Physical layer security (PLS) is an attractive paradigm for protecting information confidentiality without the use of traditional key-based cryptography. This paper proposes a design of probabilistic constellation shaping to improve the PLS performance of optical wireless channels using$M$-ary pulse amplitude modulation ($M$-PAM) with the signal-dependent noise model. Specifically, the proposed design aims to maximize the reliability (i.e., minimization of the bit error rate - BER) of the legitimate user's channel while guaranteeing that the modulationconstrained secrecy capacity is at least equal to that achieved by the uniform signaling. For this purpose, a novel upper bound for the BER of$M$-PAM constellation with signal-dependent noise channels with arbitrary input distribution is derived. Simulation results reveal that the proposed PCS design achieves a considerably lower BER of the legitimate user's channel while attaining the same secrecy capacity as the uniform signaling.

This paper explores a channel selection problem for Diversified-Range IoT (DR-IoT), a wireless communication system that operates in a band with severe out-of-band emissions and has many channels with different bandwidths. Because DR-IoT operates in a band with severe out-of-band emissions, energy detection-based techniques do not work when probing to determine whether a network is operating in a given channel. Furthermore, hundreds of overlapping channels make channel scans difficult. To facilitate channel selection, DR-IoT employs an advertising channel (ACH) to exchange channel usage information among neighboring networks. If all networks can exchange their positions and current channels, they can assign channels to minimize the interference of signals sent from different networks. However, they often cannot exchange such information due to the limited ACH communication range. To mitigate this problem, we developed two new channel selection methods that leverage the ACH and received signal strength (RSS) from coordinators of other networks: minimum received beacon strength (MRBS) and closer neighbor further block (CNFB). CNFB is specifically designed to prevent networks from contending over selected channels, which coordinators cannot communicate with each other via the ACH. Our simulation results showed that communication on channels selected by CNFB achieves a 29.1 % increase in average throughput compared to a naive random selection method without ACH while outperforming the other reference methods.

This paper studies a practical design of probabilistic constellation shaping (PCS) for enhancing the performance of physical layer security in visible light communications (VLC). In particular, we consider a wiretap VLC channel employing a probabilistically shapedM-ary pulse amplitude modulation (PAM) constellation. Considering the requirements for reliability of the legitimate user’s channel, flickering-free transmission, and symmetric constellation distribution, the optimal constellation distributions to maximize modulation-constrained secrecy capacity or the bit error rate (BER) of eavesdropper’s channel are investigated for both scenarios of known and unknown eavesdropper’s channel state information (CSI). To formulate the constraint on the channel reliability, tractable closed-form expressions for the upper bound and approximate BER ofM-ary PAM under an arbitrary symbol probability are derived. The design problem is shown to be non-convex due to the non-convex BER constraint. By proving that the upper bound BER is a concave function of the constellation distribution, a suboptimal solution based on the convex-concave procedure (CCCP) is presented. Our findings reveal that while the uniform signaling can only satisfy the BER constraint when the optical power is beyond a certain value, the proposed PCS design works in the entire region of the optical power. Some insights into the optimal constellation distribution with respect to the emitted optical power are also discussed.

This paper proposes a practical design of proba-bilistic constellation shaping (PCS) for physical layer security in visible light communications. In particular, the$M$-ary PAM symbol distribution is optimized to maximize the secrecy capacity given constraints on the legitimate user's bit error rate (BER) and flickering mitigation. For this purpose, an approximate closed-form expression for the BER of M-ary PAM under an arbitrary symbol probability is derived and the issue of flickering caused by the channel-dependent solution is described. The design problem is shown to be non-convex due to the non-convex BER constraint. Thus, a suboptimal solution based on successive convex approximation (SCA) is presented. Our findings reveal that while the uniform signaling and PCS design without BER constraint can only satisfy the BER constraint when the optical power is beyond a certain value, the proposed PCS design works in all regions of the optical power. Some insights into the optimal symbol distribution with respect to the optical power are also discussed.

Though visible light communication (VLC) systems are contained to a given room, improving their security is an important criterion in any practical deployment. This paper studies the design of artificial noise (AN) to enhance physical layer security in VLC systems in the context of input signals with no explicit amplitude constraint (e.g., multicarrier systems). In such systems, clipping is needed to constrain the input signals within the limited linear ranges of the LEDs. However, this clipping process gives rise to non-linear clipping distortion, which must be incorporated into the AN design. To solve the design problem, a sub-optimal approach is presented using the Charnes-Cooper transformation and the convex-concave procedure (CCP). Then, a novel AN transmission scheme is proposed to reduce the impact of clipping distortion, thus improving the secrecy performance. The proposed scheme exploits the typical structure of LED luminaries that are composed of multiple light-emitting chips. Specifically, LED chips in each luminaire are divided into two groups driven by separate driver circuits. One group is used to transmit the information-bearing signal, while the other group transmits the AN. Numerical results show that while clipping distortion can significantly reduce the secrecy level, with proper design AN significantly improves the secrecy performance using the proposed design methodology.

Though visible light communication (VLC) systems are contained in a given room, ensuring their security amongst users in a room is essential. In this paper, the design of artificial noise (AN) to enhance physical layer security in VLC systems is studied in the context of input signals with no explicit amplitude constraint (such as multicarrier systems). In such systems, clipping is needed to constrain the input signals within the limited linear ranges of the LEDs. However, this clipping process gives rise to non-linear clipping distortion, which must be incorporated into the AN design. To facilitate the solution of this problem, a sub-optimal design approach is presented using the Charnes-Cooper transformation and the convex-concave procedure (CCP). Numerical results show that the clipping distortion significantly reduces the secrecy level, and using AN is advantageous over the no-AN scheme in improving the secrecy performance.

When an unexpected obstacle occupies some of the lanes on a multi-lane highway, connected vehicles (CVs) have an advantage in avoiding this obstacle cooperatively. For example, a CV that detects the obstacle first can notify the following vehicles of the obstacle using vehicle-to-vehicle (V2V) communication. In turn, the following vehicles can take action to avoid the obstacle smoothly. Ishihara et al. proposed a strategy in which vehicles that receive a message notifying them of an obstacle gradually adjust their time headway to double it if they are approaching the obstacle. Thus, vehicles in the closed lane can change lanes smoothly and safely. The usefulness of this strategy was confirmed in a simulation of a two-lane road using the traffic flow simulator SUMO. In this paper, we extend this strategy to adapt three or more lanes. In the extended scheme, each vehicle approaching the obstacle selects a lane to which it changes according to the location of the obstacle and the vehicle density in each lane obtained through V2V communication, thereby improving traffic fairness among all lanes without deteriorating ride comfort. We conducted simulations with three-lane road scenarios. The simulation results show that the proposed scheme can achieve sufficiently high traffic throughput without degrading the comfort/safety and the fairness among lanes. Videos of the simulation results are available at: https://www.youtube.com/watch?v=0sDAJOZF38I.

In many real-time RFID-enabled applications (e.g., logistic tracking and warehouse controlling), a subset of wanted tags is often selected from a tag population for monitoring and querying purposes. How this subset of tags is rapidly selected, which is referred to as the subset selection problem, becomes pivotal for boosting the efficiency in RFID systems. Current state-of-the-art schemes result in high communication latencies, which are far from the optimum, and this degrades the system performance. This problem is addressed in this paper by using a simple Bit-Counting Function BCF(), which has also been employed widely by other protocols in RFID systems. In particular, we first propose a near-OPTimal SeLection protocol, denoted by OPTSL, to rapidly solve this problem based on the simple function BCF(). Second, we prove that the communication time of OPTSL is near-optimal with rigorous theoretical analysis. Finally, we conduct extensive simulations to verify that the communication time of the proposed OPT-SL is not only near-optimal but also significantly less than that of benchmark protocols.

A vehicular delay/disruption tolerant network (VDTN) is efficient in keeping communications in sintuations where natural disasters, such as earthquakes and tsunami, occur. We have implemented a VDTN-based information-sharing system with multiple radio communications, such as digital convenience radio (DCR) and Wi-Fi. The information-sharing system enables firefighters and medical staff to share medical records and the state of the disaster damage via the network. The system requires to authenticate users individually to prevent falsification or circulation of incorrect information by malicious or ignorant users. WPA2-EAP is a major authentication mechanism for enterprise systems. It, however, requires many management frame exchanges to establish a secure link and reduces time to exchange data frames. Thus, we have proposed using the IEEE 802.11ai (FILS) together with WPA2-EAP for the system. In this paper, we report the results of field experiments to measure the FILS performance on a VDTN system. Our experiment results show that FILS shortens the initial link setup times between passing vehicles to around 130 ms, which is about 10 times shorter than WPA2-EAP, and FILS increases the amount of transmitted data up to around 33 MB more than using WPA2-EAP.

Facilitating real-time query over massive IoT data streams becomes increasingly important nowadays, for that it can boost the performances of real-time network services significantly. Let δ = e1, e2, ⋯ , et, ⋯ represent an IoT data stream, where each element et arrives at time point t. In this paper, we consider the problem of how to support fast range emptiness querying over an IoT data stream δ in sliding window model with a space-efficient data structure, and we denote this problem as the (ε, L)-ARE-problem. To be more formally, subjected to the constraint of one-pass scan of stream δ, the main task of the (ε, L)-ARE-problem is to design a space-efficient data structure that is capable of always representing W(t, n), which are the n latest elements of stream δ until time point t (i.e., W(t, n) = emax{1,t-n+1}, ⋯ , et-1, et), and quickly answering an emptiness query of the form ”W(t, n) ∩ I = 0?”, with a false positive rate no larger than ε, for any query interval I of length up to L. We design a space-efficient data structure D to solve the (ε, L)-ARE-problem and prove that D has constant time cost for querying an interval, inserting a stream element and evicting outdated elements. The efficiency is demonstrated with extensive simulation results as well.

In order to improve the reliability of dynamic wireless LAN (WLAN) network systems such as a vehicular network system for traffic accident prevention, testing the system software is important. Network emulation enables to test the practical software of the system without building a physical network. Many existing network emulators are built by using a virtual Ethernet device named TUN/TAP device for enabling a network simulator to capture Ethernet frames. However, the network emulation with the TUN/TAP device cannot emulate the operation of the WLAN protocols such as ETSI DCC, which dynamically changes transmission power and interval based on receive signal strength indication (RSSI), because the TUN/TAP device cannot capture IEEE 802.11 frames and control parameters such as transmission power, RSSI. In previous work, we developed a wireless network tap device (wtap80211) and proposed a vehicular network emulator using wtap80211. In the demonstration, we will demonstrate the capability of our emulator using its prototype.

Video caching is one of the most important research issues in Content-Centric Network (CCN) and greatly affects its overall performance. The computational complexity of state-of-the-art optimal caching schemes is high, due to the arbitrary network topologies. In this paper, the popularity-aware video caching in topology-known CCN is studied. The complex arbitrary network typology is mapped into a virtual cascade network topology and a caching scheme is designed in accordance with the transformed virtual network rather than the original network. This scheme is proved optimal, and is with polynomial computational complexity. Simulations are conducted and the results show that the proposed scheme outperforms the existing schemes.

When we drive a car, we often want to know the situation of roads near our destination. Ishihara et. al. proposed a VANET based information sharing system named Real-Time Visual Car Navigation System, in which a driver can obtain Location-Dependent Information (LDI), such as pictures or videos of his/her Point of Interest (POI) by telling the automotive equipment, e.g. car navigation device, the POI. The simplest way to provide LDI to vehicles is flooding the LDI to all vehicles in the VANET, but unneeded LDI may be disseminated, and network resources may be wasted. We have proposed a data dissemination scheme based on Demand map for effectively disseminating LDI to multiple vehicles that need it. In this scheme, each vehicle has Demand map (Dmap), a data set representing the geographical distribution of the strength of demands for LDI. Each vehicle exchanges a subset of data constituting a Dmap (Dmap Information: DMI) with other vehicles. According to the information in the Dmap, each vehicle preferentially sends new LDI or forwarded LDI strongly demanded to the area containing many vehicles that demand the LDI. In this paper, we propose strategies for controlling the frequency of sending DMI and strategies for selecting DMI to be sent for reducing the communication traffic without loss of the accuracy of information in Dmaps. Simulation results show that one of the proposed strategies, LTZ strategy, achieves high accuracy of Dmaps with a small amount of communication traffic.

IEEE 802.11ad, the standard specification for millimeter-wave wireless networks, enables high-speed wireless transmission by using the 60GHz frequency. However, small cell size due to the nature of millimeter-wave wireless network leads high communication overhead caused by frequent handovers. Fast Initial Link Setup (FILS), which is standardized as IEEE 802.11ai, is one option to mitigate the overhead caused by frequent handovers. FILS can shorten the initial link setup time and hence a longer time can be obtained for data communication. However, there is no study of FILS' effects in IEEE 802.11ad wireless network. In this paper, we investigate the effects of FILS in IEEE 802.11ad wireless networks. We conducted simulation of the link setup procedure of FILS and the popular initial link setup scheme, WPA2-Enterprise, in IEEE 802.11ad wireless networks. The simulation results show that FILS can drastically shorten the initial link setups time and reduce the failure ratio of initial link setup when multiple link setups are made many stations simultaneously.

Deterioration of sewer pipes is one of the very important problems in Japan. Sewer inspections have been carried out mainly by visual check or wired remote robots with a camera. However, such inspection schemes involve high labor and/or monetary cost. Sewer inspection with boat-type video cameras or unwired robots takes a long time to check the result of the inspection because video data are obtained after the equipment is retrieved from the pipe. To realize low cost, safe and quick inspection of sewer pipes, we have proposed a sewer inspection system using drifting wireless sensor nodes. Water, soil, and the narrow space in the pipe make the long-range wireless radio communication difficult. Therefore, we have to identify suitable radio frequency and antenna configuration based on wireless communication characteristics in sewer pipes. If the frequency is high, the Fresnel zone the needed space for the line of sight is small, but the path loss becomes worse. On the other hand, if the frequency is low, the size of the Fresnel zone is large, but the path loss becomes small. We conducted wireless communication experiments using 920MHz, 2.4GHz and 5GHz band equipment in an experimental underground pipe. The measurement results show that the wireless communication distance of 5GHz IEEE802.11a is about 5m in a 200mm-diameter pipe and it is longer than 920MHz (ARIB STD-T108), 2.4GHz (IEEE802.11g, IEEE802.15.4) and with 10dBm.

The IEEE 802.11 Distributed Coordination Function (DCF) is based on the Carrier Sense Multiple Access (CSMA) algorithm for avoiding collisions of frames. In CSMA, spatial reuse can be improved by suitably changing the carrier sense threshold (CST). If the increased CST does not incur collisions and helps concurrent transmissions from multiple devices, this improves the throughput of the wireless LAN. For example, when there are two APs and multiple devices exist near each of them, each AP can transmit a frame simultaneously without causing collisions of frames since each device can receive a frame from its associated AP with a high signal power and the interference from another AP is small. In this paper, we propose a system which improves the throughput in CSMA/CA based wireless LANs by controlling the CST values of APs according to positions of mobile hosts. In the system, the CST values of multiple APs are dynamically configured by a controller which has a camera for obtaining the current positions of mobile hosts. The proposed system improves the throughput in WLAN 58% in comparison with basic DCF in a LAN where two APs are arranged at an interval of 50 m and two devices exist within 10 m from each AP.

We propose a framework for efficiently disseminating large data items associated to locations where they are produced by vehicles and desired by drivers of different vehicles in a VANET. The framework consists of a scheme for aggregating drivers' demand for location dependent data using soft-state sketches, a scheme for understanding the condition of data dissemination, and a strategy for selecting data to be transmitted according to the aggregated demands and the condition of the existence of neighboring vehicles which have the same data.

Distributing data items such as pictures and videos about traffic conditions at a location a driver wants to go through Vehicular Ad hoc Networks (VANETs) poses a great challenge due to network dynamics and high-speed mobility. In the last decade, random network coding (RNC) has been shown to support content distribution efficiently in such dynamic environments. Our goal is designing a method for continuously providing location-dependent information generated by vehicles to other vehicles being driven near the birthplace of a data item with short delays and low data delivery traffic using VANETs. So far, we have proposed a scheme called R2D2V (RNC-based Regional Data Distribution on VANETs), a rapid and reliable data dissemination method using random network coding in such a situation. R2D2V can achieve a high data delivery ratio for vehicles driving near the birthplace of the information with low data delivery traffic and short delays when the vehicle density is high. However, this scheme cannot achieve a high delivery ratio for vehicles newly coming to the birthplace of the information after the information has been generated. In this paper, we propose new schemes to mitigate the drawback of R2D2V. Our new schemes distribute a data item encoded by RNC to all vehicles driving near the birthplace of the data item by controlling the probability of sending the data in accordance with the elapsed time from data generation, vehicle's moving direction and vehicle's current location. The simulation results show that our proposed schemes can achieve a high delivery ratio for vehicles newly coming near the birthplace of the information with shorter delays and less delivery traffic than R2D2V.

When a mobile host transmitting real-time video traffic using DCCP CCID3 moves between two wireless LAN access points with different congestion situations, it is difficult to quickly change the transmission rate according to the changes of communication environment because controlling the sending rate depends on feedback information. To solve this problem, we recently proposed a predictive rate control mechanism for real-time video streaming with handover and have since been studying suitable rate estimation schemes for this mechanism. We have demonstrated that the sending rate can be estimated from the jitter of probe packets that are sent periodically to the wireless network by simulation. In this paper, we evaluate the relation between jitter and the DCCP sending rate in a real environment both with and without background traffic and RTS/CTS function. Experimental results demonstrate that the sending rate can be estimated from the jitter of probe packets sent every 200 msec with errors less than 25% of the DCCP sending rate in an IEEE802.11b WLAN with three DCCP sending nodes by enabling RTS/CTS.

Storing data on sensor nodes at a specified location is a useful technique for data-centric storage and management of location dependent data on wireless sensor networks. To decrease the cost of accessing these data, arranging replicas of data so that the distance between the consumer nodes and replica holder nodes decreases is desirable. Conventional schemes, however, are costly for updating the replicas even if they are not often used or do not support functions for ensuring their consistency. We propose a novel replica arrangement scheme, which adaptively arranges replicas at positions close to nodes for frequent sending of queries. Instead of arranging many replicas on sensor nodes, our scheme consists of nodes with pointers that point to the replica holder nodes in order to save storage for replicas. The pointers, which are smaller than replicas, are arranged so that nodes are in circular arcs surrounding the location where the original data item is associated. Simulation results show that our scheme outperforms conventional replica arrangement schemes in terms of the cost required for sending queries and replies with sufficiently low replica update cost.

Sensor nodes of wireless sensor networks are placed in observation areas and transmit data to the observer by using multi-hop communication between nodes. Because these nodes are small and have a limited power supply, they must save power in order to prolong the networkpsilas lifetime.In our previous work, we proposed a power saving technique called HGAF (hierarchical geographic adaptive fidelity)that introduces a layered structure into GAF (geographic adaptive fidelity) for more efficient power saving.HGAF divides observation area into some square cells for making clusters of sensor nodes. In this paper, we propose an extended scheme of HGAF which we called hierarchical geographical adaptive fidelity with honeycomb virtual mesh(HGAF-h). HGAF-h divides the observation area into some hexagonal cells for more reliable data transmission than HGAF. Simulation results show that HGAF-h achieves long network lifetime at networks with regularly placed sensor nodes.

We have proposed mobile Personal Area Network (mPAN) that enables mobile device’s user to exploit services from peripheral devices around the user. In the mPAN, the mobile devices and peripheral devices have to obtain an IP address, because we assume that they communicate with the Internet Protocol (IP). In this paper, we propose a protocol that assigns IP addresses to nodes in an mPAN dynamically. In an mPAN, communication between a mobile device and peripheral devices are limited within one hop. It is ideal for mobile devices like cellular phones to consume less power to use mPANs. Then, we propose a dynamic address assignment protocol specialized for one hop communication between a mobile device and peripheral devices, and that reduces power consumption of mobile devices. We implemented the prototype of the protocol and confirmed that it worked properly in wireless networks including hidden terminals.

As the first step to developing a network controlled resource assignment architecture for mobile networks, we have evaluated the effectiveness of a predictive QoS control scheme for realtime video streaming on a mobile network that supports network-triggered handover. This scheme is based on network and application cooperation and enables video streaming applications on mobile devices and the correspondent hosts to control the data transmission rate before the handover of mobile devices according to the estimated value of the available bandwidth after handover. This scheme essentially has the ability to control the transmission rate not only of a device on handover but of other devices to offer fairness in using limited shared bandwidth. The simulation results reveal that the scheme could avoid picture frame losses and starvation of the playback buffer on mobile devices after handover.

It is difficult to retain accessibility to data on other hosts in ad hoc networks because of disconnections caused by movements of hosts. This fact affects the practical use of ad hoc networks. When important data are operated on ad hoc networks, it is demanded to retain accessibility to the data from users even if there are disconnections between mobile hosts. Hara (2001) has proposed some methods for allocating replicas on ad hoc networks for achieving high accessibility to data objects shared by multiple hosts. The methods are based on an assumption that all hosts on the network know the probabilities of data access to each object and the probabilities do not change. In this paper, we handle a case that the probability of data access from each host change with time and its location. We propose a method to enhance the accessibility to data that are associated with locations and used frequently by hosts that are close to the location. We assume data object is accessed by geocast. Such kind of data will be used in personal navigation systems, systems handling virtual objects overlaid on to the real world like Space Tag and cooperative work for disaster relief etc.

A remote monitoring of various device distributed over wide area is strongly demanded to cut down their maintenance cost. With the introduction of wireless packet systems, the mobile remote monitoring system has started to propagate, because of a less limit to establish remote monitoring devices and its characteristic of always connectivity. Many small to medium sized corporations have been hesitating, although they understand this necessity, because of high investment costs involved in the maintenance of monitoring systems. One solution to this problem is the ASP (Application Service Provider). We developed the multi sharing mobile remote monitoring system MMRM. This paper will present the four layers object management model and the three layers application protocol stuck model that are basic design schemes of MMRM. The system structure and the function block diagram of the practical system TRM (Tokai-Remote Monitoring System) in which Toshiba Machine's TC-mini is used as a data logger will be introduced. In addition, system characteristics such as the delay period from trouble detection to sending alarm message will also be described.

We propose a multimedia data transmission method, Multitrack, that achieves high-speed and efficient data transmission between multiple mobile hosts and the Internet. This method enables terminals that have a low-speed link to the Internet to receive and play a high quality streaming video, and mitigates the load on the server. Multitrack is used in a cluster-type network where multiple mobile hosts are connected to each other with short-range, high-speed links. High-speed communication with hosts outside the cluster is realized by using multiple wireless links from each mobile host in the cluster and the Internet in parallel and dispersing data traffic to them. By using Multitrack, users of the hosts in the cluster can see a high quality streaming video by sharing the received multimedia data. However, because of the differences in the bandwidth and the delay, it is important to disperse traffic according to the quality of multiple links in order to offer stable multimedia data transmission. We propose an effective traffic dispersion method for this environment, and evaluate this method and other methods by simulations.

Mobile computing has become very popular. Many people can access the Internet through mobile hosts. However, wireless links used by mobile hosts have problems such as narrow bandwidth and low reliability. To offer high-speed communication on wireless links, we have proposed SHAKE (SHAring multiple paths procedure for cluster networK Environment). In SHAKE, mobile hosts that are connected by a fast local link use multiple wireless links owned by each host simultaneously to communicate with hosts on the Internet. An experimental system was implemented and evaluated. In this system, however, not only mobile hosts but also correspondent hosts on the internet require special software for SHAKE. We propose a fast WWW access method with SHAKE (Web SHAKE). The feature of Web SHAKE is that it does not require any special software on Web servers on the Internet to use SHAKE. The feature is realized by an use of HTTP proxy server that works on each mobile host. We present the result of a performance evaluation of the Web SHAKE.