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.

In this paper, we propose an adaptive power distribution algorithm which aims at improving the spectral efficiency in orthogonal frequency division multiplexing (OFDM) under the condition that the target bit error rate (BER) should be maintained and the transmit power threshold should not be exceeded. This algorithm is based on an iterative mechanism. In every iteration, the power and the corresponding number of bits are distributed to the subcarrier at which there is a modulation mode demanding the minimum average incremental transmit power per incremental bit to guarantee the pre-designated bit error rate (BER) performance. The iterative procedure terminates once the transmit power threshold is reached. The performance investigations show the proposed adaptive power distribution algorithm always outperforms the scheme of equal power distribution in a large dynamic range of transmit power threshold. Moreover, the performance improvement is very large when the transmit power threshold is required to be low.

The link adaptation scheme in the current IEEE 802.11a technical specifications only consider channel variation in the time-domain, and assume all the data subcarriers use the same modulation mode and coding rate once the transmission data rate is determined. However, in the frequency-selective fading scenario, the BER performance is severely degraded by OFDM subcarriers where deep fading occurs. We propose a frequency-domain link adaptation scheme for IEEE 802.11a, which is based on a modified adaptive bit and power loading algorithm and a modified pilot pattern. Simulation results show our proposal can greatly improve performance when perfect channel information is obtainable. We also investigate the performance of the proposed scheme in two channel mismatch situations, and show it is capable of achieving large performance gain in the most favorable environment for IEEE 802.11a, the low mobile speed environment.

We propose a combinational scheme of adaptive beamforming and adaptive loading for orthogonal frequency division multiplexing (OFDM). Two adaptive beamforming schemes based on least mean square (LMS) algorithm and pre-FFT combining are used to obtain the space diversity gain. Their difference, which lies in either the frequency-domain or time-domain pilot vector is used in the beamforming. In order to counter the severe frequency-selective fading which is inevitable in broadband wireless communications, we use the frequency-domain adaptive loading to load the bits and transmit power to the individual subcarriers. The performance investigations show that the combinational scheme based on the adaptive beamforming and adaptive loading is very effective in improving the performance of OFDM packet transmission.

The link adaptation scheme in the current orthogonal frequency division multiplexing (OFDM) systems such as IEEE802.11a only consider the channel variation in the time-domain, and assume all the data subcarriers use the same modulation mode and transmit power once the data rate is determined. However, in the frequency-selective fading environments, the error probability performance of OFDM is severely degraded by the subcarriers where the deep fading occurs. In order to deal with this issue, we propose a coded frequency-domain link adaptation scheme for OFDM packet transmission in the time division duplex (TDD) mode. This scheme is based on the concatenation of the channel coding and the adaptive bit and power loading. The simulation results show the proposed scheme can significantly improve the packet error rate (PER) performance compared with other schemes. Further investigations also show that it can contribute to large performance gain even in the challenging high-speed environments.

Helicopter videoing is one of the most popular methods to acquire on scene information for disaster management and relief. We developed an on scene disaster information transmission system using Ku-band helicopter satellite communications. The main obstacle for a helicopter satellite communication link is the interruption by the rotating blades of the helicopter. To overcome the blade interruption, we use a time diversity transmission technique at the forward link and a blade-synchronized transmission technique at the return link. Furthermore, onboard position estimation is done for the on scene videoing pictures. Some primary field experiments have been done with satisfactory results.

A real time system for disaster information collection and transmission using ka-band aeronautical satellite communications has been developed. This system is composed of three subsystems: a Ka-band aeronautical satellite communication (KASC) subsystem, a position-estimation and data-processing (PEDP) subsystem, and an information-distributing Internet application subsystem. Experiments to examine the performance of the overall system have been carried out. In this paper, we'll outline the overall experimental system and present some experiment results.

This paper describes how block-coded modulation (BCM) and multiple BCM (MBCM) with Viterbi decoding can be designed for use in Rayleigh fading and severe Rician fading channels. New codes are developed by modifying known codes to increase the minimum symbol distance, which is one of the distances that has a strong effect on the bit error rate (BER) performance under fading channels. Combined with anti-fading techniques such as fading compensation, interleaving, and branch weighting, the new codes significantly improve BER performance. Computer simulations were used to confirm the code performance.

Researchers have studied two types of digital multi-carrier modulation, wavelet packet modulation (WPM), and fractal modulation. The advantage of WPM is that it allows signal time and frequency to be divided and multiplexed. Therefore the time and frequency of noise signals, e.g., tone and impulse noise, can be identified and effectively partitioned in packets. Using this advantage, we propose a class-coded modulation method for WPM that has good bit error rate (BER) performance when the length of the code constraint is extended and can select time and frequency noise signals simultaneously. This report describes the proposed method and the computer simulations carried out to test its effectiveness.

COMETS (Communications and Broadcasting Engineering Test Satellite), which was developed to evaluate Ka-band (31/21 GHz) and millimeter-wave (47/44 GHz) advanced mobile satellite communications and 21-GHz advanced satellite broadcasting systems, is presented as well as the developed ground terminals. COMETS carries an SCPC/TDM regenerative transponder for direct mobile-to-mobile communications, and IF-filterbanks for interconnection between multibeams. For mobile and personal applications, a portable terminal for regenerative transponder experiments, and several antennas such as an active phased array antenna, a waveguide slot array antenna, and a torus reflector antenna were developed. For satellite broadcasting experiments, trellis-coded modems for HDTV transmission at 60/140 Mbps and 155 Mbps were developed.

Many authors have already published papers on methods for computing intermodulation products in satellite communications systems, in which the signals are amplified by nonlinear travelling wave tube (TWT) amplifiers. This paper describes a simple new method for calculating the output power spectrum of nonlinear satellite transponders in SCPC systems. This method uses exponential functions to describe the input-output characteristics of TWT and assumes input signals as a Gaussian process. The intermodulation spectra can be represented by simple closed-form functions which are simple to calculate and require less computation time than previously proposed methods.>

Using the Engineering Test Satellite-Five (ETS-V), L-band (1.5 GHz) propagation measurements of land mobile satellite communication channels on ordinary roads and expressways in Japan have been carried out, The total distance of the experiments is about 4,000 km. A continuous wave from the ETS-V, is received by a directional phased array antenna (Gain: 12 dBi) installed on the roof of a test van. The experimental results show that expressways and ordinary roads in rural and suburban areas are very suitable for land mobile satellite communication services. The paper describes the field experiments and statistical characteristics of the received signal levels, non-fade/fade duration distributions, fade depth and non-fade/fade state transition frequency.>