We have been developing low power cryogenic readout electronics for space borne large format far-infrared image sensors. As the circuit elements, a fully-depleted-silicon-on-insulator (FD-SOI) CMOS process was adopted because they keep good static performance even at 4.2K where where various anomalous behaviors are seen for other types of CMOS transistors. We have designed and fabricated several test circuits with the FD-SOI CMOS process and confirmed that an operational amplifier successfully works with an open loop gain over 1000 and with a power consumption around 1.3µW as designed, and the basic digital circuits worked well. These results prove that the FD-SOI CMOS process is a promising candidate of the ideal cryogenic readout electronics for far-infrared astronomical focal plane array sensors.

抄録全体を表示

Hayabusa returned to Earth on June 13, 2010, becoming the world's first explorer to complete a round-trip voyage to an asteroid. After being released from the spacecraft, the sample return capsule landed in the Woomera Prohibited Area in the desert of South Australia. The capsule recovery team from JAXA found the capsule within 1 h of its landing. The beacon tracking system that was developed by JAXA played an important role in the tracking and discovery of the sample return capsule. The system has flexibility regarding the landing position of the capsule, because it does not rely on primary radar. In this paper, we describe the beacon tracking system and evaluate the system by discussing the results of preliminary examination and of operation on the day of re-entry.

抄録全体を表示

A monopulse angle measurement method is often utilized to measure a target angle. However, this method cannot measure correct angles for multiple targets which cannot be distinguished by range, Doppler frequency and beamwidth. When the number of targets which cannot be distinguished by these parameters is restricted to two, a method which can measure two targets angles has been proposed. However, an approximation is utilized with this method, so that measured angles have errors even though the signal-to-noise ratio is infinite. Another method which can simultaneously measure azimuths and elevations for only two targets has also been proposed. However, this conventional method requires four receivers, and is therefore difficult to apply when there is a hard ware limitation. In this paper, we propose a method to measure azimuths and elevations of two targets by using two receivers and a time division system. A pairing problem has occurred due to the time division angle measurement with this method, so we also propose an algorithm to solve this pairing problem. We finally verify the proposed method by a numerical simulation and experimentation. The results show that the angles of two targets can be measured by our proposed method by using two receivers.

抄録全体を表示

Adaptive interference suppression strategies based on the transform domain approach are proposed for a satellite on-board filter bank under tone-type interferences. In the proposed methods, the three kinds of algorithms to compute the threshold level are jointly employed with the notch filter or the clipper. Simulation results show that the proposed schemes significantly improve performance under interfering environments, compared to the no suppression case.

抄録全体を表示

In this paper, the Getis statistic is applied to ALOS- PALSAR (Advanced Land Ovserving Satellite-Phased Array L-band Synthetic Aperture Radar) images for assessing the building damage caused by the Wenchuan earthquake in 2008. As a proposed image analysis, a simulated building image using mapping and projection algorithm is first presented for analysis of the Getis statistic. The results show the high accuracy of the assessment of the proposed approach. The Getis statistic is then applied to two ALOS-PALSAR images acquired before and after the Wenchuan earthquake to assess the level of building damage. Results of the Getis statistic show that the damage level is approximately 81%.

抄録全体を表示

In order to detect snow and ice on a road surface, the microwave measurement method of dielectric constants are presented. And some examples of measurements for artificial and natural snow and ice using the method are introduced. The results show reasonable estimations of the dielectric constants, and they indicate that the method could be utilized for the snow and ice detection.

抄録全体を表示

The air traffic situational awareness is an essential factor for flight safety and efficiency. Today, pilots have only two methods for situational awareness, through visual acquisition or with traffic information via voice messages from Air Traffic Controllers. These methods have limitations in reducing aircraft separation because of their delay in acquiring traffic. To improve the acquisition of traffic information, airborne surveillance with ADS-B/TIS-B has been proposed. This paper reports on the prototype TIS-B system developed by ENRI and on the results of evaluations with flight testing.

抄録全体を表示

In this paper, an active control scheme is designed for the hybrid direct methanol fuel cell (DMFC) system to achieve the following three objectives simultaneously: (i) maximize the power produced by the DMFC stack in the stable operation as high loading (for avoiding the operation of DMFC in diffusion region), (ii) keep the power produced by the DMFC stack with the high efficiency as low loading, (iii) prevent the problem of methanol crossover at a very low load. Considering the characteristics of DMFC stack during actual operation, the states V_P (t) and V_P (t) are utilized as the linguistic variables. Also considering the fuel efficiency of DMFC stack η_ƒuel as the linguistic variable, the active control scheme is designed to achieve the above multiple objectives. To clarify the reliability and stability of the proposed control scheme, an experiment is performed. Its results show that the proposed control scheme can achieve above multiple objectives efficiently.

抄録全体を表示

In this paper, we propose an energy efficient MAC protocol for wireless sensor networks. In sensor networks, reducing energy consumption is one of the critical issues for extending network lifetime. One good solution to resolve this issue is introducing listen-sleep cycles, allowing sensor nodes to turn their transceiver off during sleep periods, which was adopted by S-MAC [1]. However, in S-MAC, due to the synchronized scheduling, transmission collisions will increase in heavy traffic situations, resulting in energy waste and low throughput. Hence, in this paper, we propose probabilistic scheduled MAC (PS-MAC), in which each node determines ‘listen’ or ‘sleep’ pseudo-randomly based on its own pre-wakeup probability and pre-wakeup probabilities of its neighbor nodes in each time slot. This allows the listen-sleep schedule of nodes in each transmitter and receiver pair to be synchronized, while maintaining those of the rest of nodes to be asynchronous. Therefore, collisions can be reduced even under heavy traffic conditions, resulting in reduced energy waste and high throughput. In addition, by dynamically adjusting the pre-wakeup probabilities of sensor nodes based on the change of the network environment, system throughput and latency can be further improved. Simulation results show that PS-MAC provides significant energy savings, low delay, and high network throughput.

抄録全体を表示

The cellular phone ownership rate continues to increase, meaning one person may now own two or more. Meanwhile, a lot of terminals that receive cellular phone services through a mass broadband communication network are being commercialized. When service is received through the cellular phone, the mobile network operator authenticates the subscriber. However, service providers other than the mobile network operators provide communication services and other services through fixed networks. In this situation, if we can use the subscriber authentication that the mobile network operator provide for the fixed network service, fixed mobile convergence (FMC) will be achieved and mobile network operators will be able to better prevent unauthorized users from using their services. In addition, services will become more convenient because users will be authenticated by swiping one cellular phone when switching from using a fixed terminal to another fixed terminal. A mechanism has been developed that allows mobile network operator to authenticate their subscribers' account when using a terminal connected to a fixed network. In addition, services can be easily switched between fixed terminals by using the proposed mechanism. Moreover, a system is constructed on the basis of the proposed mechanism, and its performance is evaluated.

抄録全体を表示

This paper proposes new scheduling algorithms for best effort (BE) traffic classification in business femtocell networks. The purpose of traffic classification is to provide differentiated services to BE users depending on their traffic classes, and the concept of traffic classification is called Inter User Best Effort (IUBE) in CDMA2000 1x Evolution Data Optimized (EVDO) standard. Traffic differentiation is achieved by introducing Grade of Service (GoS) as a quality of service (QoS) parameter into the scheduler's decision metric (DM). New scheduling algorithms are called QoS Round Robin (QoS-RR), QoS Proportionally Fair (QoS-PF), QoS maximum data rate control (DRC) (QoS-maxDRC), QoS average DRC (QoS-aveDRC), QoS exponent DRC (QoS-expDRC), QoS maxDRC-PF (QoS-maxDRC-PF). Two different femtocell throughput experiments are performed using real femtocell devices in order to collect real DRC values. The first experiment examines 4, 8, 12 and 16 IUBE users, while second experiment examines 4 IUBE + 2 Voice over IP (VoIP), 8 IUBE + 2 VoIP, 12 IUBE + 2 VoIP, 16 IUBE + 2 (VoIP) users. Average sector throughput, IUBE traffic differentiation, VoIP delay bound error values are investigated to compare the performance of the proposed scheduling algorithms. In conclusion, QoS-maxDRC-PF scheduler is proposed for business femtocell environment.

抄録全体を表示

The many-to-one communication nature of wireless sensor networks (WSNs) leads to an unbalanced traffic distribution, and, accordingly, sensor nodes closer to the base station have to transmit more packets than those at the periphery of the network. This problem causes the nodes closer to the base station to deplete their energy prematurely, forming a hole surrounding the base station. This phenomenon is called the energy hole problem, and it severely reduces the network lifetime. In this paper, we present a cooperative power-aware routing algorithm for uniformly deployed WSNs. The proposed algorithm is based on the idea of replacing the constant transmission range of relaying sensor nodes with an adjusted transmission range, in such a way that each individual node consumes its energy smoothly. We formulate the dynamic transmission range adjustment optimization (DTA) problem as a 0-1 Multiple Choice Knapsack Problem (0-1 MCKP) and present a dynamic programming method to solve the optimization problem. Simulations confirm that the proposed method helps to balance the energy consumption of sensor nodes, avoiding the energy hole problem and extending the network lifetime.

抄録全体を表示

In MANET (Mobile Ad-hoc NETworks), there are two kinds of routing methods: proactive and reactive. Each has different characteristics and advantages. The latter generally employs the flooding technique to finding a routing path to the destination. However, flooding has big overheads caused by broadcasting RREQ packets to the entire network. Therefore, reducing this overhead is really needed to enable several network efficiencies. Previous studies introduced many approaches which are mainly concerned with the restriction of flooding. However, they usually configure the detailed routing path in the forward flooding procedure and ignore the factors causing the flooding overheads. In this paper, we propose the FSRS(First Search and Reverse Setting) routing protocol which is a new approach in flooding techniques and a new paradigm shift. FSRS is based on cluster topology and is composed of two main mechanisms: inter-cluster and intra-cluster flooding. Inter-cluster routing floods RREQ packets between cluster units and sets a cluster path. When the destination node receives the RREQ packet, it floods RREP packets to an intra-cluster destination which is a gateway to relay the RREP packet to a previous cluster. This is called intra-cluster routing. So to speak, a specific routing path configuration progresses in the RREP process through the reverse cluster path. Consequently, FSRS is a new kind of hybrid protocol well adapted to wireless ad-hoc networks. This suggests a basic wireless networking architecture to make a dynamic cluster topology in future work. In the simulation using NS-2, we compare it to several other protocols and verify that FSRS is a powerful protocol. In the result of the simulation, FSRS conserves energy by a maximum of 12% compared to HCR.

抄録全体を表示

BGP dictates routing between autonomous systems with rich policy mechanisms in today's Internet. Operators translate high-level policy principles into low-level configurations of multiple routers without a comprehensive understanding of the actual effect on the network behaviors, making the routing management and operation an error-prone and time-consuming procedure. A fundamental question to answer is: how to verify the intended routing principles against the actual routing effects of an ISP? In this paper, we develop a methodology RPIM (Routing Policy Inference Model) towards this end. RPIM extracts from the routing tables various policy patterns, which represent certain high-level policy intentions of network operators, and then maps the patterns into specific design primitives that the ISP employs. To the best of our knowledge, we are the first to infer routing policies in ISP networks comprehensively from the aspects of business relationship, traffic engineering, scalability and security. We apply RPIM to 11 ASes selected from RIPE NCC RIS project, and query IRR database to validate our approach. Vast majority of inferred policies are confirmed by the policy registries, and RPIM achieves 96.23% accuracy excluding validation difficulties caused by incompleteness of the IRR database.

抄録全体を表示

The doubly constrained robust Capon beamformer (DCRCB), which employs a spherical uncertainty set of the steering vector together with the constant norm constraint, can provide robustness against arbitrary array imperfections. However, its performance can be greatly degraded when the uncertainty bound of the spherical set is not properly selected. In this paper, combining the DCRCB and the weight-vector-norm-constrained beamformer (WVNCB), we suggest a new robust adaptive beamforming method which allows us to overcome the performance degradation due to improper selection of the uncertainty bound. In WVNCB, its weight vector norm is limited not to be larger than a threshold. Both WVNCB and DCRCB belong to a class of diagonal loading methods. The diagonal loading range of WVNCB, which dose not consider negative loading, is extended to match that of DCRCB which can have a negative loading level as well as a positive one. In contrast to the conventional DCRCB with a fixed uncertainty bound, the bound in the proposed method varies such that the weight vector norm constraint is satisfied. Simulation results show that the proposed beamformer outperforms both DCRCB and WVNCB, being far less sensitive to the uncertainty bound than DCRCB.

抄録全体を表示

IEEE 802.15.3c has been standardized for wireless personal area networks (WPANs) to realize high-speed wireless communications with 1Gbps throughput. In this paper we introduce a 802.15.3c WPAN prototype. The introduced 802.15.3c WPAN prototype applies the enhanced MAC functions of data separation on hybrid multiple access, long frame size, aggregation, block acknowledgment, and timing operation, which can realize Gbps throughput in IEEE 802.15.3c. Moreover, the experiment performance studies on the prototype show that around 1.6Gbps throughput can be successfully achieved and video streaming applications can be accommodated. Also, our studies provide the useful information of MAC capacity for developing the 802.15.3c devices.

抄録全体を表示

Dynamic spectrum allocation (DSA) based on secondary spectrum market is considered a promising technology to improve spectrum utilization efficiency and to relieve the wireless spectrum shortage problem. We propose a dynamic spectrum allocation algorithm named market equilibrium and game (MEG), and construct a complete secondary spectrum market. The market based on the MEG algorithm consists of two submarkets: multiple primary services providers (PSPs) and a dynamic spectrum allocation server (DSAS) form the high submarket, while the low submarket is composed of the DSAS and a number of secondary users. In the low submarket, the MEG algorithm provides a game type selection strategy. By this strategy, the DSAS can win more payoffs with lower unit spectrum price, which encourages secondary users to use more spectrum. A secondary user can also choose its preferable game type between dynamic game and Nash bargaining flexibly. On the other hand, a bargaining procedure in the high submarket is designed in the MEG algorithm to ensure that market equilibrium is quickly reached. A performance analysis shows that the strategy of game type selection is fair and feasible for both the DSAS and the secondary users. Moreover, the bargaining procedure is better than the existing algorithm which adjusts price step by step in the high submarket. Simulation results also demonstrate that the market fluctuation in the low submarket is passed to the high submarket by way of the DSAS. The MEG algorithm can effectively satisfy the highly-fluctuating demands from the secondary users. In addition, the MEG algorithm can improve the payoffs of all players and increase spectrum utilization efficiency.

抄録全体を表示

In this paper, we present a cognitive relay network with two primary transceivers that communicate via several distributed relay terminals. Spectrum sensing is deployed at the relays to sense the absence/presence of the primary transceivers based on energy detection. The primary network utilizes a two-step two-way amplify-and-forward (AF) scheme by using the cognitive radio (CR) terminals as its relay nodes when the primary network is not in operation, in contrast, the CRs communicate with their own base station (BS). In the first relaying step, the primary transceivers send their signal to the CRs/relays. Distributed beamforming is then performed in the second relaying step. Our aim is to set the beamforming weights so as to minimize the total power dissipated in the relay network while satisfying a target signal-to-noise ratio (SNR) at the primary transceivers and at the cognitive BS. This is achieved by solving an optimization problem that we formulate as a nonconvex quadratically constrained quadratic program (QCQP). This problem is solved efficiently by semidefinite relaxation (SDR) and Lagrangian duality. Simulation results are provided to demonstrate the superiority of our proposed technique, compared to classical beamforming techniques, in terms of power reduction.

抄録全体を表示

IEEE 802.11 Wireless LANs (WLANs) support multiple transmission rates. When some stations transmit at low transmission rates, the performance of the high transmission rate stations degrades heavily, and this phenomenon is known as the performance anomaly. As a solution to the performance anomaly, airtime fairness was proposed. However, the distributed coordination function (DCF) of IEEE 802.11 cannot provide airtime fairness to all competing stations because the protocol is designed to ensure fair attempt probability. In this paper, we propose a new medium access control, successful transmission time fair MAC (STF-MAC), which is fair in terms of successful transmission time and also provides the maximum aggregate throughput of a basic service set (BSS) in distributed manner. STF-MAC can be easily applied to solve the uplink/downlink fairness problem in infrastructure mode. Through simulations, we demonstrate that STF-MAC not only remedies the performance anomaly but also maximizes the aggregate throughput under the fairness constraint.

抄録全体を表示

In this paper, we evaluate the downlink performance of Transparent mode (T-mode) and Non-Transparent mode (NT-mode) in a two-hop cellular system based on IEEE 802.16j. In particular, we evaluate the performance in terms of the system capacity, optimal resource allocation, and outage probability using Monte Carlo simulation with various system parameters such as different Frequency Reuse Factors (FRFs) and the distance between Base Station (BS) and Relay Station (RS). To analyze the Signal to Interference and Noise Ratio (SINR) of the access and relay links, an SINR model is introduced for cellular multihop systems considering intra- and inter-cell interferences. Then, we present a method of optimal resource allocation for the Access Zone (AZ) and Relay Zone (RZ) to maximize the system capacity. Consequently, the simulation results provide an insight into choosing the appropriate RS position and optimal resource allocation. Through numerical examples, it is found that the FRFs of two and three are good choices to achieve the highest capacity with low outage in T- and NT-modes, respectively.

抄録全体を表示

This paper proposes a novel scheme to reduce the complexity of existing transmit diversity solutions to time domain synchronous OFDM (TDS-OFDM). The space shifted constant amplitude zero autocorrelation (CAZAC) sequence based preamble is proposed for channel estimation. Two flexible frame structures are proposed for adaptive system design as well as cyclicity reconstruction of the received inverse discrete Fourier transform (IDFT) block. With regard to channel estimation and cyclicity reconstruction, the complexity of the proposed scheme is only around 7.20% of that of the conventional solutions. Simulation results demonstrate that better bit error rate (BER) performance can be achieved over doubly selective channels.

抄録全体を表示

We propose a simple approximate model for unslotted opportunistic spectrum access networks under nonsaturation conditions. The main simplification we introduce is that all secondary users, except a tagged one, in nonsaturated setting can be approximated by saturated ones with a scaled version of backoff interval. We analyze the approximate model and verify the model using simulations.

抄録全体を表示

Although IP address lookup schemes using ternary content addressable memory (TCAM) can perform high speed packet forwarding, TCAM is much more expensive than ordinary memory in implementation cost. As a low-cost solution, binary search algorithms such as a binary trie or a binary search tree have been widely studied. This paper proposes an efficient IP address lookup scheme using balanced binary search with minimal entries and optimal prefix vectors. In the previous scheme with prefix vectors, there were numerous pairs of nearly identical entries with duplicated prefix vectors. In our scheme, these overlapping entries are combined, thereby minimizing entries and eliminating the unnecessary prefix vectors. As a result, the small balanced binary search tree can be constructed and used for a software-based address lookup in small-sized routers. The performance evaluation results show that the proposed scheme offers faster lookup speeds along with reduced memory requirements.

抄録全体を表示

Due to the lack of end-to-end paths between the communication source and destination in the Disruption Tolerant Network (DTN), its routing employs the store-carry-and-forward mechanism. In order to provide communication service in the DTN where there is only intermittent connectivity between nodes, a variety of epidemic-style routing algorithms have been proposed to achieve high message delivery probability at the cost of energy consumption. In this contribution, we investigate the problem of optimal multi-frame content transmission. By formulating the optimization problem with a Markov model, we derive the optimal policies under the two conditions of with and without energy constraint. We also investigate the performance of the proposed optimal policies through extensive numerical analyses, and conclude that the optimal policies give the best performance and the energy constraint critically degrades the system performance in the multi-frame content transmission.

抄録全体を表示

Target Q coverage is needed to secure the stability of data collection in WSN. The targets may have different level of importance then the multiple-target coverage scheme must schedule sensors according to each target's weight to increase the network lifetime. The schedule scheme previously proposed for weighted coverage uses an iterative solution to solve the problem but it has long computation time. We propose a heuristic greedy-TQC algorithm to use the residual energy of sensors to generate multiple scheduling cover sets. A simulation shows a dramatic reduction in computation time. The greedy-TQC algorithm is suitable for the frequently topology-changing WSN and for the often changing targets' weights in WSN.

抄録全体を表示

An infinitely long monopole antenna driven by a coaxial cable is revisited. The associated Weber transform and the mode-matching method are used to obtain simple simultaneous equations for the modal coefficients. Computations are performed to illustrate the behavior of current distribution and antenna admittance in terms of antenna geometries.

抄録全体を表示

A novel algorithm is presented for estimating the 3-D location (azimuth angle, elevation angle, and range) of multiple sources with a uniform circular array (UCA). Based on its centrosymmetric property, a UCA is divided into two subarrays. The steering vectors for these subarrays then yield a 2-D direction of arrival (DOA)-related rotational invariance property in the signal subspace, which enables 2-D DOA estimations using a generalized-ESPRIT algorithm. Based on the estimated 2-D DOAs, a range estimation can then be obtained for each source by defining the 1-D MUSIC spectrum. Despite its low computational complexity, the proposed algorithm can almost match the performance of the benchmark estimator 3-D MUSIC.

抄録全体を表示

This paper presents the shielding effectiveness (SE) characteristics of a metallic wall with a narrow slot when exposed to a nearby dipole source or a plane wave. In order to characterize the dipole source SE, a radiation field, including the near field from the dipole source, is calculated. The results show that the dipole source SE depends on the source and field points. This SE is different from the plane wave SE in that it fluctuates with the position of the dipole source; the fluctuation period is about 0.5λ.

抄録全体を表示

For amplify-and-forward (AF) relaying with imperfect channel estimation, we present the average symbol error rate (SER) and the diversity and multiplexing tradeoff (DMT) analysis for both opportunistic relaying (OPR) and all-participate relaying (APR) schemes. SER comparisons show that when the channel estimation quality order is no larger than 1, OPR will perform worse than APR in high SNR region. Moreover, small channel estimation quality orders will also lead to significant DMT loss.

抄録全体を表示

In this paper, we consider multiple source and destination antennas based on relay selection scheme to improve the end-to-end outage performance for decode-and-forward cooperative networks. We derive an exact closed-form expression of the outage probability for the proposed system over a Rayleigh fading channel and describe the diversity-multiplexing tradeoff of the system. We then analyze the effects of the number of source and destination antennas on the outage probabilities and diversity-multiplexing tradeoffs.

抄録全体を表示

In this letter, a generalized sidelobe canceller (GSC) with robustness against carrier frequency offset (CFO) is proposed for the uplink MC-CDMA system. It has been shown that a CFO will cause the spreading code mismatch and desired signal cancellation. By incorporating the corrected quiescent weight of the upper branch and blocking matrix of the lower branch, we create an efficient GSC that offers strongly counters the effect of the CFO. Significant performance improvement of the proposed GSC is demonstrated by simulation results.

抄録全体を表示

In non-cooperative scenarios, the estimation of direct sequence spread spectrum (DS-SS) signals has to be done in a blind manner. In this letter, we consider the spreading sequence estimation problem for DS-SS signals. First, the maximum likelihood estimate (MLE) of spreading sequence is derived, then a semidefinite relaxation (SDR) approach is proposed to cope with the exponential complexity of performing MLE. Simulation results demonstrate that the proposed approach provides significant performance improvements compared to existing methods, especially in the case of low numbers of data samples and low signal-to-noise ratio (SNR) situations.

抄録全体を表示

This letter proposes a method for choosing the best quantized beamforming vector that represents a subcarrier group, for coordinated beamforming in the downlink of multiuser multiple input multiple output-orthogonal frequency division multiplexing systems. The correlation between subcarriers is exploited for reducing the feedforward overhead, while maximizing the sum rate.

抄録全体を表示

We propose a data transmission method for resonant wireless power transmission systems. In order to transmit data, we use the coils originally designed for power transmission, no additional antennas are required. We focus on uplink data transmission and adopt the load modulation technique. This configuration yields mid-range data transmission without transmitting power. In addition, the proposal enables simultaneous power feeding and uplink data transmission. We make a prototype demonstrating resonant wireless power transmission and measure its S-parameter under some load conditions. The results confirm the potential of load modulation in supporting uplink data transmission. Additionally, the results are elucidated by analyzing an equivalent circuit. Measured S-parameter and equivalent circuit response are found to be similar.

抄録全体を表示

In this letter, we propose a power allocation scheme to optimize the ergodic secrecy rate of multiple-input single-output (MISO) fading wiretap channels with a probabilistic constraint, using the statistical channel state information (CSI) of the eavesdropper (CSI-E). The analytical expressions of the false secrecy probability are derived and used as constraints in the rate maximization problem. Moreover, we obtain a suboptimal solution by formulating the power allocation problem as a Rayleigh quotient problem.

抄録全体を表示

This letter considers a sum-rate maximization problem with user scheduling wherein each user has a minimum-rate requirement in multiple-input-multiple-output broadcast channel. The multiuser strategy used in the user scheduling is a joint transceiver scheme with block diagonal geometric mean decomposition. Since optimum solution to the user scheduling problem generally requires exhaustive search, we propose a suboptimum user scheduling algorithm with each user's minimum-rate requirement as the main constraint. In order to satisfy maximum sum-rate and minimum-rate constraints simultaneously, we additionally consider power allocation for scheduled users. Simulation results show that the proposed user scheduling algorithm, together with the user power allocation, achieves sum-rate close to the exhaustive search, while also guarantees minimum-rate requirement of each user.

抄録全体を表示

This letter proposes a slot-based opportunistic spectrum access for cognitive radio networks. To reduce the slot-boundary impact, control frames are used to achieve channel reservation. The saturation throughput of our scheme is estimated by an analytical model. The accuracy of the model is validated by extensive simulation.

抄録全体を表示

We propose an AP-based handoff management scheme in which each AP having multiple interfaces communicates with MSs by turns, prohibiting from using the same channel as neighboring APs at the same time to avoid interference. In the proposed scheme, APs support handoff management to accomplish MS-unaware handoff. Performance evaluation shows that the proposed scheme can not only achieve low handoff delay, but enhance throughput performance.

抄録全体を表示

This letter proposes a novel technique for detecting a target signal buried in clutter using principal component analysis (PCA) for pulse-Doppler radar systems. The conventional detection algorithm is based on the fast Fourier transform-constant false alarm rate (FFT-CFAR) approaches. However, the detection task becomes extremely difficult when the Doppler spectrum of the target is completely buried in the spectrum of clutter. To enhance the detection probability in the above situations, the proposed method employs the PCA algorithm, which decomposes the target and clutter signals into uncorrelated components. The performances of the proposed method and the conventional FFT-CFAR based detection method are evaluated in terms of the receiver operating characteristics (ROC) for various signal-to-clutter ratio (SCR) cases. The results of numerical simulations show that the proposed method significantly enhances the detection probability compared with that obtained using the conventional FFT-CFAR method, especially for lower SCR situations.

抄録全体を表示

ATFM (Air Traffic Flow Management) keeps air traffic flows safe and orderly. When the estimated workload exceeds capacity limit, traffic demand is controlled. In Japan, The ATFM system estimates controller's workload by a lot of parameter that depend on sector characteristics represented by traffic flow. The calculation of the value needs a lot of analysis. Author proposes a simple method for estimating the workload created by the traffic situation.

抄録全体を表示