Heiichi Yamamoto

Array Antenna Assisted Doppler Spread Compensator for OFDM

This paper proposes a novel Doppler spread compensation scheme using a linear array antenna, which is parallel to the direction of movement of the vehicle. In order to mitigate performance degradation due to Doppler spread, the compensation scheme estimates the received signal at a point that is ‘fixed’ against the ground during the observation period. Computer simulation results show the proposed compensation scheme can effectively compensate for bit error rate degradation due to Doppler spread.

PAPR reduction of OFDM signals using iterative processing and carrier interferometry codes

Generally peak-to-average power ratio (PAPR) reduction imposes transmission performance degradation or system capacity reduction. This paper proposes a method for reducing the PAPR of OFDM signals by combining carrier interferometry (CI) spreading code and iterative processing (IP). The proposed method is capable of reducing the PAPR significantly while minimizing the bit error rate (BER) performance degradation. Computer simulation results prove the effectiveness of the proposed method. Further, the proposed method does not introduce out-of-band interference, which requires filtering whose complexity depends on the filtering requirement.

Novel fast fading compensator for OFDM using space diversity with space-domain interpolator

This paper proposes a novel space diversity assisted OFDM receiver with Doppler spread compensator. A linear array antenna is set up on the vehicle. The proposed compensator estimates the received signal at the point that does not move with respect to the ground during the observation period. Computer simulation results show that the proposed scheme can mitigate the performance degradation due to Doppler spread.

An MC-CDMA signal equalization and detection scheme based on support vector machines

In this paper, we propose a novel nonlinear signal equalization and detection scheme applying the support vector machine (SVM) technique for downlink multicarrier code division multiple access (MC-CDMA) systems. The SVM is gaining popularity in the field of pattern classification due to its promising empirical performance, moderate computation complexity and its strong mathematical foundation. In the proposed scheme, the SVM-based equalizer is trained with the frequency domain received signal for the implicit frequency diversity effect. Simulations are conducted under time-varying multipath fading channel to verify the effectiveness of the proposed scheme in the presence of multiuser interference (MUI) and inter-channel interference (ICI), two major impairments that severely degrade the performance of MC-CDMA systems employing conventional linear equalizers. Simulation results confirmed that the proposed scheme effectively mitigates MUI and ICI and outperforms conventional linear equalizers with perfect channel estimation.

Simplified Realization of Pseudo-Orthogonal Carrier Interferometry OFDM by FFT Algorithm

This paper proposes new simplified design of Pseudo-orthogonal Carrier Interferometry Orthogonal Frequency Division Multiplexing (PO-CI/OFDM) system by utilizing IFFT/FFT algorithm as a substitute of PO-CI spreading and despreading. We also propose a separator design for guaranteeing that the resulted codes are still (pseudo) orthogonal to each other. This solution is capable of reducing the complexities of PO-CI/OFDM implementation significantly. Difficulties of generating PO-CI codes as complex spreading codes are successfully solved by employing two IFFT/FFTs with the proposed separator. In this paper, we show that PO-CI/OFDM using FFT algorithm (further called PO-CI-FFT/OFDM) is a very simple and low cost technique while providing good performance as the original PO-CI/OFDM. Additional multiplications and additions for PO-CI spreading/despreading and additional memory for storing the generated codes is not required when utilizing the proposed design. This solution is capable of making PO-CI/OFDM closer to the reality.

On the PAPR reduction for wavelet based transmultiplexer

This paper investigates the peak-to-average power ratio (PAPR) of a wavelet based transmultiplexer for a high-speed digital communications system. A transmultiplexer based on wavelet in conjunction with the spread spectrum technique, has been shown to exhibit good performance while having good spectral properties. On the other hand, a common issue with multicarrier modulation systems is the PAPR due to the superposition of a large number of independently modulated subcarriers in parallel at the transmitter. Reducing PAPR is essential for realizing power efficient devices, which is an important issue for future generations of mobile communication systems. Our computer simulation results clarified that Haar wavelet based transmultiplexers exhibit low PAPR values when frequency domain spreading using Hadamard code is employed. This result is similar to the case of orthogonal frequency division multiplexing (OFDM) where carrier interferometry (CI) codes were demonstrated to exhibit low PAPR values.

Sequence assignment of Walsh-Hadamard sequences for quasi-synchronous multi-code CDMA systems

In this study, we propose the sequence assignment of Walsh-Hadamard sequences suitable for quasi-synchronous multi-code transmission. One of the important properties of proposed sequences is that any sequences in a sequence set have zero even cross-correlation with any sequences in another set for any time difference. By using the proposed sequences, the BER performance is significantly improved compared with that by conventional sequences with less number of interferences. Moreover, even if all (N) sequences are used simultaneously by different users, a practical BER performance is obtained. Although the proposed sequences have good cross correlation properties, the auto-correlation properties may be worse than general spreading sequences. Therefore, some devices to overcome the effect of multipath fading should be necessary for practical use in mobile radio environment.

Signal Cancellation for Satellite Frequency Reuse by Carrier Super-Positioning Multi-level Modulation

This paper proposes a design of frequency reuse for satellite communications by carrier super-positioning for multi-level modulation which is going to be widely used. In the frequency super-positioning, the interference is caused by the undesired signal remained by the imperfectness of replica. The imperfectness is due to the phase and amplitude error between undesired signal and replica and degrades the transmission performance. This paper is trying to solve this issue by minimizing the imperfectness to satisfy multi-level modulation transmission and by making precise replica simple. We show here a design approach for implementing accurate signal canceller for QPSK and 16QAM transmission. A simple method to generate replica is also proposed as an alternative. This method does not require satellite one round trip delay measurement which was required in the conventional canceller.

Dummy Elements Add on Both Sides of Monopole-Array Assisted Doppler Spread Compensator for Digital Terrestrial Television Broadcasting Receiver

In this paper, we proposed Doppler spread compensator, which exploits dummy elements on both sides of monopole-array antennas. Dummy elements mitigate the performance degradation of the array antenna assisted Doppler spread compensator due to mutual coupling among array elements. In order to confirm the validity of the proposed scheme, we carried out computer simulations. Computer simulation results show that the proposed scheme is not only capable of mitigating deterioration due to mutual coupling, but also, expanding operating bandwidth wider than the conventional Doppler spread compensator with mutual coupling canceller, which cancels out mutual coupling in base band. INTRODUCTION Recently, the digital terrestrial television broadcasting (DTTB) has been attracted to the capabilities of high definition television (HDTV), multiple stream and additional data transmission services. DTTB services have already started in most countries. Especially, the European and Japanese DTTB systems, DVB-T (Digital Video Broadcasting for Terrestrial)[1] and ISDB-T (Integrated Services Digital Broadcasting for Terrestrial)[2] employ OFDM (Orthogonal Frequency Division Multiplexing) for its transmission scheme. OFDM is able to transmit high rate data stream in a time dispersive multi-path channel. Moreover, it has robustness against frequency selective fading due to multi-path delay spreading, because of narrow bandwidth among the sub-carriers [3]. However, the performance of OFDM has deteriorated by ICI (Inter Channel Interference) because of narrow bandwidth among sub-carriers [3]. ICI caused by Doppler spread, where a several incoming waves affected the different Doppler shift, as well as frequency offset between transmitter and receiver. In this paper, we supposed Mode3 of the Japanese DTTB system, ISDB-T, which has 5617 of sub-carriers and 1kHz of bandwidth among sub-carriers. The maximum Doppler frequency reaches 70Hz, when the carrier frequency is 770MHz and the receiver moves at the speed of 100km/h. It means that the BER (Bit Error Rate) performance is severely degraded by Doppler spread. In order to solve this problem, the linear array antenna assisted Doppler spread compensator has been proposed by a part of authors [4,5]. The conventional Doppler spread compensator was composed of linear array antenna and space domain interpolator. The space domain interpolator estimates the received signals at a fixed with respect to the ground by making use of the received signal from each array element. Consequently, it could be mitigated the deterioration of BER performance by Doppler spread effect. On the other hand, the conventional linear array antenna has been affected by mutual coupling effect due to narrow antenna spacing. In order to mitigate the mutual coupling effect, mutual coupling canceller has been attached to the conventional Doppler spread compensator. The mutual coupling canceller cancels out mutual coupling in base band domain. Therefore, it has narrow operating bandwidth compared with the television frequency band [5]. The carrier frequency of ISDB-T is from 470MHz to 770MHz. That is, the total bandwidth of DTTB is 300MHz. To alleviate the mutual coupling among array elements, we proposed dummy elements add on both sides of monopole-array. Dummy elements reduce the mutual impedance between main elements because of coupling between each dummy element and each main element. Therefore, the proposed scheme could be improved the performance of Doppler spread compensator. The rest of paper is organized as follows; Sect2 describes the proposed Doppler spread compensator. Sect3 shows computer simulation results. Sect4 summarizes the concluding remarks. 377 0-7803-9444-5/06/

Peak-to-Average Power Ratio Reduction Method Suitable for MC-CDMA System Downlink

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