This paper presents experimental results for multiuser-multiple input multiple output (MU-MIMO) with a two-dimensional antenna configuration. MU-MIMO can increase spectral efficiency significantly by employing many antennas at the base station (BS). However, the performance is upper-bounded when many antennas are arranged in a line because antenna spacing has to be small to maintain the required span for antenna arrangement. In order to overcome the problem, this paper evaluates a two-dimensional antenna configuration, where multiple antennas are set in both the horizontal and vertical directions using the testbed developed by the authors. The experimental results show that the spectral efficiency with a two-dimensional antenna configuration is 12.8 % higher than that with conventional linear array configuration when the span for the antenna arrangement in the horizontal direction is constrained to 7λ, where λ indicates the wavelength of carrier frequency.

In traditional heterogeneous cellular networks (Het-Net), base stations (BS) basically associate users based on received signal power. However, in the case of multiband HetNet, in which macro BSs and smallcell BSs use different frequency bands, this conventional cell association method is not effective because there is no interference between macro BSs and smallcell BSs. Additionally, there are huge differences in coverage and available bandwidth. These differences cause inefficient association which causes the imbalance between achievable rate and traffic demand. In order to overcome this problem, we propose a novel cell association method based on the combinatorial optimization. The proposed method considers achievable rates, traffic demands and the number of users belonging to each BSs simultaneously. Numerical simulation results show that the proposed association method achieves system rate gain twice as high as the conventional one.

This paper presents the development of an 8-by-8 real-time multiuser-multiple input multiple output (MU-MIMO) testbed and experimental results of linear and non-linear precoding subject to limited channel state information (CSI) feedback. Linear precoding techniques such as minimum mean square error precoding have already been tested and the related results are available in the literature. However, they are not capacity-achieving. Non-linear precoding techniques such as vector perturbation and Tomlinson-Harashima precoding, on the other hand, achieve in theory the capacity of MU-MIMO, but such claims have not been verified in practice to date. One reason is that theoretical non-linear precoding works rely on the assumption of full and perfect CSI at the transmitter as non-linear precoding techniques are sensitive to CSI error. The merit of this work is that it experimentally confirms (through hardware implementation and pre-field test experimentation) the feasibility of non-linear precoding subject to limited CSI feedback. Experimental results reveal that the non-linear precoding achieves higher throughput performance than the linear precoding scheme by about 35% under realistic CSI feedback.

Due to the recent mobile traffic explosion, especially in hotspots where a lot of traffic is generated in a limited space, an imbalance in the traffic load among cells occurs. Such traffic load imbalance requires the deployment of many base stations (BSs) in the hotspots. This results in the inefficient operation of cellular systems. In order to overcome this problem, load balancing techniques have been studied. There are two main approaches. One is based on antenna tilt control (TiLt-control-based Load Balancing: TL-LB) and the other is based on handover (HO) timing control (HandOver-timing-control-based Load Balancing: HO-LB). These techniques have been studied separately; however, a detailed comparison of the two techniques has not been reported so far. This paper numerically compares TL-LB and HO-LB in terms of not only the amount of user equipment (UE) distribution to neighboring cells, but also the degradation of Signal to Interference plus Noise Power Ratio (SINR), HO performance, and the change in the number of UEs in each cell. Numerical results show that TL-LB is superior to HO-LB in terms of the amount of UE distribution, SINR, and HO performance. With TL-LB, about 65% of UEs in a cell are distributed to neighboring cells with little degradation of SINR and HO performance. In contrast, with HO-LB, no more than 43% of UEs can be distributed to neighboring cells at the expense of 5th percentile SINR degradation of 21 dB and significant degradation in HO performance. The results also show that TL-LB is inferior to HO-LB in terms of the change in the number of UEs in each cell. However, this disadvantage of TL-LB can be overcome by appropriate cooperation control with neighboring cells. It can be concluded that TL-LB with appropriate cooperation control is much more effective than HO-LB as a load balancing technique.

In this paper, we propose a method to estimate the distance between objects attached with radio-frequency identification (RFID) tags that are used for finding lost objects. Many systems for finding lost objects adopt real-time location systems (RTLSs) using received signal strength indication (RSSI). The fundamental structure of a general method for an RTLS using RSSI involves the creation of a number of reference nodes whose locations are known in advance. Crowded objects often form a group; hence, it is very helpful to find some object members of the group in a certain place so as to find the lost object belonging to the group. However, an RTLS is not required to know the objects located in a certain place or to estimate the distance between these objects. Hence, we propose a method to estimate the distance between objects rather than the individual object locations without using a method to obtain location-dependant information.

A large number of cells will be deployed to provide high speed services in any places using the Long-Term Evolution (LTE) system. The management of such a large number of cells increases the operating expenditure (OPEX). Self-organizing networks (SON) attracted interest as an effective way to reduce OPEX. One of the main targets in SON is the self-optimization of handover (HO) that realizes mobility robustness. HO optimization algorithms adjust HO parameters between the serving and the reconnected cells based on the HO failure logs and cell selection, which is the procedure used to select a suitable reconnected cell, is very important for HO optimization algorithms. In this paper, we propose a cell selection scheme to enhance the performance of HO optimization. In the proposed scheme, both the uplink and downlink channel quality is considered when selecting a suitable reconnected cell. Through the computer simulation, we can see that the proposed scheme reduces the HO failure rate and the number of HO failures by 3 percentage points and 38%, respectively, compared to the conventional scheme based solely on downlink channel quality.

This paper presents the development and experimentation of linear precoding (LP) and non-linear precoding (NLP) on a real-time multiuser-multiple input multiple output (MU-MIMO) testbed subject to limited channel state information (CSI) feedback. LP techniques such as zero-forcing and minimum mean square error precoding have already been experimented and the related results are available in the literature. However, they are not capacity-achieving. NLP techniques such as vector perturbation and Tomlinson-Harashima precoding (THP), on the other hand, achieve in theory the capacity of MU-MIMO, but such claims have not been verified in practice, to date. One reason is that theoretical NLP works rely on the assumption of full and perfect CSI at the transmitter as NLP techniques are sensitive to CSI error. The merit of this work is to experimentally confirm (through hardware implementation and pre-field test experimentation) the feasibility of NLP subject to limited CSI feedback using the fading simulator. Experimental results reveal that the testbed achieves less than 2 dB and 3 dB degradation of the block error rate compared to the floating point computer simulations in LP and NLP, respectively.

Cell Range Expansion (CRE) combined with Inter-Cell Interference Coordination (ICIC) in Heterogeneous Networks (HetNet) is a promising technique to enhance the utilization of the resource in pico cells. CRE increases the number of the UE sets connected to pico cells (pico UEs) by changing the trigger timing of the handover (HO). However, inappropriate trigger timing of HO increases HO failures and inefficient HOs, thereby degrading HO performance. HO performance directly affects the continuity of the communication service. Hence, not only the utilization of the resource in pico cells but HO performance should be taken into consideration when CRE is adopted. In this paper, we evaluate the effect of CRE on HO performance through system level simulations, and clarify the application range of CRE. As an example, we examine the CRE bias values which keep the HO failure rate to under 1% and the Ping-Pong HO rate to under about 1%. It is shown that the applicable CRE bias values range from 0 dB to 6 dB, which is smaller than the applicable CRE bias values reported by the conventional studies which range from 0 dB to 9 dB. We also show that the CRE bias values over 6 dB result in high HO failure rates over 5%. Therefore, CRE should be adopted with consideration of HO performance in order to keep good HO performance.

This paper studies additional cellular network deployments with the application of coordinated multi-point (CoMP) operation on the LTE-Advanced downlink. It clarifies which approach in additional deployment, either with a macro or pico base station (BS), is the most advantageous to CoMP and spectrum splitting. Cell splitting due to additional deployment is indispensable to having a huge network capacity, and there are two approaches in additional network deployment. One is a homogeneous-based additional macro BS deployment, and the other is a heterogeneous-based additional pico BS deployment. When CoMP is applied to additional deployment, additional macro deployment is preferable because additional macro deployment maintains the initial cost associated with the distribution of the rich backbone network required for simultaneous joint transmission. On the other hand, spectrum splitting is useful for additional pico deployment. Spectrum splitting means that a different spectrum is assigned to the additional BS although the occupied bandwidth for the original BS is reduced by half. System level simulations demonstrate that CoMP is superior to spectrum splitting with additional macro deployment in terms of average user throughput as well as 5% worst user throughput. The 5% worst user throughput gain due to CoMP is 56.8% compared to the original network deployment. On the other hand, spectrum splitting is superior to CoMP in additional pico deployment. However, the gain due to spectrum splitting largely depends on user distribution. If users are uniformly distributed, additional macro deployment with CoMP is superior to additional pico deployment with spectrum splitting, especially in terms of the 5% worst user throughput gain.

This work analyzes the optimal pico base station (BS) deployment in heterogeneous cellular networks (HetNet) with hotspots. Most of conventional works for HetNet focused on interference coordination and effective cell association methods, however, the problem of pico BS deployment (cell planning) for HetNet with hotspots has not been analyzed so much. In this paper, we extend the previously proposed optimization problem in terms of network parameters (spectrum splitting ratio and SINR bias value) to the optimal pico BS locations to maximize the system rate. Furthermore, the average user and outage user rates are evaluated numerically to show the effectiveness of the proposed optimization method. Numerical results show that the optimized pico BS locations can improve both the average and outage user rates in HetNet with hotspots.

This paper proposes an actual down link radio resource allocation scheme at pico base stations (PBS) in time domain multiplexing - inter-cell interference coordination (TDM-ICIC). Since TDM-ICIC is useful for a heterogeneous network coexisting with macro BSs (MBS) and PBSs, considerable research has been conducted on TDM-ICIC. However, previous studies have not explored actual resource allocation, but have instead focused on theoretical capacity clarification. In the proposed method, user equipment (UE) attached to a PBS is classified into two groups: one is defined as the "A-PUE" and the other as the "CRE-UE". The A-PUE is a UE which is always attached to the PBS. The CRE-UE becomes attached to the PBS through the application of cell range expansion (CRE). In the proposed method, UE prioritization based on the UE classification takes precedence over proportional fairness scheduling (PFS). The UE prioritization depends on the interference condition due to the transmission condition at the MBS. System level simulations demonstrate two reasonable candidates in resource allocation when the MBS mutes the signal. One is based on PFS and is an effective approach for improving the average user throughput in each UE group compared to that without the TDM-ICIC. The other is prioritized resource allocation for the CRE-UE, which can correct the imbalance in the average user throughput between two groups. By applying the prioritized resource allocation, the imbalance in the average user throughput decreases from more than 200% to 25%.

Recently, a new multiple access scheme called interleave-division multiple access (IDMA) has been studied where different interleavers are used to distinguish users. This paper focuses on orthogonal frequency division multiplexing (OFDM) -IDMA, which is a combination of OFDM and IDMA, and investigates the throughput performance of OFDM-IDMA for the uplink in multi-cell environment. We analyze the effect of parameters such as the number of iterations on the multiuser detector and the number of users cancelled at the iterative multiuser detector in the base station. Additionally, the throughput performance of OFDM-IDMA is compared with that of OFDMA with an identical transmission rate. The simulation results show that the cell throughput of OFDM-IDMA in multi-cell environment approaches about 90 % of that in an isolated single-cell environment, while the throughput of OFDMA in multi-cell environment degrades by 57.9 % compared to that in single-cell environment due to its less robustness against inter-cell interference than OFDM-IDMA.

A large number of cells will be deployed to provide high speed services in any places using the Long-Term Evolution (LTE) system. The management of such a large number of cells increases the operating expenditure (OPEX). Self-organizing network (SON) attracts attention as an effective way to reduce OPEX. This paper proposes a self-optimization algorithm for handover (HO) parameters. In conventional studies, the HO optimization techniques are discussed in models with stationary mobility of user equipment (UE). On the other hand, the key feature of the proposed algorithm is the mobility robustness, which means that the HO performance is robust against the change in UE mobility. In order to realize the mobility robustness, the proposed algorithm adaptively adjusts the HO parameters considering cause of HO failures, which changes in UE mobility. We examine the performance of the proposed algorithm through the computer simulations and confirm the mobility robustness. The simulation study demonstrates the following; The HO parameters are initially set to the optimum values for UEs with 3 km/h based on the random walk. Then, when the mobility changes from 3 km/h random walk to 300 km/h linear motion, the HO failure rates increases to 19%. The proposed algorithm reduces such increasing HO failure rates less than 0.2%.

TCP service constructs high quality end-to-end communication link. TCP needs two way communication links. First link and second one are necessary for transmitting data packet from source to destination and ACK packet form destination to source, respectively. Therefore, TCP throughput strictly depends on both links. In wireless communication, the link speed is time selective due to shadowing effect. When the link speed is dramatically changed during the event of downloading, the impact of time selective link speed should be significant. In this paper, we clarify the impact of fluctuating link speed to TCP throughput by network simulator. In addition, we propose the adaptive link speed control of ACK link for achieving large ACK throughput. We also confirm the effect of proposed technique by network simulator.

SC-FDMA is a multiple access technique adopted in LTE uplink transmission. SC-FDMA, as well as OFDMA, can improve system throughput by assigning different frequency portions of system bandwidth to different user equipments (UEs) adaptively based on their channel quality information. In SC-FDMA uplink cellular system, interference arising from UEs in neighboring cells degrades system performance, especially the performance of the cell-edge UE. To overcome this drawback, many papers propose the Fractional Frequency Reuse (FFR) technique and analyze its influence. However, these studies have different conclusions on the effectiveness of FFR, and the throughput gain of FFR depends on the evaluating conditions. In this paper, we reveal the conditions where FFR is effective by demonstrating the throughput gain of FFR in SC-FDMA uplink cellular system. In order to analyze the throughput gain of FFR, we focus on the performance relationship between FFR and frequency selective scheduling (FSS). From the analysis, the throughput gain of FFR is small because of the degradation of the FSS gain, and FFR is effective when the following conditions are met; (i) the number of UEs is small, (ii) the multipath delay spread is large or equal to 0.

In order to reduce the reception completion time of data units in the application layer, a novel TCP-oriented multi-layer packet scheduler (TCP-oriented MLPS) is proposed in this paper. The proposed scheduler firstly narrows down the number of candidate users of the packet scheduler based on the congestion window in the TCP layer, and then allocates resources to the selected candidate users preferentially with the proportional fairness packet scheduler (PFPS) to achieve better fairness and capacity performances simultaneously. Simulations are conducted using periodic file transfer protocol (FTP) traffic models of 5 seconds with Long Term Evolution (LTE) air interface numerology. Simulation results show that the proposed TCP-oriented MLPS achieves up to 279.2% improvement of the number of data units in the application layer, which satisfies with the target reception completion time. Moreover, the simulation results also show that the degradations in the physical layer introduced by the proposed TCP-oriented MLPS in terms of the average cell throughput and 5% worst user throughput are very slight.

This paper proposes an open loop beamforming scheme in frequency division duplex (FDD) downlink multiuser multiple input multiple output (MIMO) transmissions. The proposed scheme estimates the downlink channel matrix by uplink direction of arrival (DOA) estimation, and generates the beamforming weight such that the effect of overlapping beams is cancelled at the respective receivers by applying the dirty paper coding principle. The simulation results show that the proposed scheme provides a gain up to 20 dB in the received signal to noise plus interference ratio (SINR) at the 50% CDF compared to the conventional zero-forcing beamforming. In addition, it is shown that the proposed scheme has a superior performance to the limited feedback closed loop scheme.

This paper presents throughput performance of 2 × 2 multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) using a testbed in line with the Long Term Evolution (LTE) numerology. Then, this paper clarifies the relation among the throughput, modulation schemes and antenna polarization. The field experiments clearly demonstrate that a measured throughput exceeding 200 Mbps can be obtained in a coverage area more than 50% and a throughput of 456.0 Mbps is achieved for a limited number of users even when a maximum Doppler frequency is higher than 125 Hz. In addition, it is found that the single polarization antenna configuration is suitable for 16QAM while the dual polarization antenna configuration is suitable for 64QAM. It is concluded from analysis of the eigenvalue ratio and signal to noise power ratio that the aforementioned trade-off is caused by sensitivity to the eigenvalue ratio depending on the modulation scheme and distribution of the eigenvalue ratio depending on the MIMO antenna configuration.

In order to reduce the peak-to-average power ratio property, single-carrier frequency-division multiple access (SC-FDMA) has been selected as the uplink access scheme in the Long Term Evolution (LTE) system. Aiming to derive the maximum performance of the LTE uplink in terms of both average cell throughput and cell-edge user throughput, the optimization formulation of packet scheduling problem in LTE uplink is proposed in this paper. The optimization formulation defines the packet scheduling problem as a transform of the knapsack problem and utilizes the integer linear programming (ILP) method to provide the feasible optimum resource allocation based on the combination of allocable resources with various constraints in LTE uplink. Moreover, to reduce the complexity of the ILP, a limitation on the valid combination of allocable resources is also considered. Simulation results show that the feasible optimum solution derived by the proposed optimization formulation, has a significant improvement of up to 40% and 263.8% over the heuristic proportional fairness packet scheduling in terms of the average cell throughput and cell-edge user throughput, respectively. The feasible optimum solution derived by the proposed optimization formation is useful for evaluating various heuristic resource allocation algorithms.

This paper presents field experiment results for rotational orthogonal frequency division multiplexing (R-OFDM) transmission and demonstrates that R-OFDM is superior to conventional OFDM even in actual radio transmission. R-OFDM is a multi-carrier transmission scheme proposed by the authors. It is characterized by the use of rotational code division multiplexing that enables OFDM to obtain suitable frequency diversity gain. The authors previously implemented R-OFDM on a 100 MHz bandwidth testbed system and evaluated it in the laboratory. Measured results were in good agreement with simulation results. In addition, although the laboratory measurements made it clear that R-OFDM is superior to OFDM, the results assumed the typical radio channel conditions provided by a fading simulator. In order to confirm the effectiveness of R-OFDM, field experiments are indispensable. Therefore, this paper conducts field experiments with a measurement vehicle driven under conditions where OFDM demands frequency diversity. When the coverage of R-OFDM is measured, coverage with a packet error rate (PER) of 1% with OFDM is expanded by 12%. In addition, the measured PER performance against the measured signal-to-noise power ratio (SNR) clarifies that, by using R-OFDM, the SNR required to obtain a PER of 1% can be reduced by 3.3 dB compared with OFDM. Furthermore, OFDM throughput under severe SNR conditions can be improved by R-OFDM and R-OFDM throughput achieves 1.6 times as large as OFDM throughput.

Orthogonal frequency division multiple access (OFDMA) systems have recently drawn considerable attention as potential candidates for future generation cellular systems. To achieve proportional fairness among users while improving user's satisfaction in the upper layer, e.g. application and transmission control protocol (TCP) layers, we propose a novel multi-layer optimization approach for packet scheduling in OFDMA-based cellular systems, whereby the scheduler is designed not only based on optimization of the quality-of-service (QoS) class in the application layer, and fairness over users, but also based on the optimization of the throughput performance in the TCP layer. Simulations are conducted using TCP applications with the ultra mobile broadband (UMB) air interface numerology. Simulation results show that the proposed packet scheduling achieves up to 27.3% improvement over the proportional fairness scheduler in terms of the average system TCP throughput in the TCP layer, when resource usable rate for TCP applications is lower. Meanwhile, the proposed packet scheduling also performs with comparable fairness in the physical layer relative to the proportional fairness scheduler.

In 3.9G cellular systems, which have many specific components, operators have to manipulate many parameters of each component. One of the critical parameters is the termination target of H-ARQ. It is supposed that the termination target influences system performance in terms of both throughput and delay because the termination target involves a trade-off between the gain of high modulation order and the loss of continuous resource assignment by H-ARQ. The link-level performance of turbo coded H-ARQ has already been reported, however, the influence of the termination target on system performance is still to be fully studied. The purpose of this study is to determine the optimal termination target and to examine which parameter influences sector throughput. It was found that the optimal termination target depends on the propagation model and average SINR. By selecting the optimal termination target, the system throughput can achieve 20 % gain compared to a system using a non-optimal termination target.

In next-generation cellular systems including 3.9G and IMT-advanced systems, voice-over-IP (VoIP) services will be provided to users instead of conventional circuit switch-based voice calls. VoIP packets have peculiar characteristics that the packet length is short and packets are frequently generated. These phenomena require significant radio resources to send control channels in which resource assignment messages are conveyed ahead of VoIP packets transmission. In order to deal with this issue, persistent scheduling was proposed. There are several reports on persistent scheduling; however, sufficient study on it has not yet been conducted. This paper proposes persistent scheduling schemes that allow multiple resource usages using a threshold of queuing latency and then shows performance results based on ultra mobile broadband (UMB) system, which was standardized by the Third Generation Partnership Project 2 (3GPP2) as a 3.9G cellular system. Through computer simulations, it turns out that the proposed persistent scheduler gives improvement of 30% in terms of VoIP capacity compared to the basic persistent scheduler.

Wireless networks with very low latency are desired for users to enjoy real-time applications without stress to users. The authors have been studying to realize an ultra low-latency mobile network and concluded that a medium access control (MAC) protocol is a key component for the realization. This paper proposes a MAC protocol suitable for delay-sensitive real-time applications. Numerical results from simulation studies demonstrate that, for instance, the proposed MAC protocol can accommodate more than 50% of the traffic compared to the IEEE 802.11 distributed coordination function (DCF) for a real-time application service. In addition, simulation results revealed that the proposed MAC protocol provides very short delay jitter, which is one of the crucial performance measures for real-time applications, regardless of traffic loads.

In order to realize ultra low-latency mobile networks whose target is a unidirectional end-to-end latency of 10 milliseconds per IP packet, we proposed an adaptive error recovery scheme. The simulation results, which verified the effectiveness of the proposed scheme, need to be complemented by more realistic testing. Hence, we have implemented the proposed scheme using field programmable gate array (FPGA) and developed a testbed. The experimental evaluation results obtained using the testbed show similar IP packet error rate (IP PER) performances to those of the simulation results. Moreover, the IP PER performances with an end-to-end latency limitation (including transmission latency and processing latency) are firstly evaluated using the testbed. The experimental results verify the effectiveness of the proposed adaptive error recovery scheme using the testbed and indicate the possibility of realizing ultra low-latency mobile networks using the proposed error recovery scheme.

This paper reports the pneumatic PDMS micro hand as an end-effector of robot and miniaturized parallel link robot (guide robot) for manipulating a tiny and delicate object. Micro finger structure for the micro hand consists of bonded two films having different stiffness. Balloon structures are designed between the two films. Swelling of the balloon structure by applied pressure generates bending motion of the micro finger. This combination of the micro hand is based on the human being's finger and/or hand. The guide robot has several design specifications such as multi degrees of freedom joint as a human, small size, highly accurate directional control and water/ sterilization proof. Micro manipulation robot system is developed by assembling the micro finger with two or three degree of freedom, the guide robot and VR (virtual reality) interface device. The hybrid motion and the manipulation of a single egg (phi1 mm) of fish and a hair (phi100 mum) in macro world is successfully realized

To realize an ultra low-latency mobile network that has a quite short end-to-end latency, we present an adaptive error recovery scheme. In the proposed scheme, a combination of selective repeat (SR) and stop-and-wait (SW) ARQ (automatic repeat request), is adopted at the link layer. In addition, an adaptive FEC (forward error correction) scheme that has a different redundancy rate depending on the number of retransmissions is adopted at the physical layer. Theoretic analyses show that the proposed SR-SW-ARQ has a shorter transmission latency than that of the conventional SW-ARQ protocol when the error rate is sufficiently low. Simulations of the proposed adaptive SR-SW-ARQ/FEC scheme were conducted based on the flat Rayleigh channel. The simulation results verify that the proposed scheme provides better performance in terms of a normalized throughput at the link layer and less transmission latency compared to a scheme that has a static redundancy FEC scheme and SR-SW-ARQ protocol

A number of wireless systems have recently adopted an adaptive modulation scheme to improve frequency efficiency. Unlike mobile systems, FWA (fixed wireless access) systems including IEEE 802.16 systems used for MAN (metropolitan area network) are allowed to use quasi-millimeter and millimeter bands, but those are vulnerable to rain attenuation. Adaptive modulation scheme is effective in those systems to improve the availability of wireless links. A 26 GHz-band broadband FWA system with a five-level (1024 QAM to BPSK) adaptive modulation scheme was proposed and developed by the authors for field experiments. This paper introduces field experimental results concerning switching thresholds for adaptive modulation controls using the developed FWA system. The numerical results reveal that conventional ideas, in which identical switching thresholds in terms of BER (bit error rate) apply to all modulation methods and switching thresholds maximizing Layer-2 throughput, can neither obtain the maximum TCP (transmission control protocol) throughput nor satisfy the upper limit of the UDP (user datagram protocol) packet loss rate.

In satellite communications systems, in addition to frequency resources, total satellite transmitting power, (i.e., satellite power) is a crucial radio resource, due to the limited capacity of onboard electric generators. To increase system capacity, satellite power constraints have to be taken into account, as well as the frequency constraints. As one approach to this issue, we propose a traffic distribution algorithm using linear programming, which maximizes the accommodated traffic in a multiple-satellite system under satellite power constraints. The algorithms are applicable to all types of satellite systems with multiple satellites (geosynchronous Earth orbit, medium Earth orbit, low Earth orbit, or a combination of any) to increase system capacity with respect to the total amount of traffic accommodated by the systems. Finally, this paper evaluates the performance of the proposed algorithm by distributing traffic demand on the earth's surface to cells irradiated by spot-beams of a satellite and allocating frequency resources to the cells. By using the algorithm that permits power constraints, the ratio of accommodated traffic in a system was improved 12% compared with the case when no power constraints were used.

In a mesh wireless network system that consists of plural wireless nodes, it is important that all wireless nodes share the same time. For example, in a TDD wireless system, the frequency resources utilization over the network can be improved by acquiring TDD frame synchronization. This paper proposes a novel scheme that autonomously realizes the synchronization in a whole wireless network without centralized control. The proposed scheme just needs information from adjacent wireless nodes and other mechanisms are not necessary. In addition, this scheme maintains synchronization in the link connected-area, if the network topology changes or node failure occurs in a local area. The proposed scheme responds flexibly to changing the network topology. The scheme is applicable in the case where many nodes join in and out frequently in the network, such as in nomadic wireless access. This paper discusses the procedures of the proposed synchronization scheme and presents examples of establishment network-wide synchronization and recovery from link failure.

Broadband fixed wireless access (BFWA) systems with multi-hop mesh topology have attracted considerable attention as a promising approach for the next generation high quality, high capacity and high density access infrastructure. This paper deals with the problem of adaptive allocation of radio channels and the routing of the communications traffic by the traffic engineering in the multi-hop mesh wireless networks. A mathematical model and formulation are first presented for the problem and a solution algorithm with a heuristic approach is then proposed. Finally, the performance and the characteristics of the proposed algorithm are evaluated through the numerical results for some example network scenarios.

Broadband fixed wireless access (BFWA) networks with Multipoint-to-Multipoint (MP-MP) systems of mesh topology have recently been considered as a promising approach to realize high quality and high performance networks. Needless to say, it is of prime importance to adopt an effective frequency assignment method suitable for MP-MP systems in order to make maximum use of frequency resources over the system. From the viewpoint of the scalability to network growth, a distributed architecture is preferable compared to a centralized architecture for assigning frequency. This paper firstly identifies constraints on frequency assignment for MP-MP systems and then, proposes an autonomous frequency assignment method. The proposed method dynamically determines an optimum frequency slot for every radio channel in every wireless link, where the number of radio channels is adaptively changed to deal with traffic and link quality changes. In the method, the optimum frequency slot is selected by using an evaluation function. This paper introduces three kinds of evaluation functions and investigates their performances from simulation results.

Broadband fixed wireless access (BFWA) networks with multipoint-to-multipoint (MP-MP) system of mesh topology have attracted considerable attention as a promising approach to realize high quality and performance networks. Selection of a suitable duplex mode plays an important role to attain efficient frequency resource utilization in wireless systems. This paper is intended to identify the optimum duplex mode for MP-MP networks carrying asymmetric traffic. Numerical evaluation of duplex modes-FDD(frequency division duplex), single-carrier TDD (time division duplex), and multi-carrier TDD, which have not been studied in detail, is presented to achieve the purpose of this paper. In addition, two resource allocation algorithms are introduced for multi-carrier TDD to attain an efficient usage of the frequency resources and it is demonstrated that one of the algorithms realizes not only efficient usage of the resources but also robustness to the traffic change. It is concluded that the multi-carrier TDD is the optimal selection from the viewpoints of the resource utilization and the system implementation.

In satellite communications systems, the total satellite transmitting power (in short, 'satellite power') is one of the important radio resources, as well as spectrum resources, because of the limited capability of onboard electric generators. Therefore, for attaining optimum satellite radio resource utilization, it is not enough to just consider the spectrum resources but also to take account of the satellite power. This paper proposes algorithms using the linear programming for optimally distributing the traffic demand to multiple satellites in a system. The algorithms are applicable to any kind of satellite system with multiple satellites (GEO, MEO, LEO or combination of any) to increase the system capacity in terms of the total amount of traffic accommodated by the system. Numerical examples demonstrate that the proposed algorithms contribute to maximizing the system capacity.

Behavior of deformable cylindrical actuators is qualitatively investigated with respect to constraint topology. Elastic shells expanded by air pressure have a capability of generating various motion directly by imposing mechanical constraints on the shells. In this paper, we propose a qualitative analysis of the motion of deformable cylindrical actuators with mechanical constraints.

FDMA/TDMA non-GEO MSS (mobile satellite services) systems generally require a pre-planned pool of radio resources, i.e., frequency and time slot plan (FTSP), for each gateway Earth station (GES) prior to the real-time channel allocation by the multiple GESs sharing the resources harmoniously. The time-variant nature of those systems implies that a dynamic FTSP planning method is crucial to the operation to cope with time-variant traffic demand and inter-beam interference condition. This paper proposes and compares two resource assignment algorithms (spread type algorithm and concentrated-type algorithm). Numerical evaluation demonstrates that the spread type algorithm is very effective and promising in the FTSP generation for such systems.

This paper describes efficient transmission bandwidth management based on flexible channel assignment and effective grade of service (GOS) control methods for nongeostationary orbit mobile satellite service (NGSO MSS) networks. Our basic approach for the flexible channel assignment is to use linear programming (FLEXCA-LP), and to apply the column generation technique for further reduction of the total bandwidth requirement. These methods efficiently assign channels, taking account of moving spot beam coverage and dynamic traffic load variation for large-scale networks. The GOS is investigated for the channel assignment by FLEXCA-LP to make the GOS of ongoing calls better than that of fresh calls as stipulated in ITU-T Recommendations. We propose a few effective means to improve the results of FLEXCA-LP by reducing the disruption possibility of ongoing calls. One is to add channels utilizing a hysteresis concept. The others are effective use of GOS control techniques for NGSO MSS networks. These techniques are evaluated by a simulation study to identify promising techniques. Under time-variant conditions, we show that a reliable channel assignment plan is generated first by FLEXCA-LP considering the traffic load of fresh calls only and then by GOS control techniques to improve handover failure and call disruption rates.

We have proposed the concept of distributed micro motion systems (DMMS) in order to coordinate simple motions of many microactuators arranged on a wafer so as to perform a more complicated task. A two-dimensional conveyance system in a plane is studied as an example of DMMS. A system design has been presented with the aim of controlling many microactuators in a similar way as the cellular automaton. In this paper, we focus on a microactuator and define a micro-axel as an elemental unit of DMMS. We have previously reported the development and operation of a one-dimensional conveyance system using a fluidic micro-axel array. We improved the conveyance system and developed a two-dimensional system to perform a positioning task. This paper describes the design, fabrication, and operation of a fluidic micro-axel array for the two-dimensional conveyance system. The experiments to convey objects to the fixed desired position by the fabricated two-dimensional conveyance system performed successfully.

A conveyance system based on the concept of distributed micromotion systems (DMMSs) fabricated by IC-compatible micromachining processes is proposed. The DMMS consists of many smart modules which have microsensors, microactuators, and controllers. Each module has primary autonomy to determine its motion based on information from surrounding modules. Information processing in DMMS is similar to that in a cellular automaton. The key idea is to coordinate simple motions of microactuators in order to carry objects. As an example, a positioning system that can convey objects to a desired point on a X-Y plane is discussed. The control scheme of the conveyance system and a microactuator that uses controlled air flow to levitate and convey objects are described.>