IEICE TRANSACTIONS on Communications

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Advance publication (published online immediately after acceptance)

Volume E90-B No.8  (Publication Date:2007/08/01)

    Special Section on Feature Topics on Latest Trends in Optical Networks
  • FOREWORD Open Access

    Masayuki MURATA  

     
    FOREWORD

      Page(s):
    1889-1889
  • Prospects and Challenges of Multi-Layer Optical Networks Open Access

    Ken-ichi SATO  Hiroshi HASEGAWA  

     
    SURVEY PAPER-Traffic Engineering and Multi-Layer Networking

      Page(s):
    1890-1902

    This paper investigates the prospects and challenges of hierarchical optical path networks. The merits and issues of introducing higher order optical paths are elucidated. State of the art of the key enabling technologies are demonstrated including hierarchical optical cross-connect switch architectures, hierarchical optical path network design algorithms, a newly developed waveband filter, and waveband conversion technologies.

  • Framework for PCE Based Multi-Layer Service Networks

    Mallik TATIPAMULA  Eiji OKI  Ichiro INOUE  Kohei SHIOMOTO  Zafar ALI  

     
    SURVEY PAPER-Traffic Engineering and Multi-Layer Networking

      Page(s):
    1903-1911

    Implementing the fast-responding multi-layer service network (MLSN) functionality will allow the IP/MPLS service network logical topology and Optical Virtual Network topology to be reconfigured dynamically according to the traffic pattern on the network. Direct links can be created or removed in the logical IP/MPLS service network topology, when either extra capacity in MLSN core is needed or existing capacity in core is no longer required. Reconfiguring the logical and virtual network topologies constitute a new manner by which Traffic Engineering (TE) can solve or avoid network congestion problems and service degradations. As both IP and optical network layers are involved, this is called Multi-layer Traffic Engineering. We proposed border model based MLSN architecture in [5]. In this paper, we define the realization of Multi-Layer TE functions using Path Computation Element (PCE) for Border model based MLSN. It defines nodal requirements for multi-layer TE. Requirements of communication protocol between PCC (Path Computation Client) and PCE is introduced. It presents Virtual Network Topology (VNT) scenarios and steps involved along with examples for PCE-based VNT reconfiguration triggered by network failure, where VNT is a set of different layer's network resource accumulation.

  • Latest Trends in Traffic Matrix Modeling and Its Application to Multilayer TE

    Rie HAYASHI  Takashi MIYAMURA  Daisaku SHIMAZAKI  Eiji OKI  Kohei SHIOMOTO  

     
    SURVEY PAPER-Traffic Engineering and Multi-Layer Networking

      Page(s):
    1912-1921

    We survey traffic matrix models, whose elements represent the traffic demand between source-destination pair nodes. Modeling the traffic matrix is useful for multilayer Traffic Engineering (TE) in IP optical networks. Multilayer TE techniques make the network so designed flexible and reliable. This is because it allows reconfiguration of the virtual network topology (VNT), which consists of a set of several lower-layer (optical) paths and is provided to the higher layer, in response to fluctuations (diurnal) in traffic demand. It is, therefore, important to synthetically generate traffic matrices as close to the real ones as possible to maximize the performance of multilayer TE. We compare several models and clarify their applicability to VNT design and control. We find that it is difficult in practice to make an accurate traffic matrix with conventional schemes because of the high cost for data measurement and the complicated calculations involved. To overcome these problems, we newly introduce a simplified traffic matrix model that is practical; it well mirrors real networks. Next, this paper presents our developed server, the IP Optical TE server. It performs multilayer TE in IP optical networks. We evaluate the effectiveness of multilayer TE using our developed IP Optical server and the simplified traffic matrix. We confirm that multilayer TE offers significant CAPEX savings. Similarly, we demonstrate basic traffic control in IP optical networks, and confirm the dynamic control of the network and the feasibility of the IP Optical TE server.

  • On Constraints for Path Computation in Multi-Layer Switched Networks

    Bijan JABBARI  Shujia GONG  Eiji OKI  

     
    SURVEY PAPER-Traffic Engineering and Multi-Layer Networking

      Page(s):
    1922-1927

    This paper considers optical transport and packet networks and discusses the constraints and solutions in computation of traffic engineering paths. We categorize the constraints into prunable or non-prunable classes. The former involves a simple metric which can be applied for filtering to determine the path. The latter requires a methodic consideration of more complicated network element attributes. An example of this type of constraints is path loss in which the metric can be evaluated only on a path basis, as opposed to simply applying the metric to the link. Another form of non-prunable constraint requires adaptation and common vector operation. Examples are the switching type adaptation and wavelength continuity, respectively. We provide possible solutions to cases with different classes of constraints and address the problem of path computation in support of traffic engineering in multi-layer networks where a set of constrains are concurrently present. The solutions include the application of channel graph and common vector to support switching type adaptation and label continuity, respectively.

  • Latest Trends in Generalized Multi-Protocol Label Switching Standardization

    Tomonori TAKEDA  Adrian FARREL  

     
    SURVEY PAPER-Standard and Interoperability

      Page(s):
    1928-1935

    This paper presents the latest trends in Generalized Multi-Protocol Label Switching (GMPLS) standardization within the Internet Engineering Task Force (IETF). GMPLS, a suite of control and management plane protocols, represents an extension of MPLS to cover any connection-oriented technology, such as packet (or MPLS), Time Division Multiplexing (TDM), lambda and fiber. GMPLS allows automated network operations, distributed at the network equipment level, with multi-vendor and multi-layer interoperability. As such, it is expected that GMPLS will enable control and management of the transport network by standardized mechanisms, rather than proprietary management systems and interfaces. In addition, GMPLS offers opportunities to integrate control and management of multiple network layers. The basic suite of GMPLS protocols, namely signaling, routing and link management, has been already standardized, and has been shown to be stable and functional through several years of testing and early deployments. Now carriers are looking at how they can leverage the protocols to realize revenue and activate advanced services. Accordingly, discussion in the IETF has shifted to how to apply GMPLS protocols to support various scenarios and use cases. After briefly reviewing GMPLS basics, this paper presents the latest trends in GMPLS standardization, with a focus on deployment strategies, service aspects, and operation and management.

  • GMPLS Interoperability Tests in Kei-han-na Info-Communication Open Laboratory on JGN II Network

    Satoru OKAMOTO  Wataru IMAJUKU  Tomohiro OTANI  Itaru NISHIOKA  Akira NAGATA  Mikako NANBA  Hideki OTSUKI  Masatoshi SUZUKI  Naoaki YAMANAKA  

     
    SURVEY PAPER-Standard and Interoperability

      Page(s):
    1936-1943

    Generalized Multi-protocol Label Switching (GMPLS) technologies are expected a key technology that creates high-performance Internet backbone networks. There were many GMPLS interoperability trials. However, most of them reported the successful results only. How to set up a trial network and how to test it was generally not discussed. In this paper, as a kind of tutorial, detailed GMPLS field trials in the National Institute of Information and Communications Technology (NICT) Kei-han-na Info-Communication Open Laboratory, Interoperability Working Group (WG) are reported. The interoperability WG is aiming at the leading edge GMPLS protocol based Inter-Carrier Interface that utilizes wide-bandwidth, cost-effective photonic technology to implement IP-centric managed networks. The interoperability WG is a consortium for researching the GMPLS protocol and advancing a de facto standard in this area. Its experimental results, new ideas, and protocols are submitted to standardization bodies such as the International Telecommunications Union-Telecommunication standardization sector (ITU-T), the Internet Engineering Task Force (IETF), and the Optical Internetworking Forum (OIF). This paper introduces the activities of the interoperability WG; they include a nationwide GMPLS field trial using the JGN II network with multi-vendor, multi-switching-capable equipment and a GMPLS multi routing area trial that used a multi-vendor lambda-switching-capable network.

  • Optical Networks Functional Evolution and Control Technologies

    Peter SZEGEDI  Tomasz GAJEWSKI  Wataru IMAJUKU  Satoru OKAMOTO  

     
    SURVEY PAPER-Standard and Interoperability

      Page(s):
    1944-1951

    In this paper the current trends in the optical networking including the physical components, technologies and control architectures are discussed. The possible interaction schemes and implementation models of the automatic communication between applications and network as well as between ASON/GMPLS based network domains are proposed. Finally, the related research activities based on simulation results of control plane dimensioning are illustrated and real test bed experiments on OIF worldwide interoperability demonstration and the ongoing European IST project MUPBED are disseminated.

  • GMPLS Based Survivable Photonic Network Architecture

    Wataru IMAJUKU  Takuya OHARA  Yoshiaki SONE  Ippei SHAKE  Yasunori SAMESHIMA  Masahiko JINNO  

     
    SURVEY PAPER-Protection and Restoration

      Page(s):
    1952-1959

    The objective of this paper is to survey the Generalized Multi-Protocol Label Switching (GMPLS) based recovery technology for optical transport networks. This paper introduces standardization activities of the GMPLS based recovery technology in the Internet Engineering Task Force (IETF), and recent progress of related experiments. In addition, this paper extracts requirements for the GMPLS based recovery technology through the evaluation of existing network elements, which can be client nodes of the optical transport networks. The results of field evaluations on the GMPLS based recovery technology are also introduced in this paper. Then, this paper addresses the issues for future deployment of the GMPLS based recovery technology for the optical transport networks.

  • A Challenge to Access/Backbone Integrated Network

    Hironari MATSUDA  Takuya KAMINOGOU  Tadahiko YASUI  

     
    SURVEY PAPER-Systems and Technologies

      Page(s):
    1960-1967

    An integration of the access/backbone network is expected to become indispensable in the future. We analyze the current and future optical networks and we describe the promising technologies. GMPLS architecture in backbone networks and WDM PON architecture in access networks will play the most important roles. We overview recent studies on the access/backbone integrated network to achieve guaranteed QoS. We also describe the developed system architecture as a milestone toward the access/backbone integrated network.

  • Multiple-Length Variable-Weight Optical Orthogonal Codes for Supporting Multirate Multimedia Services in Optical CDMA Networks

    Nasaruddin  Tetsuo TSUJIOKA  

     
    SURVEY PAPER-Systems and Technologies

      Page(s):
    1968-1978

    Future optical code division multiple access (CDMA) networks should be designed for multirate and fully integrated multimedia services. In the conventional schemes, multilength optical orthogonal codes (OOCs) are designed to support multirate systems, while variable-weight OOCs are designed to support differentiated quality of service (QoS) for multimedia applications. In this paper, a novel class of optical signature codes; multiple-length variable-weight optical orthogonal codes (MLVW-OOC) is proposed for supporting multirate and integrated multimedia services in optical CDMA networks. The proposed MLVW-OOC has features that are easy to construct variable-weight codes and expanded to multiple-length codes. A construction method for designing MLVW-OOCs up to three levels of codes is discussed. The designed MLVW-OOCs can support differentiated requirements on data rates and QoS for several types of services in the networks. A code analysis for obtaining the value of cross-correlation constraints or multiple access interference (MAI) computation for several levels of codes is also suggested. The cross-correlation constraints of the proposed codes are better than the conventional codes such as multilength OOCs. Finally, the bit error probability performance of the two-level MLVW-OOC is evaluated analytically. The results show that the proposed MLVW-OOC can provide differentiated bit error probability performances for several combinations of data rates and QoS.

  • Regular Section
  • A Novel Elliptic Curve Dynamic Access Control System

    Jyh-Horng WEN  Ming-Chang WU  Tzer-Shyong CHEN  

     
    PAPER-Fundamental Theories for Communications

      Page(s):
    1979-1987

    This study employs secret codes and secret keys based on the elliptic curve to construct an elliptic curve cryptosystem with a dynamic access control system. Consequently, the storage space needed for the secret key generated by an elliptic curve dynamic access control system is smaller than that needed for the secret key generated by exponential operation built on the secure filter (SF) dynamic access control system. Using the elliptic curve to encrypt/decrypt on the secure filter improves the efficiency and security of using exponential operation on the secure filter in the dynamic access control system. With the proposed dynamic elliptic curve access control system, the trusted central authority (CA) can add/delete classes and relationships and change the secret keys at any time to achieve an efficient control and management. Furthermore, different possible attacks are used to analyze the security risks. Since attackers can only obtain the general equations for the elliptic curve dynamic access control system, they are unable to effectively perform an elliptic curve polynomial (ECP) conversion, or to solve the elliptic curve discrete logarithm problem (ECDLP). Thus, the proposed elliptic curve dynamic access control system is secure.

  • Construction of 16-QAM and 64-QAM OFDM Codes with Low PAPR and Large Euclidean Distance

    Houshou CHEN  Hsinying LIANG  

     
    PAPER-Fundamental Theories for Communications

      Page(s):
    1988-1996

    This paper considers reduction of the peak-to-average power ratio (PAPR) of M-quadrature amplitude modulation (QAM) signals in orthogonal frequency division multiplexing (OFDM) systems. It is known that a 16-QAM or 64-QAM constellation can be written as the vector sum of two or three QPSK constellations respectively. We can then use the Golay complementary sequences over Z4 to construct 16-QAM or 64-QAM OFDM sequences with low PAPR. In this paper, we further examine the squared Euclidean distance of these M-QAM sequences and their variations. Our goal here is to combine the block coded modulation (BCM) and Golay complementary sequences to trade off the PAPR, the code rate, and the squared Euclidean distance of M-QAM OFDM signals. In particular, some 16-QAM and 64-QAM OFDM sequences with low PAPR and large squared Euclidean distance are presented.

  • Adaptive Decision Feedback Channel Estimation with Periodic Phase Correction for Frequency-Domain Equalization in DS-CDMA Mobile Radios

    Le LIU  Fumiyuki ADACHI  

     
    PAPER-Transmission Systems and Transmission Equipment for Communications

      Page(s):
    1997-2005

    Recently, the decision feedback channel estimation based on the minimum mean square error criterion (DF-MMSE-CE) using a fixed DF filter coefficient has been proposed to improve the channel estimation accuracy for DS-CDMA with frequency-domain equalization (FDE). In this paper, we propose adaptive DF (ADF)-MMSE-CE, in which the DF filter coefficient is adapted to changing channel conditions based on a recursive least square (RLS) algorithm. Furthermore, the channel estimate is phase corrected upon the reception of the periodically inserted pilot chip blocks. The average BER performance of DS-CDMA with MMSE-FDE using ADF-MMSE-CE is evaluated by computer simulation in a frequency-selective Rayleigh fading channel and the simulation results show that our proposed scheme is very robust against fast fading.

  • Low Complexity Resource Allocation Algorithm by Multiple Attribute Weighing and User Ranking for OFDMA Systems

    Maduranga LIYANAGE  Iwao SASASE  

     
    PAPER-Transmission Systems and Transmission Equipment for Communications

      Page(s):
    2006-2015

    We propose an effective subcarrier allocation scheme for multiuser orthogonal frequency division multiple access (OFDMA) system in the downlink transmission with low computational complexity. In the proposed scheme, by taking multiple attributes of a user's channel, such as carrier gain decrease rate and variation from the mean channel gain of the system, to determine a rank for the user, subcarriers are then allocated depending on the individual user's rank. Different channel characteristics are used to better understand a user's need for subcarriers and hence determine a priority for the user. We also adopt an attribute weighing scheme to enhance the performance of the proposed scheme. The scheme is computationally efficient, since it avoids using iterations for the algorithm convergence and also common water-filling calculations that become more complex with increasing system parameters. Low complexity is achieved by allocating subcarriers to users depending on their determined rank. Our proposed scheme is simulated in comparison with other mathematically efficient subcarrier allocation schemes as well as with a conventional greedy allocation scheme. It is shown that the proposed method demonstrates competitive results with the simulated schemes.

  • Reconfigurable Optical Add/Drop Multiplexer with 8.0 dB Net Gain Using Dual-Pass Amplified Scheme

    Shien-Kuei LIAW  Ming-Hung CHANG  Chun-Jung WANG  Yi-Tseng LIN  

     
    PAPER-Fiber-Optic Transmission for Communications

      Page(s):
    2016-2021

    We propose an N-channel power-compensated reconfigurable optical add/drop multiplexer (ROADM) based on using fiber Bragg gratings (FBGs). Both tunable FBGs and wavelength-fixed FBGs are used in this ROADM. By using the dual-pass amplification scheme with two pieces of erbium doped fibers, an 8.0 dB optical net gain has been achieved with a gain variation less than 0.5 dB for each add/drop/pass-through channel. System performance was studied for a four-WDM-channel 10 Gb/s100-km lightwave transmission trial network and bit error rate of 10-9 is observed for the 50 km added signal, 100 km pass-through signal and 50 km dropped signal at -18.3, -19.4 and -18.9 dBm received power, respectively. Only 1.1 dB of power penalty was observed compared to the back-to-back transmission.

  • Co-DRR: An Integrated Uplink and Downlink Scheduler for Bandwidth Management over Wireless LANs

    Huan-Yun WEI  Ching-Chuang CHIANG  Ying-Dar LIN  

     
    PAPER-Network

      Page(s):
    2022-2033

    Bandwidth management over wired bottleneck links has been an effective way to utilize network resources. For the rapidly emerging IEEE 802.11b Wireless LAN (WLAN), the limited WLAN bandwidth becomes a new bottleneck and requires bandwidth management. Most possible existing solutions only exclusively focus on optimizing multimedia traffic, pure downlink or pure uplink fairness, or are incompatible with IEEE 802.11b. This study proposes a cooperative deficit round robin (co-DRR), an IEEE 802.11b-compatible host-based fair scheduling algorithm based on the deficit round robin (DRR) and distributed-DRR (DDRR) schemes, to make the uplink and downlink quantum calculations cooperate to simultaneously control uplink and downlink bandwidth. Co-DRR uses the standard PCF mode to utilize the contention-free period to compensate for the unfairness in the contention period. Numerical results demonstrate that: co-DRR can scale up to 100 mobile hosts even under high bit error rate (0.0001) while simultaneously achieving uplink/downlink long-term fairness (CoV<0.01) among competing mobile hosts.

  • Asymmetric Attribute Aggregation in Hierarchical Networks

    Lei LEI  Yuefeng JI  Lin GUO  

     
    PAPER-Network

      Page(s):
    2034-2045

    To achieve scalability and security, large networks are often structured hierarchically as a collection of domains. In hierarchical networks, the topology and QoS parameters of a domain have to be first aggregated before being propagated to other domains. However, topology aggregation may distort useful information. Although spanning tree aggregation can perfectly encode attribute information of symmetric networks, it can not be applied to asymmetric networks directly. In this paper, we propose a spanning tree based attribute aggregation method for asymmetric networks. The time complexity of the proposed method and the space complexity of its resulted aggregated topology are the same with that of the spanning tree aggregation method in symmetric networks. This method can guarantee that the attributes of more than half of the links in the networks are unaltered after aggregation. Simulation results show that the proposed method achieves the best tradeoff between information accuracy and space complexity among the existing asymmetric attribute aggregation methods.

  • A Novel Approach to Supporting Multipoint-to-Point Video Transmission over Wireless Ad Hoc Networks

    CheeOnn CHOW  Hiroshi ISHII  

     
    PAPER-Network

      Page(s):
    2046-2055

    It is predicted that there will be a high demand for video applications in future wireless networks including wireless ad hoc networks. However, supporting video applications over mobile ad hoc networks is more complicated than with other networks due to the lack of support from a preinstalled infrastructure. In this paper, we tackle this problem by adopting the concept of multipoint-to-point video transmission used in wire-line networks. A novel framework designed with features to accommodate the characteristics of ad hoc networks is presented. There are two key features in our proposal. First, Multiple Description Coding (MDC) scheme is used for video coding to reduce the redundancy by avoiding the transmission of duplicate video frames. Second, the routing protocol is expanded to include finding disjoint routes from video sources to the receiver so that a single link breakage or a single intermediate node failure affects transmission from only the minimum number of nodes. Furthermore, the use of disjoint routes also enables the workload to be distributed more evenly within the network. A simulation study was carried out using NS-2 to demonstrate the performance of the proposed mechanism. We show that the proposed mechanism outperforms conventional point-to-point transmission, especially under conditions of high mobility.

  • Mobility-Assisted Relocation for Self-Deployment in Wireless Sensor Networks

    Xiaoling WU  Jinsung CHO  Brian J. D'AURIOL  Sungyoung LEE  

     
    PAPER-Network

      Page(s):
    2056-2069

    Sensor network deployment is very challenging due to the hostile and unpredictable nature of environments. The field coverage of wireless sensor networks (WSNs) can be enhanced and consequently network lifetime can be prolonged by optimizing the sensor deployment with a finite number of mobile sensors. In this paper, we introduce a comprehensive taxonomy for WSN self-deployment in which three sensor relocation algorithms are proposed to match the mobility degree of sensor nodes, particle swarm optimization based algorithm (PSOA), relay shift based algorithm (RSBA) and energy efficient fuzzy optimization algorithm (EFOA). PSOA regards the sensors in the network as a swarm, and reorganizes the sensors by the particle swarm optimization (PSO) algorithm, in the full sensor mobility case. RSBA and EFOA assume relatively limited sensor mobility, i.e., the movement distance is bounded by a threshold, to further reduce energy consumption. In the zero mobility case, static topology control or scheduling schemes can be used such as optimal cluster formation. Simulation results show that our approaches greatly improve the network coverage as well as energy efficiency compared with related works.

  • A Cross-Layer Retransmission Control for Improving TCP Performance in Wireless LAN

    Satoshi OHZAHATA  Shigetomo KIMURA  Yoshihiko EBIHARA  Konosuke KAWASHIMA  

     
    PAPER-Network

      Page(s):
    2070-2080

    In this paper we propose a cross-layer retransmission control for TCP communication over a wireless link. With our proposed control, a retransmission delay for lost packet is reduced, packet losses in the wireless link are eliminated and all packets are delivered in the correct order. No change is required to TCP itself or to the sender. Our proposed method is implemented in a queue between the media access control (MAC) layer and logical link layer in a base station, and is designed to assist local retransmission control in the MAC layer. Computer simulations show that our proposed method can maximally use the bandwidth of the wireless link under high bit error rates conditions with conventional TCP control. The fairness problem of TCP communication between connections with different bit error rates in a wireless link is also improved, and MAC level fairness is also controllable.

  • QoS Control Mechanism Based on Real-Time Measurement of Elephant Flows

    Rie HAYASHI  Takashi MIYAMURA  Eiji OKI  Kohei SHIOMOTO  

     
    PAPER-Network

      Page(s):
    2081-2089

    This proposes a scalable QoS control scheme, called Elephant Flow Control Scheme (EFCS) for high-speed large-capacity networks; it controls congestion and provides appropriate bandwidth to normal users' flows by controlling just the elephant flows. EFCS introduces a sampling packet threshold and drops packets considering flow size. EFCS also adopts a compensation parameter to control elephant flows to an appropriate level. Numerical results show that the sampling threshold increases control accuracy by 20% while reducing the amount of memory needed for packet sampling by 60% amount of memory by packet sampling; the elephant flows are controlled as intended by the compensation parameter. As a result, EFCS provides sufficient bandwidth to normal TCP flows in a scalable manner.

  • Adaptive Orthonormal Random Beamforming and Multi-Beam Selection for Cellular Systems

    Kai ZHANG  Zhisheng NIU  

     
    PAPER-Wireless Communication Technologies

      Page(s):
    2090-2096

    Channel state information (CSI) at transmitter plays an important role for multiuser MIMO broadcast channels, but full CSI at transmitter is not available for many practical systems. Previous work has proposed orthonormal random beamforming (ORBF) [16] for MIMO broadcast channels with partial channel state information (CSI) feedback, and shown that ORBF achieves the optimal sum-rate capacity for a large number of users. However, for cellular systems with moderate number of users, i.e., no more than 64, ORBF only achieves slight performance gain. Therefore, we analyze the performance of ORBF with moderate number of users and total transmit power constraint and show that ORBF scheme is more efficient under low SNR. Then we propose an adaptive ORBF scheme that selects the number of random beams for simultaneous transmission according to the average signal-to-noise ratio (SNR). Moreover, a multi-beam selection (MBS) scheme that jointly selects the number and the subset of the multiple beams is proposed to further improve the system performance for low SNR cases. The simulation results show that the proposed schemes achieve significant performance improvement when the number of users is moderate.

  • Analytical BER Evaluation of ZF Transmit Beamformer with Channel Estimation Error

    Seungjae BAHNG  

     
    PAPER-Wireless Communication Technologies

      Page(s):
    2097-2102

    The minimum mean square error (MMSE) multiple antenna transmission scheme for a code division multiple access (CDMA) system was recently developed by Choi and Perreau [1]. In this paper, we first show that the zero-forcing (ZF) transmit beamformer for multiple antenna CDMA system has the same form as the MMSE beamformer given by Choi and Perreau. We then develop an analytical method to obtain a closed-form expression of the bit error rate (BER) of the ZF transmit beamformer when there are channel estimation errors. The analytical and simulation results show good agreement, and confirm the importance of accurate channel state information (CSI) at the transmitter when using the ZF transmit beamformer.

  • Highly Efficient Sparse Multipath Channel Estimator with Chu-Sequence Preamble for Frequency-Domain MIMO DFE Receiver

    Jeng-Kuang HWANG  Rih-Lung CHUNG  Meng-Fu TSAI  Juinn-Horng DENG  

     
    PAPER-Wireless Communication Technologies

      Page(s):
    2103-2110

    In this paper, a sparse multipath channel estimation algorithm is proposed for multiple-input multiple-output (MIMO) single-carrier systems with frequency-domain decision feedback equalizer (FD-DFE). This algorithm exploits the orthogonality of an optimal MIMO preamble based on repeated, phase-rotated, Chu (RPC) sequences, leading to a dramatic reduction in computation. Furthermore, the proposed algorithm employs an improved non-iterative procedure utilizing the Generalized AIC criterion (GAIC), resulting in further computational saving and performance improvement. The proposed scheme is simulated for 802.16d SCa-PHY and SUI-5 sparse channel model under a 22 spatial multiplexing scenario, with the MIMO FD-DFE as the receiver. The result shows that the channel estimation accuracy is significantly improved, and the performance loss compared to the known channel case is only 0.7 dB at the BER of 10-3.

  • Performance Analysis of Source-Destination ARQ Scheme for Multiroute Coding in Wireless Multihop Networks

    Hiraku OKADA  Masato SAITO  Tadahiro WADA  Kouji OHUCHI  

     
    PAPER-Terrestrial Radio Communications

      Page(s):
    2111-2119

    For reducing bit errors on wireless channels, we have proposed the multiroute coding scheme on multiple routes for wireless multihop networks. In this paper, we introduce ARQ to our multiroute coding scheme. In our multiroute coding scheme, a destination node combines and decodes subpackets which are encoded and divided by a source node. Each intermediate node relays a subpacket, that is, only a part of a packet. Therefore, intermediate nodes cannot detect packet errors, and only a destination node can do so after combining and decoding subpackets. We propose an ARQ scheme between a source node and a destination node. We analyze the proposed ARQ scheme and evaluate the system performance.

  • Improvement of Anti-Collision Performance for the ISO 18000-6 Type B RFID System

    Dae-Ken KWON  Wan-Jin KIM  Hyoung-Nam KIM  

     
    PAPER-Terrestrial Radio Communications

      Page(s):
    2120-2125

    This paper proposes a novel method to suppress tag collision in the ISO 18000-6 type B protocol which is one of the standard protocols of UHF RFID systems. The anti-collision performance in terms of the total identification time is improved by reducing the length of bits and the number of transmission commands required for multi-tag identification in the ISO 18000-6 type B protocol. Simulation results show that the proposed method improves the multi-tag identification time by about 15% over the conventional method, irrespective of the number of tags.

  • A Study on the System Imbalance of the Single-Switch Converter for the Conductive Common Mode Noise Reduction

    Nimit BOONPIROM  Yothin PREMPRANEERACH  Kitti PAITHOONWATANAKIJ  Kraison AUNCHALEEVARAPAN  Shuichi NITTA  

     
    PAPER-Electromagnetic Compatibility(EMC)

      Page(s):
    2126-2137

    This paper reduces system imbalance by replacing the single-switch converter with a synchronized double-switch converter based on two active switches technique and hybrid balance technique, including active balance and passive balance for common mode noise reduction. The system balance is experimentally evaluated by the common mode rejection ratio (CMRR). Finally, examples show that the CMRR of the single-switch converter is improved from 1.67 dB to 32.04 dB when the double-converter with two active switches technique is applied and to 41.5 dB when the double-switch converter with hybrid balance technique is applied.

  • A Study on Electromagnetic Wave Absorber for W-Band Radars Using Permalloy

    Dong Il KIM  Chang-Mook CHOI  Rui LI  Dae Hee LEE  

     
    PAPER-Electromagnetic Compatibility(EMC)

      Page(s):
    2138-2142

    In this paper, we use Permalloy and CPE (Permalloy: CPE=70:30 wt.%) to fabricate the electromagnetic (EM) wave absorber for W-band radars. The EM wave absorption abilities at different thicknesses were simulated using material properties of the EM wave absotber, and an EM wave absorber was manufactured based on the simulated design. The comparisons of simulated and measured results show good agreement. Measurements show that a 1.15 mm thick EM wave absorber has absorption ability higher than 18 dB at 94 GHz for missile guidance radars, and a 1.4 mm EM wave absorber has absorption ability higher than 20 dB at 76 GHz for collision-avoidance radars.

  • A Recursive Data Least Square Algorithm and Its Channel Equalization Application

    Jun-Seok LIM  Jea-Soo KIM  Koeng-Mo SUNG  

     
    LETTER-Fundamental Theories for Communications

      Page(s):
    2143-2146

    Using the recursive generalized eigendecomposition method, we develop a recursive form solution to the data least squares (DLS) problem in which the error is assumed to lie in the data matrix only. We apply it to a linear channel equalizer. Simulations shows that the DLS-based equalizer outperforms the ordinary least squares-based one in a channel equalization problem.

  • Speech Enhancement by Overweighting Gain with Nonlinear Structure in Wavelet Packet Transform

    Sung-il JUNG  Younghun KWON  Sung-il YANG  

     
    LETTER-Fundamental Theories for Communications

      Page(s):
    2147-2150

    A speech enhancement method is proposed that can be implemented efficiently due to its use of wavelet packet transform. The proposed method uses a modified spectral subtraction with noise estimation by a least-squares line method and with an overweighting gain per subband with nonlinear structure, where the overweighting gain is used for suppressing the residue of musical noise and the subband is used for applying the weighted values according to the change of signals. The enhanced speech by our method has the following properties: 1) the speech intelligibility can be assured reliably; 2) the musical noise can be reduced efficiently. Various assessments confirmed that the performance of the proposed method was better than that of the compared methods in various noise-level conditions. Especially, the proposed method showed good results even at low SNR.

  • Low Complexity Encoding Based on Richardson's LDPC Codes

    Hyunseuk YOO  Chang Hui CHOE  Moon Ho LEE  

     
    LETTER-Fundamental Theories for Communications

      Page(s):
    2151-2154

    The key weakness of Low-Density Parity Check codes is the complexity of the encoding scheme. The generator matrices can be made by Gaussian elimination of parity check matrices for normal block codes. Richardson succeeded in making parity bits from parity check matrices by the low density computation. In this letter, we focus on the execution of numerical experiments which show that even if the matrix D, which is the part of the Richardson's LDPC matrix, is restricted, proposed LDPC codes is lower complexity than Richardson's LDPC codes. The constraint of D results in reducing complexity from O(n + g2) to O(n) due to the omission of computing inverse matrices of φ and T in Richardson's encoding scheme. All the sub-matrices in parity check matrix are composed of Circulant Permutation Matrices based on Galois Fields.

  • Distribution of the Node Degree for Wireless Ad Hoc Networks in Shadow Fading Environments

    Chih-Cheng TSENG  Hsuan-Tsang CHEN  Kwang-Cheng CHEN  

     
    LETTER-Network

      Page(s):
    2155-2158

    Probability distribution of the node degree has long been regarded as one of the important metrics to characterize the wireless ad hoc networks. However, there is no exact formulation for this probability distribution when shadow fading effects are considered. In this letter, by deriving the conditional probability of the node degree and the joint distribution of the distances between nodes and a randomly selected reference node (RSRN), we show that the probability distribution of the node degree for the wireless ad hoc networks in the shadow fading environments is binomial.

  • Capacity Analysis of Wireless Packet Data Systems with Transmit Diversity in a Correlated Rayleigh Fading Environment

    Myoung-Won LEE  Cheol MUN  Jong-Gwan YOOK  Han-Kyu PARK  

     
    LETTER-Wireless Communication Technologies

      Page(s):
    2159-2162

    A precise analysis of the capacity of a wireless downlink packet data system with a fair scheduler is presented. We assume the use of a transmit diversity scheme is operating at each link under the assumption of spatially correlated Rayleigh fading. Numerical results show that spatial fading correlation of the channel improves the capacity of multiuser diversity by reducing the space diversity gain of transmit diversity in each link.

  • Efficient Traffic Management for Reverse Traffic Channels in High-Speed CDMA Systems

    Woon-Young YEO  Hyejeong LEE  Dong-Ho CHO  

     
    LETTER-Wireless Communication Technologies

      Page(s):
    2163-2167

    We point out the unstable operation of reverse traffic management in the cdma2000 1xEV-DO system, and propose a new rate control scheme that controls the reverse traffic load more precisely. The proposed scheme is modeled as a multidimensional Markov process and compared with the conventional scheme. The analysis results show that the proposed rate control scheme has a lower overload probability and higher reverse link throughput than the conventional one.

  • Efficient Adaptive Transmission Technique for Coded Multiuser OFDMA Systems

    Duho RHEE  Joong Hyung KWON  Ilmu BYUN  Kwang Soon KIM  

     
    LETTER-Wireless Communication Technologies

      Page(s):
    2168-2171

    In previous literature on adaptive transmission in multiuser OFDMA systems, only uncoded case or capacity (coded with infinite length of codeword) has been considered. In this paper, an adaptive transmission algorithm for coded OFDMA systems with practical codeword lengths is investigated. Also, in order to keep the feedback overhead within a practical range, a two-step partial CQI scheme is adopted, which has both better performance and reduced feedback overhead compared to conventional partial CQI schemes. By allowing a long codeword block across all allocated sub-bands with appropriate power and modulation order allocation rather than using short codeword blocks to each sub-band, high coding gain can be obtained, which leads to performance improvement.

  • Low Peak-to-Minimum Power Ratio Transmission Scheme for Coordinate Interleaved Orthogonal Design with Two Transmit Antennas over Time-Selective Fading Channels

    Hoojin LEE  Edward J. POWERS  

     
    LETTER-Wireless Communication Technologies

      Page(s):
    2172-2174

    Recently, space-time block codes (STBCs) obtained from coordinate interleaved orthogonal designs (CIODs) have attracted considerable attention, due to the advantages of full-diversity transmission and single-symbol decodability. In this letter, we design a novel STBC from CIOD for two transmit antennas. The proposed code guarantees full-diversity and full-rate along with low peak-to-minimum power ratio (PMPR). Furthermore, in contrast to the existing Alamouti code, the performance of the proposed code is not degraded even in severely time-selective fading channels.

  • Blind Subspace-Based CFO Estimation via Polynomial Rooting for MC-CDMA Systems

    Chiao-Chan HUANG  Ann-Chen CHANG  Ing-Jiunn SU  

     
    LETTER-Wireless Communication Technologies

      Page(s):
    2175-2178

    In this letter, we present a blind carrier frequency offset (CFO) estimator by exploiting the subspace-based technique for multicarrier-code division multiple access (MC-CDMA) systems. Relative high accuracy and low-complexity to the CFO estimation can be achieved by rooting a polynomial. Simulation results are provided for illustrating the effectiveness of the proposed blind polynomial rooting estimator.

  • Compact and Broadband Circularly Polarized Microstrip Antenna with Ring-Slot on Ground Plane

    Masataka YASUKAWA  

     
    LETTER-Antennas and Propagation

      Page(s):
    2179-2181

    For a microstrip antenna (MSA) with a ring-shaped slot on formed on the ground plane, downsizing the microstrip patch and expanding the circularly polarized bandwidth have been achieved successfully. The dimensions of the patch are 6.8 mm7.4 mm and the minimum axial ratio (AR) of 0.6 dB is obtained at 6.1 GHz. In addition, its AR is less than 3 dB at the relative bandwidth of 3.5%. The bandwidth of the proposed MSA is twice that of conventional single-feeding circularly polarized MSAs; however, its size is only half that of conventional MSAs.

  • A Novel Approach to a Robust a Priori SNR Estimator in Speech Enhancement

    Yun-Sik PARK  Joon-Hyuk CHANG  

     
    LETTER-Multimedia Systems for Communications

      Page(s):
    2182-2185

    This paper presents a novel approach to single channel speech enhancement in noisy environments. Widely adopted noise reduction techniques based on the spectral subtraction are generally expressed as a spectral gain depending on the signal-to-noise ratio (SNR) [1]-[4]. As the estimation method of the SNR, the well-known decision-directed (DD) estimator of Ephraim and Malah efficiently is known to reduces musical noise in noise frames, but the a priori SNR, which is a crucial parameter of the spectral gain, follows the a posteriori SNR with a delay of one frame in speech frames [5]. Therefore, the noise suppression gain using the delayed a priori SNR, which is estimated by the DD algorithm matches the previous frame rather than the current one, so after noise suppression, this degrades the performance of a noise reduction during abrupt transient parts. To overcome this artifact, we propose a computationally simple but effective speech enhancement technique based on the sigmoid type function to adaptively determine the weighting factor of the DD algorithm. Actually, the proposed approach avoids the delay problem of the a priori SNR while maintaining the advantage of the DD algorithm. The performance of the proposed enhancement algorithm is evaluated by the objective and subjective test under various environments and yields better results compared with the conventional DD scheme based approach.

  • Improved Global Soft Decision Using Smoothed Global Likelihood Ratio for Speech Enhancement

    Joon-Hyuk CHANG  Dong Seok JEONG  Nam Soo KIM  Sangki KANG  

     
    LETTER-Multimedia Systems for Communications

      Page(s):
    2186-2189

    In this letter, we propose an improved global soft decision for noisy speech enhancement. From an investigation of statistical model-based speech enhancement, it is discovered that a global soft decision has a fundamental drawback at the speech tail regions of speech signals. For that reason, we propose a new solution based on a smoothed likelihood ratio for the global soft decision. Performances of the proposed method are evaluated by subjective tests under various environments and show better results compared with the our previous work.

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