IEICE Transactions on Communications
Online ISSN : 1745-1345
Print ISSN : 0916-8516
Volume E95.B, Issue 7
Displaying 1-47 of 47 articles from this issue
Special Section on Future Internet Technologies against Present Crises
  • Katsuyoshi IIDA
    2012 Volume E95.B Issue 7 Pages 2181
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL FREE ACCESS
    Download PDF (110K)
  • Katsuyuki YAMAZAKI, Hiroshi YAMAMOTO, Masanao SHINOHARA, Toshihiko KAN ...
    Article type: INVITED PAPER
    2012 Volume E95.B Issue 7 Pages 2182-2190
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL FREE ACCESS
    Because large earthquakes have repeatedly occurred in subduction zones, it is important to observe seismic activities on the sea floor. An ocean bottom cabled seismometers (OBCS) system is the most suitable tool for this purpose since data can be obtained in real-time. Although the existing OBCS systems are useful for the study of seismic activities, the number of stations is limited due to their cost. Therefore, lower cost in both production and installation is desired. We have developed a new OBCS system utilizing IP technologies. IP technologies yield the new OBCS system that are more compact and less expensive, while a large amount of complex hardware is used in the existing OBCS system. System reliability is ensured by using IP network technologies that provide redundancy. The new OBCS system was first installed to observe the Niigata-Kobe tectonic zone in the Japan Sea on September 2010. Although this first OBCS system has a total length of 25km, it has been proven that seismic data can be successfully obtained and that the new OBCS system is effective and useful for the dense observation of seismogenic activities on the sea floor around Japan.
    Download PDF (3403K)
  • Katsuhiro HORIBA, Keiko OKAWA, Jun MURAI
    Article type: INVITED PAPER
    2012 Volume E95.B Issue 7 Pages 2191-2199
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL FREE ACCESS
    On the 11th of March, 2011, a massive earthquake hit the northeast region of Japan. The government of Japan needed to publish information regarding the earthquake and its influences. However, their capacity of Web services overflowed. They called the industry and academia for help for providing stable information service to the people. Industry and academia formed a team to answer the call and named themselves the “EQ project”. This paper describes how the EQ Project was organized and operated, and gives analyses of the statistics. An academic organization took the lead in the EQ Project. Ten organizations which consisted of commercial IT industry and academics specialized in Internet technology, were participating in the EQ Project and they structured the three clusters based on their relationships and technological approach. In WIDE Cluster, one of three clusters in the structure of EQ, the peak number of file accesses per day was over 90 thousand, the mobile browsers was 3.4% and foreign languages (translated contents) were referred 35%. We have also discussed the future information distribution strategies in emergency situation based on the experiences of the EQ Project, and proposed nine suggestions to the MEXT as a future strategy.
    Download PDF (2043K)
  • Kotaro KATAOKA, Keisuke UEHARA, Masafumi OE, Jun MURAI
    Article type: PAPER
    2012 Volume E95.B Issue 7 Pages 2200-2209
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In disaster sites of 2011 Tohoku Earthquake, digital communication was virtually unavailable due to the serious damage to the existing Internet and ICT resources. Thus there were urgent demands for recovering the Internet connectivity and first aid communication tools. This paper describes the design and deployment of networking systems that provide Internet connectivity using 3G mobile links or VSAT satellite links. In this paper we examine two approaches for post-disaster networking: quickly deployable package and on-demand networking. Based on a comparison of their characteristics and deployment experiences, this paper tries to extract lessons that contribute to improving the preparedness to another disaster. This paper also shares our significant operational experience acquired through supporting a maximum of 54 sites in Tohoku area including evacuation shelters, temporary hospitals and local government offices.
    Download PDF (8412K)
  • Takeru INOUE, Shin-ichi MINATO
    Article type: PAPER
    2012 Volume E95.B Issue 7 Pages 2210-2221
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Several web sites providing disaster-related information failed repeatedly after the Great East Japan Earthquake, due to flash crowds caused by Twitter users. Twitter, which was intensively used for information sharing in the aftermath of the earthquake, relies on URL shorteners like bit.ly to offset its strict limit on message length. In order to mitigate the flash crowds, we examine the current Web usage and find that URL shorteners constitute a layer of indirection; a significant part of Web traffic is guided by them. This implies that flash crowds can be controlled by URL shorteners. We developed a new URL shortener, named rcdn.info, just after the earthquake; rcdn.info redirects users to a replica created on a CoralCDN, if the original site is likely to become overloaded. This surprisingly simple solution worked very well in the emergency. We also conduct a thorough analysis of the request log and present several views that capture user behavior in the emergency from various aspects. Interestingly, the traffic significantly grew up at previously unpopular (i.e., small) sites during the disaster; this traffic shift could lead to the failure of several sites. Finally, we show that rcdn.info has great potential in mitigating such failures. We believe that our experience will help the research community tackle future disasters.
    Download PDF (2349K)
  • Qiang YANG, Chunming WU, Min ZHANG
    Article type: PAPER
    2012 Volume E95.B Issue 7 Pages 2222-2231
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    The proper allocation of network resources from a common physical substrate to a set of virtual networks (VNs) is one of the key technical challenges of network virtualization. While a variety of state-of-the-art algorithms have been proposed in an attempt to address this issue from different facets, the challenge still remains in the context of large-scale networks as the existing solutions mainly perform in a centralized manner which requires maintaining the overall and up-to-date information of the underlying substrate network. This implies the restricted scalability and computational efficiency when the network scale becomes large. This paper tackles the virtual network mapping problem and proposes a novel hierarchical algorithm in conjunction with a substrate network decomposition approach. By appropriately transforming the underlying substrate network into a collection of sub-networks, the hierarchical virtual network mapping algorithm can be carried out through a global virtual network mapping algorithm (GVNMA) and a local virtual network mapping algorithm (LVNMA) operated in the network central server and within individual sub-networks respectively with their cooperation and coordination as necessary. The proposed algorithm is assessed against the centralized approaches through a set of numerical simulation experiments for a range of network scenarios. The results show that the proposed hierarchical approach can be about 5-20 times faster for VN mapping tasks than conventional centralized approaches with acceptable communication overhead between GVNCA and LVNCA for all examined networks, whilst performs almost as well as the centralized solutions.
    Download PDF (1329K)
  • Tuan Anh LE, Rim HAW, Choong Seon HONG, Sungwon LEE
    Article type: PAPER
    2012 Volume E95.B Issue 7 Pages 2232-2244
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Cubic TCP, one of transport protocols designed for high bandwidth-delay product (BDP) networks, has successfully been deployed in the Internet. Multi-homed computers with multiple interfaces to access the Internet via high speed links will become more popular. In this work, we introduce an extended version of Cubic TCP for multiple paths, called MPCubic. The extension process is approached from an analysis model of Cubic by using coordinated congestion control between paths. MPCubic can spread its traffic across paths in load-balancing manner, while preserving fair sharing with regular TCP, Cubic, and MPTCP at common bottlenecks. Moreover, to improve resilience to link failure, we propose a multipath fast recovery algorithm. The algorithm can significantly reduce the recovery time of data rate after restoration of failed links. These techniques can be useful for resilient high-bandwidth applications (for example, tele-health conference) in disaster-affected areas. Our simulation results show that MPCubic can achieve stability, throughput improvement, fairness, load-balancing, and quick data rate recovery from link failure under a variety of network conditions.
    Download PDF (1859K)
Regular Section
  • Jung-Yoon KIM, Hyoung-Kee CHOI
    Article type: PAPER
    Subject area: Fundamental Theories for Communications
    2012 Volume E95.B Issue 7 Pages 2245-2256
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Multimedia transactions between vehicles are expected to become a promising application in VANETs but security is a fundamental issue that must be resolved before such transactions can become practical and trusted. Existing certificate-based digital signature schemes are ineffective for ensuring the security of multimedia transactions in VANETs. This ineffectiveness exists because there is no guarantee that (1) vehicles can download the latest certificate revocation lists or that (2) vehicles can complete a multimedia transaction before leaving their communication range. These two problems result, respectively, from a lack of infrastructure and from the inconsistent connectivity inherent in VANETs. In this paper, we propose a digital signature approach that combines a certificateless signature scheme and short-lived public keys to alleviate these problems. We then propose a security protocol that uses the proposed signature approach for multimedia transactions between vehicles. The proposed protocol enables vehicles to trade in multimedia resources without an online trust authority. We provide an analytical approach to optimizing the security of the proposed protocol. The security and performance of our protocol are evaluated via simulation and theoretical analysis. Based on these evaluations, we contend that the proposed protocol is practical for multimedia transactions in VANETs in terms of security and performance.
    Download PDF (1711K)
  • Toru KITAYABU, Mao HAGIWARA, Hiroyasu ISHIKAWA, Hiroshi SHIRAI
    Article type: PAPER
    Subject area: Fundamental Theories for Communications
    2012 Volume E95.B Issue 7 Pages 2257-2265
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    A novel delta-sigma modulator that employs a non-uniform quantizer whose spacing is adjusted by reference to the statistical properties of the input signal is proposed. The proposed delta-sigma modulator has less quantization noise compared to the one that uses a uniform quantizer with the same number of output values. With respect to the quantizer on its own, Lloyd proposed a non-uniform quantizer that is best for minimizing the average quantization noise power. The applicable condition of the method is that the statistical properties of the input signal, the probability density, are given. However, the procedure cannot be directly applied to the quantizer in the delta-sigma modulator because it jeopardizes the modulator's stability. In this paper, a procedure is proposed that determine the spacing of the quantizer with avoiding instability. Simulation results show that the proposed method reduces quantization noise by up to 3.8dB and 2.8dB with the input signal having a PAPR of 16dB and 12dB, respectively, compared to the one employing a uniform quantizer. Two alternative types of probability density function (PDF) are used in the proposed method for the calculation of the output values. One is the PDF of the input signal to the delta-sigma modulator and the other is an approximated PDF of the input signal to the quantizer inside the delta-sigma modulator. Both approaches are evaluated to find that the latter gives lower quantization noise.
    Download PDF (2381K)
  • Takayuki SHIMIZU, Hisato IWAI, Hideichi SASAOKA
    Article type: PAPER
    Subject area: Fundamental Theories for Communications
    2012 Volume E95.B Issue 7 Pages 2266-2277
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    We consider secret key agreement for multiple terminals based on radio propagation characteristics in a wireless relaying system where more than two terminals communicate with each other via a relay. In this system, the multiple terminals share a common secret key generated from their radio propagation characteristics with the help of the relay in the presence of an eavesdropper. In this paper, we present three secret key agreement schemes: an amplify-and-forward (AF) scheme, a signal-combining amplify-and-forward (SC-AF) scheme, and a multiple-access amplify-and-forward (MA-AF) scheme. The key idea of these schemes is that each terminal shares the fading coefficients between all terminals and the relay, and use them as the source of a secret key. The AF scheme is based on a conventional amplify-and-forward two-way relaying method, whereas in the SC-AF scheme and the MA-AF scheme, we apply the idea of analog network coding to secret key agreement. We analyze eavesdropping strategies and show that the AF scheme is not secure if the eavesdropper is located near the relay and can receive signals from the relay without multipath fading and noise. Simulation results show that the SC-AF and MA-AF schemes are effective.
    Download PDF (1188K)
  • Peng OUYANG, Shouyi YIN, Leibo LIU, Shaojun WEI
    Article type: PAPER
    Subject area: Energy in Electronics Communications
    2012 Volume E95.B Issue 7 Pages 2278-2285
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    More and more mobile devices adopt multi-battery and dynamic voltage scaling policy (DVS) to reduce the energy consumption and extend the battery runtime. However, since the nonlinear characteristics of the multi-battery are not considered, the practical efficiency is not good enough. In order to reduce the energy consumption and extend the battery runtime, this paper proposes an approach based on the battery characteristics to implement the co-optimization of the multi-battery scheduling and dynamic voltage scaling on multi-battery powered systems. In this work, considering the nonlinear discharging characteristics of the existing batteries, we use the Markov process to depict the multi-battery discharging behavior, and build a multi-objective optimal model to denote the energy consumption and battery states, then propose a binary tree based algorithm to solve this model. By means of this method, we get an optimal and applicable scheme about multi-battery scheduling and dynamic voltage scaling. Experimental results show that this approach achieves an average improvement in battery runtime of 17.5% over the current methods in physical implementation.
    Download PDF (919K)
  • Masahito JINNO, Po-Yuan CHEN, Ming-Shih LIN, Katsuaki MURATA, Koosuke ...
    Article type: PAPER
    Subject area: Energy in Electronics Communications
    2012 Volume E95.B Issue 7 Pages 2286-2295
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In DC/DC converters with low output voltage and high output current, the technique of synchronous rectification is widely used for improving the output efficiency. However, SR buck converters can experience the abnormal phenomenon called “self turn-on” which will occur in the low-side switch under some circuit conditions. “Self turn-on” is a malfunction of the low-side switch, basically caused by the resonance of the parasitic inductance and the parasitic capacitance. It results in noticeable power dissipation. In this paper, the phenomenon will be clearly described and investigated. With the theoretical analysis and the experimental verification, strategies that can suppress this phenomenon are proposed.
    Download PDF (1269K)
  • Heon HUH
    Article type: PAPER
    Subject area: Transmission Systems and Transmission Equipment for Communications
    2012 Volume E95.B Issue 7 Pages 2296-2301
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Orthogonal frequency-division multiplexing (OFDM) is a popular air interface technology that is adopted as a standard modulation scheme for 4G communication systems owing to its excellent spectral efficiency. For OFDM systems, synchronization problems have received much attention along with peak-to-average power ratio (PAPR) reduction. In addition to frequency offset estimation, frame synchronization is a challenging problem that must be solved to achieve optimal system performance. In this paper, we present a maximum likelihood (ML) frame synchronizer for OFDM systems. The synchronizer exploits a synchronization word and cyclic prefixes together to improve the synchronization performance. Numerical results show that the performance of the proposed frame synchronizer is better than that of conventional schemes. The proposed synchronizer can be used as a reference for evaluating the performance of other suboptimal frame synchronizers. We also modify the proposed frame synchronizer to reduce the implementation complexity and propose a near-ML synchronizer for time-varying fading channels.
    Download PDF (491K)
  • Mitsuhiro TATEDA, Kei OZAWA
    Article type: PAPER
    Subject area: Fiber-Optic Transmission for Communications
    2012 Volume E95.B Issue 7 Pages 2302-2305
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Some optical components have polarization dependent loss (PDL), which degrades the performance of optical measurement systems. Various PDL suppression methods have been proposd, most of them have rather complicated structures. In this paper we propose a new simple method for PDL suppression, in which a single birefringent element is concatenated to a PDL device with their birefringent axes offset by π/4. The effectiveness of the proposed method is verified by experiments, that is, polarization dependent loss variation amplitude V of a device relative to its average loss is reduced from 90% to 2% by using a 2m long PANDA fiber for an LED light source whose central wavelength λ0 and spectral width Δλ are 847nm and 55nm, respectively. Furthermore, for an SLD light source with λ0=1539nm and Δλ=71nm, V as much as 80% is reduced to 2% by using the same PANDA fiber.
    Download PDF (1046K)
  • Kazuya ZAITSU, Koji YAMAMOTO, Yasuto KURODA, Kazunari INOUE, Shingo AT ...
    Article type: PAPER
    Subject area: Network System
    2012 Volume E95.B Issue 7 Pages 2306-2314
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Ternary content addressable memory (TCAM) is becoming very popular for designing high-throughput forwarding engines on routers. However, TCAM has potential problems in terms of hardware and power costs, which limits its ability to deploy large amounts of capacity in IP routers. In this paper, we propose new hardware architecture for fast forwarding engines, called fast prefix search RAM-based hardware (FPS-RAM). We designed FPS-RAM hardware with the intent of maintaining the same search performance and physical user interface as TCAM because our objective is to replace the TCAM in the market. Our RAM-based hardware architecture is completely different from that of TCAM and has dramatically reduced the costs and power consumption to 62% and 52%, respectively. We implemented FPS-RAM on an FPGA to examine its lookup operation.
    Download PDF (1571K)
  • Kouji SUGISONO, Hirofumi YAMAZAKI, Hideaki IWATA, Atsushi HIRAMATSU
    Article type: PAPER
    Subject area: Network
    2012 Volume E95.B Issue 7 Pages 2315-2322
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    A packet network architecture called “functionally distributed transport networking” is being studied, where control elements (CEs) are separated from the forwarding elements (FEs) of all routers in a network, and a centralized CE manages the control functions for all FEs. A crucial issue to be addressed in this network architecture is the occurrence of bottlenecks in the CE performance, and rapid network restoration after failures is the main problem to be solved. Thus, we propose here a fast backup route determination method suitable for this network architecture, and we also show the practicality of this architecture. Most failures can be categorized as single-node or single-link failures. The proposed method prepares backup routes for all possible single-node failures in advance and computes backup routes for single-link failures after the failure occurs. The number of possible single-node failures is much less than that of possible single-link failures, and the preparation of backup routes for single-node failures is practical under the memory requirements. Two techniques are used in computing backup routes for single-link failures in order to reduce the computation time. One is to calculate only the routes affected by the link failure. The other is to use an algorithm to compute backup routes for single-link failures based on preplanned backup routes for single-node failures. To demonstrate the practicality of our method, we evaluated the amount of memory and computation time needed to prepare backup routes for all single-node failures, and we carried out simulations with various network topologies to evaluate the route computation time required for a single-link failure.
    Download PDF (996K)
  • Fulong JIANG, Hao LIU, Longxing SHI
    Article type: PAPER
    Subject area: Network
    2012 Volume E95.B Issue 7 Pages 2323-2329
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Combining scheduled channel polling with channel diversity is a promising way for a MAC protocol to achieve high energy efficiency and performance under both light and heavy traffic conditions. However, the deafness problem may cancel out the benefit of channel diversity. In this paper, we first investigate the deafness problem of scheduled multi-channel polling MACs with experiments. Then we propose and evaluate two schemes to handle the deafness problem. Our experiment shows that deafness is a significant reason for performance degradation in scheduled multi-channel polling MACs. A proper scheme should be chosen depending on the traffic pattern and the design objective.
    Download PDF (1392K)
  • Wenjie CHEN, Yukinobu FUKUSHIMA, Tokumi YOKOHIRA
    Article type: PAPER
    Subject area: Network
    2012 Volume E95.B Issue 7 Pages 2330-2343
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Light trail architecture is attracting attention as a new optical wavelength-division multiplexing network architecture that can be built with currently available devices and can achieve bandwidth allocation with granularity finer than a wavelength. Because a light trail is a shared medium, we need a medium access control (MAC) protocol to prevent collisions. Although MAC protocols using token passing can prevent collisions, the bandwidths of links that are located upstream of the token holding node are kept idle. We first propose a dynamic light trail splitting method for increasing throughput of a light trail by using such idle bandwidths. Our method splits a trail into upstream and downstream trails at the token holding node, and independent data transmission on the two trails are permitted. As a result, we expect that the split trail architecture will achieve higher throughput than the original non-split trail architecture. The degree of performance improvement with the split trail architecture depends on how appropriately we determine the upstream and downstream token holding times of every transmission node. Thus, we formulate a problem in which we optimize the token holding times to accommodate requested traffic volume as a linear programming problem. We then derive the throughput of the split trail architecture by solving the problem using the NUOPT solver and investigate the degree of improvement over the original architecture. In addition, we evaluate the end-to-end delay of the split trail architecture by simulation. According to numerical examples, the split trail architecture achieves 1) almost the same throughput as the original one for the worst-case traffic pattern where every transmission node sends data to the terminating node of the trail only, 2) about 1.6 times higher throughput for a uniform traffic pattern where every node pair requests the same traffic volume and an extremely unbalanced traffic pattern where only a few node pairs request huge traffic volume, 3) about 1.9 time higher throughput for the split trail architecture's good-case traffic pattern where every transmission node sends data to its adjacent downstream node only, and 4) the end-to-end delay enough to satisfy any application's QoS requirement according to ITU-T Recommendation Y.1541.
    Download PDF (2067K)
  • Hui WANG, Yuichi NISHIDA, Yukinobu FUKUSHIMA, Tokumi YOKOHIRA, Zhen WU
    Article type: PAPER
    Subject area: Internet
    2012 Volume E95.B Issue 7 Pages 2344-2357
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    To improve TCP throughput even if the maximum receiving window size is small, a TCP performance enhancing proxy (PEP) using a UDP-like packet sending policy with error control has been proposed. The PEP operates on a router along a TCP connection. When the PEP receives a data packet from the source host, it transmits the packet to the destination host, copies the packet into the local buffer (PEP buffer) in case the packets need to be transmitted and sends a premature ACK acknowledging receipt of the packet to the source host. In the PEP, the number of prematurely acknowledged packets in the PEP buffer is limited to a fixed threshold (watermark) value to avoid network congestion. Although the watermark value should be adjusted to changes in the network conditions, watermark adjusting algorithms have not been investigated. In this paper, we propose a watermark adjusting algorithm the goal of which is to maximize the throughput of each connection as much as possible without excessively suppressing the throughputs of the other connections. In our proposed algorithm, a newly established connection uses the initial watermark value of zero to avoid drastic network congestion and increases the value as long as its throughput increases. In addition, when a new connection is established, every already-established connection halves its watermark value to allow the newly established connection to use some portion of the bandwidth and increases again as long as its throughput increases. We compare the proposed algorithm (CW method) with other methods: the FW method that uses a fixed large watermark value and the NP method that does not use the PEP. Numerical results with respect to throughput and fairness showed that the CW method is generally superior to the other two methods.
    Download PDF (5788K)
  • Masato UCHIDA, Shuichi NAWATA, Yu GU, Masato TSURU, Yuji OIE
    Article type: PAPER
    Subject area: Network Management/Operation
    2012 Volume E95.B Issue 7 Pages 2358-2367
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    We propose an anomaly detection method for finding patterns in network traffic that do not conform to legitimate (i.e., normal) behavior. The proposed method trains a baseline model describing the normal behavior of network traffic without using manually labeled traffic data. The trained baseline model is used as the basis for comparison with the audit network traffic. This anomaly detection works in an unsupervised manner through the use of time-periodic packet sampling, which is used in a manner that differs from its intended purpose — the lossy nature of packet sampling is used to extract normal packets from the unlabeled original traffic data. Evaluation using actual traffic traces showed that the proposed method has false positive and false negative rates in the detection of anomalies regarding TCP SYN packets comparable to those of a conventional method that uses manually labeled traffic data to train the baseline model. Performance variation due to the probabilistic nature of sampled traffic data is mitigated by using ensemble anomaly detection that collectively exploits multiple baseline models in parallel. Alarm sensitivity is adjusted for the intended use by using maximum- and minimum-based anomaly detection that effectively take advantage of the performance variations among the multiple baseline models. Testing using actual traffic traces showed that the proposed anomaly detection method performs as well as one using manually labeled traffic data and better than one using randomly sampled (unlabeled) traffic data.
    Download PDF (1112K)
  • Huiling JIANG, Ryo YAMAGUCHI, Keizo CHO
    Article type: PAPER
    Subject area: Antennas and Propagation
    2012 Volume E95.B Issue 7 Pages 2368-2376
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    High frequency bands such as the 3-GHz band have received much attention as frequency resources for broadband mobile communication systems. Radio Frequency (RF) integrated antennas are considered to be useful as base station antennas in decreasing the feeding loss that is otherwise inevitable in high frequency bands and they ensure sufficient power for broadband transmission. One problem in actualizing RF integrated antennas is miniaturizing the duplexer, which is generally large, among the RF circuitry components. To downsize the duplexer, we consider separately locating the transmitter (Tx) and receiver (Rx) antennas. To suppress further the mutual coupling between the Tx and Rx antennas, we investigate a filter integrated antenna configuration. In this paper, we consider an aperture coupled patch antenna as the base antenna configuration and propose a new filter integrated antenna that comprises multiple rectangular elements installed between the coupling slot and radiation element of the Rx antenna. The simulation and measurement results confirm that the new antenna reduces the mutual coupling in the transmission frequency band up to 5.7dB compared to the conventional slot coupled patch antenna configuration.
    Download PDF (2682K)
  • Heedong CHOI, Yasutaka OGAWA, Toshihiko NISHIMURA, Takeo OHGANE
    Article type: PAPER
    Subject area: Antennas and Propagation
    2012 Volume E95.B Issue 7 Pages 2377-2385
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    A time-reversal (TR) approach with multiple signal classification (MUSIC) provides super-resolution for detection and localization using multistatic data collected from an array antenna system. The theory of TR-MUSIC assumes that the number of antenna elements is greater than that of scatterers (targets). Furthermore, it requires many sets of frequency-domain data (snapshots) in seriously noisy environments. Unfortunately, these conditions are not practical for real environments due to the restriction of a reasonable antenna structure as well as limited measurement time. We propose an approach that treats both noise reduction and relaxation of the transceiver restriction by using a time-domain gating technique accompanied with the Fourier transform before applying the TR-MUSIC imaging algorithm. Instead of utilizing the conventional multistatic data matrix (MDM), we employ a modified MDM obtained from the gating technique. The resulting imaging functions yield more reliable images with only a few snapshots regardless of the limitation of the antenna arrays.
    Download PDF (3853K)
  • Jung-Hoon KIM, Tae-Heon JANG, Sung-Kuk LIM, Songjun LEE, Sung-Il YANG
    Article type: PAPER
    Subject area: Electromagnetic Compatibility (EMC)
    2012 Volume E95.B Issue 7 Pages 2386-2392
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    This paper presents a method to improve field uniformity using two TX antennas in a reverberation chamber with less steps of a stirrer. A mode-stirred reverberation chamber (MSRC) is considered as an alternative to the semi-anechoic chamber for an electromagnetic compatibility test because it provides a large test volume, a statistically uniform field, and a high maximum electric field. To improve field uniformity, we introduce two transmitting antennas for excitation in an MSRC, and predict statistical distribution of the complex reflection coefficients (scattering parameters). To prove the validation of our theory and the reliability of measurement results, three kinds of stirrers with different shape and sizes were fabricated and their efficiencies were measured in an MSRC, and then field uniformities have been investigated for 1-3GHz frequency within the maximum number of independent samples that stirrers can provide. The measurement results show that the average received power is about 1.5 times as high as when using one transmitting antenna, and field uniformity is improved. Use of two transmitting antennas in an MSRC is regarded as a useful method to improve field uniformity at less stirrer steps, for radiated immunity tests.
    Download PDF (2050K)
  • Ehab MAHMOUD MOHAMED, Osamu MUTA, Hiroshi FURUKAWA
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2393-2404
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    The authors have proposed Multi-Input Multi-Output (MIMO)-Constant Envelope Modulation, (MIMO-CEM), as a power and complexity efficient alternative to MIMO-OFDM, suitable for wireless backhaul networks in which relay nodes are fixed in their positions. One of the major problems hindering the real application of MIMO-CEM is to estimate MIMO channel characteristics. MIMO-CEM is based upon two contrary schemes; one is nonlinear equalization such as maximum likelihood sequence estimator, which needs accurate channel information to replicate the received signal passing through it. The other is a low resolution analog-to-digital converter (ADC), e.g., 1-bit in the default operation that removes the received signal amplitude fluctuation. In this paper, as a solution to the channel estimation problem in MIMO-CEM with low resolution ADC receiver, we propose an adaptive MIMO-CEM channel estimation scheme where iterative adaptive channel estimation is carried out to minimize the error between the received preamble signal and the replicated one. We also prove that Code Division Multiplexing (CDM) preamble transmission is effective in estimating MIMO channel parameters in the presence of large quantization noise. Computer simulation results show that MIMO-CEM with the proposed channel estimator using CDM preambles achieves identical BER performance to that with the ideal channel estimation even in presence of severe quantization noise caused by a low resolution ADC.
    Download PDF (2303K)
  • Hyunwook YANG, Seungwon CHOI
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2405-2413
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In this paper, we present an algorithm for reducing the transmit normalization factor by perturbing the transmit signal in a Multi-User Multiple Input Multiple Output (MU-MIMO) system which uses the channel inverse matrix as its precoding matrix. A base station must normalize unnormalized transmit signals due to the limitation of the constant transmit power. This paper defines the norm of the unnormalized transmit signal as the transmit normalization factor used to normalize the transmit signal. Recalling that the transmit normalization factor consists of a combination of the singular values from the channel inverse matrix, we provide a codebook that successively reduces the coefficients of these singular values. Through computer simulations, the proposed algorithm is compared to sphere encoding in terms of the Bit Error Rate (BER) and the outage probability in a MU-MIMO signal environment. Sphere encoding is known to be an optimal solution amongst the perturbation methods that reduce the transmit normalization factor [1]. This work demonstrates that the proposed algorithm is has very good performance, comparable to that of sphere encoding, while its computational load is nearly 200 times less. Since the codebook in our algorithm depends only on the given channel, the difference in the computational complexity becomes even greater when the channel state is not changed, because the codebook can be reused. Furthermore, the codebook exhibits the characteristic of robustness to the maximum Doppler shift.
    Download PDF (946K)
  • Sann Maw MAUNG, Iwao SASASE
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2414-2423
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In the MIMO-OFDM multiple access channel (MIMO-OFDM-MAC) uplink scenario, the base station decides the uplink parameters for multiple users based on channel state information (CSI) from each user in the system. The performance of MIMO-OFDM-MAC systems can be significantly improved by using an adaptive transmission and resource allocation schemes which consider the correlation effect of line of sight (LOS) and non line of sight (NLOS) channel conditions for different users in the system. A lot of papers have been published on resource allocation schemes for MIMO-OFDM systems. However, most of these resource allocation schemes have been considered for MIMO-OFDMA systems, where users are separated in the frequency domain and each user uses the same uplink and downlink channels in the same channel conditions. On the other hand, in the mulituser MIMO-OFDM systems, more than one user can be assigned the same frequency and channel conditions for the MIMO-OFDM broadcast channel (downlink) and MIMO-OFDM-MAC channel (uplink) are not the same. Therefore, the same resource allocation schemes for the conventional MIMO-OFDM systems can not be applied to multiuser MIMO-OFDM systems with different uplink and downlink channel conditions. Until now, most of the resource allocation schemes have been considered only for downlink MIMO-OFDM broadcast (MIMO-OFDM-BC) channel and very few papers tackle the fairness among users. Moreover, no paper considers a scheme to realize proportional data rate fairness among users in the MIMO-OFDM-MAC condition. In this paper, we propose a proportional data rate fairness resource allocation scheme with adaptive bit loading for MIMO-ODFM-MAC systems by considering the correlation effects of LOS and NLOS channel conditions in both spatial and frequency domains. Computer simulation results show that the proposed scheme can give larger system capacity while maintaining the proportional data rate fairness requirements among users in the system under the constraint of total transmit power and predetermined target BER.
    Download PDF (2281K)
  • Yoriaki ABE, Shouhei KIDERA, Tetsuo KIRIMOTO
    Article type: PAPER
    Subject area: Sensing
    2012 Volume E95.B Issue 7 Pages 2424-2432
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Ultra-wideband (UWB) pulse radars have a definite advantage in high-range resolution imaging, and are suitable for short-range measurements, particularly at disaster sites or security scenes where optical sensors are rarely suitable because of dust or strong backlighting. Although we have already proposed an accurate imaging algorithm called Range Points Migration (RPM), its reconstructible area is too small to identify the shape of an object if it is far from the radar and the size of the aperture is inadequate. To resolve this problem, this paper proposes a novel image expansion method based on ellipse extrapolation; it enhances extrapolation accuracy by deriving direct estimates of the observed range points distributed in the data space. Numerical validation shows that the proposed method accurately extrapolates part of the target boundary, even if an extremely small region of the target boundary is obtained by RPM.
    Download PDF (3884K)
  • Jing PENG, Falin WU, Ming ZHU, Feixue WANG, Kefei ZHANG
    Article type: PAPER
    Subject area: Navigation, Guidance and Control Systems
    2012 Volume E95.B Issue 7 Pages 2433-2441
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In this paper, an improved GPS/RFID integration method based on Sequential Iterated Reduced Sigma Point Kalman Filter (SIRSPKF) is proposed for vehicle navigation applications. It is applied to improve the accuracy, reliability and availability of satellite positioning in the areas where the satellite visibility is limited. An RFID system is employed to assist the GPS system in achieving high accuracy positioning. Further, to reduce the measurement noise and decrease the computational complexity caused by the integrated GPS/RFID, SIRSPKF is investigated as the dominant filter for the proposed integration. Performances and computational complexities of different integration scenarios with different filters are compared in this paper. A field experiment shows that both accuracy and availability of positioning can be improved significantly by this low-cost GPS/RFID integration method with the reduced computational load.
    Download PDF (1900K)
  • Jeehwan NOH, Chungyong LEE
    Article type: LETTER
    Subject area: Fundamental Theories for Communications
    2012 Volume E95.B Issue 7 Pages 2442-2445
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    This letter considers a two-way relaying network where two nodes exchange their information based on the principle of physical layer network coding (PNC). We study the amplify-and-forward (AF) relay filter design with multiple-input multiple-output (MIMO) system. In order to maximize the sum-rate for information exchange, we propose a relay filter for two-way relaying network. Simulation results show that the proposed scheme performs better than the conventional schemes for two-way relay channel.
    Download PDF (281K)
  • Young-Woo KWAK, Jong-Ho LEE, Yong-Hwa KIM, Seong-Cheol KIM
    Article type: LETTER
    Subject area: Fundamental Theories for Communications
    2012 Volume E95.B Issue 7 Pages 2446-2450
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In this letter, a precoding design for a multiple-input multiple-output (MIMO) full-duplex relay (FDR) system is proposed. For this system, mitigating the self-interference imposed by the transmit antennas on the receive antennas in the same relay station is crucial for improving the performance of the FDR system. The precoding scheme designed in this study uses block-diagonalization (BD). Using this precoding scheme, FDR capacity analysis is performed in the MIMO downlink relay system. Numerical results on system performance in terms of capacity are shown and discussed.
    Download PDF (121K)
  • Seung-Woo HONG, Euisin LEE, Ho-Yong RYU, Sang-Ha KIM
    Article type: LETTER
    Subject area: Network
    2012 Volume E95.B Issue 7 Pages 2451-2454
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    For monitoring of a large-scale continuous object, a large number of sensor nodes might be participated with object detection and tracking. In order to reduce huge quantities of data from the sensor nodes, previous studies focus on representative selection for data reporting to a sink. However, they simply choose representatives among a large number of candidates without consideration of node deployment environments and detection accuracy. Hence, this letter proposes a novel object tracking scheme that first makes a small set of candidates and then chooses a small number of representatives in the set. Also, since the scheme also considers object alteration for representative selection, it can provide high energy-efficiency despite reducing data reporting.
    Download PDF (377K)
  • Sungkee NOH, Euisin LEE, Soochang PARK, Seungmin OH, Sang-Ha KIM
    Article type: LETTER
    Subject area: Network
    2012 Volume E95.B Issue 7 Pages 2455-2458
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    Recently, a flexible loss recovery scheme, called Active Caching (AC) has been proposed to accomplish a Desired Communication Reliability (DCR) about the whole data packets at a source depending on the various applications. However, since AC does not consider the packet delivery rate of each wireless link on multi-hop forwarding paths, it increases the number of totally transmitted packets to achieve a DCR and thus grows the energy consumption of sensor nodes. Thus, this letter proposes a novel recovery scheme which can minimize the number of totally transmitted packets while satisfying a DCR. By geometric programming, the proposed scheme allocates an optimized one-hop packet transmission rate of each wireless link on the multi-hop forwarding path.
    Download PDF (647K)
  • Jin Seok KIM, Dae Hyun YUM, Sung Je HONG, Jong KIM, Pil Joong LEE
    Article type: LETTER
    Subject area: Network
    2012 Volume E95.B Issue 7 Pages 2459-2462
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    As deployment of wireless ad hoc networks for location-based services increases, accurate localization of mobile nodes is becoming more important. Localization of a mobile node is achieved by estimating its distances from a group of anchor nodes. If some anchors are malicious and colluding, localization accuracy cannot be guaranteed. In this article, we present the security conditions for exact localization in the presence of colluding malicious anchors. We first derive the minimum number of truthful anchors that are required for exact localization in 2-D Euclidean space where some anchors may be collinear. Second, we extend our security condition to 3-D localization where some anchors may be coplanar.
    Download PDF (569K)
  • Jihun HA, Yongtae PARK, Byungjo KIM, Eunah KIM, Sunhee YANG, Hyogon KI ...
    Article type: LETTER
    Subject area: Network
    2012 Volume E95.B Issue 7 Pages 2463-2466
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    When the residual resources on a virtualized substrate network (SN) are insufficient to meet the resource demands from the requested virtual network (VN) at specific locations, we can attempt to accommodate the VN by allocating resources at alternative locations and transparently serve the accesses to the VN by having them internally rerouted to the actually allocated locations. In this letter, we explore the feasibility of nodal resource splitting in such alternative allocation scenarios. We find that in order to facilitate such alternative allocations, we should first define the node-link resource dependencies. Once the dependencies are given, we demonstrate that the splitting can visibly improve the SN utilization and the request rejection rate for VN embedding requests under many network scenarios.
    Download PDF (250K)
  • Haoliang SUN, Xiaohui HU, Lixiang LIU
    Article type: LETTER
    Subject area: Internet
    2012 Volume E95.B Issue 7 Pages 2467-2471
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    The existing routing protocols for the interplanetary backbone network did not consider future link connection and link congestion. A novel routing protocol named CAMARP for the interplanetary backbone network is proposed in this letter. We use wait delay to consider future link connection and make the best next hop selection. A load balancing mechanism is used to avoid congestion. The proposed method leads to a better and more efficient distribution of traffic, and also leads to lower packet drop rates and higher throughput. CAMARP demonstrates good performance in the experiment.
    Download PDF (440K)
  • Lu GAN, Xiao Qing WANG, Hong Shu LIAO
    Article type: LETTER
    Subject area: Antennas and Propagation
    2012 Volume E95.B Issue 7 Pages 2472-2476
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In this letter, a new method is proposed to solve the direction-of-arrivals (DOAs) estimation problem of coherently distributed sources based on the block-sparse signal model of compressed sensing (CS) and the convex optimization theory. We make use of a certain number of point sources and the CS array architecture to establish the compressive version of the discrete model of coherently distributed sources. The central DOA and the angular spread can be estimated simultaneously by solving a convex optimization problem which employs a joint norm constraint. As a result we can avoid the two-dimensional search used in conventional algorithms. Furthermore, the multiple-measurement-vectors (MMV) scenario is also considered to achieve robust estimation. The effectiveness of our method is confirmed by simulation results.
    Download PDF (366K)
  • Chang-Hwan PARK, Han-Seong KIM, Yong-Soo CHO
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2477-2480
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In OFDMA-based digital duplexing (DD) systems, the effective channel impulse response (CIR) is lengthened due to time difference of arrivals (TDoAs) from adjacent subscriber stations (SSs). In this letter, a time-domain shortening filter (TSF) is proposed to shorten the effective CIR by maximizing signal-to-interference ratio for pulse shortening (SIRPS). A time-domain window (TW) is also proposed to reduce the effect of inter-carrier interference (ICI) due to CFO in OFDMA-based DD systems, by maximizing the signal-to-interference and noise ratio for window (SINRW).
    Download PDF (166K)
  • Jungwoo LEE
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2481-2484
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In the reverse link of OFDMA, different users (subcarriers) may have different frequency offsets, which causes severe performance degradation. It is also difficult to estimate/compensate these frequency offsets in the reverse link. Even if the frequency offsets are correctly estimated, the compensation of one subcarrier (or user) may worsen the inter-carrier interference from the frequency offsets of other subcarriers (users). One of the key ideas in this letter is to merge frequency offset compensation into the FFT matrix. The new inverse transform matrix is used in lieu of regular FFT. A single MMSE-based transform is used to perform both inverse Fourier transform and frequency offset compensation. Compared to the conventional methods such as circular convolution, this approach has lower computational complexity with comparable performance.
    Download PDF (180K)
  • Wei LIU, Wu-yang JIANG, Hanwen LUO, Ming DING
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2485-2488
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    The conventional semi-orthogonal user pairing algorithm in uplink virtual MIMO systems can be used to improve the total system throughput but it usually fails to maintain good throughput performance for users experiencing relatively poor channel conditions. A novel user paring algorithm is presented in this paper to solve this fairness issue. Based on our analysis of the MMSE receiver, a new criterion called “inverse selection” is proposed for use in conjunction with the semi-orthogonal user selection. Simulation results show that the proposed algorithm can significantly improve the throughput of users with poor channel condition at only a small reduction of the overall throughput.
    Download PDF (330K)
  • Ying-pei LIN, Chen HE, Ling-ge JIANG, Di HE
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2489-2493
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    A sensing efficiency optimization scheme based on two-stage spectrum sensing that maximizes the achievable throughput of the secondary network and minimizes the average sensing time is proposed in this paper. A selection method for the threshold is proposed and proved to ensure optimal sensing performance. An effective iterative algorithm is presented to solve the constructed efficiency optimization problem.
    Download PDF (454K)
  • Ping YANG, Yue XIAO, Qian TANG, Bin ZHOU, Shaoqian LI
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2494-2497
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In this letter, an ordered sphere decoding (OSD) algorithm for spatial modulation (SM) is proposed to reduce receiver complexity. The proposed algorithm relies on a developed matched filter (MF), where the initial solution vector is obtained and the transmit-antenna set is sorted, so as to perform a fast tree search. Furthermore, a threshold parameter is introduced to balance the tradeoff between complexity and performance. Simulation results show that the proposed SM-OSD algorithm achieves considerable complexity reduction compared to the SM-SD, especially in unbalanced multiple-input multiple output (MIMO) channels.
    Download PDF (230K)
  • Ilku NAM, Hyunwon MOON, Doo Hyung WOO
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2498-2500
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In this paper, a wideband CMOS radio frequency (RF) front-end for digital video broadcasting-handheld (DVB-H) receiver is proposed. The RF front-end circuit is composed of a single-ended resistive feedback low noise amplifier (LNA), a single-to-differential amplifier, an I/Q down-conversion mixer with linearized transconductors employing third order intermodulation distortion cancellation, and a divide-by-two circuit with LO buffers. By employing a third order intermodulation (IMD3) cancellation technique and vertical NPN bipolar junction transistor (BJT) switching pair for an I/Q down-conversion mixer, the proposed RF front-end circuit has high linearity and low low-frequency noise performance. It is fabricated in a 0.18µm deep n-well CMOS technology and draws 12mA from a 1.8V supply voltage. It shows a voltage gain of 31dB, a noise figure (NF) lower than 2.6dB, and an IIP3 of -8dBm from 470MHz to 862MHz.
    Download PDF (363K)
  • Chanho YOON, Hoojin LEE, Joonhyuk KANG
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2012 Volume E95.B Issue 7 Pages 2501-2504
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In this letter, we provide an asymptotic error rate performance evaluation of space-time block codes from coordinate interleaved orthogonal designs (STBCs-CIODs), especially in shadowed Rayleigh fading channels. By evaluating a simplified probability density function (PDF) of Rayleigh and Rayleigh-lognormal channels affecting the STBC-CIOD system, we derive an accurate closed-form approximation for the tight upper and lower bounds on the symbol error rate (SER). We show that shadowing asymptotically affects coding gain only, and conclude that an increase in diversity order under shadowing causes slower convergence to asymptotic bound due to the relatively larger loss of coding gain. By comparing the derived formulas and Monte-Carlo simulations, we validate the accuracy of the theoretical results.
    Download PDF (221K)
  • Woongryul JEON, Jeeyeon KIM, Junghyun NAM, Youngsook LEE, Dongho WON
    Article type: LETTER
    Subject area: Terrestrial Wireless Communication/Broadcasting Technologies
    2012 Volume E95.B Issue 7 Pages 2505-2508
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    As anonymity increasingly becomes a necessary and legitimate aim in many applications, a number of anonymous authentication schemes have been suggested over the years. Among the many schemes is Lee and Kwon's password-based authentication scheme for wireless environments. Compared with previous schemes, Lee and Kwon's scheme not only improves anonymity by employing random temporary IDs but also provides user-friendliness by allowing human-memorable passwords. In this letter, we point out that Lee and Kwon's scheme, despite its many merits, is vulnerable to off-line password guessing attacks and a forgery attack. In addition, we show how to eliminate these vulnerabilities.
    Download PDF (207K)
  • Linbo ZHAI, Xiaomin ZHANG, Gang XIE
    Article type: LETTER
    Subject area: Terrestrial Wireless Communication/Broadcasting Technologies
    2012 Volume E95.B Issue 7 Pages 2509-2512
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    This letter presents a model with queueing theory to analyze the performance of non-saturated IEEE 802.11 DCF networks. We use the closed queueing network model and derive an approximate representation of throughput which can reveal the relationship between the throughput and the total offered load under finite traffic load conditions. The accuracy of the model is verified by extensive simulations.
    Download PDF (330K)
  • Jae-Hun CHOI, Joon-Hyuk CHANG
    Article type: LETTER
    Subject area: Multimedia Systems for Communications
    2012 Volume E95.B Issue 7 Pages 2513-2516
    Published: July 01, 2012
    Released on J-STAGE: July 01, 2012
    JOURNAL RESTRICTED ACCESS
    In this paper, we present a speech enhancement technique based on the ambient noise classification that incorporates the Gaussian mixture model (GMM). The principal parameters of the statistical model-based speech enhancement algorithm such as the weighting parameter in the decision-directed (DD) method and the long-term smoothing parameter of the noise estimation, are set according to the classified context to ensure best performance under each noise. For real-time context awareness, the noise classification is performed on a frame-by-frame basis using the GMM with the soft decision framework. The speech absence probability (SAP) is used in detecting the speech absence periods and updating the likelihood of the GMM.
    Download PDF (81K)
Errata
feedback
Top