The technology of encapsulating a microwave signal into a terahertz carrier and an optical signal is proposed and demonstrated experimentally. Broad bandwidth terahertz radio can encapsulate existing microwave services, including advanced mobile communication signals, by using photonics technology. The concept of radio-on-terahertz-over-fiber helps to realize the future design of mobile fronthaul links. These links will have seamless connectivity between radio and optical networks because of the low latency of the links, which results from the use of analog signal transmission technology.

Abstract R&D on new generation mobile network has attracted a growing interest over the world on the background of rapid market growth for 2nd and 3rd generation cellular networks and wireless LANs/MANs. The National Institute of Information and Communications Technology (NICT) started the New Generation Mobile Network Project in April 2002, and has developed fundamental technologies to enable seamless and secure integration of various wireless access networks such as existing cellular networks, wireless LANs, home networks, intelligent transport systems (ITS), the Beyond‐3G (B3G) cellular and other wireless access systems. This paper overviews the achievements of the project focusing on network and access technologies. Copyright © 2007 John Wiley & Sons, Ltd.

A 26-GHz band short-range UWB radar system with an embedded compact MMIC-based RF module has been described. In this paper, the principles of detection will be first discussed and then system design for impulse radar and the radar system presented. The results of our experiments suggest that our radar system is capable of detecting targets with a range resolution of around 9 cm.

In this paper we describe overview of the test-bed using gigabit millimeter-wave broadband wireless access systems using 32/18/37 GHz bands. Then, specification and performance of a portable customer-premise equipment employing 4-states combination of adaptive modulation and forward error correction at 32 GHz as a part of the test-bed is introduced. Empirically derived formula of the number of rain fade events per year is also derived to assist designing for unavailability at millimeter wave links.

At starting of the service operation of 2 GHz band IMT-2000 system in Japan, it is important to make clear the mutual interference problem which may occur between IMT-2000 mobile radio systems and existing mobile radio systems, etc. Concerning about this study, Japanese Association of Radio Industries and Businesses established an investigation and examination meeting from fiscal year 1998 to 2001. After this meeting, especially about nonlinear interference that will occur when interfering wave is very high and nonlinearity of interfered receiver amplifier becomes important, specialist team of nonlinear interference is continuing to study this problem. This paper describes the theoretical study result on intermodulation (IM) spectrum generated by a wideband continuous modulation wave and generation of interfering wave caused by IM, on the nonlinear interference by which a narrowband mobile radio system (NBMR) is disturbed by a wideband mobile radio system (WBMR). In this study, the N-modulation waves model and the 3rd order intercept point input level method (IIP3) in [RC Sagers (1983)] was applied by using parameters of direct spread code division multiple access (DS-CDMA) system as WBMR and personal handyphone system (PHS) as a typical NBMR. The bit error rate characteristics (BER) of PHS receiver were estimated through comparison of measured data and theoretical analysis result of the desired signal and undesired signal ratio (D/U) to BER. The comparison result of estimated and measured BER of a NBWR receiver was reported by using a guard band between WBMR and NBWR system receiver as a parameter.

This paper presents a multimode block-coded modulation method that enables both multimode transmission and coding gain. In multimode transmission, the property of data is changed for each mode, and the data are adaptively transmitted. In our method, all modes are constructed by separate multilevel block codes, wherein the number of levels, set partition, rate, and distance properties of each mode may differ from those of the other modes. Different modes may also have different signal constellations, that is, different modulation methods. The code length is the same for all modes, and the mode can be switched at each block boundary, if desired. This method uses one-way transmission where the transmitter has no feedback information from the receiver. In decoding, the maximum-likelihood decoding is carried out using the Viterbi (1967) algorithm. The decoding of all modes, including decoding of the mode index, can be accomplished using one trellis diagram. This paper describes the multimode encoding and decoding method, and analyzes the distance properties and upper bounds for inter- and intramodes. It is clarified at which distance the code should be increased to reduce the decoding mode error. Three design examples are presented for unequal error protection/equal error protection, variable rate, and hybrid additive white Gaussian noise/flat-fading codes.

In digital radio communication systems using the millimeter-wave band, phase noise created by local oscillators is a serious problem. This is because imperfect up/down conversion at transmitters and receivers using local oscillators degrades the bit-error rate (BER) performance, especially when many multipliers are used to get the millimeter-wave frequency. A BER derivation based on the probability of the frequency deviation and calculated and simulated BER performances of gray-coded coherent-QPSK transmission systems are reported. The results of a computer simulation show the validity of our approach.

We describe a method of one-way multimode block-coded modulation for mobile communication systems. One-way multimode block-coded modulation is a form of multilevel block-coded modulation (BCM) with multimode characteristics. It also provides large coding gains. The method generates codes with various properties for every mode. The BCM for mobile communications was composed on the basis of a multimode BCM. Different modes of the code have different code distances, so that each mode can adapt to specific transmission environments, such as an additive white Gaussian noise or a flat fading noise environment. We evaluated the method using computer simulation.

We propose a new scheme for beamforming that involves selecting the direction of arrival (DOA) of the signals impinging on an array antenna. In this approach, the received signal is modeled on the basis of the angular spread of the DOA. First, the local-scattering parameters that indicate the extent of the angular spread for each DOAs are estimated, and then the desired DOA is selected by comparing the size of the parameters. We also propose a method of estimating these parameters using only the received signals. Simulations showed that local-scattering parameters are related to the bit-error rate and that the proposed scheme for beamforming can improve the rate.