Noriyoshi Suzuki

Estimation and exclusion of multipath range error for robust positioning

In integrated systems for accurate positioning, which consist of GNSS, INS, and other sensors, the GNSS positioning accuracy has a decisive influence on the performance of the entire system and thus is very important. However, GNSS usually exhibits poor positioning results in urban canyon environments due to pseudorange measurement errors caused by multipath creation, which leads to performance degradation of the entire positioning system. For this reason, in order to maintain the accuracy of an integrated positioning system, it is necessary to determine when the GNSS positioning is accurate and which satellites can have their pseudorange measured accurately without multipath errors. Thus, the objective of our work is to detect the multipath errors in the satellite signals and exclude these signals to improve the positioning accuracy of GNSS, especially in an urban canyon environment. One of the previous technologies for tackling this problem is RAIM, which checks the residual of the least square and identifies the suspicious satellites. However, it presumes a Gaussian measurement error that is more common in an open-sky environment than in the urban canyon environment. On the other hand, our proposed method can estimate the size of the pseudorange error directly from the information of altitude positioning error, which is available with an altitude map. This method can estimate even the size of non-Gaussian error due to multipath in the urban canyon environment. Then, the estimated pseudorange error is utilized to weight satellite signals and improve the positioning accuracy. The proposed method was tested with a low-cost GNSS receiver mounted on a test vehicle in a test drive in Nagoya, Japan, which is a typical urban canyon environment. The experimental result shows that the estimated pseudorange error is accurate enough to exclude erroneous satellites and improve the GNSS positioning accuracy.

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.

Prediction of Line-of-Sight Propagation Loss in Inter-Vehicle Communication Environments

This paper presents a prediction formula of propagation loss for low antenna height scenarios on a line-of-sight (LOS) straight-line road having an intersection, for modeling the propagation loss characteristic in inter-vehicle communications (IVCs). The regression analysis is applied to the propagation loss data generated by computer simulation based on the geometrical optics theory, and the regression formula is established as a dual-slope model having variables of propagation distance, frequency, road width, and antenna height. In this analysis, the position of breakpoint is determined so that the RMS error of the regression becomes the smallest on both slope regions because its position is an important factor for good prediction accuracy. Furthermore, the comparison between predicted and measured propagation losses is performed in 2 GHz and 5 GHz bands, and the effectiveness of the prediction formula is confirmed by evaluating the prediction errors.

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.

Effect of Number of Elements of a Reactively Loaded Ring Antenna Array on the Performance of Beamwidth Variation

We herein investigate the effect of the number of elements of a previously studied reactively loaded ring antenna array with respect to electronically variable beamwidth performance. The antenna has a unique ability to increase the effective antenna length by adding parasitic ring elements, which contributes to higher performance with respect to beamwidth variation. Monte Carlo (MC) simulations clarify that variable range of beamwidth can be improved effectively by increasing the number of ring elements M to 5. It is herein demonstrated for the case of M = 5 that the beamwidth toward the broadside direction can be controlled from 40deg to 145deg in the E plane, while maintaining the voltage standing-wave ratio (VSWR) to less than 3.0, where the antenna size is 0.32lambda times 1.32lambda. In addition, it is also confirmed that the number of estimated directions-of-arrival (DOAs) based on the reactance-domain multiple signal classification (MUSIC) algorithm can be also increased by increasing the number of ring elements.

Periodic Broadcast Timing Reservation Multiple Access for Inter-vehicle Communication

The present study investigates a Medium Access Control (MAC) protocol for reliable inter-vehicle communications (IVC) to support safe driving with the goal of reducing road traffic accidents. A number of studies have evaluated the performance of the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. However, the communication quality provided by the CSMA/CA protocol is seriously degraded by the hidden terminal problem in IVC. Therefore, we propose a new MAC protocol, referred to as Periodic Broadcast-Timing Reservation Multiple Access (PB-TRMA), which can autonomously control transmission timing and avoid packet collisions by enhancing the Network Allocation Vector (NAV) for periodic broadcast communications. The simulation results show that the proposed protocol can resolve the hidden terminal problem and mitigate data packet collisions. Moreover, the behavior of PB-TRMA is similar to that of Time-Division Multiple Access (TDMA). In addition, we show that two procedures, namely, packet collision retrieval and hidden terminal detection, are essential ingredients in PB-TRMA in order to achieve high quality performance.

Proposal for a new localisation method using tightly coupled integration based on a precise estimation of trajectory from GPS Doppler

Driver assistance systems require the function of precise localisation. However, the accuracy of standard global positioning system (GPS) is inadequate for this. In this paper, a new method for precise localisation using the tightly coupled integration of inertial navigation system (INS) and raw GPS data is investigated. GPS Doppler corresponds to the relative velocity between the satellite and the receiver. Our new method enables us to make a robust and accurate estimation of the vehicle trajectory based on INS and GPS Doppler. Furthermore, the total optimisation by combining GPS pseudorange data with the accurate trajectory enables us to estimate the position of the vehicle precisely.

Performance Evaluation of MIMO-STBC for Inter-Vehicle Communications in a Shadowing Environment Generated by a Large Vehicle

The present study investigates an inter-vehicle communication (IVC) scheme for safety driving support systems, such as collision avoidance warning systems at intersections. In order to realize high communication reliability, we apply a multiple-input multiple-output (MIMO) with space-time block coding (STBC) method in the IVC system. We investigate the transmission quality of the method in collisions when making a right turn, as an example of a dangerous situation. A key transmission feature of the MIMO system is determined by radio wave propagation. Therefore, the radio wave propagation at an intersection in this dangerous situation is analyzed by computer simulation using the ray-tracing method and by radio wave measurements in a field experiment. In addition, we propose propagation channel models in a shadowing environment generated by a large vehicle. Finally, we clarify the effectiveness of the proposed MIMO-STBC scheme by computer simulations.

Multi-hop transmission scheme compatible with single-hop periodic broadcast in vehicle-to-vehicle communications

Decentralized time division multiple access (D-TDMA) is an autonomous slotted protocol originally designed for the single-hop periodic broadcast of safety messages. With the arrival of new ITS applications based on multiple wireless link transmissions, however, the introduction of new mechanisms is essential to share the time domain between single-hop periodic broadcast (safety messages) and multi-hop transmission. Because the scarce 10 MHz-band is going to be used as one communication channel in Japan, a highly reliable medium access control (MAC) scheme is required to handle both safety and multi-hop messages. We propose the multi-hop transmission scheme compatible with single-hop periodic broadcast. In our solution, each terminal that transmits a multi-hop packet first starts a slot reservation procedure to avoid packet collisions with safety messages and thus maintain as high a delivery rate as possible. Then, the transmitting nodes use the D-TDMA structure to check the reception of the multi-hop packet at the relay side. If any failure is detected, the packet is retransmitted as soon as possible. Concerning the routing algorithm, we assume that messages are routed to the destination along the road having the best vehicular traffic and that the road information is provided by D-TDMA. Computer simulations were conducted for an urban environment in which vehicles are moving. The simulation results show that our scheme maintains the delivery rate of safety messages and can recover multi-hop packets in the case of transmission failure.