A variable partition duplex scheme on packet reservation multiple access protocol (VPD-PRMA) is analyzed in this paper. We assume a four-state speech model for a conversational pair and successfully obtain performance measures by approximate Markovian analysis. Analytical results show that they quite fit simulation results; and VPD-PRMA can get higher statistical multiplexing gain than fixed partition duplex (FPD)-PRMA, due to the trunking effect. We further investigate the effect of design parameters of permission probability and enlarged reservation duration on system performance by computer simulation. Simulation results shows that it exists appropriate values for these two design parameters so that the packet dropping probability can be minimized. The adjustment of permission probability can greatly improve the performance of uplink traffic with slight deterioration of the performance of downlink traffic; the provision of enlarged reservation duration scheme can enhance the system performance.

A new method using new test structure, which is connected 15.4 million MOS transistor, for evaluating extrinsic oxide breakdown is proposed. The active gate area which is needed to predict reliability will be shown. And by using this new method, activation energy not only for the intrinsic breakdown but also for the extrinsic breakdown are obtained.

We previously proposed a next generation cellular system for IMT-2000 based on the Wideband DS-CDMA with TDD scheme (W-CDMA/TDD) and have evaluated its performance by computer simulation, laboratory and field experiment. With the W-CDMA/TDD, because of its correlation between the downlink and the uplink, transmission and reception space diversity (SD) at a base station and open-loop transmit power control (TPC) can be simply realized. This paper reports performance of laboratory and field experiments using a developed testbed. The results shows it has been confirmed that transmission and reception SD and open-loop TPC have sufficient performance under a field environment as well as laboratory environment.

We previously proposed a next generation cellular system for IMT-2000 based on wideband DS-CDMA with TDD scheme and have evaluated its performance by computer simulation, laboratory and field experiments. This paper presents the design concept of TDD-mode operation on wideband DS-CDMA systems. These systems employ almost the same techniques with a little difference as FDD-mode. We also present the schemes of the TDD-mode specific techniques such as fast cell search, transmission diversity and transmitter power control and show the evaluation results of them are effective. Performance can be improved by use of enhanced techniques such as interference cancellation and adaptive antenna array diversity.

This paper proposes a new MAC protocol and physical channel control schemes for TDMA-TDD multi-slot packet channel. The goal of this study is to support both circuit-switched and packet-switched communications on the same resources and to enable high-speed packet transmission using a multi-slot packet channel. In the proposed channel control schemes, three points are taken into account; 1) effective sharing of time slots and frequencies with minimum impact on circuit communications, 2) compatibility with the existing access protocol and equipment, and 3) dynamic allocation of uplink and downlink slots. As for the MAC protocol, we adopt BRS (Block Reservation Scheme) and adaptive access control scheme to the proposed MAC protocol. In addition, to overcome the inherent disadvantage of TDD channels, packet scheduling and access randomizing control are newly proposed in this paper. The results of throughput and delay evaluations confirm that downlink capacity can be drastically enhanced by the dynamic allocation of uplink and downlink slots while corruption under heavy traffic loads is prevented by applying the adaptive traffic load control scheme.

We propose a new bit timing recovery (BTR) scheme, what we call Step Sampled BTR (SSBTR), that can lower the sampling clock frequency and shorten the clock phase convergence time, for burst signals in high bit rate wireless access systems. The SSBTR scheme has the following characteristics. A sine wave resulting from the BTR code passing through a Nyquist Transmission System is always used, the sampling clock has a lower frequency than the system clock, and the clock phase of Intermediate Frequency (IF) signal input can be estimated from as few as 3 sampled data. The SSBTR scheme corrects the clock phase only once in a burst signal. Therefore, in some wireless access systems, some kind of operation must be performed after the SSBTR, in order to deal with long burst signals, instability of the system clock, and so on. In other wireless access systems that do not have these problems, clock phase can be fixed by the SSBTR scheme alone. The preformance of the SSBTR scheme with respect to additive white Gaussian noise (AWGN) was examined by computer simulation. In addition, when SSBTR is implemented in hardware, there are imperfections in the circuitry that lead to phase estimation error and thus deterioration, so we studied the effects of several such imperfections by computer simulation. The results of these simulations clarify the performance of the SSBTR scheme.

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.

An increase in the system capacity and maximum user bit rate is required for wireless multimedia communications that offer high speed signal transmission such as simultaneous voice and data transmission. This paper proposes a Time Division Multiple Access-Time Division Duplex method combined with an Alternated Frequency Duplexer (TDMA/TDD-AF) for TDMA based wireless personal communications. The newly proposed duplexing method uses the same frequency band and all time slots within a TDMA frame for both up-stream and down-stream transmission. This enables a two-fold increase in the number of time slots within a TDMA frame and the maximum user bit rate compared with the conventional TDMA/TDD method. Transmitter diversity is also applied to improve the transmission quality under multipath fading environments. The traffic performance of the proposed method is approximated theoretically compared with the conventional TDMA/TDD systems on the assumption that an infinite number of terminals are in a cell. The results indicate that the TDMA/TDD-AF method significantly improves the blocking probability when the system is asynchronized among adjacent cells and the number of usable carriers is high.

This paper proposes linear predictive transmission diversity for TDMA/TDD personal communication systems and evaluates the effects of fading correlation and unequal average signal power Rayleigh fading on these system. The average bit error rate (BER) performance is calculated by computer simulation and the BER of zero order prediction is theoretically analyzed. The performance degradation caused by the error from prediction, fading correlation, and unequal average signal power is found to be almost independent of each other.

Hybrid direct sequence/slow frequency hopping-time division duplex (DS/SFH-TDD) multiple access system has some good features of each system. However it has a problem of hit between multiple users. If the designed frequency hopping patterns are inadequate, the quality of the multiple access system is degraded due to the frequent hit. In this paper, we propose an adaptive hopping pattern control system which is able to avoid the multiple access interference of hit. The proposed system decreases the influence of hit and increases the user capacity in the cell. And this adaptive hopping pattern control is applied to both single-cell and multi-cell systems. By computer simulation to evaluate the performance of this system, we found that this system is effective in increasing the multiple access capability.

An antenna and multi-carrier combined diversity system using Time Division Duplex (TDD) is proposed to combat with multi-path channel problem which produces frequency-selective fading and degrades the quality of signal transimission. So far multi-carrier modulation technique has been studied to solve this problem. On the other hand, TDD method has been studied to use a transmitter antenna diversity as pre-diversity against flat fading (non-selective fading). Our proposed system merges these two methods in a micro-cellular system as follows. On the reverse link, the base station can select the best combination between the carriers and antennas after receiving the multi-carrier signal from the mobile station. On the forward link, the same combination selected on the reverse link can be used to send the signal from the base station with multi-antenna to the mobile station with a single antenna and produces pre-diversity (transmitter diversity) effect which can reduce the complexity at the mobile station. The pre-diversity must be based on TDD function because the channel has to be observed before the signal transimission. By computer simulations we find that our proposed system can achieve far better performance than conventional systems.

The quality of Si substrates affecting the oxide reliability was investigated using various kinds of test structures like flat capacitor, field edge array and gate edge array. The field edge array test structure which resembles the conditions found for real device is shown to be quite effective to determine the quality of oxides. Oxide grown on a P type epitaxial layer on P+ silicon substrate shows the highest reliability in all test structures. Gettering of heavy metals and/or crystal defects by the P+ silicon substrate is the dominant mechanism for the improvement of the oxide reliability. H2 annealed silicon shows a good reliability if monitored using the flat capacitor. However, using the field edge array test structure, which is strongly influenced by real device process, the reliability of the oxide grown on H2 annealed silicon degrades.

This paper proposes a symbol rate controlled adaptive modulation/TDMA/TDD for future wireless personal communication systems. The proposed system controls the symbol rate according to the channel conditions to achieve wide dynamic range of the modulation parameter control as well as to improve the delay spread immunity. The main purpose of the proposed system is to increase the data throughput with keeping a certain transmission quality, especially in frequency selective fading environments. For this purpose, the proposed system predicts the C/N0 (carrier power-to-noise spectral density ratio) and the delay spread separately, and selects the optimum symbol rate that gives the maximum bit rate within a given bandwidth satisfying the required BER. The simulated results show that the proposed system can achieve higher transmission quality in comparison with the fixed symbol rate transmission system in both flat Rayleigh and frequency selective fading environments. The results also show that the proposed system is very effective to achieve higher bit rate transmission in frequency selective fading environments.

This paper proposes a new burst coherent demodulator that improves transmission quality of microcellular TDMA/TDD systems for personal communications and has configuration suitable for low power consumption with LSIC-implementation. To achieve the better transmission quality, the proposed demodulator employs coherent detection with a unique carrier recovery scheme that can operate without any preamble for carrier recovery. In addition, the demodulator uses a clock recovery scheme with clock phase estimation using twice differentiation, which eliminates hangup and attains fast clock acquisition at 2 samples/symbol. Experimental results clarify the superiority of the proposed coherent demodulator for microcellular TDMA/TDD systems. The proposed coherent demodulator reduces the irreducible frame error rate by 40%, and achieves 4dB improvement at the frame error rate of 10% compared with differential detection under the Rayleigh fading (fD/fs=810-5, τrms/Ts=510-2) typical of personal communication environments.

This paper proposes a semi-autonomous frame synchronization scheme for a TDMA (Time Division Multiple Access)-TDD (Time Division Duplexing) personal communication system to realize accurate frame synchronization in a simple manner. The proposed scheme selects specific adjacent base stations by the station indicator (SID), carries out high resolution frame timing control, and compensates the propagation delay between base stations by using geographical data. This autonomously synchronizes all base stations to each other. Computer simulation and analysis results confirm the accurate and stable TDMA frame synchronization of all base stations even in fading environments.

This paper proposes a digitalized quadrature modulator for burst-by-burst carrier frequency hopping in TDMA-TDD systems. It employs digital frequency synthesis and a multiplexing modulation scheme to give the frequency offset to the modulated IF signal. Moreover, to reduce the frequency settling time of the RF synthesizer below the guard time duration, a phase and frequency preset (PFP) PLL synthesizer is employed. By employing the digital modulation scheme, the proposed modulator needs only one D/A converter, as a result, the complexity of adjusting the DC offset and amplitude between analog signals of the in-phase and the quadrature phase is eliminated. The performance of the proposed modulator is analyzed theoretically and simulated by computers. Theoretical analyses show that the frequency settling time with 15MHz hopping width in the 1900MHz band is reduced by more than 75% from that of the conventional synthesizer. The settling time is less than 40µs which is shorter than the typical guard time of the burst signal format. The analyses also show that the power consumption of the proposed modulator is lower than that of the conventional modulator employing a full band digital frequency converter. Furthermore, the computer simulation confirms that the power spectra and the constellations of the proposed modulator for the coherent and the π/4-shift QPSK modulation schemes can be successfully generated.

This paper describes the formation of ultra-thin tantalum oxide capacitors, using rapid thermal nitridation (RTN) of the storage-node polycrystalline-silicon surface prior to low-pressure chemical vapor deposition of tantalum oxide, using penta-ethoxy-tantalum [(Ta(OC2H5)5) and oxygen gas mixture. The films are annealed at 600-900 in dry O2 atmosphere. Densification of the as-deposited film by annealing in dry O2 is indispensable to the formation of highly reliable ultra-thin tantalum oxide capacitors. The RTN treatment reduces the SiO2 equivalent thickness and leakage current of the tantalum oxide film, and improves the time dependent dielectric breakdown characteristics of the film.

A new technique for evaluating gate oxide reliability using photon emission method has been developed. This method enables the measurements of the initial breakdown characteristics, reliability testing and failure analysis consistently. From the experimental results, followings are clarified for the first time using this technique. Failure modes in the initial characteristics have close correlation to TDDB characteristics and both characteristics correspond to the location of breakdown spot. The results suggest measures to improve the reliability of gate oxide and the existance of new failure mechanism.