IEICE Transactions on Communications
Online ISSN : 1745-1345
Print ISSN : 0916-8516
Volume E91.B, Issue 10
Displaying 1-50 of 53 articles from this issue
Special Section on Next-Generation Mobile Multimedia Communications
  • Tomoyuki OHYA
    2008 Volume E91.B Issue 10 Pages 3051
    Published: October 01, 2008
    Released on J-STAGE: July 01, 2018
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  • Hye-Soo KIM, Byeong-Doo CHOI, Chun-Su PARK, Sang-Hee PARK, Sung-Jea KO
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3052-3059
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Video transmission over mobile worldwide interoperability for microwave access (WiMAX) can be serverly degraded due to the effect of fading and handoff. In this paper, we propose a channel adaptive error resilience scheme for video transmission over mobile WiMAX. When the channel condition begins to trigger handoff, the current frame is stored in the long-term memory for the forward error correction, and the following frames are encoded by using double motion vectors (MVs) in the sense of multi-hypothesis motion compensation. Even if a whole frame is lost, we can reconstruct the following frames using the stored frame in the long-term memory. However, the error propagation still remains in this forward error resilience method. To refresh the erroneous frames to the decoder, the encoder utilizes the channel adaptive refreshing (CAR). In the CAR, the channel rate is first predicted using channel parameter, a carrier to interference and noise ratio (CINR), and the encoder adaptively determines the number of blocks to be encoded in the intra mode based on the feedback information. Performance evaluations are presented to demonstrate the effectiveness of the proposed method.
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  • Wan Yeon LEE, Kyong Hoon KIM, Young Woong KO
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3060-3068
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    To fully utilize the limited battery energy of mobile electronic devices, we propose an adaptive adjustment method of processing quality for multiple image stream tasks running with widely varying execution times. This adjustment method completes the worst-case executions of the tasks with a given budget of energy, and maximizes the total reward value of processing quality obtained during their executions by exploiting the probability distribution of task execution times. The proposed method derives the maximum reward value for the tasks being executable with arbitrary processing quality, and near maximum value for the tasks being executable with a finite number of processing qualities. Our evaluation on a prototype system shows that the proposed method achieves larger reward values, by up to 57%, than the previous method.
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  • Liang CHEN, Le JIN, Feng HE, Hanwen CHENG, Lenan WU
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3069-3076
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In next generation mobile multimedia communications, different wireless access networks are expected to cooperate. However, it is a challenging task to choose an optimal transmission path in this scenario. This paper focuses on the problem of selecting the optimal access network for multicast services in the cooperative mobile and broadcasting networks. An algorithm is proposed, which considers multiple decision factors and multiple optimization objectives. An analytic hierarchy process (AHP) method is applied to schedule the service queue and an artificial neural network (ANN) is used to improve the flexibility of the algorithm. Simulation results show that by applying the AHP method, a group of weight ratios can be obtained to improve the performance of multiple objectives. And ANN method is effective to adaptively adjust weight ratios when users' new waiting threshold is generated.
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  • Yasufumi MORIOKA, Takeshi HIGASHINO, Katsutoshi TSUKAMOTO, Shozo KOMAK ...
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3077-3084
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Recent rapid development of high-speed wireless access technologies has created mixed WLAN (Wireless LAN) environments where QoS capable APs coexist with legacy APs. To provide QoS guarantee in this mixed WLAN environment, this paper proposes a new AP selection algorithm. The proposed algorithm assigns an STA (Station) to an AP in the overall WLAN service area. Simulation results show improvement in the VoIP performance in terms of an eMOS (estimated Mean Opinion Score) value and the FTP throughput compared to conventional algorithms.
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  • Jong-Ok KIM, Toshiaki YAMAMOTO, Akira YAMAGUCHI, Sadao OBANA
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3085-3094
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    To meet the bandwidth requirements of multimedia services, multipath transmission is a promising solution. In this paper, we consider multi-access networks, where WiMAX and WiFi links are set up at the same time. Multipath transmission suffers from the intrinsic problem of out-of-order packet delivery. This has an adverse impact on TCP and even UDP-based delay sensitive applications. However, multimedia streaming services allow some tolerance to transmission delay. Motivated by this observation, we investigate how to split multimedia flows over heterogeneous links. Wireless link capacity varies widely over time due to dynamic radio conditions. The capacity variations should be promptly reflected in traffic splitting in order to accomplish an equal load-balance. A practical prototype system has been implemented. We have performed extensive measurements from a prototype system. Through practical experimental results, we could verify two major research goals. One is that multimedia splitting can improve the overall network performance (e. g., the permitted multimedia sessions or the aggregated bandwidth) while still keeping an acceptable media quality. The other is an adaptation capability to varying link quality. It has been widely investigated under various radio conditions and different monitoring intervals. It is shown that the adaptive technique is effective under dynamic radio environments.
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  • Yang LI, Dong-Won KUM, Ju-Eun KANG, You-Ze CHO
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3095-3102
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper analyzes the limitations of the multihoming support in the Proxy Mobile IPv6 protocol, then proposes an enhanced multihoming support scheme based on a per-interface address configuration method. The proposed scheme can provide a more flexible multihoming support and also maintain application session continuity during a handoff between two interfaces by using IPv6 extension headers. Plus, flow distribution with filters is also used to realize the advantages of multihoming. Simulation results with the OPNET validate the proposed multihoming support scheme for convergent networks.
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  • Liang XU, Koji YAMAMOTO, Hidekazu MURATA, Susumu YOSHIDA
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3103-3112
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In the present paper, the use of a combination of channel-bonding and multi-channel techniques is proposed to improve the performance of wireless mesh networks (WMNs). It is necessary to increase the network throughput by broadening the bandwidth, and two approaches to effectively utilize the broadened bandwidth can be considered. One is the multi-channel technique, in which multiple separate frequency channels are used simultaneously for information transmission. The other is the channel-bonding technique used in IEEE 802.11n, which joins multiple frequency channels into a single broader channel. The former can reduce the channel traffic to mitigate the effect of packet collision, while the latter can increase the transmission rate. In the present paper, these two approaches are compared and their respective advantages are clarified in terms of the network throughput and delay performance assuming the same total bandwidth and a CSMA protocol. Our numerical and simulation results indicate that under low-traffic conditions, the channel-bonding technique can achieve low delay, while under traffic congestion conditions, the network performance can be improved by using multi-channel technique. Based on this result, the use of a combination of these two techniques is proposed for a WMN, and show that it is better to use a proper channel technique according to the network traffic condition. The findings of the present study also contribute to improving the performance of a multimedia network, which consists of different traffic types of applications.
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  • Jaturong SANGIAMWONG, Kengo YAGYU, Toshihiro SUZUKI
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3113-3121
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper proposes two novel hidden node problem aware routing metrics for wireless local area network (WLAN) mesh networks. To select the path that is least affected by the serious hidden node problem, we propose two routing metrics, MNn and MPCP, that take into account the number of neighboring nodes (Nn) and the packet collision probability (PCP), respectively. The PCP is estimated from neighbor information that is periodically gathered as state announcement packets, which include the transmission time ratio and the neighbor list. Simulation results show that the first proposed MNn routing metric tends to be less effective as the number of WLAN nodes increases, i. e., the mesh network becomes denser. On the other hand, with an acceptable increased in the control overhead in the mesh network due to the neighbor information, the second proposed MPCP routing metric improves the number of allowable concurrent voice over Internet Protocol (VoIP) calls and the user datagram protocol (UDP) data throughput compared to the MNn metric. The MPCP also provides better performance than the other conventional routing metrics, the hop count, and the Airtime proposed in IEEE 802.11s.
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  • Kazuo MORI, Katsuhiro NAITO, Hideo KOBAYASHI
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3122-3131
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper proposes an asymmetric traffic accommodation scheme using a multihop transmission technique for CDMA/FDD cellular communication systems. The proposed scheme exploits the multihop transmission to downlink packet transmissions, which require the large transmission power at their single-hop transmissions, in order to increase the downlink capacity. In these multihop transmissions, vacant uplink band is used for the transmissions from relay stations to destination mobile stations, and this leads more capacity enhancement in the downlink communications. The relay route selection method and power control method for the multihop transmissions are also investigated in the proposed scheme. The proposed scheme is evaluated by computer simulation and the results show that the proposed scheme can achieve better system performance.
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  • Makoto YOSHINO, Kenichiro SATO, Ryoichi SHINKUMA, Tatsuro TAKAHASHI
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3132-3140
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    When the number of users in a service area increases in mobile multimedia services, no individual user can obtain satisfactory radio resources such as bandwidth and signal power because the resources are limited and shared. A solution for such a problem is user-position control. In the user-position control, the operator informs users of better communication areas (or spots) and navigates them to these positions. However, because of subjective costs caused by subjects moving from their original to a new position, they do not always attempt to move. To motivate users to contribute their resources in network services that require resource contributions for users, incentive-rewarding mechanisms have been proposed. However, there are no mechanisms that distribute rewards appropriately according to various subjective factors involving users. Furthermore, since the conventional mechanisms limit how rewards are paid, they are applicable only for the network service they targeted. In this paper, we propose a novel incentive-rewarding mechanism to solve these problems, using an external evaluator and interactive learning agents. We also investigated ways of appropriately controlling rewards based on user contributions and system service quality. We applied the proposed mechanism and reward control to the user-position control, and demonstrated its validity.
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  • Illsoo SOHN, Byong Ok LEE, Kwang Bok LEE
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3141-3148
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Recently, multimedia services are increasing with the widespread use of various wireless applications such as web browsers, real-time video, and interactive games, which results in traffic asymmetry between the uplink and downlink. Hence, time division duplex (TDD) systems which provide advantages in efficient bandwidth utilization under asymmetric traffic environments have become one of the most important issues in future mobile cellular systems. It is known that two types of intercell interference, referred to as crossed-slot interference, additionally arise in TDD systems; the performances of the uplink and downlink transmissions are degraded by BS-to-BS crossed-slot interference and MS-to-MS crossed-slot interference, respectively. The resulting performance unbalance between the uplink and downlink makes network deployment severely inefficient. Previous works have proposed intelligent time slot allocation algorithms to mitigate the crossed-slot interference problem. However, they require centralized control, which causes large signaling overhead in the network. In this paper, we propose to change the shape of the cellular structure itself. The conventional cellular structure is easily transformed into the proposed cellular structure with distributed receive antennas (DRAs). We set up statistical Markov chain traffic model and analyze the bit error performances of the conventional cellular structure and proposed cellular structure under asymmetric traffic environments. Numerical results show that the uplink and downlink performances of the proposed cellular structure become balanced with the proper number of DRAs and thus the proposed cellular structure is notably cost-effective in network deployment compared to the conventional cellular structure. As a result, extending the conventional cellular structure into the proposed cellular structure with DRAs is a remarkably cost-effective solution to support asymmetric traffic environments in future mobile cellular systems.
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  • Yusuke NAKASHIMA, Hosei MATSUOKA, Takeshi YOSHIMURA, Hiroshi MIURA, Se ...
    Article type: PAPER
    2008 Volume E91.B Issue 10 Pages 3149-3156
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Data transmission via audio link on AM radio system is shown to be achievable by using Acoustic OFDM. We employ Acoustic OFDM to embed data onto audio contents that are then broadcast as AM radio signals. We tuned the parameters, and performed experiments. Text data as URL can be delivered to mobile phone through existing MF AM radio system and radios.
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  • Jae-Heung YEOM, Yong-Hwan LEE
    Article type: LETTER
    2008 Volume E91.B Issue 10 Pages 3157-3161
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    The institute of electrical and electronics engineers (IEEE) 802.16e is designed to support a wide range of applications with various quality of service requirements. Since MAP signaling overhead can unacceptably be large for voice traffic, IEEE 802.16e suggests the use of multicast sub-MAPS whose messages are encoded according to the channel condition. In this case, it is desirable for the base station to properly choose a modulation and coding set associated with the channel condition. In this letter, we consider the use of an adaptive modulation coding scheme for the multicast sub-MAPs without explicit information on the channel condition. The proposed scheme can achieve the same MAP coverage as the broadcast MAP while minimizing the signaling overhead. Simulation results show that when it is applied to voice-over-internet protocol (VoIP) services, the proposed scheme can significantly enhance the VoIP capacity.
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Regular Section
  • Lin-Chuan TSAI, Kuo-Chih CHU
    Article type: PAPER
    Subject area: Devices/Circuits for Communications
    2008 Volume E91.B Issue 10 Pages 3162-3165
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In this paper, a new formulation of equal-length three-section open stubs having two zeros located on the unit circle and one zero at z=-1 (θ=π) in the Z-plane is presented. In particular, new filter configurations consisting of equal-length two-section open stubs, cascade lines, open stubs, and three-section open stubs are employed to emulate the discrete-time filters. To examine the validity of our formulation, we realized two discrete-time Chebyshev type II low-pass filters in the form of microstrip lines. The frequency responses of these two filters are measured to validate this new formulation.
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  • Abolfazl GHASSEMI, T. Aaron GULLIVER
    Article type: PAPER
    Subject area: Transmission Systems and Transmission Equipment for Communications
    2008 Volume E91.B Issue 10 Pages 3166-3173
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Partial transmit sequence (PTS) is a well known technique used to reduce the peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) signal. However, it has relatively high complexity due to the computation of multiple inverse fast Fourier transforms (IFFTs). To reduce this complexity, we use intermediate signals within a decimation in frequency (DIF) radix IFFT and propose a new PTS subblocking technique which requires the computation of only partial IFFTs. Performance results are presented which show a PAPR reduction similar to that with other techniques such as original PTS (O-PTS). Further, we show that complexity reduction can be achieved with either low or high radix IFFT algorithms.
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  • Shoji KAKEHASHI, Hiroshi HASEGAWA, Ken-ichi SATO
    Article type: PAPER
    Subject area: Switching for Communications
    2008 Volume E91.B Issue 10 Pages 3174-3184
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper proposes new switch architectures for hierarchical optical path cross-connect (HOXC) systems. The architectures allow incremental expansion of system scale in terms of the number of input/output fiber ports, wavebands, and optical paths per waveband. These features assure the cost-effective introduction of HOXCs even at the outset when traffic volume is not so large. Furthermore the effectiveness of the proposed switch architectures is demonstrated in a comparison with single-layer OXCs (conventional OXCs). The results provide useful criteria for the introduction of HOXCs in terms of hardware scale.
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  • Rie HAYASHI, Eiji OKI, Kohei SHIOMOTO
    Article type: PAPER
    Subject area: Network
    2008 Volume E91.B Issue 10 Pages 3185-3193
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper evaluates three inter-domain redundancy path computation methods based on PCE (Path Computation Element). Some inter-domain paths carry traffic that must be assured of high quality and high reliability transfer such as telephony over IP and premium virtual private networks (VPNs). It is, therefore, important to set inter-domain redundancy paths, i. e. primary and secondary paths. The first scheme utilizes an existing protocol and the basic PCE implementation. It does not need any extension or modification. In the second scheme, PCEs make a virtual shortest path tree (VSPT) considering the candidates of primary paths that have corresponding secondary paths. The goal is to reduce blocking probability; corresponding secondary paths may be found more often after a primary path is decided; no protocol extension is necessary. In the third scheme, PCEs make a VSPT considering all candidates of primary and secondary paths. Blocking probability is further decreased since all possible candidates are located, and the sum of primary and secondary path cost is reduced by choosing the pair with minimum cost among all path pairs. Numerical evaluations show that the second and third schemes offer only a few percent reduction in blocking probability and path pair total cost, while the overheads imposed by protocol revision and increase of the amount of calculation and information to be exchanged are large. This suggests that the first scheme, the most basic and simple one, is the best choice.
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  • Ayumi BANNO, Fumio TERAOKA
    Article type: PAPER
    Subject area: Network
    2008 Volume E91.B Issue 10 Pages 3194-3204
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper proposes a protocol called νLIN6 which supports both network mobility and host mobility in IPv6. There are several proposals to support network mobility and host mobility. Network Mobility (NEMO) Basic Support Protocol has several problems such as pinball routing, large header overhead due to multiple levels of tunneling, and a single point of failure. Optimized NEMO (ONEMO) and Mobile IP with Address Translation (MAT) are solutions to provide route optimization, but they generate a lot of signaling messages at a handover. In νLIN6, packet relay is required only once regardless of the nested level in network mobility while optimal routing is always provided in host mobility. A fixedsized extension header is used in network mobility while there is no header overhead in host mobility. νLIN6 is more tolerant of network failure and mobility agent failure than NEMO Basic Support Protocol. It also allows ordinary IPv6 nodes to communicate with mobile nodes and nodes in the mobile network. We implemented νLIN6 on NetBSD 2.0 Release. Our measurement results showed νLIN6 can provide host mobility and network mobility with low overhead.
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  • Toshiro NUNOME, Shuji TASAKA, Ken NAKAOKA
    Article type: PAPER
    Subject area: Network
    2008 Volume E91.B Issue 10 Pages 3205-3215
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper performs application-level QoS and user-level QoS assessment of audio-video streaming in cross-layer designed wireless ad hoc networks. In order to achieve high QoS at the user-level, we employ link quality-based routing in the network layer and media synchronization control in the application layer. We adopt three link quality-based routing protocols: OLSR-SS (Signal Strength), AODV-SS, and LQHR (Link Quality-Based Hybrid Routing). OLSR-SS is a proactive routing protocol, while AODV-SS is a reactive one. LQHR is a hybrid protocol, which is a combination of proactive and reactive routing protocols. For applicationlevel QoS assessment, we performed computer simulation with ns-2 where an IEEE 802.11b mesh topology network with 24 nodes was assumed. We also assessed user-level QoS by a subjective experiment with 30 assessors. From the assessment results, we find AODV-SS the best for networks with long inter-node distances, while LQHR outperforms AODV-SS for short inter-node distances. In addition, we also examine characteristics of the three schemes with respect to the application-level QoS in random topology networks.
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  • Takahiro MATSUDA, Taku NOGUCHI, Tetsuya TAKINE
    Article type: PAPER
    Subject area: Network
    2008 Volume E91.B Issue 10 Pages 3216-3225
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In this paper, we consider the broadcast storm problem in dense wireless ad hoc networks where interference among densely populated wireless nodes causes significant packet loss. To resolve the problem, we apply randomized network coding (RNC) to the networks. RNC is a completely different approach from existing techniques to resolve the problem, and it reduces the number of outstanding packets in the networks by encoding several packets into a single packet. RNC is a kind of linear network coding, and it is suited to wireless ad hoc networks because it can be implemented in a completely distributed manner. We describe a procedure for implementing the wireless ad hoc broadcasting with RNC. Further, with several simulation scenarios, we provide some insights on the relationship between the system parameters and performance and find that there is the optimal length of coding vectors for RNC in terms of packet loss probability. We also show a guideline for the parameter setting to resolve the broadcast storm problem successfully.
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  • Yasuyuki OKUMURA
    Article type: PAPER
    Subject area: Network
    2008 Volume E91.B Issue 10 Pages 3226-3231
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper proposes an improved dynamic bandwidth allocation algorithm for dual Quality of Service (QoS) classes to maximize the utilization rate of the Resilient Packet Ring (RPR). To achieve dynamic bandwidth allocation for the two QoS classes in the RPR, each node measures the high priority traffic flow and assigns the appropriate bandwidth; the remaining bandwidth is used for low priority traffic. It passes a control frame containing the measured bandwidth of the high priority traffic to the other nodes. Based on the advertised high priority traffic bandwidth, any node that is congested transmits, to the other nodes, a fairness message to fairly allocate the remaining low priority bandwidth. Simulations demonstrate that the proposed algorithm enhances the utilization rate and reduces the delay of high priority frames.
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  • Tetsuya KAWAI, Naoki WAKAMIYA, Masayuki MURATA
    Article type: PAPER
    Subject area: Network
    2008 Volume E91.B Issue 10 Pages 3232-3240
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Wireless sensor networks are expected to become an important social infrastructure which helps our life to be safe, secure, and comfortable. In this paper, we propose design methodology of an architecture for fast and reliable transmission of urgent information in wireless sensor networks. In this methodology, instead of establishing single complicated monolithic mechanism, several simple and fully-distributed control mechanisms which function in different spatial and temporal levels are incorporated on each node. These mechanisms work autonomously and independently responding to the surrounding situation. We also show an example of a network architecture designed following the methodology. We evaluated the performance of the architecture by extensive simulation and practical experiments and our claim was supported by the results of these experiments.
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  • Suhua TANG, Mehdad N. SHIRAZI, Oyunchimeg SHAGDAR, Ryutaro SUZUKI, Sad ...
    Article type: PAPER
    Subject area: Network
    2008 Volume E91.B Issue 10 Pages 3241-3250
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In Mobile Ad hoc Networks (MANET) geographic routing is characterized by local forwarding decision. Links with a long progress are preferred under the greedy forwarding rule. However in a real system long links tend to have a high packet loss rate due to multipath fading. A sub-optimal solution may separately exploit path diversity or rate adaptation. In this paper we study channel efficiency of multi-hop forwarding and try to jointly optimize rate adaptation and forwarder selection in geographic routing by the tradeoff between progress and instantaneous rate. We define a new metric-Bit Transfer Speed (BTS)-as the ratio of the progress made towards the destination to the equivalent time taken to transfer a payload bit. This metric takes overhead, rate and progress into account. Then we propose a packet forwarding scheme that Opportunistically exploits both long Progress and Adaptive Rate (OPAR) by a cross-layer design of routing and MAC. In OPAR each node selects for a packet the forwarder with the highest BTS. The forwarder changes as local topology (progress), packet size (overhead ratio) or channel state (data rate) varies. Simulation results show that compared with the normalized advance (NADV) [7] scheme and contention-based forwarding (CBF) [17] scheme, OPAR has lower packet loss and can effectively reduce channel occupation time by over 30% in the scenario with moderate mobility speeds.
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  • Ruhui ZHANG, Makoto IWATA
    Article type: PAPER
    Subject area: Network Management/Operation
    2008 Volume E91.B Issue 10 Pages 3251-3261
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    The development of network technology reveals the clear trend that mobile devices will soon be equipped with more and more network-based functions and services. This increase also results in more intrusions and attacks on mobile devices; therefore, mobile security mechanisms are becoming indispensable. In this paper, we propose a novel signature matching scheme for mobile security. This scheme not only emphasizes a small resource requirement and an optimal scan speed, which are both important for resource-limited mobile devices, but also focuses on practical features such as stable performance, fast signature set updates and hardware implementation. This scheme is based on the finite state machine (FSM) approach widely used for string matching. An SRAM-based two-level finite state machine (TFSM) solution is introduced to utilize the unbalanced transition distribution in the original FSM to decrease the memory requirement, and to shorten the critical path of the single-FSM solution. By adjusting the boundary of the two FSMs, optimum memory usage and throughput are obtainable. The hardware circuit of our scheme is designed and evaluated by both FPGA and ASIC technology. The result of FPGA evaluation shows that 2,168 unique patterns with a total of 32,776 characters are stored in 177.75KB SelectRAM blocks of Xilinx XC4VLX40 FPGA and a 3.0Gbps throughput is achieved. The result of ASIC evaluation with 180nm-CMOS library shows a throughput of over 4.5Gbps with 132KB of SRAM. Because of the small amount of memory and logic cell requirements, as well as the scalability of our scheme, higher performance is achieved by instantiating several signature matching engines when more resources are provided.
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  • Yoshio KARASAWA, Changarkame VANMANY
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3262-3271
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In order to evaluate the effect of Nakagami-Rice fading on Orthogonal Frequency Division Multiplex (OFDM) signal transmission when the delay profile exceeds the guard interval, a simple prediction model is developed by extending the Equivalent Transmission-Path (ETP) model for Rayleigh fading. The validity of the model is demonstrated by comparing the calculated values of BER to those obtained by computer simulation. Using the newly developed ETP-OFDM model, digital transmission characteristics of the OFDM signal in a multipath environment when the delay profile exceeds the guard interval are shown as a function of K factor, delay spread, guard interval and OFDM symbol period.
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  • Sangho CHOE, Murat UYSAL
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3272-3280
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In this paper, we present and analyze a predictive closedloop power control (CLPC) scheme which employs a comb-type sample arrangement to effectively compensate multiple power control group (PCG) delays over mobile fading channels. We consider both least squares and recursive least squares filters in our CLPC scheme. The effects of channel estimation error, prediction filter error, and power control bit transmission error on the performance of the proposed CLPC method along with competing non-predictive and predictive CLPC schemes are thoroughly investigated. Our results clearly indicate the superiority of the proposed scheme with its improved robustness under non-ideal conditions. Furthermore, we carry out a Monte-Carlo simulation study of a 5×5 square grid cellular network and evaluate the user capacity. Capacity improvements up to 90% are observed for a typical cellular network scenario.
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  • Ki-Hong PARK, Hong-Chuan YANG, Young-Chai KO
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3281-3287
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Transmit diversity systems based on orthogonal space-time block coding (OSTBC) usually suffer from rate loss and power spreading. Proper antenna selection scheme can help to more effectively utilize the transmit antennas and transmission power in such systems. In this paper, we propose a new antenna selection scheme for such systems based on the idea of antenna switching. In particular, targeting at reducing the number of pilot channels and RF chains, the transmitter now replaces the antennas with the lowest received SNR with unused ones if the output SNR of space time decoder at the receiver is below a certain threshold. With this new scheme, not only the number of pilot channels and RF chains to be implemented is decreased, the average amount of feedback information is also reduced. To analyze the performance of this scheme, we derive the exact integral closed form for the probability density function (PDF) of the received SNR. We show through numerical examples that the proposed scheme offers better performance than traditional OSTBC systems using all available transmitting antennas, with a small amount of feedback information. We also examine the effect of different antenna configuration and feedback delay.
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  • Hai LIN, Takeshi NAKAO, Weiming LU, Katsumi YAMASHITA
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3288-3296
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In an orthogonal frequency division multiplexing (OFDM) receiver with direct-conversion architecture, carrier frequency offset (CFO) and direct-current offset (DCO), which cause severe performance degradation, need to be estimated and compensated. Recently, by investigating the subspace of OFDM signal after coarse DCO cancellation using timedomain average, we have proposed a nullspace-based estimator (NSE), for blind CFO and DCO estimation. In this paper, based on an analysis of the cost function of the NSE, we propose a common nullspace based estimator (CNSE). It is shown that by matching the frequency occupation of the received OFDM signal with CFO and DCO, the CNSE can achieve the full performance potential of the NSE. Also, the performance analysis reveals that the CNSE can asymptotically approach the Cramer-Rao bound (CRB) of OFDM CFO estimation in the presence of DCO. Finally the analysis results are confirmed by simulations.
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  • Kiyoshi TAKAHASHI, Takuya TERASAWA, Toshinori TSUBOI
    Article type: PAPER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3297-3306
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    We propose a medium access control (MAC) protocol for real-time applications in one-hop ad-hoc wireless networks. It is a distributed mechanism that takes account of priority and has a bounded packet delay. Nodes use energy signals to contend for the right to access the channel. Nodes, which have a packet to transmit, send energy signals or listen to the channel based on their binary frame. The node that has sent energy signals and has not heard any energy signals wins the right to access the channel. We use two schemes to determine the binary frame: at the beginning of a session, a node determines it based on its priority level and a random number; after successful transmission, based on a count of successful packet transmissions. With the first scheme, in order to reduce contention losses, the nodes that had won the right to access the channel but failed in transmission have priority over the other nodes. With the second scheme, the node that has the largest count, the one that has been waiting the longest, can send a packet without risking collision. The protocol provides higher probability of successful transmission and a limit on maximum packet delay. An analysis of the protocol provides conditions for the protocol to be stable. We evaluate the performance of the proposed protocol using simulations of a network with a mixed population of data and real-time nodes, whose source is constant bit rate (CBR) and a two state Markov on/off process.
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  • Osamu MATSUO, Hirofumi MATSUO, Yoichi ISHIZUKA, Hiroyuki OTA
    Article type: PAPER
    Subject area: Energy in Electronics Communications
    2008 Volume E91.B Issue 10 Pages 3307-3312
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper presents the analysis of a new multi-oscillated current resonant type DC-DC converter. Current resonant converters have several remarkable features such as high efficiency, small size, low cost and low noise, and are frequently employed in many portable electronic systems such as personal computers, cellular phones and flat panel displays. The current resonant type converter generally employs pulse frequency modulation for constant voltage control in the output. For this reason, the magnetizing current through the converter not only causes a power loss under a light load, but also a loss during stand-by. Therefore, this type of converter has a problem in that the required smaller size cannot be achieved, because an auxiliary source is necessary for stand-by. In order to solve these problems, a new current resonant type power supply is proposed in which two driving methods are employed. In these driving methods, one MOSFET as a main switch is driven by an auxiliary winding of the transformer and another MOSFET as a main switch is driven by the driving IC with a low withstand voltage. Good agreement of the observed and simulated waveforms was confirmed. In addition, eight distinct states and four distinct operating modes, which compose of the sequence of states, were clarified by experimental and simulated analysis.
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  • Gin-Der WU, Pang-Hsuan HUANG
    Article type: PAPER
    Subject area: Multimedia Systems for Communications
    2008 Volume E91.B Issue 10 Pages 3313-3325
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In this paper, we proposed a novel entropy-based image watermarking method in wavelet domain. Unlike traditional entropy, we use the normalized energy instead of the probability which is called energy-based entropy (EBE). Based on EBE, the watermark can be embedded robustly and imperceptibly. In our proposed method, the wavelet-trees are grouped into super-trees. Then each super-tree is also divided into five subblocks. According to the watermark bit state, the EBE of each sub-block will be modified respectively. In an experiment, three images (Lenna, Goldhill and Peppers) are chosen for evaluating the performance. The PSNR of these watermarked images are 44.039, 43.51 and 43.67. Compared with Wang et al. [18], it greatly increases the PSNR, by about 5.8, 4.8 and 3.9 dB respectively. For the consideration of the capacity for embedding, the maximum number of watermark bits is also increased. The experimental results show that the proposed entropy-based watermarking method performs well in JPEG compression, filtering (Gaussian filter, median filter and sharpen) and geometrical attacks (pixel shift and rotation). In addition, it is also very robust to against the multiple watermark attack.
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  • Kye-Hwan LEE, Sang-Ick KANG, Deok-Hwan KIM, Joon-Hyuk CHANG
    Article type: LETTER
    Subject area: Fundamental Theories for Communications
    2008 Volume E91.B Issue 10 Pages 3326-3329
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    We propose an effective voice-based gender identification method using a support vector machine (SVM). The SVM is a binary classification algorithm that classifies two groups by finding the voluntary nonlinear boundary in a feature space and is known to yield high classification performance. In the present work, we compare the identification performance of the SVM with that of a Gaussian mixture model (GMM)-based method using the mel frequency cepstral coefficients (MFCC). A novel approach of incorporating a features fusion scheme based on a combination of the MFCC and the fundamental frequency is proposed with the aim of improving the performance of gender identification. Experimental results demonstrate that the gender identification performance using the SVM is significantly better than that of the GMM-based scheme. Moreover, the performance is substantially improved when the proposed features fusion technique is applied.
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  • MD. NOORUZZAMAN, Yuichi HARADA, Osanori KOYAMA, Yutaka KATSUYAMA
    Article type: LETTER
    Subject area: Fiber-Optic Transmission for Communications
    2008 Volume E91.B Issue 10 Pages 3330-3333
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    A stackable reconfigurable optical add/drop multilplexer has been proposed to give wavelength transparency to IP-over-CWDM networks. It was clarified by experiments that the proposed structure was wavelength transparent.
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  • Intark HAN, Hong-Shik PARK, Man-Soo HAN
    Article type: LETTER
    Subject area: Fiber-Optic Transmission for Communications
    2008 Volume E91.B Issue 10 Pages 3334-3337
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    A fast class-of-service oriented packet scheduling (FCOPS) has a service fairness problem since a credit pool for a service class is initialized at the beginning of a transmission cycle whose starting moment is fixed at a specific ONU. To remedy the service unfairness of FCOPS, we suggest an enhanced class-of-service oriented packet scheduling (ECOPS) that uses a new initialization cycle whose starting moment is fairly distributed to each ONU. Also, ECOPS generates a colorless grant to utilize the resource wastage, when traffic is light and the total sum of grants of an ONU is less than a minimum size. Using simulation, we validate ECOPS as superior to FCOPS in the mean delay and the service fairness.
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  • Taejoon PARK
    Article type: LETTER
    Subject area: Network
    2008 Volume E91.B Issue 10 Pages 3338-3341
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In wireless ad hoc networks, providing an authentication service to verify that the broadcast packet is from the claimed sender without modification, is challenging due mainly to the inherently lossy wireless links. This paper presents a novel Secure and Reliable Broadcasting that reinforces the broadcast authentication with reliability and energy-efficiency capabilities by using the cooperative diversity to superimpose two distinct signals. The proposed protocol achieves significant savings of transmission power and fair assurance of reliability among receivers.
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  • Ann-Chen CHANG, Chun HSU, Ing-Jiunn SU
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3342-3346
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This letter presents an efficient adaptive beamformer to deal with the multipath environments created by signal source scatterings. To improve the performance possible with the fixed forgetting factor, the regular adaptive forgetting factor algorithm is derived and applied to the subarray recursive least squares (RLS) beamforming. Simulations confirm that the proposed scheme has better performance than not only the conventional RLS algorithm but also the subarray RLS and adaptive forgetting factor RLS algorithms.
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  • Xuewen LIAO, Shihua ZHU, Erlin ZENG
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3347-3350
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Multipath energy capture and inter-symbol interference (ISI) are two intractable problems in high-data-rate Ultra-wideband (UWB) systems. To tackle the problems and simplify the receiver, we propose an adaptive interference avoidance scheme based on Pre-RAKE combining technique. The symbol repetition period (SRP) is regarded a changeable parameter in an ordered set to avoid severe interference paths and guarantee high data-rate. The set is known to both the transmitter and receiver. The index of the selected SRP is then sent to the receiver to coordinate the transmitter and receiver. The SRP can be updated adaptively according to the variations of the channels. Both theoretical analysis and simulations show that the ISI is mitigated and the transmission rate is improved simultaneously compared to the constant SRP transmission scheme.
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  • Wei MIAO, Yunzhou LI, Xiang CHEN, Shidong ZHOU, Jing WANG
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3351-3354
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This letter addresses the problem of robust transceiver design for the multiuser multiple-input-multiple-output (MIMO) downlink where the channel state information at the base station (BS) is imperfect. A stochastic approach which minimizes the expectation of the total mean square error (MSE) of the downlink conditioned on the channel estimates under a total transmit power constraint is adopted. The iterative algorithm reported in [2] is improved to handle the proposed robust optimization problem. Simulation results show that our proposed robust scheme effectively reduces the performance loss due to channel uncertainties and outperforms existing methods, especially when the channel errors of the users are different.
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  • JunKyoung LEE, JangHoon YANG, DongKu KIM
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3355-3359
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    A scheme of the superimposing additional data signal in the time domain for orthogonal frequency division multiplexing (OFDM) system is proposed. The proposed scheme has a tradeoff between the degree of freedom for data transmission and inter-carrier interference (ICI), which provides the flexibility of data rate decision when the finite number of modulation and coding levels are available for the given channel condition. A performance analysis of the bit error rate (BER) confirms this tradeoff. In simulation on the practical environment which experiences multipath fading and error of channel estimation, the results show that much improvement of spectral efficiency has been achieved while keeping as nearly good bit error rate as the conventional OFDM. Moreover, the single carrier transmission of the superimposed additional data in the time domain also gives an opportunity of boosting the signal power up to the peak to average power ratio (PAPR) margin of the OFDM system.
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  • Qinghai YANG, Kyung Sup KWAK
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3360-3363
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In this letter, we investigate the outage performance for decode-and-forward relaying under Rayleigh fading in the presence of multiple unequal-powered Rayleigh co-channel interferers. A close-form expression for the outage probability is derived and simulation results verify the theoretical solution.
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  • Ju-Ya CHEN, Meng-Hong HSIEH
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3364-3367
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Frequency offset estimation is an important technique in receiver design of wireless communications. In many applications, sampled single frequency tone is selected as training symbol/sequence for frequency synchronization. Under this assumption, frequency offset estimation can be regarded as the problem of single carrier frequency offset estimation. In this Letter, an approximate maximum likelihood frequency estimator is proposed. This estimator is efficient at moderate and high SNR's. Compared with other estimators, the proposed estimator is less sensitive to the variance threshold and offers feasible levels of computation complexity. The proposed estimator is suitable for high frequency offset cases and coarse/fine frequency synchronization applications.
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  • Changhyeon CHAE, Taejin JUNG, Intae HWANG
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3368-3370
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    A new Space-Time Block Code (STBC) achieving full rate and full diversity for general QAM and four transmit antennas is proposed. This code also possesses a quasi-orthogonal (QO) property like the conventional Minimum Decoding Complexity QO-STBC (MDC-QO-STBC), leadingg to joint ML detection of only two real symbols. The proposed code is shown to exhibit the identical error performance with the existing MDC-QO-STBC. However, the proposed code has an advantage in transceiver implementation since this code can be modified so that the increase of PAPR occurs on only two transmit antennas, whereas MDC-QO-STBC incurs a PAPR increase on all transmit antennas.
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  • Yong-Hwa KIM, Seong-Cheol KIM
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3371-3374
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    Phase noise (PHN) can cause the common phase error (CPE) and the inter-carrier interference (ICI), both of which impair the accurate channel estimation in orthogonal frequency division multiplexing (OFDM) systems. In this letter, we build a new signal model parameterized by the channel impulse response, the CPE and the ICI. Based on this model, we derive the maximum likelihood estimator (MLE) and the minimum mean square error estimator (MMSEE). Simulation results show that the proposed schemes significantly improve the performance of OFDM systems in the presence of PHN.
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  • Tsui-Tsai LIN
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3375-3378
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    In this letter, a decision-directed MOE detector with excellent robustness against signature waveform mismatch is proposed for DS-CDMA systems. Both the theoretic analysis and computer simulation results demonstrate that the proposed detector can provide better SINR performance than that of conventional detectors.
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  • Sung-Min OH, Sunghyun CHO, Jae-Hyun KIM, Jonghyung KWUN
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3379-3382
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This letter proposes an efficient uplink scheduling algorithm for the voice over Internet protocol (VoIP) service with variable frame-duration according to the voice activity in IEEE 802.16e/m systems. The proposed algorithm dynamically changes the grant-interval to save the uplink bandwidth, and it uses the random access scheme when the voice activity changes from silent-period to talk-spurt. Numerical results show that the proposed algorithm can increase the VoIP capacity by 26 percent compared to the conventional extended real-time polling service (ertPS).
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  • Seungjae BAHNG, Youn-Ok PARK, Jaekwon KIM
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3383-3386
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    The performance of the ordered successive interference cancellation (OSIC) signal detection method is well known to depend on the successful detection of the first layer. In a previous work, in an effort to mitigate the error propagation effect, all the constellation points were tried as the first layer symbol, thereby achieving a better performance. In this letter, we show that the selection of the first layer impacts the error performance significantly, and based on the observation, we propose a novel signal detection method QR-LRL. In the proposed work, the least reliable layer (LRL) is chosen to be the first layer, which is shown to be the best choice in terms of noise enhancement in detecting the other layers. Also, we discuss Log Likelihood Ratio (LLR) computation when the proposed method is used. Computer simulations confirm the efficacy of the proposed method.
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  • Chan-Byoung CHAE, Seijoon SHIM, Robert W. HEATH, Jr.
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3387-3390
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    We propose an antenna grouping method that improves the error rate performance of space-time codes in a wide range of mobility environments. The idea is to group symbols to antennas based on limited feedback from the mobile station to utilize all antennas. Our approach requires only two bits of feedback information to achieve better link performance and full rate for a certain four transmit antenna system. Numerical results confirm the bit/frame error gains over the Alamouti-based space-time block code and antenna subset selection strategies.
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  • Zhu XIAO, Ke-Chu YI, Bin TIAN, Yong-Chao WANG
    Article type: LETTER
    Subject area: Wireless Communication Technologies
    2008 Volume E91.B Issue 10 Pages 3391-3394
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This letter proposes a UWB signaling localization scheme for indoor multipath channel. It demonstrates that the proposed method does not require LOS path (LP) and is suitable for severe non line-of-sight (NLOS) condition. A low-complexity TOA estimation algorithm, the strongest path (SP) detection by convolution, is designed, which is easier to implement than the LP detection since it dispenses with the process of threshold setting. Experiments under NLOS channels in IEEE.802.15.4a are conducted and the localization influences due to the algorithm parameters are discussed. The results prove the feasibility of the proposed localization scheme under the indoor multipath NLOS environment.
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  • Tein-Yaw CHUNG, Kuan-Chun LEE, Hsiao-Chih LEE
    Article type: LETTER
    Subject area: Terrestrial Radio Communications
    2008 Volume E91.B Issue 10 Pages 3395-3398
    Published: October 01, 2008
    Released on J-STAGE: March 01, 2010
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    This paper derived a closed-form expression for inter-flow capacity of a backhaul wireless mesh network (WMN) with centralized scheduling by employing a ring-based approach. Through the definition of an interference area, we are able to accurately describe a bottleneck collision area for a WMN and calculate the upper bound of inter-flow capacity. The closed-form expression shows that the upper bound is a function of the ratio between transmission range and network radius. Simulations and numerical analysis show that our analytic solution can better estimate the inter-flow capacity of WMNs than that of previous approach.
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