, network applications use virtual IP addresses to achieve a continuous communication at the time when real IP addresses change due to the switching of access networks or node movements. In NTMobile, we implement a packet manipulation method in the Linux kernel module so as to achieve high levels of throughput performance.

As a traffic adaptation technique in cluster-based wireless sensor networks (WSNs) employing IEEE 802.15.4 medium access control (MAC), the traffic adaptive 2-level active period control has been proposed in order to handle temporal and geographical nonuniform traffic fluctuations. This paper proposes a backoff control mechanism for the traffic adaptive 2-level active period control to enhance the system performance, especially transmission performance. The proposed mechanism autonomously adjusts the starting time of the backoff for the contention based channel accesses at the contention access period (CAP) specified by IEEE 802.15.4 MAC, and then, distributes the channel access timing to the wide range within the CAP, leading to lower channel access congestion. The results evaluated by computer simulation show that the proposed mechanism can improve the delay performance with keeping the throughput enhancement in the cluster-based WSNs under non-uniform traffic environments.

The traffic adaptive 2-level active period control has been proposed for performance enhancement in cluster-based wireless sensor networks (WSNs) employing IEEE 802.15.4 medium access control (MAC) under temporal and geographical non-uniform traffic distribution. This paper proposes an adaptive backoff window control method for the traffic adaptive 2-level active period control. The proposed method adjusts the backoff window size according to the length of current active period, which is determined by the 2-level active period control, and the point of channel access in the active period and the elapsed time for transmitting packets. The results evaluated by computer simulation show that the proposed method can improve the throughput performance as well as energy efficiency in the cluster-based WSNs with non-uniform traffic distribution.

This paper proposes an asymmetric traffic accommodation scheme using a multihop transmission technique for CDMA/FDD cellular communication systems. The proposed scheme exploits the multihop transmission for downlink packet transmissions, which require the large transmission power at their single-hop transmissions, in order to increase the downlink capacity. In these multihop transmissions, the uplink band is used for the transmissions from relay stations to destination mobile stations, and this leads more capacity enhancement in the downlink communications. The route selection method and power control for the multihop transmissions are also investigated for the proposed scheme. The proposed scheme is evaluated by computer simulation and the results show that the proposed scheme can achieve better system performance.

This paper proposes a dynamic frequency subband and code channel assignment method for multicast band division multicarrier CDMA systems. The proposed method introduces multiple channel multicast transmissions, where the multicast transmission is divided into two channels; one is for all users in the multicast group, and the other is for a part of the multicast users. The base stations individually assign the frequency subbands and code channels to these two multicast channels. The optimum and suboptimum solutions are proposed for the two-layered frequency subband and code channel assignment. The evaluation results show that the proposed method has superior throughput performance to the single channel multicast systems

The future satellite communication systems are required to support the higher transmission data rate for providing multimedia services by employing the efficient modulation method such as multi-level QAM. However, the employment of conventional single carrier transmission method with multi-level QAM would cause the fatal degradation of signal quality due to the non-linear amplifiers located at the Earth station and satellite. To overcome this problem, this paper proposes the multi-level QAM-OFDM technique with IDAR method designed for satellite channel. In the IDAR method, the characteristics of non-linear amplifiers are required to be known at the receiver. This paper also proposes the estimation method for the characteristics of the non-linear amplifiers by using low PAPR preamble symbols. Various computer simulations are conducted in this paper to verify the effectiveness of proposed method in the non-linear satellite channel