In this paper, a newly developed fading simulator (FS) is presented. This FS can produce the same fading situation repeatedly and the DSP (Digital Signal Processor) is used for its implementation. The structure and performance of the FS are also presented.

The paper proposes a new multicarrier 16QAM system for high-quality and high-bit-rate transmission with high spectral efficiency in land mobile radio communications. The proposed system uses a multicarrier transmission scheme to provide immunity against frequency-selective fading distortion. It also uses pilot-symbol-aided 16QAM to increase spectral efficiency, and it combines space diversity and FEC with maximum likelihood decoding to improve the bit error rate (BER) performance. Computer simulation shows that a BER of less than 10-4 is obtained over frequency-selective fading channels with rms delay spread of less than 5.4µs. Using a bandwidth of 200kHz the proposed system can achieve high-quality transmission with a total information rate of 256kbit/s.

This paper gives field experimental results on 16-ary quadrature amplitude modulation/time division multiple access (16QAM/TDMA) and trellis coded 16QAM/TDMA systems for land mobile communications in order to evaluate its capability of achieving large capacity and high quality data transmission. Pilot symbol aided space diversity and symbol timing synchronization based on maximum likelihood (ML) estimation are applied to both 16QAM/TDMA and trellis coded 16QAM/TDMA to improve transmission quality. For the trellis coded 16QAM/TDMA, trellis coding with Viterbi decoding and 2-frame symbol interleaving are further employed. The field experiments were conducted in the Tokyo metropolitan area of Japan. The results show that 16QAM/TDMA and trellis coded 16QAM/TDMA are practical modulation/access schemes for land mobile communication systems.

In recent years, various applications based on propagation characteristics have been developed. They generally utilize the locality of the fading characteristics of multipath environments. On the other hand, if a received signal at a remote location can be estimated beyond the correlation distance of the multipath fading environment, a wide variety of new applications can be possible. In this paper, we attempt to estimate a received signal at a remote location using the MUSIC method and the least squares method. Based on the plane wave assumption for each arriving wave, multipath environment is analyzed through estimation of the directions of arrival by the MUISC method and the complex amplitudes of the received signals by the least squares method, respectively. We present evaluation results on the estimation performance of the method by computer simulations.

We consider secret key agreement for multiple terminals based on radio propagation characteristics in a wireless relaying system where more than two terminals communicate with each other via a relay. In this system, the multiple terminals share a common secret key generated from their radio propagation characteristics with the help of the relay in the presence of an eavesdropper. In this paper, we present three secret key agreement schemes: an amplify-and-forward (AF) scheme, a signal-combining amplify-and-forward (SC-AF) scheme, and a multiple-access amplify-and-forward (MA-AF) scheme. The key idea of these schemes is that each terminal shares the fading coefficients between all terminals and the relay, and use them as the source of a secret key. The AF scheme is based on a conventional amplify-and-forward two-way relaying method, whereas in the SC-AF scheme and the MA-AF scheme, we apply the idea of analog network coding to secret key agreement. We analyze eavesdropping strategies and show that the AF scheme is not secure if the eavesdropper is located near the relay and can receive signals from the relay without multipath fading and noise. Simulation results show that the SC-AF and MA-AF schemes are effective.

This paper studies the effect of frequency re-using patterns on the channel capacity in the forward link of orthogonal code division multiple access (CDMA) cellular systems. The received carrier-to-interference ratio (CIR) determined by computer simulation shows that re-using the same frequency channel on every third sector (3-sector layout) provides superior channel capacity than does every-sector re-use (1-sector layout).

Research and standardization activities on FPLMTS are under way throughout the world. This paper shows recent study results on radio transmission technologies in ARIB (Association of Radio Industries and Businesses), which in the standardization organization in Japan. On-going study shows two TDMA based and four CDMA based radio transmission technologies under study. These technologies need to be further studied in detail. The proposal from ARIB is expected to be summarized around the end of the year 1996.

This paper proposes the use, in integrated wireless systems, of the Reserved Idle Signal Multiple Access with Collision Resolution (R-ISMA/CR) protocol for applications in future multimedia mobile communications. It is applied to the integrated voice and data wireless system. Moreover, the consideration is made of the integrated voice and the low-bit video wireless system in R-ISMA/CR. To integrate video we employed not only a packed discard for video packets when the video packet delay is more than a threshold value, but also the connection packet (CP) technique for improving the channel utilization. Finally the integration of voice, data, and low-bit-video wireless system in R-ISMA/CR is considered. The performance are evaluated mainly by simulations.

A slow frequency-hopping/16-ary quadrature amplitude modulation (slow-FH/16QAM) system based on time-division-multiple-access (TDMA) is appropriate for third-generation land mobile cellular communications because of its high immunity to interference. The system uses 16QAM for high spectral efficiency and slow-FH and forward-error-correction (FEC) for high-quality transmission. To reduce sensitivity to interference, the system uses an improved decoding scheme based on a minimum Euclidean-distance which is effective when the interference level is dispersed by FH. The bit error rate (BER) of the system due to interference has been evaluated in a previous study, both theoretically and by computer simulation. Although computer-simulated results showed that the system improved the BER, the hardware feasibility was not considered. This paper presents a hardware implementation of the system and the results of experimental transmission using equipment we developed to verify the system and to confirm the BER performance. The laboratory experimental results indicated that the system could provide high-quality transmission over a channel that has frequency-selective fading and co-channel interference. This system provided an Eb/N0 of 9 dB with space diversity and one of 15 dB without it, when BER=10-3 and fd=120 Hz. Field experiments were also conducted in a suburban area of Tokyo to demonstrate the BER performance. The results meant that the system could lower sensitivity to vehicle velocity more than a system without FH and that the BER performance of the system was improved notably against that of a system without FH, especially at low vehicle velocity.

This paper proposes the reserved idle signal multiple access with collision resolution (R-ISMA/CR) protocol, which can maintain stability without being influenced by the retransmission probability. The R-ISMA/CR makes use of the multi-idle signals at the base station and the manipulating counter at the terminals. The performance of this protocol is evaluated by using the maximum throughput analysis and simulations.