IEICE Transactions on Communications
Online ISSN : 1745-1345
Print ISSN : 0916-8516
Volume E94.B, Issue 1
Displaying 1-50 of 52 articles from this issue
IEICE/IEEE Joint Special Section on Autonomous Decentralized Systems Technologies and Their Application to Networked Systems
  • Yukikazu NAKAMOTO
    2011 Volume E94.B Issue 1 Pages 1
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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  • Md. Emdadul HAQUE, Shoichi MURAKAMI, Xiaodong LU, Kinji MORI
    Article type: PAPER
    Subject area: Community
    2011 Volume E94.B Issue 1 Pages 2-9
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Wireless sensor networks represent a new data collection paradigm in which expandability plays an important role. In a practical monitoring environment, for example, food factory monitoring system, sensor relocations and reorganizations are necessary with reorganization of production lines and starting of new production lines. These relocations sometime make congestion in some area of the network. In this dynamic changing environment online expansion is a challenging problem for resource constraint network. This paper proposes a two-tier autonomous decentralized community architecture for wireless sensor network to solve the problem. The first layer consists of sensors and second layer consists of routers. In the architecture routers make community (a group of nodes mutually cooperate for a common goal is a community). The goal of this paper is to introduce the concept of sharing information among routers of the community to decrease sensor connection time for the network especially for the dynamic changing environment. Results show that our proposed technologies can reduce sensor connection time to achieve online expansion.
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  • Fan WEI, Xiaodong LU, Kinji MORI
    Article type: PAPER
    Subject area: Community
    2011 Volume E94.B Issue 1 Pages 10-17
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Wireless Sensor Network(WSN) is widely used in Emergency Management System(EMS) to assure high safety. Real-timely transmitting emergency information in dynamically changing environment should be assured in mission critical district. Conventional methods based on static situations and centralized approaches can not satisfy this requirement. In this paper, to assure real-time property, autonomous community construction technology is proposed to set special area called community which includes a special passage composed of several routers for emergency information's transmission and routers around this passage in one hop range. Emergency information's transmission is protected by routers around this passage from interference of other sensing information's transmission in and outside community. Moreover, autonomous community reconstruction technology is proposed to guarantee real-time property at failure conditions. In this technology, community members autonomously cooperate and coordinate with each other to setup a bypass in community for transmitting emergency information if fault happens. Evaluation results indicate effectiveness of proposed technology.
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  • Atsushi ITO, Yoshiaki KAKUDA, Tomoyuki OHTA, Shinji INOUE
    Article type: PAPER
    Subject area: Assurance
    2011 Volume E94.B Issue 1 Pages 18-29
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    One of the most important duties of government is to maintain safety. In 2007, the Ministry of Internal Affairs and Communications of Japan tested 16 different models of a safety support system for children on school routes. One of the models was constructed and tested at a school in an area of the city of Hiroshima from September to December of 2007. A consortium was established by the city of Hiroshima; Hiroshima City University; Chugoku Electric Power Co., Inc.; and KDDI Corporation to conduct this project. For the model project, we developed a new safety support system for children on school routes by using a mobile ad hoc network constructed from mobile phones with the Bluetooth function. About 500 students and 50 volunteers used this system for four months. The support system provided good performance and accuracy in maintaining the safety of students on the way to school [7]. The basic idea of the safety support system is the grouping of children and volunteers using a mobile ad hoc network. In this paper, we present an outline of this system and evaluate the performance of grouping and the effectiveness of our approach.
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  • Xiaodong LU, Yefeng LIU, Tatsuya TSUDA, Kinji MORI
    Article type: PAPER
    Subject area: Assurance
    2011 Volume E94.B Issue 1 Pages 30-36
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In Video-on-Demand (VoD) services, the playback continuity is one of the most crucial factors for end-user to judge service quality. It is even more significant than the actual video image quality since new generation VoD users commonly have heterogeneous requirements on service according to their context. Moreover, managing dynamic situations in VoD service is always a challenge, especially in the unpredictable user preferences and network conditions. In this paper, i) Autonomous Decentralized VoD System (ADVODS) has been proposed to satisfy different service quality demands of users and, ii) the Autonomous Node Allocation Technology (ANAT) is proposed for assuring service continuity. With the help of autonomous nodes and mobile agents, ANAT can applies different backup policies to users with different Service Level Agreements (SLA), and dynamically update the backup schema to adapt the changing situations such as various service time or congestion events. Drawing on the evaluation results this paper shows that proposed system architecture has a better performance on streaming service provision and continuity.
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  • Hiroshi NAKAGAWA, Satoshi TESHIMA, Tomoyuki OHTA, Yoshiaki KAKUDA
    Article type: PAPER
    Subject area: Assurance
    2011 Volume E94.B Issue 1 Pages 37-44
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Recently in ad hoc networks, routing schemes using location information which is provided by GPS (Global Position System) have been proposed. However, many routing schemes using location information assume that a source node has already known the location information of the destination node and they do not adapt to large ad hoc networks. On another front, the autonomous clustering scheme has been proposed to construct the hierarchical structure in ad hoc networks and adapt to large ad hoc networks. However, even when the hierarchical structure is introduced, there is some problem. The data delivery ratio becomes lower as the node speed becomes higher, and clusterheads have much overhead in the hierarchical routing scheme based on the autonomous clustering scheme. In order to cope with these problems, this paper proposes a new Hierarchical Geographical Routing with Alternative Paths (Hi-GRAP) using the autonomous clustering scheme and shows the effectiveness of the proposed hierarchical geographical routing in comparison with GPSR, Hi-AODV and AODV through simulation experiments with respect to the amount of control packets and the data delivery ratio.
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  • Fumiaki INOUE, Yongbing ZHANG, Yusheng JI
    Article type: PAPER
    Subject area: Scalability & Timeliness
    2011 Volume E94.B Issue 1 Pages 45-54
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    We propose a distributed data management approach in this paper for a large-scale position-tracking system composed of multiple small systems based on wireless tag technologies such as RFID and Wi-Fi tags. Each of these small systems is called a domain, and a domain server manages the position data of the users belonging to its managing domain and also to the other domains but temporarily residing in its domain. The domain servers collaborate with each other to globally manage the position data, realizing the global position tracking. Several domains can be further grouped to form a larger domain, called a higher-domain, so that the whole system is constructed in a hierarchical structure. We implemented the proposed approach in an experimental environment, and conducted a performance evaluation on the proposed approach and compared it with an existing approach wherein a central server is used to manage the position data of all the users. The results showed that the position data processing load is distributed among the domain servers and the traffic for position data transmission over the backbone network can be significantly restrained.
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  • Tomotaka WADA, Junya FUKUMOTO, Kazuhiro OHTSUKI, Hiromi OKADA
    Article type: PAPER
    Subject area: Scalability & Timeliness
    2011 Volume E94.B Issue 1 Pages 55-63
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Various recent intelligent transport system projects are promoting vehicle safety and efficient vehicular traffic control all over the world. One of ITS applications is a system that solves road traffic problems by using vehicular communications technology. Inter-vehicle communication (IVC) is the communications technology for vehicles to exchange moving vehicle information by wireless networks without any base stations. The Vehicular Ad-hoc Network (VANET) is expected to provide new applications for passengers of vehicles by enabling vehicles to communicate with each other via IVC as well as with roadside base stations via roadside-to-vehicle communications. However, when each vehicle transmits its own information to neighboring vehicles, the amount of information being transmitted increases significantly. To solve this problem, we present a novel real-time recognition method for vehicular traffic congestion via VANET with IVC. Vehicles collect the original GPS information of other vehicles by communicating with each other, and they create content that may be useful for drivers by analyzing that original information. The proposed method can reduce the information amount and deliver the analyzed contents to other vehicles efficiently. Computer simulation results show that the proposed method provides real-time information of vehicular accidents and traffic congestion to distant vehicles accurately.
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  • Akeo MASUDA, Cristel PELSSER, Kohei SHIOMOTO
    Article type: PAPER
    Subject area: Scalability & Timeliness
    2011 Volume E94.B Issue 1 Pages 64-76
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    The Internet has grown extremely fast in the last two decades. The number of routes to be supported by the routers has become very large. Moreover, the number of messages exchanged to distribute the routes has increased even faster. In this paper, we propose SpliTable, a scalable way to support the Internet routes in a Service Provider network. In our proposal, BGP route selection is done by distributed servers on behalf of the routers. They are called route selection servers. The selected routes are then stored in distributed routing tables. Each router maintains only its share of Internet routes, not the routes for each Internet prefix as it is the case today. We adapted the concept of Distributed Hash Tables (DHT) for that purpose. We show analytically that our proposal is more scalable in the number of routes supported in each router than current iBGP route distribution solutions. Moreover, the number of control messages exchanged with our proposal is bounded contrary to current sparse iBGP route distribution solutions which may never converge. We confirm these findings in an evaluation of a prototype implementation.
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Regular Section
  • Wei CHEN, Juan WANG, Jing JIN
    Article type: PAPER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 77-85
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Transmission coordination mechanism (TCM) aids opportunistic routing (OR) to reduce the total number of packet transmissions and improve end-to-end throughput. Existing paradigms based on batch map partitions packets of communication session into segments, and transmit packet segments in batch mode sequentially. However, the rate of successful transmission coordination oscillates due to the oscillation of the number of packets batch transmitted. In this paper, we propose batch sliding window-based TCM to improve the performance of OR. By transmitting packets in continuous batch mode, batch sliding window-based TCM can hold the rate of successful transmission coordination steady. Simulation results show the average end-to-end throughput gain of the proposed TCM is 15.4% over existing batch map-based TCM.
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  • Dac-Tu HO, Jingyu PARK, Shigeru SHIMAMOTO, Jun KITAORI
    Article type: PAPER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 86-96
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    This paper proposes a new kind of communication system for air traffic control over the oceans; it is particularly effective at handling high air traffic loads due to many oceanic flights. In this system, each aircraft position report is sent to its relevant ground station by forwardly relaying them via a multi hop ad-hoc network that is formed by the aircraft between this aircraft and the ground station. In addition, an effective multiple access scheme with optimal values is also proposed. This scheme enables the various aircraft involved in relaying the signal to operate autonomously in a flight-route airspace. Furthermore, two useful schemes are proposed for efficient timeslot reuse and timeslot assignment in cases of low aircraft densities: the position aided timeslot reuse (PATR) and distance based timeslot assignment (DBTA), respectively. Finally, another scheme is proposed to improve the achievable relayed packet rate under low aircraft densities, which is called interference-based node selection (IB-NS). In all, the proposed system combined with those three schemes show the availability to utilize this system for air traffic control communications, specifically on high traffic ocean routes.
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  • Xiaoming WANG, Xiaohong JIANG, Tao YANG, Qiaoliang LI, Yingshu LI
    Article type: PAPER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 97-108
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Routing is still a challenging issue for wireless sensor networks (WSNs), in particular for WSNs with a non-uniform deployment of nodes. This paper introduces a Node Aggregation Degree-aware Random Routing (NADRR) algorithm for non-uniform WSNs with the help of two new concepts, namely the Local Vertical Aggregation Degree (LVAD) and Local Horizontal Aggregation Degree (LHAD). Our basic idea is to first apply the LVAD and LHAD to determine one size-proper forwarding region (rather than a fixed-size one as in uniform node deployment case) for each node participating in routing, then select the next hop node from the size-proper forwarding region in a probabilistic way, considering both the residual energy and distribution of nodes. In this way, a good adaptability to the non-uniform deployment of nodes can be guaranteed by the new routing algorithm. Extensive simulation results show that in comparison with other classical geographic position based routing algorithms, such as GPSR, TPGF and CR, the proposed NADRR algorithm can result in lower node energy consumption, better balance of node energy consumption, higher routing success rate and longer network lifetime.
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  • Shohei KAMAMURA, Takashi MIYAMURA, Yoshihiko UEMATSU, Kohei SHIOMOTO
    Article type: PAPER
    Subject area: Internet
    2011 Volume E94.B Issue 1 Pages 109-117
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    IP Fast Reroute techniques have been proposed to achieve fast failure recovery, just a few milliseconds. The basic idea of IP Fast Reroute is to reduce recovery time by precomputing backup routes. The multiple routing configurations (MRC) algorithm was proposed to implement IP Fast Reroute. MRC prepares backup configurations, which are used for finding a detour route after a failure. However, this algorithm establishes too many backup configurations to recover from failures. We propose a new backup configuration computation algorithm that creates the fewest possible configurations. The basic idea is to construct a spanning tree that excludes failure links in each backup configuration. We show that the effectiveness of our algorithm is especially high in large-scale power-law networks.
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  • Takeshi USUI, Takeshi KUBO, Yoshinori KITATSUJI, Hidetoshi YOKOTA
    Article type: PAPER
    Subject area: Network Management/Operation
    2011 Volume E94.B Issue 1 Pages 118-127
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    The number of SIP-based services provided by network service providers (NSPs) is increasing. SIP allows NSPs to control services and to collect the information relating to charging for the usage of their customer communications. Monitoring SIP messages (exchanged between SIP proxy servers and user terminals) is vital for providing the stable SIP-based services. Monitoring SIP messages enables NSPs to quickly discover a fault location where SIP messages are lost, and to determine the subsequent recovery solutions. This paper proposes a lightweight method for determining the location of SIP message loss through relationships based on the SIP's retransmission mechanism. Numerical analyses show that the proposed method can locate the lossy links of SIP messages with a low probability of detection failure.
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  • Jianxin LIAO, Cheng ZHANG, Tonghong LI, Xiaomin ZHU
    Article type: PAPER
    Subject area: Network Management/Operation
    2011 Volume E94.B Issue 1 Pages 128-138
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    To reduce the inaccuracy caused by inappropriate time window, we propose two probabilistic fault localization schemes based on the idea of “extending time window.” The global window extension algorithm (GWE) uses a window extension strategy for all candidate faults, while the on-demand window extension algorithm (OWE) uses the extended window only for a small set of faults when necessary. Both algorithms can increase the metric values of actual faults and thus improve the accuracy of fault localization. Simulation results show that both schemes perform better than existing algorithms. Furthermore, OWE performs better than GWE at the cost of a bit more computing time.
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  • Xin NIE, Jianhua ZHANG, Ping ZHANG
    Article type: PAPER
    Subject area: Antennas and Propagation
    2011 Volume E94.B Issue 1 Pages 139-149
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Relay, which promises to enhance the performance of future communication networks, is one of the most promising techniques for IMT-Advanced systems. In this paper, multiple-input multiple-output (MIMO) relay channels based on outdoor measurements are investigated. We focus on the link between the base station (BS) and the relay station (RS) as well as the link between the RS and the mobile station (MS). First of all, the channels were measured employing a real-time channel sounder in IMT-Advanced frequency band (2.35GHz with 50MHz bandwidth). Then, the parameters of multipath components (MPCs) are extracted utilizing space-alternating generalized expectation algorithm. MPC parameters of the two links are statistically analyzed and compared. The polarization and spatial statistics are gotten. The trends of power azimuth spectrum (PAS) and cross-polarization discrimination (XPD) with the separation between the RS and the MS are investigated. Based on the PAS, the propagation mechanisms of line-of-sight and non-line-of-sight scenarios are analyzed. Furthermore, an approximate closed-form expression of channel correlation is derived. The impacts of PAS and XPD on the channel correlation are studied. Finally, some guidelines for the antenna configurations of the BS, the RS and the MS are presented. The results reveal the different characteristics of relay channels and provide the basis for the practical deployment of relay systems.
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  • Jianqing WANG, Kenichiro MASAMI, Qiong WANG
    Article type: PAPER
    Subject area: Antennas and Propagation
    2011 Volume E94.B Issue 1 Pages 150-157
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    The objective of this study is to investigate the feasibility of an ultra wideband (UWB) impulse radio system for in-body to off-body wireless communication for biomedical applications. At first, a UWB antenna is designed in the UWB low band for implant use in the chest. Then the channel model is extracted and established based on the finite difference time domain (FDTD) simulation with an anatomical human body model. The established channel model consists of a small set of parameters for generating discrete time impulse responses. The generated model shows good agreement with the FDTD-calculated result in terms of key communication metrics. For effective communication over the multipath-affected channel, the pulse position modulation is employed and a 2-finger RAKE structure with a constant temporal delay is proposed in the receiver. The bit error rate performance has shown the validity of the system in the in-body to off-body chest channel.
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  • Jae-Ho LEE, Takuichi HIRANO, Jiro HIROKAWA, Makoto ANDO
    Article type: PAPER
    Subject area: Antennas and Propagation
    2011 Volume E94.B Issue 1 Pages 158-165
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Method of moments (MoM) is an efficient design and analysis method for waveguide slot arrays. A rectangular entire-domain basis function is one of the most popular approximations for the slot aperture fields. MoM with only one basis function does not provide sufficient accuracy and the use of higher order mode of basis functions is inevitable to guarantee accuracy. However, including the higher order modes in MoM results in a rapid increase in the computational time as well as the analysis complexity; this is a serious drawback especially in the slot parameter optimization. The authors propose the slot correction length that compensates for the omission of higher order mode of basis functions. This length is constant for a wide range of couplings and frequency bands for various types of slots. The validity and universality of the concept of slot correction length are demonstrated for various slots and slot parameters. Practical slot array design can be drastically simplified by the use of MoM with only one basis function together with the slot correction length. As an example, a linear waveguide array of reflection-cancelling slot pairs is successfully designed.
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  • Ang FENG, Qinye YIN
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 166-174
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In this paper, we design a practical time-reversal quasi-orthogonal space-time block code (TR-QO-STBC) system for broadband multi-input multi-output (MIMO) communications. We first modify the TR-QO-STBC encoding structure so that the interference between the transmitted blocks can be completely removed by linear processing. Two low complex decision-feedback equalization (DFE) schemes are then proposed. One is built from the frequency-domain decision-feedback equalization (FD-DFE). The derived bi-directive FD-DFE (BiD-FD-DFE) cancels the interference among the successive symbols along the time axis. The other one is the enhanced V-BLAST, which cancels the interference between the real and imaginary parts of the spectral components. They have distinct performance characteristics due to the different interference-cancellation strategies. The underlying orthogonal and symmetric characters of TR-QO-STBC are exploited to reduce the computational complexity. Computer simulations confirm that the proposed equalizers can achieve better performance than the existing schemes.
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  • Jaewoo SO
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 175-182
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Broadcasting information to users about new resource assignments generates a substantial mapping overhead. The mapping overhead influences the system throughput and, in particular, seriously affects the performance of voice-over-Internet protocol (VoIP) services. Persistent scheduling was introduced to reduce the mapping overhead. However, up to now no studies have mathematically analyzed the performance of the persistent scheduling. This paper develops analytical and simulation models and evaluates the performance of the persistent scheduling for VoIP services in mobile WiMAX systems.
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  • Liming ZHENG, Jooin WOO, Kazuhiko FUKAWA, Hiroshi SUZUKI, Satoshi SUYA ...
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 183-193
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    This paper proposes a low-complexity algorithm to calculate log likelihood ratios (LLRs) of coded bits, which is necessary for channel decoding in coded MIMO mobile communications. An approximate LLR needs to find a pair of transmitted signal candidates that can maximize the log likelihood function under a constraint that a coded bit is equal to either one or zero. The proposed algorithm can find such a pair simultaneously, whereas conventional ones find them individually. Specifically, the proposed method searches for such candidates in directions of the noise enhancement using the MMSE detection as a starting point. First, an inverse matrix which the MMSE weight matrix includes is obtained and then the power method derives eigenvectors of the inverse matrix as the directions of the noise enhancement. With some eigenvectors, one-dimensional search and hard decision are performed. From the resultant signals, the transmitted signal candidates to be required are selected on the basis of the log likelihood function. Computer simulations with 4×4 MIMO-OFDM, 16QAM, and convolutional codes (rate =1/2,2/3) demonstrate that the proposed algorithm requires only 1.0dB more Eb/N0 than that of the maximum likelihood detection (MLD) in order to achieve packet error rate of 10-3, while reducing the complexity to about 0.2% of that of MLD.
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  • Fumihito SASAMORI, Ziyan JIA, Shiro HANDA, Shinjiro OSHITA
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 194-202
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Orthogonal frequency division multiplexing (OFDM) communication systems have great advantages, such as high spectrum efficiency and robustness against multipath fading. In order to enhance the advantages, this paper investigates an efficient utilization of both diversity combining and higher-level modulation (adaptive modulation) with a repetition code on the frequency domain in the OFDM systems. The repetition coded OFDM systems can achieve an improvement of performance with such a simple structure as one pair of transmit/receive antennas. In this paper, we derive simple closed-form equations for bit error probability (BEP) and throughput, and then improvements of those performances in the proposed OFDM systems are verified by both theoretical analysis and Monte Carlo simulation.
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  • Kai LIU, Jinhua GUO, Ning LU, Fuqiang LIU, Xinhong WANG, Ping WANG
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 203-214
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Dedicated Short Range Communication (DSRC) employs one control channel for safety-oriented applications and six service channels for non-safety commercial applications. However, most existing multi-channel schemes require all neighboring vehicles periodically (e.g. every 100 milliseconds) tune to the control channel for a full update of safety-oriented data before they can switch to the service channels for non-safety services. The safety exchange interval increases with the increase of traffic density. Consequently, under high traffic densities, the service channels are often completely idle while the control channel is congested. We propose a RSU Assisted Multi-channel Coordination MAC (RAMC) protocol that fully utilizes all channels to provide simultaneous safety and non-safety communications. Within the radio range of a roadside unit (RSU), vehicles are free to tune to any service channel. The RSU monitors all the safety messages being transmitted in both the control and service channels. Periodically, the RSU broadcasts a consolidated traffic view report to all neighboring vehicles in all channels. Therefore, a vehicle can operate in a service channel as long as it needs to achieve high throughput for non-safety applications, while maintaining adequate and timely safety awareness. Our simulation results show that the proposed RAMC protocol consistently achieves very high percentage of non-safety usage, while maintaining high safety message delivery ratios in various traffic density conditions.
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  • Tetsuo KIRIMOTO, Takeshi AMISHIMA, Atsushi OKAMURA
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 215-221
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    ICA (Independent Component Analysis) has a remarkable capability of separating mixtures of stochastic random signals. However, we often face problems of separating mixtures of deterministic signals, especially sinusoidal signals, in some applications such as radar systems and communication systems. One may ask if ICA is effective for deterministic signals. In this paper, we analyze the basic performance of ICA in separating mixtures of complex sinusoidal signals, which utilizes the fourth order cumulant as a criterion of independency of signals. We theoretically show that ICA can separate mixtures of deterministic sinusoidal signals. Then, we conduct computer simulations and radio experiments with a linear array antenna to confirm the theoretical result. We will show that ICA is successful in separating mixtures of sinusoidal signals with frequency difference less than FFT resolution and with DOA (Direction of Arrival) difference less than Rayleigh criterion.
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  • Chih-Cheng KUO, Wern-Ho SHEEN, Chang-Lung HSIAO
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 222-233
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Channel-factorization aided detector (CFAD) is one of the important low-complexity detectors used in multiple input, multiple output (MIMO) receivers. Through channel factorization, this method transforms the original MIMO system into an equivalent system with a better-conditioned channel where detection is performed with a low-complexity detector; the estimate is then transferred back to the original system to obtain the final decision. Traditionally, the channel factorization is done with the lattice reduction algorithms such as the Lenstra-Lenstra-Lovász (LLL) and Seysen's algorithms with no consideration of the low-complexity detector used. In this paper, we propose a different approach: the channel factorization is designed specifically for the minimum mean-square-error (MMSE) detector that is a popular low-complexity detector in CFADs. Two new types of factorization algorithms are proposed. Type-I is LLL based, where the well-known DLLL-extended algorithm, the LLL algorithm working on the dual matrix of the extended channel matrix, is a member of this type but with a higher complexity. DLLL-extended is the best-performed factorization algorithm found in the literature, Type-II is greedy-search based where its members are differentiated with different algorithm's parameters. Type-II algorithms can provide around 0.5-1.0dB gain over Type-I algorithms and have a fixed computational complexity which is advantageous in hardware implementation.
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  • Kyoung-Young SONG, Jong-Seon NO, Habong CHUNG
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 234-242
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In this paper, the performance of the soft-decision-and-forward (SDF) protocol in the cooperative communication network with one source, one relay, and one destination, where each node has two transmit and receive antennas, is analyzed in terms of the bit error rate (BER) obtained from the pairwise error probability (PEP). Using the moment generating function and Q-function approximation, the PEP of SDF protocol is calculated and we confirm that the SDF with two antennas achieves the full diversity order. For the slow-varying Rayleigh fading channel, the optimal power allocation ratio can be determined so as to minimize the average PEP (or BER). Due to the difficulty of deriving the optimal value analytically, an alternative strategy of maximizing the product signal-to-noise ratio (SNR) of direct and relay links, which we call the suboptimal power allocation, is considered. Through a numerical analysis, we show that the performance gap between the suboptimal and optimal power allocation strategies is negligible in the high SNR region.
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  • Yasuyuki HATAKAWA, Masashi FUSHIKI, Satoshi KONISHI
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 243-252
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    This paper proposes a multiple-input multiple-output (MIMO) precoding scheme for the down link of single user (SU) cooperative base station (BS) systems. The proposed precoding scheme mitigates the performance degradation caused by large inter-BS path-loss imbalance and large intra-BS antenna correlation by controlling two parameters. The proposed precoding scheme multiplexes the multiple layers by adjusting the amplitude of each layer, and then decreases the occurrence probability of the small absolute value of the log likelihood ratio (LLR), and so reduces the bit error rate (BER). Link level simulation results show that the proposed precoding scheme decreases the required signal-to-noise ratio (SNR) of BER =0.001 by 5.5dB, 2.2dB, and 0.7dB in the case of QPSK and coding rate 1/1, 3/4, and 1/2 respectively. The proposed precoding scheme is also evaluated in terms of spectrum efficiency using rank adaptation and adaptive modulation, showing that it improves the spectrum efficiency when the SNR per a receiver antenna is higher than 4dB.
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  • Mohammadreza KESHAVARZI, Abbas MOHAMMADI, Abdolali ABDIPOUR, Fadhel M. ...
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 253-261
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    The effect of DC offset on multi-input multi-output (MIMO) direct transceivers with adaptive modulation (AM) is discussed in this paper. A variable-rate variable-power (VRVP) AM system with perfect channel state information (P-CSI) at both the transmitter and receiver in a MIMO scenario is considered. The DC offset is modeled as a zero mean complex Gaussian distributed random variable. By this modeling of the DC offset, the analytical expression for degraded bit error rate (BER) is derived. To derive this analytical expression, we establish a reasonable approximation. The good agreement between the analytical and simulation results shows that the approximation is valid and confirms the accuracy of the analytical expressions. Moreover, an approach to improve the degraded BER in these systems is introduced. For this purpose, we introduce a design for AM MIMO systems that takes account of DC offset and its effectiveness is confirmed. Throughput analysis for the AM MIMO system in the presence of DC offset is presented in this paper too. An analytical expression for throughput is derived and approximated to a simpler equation. At last, throughput results are compared to the simulation outcomes.
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  • Seigo NAKAO, Tomohumi TAKATA, Daichi IMAMURA, Katsuhiko HIRAMATSU
    Article type: PAPER
    Subject area: Terrestrial Wireless Communication/Broadcasting Technologies
    2011 Volume E94.B Issue 1 Pages 262-272
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Hybrid automatic repeat request (HARQ) is employed for the Evolved Universal Terrestrial Radio Access (E-UTRA) downlink. The base station not only decodes the ACK/NACK signals from the user equipment (UE), but also detects a termination of the transmission (DTX) of the ACK/NACK signals caused by the mis-detection of the downlink control information (DCI) at the UE side. Since ACK/NACK signals from UEs are multiplexed by CDMA, there are sometimes severe inter-code interference (ICI) effects, which significantly degrade the performance of ACK/NACK signals. In order to mitigate such ICI effects, in [1],[2], we proposed a novel phase rotation scheme on the constellations of the uplink ACK/NACK signals, and confirmed the effects on the ACK/NACK bit error rate performance; however, the previous paper did not analyze the effects of the phase rotation on the DTX detection performance. Hence, in this paper, we further analyze the effects of the phase rotation for the ACK/NACK signals in conjunction with a new DTX detection scheme which utilizes equalizer outputs, and investigate the performance of the proposed scheme by means of computer simulations.
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  • Ali MOQISEH, Mahdi HADAVI, Mohammad M. NAYEBI
    Article type: PAPER
    Subject area: Sensing
    2011 Volume E94.B Issue 1 Pages 273-281
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In this paper, the inherent problem of the Hough transform when applied to search radars is considered. This problem makes the detection probability of a target depend on the length of the target line in the data space in addition to the received SNR from it. It is shown that this problem results in a non-uniform distribution of noise power in the parameter space. In other words, noise power in some regions of the parameter space is greater than in others. Therefore, the detection probability of the targets covered by these regions will decrease. Our solution is to modify the Hough detector to remove the problem. This modification uses non-uniform quantization in the parameter space based on the Maximum Entropy Quantization method. The details of implementing the modified Hough detector in a search radar are presented according to this quantization method. Then, it is shown that by using this method the detection performance of the target will not depend on its length in the data space. The performance of the modified Hough detector is also compared with the standard Hough detector by considering their probability of detection and probability of false alarm. This comparison shows the performance improvement of the modified detector.
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  • Qiuliang XIE, Kewu PENG, Fang YANG, Zhaocheng WANG, Zhixing YANG
    Article type: LETTER
    Subject area: Fundamental Theories for Communications
    2011 Volume E94.B Issue 1 Pages 282-284
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    A BICM-ID system with 3-dimensional rotated BPSK constellation and signal space diversity (SSD) is proposed to combat the effect of Rayleigh fading. A new criterion based on mutual information is proposed to find the optimal rotation matrix, and the labeling that fits well with the outer code is presented. Simulation results show that at BER of 10-5 over a Rayleigh fading channel, with the code length of 192,000bits and the iteration number of 100, the performance of the proposed system is only about 0.8dB from the Gaussian-input Shannon limit and exceeds the limit constrained by the traditional QPSK input without rotation or SSD, at the spectrum efficiency of 1bit/s/Hz.
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  • Zhiyan ZHANG, Jianhua ZHANG, Wei XU, Yanyan ZHANG, Yi LIU
    Article type: LETTER
    Subject area: Transmission Systems and Transmission Equipment for Communications
    2011 Volume E94.B Issue 1 Pages 285-289
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In the localized Discrete Fourier Transform-Spread-Orthogonal Frequency Division Multiplexing (DFT-S-OFDM) uplink cooperative system, multiple carrier frequency offsets (MCFO), arising from the nodes' separate oscillators and Doppler spreads, drastically degrade the performance of the receiver. To solve the problem, this letter proposes an efficient MCFO compensation method which fully exploits the diversity gain of space frequency block coded (SFBC) and the characteristic of inter-carrier interference (ICI). Moreover, the bit error ratio (BER) lower bound of the proposed algorithm is theoretically derived. Simulation results validate the theoretical analysis and demonstrate that the proposed MCFO compensation method can achieve robust BER performance in a wide range of MCFO in the multipath Rayleigh fading channel.
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  • Yeomyung YOON, Hyogon KIM
    Article type: LETTER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 290-292
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In the IEEE 802.11p WAVE system, applications can directly control the transmission power of the messages sent in WAVE Short Message Protocol (WSMP). This feature enables the vehicles to control the transmission range based on the application requirements and/or the vehicle density. Seemingly straightforward, however, the distributed power control between vehicles can easily go awry. Unless carefully coordinated, the power assignments can irrevocably deviate from the vehicle density pattern. In this letter, we first show that such anomaly happens for a straightforward power control where the power level reacts to the number of messages heard from ambient vehicles. Then in order to resolve the anomaly, we propose an application layer scheme that adapts the WSMP transmission power so that the power assignments precisely reflect the vehicle density pattern.
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  • Euisin LEE, Soochang PARK, Hosung PARK, Sang-Ha KIM
    Article type: LETTER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 293-296
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Quantity-based event reliability protocols have been proposed for reliable event detection in wireless sensor networks. They support the event reliability by achieving the desired number of data packets successfully transmitted from sensor nodes sensing an event to a sink by controlling the transport process. However, since many data collisions and buffer overflows frequently happen due to data congestions on limited data delivery paths from an event to a sink, the quantity-based event reliability protocols are hard to achieve the desired number due to lost data packets. Thus, this letter proposes a Quality-based Event Reliability Protocol (QERP) utilizing a property that the data packets from sensor nodes have different Contribution Degree (CD) values for event detection according to their environmental conditions. QERP selects sensor nodes to forward their data packets according to CD, and differentially transports the data packets by CD-based buffer management and load balancing.
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  • Taehong KIM, Daeyoung KIM, Chong Poh KIT
    Article type: LETTER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 297-301
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    For wireless sensor networks in which resources are limited and network topology dynamically changes, we propose the one-hop neighbor based broadcast scheduling (ONBS) algorithm to provide reliable delivery service of broadcast packets. The proposed algorithm reduces the scheduling overhead by allowing each joining node to decide its broadcast schedule based on only its one-hop neighbor information in an on-line and distributed manner. Also, once the broadcast schedule is decided, it is not changed to accommodate a newly joining node in order to prevent the consecutive changes of existing schedules. The network simulation results show that the proposed algorithm provides low latency and high reachability despite low overhead and on-line algorithm design.
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  • Yuehuai MA, Youyun XU, Jin-Long WANG
    Article type: LETTER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 302-306
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    We consider the problem of transmit power and bit rate allocation for OFDM based cognitive radio systems. An efficient allocation algorithm which mainly consists of two steps is proposed to maximize the sum rate of secondary users. In the first step of the algorithm, original nonlinear problem is converted to a convex problem which is solved by dual methods, and in the second step the final resource allocation results is obtained via iterative power rescale operation. Numerical results show the effectiveness of the proposed algorithm.
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  • Soochang PARK, Euisin LEE, Min-Sook JIN, Sang-Ha KIM
    Article type: LETTER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 307-310
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In large-scale wireless sensor networks, in order to support group mobility of mobile sinks, this letter proposes a novel strategy for energy-efficient and robust data dissemination to the sinks based on cluster-based communication. The novel strategy is composed of two major mechanisms for reduction of structure construction overhead and routing state maintenance overhead: 1) a virtual infrastructure construction through grid-referred clustering and 2) inter-cluster communication by geographic routing relying on recursive location search. Based on the two major mechanisms, the strategy provides representative location management per sink group, distributed data collection, and per-cluster foot-print chaining in order to effectively adapt the traditional strategy for individual mobile sinks. Simulation results prove the proposed strategy shows better performances in terms of energy efficiency and robustness of data dissemination.
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  • In Hwan LEE, Sooyoung YANG, Sung Ho CHO, Hyung Seok KIM
    Article type: LETTER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 311-314
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    The wireless robotic sensor network (WRSN) is a combination of a mobile robot and wireless sensor networks. In WRSN, robots perform high-level missions such as human rescue, exploration in dangerous areas, and maintenance and repair of unmanned networks in cooperation with surrounding sensor nodes. In such a network, robots should move to the accident site as soon as possible. This paper proposes a distance-aware robot routing (DAR) algorithm, which focuses on how to pick the shortest path for the mobile robot by considering characteristics different from packet routing. Simulations are performed to demonstrate the benefits of using the proposed algorithm.
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  • Yulia PONOMARCHUK, Dae-Wha SEO
    Article type: LETTER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 315-318
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    This paper proposes a lightweight, fast and efficient method for the detection of jamming attacks, interference, and other anomalies in electronic shelf label (ESL) systems and wireless sensor networks (WSNs) with periodic data transmission. The proposed method is based on the thresholding technique, which is applied to selected parameters of traffic and allows discrimination of random failures from anomalies and intrusions. It does not require the installation of additional hardware and does not create extra communication costs; its computational requirements are negligible, since it is based on statistical methods. Herein recommendations are provided for choosing a thresholds type. Extensive simulations, made by Castalia simulator for WSNs, show that the proposed method has superior accuracy compared to existing algorithms.
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  • Xujie LI, Weiwei XIA, Lianfeng SHEN
    Article type: LETTER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 319-321
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    This letter presents an analytical study of the reverse link Erlang capacity of 3G/Ad Hoc Integrated networks. In the considered integrated network, 3G networks and Ad Hoc networks operate over the same frequency band and hence cause interference to each other. The reverse link Erlang capacity is analyzed and discussed in two cases: Ad Hoc networks use and do not use power control.
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  • Sungwook KIM
    Article type: LETTER
    Subject area: Network
    2011 Volume E94.B Issue 1 Pages 322-325
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In this paper, a new adaptive online price control scheme is formalized based on the Stackelberg game model. To provide the most desirable network performance, the proposed scheme consists of two different control mechanisms; user-based and operator-based mechanisms. By using the hierarchical interaction strategy, control decisions in each mechanism act cooperatively and collaborate with each other to satisfy conflicting performance criteria. With a simulation study, the proposed scheme can adaptively adjust the network price to approximate an optimized solution under widely diverse network situations.
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  • Jae-Ho LEE, Jiro HIROKAWA, Makoto ANDO
    Article type: LETTER
    Subject area: Antennas and Propagation
    2011 Volume E94.B Issue 1 Pages 326-329
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Post-wall waveguide with a linear array of reflection-canceling slot pairs and center-feed is designed to cancel the frequency dependent tilting of the main beam and enhance the bandwidth of the antenna boresight gain. The array is fed at the center of the waveguide from the backside; the length of the radiating waveguide is halved and the long line effect in traveling wave operation is suppressed. Authors establish the array design procedure in separate steps to reduce the computational load in the iterative optimization by using Ansoft HFSS simulator. A center-feed linear array as well as an end-feed equivalent with uniform excitation is designed for 25.6GHz operation and measured. The measured performances confirm the design and the advantage of the centre-feed; a frequency independent boresight beam is observed and the frequency bandwidth for 3dB gain reduction is enhanced by 1.5 times compared to the end-feed array.
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  • Hyo Joon EOM, Jin Joo KIM, Jang Soo OCK, Young Seung LEE, Jong Hwa KWO ...
    Article type: LETTER
    Subject area: Electromagnetic Compatibility (EMC)
    2011 Volume E94.B Issue 1 Pages 330-333
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Wave propagation along shielded offset striplines is investigated. The mode-matching method is applied to obtain TE and TM mode dispersion relations in simple series form. Computations are performed to illustrate field propagation characteristics for various offset stripline geometries.
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  • Jung-Hoon KIM, Hye-Kwang KIM, Eugene RHEE, Sung-Il YANG
    Article type: LETTER
    Subject area: Electromagnetic Compatibility (EMC)
    2011 Volume E94.B Issue 1 Pages 334-337
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    This letter presents the field uniformity characteristics of a triangular prism reverberation chamber. A reverberation chamber that generally uses a stirrer to create a uniform electric field inside is an alternative to the semi-anechoic chamber for an electromagnetic compatibility test. To overcome the size and maintenance problems of a stirrer, we propose to replace it with a Quadratic Residue Diffuser which is commonly used in acoustics. To confirm that the diffuser is a valid alternative to the stirrer, a diffuser and an equilateral triangular prism reverberation chamber are designed and fabricated for 2.3-3.0GHz operation. To investigate the field uniformity characteristics by varying the location of the transmitting antenna, both simulation and measurement in the triangular prism reverberation chamber were also done at its two positions, respectively. A commercial program XFDTD 6.2, engaging the finite difference time domain (FDTD), is used for simulation and a cumulative probability distribution, which the IEC 61000-4-21 recommends, is used to evaluate the field uniformity. Both simulation and measurement results show that the field uniformity in the chamber satisfies the international standard requirement of ±6dB tolerance and ±3dB standard deviation, which means that a diffuser can be substituted for a stirrer.
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  • Janghoon YANG, Seunghun JANG, Dong Ku KIM
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 338-341
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    Achievable rates of two different transmission schemes of the two-cell cooperative single user (CSU) multi-input multi-output (MIMO) system with hybrid feedback is studied, in which one cell has the channel state information (CSI) from a mobile station (MS) and the other has channel covariance information (CCI) from it. Disjoint encoding over two base stations (BSs) is shown to achieve the capacity of the CSU-MIMO with hybrid feedback. Rather than finding an optimal transmission scheme, a suboptimal one is proposed such that the transmit directions of the BSs with CSI and CCI are eigen directions of the instantaneous channel correlation matrix and transmit covariance matrix respectively. The optimum power allocation for these transmit directions is derived as an iterative power allocation (IPA) similar to that of the MIMO multiple access channel (MAC) with CCI only. We also propose a simple disjoint power allocation (DPA). The simulation results show that the proposed transmit directions and IPA for the CSU-MIMO with hybrid feedback outperforms the MIMO-MAC with CCI only, while the DPA achieves almost the same performance as the IPA, only when the SNR is low.
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  • Haiming WANG, Xiqi GAO, Bin JIANG, Xiaohu YOU, Wei HONG
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 342-345
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In this letter, an improved channel estimator for MIMO-SCBT systems is proposed. Pilot blocks are constructed using quadriphase complementary sequences (QCSs) which enable both one-sided (OSD) and two-sided (TSD) channel estimation (CE). And OSD-CE and TSD-CE are combined to provide improved performance in frequency-selective fast and slow fading channels and to maintain low-complexity implementations. Simulation results demonstrate the performance merits of the proposed scheme.
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  • Sungho HWANG, Soonchul PARK, Ho-Shin CHO
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 346-349
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In this paper, we mathematically derive a matrix-form solution named resource allocation matrix (RAM) for sub-band allocation in an orthogonal frequency division multiple access (OFDMA) system. The proposed scheme is designed to enhance throughput under a strict user fairness condition such that every user has an equal number of sub-bands per frame. The RAM designates the most preferable sub-band for every user. The proposed scheme is evaluated in terms of throughput and user fairness by comparison with the proportional fairness (PF) scheme and greedy scheme. Numerical results show that the proposed scheme has overwhelming superiority to other schemes in terms of fairness and tight competitive in terms of throughput.
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  • Kyongkuk CHO, Jaeyoon LEE, Dongweon YOON
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 350-354
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In OFDM systems, in-phase and quadrature (I/Q) imbalances generated in the analog front-end introduce inter-channel interference and, consequently, error performance degradation. This letter provides an exact expression involving the two-dimensional (2-D) Gaussian Q-function for the error probability of an arbitrary 2-D modulated OFDM signal with I/Q imbalances. The effects of I/Q imbalances on the distribution of an AWGN and the error performance are analyzed.
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  • Joondoo KIM, Jiwon KANG, Chungyong LEE
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 355-358
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    We propose a multiuser MIMO precoding algorithm that combines the block Tomlinson-Harashima precoding and the vector perturbation (BTHP-VP). BTHP-VP supports multi-stream transmission without additional estimation of each user's effective channel and achieves full spatial diversity. Computer simulations show that BTHP-VP can achieve similar sum rate and improved BER performance compared to the BTHP with maximum likelihood receiver.
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  • Jianxiong HUANG, Taiyi ZHANG, Runping YUAN, Jing ZHANG
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2011 Volume E94.B Issue 1 Pages 359-363
    Published: January 01, 2011
    Released on J-STAGE: January 01, 2011
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    In this letter, the performance of opportunistic-based two-way relaying with beamforming over Nakagami-m fading channels is investigated. We provide an approximate expression for the cumulative distribution function of the end-to-end signal-to-noise ratio to derive the closed-form lower bounds for the outage probability and average bit error probability as well as the closed-form upper bound for the ergodic capacity. Simulation results demonstrate the tightness of the derived bounds.
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