Nobuo Itoh

HDTV Mobile Reception in Automobiles

Mobile reception of digital terrestrial broadcasting carrying an 18-Mb/s digital HDTV signals is achieved. The effect of diversity reception in moving automobiles for a 64 quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM) signal is investigated by prototype hardware. There are two methods for diversity reception of OFDM signals. The first is the Doppler compensation directivity control system. For this method, high-performance on-glass antennas and new diversity reception systems for OFDM reception have been developed to verify HDTV service availability in mobile reception environments. Novel horizontally polarized on-glass antennas suitable for DTV were developed. The antenna elements were printed on the inside surface of the rear window glass of a passenger van. OFDM signals received by the four antenna elements were weighted and combined using maximal ratio combining (MRC). The experiments were conducted in urban areas and they showed that employing diversity techniques would make HDTV mobile reception possible in many areas. The other method is post-FFT diversity. In the receiver, MRC is performed after an FFT operation on each branch signal. Experimental results show that accurate HDTV mobile reception can be achieved by using a four-branch MRC system. Also, the minimum usable electric field strength could be reduced compared with that of a single dipole antenna.

Advanced transmission cycle control scheme for autonomous decentralized TDMA protocol in safe driving support systems

When the volume of traffic on a roadway is so high such as traffic jam, medium access control (MAC) protocols in inter-vehicle communication (IVC) systems do not work well. The primary reason is the huge amount of communication traffic, which could be resolved by conventional transmission cycle control (TCC) schemes. However, when using TCC schemes, the failure of packet transmission extends the communication interval between vehicles, which can cause driving support systems that use IVC to malfunction. This paper proposes an advanced TCC scheme for realizing a safe driving support system. The proposed scheme exploits the frame-information exchange in the autonomous decentralized TDMA protocol, so that subsequent packets are transmitted rapidly even when failure occurs. Such a scheme is shown to be effective in terms of both communication quality and driving support systems.

Adaptive beam steering reception system for ISDB-T based on pre-FFT diversity technique

The reception of high-definition television in a mobile environment with the same quality as that achieved at home has been considered to be difficult to achieve. In an attempt to solve this problem, we have developed an adaptive beam steering reception system and evaluated the performance of this new system by both indoor and outdoor experiments involving the reception of high-definition television. The experimental results revealed that the reception performance was significantly improved, such that terrestrial digital television broadcasts can be received in high-speed moving environments, and with the same stability as broadcasts that are received at home in a fixed reception area.

Maximum likelihood decoding for wavelet packet modulation

The multi-carrier modulation (MCM) technique is an attractive approach for high-speed digital radio communication systems in order to achieve a high spectral efficiency and to combat the frequency selectivity of the channel. Orthogonal frequency division multiplexing (OFDM) is a kind of MCM technique. Wavelet packet modulation (WPM) is another kind of MCM technique using the wavelet transformation instead of the Fourier transformation to multiplex information symbol sequences. In this paper we propose a maximum likelihood decoding method for WPM without coding before transmitting the signal. The proposed method performs maximum likelihood sequence estimation by utilizing a signal obtained in an intermediate stage of the demultiplexing process. Then, bit error performance under a flat fading channel and frequency-selective fading channel is evaluated by computer simulation. According to the results, the proposed method can improve the bit error performance in the region of high Doppler frequency.

An adaptive array direction control LSI for mobile digital HDTV receivers

This work presents a multi-antenna diversity LSI that enables the mobile reception of digital HDTV. A unique algorithm of four-branch combination with three-band division method drastically improves the performance of mobile reception, especially in high-speed environments. The rate of reception is 97% field-testing result in Japan.

A Novel MIMO-STBC Scheme for Inter-Vehicle Communications at Intersection

This paper proposes an inter-vehicle communication (IVC) scheme for safety driving support systems that transmits collision avoidance warnings at intersections. In order to realize high communication reliability, a transmission scheme based on multiple-input multiple-output (MIMO) with space-time block coding (STBC) is proposed. A key transmission feature of MIMO systems is determined by radio wave propagation. Therefore, the radio wave propagation at an intersection is analyzed by computer simulations using the ray-tracing method. In addition, this paper verifies the effectiveness of the proposed scheme using the propagation characteristics in computer simulations

A Novel Multi-Service Simultaneous Reception by Sharing Diversity Branches

In this paper, we propose a new concept of receiver structure with diversity reception technique to realize multi-service simultaneous reception, which shares diversity branches between receiving communication services. In the proposed receiver structure, each diversity branch selects the receiving services dynamically according to channel states, and each communication service is always selected by at least one branch to realize multi-service simultaneous reception. A basic algorithm is also described to select combinations of a diversity branch and a receiving communication service. The total number of branches decreases and the effective number of branches per communication service increases, by sharing the branches between communication services in the proposed receiver. Simulation results are shown that the proposed diversity receiver achieves both complexity reduction and performance improvement.

Reception Quality of Terrestrial Digital Broadcasting Signals while Traveling at High Speed

To receive terrestrial digital broadcasting signals in an automobile, we previously proposed a method for controling the antenna directional pattern and demonstrated the effectiveness of the method by field experiment in an urban area. We have now investigated the reception quality during high-speed traveling and clarified the performance of doppler-shift compensation in the proposed method. A field experiment demonstrated that high-definition television (HDTV) signals can be received in an automobile traveling at about 100 km an hour.

An adaptive array for multi-carrier transmission

The authors have proposed a novel algorithm for an adaptive array that is suitable for the multi-carrier transmission. It has already been confirmed that multi-carrier waves can be suppressed by the adaptive array in the multi-carrier transmission system (Fujimoto et al.). In this paper it is shown through computer simulation that not only the multipath waves but also the co-channel interference waves can be suppressed by the adaptive array.