In the current inter-vehicle communication (IVC) systems such as IEEE802.11p, the CSMA/CA scheme for the MAC scheme and the OFDM for the modulation scheme are most commonly used for the media access scheme and the modulation scheme respectively. These systems are assumed to be used in the application such as safety driving assistance, reducing traffic congestions and so on. On the other hand, since the required application in ITS must cover various field, development of the inter-vehicle communication scheme that has different characteristics from IEEE802.11p for high speed and large capacity data transmission is required for new applications such short range ad hoc network without base stations. In this paper, a new DS-CDMA IVC system using successive interference canceller (SIC) is proposed and its performance is compared with the CSMA/OFDM IVC. As the result of simulation, in the broad cast based wide range IVC, the CSMA/OFDM system can achieve better packet error rate (PER) performance than the proposed DS-CDMA IVC system. On the other hand, it was confirmed that the proposed DS-CDMA IVC system has better packet error rate performance with short latencies in the short range IVC where many short packets are exchange between vehicles.

In Japanese Digital Terrestrial Television Broadcasting (DTTB), the identification of multi-path is important to improve its reception characteristics. In order to enhance the resolution of the delay profile, it is effective that continuous multiple channel transfer functions are connected and the frequency bandwidth is extended. However, the guard band is existing between each channel and the transfer function is not obtained directly. The phases of each channel are not synchronized because the each channel is broadcasting independently. In this paper, the scheme to connect multiple channel transfer functions is proposed. In the proposed scheme, interpolation of guard band by using the linear prediction filter based on the RLS(Recursive Least Square) algorithm and compensation of phase between adjacent channels are performed. As the result, it was conformed that resolution enhancement of the delay profile is possible. It is possible to improve the time resolution of the delay profile that has 0.024[μs].

In this paper, LMS (Least Mean Square) adaptive array antenna is applied to IVC(Inter-Vehicle Communication) in order to reduce interference which is caused by surrounding vehicles. The LMS adaptive array antenna has a characteristic that the control of directivity is possible according to surrounding radio wave condition, if the receiving vehicle knows the information of the target vehicle. Under the case where the adaptive array antenna is used in IVC systems, packet error rate characteristic, throughput performance and improvement in near-far problem are evaluated by comparing with the performance of the IVC system using omni-directional antenna.

This paper discusses an interference DAA (Detection And Avoidance) technique for coexisting pulse based UWB and OFDM systems when the both systems are operated in the same frequency band. In a UWB transmitter-receiver, utilization of the OFDM system is detected by correlating with the GI (Guard Interval) signals. And also timing of the GI period is detected for interference mitigation. The UWB signal is emitted during GI period to mitigate the effect of interference to the OFDM system from the UWB system. The coexisting signal detection performances are evaluated by DER (Detection Error Rate), FAR (False Alarm Rate) and also RMSE (Root Mean Square Error) of detected GI period timing. The BER (Bit Error Rate) performances of the OFDM system are also evaluated to show the availability of proposed DAA technique.

Ultra Wideband (UWB) is an attractive technique that enable sharing spectrum with other radio systems to spread spectrum extremely wideband. However, there are potential interferences among those using in the same frequency bands and close range. This paper discusses the interference DAA (Detection And Avoidance) technique for coexisting pulse based UWB and OFDM systems. In a UWB transmitter-receiver, utilization of the OFDM signal is detected by correlating the GI (Guard Interval) signal, and the timing of GI period is also detected. The UWB signal is emitted during the GI period to mitigate the effect of interference to the OFDM signals from the UWB system. The DER (Detection Error Rate), FAR (False Alarm Rate) and BER (Bit Error Rate) performances are evaluated to show the availability of proposed DAA technique.

In this paper, an iterative detection scheme of pre-coded OFDM is proposed. The proposed scheme recovers the pre-coded data symbols correspond to the carriers whose reception powers are degraded by frequency selective fading by using the data symbols after decision and the data symbols are detected again using the recovered pre-coded data symbols. As the result of numerical analysis, it is confirmed that better performance under severe frequency selective fading channels can be achieved by iteratively repeating the proposed scheme combined with convolutional error correcting code.

In this paper, an iterative detection scheme of precoded OFDM is proposed. The proposed scheme recovers the precoded data symbols correspond to the carriers whose reception powers are degraded by frequency selective fading by using the data symbols after decision and the data symbols are detected again using the recovered precoded data symbols. As the result of numerical analysis, it is confirmed that better performance under severe frequency selective fading channels can be achieved by iteratively repeating the proposed scheme

In the communication systems using OFDM, it is necessary to compensate the influence of frequency selective fading caused by multi-path. In this paper we propose a MAP data reconstruction from the data symbols spread in the frequency domain in OFDM transmission. The performance of the proposed scheme is examined by computer simulation and good performance is confirmed.

In OFDM transmission, a loss of sub-carrier orthogonality due to Doppler-spread of the channel leads to inter-carrier interference (ICI). We have proposed a method to reduce the ICI caused by the Doppler spread of the channel. The transmission channel is modeled by a combination of multiple Doppler-shifted propagation paths, and their parameters such as attenuation, relative delay and Doppler-shift are estimated using scattered pilot symbols. The ICI is canceled by multiplying the inverse matrix of the estimated channel matrix with the received OFDM symbol vector. However, the ICI canceller causes enhancement of noise component, so it can't improve the bit error rate characteristics sufficiently. In this paper, we propose the new ICI canceller based on MMSE, which does not cause enhancement of noise component. As the result of computer simulation, it was confirmed that the ICI canceller based on MMSE could reduce the bit error rate more than ICI canceller based on zero-forcing under the Doppler-spread channel.

The paper proposes to develop the ability of planning in learning by problem-solving, providing the learners with a repertoire of problem types as constructs of plans and their expansions into sub plans as well as sample problems with solutions indexed by hierarchical use of plans and sub plans for solving the problems. The learners can construct their plans on the system-supported planning environment and retrieve solutions of sample problems by way of the structured solution plan indices. The system critiques their plans and checks, through interaction with the learners, the interim results of executing any subproblems in the solution path. A prototype system was implemented and tested in order to assess the significance of providing such an environment in developing ability of planning. The pre-post test evaluation in steps strongly suggested importance of providing sample problems with plan indices in order for the learners to be confident of applicability of newly learned plans.

In the OFDM SFN (single frequency network) system, where the received signal from the main broadcast station is rebroadcast at the relay station, the area where the delay spread of the received signal is longer than the guard interval length increases as compared to the SFN system where the signals are transmitted at the same time both from the main station and from the relay station. If the channel delay spread is longer than the guard interval length, inter-symbol interference (ISI) and inter-carrier interference (ICI) are generated at the receiver and the bit error rate (BER) characteristics are much degraded. Therefore, the service area of the OFDM SFN system where the signal is re-broadcast at the relay station is narrower that that of the OFDM system where the signals are broadcast at the same time from both stations. In order to improve this problem, an SFN system that rebroadcasts the received signal from the main station after adding an appropriate delay is proposed. We propose an array antenna receiver using a maximum ratio combining technique for the SFN system, where additive delay is inserted to the signal at the relay station. By theoretical analyses and computer simulations, better BER characteristics than the conventional system are confirmed.

In OFDM transmission, a loss of sub-carrier orthogonality due to Doppler-spread of the channel leads to intercarrier interference (ICI), especially under mobile reception environments. ICI causes significant degradation of bit error rate characteristics and this influence becomes larger as the carrier frequency or moving velocity of the receiver increases. In this paper, a method to reduce the ICI caused by Doppler-spread of the channel is proposed. In the proposed method, the transmission channel is modeled by a combination of multiple Doppler-shifted propagation paths and their parameters such as attenuation, relative delay and Doppler-shift are estimated using scattered pilot symbols. Then, ICI is canceled by multiplying the inverse matrix of the estimated channel matrix to the received OFDM symbol vector. As the result of computer simulation, it is confirmed that the proposed method can improve the bit error rate characteristics under Doppler-spread channel.

OFDM is widely known as a modulation scheme which can utilize the given frequency band very efficiently, even if the channel is distorted by multipath propagation. However, in order to improve the efficiency, a high-precision estimation technique is recommended. In this paper, we pay attention to the method which introduces a condition based on the propagation path model in order to obtain better precision. Although this method performs better than another conventional method especially under the fading environment, this method has large computational complexity. Hence, we simplify this method by using the FFT algorithm to make this method more effective. As a result, the proposed system performs better than the conventional system especially under fading environments, and the computational complexity is reduced.

As an application of NLP to computer-assisted language learning(CALL), we propose a diagnostic processing of Japanese being able to detect errors and inappropriateness of sentences composed by the students in the given situation and the context of the exercise texts. Using LTAG(Lexicalized Tree Adjoining Grammar) formalism, we have implemented a prototype of such a diagnostic parser as a component of a CALL system being developed.

An OFDM system is widely known as a modulation scheme, which can reduce the effect of frequency selective fading. However, under a large frequency selective fading environment, it is difficult to demodulate correctly even with appropriate equalization. In this paper, an OFDM system applying a frequency diversity scheme is proposed. In this system, the same symbols are transmitted on several sets of carriers, and at the receiver end, these symbols are combined so as to maximize the signal to noise ratio. As the experimental result, it is shown that as the fading level becomes larger, the proposed system provides a larger gain in the bit error rate characteristics than the conventional system.

A TDM wireless local area network system using a spread spectrum signal for its access control is analyzed. By using a spread spectrum control signal, it is possible to control the network system under severe environments where a TDM only system can't operate well. Moreover, in this system, the spread spectrum control signal is used to measure the channel characteristics between nodes and the information are used to equalize the TDM data transmission channel. This improves the performance of the adaptive equalizer and realize fast data transmission. The measured channel characteristics can be used as a criterion for routing operations.

The tap selecting digital adaptive FM multipath distortion canceller is described. In order to implement hardware of FM multipath distortion canceller, the convergence property of it is examined by computer simulation with finite bit length variables. As the result, a good DU ratio and fast convergence speed is confirmed. Moreover, simplification of hardware and structure of it is examined in practice.