We have developed a new type of 3D LIDAR, which is small, light weight and low cost. The size and weight are important factors of the aimed sensor to use with wide range of robot vehicles, helicopters and airplane, and small vehicles. To achieve compact size and light weight construction the sensor has single pair of laser transmitter and receiver, and scanning motor on which a vibrating mirror is placed. The mirror is driven by the resonant frequency current supplied through contactless power supply unit. Experimental results of the prototype shows that the sensor of comparable size and weight with recent 2D sensors can obtain 3D range data of 8000 points in 20 Hz with 270 degree horizontal and 40 degree vertical views both in indoor and outdoor.

We propose a method to recognize cups on desks and to detect liquids in cups with a depth camera using triangulation. When we measure an opaque liquid in a cup with the depth camera, the liquid surface is measured. On the other hand, when we measure a transparent liquid, the raised bottom is measured due to the principle of light refraction and triangulation. We formulated it theoretically, and confirmed that the theory is consistent with the experimental results. Therefore, it is possible to detect the existence of liquids in cups using the measured height based on this theory. In our experiments, the proposed method have successfully detected various transparent or opaque liquids.

We present a new matching algorithm considering a priori (the prior probability) based on Bayes' theorem. Performance of point cloud registration between target and source clouds is effectively improved by introducing maximum a posteriori (MAP) estimation. The standard Iterative Closest Point (ICP) algorithm for the registration sometimes falls into misalignment due to measurement errors, narrow sensing field of view, or the movement of objects during measurement. Our approach resolves such problems by considering both the likelihood of the measurement and the prior probability of the initial guess for registration in the objective function. We have implemented a new 6DOF Iterative Closest Point matching using MAP estimation, and evaluated the method in real environments comparing with conventional registration methods. The experimental results have shown that our proposed method has wide convergence region and matches point clouds accurately preventing the misalignment problem.

This paper proposes new over-the-air inter-node carrier phase synchronization to maintain constant inter-node carrier phase offset among wireless nodes participating cooperative coherent transmission over slow Rayleigh fading channels. In the proposed method, one of the two nodes updates its carrier frequency and carrier phase periodically using the measured bi-directional channel parameters. In OFDMA systems, bi-directional channels are measured in distributed subcarriers to attain frequency diversity effect. In the presence of phase noise, one node can track the other node's phase error using the proposed synchronization. Numerical results show that the proposed method maintains inter-node carrier phase alignment error less than 5 degrees. It is also revealed that the proposed method achieves accurate synchronization with feasible amount of signaling and complexity in LTE-advanced.

This paper proposes an ultra accurate inter-node carrier frequency synchronization which keeps carrier frequency offset between wireless nodes less than 1Hz in slowly time-varying Rician fading channels. In the proposed method, one of the two nodes adjusts its carrier frequency to be close to the other node's carrier frequency based on bi-directional channel measurements. We demonstrate that the proposed scheme achieves very small inter-node carrier frequency offset, e.g. less than 0.01 Hz. This synchronization scheme is useful in improving performance of wireless applications, such as cooperative coherent transmission or mobility measurements.

This paper proposes an ultra accurate carrier frequency synchronization for OFDMA/TDD systems, which keeps carrier frequency offset between two wireless nodes less than 0.01Hz in frequency-selective Rayleigh fading environments. In the proposed method, bi-directional channels are measured in multiple subbands of an OFDMA system. One of the two nodes corrects its carrier frequency with high accuracy using the bidirectional channel parameters corresponding to subbands of good channel quality. Numerical results show that appropriate weighting and averaging of relative phases of bi-directional channel parameters over multiple subbands improves performance of inter-node carrier frequency syhcoronization. The proposed method is a promising techology towards cooperative coherent transmission or low-power wireless communications.

This paper proposes an efficient multiuser relaying scheme in OFDMA systems. In the proposed scheme, multiple terminals transmit packets simultaneously in the same subband and multiple relay stations retransmit their received signals in different subbands after subband conversion. The base station (BS) extracts each packet from multi-dimensional signals received at the different subbands. In advance of data transmission, the BS's scheduler selects appropriate terminals for packet transmission such that the BS can detect each packet correctly. Numerical results show that the proposed relaying scheme achieves much higher system throughput than the conventional relaying scheme.

This paper investigates an amplify and forward (AF) relaying scheme compatible with a legacy wireless system in cellular environments. In the proposed scheme, terminals and relay stations use different frequency bands for signal transmission. The two frequency bands for terminals and for relay stations are used by individual frequency reuse factors in cellular environments. We study frequency planning and a relay station's location for high spectral efficiency. The numerical results show that the spectral efficiency of a relaying scheme is enhanced by deploying a relay station close to the base station (BS) and using frequency reuse factor 1 for a relay station to BS link.

This paper proposes cooperative control for antenna array calibration to exploit channel reciprocity in OFDMA/TDD systems. The proposed scheme seeks a cooperative supporter which is another terminal or a fixed station close to the terminal. In cooperative calibration mode, the terminal compensates mismatch of analog gains between antennas, based on bidirectional channel measurements between the terminal and the supporter. The proposed scheme selects adaptively cooperative or normal calibration mode through a base station, depending on the terminal's situation. The numerical results show that the proposed scheme improves calibration accuracy significantly compared to the case of no cooperative calibration. The proposed scheme keeps phase error less than 5deg in any position of terminal in a cell, maintaining practical amount of control signalling and complexity.

This paper proposes a new antenna array calibration using frequency selection in OFDMA/TDD systems. In the proposed method, subbands or frequencies of good channel conditions are initially selected for accurate channel measurement. Next, the relative calibration is performed at the selected subbands, in which mismatch of analog gains in multiple antennas is compensated by use of measured channel parameters on uplink and downlink. Third, the calibration parameters are interpolated in frequency domain for whole bandwidth. The proposed method keeps more accurate channel reciprocity for whole bandwidth than the conventional method which does not use the frequency selection. The proposed method is effective in exploiting channel reciprocity at both base station and terminals keeping feasible feedback amount and low-cost operation.

This paper proposes transmit power control (TPC) for pilot-based channel quality indicator (CQI) reporting in OFDMA/TDD systems. In the proposed TPC scheme, the terminal controls transmit power of pilot signals for CQI reporting, such that the base station (BS) can receive the pilot signals with higher power than the BS's interference-plus-noise power. In the proposed TPC scheme, the terminal determines appropriate transmit power using downlink pilot signals. The numerical results show that uplink signalling for CQI reporting can be effectively reduced by updating transmit power level in longer period than period of pilot signal transmission. Using appropriate period of updating the transmit power, the terminal can report one unit of CQI using a small number of uplink symbols, e.g. 1.5 symbols, keeping accuracy of CQI reporting.

This paper proposes a new partial channel state information (CSI) reporting for spatial scheduling in TDD/MIMO systems. In the proposed method, a terminal transmits pilot signals using transmit beams which have large channel gains between the base station (BS) and the terminal. Then, the BS can obtain partial CSI through responses of the pilot signals. Furthermore, adaptive allocation of pilot signals is proposed, in which pilot signals for CSI reporting are adaptively allocated to terminals depending on the number of terminals. We evaluate system throughput of spatial scheduling under the partial CSI reporting from multiple terminals. Numerical results show that the proposed method reduces uplink radio resources for CSI reporting effectively, keeping high system throughput of spatial scheduling.

In this paper, we propose OFDMA/TDD/MIMO system with spatial scheduling, showing frame structure and control procedures to achieve the proposed system. The frame structure includes all functions required for spatial scheduling in a subband of 200 kHz and in a frame time of 2.5 ms. We show that the frame structure can be a realistic solution to achieve spatial scheduling on subband basis. From the presented frame structure, about 60% of total radio resources are expected to be available for data symbol transmission. Furthermore, we estimate that data rate up to 570 Mbps can be supported on MAC layer for both uplink and downlink, under total bandwidth of 100 MHz.

This paper presents uplink spatial scheduling with adaptive transmit beamforming, where terminals perform system-based transmit beamforming in multiuser multi-input multi-output (MIMO) systems. In the presented spatial scheduling, the base station (BS) selects appropriate combination of terminals and their transmit beamforming among possible terminals. In the selection process, a terminal and its transmit beamforming for a signal are successively selected, considering the effect of the other predetermined signals. In performance evaluation, we show that the spatial scheduling achieves much larger system throughput than the system without spatial scheduling. We also present a basic system configuration in which the BS reports the target transmit beamforming to the selected terminal efficiently in time-division duplex (TDD) system downlink

This paper presents downlink spatial scheduling which nullifies interference among multiplexed signals perfectly in multiuser MIMO systems. Under the base station's zero-forcing transmit beamforming, each terminal can receive packet of interest without interference from the other multiplexed packets. The scheduling algorithm successively selects appropriate terminals for packet transmission in the presence of already selected packets. We show that the downlink spatial scheduler is equivalent to the virtual uplink spatial scheduler in terms of received signal characteristics. Applying the uplink scheduling concept to downlink, the downlink spatial scheduler achieves much higher system throughput than the system without spatial scheduling. Also, it is shown that the spatial scheduler has similar system throughput in uplink and downlink

This paper propose a new control scheme that the base station (BS) controls the terminal's transmit beamforming in time-division duplex (TDD)/multi-input multi-output (MIMO) systems. In the proposed scheme, the BS transmits pilot signals using proper downlink beamforming to instruct target beamforming to the terminal. Using responses of the pilot signals, the terminal computes weight for transmit beamforming. We theoretically show that the BS can control not only a single terminal's transmit beamforming but also multiple terminals' transmit beamforming simultaneously. Furthermore, efficient weight computation at the terminal is investigated to yield accurate transmit beamforming in the presence of noise. Numerical results show that the terminal can yield transmit beamforming close to the target beamforming in noise environments

This paper proposes a pilot-based channel state information (CSI) feedback in time-division duplex (TDD) / multi-input multi-output (MIMO) system, which enables the transmitter to perform transmit beamforming considering the receiver's interference. In the proposed method, the receiver sends reverse-link pilot signals spatially prefiltered by linear precoder dependent on the receiver's interference characteristics. The transmitter exploits responses of the reverse-link pilot signals to perform transmit beamforming considering the receiver's interference. The transmitter also predicts the receiver's output signal-to-interference-plus-noise power ratio (SINR) for each data stream. From simulation results, it is found that the transmitter achieves efficient transmission performance maintaining small control errors based on the proposed CSI feedback.

This paper proposes a new uplink signalling to report the terminal's channel quality in multiple subbands to the base station (BS) using channel reciprocity in orthogonal frequency division multiple access / time division duplex (OFDMA/TDD) systems. In the proposed method, the terminal transmits uplink pilot signals in the subbands with different transmit power which is inversely proportional to the subband- based interference-plus-noise power. The BS can obtain knowledge of the terminal's received signal-to-interference-plus-noise power ratio (SINR) on subband basis, measuring the pilot signal power. In performance evaluation, accuracy of the channel quality reporting and amount of the control signalling are examined. From numerical results, it is found that the proposed method becomes effective as the number of subbands and terminals for channel quality reporting increases.

This paper proposes a novel pre-FFT type OFDM adaptive array antenna called "Eigenvector Combining". The eigenvector combining is a realization of a post-FFT type OFDM adaptive array antenna through a pre-FFT signal processing, so it can achieve excellent performance with less computational complexity and shorter training symbols. Numerical results demonstrate that the proposed eigenvector combining shows excellent bit error rate performance close to the lower bound just with two training symbols.

This paper theoretically analyzes the performance of multicarrier code division multiplexing (MC-CDM) and cyclically prefixed direct-sequence code division multiplexing (CP-DS-CDM) in multipath fading channels. The paper shows the relationship among the SNIR, diversity order obtained and BER lower bound for MC-CDM and CP-DS-CDM, and demonstrates some computer simulation results on performance comparison.

This paper presents a rapid initial weight computation method for adaptive array antennas. The proposed method estimates a correlation matrix and a correlation vector, where the correlation matrix is estimated using not only received samples with the desired signal, but also those before starting the transmission of the desired signal. The proposed method reduces the number of known symbols required for weight convergence. Furthermore, the combined use of the proposed method and the decision-feedback minimum mean square error combining method significantly improves weight convergence. Numerical results show that the combined method converges an array with sixteen antennas by using less than ten known symbols.

It is well known that orthogonal frequency-division multiplexing (OFDM) is robust to frequency-selective fading in wireless channels due to the exploitation of a guard interval that is inserted at the beginning of each OFDM symbol. However, once delayed signals beyond the guard interval are introduced in a channel with a large delay spread, intersymbol interference causes a severe degradation in the transmission performance. In this paper, we propose a novel pre-fast Fourier transform (FFT) OFDM adaptive antenna array, which requires only one FFT processor at a receiver, for suppressing such delayed signals. We derive the optimum weight set for beamformers based on the max- imum signal-to-noise-and-interference power ratio (Max-SNIR) and the minimum mean square error (mmse) criteria, respectively. In addition, we propose a novel mmse-criterion-based commuta- tive optimization scheme, which is more robust to the estimation error of the channel state information. Furthermore, we show the equivalence between the Max-SNIR-criterion-based scheme and the proposed commutative optimization scheme. Computer simu- lation results show its good performance even in channels where directions of arrival of arriving waves are randomly determined.

Weight-convergence analysis of adaptive antenna arrays based on the sample matrix inversion (SMI) algorithm is presented. First, we derive a required number of samples for weight computation to achieve an output signal-to-interference-plus-noise ratio -10 log/sub 10/ r dB (r /spl les/ 1) below an optimum value. Next, we evaluate weight convergence of code-division multiple-access adaptive antenna arrays based on the SMI algorithm, where two types of weight computational methods are compared between "chip-level computation" and "symbol-level computation". Analytical and simulation results reveal that "chip-level computation", before despreading process, enables faster convergence than "symbol-level computation", after the despreading process.

The paper presents a rapid initial weight computation method for adaptive array antennas. The proposed method estimates a correlation matrix using not only samples received with the desired signal, but also those received from other sources. The proposed method reduces the number of known symbols required for weight convergence. Furthermore, the combined use of the proposed method and the decision-feedback MMSE combining method improves weight convergence significantly. Numerical results show that the combined method converges an array with 16 antennas by using less than 10 known symbols.

The paper proposes a TDD-SDMA/TDMA system with a multi-slot assignment to deal with asymmetric traffic in wireless networks, where the packet-based data service is supported. The proposed system assigns more than one time slot for the downlink to each terminal so as to deal with the asymmetric traffic. We also present an efficient algorithm to decide the priority of time slots for the downlink, and by which the maximum potential transmission rate can be obtained for the downlink. The performance of the proposed system is evaluated by computer simulation in terms of the average delay and the average transmission rate and compared with those of a conventional system with a symmetric time slots assignment. It is verified that a significant improvement on system performance can be achieved if the TDD-SDMA/TDMA system employs the proposed multi-slot assignment scheme.

This paper proposes a new maximum likelihood OFDM receiver for multipath fading environment with large delay spread. The large delay difference over the guard interval (GI) duration of the OFDM signal generally results in intersymbol interference (ISI) between temporally adjacent symbols and interchannel interference (ICI). Both of them spread over a large number of subcarriers. The new OFDM receiver consists of equalizers for both ISI and ICI and an accurate channel impulse response estimator. Furthermore, it introduces a temporal-window technique for the FFT-window in order to suppress the ICI, which is very effective for reducing the complexity of ICI equalization by maximum likelihood sequence estimator (MLSE). Computer simulation is conducted in order to verify the performance of the proposed OFDM receiver, and its effectiveness is shown.

It is well known that OFDM scheme is robust to frequency selective fading in wireless channels. However, once delayed signals beyond the guard interval and Doppler-shifted signals are introduced in the channel, inter-subcarrier interference and inter-symbol interference give a severe degradation in the transmission performance. This paper proposes a novel OFDM adaptive antenna array which can suppress both delayed signals and Doppler-shifted signals. The proposed adaptive antenna array has a simple structure and by forcing virtual subcarrier outputs to be zero, it can steer its nulls toward incoming Doppler-shifted signals, even when they have no time delay. Computer simulation results show its excellent performance, for a case where four signals are incident on an eight-element circular array, such as one signal with no time delay, one Doppler-shifted signal with no time delay, one Doppler-shift signal with time delay within the guard interval, and one signal with time delay beyond the guard interval.

This paper presents the performance of cellular SDMA/TDMA systems with variable bit rate traffic. We employ a time slot assignment algorithm, which assigns a time slot to a new user considering not only the signal quality of the new user, but also that of active users. To support different multimedia services, a modulation scheme is adaptively selected according to the QoS (quality of service) requirement. Blocking probability, forced termination probability, and average delay of different services are evaluated in a cellular environment.

This paper presents an analysis of a RAKE receiver in a W-CDMA downlink. The base station employs transmit beamforming, while each user employs R-finger RAKE receiver under selective fading channels. Spreading sequences are composed of Walsh codes and a common long code based on 3GPP standardization. We derive an exact expression for the instantaneous signal-to-interference-plus-noise ratio (SINR) at the output of the RAKE receiver. In the derivation process, the effect of spreading sequences, downlink beamforming, and the RAKE receiver are taken into account. Simulation examples for a 4-finger RAKE receiver are given to verify the derived expression. Our expression can be applied to evaluate transmit beamforming as well as to evaluate the performance of the RAKE receiver.

We present a simple uplink access technique for packet data communications in a mobile environment. This technique is an application of a random-access communication scheme with slotted ALOHA to a wireless cellular system. All base stations connected to a control station use a common frequency and have synchronized slots. Mobile terminals can transmit packets at any time and do not require slot reservation, handover control, or transmission power control. This system can perform base station diversity reception with selective combining or with maximal ratio combining (MRC) in the uplink. Computer simulation shows that throughput is much improved when base stations use adaptive array antennas. In addition, the effects of the limitation of retransmissions on throughput and service fairness for all mobile terminals are analyzed.

This paper focuses on the multibeam combining techniques to enhance the capacity of CDMA systems. In multibeam combining systems, one sector area is covered by a 2-beam antenna. Signals are received by two beams and combined to yield a output. The combining weights are determined by the received levels of two beams. A comparison of the capacity between cellular CDMA systems with and without multibeam combining techniques is presented.