A flexible symbol-timing synchronization met-hod is a one that uses a common sampling clock to find synchronization points for radio communication systems that have different symbol rates. This method estimates synchronization points from state patterns calculated using the symbol rate, sampling clock, and number of observed symbols. Decreasing the number of state patterns is one of best ways to reduce the amount of device resources needed to store the patterns. In this paper, we propose a new pattern generation method in which the number of generated patterns does not increase when the sampling clocks of the communications systems are different. To show the feasibility of this method for symbol-timing synchronization, we analyzed a relationship between the number of samples and the number of state patterns and calculated the BER (bit error rate) in AWGN (additive white Gaussian noise) and one-path flat Rayleigh fading environments by computer simulation.

In a two-layer self-diplexing antenna fed at two ports, theoretical analysis has already shown that the isolation characteristics can be improved by adjusting the angle between the feed locations of the transmitting and receiving antennas. In this letter, we experimentally investigate the isolation characteristics of the self-diplexing array antenna. First, calculated and experimental results for each feed location of the element antenna are compared and good agreement is found. Second, experimental results with a 19-element planar array indicate that a self-diplexing antenna with suitably chosen feed configuration is effective in improving the isolation in a phased array antenna.

In this paper, a new configuration method of multimode software radio system by parameter controlled and telecommunication component block embedded digital signal processing hardware (DSPH) is proposed for the future flexible multimedia communications. In this method, in advance, basic telecommunication component blocks are implemented in the DSPH like DSP and FPGA. And, external parameters, which are simple but important information, change the specification of each block. This proposed method has the following features: i) People need to have only one mobile handset and select communication services as they like. ii) The volume of download software is reduced drastically in comparison with conventional full-download-type software radio system. iii) Since important component blocks have already been implemented into the DSPH except for some external parameters in advance, the know-how related to the implementation of DSPH never leak out. In this paper, we evaluate the effectiveness of the proposed configuration method by using computer simulation and developed experimental prototype and comparing with full-download-type software radio system from the viewpoint of the volume of download software. Finally, we introduce several new software radio systems by using the proposed configuration method.

This paper proposes a new type of optically controlled BFN (beam forming network), an electro-optic BFN using an optical waveguide structure. In this BFN, antenna beam forming is performed using conventional optical variable phase shifters and conventional optical variable directional couplers. An electro-optic BFN can easily utilize monolithic integration capability that will be advantageous to microwave stabilization. In order to discuss practical applicability, microwave characteristics and beam forming characteristics were examined using an experimental BFN fabricated on a LiNbO3 substrate. Resulting from electro-optic lightwave control, linear phase shifting and variable amplitude distribution were measured at various microwave frequencies. Without any other control except for optical offset frequency locking and applying constant voltages, typical short term fluctuation in L-band microwave was measured to be within 3 degreesp-p in phase and 2.5 dBp-p in amplitude, respectively. For the first time, an electro-optic BFN was successful in performing beam forming in an L-band array antenna as well as coaxial cables. It was also verified that radiation pattern measured in 60 degree beam steering using the experimental BFN was comparable to that calculated using conventional microwave BFNs. The experimental results show the feasibility of utilizing an electro-optic BFN in future advanced microwave/millimeter-wave array antenna systems.

This paper presents a novel four-sector shaped-beam antenna suitable for base station antennas in 60-GHz wireless local area networks (LANs). The antenna has a plateau configuration, whose four side walls have four linearly arranged microstrip antennas. Each trapezoidal facet excites a shaped beam in the elevation plane in order to meet link-budget requirement between base station and remote terminal, taking account of directional patters of remote terminal antennas. Low-loss curved microstrip-line is applied to connect the three-dimensional antennas with active circuits mounted on a flat carrier plate. This antenna has been adopted as the base station antenna in 60-GHz wireless LANs. The first-stage transmission experiment confirms the usefulness of shaped-beam antennas in the 60-GHz band.

In order to realize a future seamless high-speed road-vehicle communication system, we have proposed using code division multiplexing (CDM) radio transmission scheme by using cyclic shifted-and-extended (CSE) codes as spread codes. As the CSE codes are generated by cyclically shifting and extending a conventionally used code, the number of codes generated from a code is limited to the length of the shift interval and the tolerable period of delayed waves also depends on the length. In this paper, based on CSE codes, we propose a method to minimize the length of the shift interval and a cancellation technique with a simple calculation in order to eliminate the interference from delayed waves caused by the reduction of the length of shift interval. The concept and the BER performances in AWGN, two-paths, and multi-path fading environments are described in this paper. As a result, the maximum transmission rate of CSE-based-CDM transmission per one-code using the newly proposed transmission scheme is 3 times as large as that using conventional CSE codes and DQPSK-CDM transmission scheme.

This paper presents the successful performance of an optical waveguide phase controller for microwave signals generated by heterodyne photodetection. A 22 optical waveguide structure with four optical phase shifters was fabricated on a LiNbO3 substrate. As a result of heterodyne photodetection of two optical signals from wavelength-tunable laser diodes, two microwave signals at 585 MHz were generated and phase shifted in the manner of electro-optical phase retardation. The monolithic waveguide structure allowed linear phase shifting more than 1800 degrees. Similar phase shifting performances were also confirmed over a wide microwave frequency range from 300 MHz to 1.3 GHz. The optical waveguide structure demonstrated here will be applicable to fiber-optic fed microwave systems such as a phased array antenna.

In this paper, we newly developed a small-size software radio terminal that can realize global positioning service (GPS) navigation system, vehicle information and communication system (VICS), electronic toll collection system (ETC), AM/FM radio broadcasting services on middle wave (MW) and very high frequency (VHF) bands, FM multiplex broadcasting system, and several modulation schemes such as BPSK, ASK, QPSK, GMSK, and π/4QPSK by downloading software to realize each system from wired and wireless networks. The developed terminal realizes simultaneous multiple services when users would like to use several radio communication services in the driving situation by using our proposed multitask algorithm. The developed terminal has a size of 17.5 cm wide, 19.0 cm deep, and 5 cm high and worked at DC-12.0 V and around 2 A. The size and electrical power consumption are quite small and low and acceptable for consumers such as car drivers. In this paper, we introduce the configuration and proposed key technologies in our developed terminal and measure the software configuration time.

We have proposed two types of software download methods for software radio (SR) based intelligent transport systems (ITS): (1) broadcasting-type software download method and (2) communication-type software download method. In this paper, we study their feasibility of their employment in a newly developed prototype. We give tangible examples of method (1) using the vehicle information and communication system (VICS) and method (2) using the dedicated short range communication (DSRC) system. We describe the download formats and procedures for both methods and use the experimental prototype to evaluate the basic software download time and configuration time. Moreover we also propose architecture of SR-based multimode terminal that can reduce download time and utilize over-the-air software download services by VICS and DSRC links.

We have experimentally measured the propagation characteristics of 60-GHz-band millimeter wave between two vehicles to design of inter-vehicle communication (IVC) system in intelligent transport systems (ITS). Received power and bit error rates of 1-Mbps data transmission between a transmitter mounted on a leading vehicle and two receivers attached on a following vehicle were measured. A two-ray propagation model was devised to calculate the instantaneous propagation characteristics, and these estimations agree well with the measured characteristics. The feasibility of 1-Mbps data transmission between the running vehicles on an actual expressway was demonstrated. The cumulative distribution of received power between the two running vehicles when their height from the road surface fluctuated was also determined from the proposed two-ray propagation model and experimental measurements.

This paper proposes an autonomous relay access algorithm that provides an intelligent wireless network structure for inter-vehicle communication systems. The proposed algorithm introduces a special classification among mobile terminals and assigns terminals to one of several terminal groups, which are adaptively and autonomously constructed according to traffic conditions. The proposed algorithm uses the terminal groups to conduct relay access transmission among terminals, and achieves a high rate of successful inter-terminal transmission. Computer simulation confirms that the proposed algorithm can achieve a lower blocking probability than that without a relay access scheme.

An adaptive modulated orthogonal frequency division multiplexing (OFDM) radio transmission scheme that enables efficient data transmission in multipath fading environments is newly proposed. This scheme can be used in standardized multimedia mobile access systems such as ETSI-BRAN, and ARIB-MMAC. It is based on estimating the delay spread and the carrier-to-noise power density ratio (C/N0). The estimation is done using channel estimation symbols that are inserted into the frames of the standard OFDM radio transmission scheme. Computer simulations show that the estimation method results in an average BER close to those when propagation characteristics are perfectly estimated. Furthermore, when the adaptive OFDM transmission scheme is based on BPSK, QPSK or 16 QAM, the average BER is almost close to that when BPSK-OFDM is only used, and the average transmission rate is 1.8 times as high. Using an error-correction code based on convolutional code results in an average BER lower than that with the BPSK- and QPSK-OFDM schemes.

In this paper, a low-cost radio-on-fiber (ROF) system for a 36 GHz band road-vehicle communication system (RVCS) is proposed and demonstrated. Optical components for 10 Gb/s baseband transmission systems, which are becoming lower in cost, are used for the proposed system. The signal is transmitted in the optical link in the form of an intermediate frequency (IF) signal of the 5.8 GHz band. The third subharmonic of a local oscillator wave (LO) is transmitted simultaneously with the IF signal from the central station to the remote stations (RSs). This scheme enables the realization of RSs without costly millimeter-wave synthesizers. In such a configuration, the influence of intermodulation distortion between the IF signal and the LO subharmonic and degradation of the carrier-to-noise ratio (CNR) could possibly be a problem, and so an analysis and experiments were carried. It was clarified that the compression of dynamic range caused by the simultaneous transmission was small. Frequency tripling of the LO degraded the CNR of the LO; however, this effect was compensated for by increasing the optical modulation index (OMI) of the LO subharmonic. Increasing the OMI of the LO subharmonic proved to have no influence on the IM3 characteristics of the RF signal analytically and experimentally. The proposed low-cost system proved to have sufficient characteristics for millimeter-wave RVCS.

A symbol timing synchronization method is proposed for the realization of a multi-mode and multi-service software radio receiver. The method enables an accurate search for the optimum symbol timing without any redundant hardware such as sampling rate conversion devices, when the system clock is non-integer times for the target systems' symbol rates. Accordingly, a multimode and multi-service receiver can set an arbitrary system clock for the target systems' symbol rates, and the number of A/D converters can be reduced to the minimum. Also, it may lead to a reduction of the implementation time for digital signal processing hardware, and reduce the burden on the memory in a multi-mode and multi-service software radio receiver, since no sampling rate conversion is needed. The effectiveness of the proposed method for use with a multi-mode and multi-service software radio receiver for future ITS services, which are GPS (Global Positioning System), ETC (Electric Toll Collection system), and Japanese PHS (Personal Handy-phone System) is assumed, and the supposed system is evaluated by computer simulation. The jitter performance under an AWGN (Additive White Gaussian Noise) environment is first simulated, and the necessary number of over-samples and observation symbols are defined by the value of jitter which gives a theoretical value of the BER, respectively. Moreover, the bit error rate performance under a fading environment condition where the attenuation of a signal level fluctuates more rapidly than in a noise environment is calculated, and it is shown that the proposed method enables an accurate search for the optimum synchronization timing caused by a cycle slip even if the signal level is quite low, and allows one handset to adopt a system clock for several systems.

In this paper, we propose a new content delivery platform on the ITS (Intelligent Transport Systems) road-vehicle communication system on the basis of ROF (Radio over Fiber). The platform is strongly motivated by the ROF communication system capabilities of (1) broadband access, (2) integrated multiple service transmission interface, and (3) simultaneous use of a single and downsized vehicle terminal shared among multiple services based on a multi-mode software radio system. Content is delivered on per reservation basis, as is carefully envisaged as a primary service which is subjected to immaturity of early ITS road-vehicle communication systems, and is provided in limited service areas such as parking on main highways. After the reservation, requested content is stored in a cache connected to a ROF local station via optical fiber. At the designated time, the content is delivered from the cache to a target terminal by way of the ROF local station at high-speed. It can also be done by moving the content from the cache to another cache depending on the target terminal location in a flexible and reliable manner, even if the target terminal could not reach the place at the time designated in the reservation. Such flexibility and reliability are required for consequent practical application, and are provided using information given in the reservations. We implement a preliminary system to evaluate the proposed platform from the viewpoints of (1) processing time from logging into the system for a reservation to delivering content to the target terminal and (2) amount of control traffic required for the delivery. The results show that the proposed platform in which content is delivered from a cache connected with a ROF local station distributed geographically is effective. We also evaluate content delivery throughput using the system connected with an actual ROF local station, and show that the effective throughput is 40 Mbps and the proposed platform is a promising ITS service platform. The paper concludes by discussing future study toward realizing a more promising and practical system.

A method for estimating propagation characteristics is described that uses the characteristics of pilot-data-inserted orthogonal frequency division multiplexing (OFDM) signal and is suitable for high-mobility OFDM transmission scheme. Several pilot data are inserted periodically along the frequency axis before the inverse fast Fourier transformation (IFFT) process in the transmitter. At the receiver, the received OFDM signal is correlated with a prepared distinctive OFDM signal in which several pilot data are inserted in the same positions as in the transmitted OFDM symbols and zeros are inserted in the other positions. The propagation characteristics can be estimated precisely and used to cancel any interference caused by delayed waves. Computer simulation shows that this method can estimate the propagation characteristics, which can then be used to cancel the interference caused by delayed waves before the FFT at the receiver under fast multipath fading conditions.

We developed Millimeter-wave high speed spot communication system using radio-over-fiber technology for ITS telecommunication use. This system has wide bandwidth and provides a high-capacity channel between the base station and parked vehicles. The installation conditions (height, elevation angle) of the base station antenna of this system that enabled the largest possible communication area were obtained by simulation. In addition, we measured propagation and transmission characteristics. The width of the error-free service area was 8 m, which enables three vehicles to be served in one service area.

CRL (Communications Research Laboratory, Independent Administrative Institution Japan) is developing a road to vehicle multiple-service communication system based on RoF (Radio over Fiber) technology in a millimeter-wave frequency region of 36-37 GHz. In the experimental system, vehicle can receive three wireless services such as PHS (Personal Handy-phone System), ETC (Electronic Toll Collection system), SB (Satellite Broadcasting). In this paper, the system concept and experimental system configuration are introduced. Furthermore, SDR (Software Defined Radio) mobile terminal technology is mentioned and a new concept for a next generation mobile communication network system based on RoF is proposed.

Millimeter-wave (MMW) communication systems, specially from 60 GHz band, are expected to play a key role in realizing the intelligent transportation system (ITS) for high date rate and mulitmedia communications. During the last years, System-in-package (SiP) solutions for MMW RF-transceiver have become an attractive alternative to System-on-Chip (SoC) approaches. In the scheme, active circuits are integrated with passive circuit much tightly. Traditional distributed hybrid circuit concept, such as ADS and Microwave Office, is not quite applicable for SiP, specially in MMW frequency. In this paper, an improved finite-difference time-domain formulation using the matrix theory and an improved integral transform is presented to solve hybrid high-order linear lumped circuit and passive circuit problem implicitly instead of explicit method used for traditional FDTD method. In this improved method, general high-order linear lumped circuit is expressed firstly as not only one equation but also equations set according kirchhoff's laws. Then, a local iterative matrix expression connecting with each active circuit can be built when EM fields, current/current density and interior variable of equations set are treated as separated vector element. In order to make this formulation stable, an improved integral transform is proposed to reform the matrix's condition number. Simulations show that the results by our improved FDTD formulation can effectively not only keep the accuracy of passive circuit, but also integrate high-order linear lumped circuit expressed by equations set as well as one equation.