IEICE Transactions on Communications
Online ISSN : 1745-1345
Print ISSN : 0916-8516
Volume E97.B, Issue 4
Displaying 1-24 of 24 articles from this issue
Regular Section
  • Ning WANG, Zhiguo DING, Xuchu DAI
    Article type: PAPER
    Subject area: Fundamental Theories for Communications
    2014 Volume E97.B Issue 4 Pages 702-711
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    In this paper, we focus on the multi-way relaying channel where K users wish to exchange information with each other within two phases. Precoding at each user and the relay is carefully constructed to ensure that the signals from the same user pair are grouped together and cross-pair interference can be cancelled. Reliable detection is challenging at the relay since the observation constellation is no longer one of the regular ones, due to the fact that a relay observation is the superposition of the messages from one of the $\frac{1}{2}K(K-1)$ user pairs. When the trellis coded modulation is used at each node, a simple constellation mapping function and a reduced-states decoding scheme can be applied at the relay, which result in much lower complexity. Furthermore, a modified version of the decoding method is also developed which is called the re-encoding-avoidance scheme at the relay. Monte-Carlo simulation results are provided to demonstrate the performance of the proposed scheme.
    Download PDF (1242K)
  • Masaharu IMAI, Yoshio SUGIZAKI, Koichi ASATANI
    Article type: PAPER
    Subject area: Network
    2014 Volume E97.B Issue 4 Pages 712-720
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    The Internet real-time applications are growing rapidly, and available bandwidth estimation is required. Available bandwidth estimation methods by end host have been studied e.g. Pathload and pathChirp. These methods parameterize probe packet volume and observe the delay variation to estimate available bandwidth. In these methods, the probe packets impose heavy overhead loads on the network. In this paper, we propose a new available bandwidth estimation method based on the frequency of minimum RTT of probe packets in multi hop links. This method estimates bandwidth utilization and available bandwidth of a bottleneck link without significantly increasing network overhead. Estimation accuracies are evaluated for available bandwidth by implementing the proposed method. The proposed method shows better performance than pathChirp or Pathload, requiring fewer probe packets and less estimation time simultaneously.
    Download PDF (2465K)
  • Shunsuke AOKI, Kaoru SEZAKI
    Article type: PAPER
    Subject area: Network
    2014 Volume E97.B Issue 4 Pages 721-729
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    Participatory sensing is an emerging system that allows the increasing number of smartphone users to share effectively the minute statistical information collected by themselves. This system relies on participants' active contribution including intentional input data. However, a number of privacy concerns will hinder the spread of participatory sensing applications. It is difficult for resource-constrained mobile phones to rely on complicated encryption schemes. We should prepare a privacy-preserving participatory sensing scheme with low computation complexity. Moreover, an environment that can reassure participants and encourage their participation in participatory sensing is strongly required because the quality of the statistical data is dependent on the active contribution of general users. In this article, we present MNS-RRT algorithms, which is the combination of negative surveys and randomized response techniques, for preserving privacy in participatory sensing, with high levels of data integrity. By using our method, participatory sensing applications can deal with a data having two selections in a dimension. We evaluated how this scheme can preserve the privacy while ensuring data integrity.
    Download PDF (2296K)
  • Tao QIN, Wei LI, Chenxu WANG, Xingjun ZHANG
    Article type: PAPER
    Subject area: Network
    2014 Volume E97.B Issue 4 Pages 730-737
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    With the ever-growing prevalence of web 2.0, users can access information and resources easily and ubiquitously. It becomes increasingly important to understand the characteristics of user's complex behavior for efficient network management and security monitoring. In this paper, we develop a novel method to visualize and measure user's web-communication-behavior character in large-scale networks. First, we employ the active and passive monitoring methods to collect more than 20,000 IP addresses providing web services, which are divided into 12 types according to the content they provide, e.g. News, music, movie and etc, and then the IP address library is established with elements as (servicetype, IPaddress). User's behaviors are complex as they stay in multiple service types during any specific time period, we propose the behavior spectrum to model this kind of behavior characteristics in an easily understandable way. Secondly, two kinds of user's behavior characters are analyzed: the character at particular time instants and the dynamic changing characters among continuous time points. We then employ Renyi cross entropy to classify the users into different groups with the expectation that users in the same groups have similar behavior profiles. Finally, we demonstrated the application of behavior spectrum in profiling network traffic patterns and finding illegal users. The efficiency and correctness of the proposed methods are verified by the experimental results using the actual traffic traces collected from the Northwest Regional Center of China Education and Research Network (CERNET).
    Download PDF (2245K)
  • Taichi KAWANO, Kazuhisa YAMAGISHI, Takanori HAYASHI
    Article type: PAPER
    Subject area: Network
    2014 Volume E97.B Issue 4 Pages 738-745
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    The International Telecommunication Union has standardized many subjective assessment methods for stereoscopic three-dimensional (3D) and 2D video quality. The same methods are used for 3D and 2D videos. The assessment time, stability, and discrimination ability, which means the ability to identify differences in video quality, are important factors in subjective assessment methods. Many studies on these factors have been done for 2D video quality. However, these factors for 3D video quality have not been sufficiently studied. To address this, we conduct subjective quality assessments for 3D and 2D videos using the absolute category rating (ACR), degradation category rating (DCR), and double stimulus continuous quality-scale (DSCQS) methods that are defined in ITU Recommendations. We first investigate the Pearson's correlation coefficients and Spearman's rank correlation coefficients between different pairings of the three methods to clarify which method is most efficient in terms of assessment time. The different pairings of the three methods exhibit high coefficients. These results indicate that the order relation of the mean opinion score (MOS) and the distance between the MOSs for these methods are almost the same. Therefore, for generally investigating the quality characteristics, the ACR method is most efficient because it has the shortest assessment time. Next, we analyze the stability of these subjective assessment methods. We clarify that the confidence intervals (CIs) of the MOSs for 3D video are almost the same as those for 2D video and that the stability of the DCR method is higher than that of the other methods. The DSCQS method has the smallest CIs for high-quality video. Finally, we investigate the discrimination ability of these subjective assessment methods. The results show that the DCR method performs better than the others in terms of the number of paired MOSs with a significant difference for low-quality video. However, we confirm that the DSCQS method performs better than the others for high-quality video.
    Download PDF (1097K)
  • Wei FENG, Suili FENG, Yuehua DING, Yongzhong ZHANG
    Article type: PAPER
    Subject area: Network
    2014 Volume E97.B Issue 4 Pages 746-754
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    The rapid variation of wireless channels and feedback delay make the available channel state information (CSI) outdated in dynamic wireless multi-hop networks, which significantly degrades the accuracy of cross-layer resource allocation. To deal with this problem, a cross-layer resource allocation scheme is proposed for wireless multi-hop networks by taking the outdated CSI into account and basing compensation on the results of channel prediction. The cross-layer resource allocation is formulated as a network utility maximization problem, which jointly considers congestion control, channel allocation, power control, scheduling and routing with the compensated CSI. Based on a dual decomposition approach, the problem is solved in a distributed manner. Simulation results show that the proposed algorithm can reasonably allocate the resources, and significantly improve the throughput and energy efficiency in the network.
    Download PDF (1233K)
  • Ying YANG, Wenxiang DONG, Weiqiang LIU, Weidong WANG
    Article type: PAPER
    Subject area: Network
    2014 Volume E97.B Issue 4 Pages 755-764
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    Mobility load balancing (MLB) is a key technology for self-organization networks (SONs). In this paper, we explore the mobility load balancing problem and propose a unified cell specific offset adjusting algorithm (UCSOA) which more accurately adjusts the largely uneven load between neighboring cells and is easily implemented in practice with low computing complexity and signal overhead. Moreover, we evaluate the UCSOA algorithm in two different traffic conditions and prove that the UCSOA algorithm can get the lower call blocking rates and handover failure rates. Furthermore, the interdependency of the proposed UCSOA algorithm's performance and that of the inter-cell interference coordination (ICIC) algorithm is explored. A self-organization soft frequency reuse scheme is proposed. It demonstrates UCSOA algorithm and ICIC algorithm can obtain a positive effect for each other and improve the network performance in LTE system.
    Download PDF (1664K)
  • MyungKeun YOON, JinWoo SON, Seon-Ho SHIN
    Article type: PAPER
    Subject area: Internet
    2014 Volume E97.B Issue 4 Pages 765-772
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    We propose a new Bloom filter that efficiently filters out non-members. With extra bits assigned and asymmetrically distributed, the new filter reduces hash computations and memory accesses. For an error rate of 10-6, the new filter reduces cost by 31.31% with 4.33% additional space, while the standard method saves offers a 20.42% reduction.
    Download PDF (976K)
  • Dinh Thanh LE, Nguyen Quoc DINH, Yoshio KARASAWA
    Article type: PAPER
    Subject area: Antennas and Propagation
    2014 Volume E97.B Issue 4 Pages 773-782
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    This paper presents a new technique to enhance the bandwidth of a printed dipole antenna for ultra-wideband applications. The basic idea is to exploit mutual coupling between the feeding line, which is designed closed and paralleled to dipole arms, the dipole arms and other elements of the antenna. Dipole arms, feeding lines as well as other parts are investigated in order to expand antenna bandwidth while still retaining antenna compactness. Based on the proposed technique, we develop two sample printed dipole antennas for advanced wireless communications. One is an ultra-wideband antenna which is suitable for multi-band-mode ultra-wideband applications or being a sensing antenna in cognitive radio. The other is a reconfigurable antenna which would be applicable for wideband cognitive radios. Antenna characteristics such as radiation patterns, current distributions, and gains at different frequencies are also investigated for both sample antennas.
    Download PDF (2494K)
  • Shunji TANAKA, Tomohiko MITANI, Yoshio EBIHARA
    Article type: PAPER
    Subject area: Antennas and Propagation
    2014 Volume E97.B Issue 4 Pages 783-790
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    An efficient beamforming algorithm for large-scale phased arrays with lossy digital phase shifters is presented. This problem, which arises in microwave power transmission from solar power satellites, is to maximize the array gain in a desired direction with the gain loss of the phase shifters taken into account. In this paper the problem is first formulated as a discrete optimization problem, which is then decomposed into element-wise subproblems by the real rotation theorem. Based on this approach, a polynomial-time algorithm to solve the problem numerically is constructed and its effectiveness is verified by numerical simulations.
    Download PDF (1435K)
  • Ryotaro SUGA, Kazuyuki SAITO, Masaharu TAKAHASHI, Koichi ITO
    Article type: PAPER
    Subject area: Antennas and Propagation
    2014 Volume E97.B Issue 4 Pages 791-797
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    In recent years, magnetic resonance imaging (MRI) systems that operate up to under 3T are being used in clinical practice in Japan. In order to achieve the requirements of higher image quality and shorter imaging times, devices that utilize high magnetic fields (> 3T) and high power electromagnetic (EM) wave pulses have been developed. The rise of the static magnetic field is proportional to the increase of the EM wave frequency which raises the issue of variation in capacitance used in the radio frequency (RF) coil for MRI system. In addition, increasing power causes problems of withstanding voltage and these approaches leads to generation of non-uniform magnetic field inside the RF coil. Therefore, we proposed a birdcage coil without the use of lumped circuit elements for MRI systems in previous study. However, it is difficult to fabricate this birdcage coil. Hence, simply-structured birdcage coil with no lumped circuit elements is desired. In this paper, we propose a simply-structured birdcage coil with no lumped circuit elements for a 4T MRI system. In addition, the authors investigated the input impedance and magnetic field distribution of the proposed coil by FDTD calculations and measurements. The results confirm that the proposed birdcage coil matches the performance of the conventional birdcage coil which includes several capacitors.
    Download PDF (2305K)
  • Takashi TOMURA, Jiro HIROKAWA, Takuichi HIRANO, Makoto ANDO
    Article type: PAPER
    Subject area: Antennas and Propagation
    2014 Volume E97.B Issue 4 Pages 798-806
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    A 16×16-element corporate-feed waveguide slot array antenna in the 60-GHz band is designed to achieve broadband reflection and high antenna efficiency. The sub-arrays consisting of 2×2-elements are designed to improve the reflection bandwidth by implementing lower Q and triple resonance. The designed antenna is fabricated by diffusion bonding of thin copper plates. A wide reflection bandwidth with VSWR less than 2.0 is obtained over 21.5%, 13.2GHz (54.7-67.8GHz). The measured gain is 32.6dBi and the corresponding antenna efficiency is 76.5%. The broad bandwidth of more than 31.5-dBi gain is realized over 19.2%, 11.9GHz (56.1-68.0GHz). The gain in bandwidth covers the whole of the license-free 60-GHz band (57-66GHz).
    Download PDF (3342K)
  • Kenta UMEBAYASHI, Genichiro MURATA, Yasuo SUZUKI
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 807-816
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    This paper investigates a signal detection method with a RAKE combiner for the case wherein the receiving signals use the same spreading code. In the case where multiple user interference with the same spreading code (MUI-SC) occurs, blind channel estimation is difficult and as far as we know has not been investigated. To tackle the issue of MUI-SC, we propose two blind channel estimation methods based on the multimodulus algorithm (MMA), i.e., MMA-IQ and MMA-I methods. When a one dimensional modulation scheme, such as differential binary phase-shift keying (DBPSK), is used, the output of the MMA-IQ channel estimation method can, under MUI-SC, have two states. The first state is that the channel estimate corresponds to a channel response for one of the received signals, and the second state is that the channel estimate corresponds to combined channel responses for two of the received signals. This is because the MMA-IQ uses two degrees of freedom (both axes in the IQ-plane), however one DBPSK signal uses only one degree of freedom. In the case of the second state, it is possible to detect two signals/packets at once. However, in the MMA-IQ, the receiver has to recognize the state of the channel estimate before the signal detection, thus we also propose a state recognition method. In the MMA-I channel estimation method, only the I-axis is used thus the channel estimate always corresponds the case with one signal. Numerical results show that the average number of detected packets of the MMA-IQ is more than that of the MMA-I in high signal-to-noise power ratio case. In addition, several aspects of the MMA-I and MMA-IQ based RAKE signal detection methods are shown.
    Download PDF (2309K)
  • Yeong Jun KIM, Tae Hwan HONG, Yong Soo CHO
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 817-825
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    In this paper, a new technique is proposed to reduce the frequency of cell search by user equipment (UE) in the presence of femtocells. A new common signal (CS) and a separate set of primary synchronization signals (PSSs) are employed to facilitate efficient cell search in a next-geration LTE-based system. The velocity of the UE is also utilized to determine cell search mode. A slow UE recognizes the presence of femtocells using the CS, so that it can make separate searches for macrocells and femtocells. A fast UE will not search for femtocells since the coverage of femtocells is restricted to a small region. The fast UE detects the macrocell boundary using the PSSs transmitted from neighboring macrocells, so that it can search for macrocells only at the macrocell boundary. The effects of CS and UE velocity on the number of cell searches are analyzed. The performance of the proposed technique is evaluated by computer simulations.
    Download PDF (1561K)
  • Shiann-Tsong SHEU, Yen-Chieh CHENG, Jung-Shyr WU, Frank Chee-Da TSAI, ...
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 826-842
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    The emerging Wireless Access in Vehicular Environment (WAVE) architecture, which aims to provide critical traffic information and Internet services, has recently been standardized in the IEEE 802.11p specification. A typical WAVE network consists of one road-side-unit (RSU) and one or more on-board-units (OBUs), wherein the RSU supports one control channel (CCH) and one or more service channels (SCH) for the OBUs to access. Generally, an OBU is equipped with a single transceiver and needs to periodically switch between the CCH and one of the SCHs in order to receive emergency messages and service information from the CCH and to deliver Internet traffic over an SCH. Synchronizing all OBUs to alternatively access the CCH and SCHs is estimated to waste as much as 50% of the channel's resources. To improve efficiency, we propose an innovative scheme, namely coordinated interleaving access (CIA) scheme, which optimizes the SCH throughput by smartly grouping the OBUs to let them access the CCH and SCHs in an interleaved and parallel manner. To further the capability of CIA scheme, an enhanced version is also proposed to handle the case where OBUs with multiple transceivers. Performance analysis and evaluation indicates that the proposed CIA scheme achieves a significant improvement in resource. Thus it can be advantageous to adapt it into the IEEE 802.11p protocol for its adoption in multi-channel wireless vehicular networks.
    Download PDF (3564K)
  • Minjoong RIM, Seungyeob CHAE, Xianglan JIN, Dae-Woon LIM
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 843-848
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    In this paper, we consider power allocation over multiple transmit antennas in a distributed transmit antenna system with delay diversity assuming that the power delay profile (PDP) is available for each transmit antenna. This paper demonstrates that the optimal power allocation for outage minimization greatly depends on the system's operating signal-to-noise ratio (SNR) range. With a low operating SNR, it is required to assign all power to the antenna closest to the receiver. On the other hand, when the operating SNR is sufficiently high, power must be allocated proportional to the number of the non-zero elements in the PDP for each antenna.
    Download PDF (1491K)
  • Shiann-Tsong SHEU, Yen-Chieh CHENG, Ping-Jung HSIEH, Jung-Shyr WU, Luw ...
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 849-866
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    Wireless access in the vehicular environment (WAVE) architecture of intelligent transportation system (ITS) has been standardized in the IEEE 802.11p specification and it is going to be widely deployed in many roadway environments in order to provide prompt emergency information and internet services. A typical WAVE network consists of a number of WAVE devices, in which one is the road-side-unit (RSU) and the others are on-board-units (OBUs), and supports one control channel (CCH) and one or more service channels (SCH) for OBU access. The CCH is used to transport the emergency messages and service information of SCHs and the SCHs could be used to carry internet traffic and non-critical safety traffic of OBUs. However, the IEEE 802.11p contention-based medium access control protocol would suffer degraded transmission efficiency if the number of OBUs contending on an SCH is large. Moreover, synchronizing all WAVE devices to periodically and equally access the CCH and an SCH will waste as much as 50% of the channel resources of the SCH [1]. As a solution, we propose an efficiency-improvement scheme, namely the agent-based coordination (ABC) scheme, which improves the SCH throughput by means of electing one OBU to be the agent to schedule the other OBUs so that they obtain the access opportunities on one SCH and access the other SCH served by RSU in a contention-free manner. Based on the ABC scheme, three different scheduling and/or relaying strategies are further proposed and compared. Numerical results and simulation results confirm that the proposed ABC scheme significantly promotes the standard transmission efficiency.
    Download PDF (3862K)
  • Samuli TIIRO, Kenta UMEBAYASHI, Janne LEHTOMÄKI, Yasuo SUZUKI
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 867-874
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    Cognitive radio (CR) systems aim for more efficient spectrum utilization by having so called secondary users (SUs) transmit on a frequency band reserved for licensed primary users (PUs). The secondary transmissions are allowed provided that no harmful interference will be caused to the PUs. SU terminals with multiple antennas can employ transmit power control with transmit precoding in order to control the interference levels. In most of the existing works, perfect channel state information (CSI) is assumed to be available for the SUs. However, in practical systems where perfect CSI is not available, the SUs are not able to guarantee that the interference constraints are sufficiently satisfied. In this paper, we investigate the problem of spectrum sharing for multiantenna CR systems using estimated CSI. Due to the random nature of the estimation error, we set a probabilistic interference constraint and, in order to satisfy it, provide a density function for the interference power. In addition, we present a power control framework for the SU to meet the probabilistic interference constraint.
    Download PDF (1199K)
  • Keiichi MIZUTANI, Zhou LAN, Hiroshi HARADA
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 875-885
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    This paper proposes out-of-band emission reduction schemes for IEEE 802.11af based Wireless Local Area Network (WLAN) systems operating in TV White Spaces (TVWS). IEEE 802.11af adopts Orthogonal Frequency Division Multiplexing (OFDM) to exploit the TVWS spectrum effectively. The combination of the OFDM and TVWS may be able to solve the problem of frequency depletion. However the TVWS transmitter must satisfy a strict transmission spectrum mask and reduce out-of-band emission to protect the primary users. The digital convolution filter is one way of reducing the out-of-band emission. Unfortunately, implementing a strict mask needs a large number of filter taps, which causes high implementation complexity. Time-domain windowing is another effective approach. This scheme reduces out-of-band emission with low complexity but at the price of shortening the effective guard interval. This paper proposes a mechanism that jointly uses these two schemes for out-of-band emission reduction. Moreover, the appropriate windowing duration design is proposed in terms of both the out-of-band emission suppression and throughput performance for all mandatory mode of IEEE 802.11af system. The proposed time-domain windowing design reduces the number of multiplier by 96.5%.
    Download PDF (2872K)
  • Keiichi MIZUTANI, Zhou LAN, Hiroshi HARADA
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 886-895
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    Demand for wireless communication is increasing significantly, but the frequency resources available for wireless communication are quite limited. Currently, various countries are prompting the use of TV white spaces (TVWS). IEEE 802.11 Working Group (WG) has started a Task Group (TG), namely IEEE 802.11af, to develop an international standard for Wireless local Area Networks (WLANs) in TVWS. In order to increase maximum throughput, a channel aggregation mechanism is introduced in the draft standard. In Japan, ISDB-T based area-one-segment broadcasting system (Area-1seg) which is a digital TV broadcast service in limited areas has been permitted to offer actual TVWS services since April 2012. The operation of the IEEE 802.11af system shall not jeopardize the Area-1seg system due to the common operating frequency band. If the Area-1seg partially overlaps with the IEEE 802.11af in some frequency, the IEEE 802.11af cannot use the channel aggregation mechanism due to a lack of channels. As a result, the throughput of the IEEE 802.11af deteriorates. In this paper, the physical layer of IEEE 802.11af D4.0 is introduced briefly, and a partial subcarrier system for IEEE 802.11af is proposed to efficiently use the TVWS spectrum. The IEEE 802.11af co-exist with the Area-1seg by using null subcarriers. Computer simulation shows up to around 70% throughput gain is achieved with the proposed mechanism.
    Download PDF (2646K)
  • Kyunghoon WON, Dongjun LEE, Wonjun HWANG, Hyung-Jin CHOI
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 896-904
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    D2D (Device-to-Device) communication has received considerable attention in recent years as one of the key technologies for future communication systems. Among the typical D2D communication systems, FlashLinQ (FLQ) adopted single-tone OFDM (Orthogonal Frequency Division Multiplexing) transmission which enables wide-sense discovery and distributed channel-aware link scheduling. Although synchronization based on a CES (Common External Source) is basically assumed in FLQ, a means to support devices when they are unable to use a CES is still necessary. In most OFDM systems, CFO (Carrier Frequency Offset) induces ICI (Inter Channel Interference) which degrades overall system performance drastically. Especially in D2D systems, ICI can be amplified due to different path losses between link and a precise estimation and correction of CFO is very important. Many CFO estimation algorithms based on DA (Data Aided) and NDA (None Data Aided) were proposed for OFDM systems, but there are several constraint conditions on frequency synchronization in D2D systems. Therefore, in this paper, we propose a new NDA-CFO estimation method for OFDM based D2D systems. The proposed method is based on the characteristics of single-tone OFDM signal, and is composed of two estimation stages: initial estimation and feed-back estimation. In initial estimation, the estimation of CFO is obtained by using two correlation results in a symbol. Also, estimation range can be adaptively defined as the distance between the two windows. In feed-back estimation, the distance between the two correlation results is gradually increased by re-using the estimated CFO and the correlation results. Therefore, more precise CFO estimation can be obtained. A numerical analysis and performance evaluation verify that the proposed method has a large estimation range and achieves precise estimation performance compared to the conventional methods.
    Download PDF (2470K)
  • Yoshihito DOI, Mamiko INAMORI, Yukitoshi SANADA
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2014 Volume E97.B Issue 4 Pages 905-914
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    This paper presents a low complexity joint decoding scheme of block coded signals in an overloaded multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system. In previous literature, a joint maximum likelihood decoding scheme of block coded signals has been evaluated through theoretical analysis. The diversity gain with block coding prevents the performance degradation induced by signal multiplexing. However, the computational complexity of the joint decoding scheme increases exponentially with the number of multiplexed signal streams. Thus, this paper proposes a two step joint decoding scheme for block coded signals. The first step of the proposed scheme calculates metrics to reduce the number of the candidate codewords using decoding based on joint maximum likelihood symbol detection. The second step of the proposed scheme carries out joint decoding on the reduced candidate codewords. It is shown that the proposed scheme reduces the complexity by about 1/174 for 4 signal stream transmission.
    Download PDF (2283K)
  • Xian-Bin LI, Yue-Ke WANG, Jian-Yun CHEN, Shi-ce NI
    Article type: PAPER
    Subject area: Navigation, Guidance and Control Systems
    2014 Volume E97.B Issue 4 Pages 915-922
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    Introducing inter-satellite ranging and communication links in a Global Navigation Satellite System (GNSS) can improve its performance. In view of the highly dynamic characteristics and the rapid but reliable acquisition requirement of inter-satellite link (ISL) signal of navigation constellation, we utilize navigation data, which is the special resource of navigation satellites, to assist signal acquisition. In this paper, we introduce a method that uses the navigation data for signal acquisition from three aspects: search space, search algorithm, and detector structure. First, an iteration method to calculate the search space is presented. Then the most efficient algorithm is selected by comparing the computation complexity of different search algorithms. Finally, with the navigation data, we also propose a method to guarantee the detecting probability constant by adjusting the non-coherent times. An analysis shows that with the assistance of navigation data, we can reduce the computing cost of ISL signal acquisition significantly, as well effectively enhancing acquisition speed and stabling the detection probability.
    Download PDF (1483K)
  • Lan YANG, Zulin WANG, Qin HUANG, Lei ZHAO
    Article type: PAPER
    Subject area: Navigation, Guidance and Control Systems
    2014 Volume E97.B Issue 4 Pages 923-929
    Published: April 01, 2014
    Released on J-STAGE: April 01, 2014
    JOURNAL RESTRICTED ACCESS
    The auto-correlation function (ACF) of Binary Offset Carrier (BOC) modulated signals has multiple peaks which raise the problem of ambiguity in acquisition and tracking. In this paper, the ACF is split into several sub-correlation functions (SCFs) through dividing the integration period of ACF into several partials. Then a pseudo correlation function (PCF) is constructed from the SCFs through a combination function to eliminate all side-peaks. The unambiguous tracking method based on the PCF achieves better code phase tracking accuracy than the conventional methods in AWGN environment. It only requires half computation cost of Bump-Jumping (BJ) and nearly quarter of Double-Estimator, although offers slightly less accurate tracking than BJ and Double-Estimator in multi-path environment. Moreover, this method suits all kinds of BOC signals without any auxiliary correlators.
    Download PDF (1766K)
feedback
Top