S. Kato

Soft-decision Viterbi decoding with diversity combining (mobile satellite communications)

Diversity combining methods for convolutional coded and soft-decision Viterbi decoded channels in mobile satellite communication systems are evaluated. Computer simulations confirm that the pre-Viterbi-decoding maximal-ratio combining method has better performance than other methods in Rician fading channels. Bit error probability performances derived from the analysis model using the probability density function of Rician fading and the bit error probability performance of Viterbi decoding in additive white Gaussian noise (AWGN) channels are shown to agree with the simulation results. The diversity method is applied to trellis-coded 8PSK modulation and coherent detection/differential detection, and their performances are compared with conventional QPSK modulation and coherent detection with high-coding-rate and high-coding-gain Viterbi decoding. QPSK with high-coding-rate Viterbi decoding can be an attractive candidate for mobile satellite systems as well as trellis-coded 8PSK.<<ETX>>

A feedback-loop type transmission power control for low speed TDMA satellite communication systems

A feedback-loop-type transmission power control (TXPC) scheme, coupled with first- and second-order prediction methods, is proposed, and the optimum control period and residual control error are analyzed. In order to minimize residual control error, the three main factors contributing to such error are analyzed. First, to minimize level detection error, a channel pseudo-error estimation method is proposed and analyzed experimentally for quasi-signal-level detection. Second, rain attenuation rates in Ka bands are measured and analyzed statistically. Finally, the optimum control period of the proposed TXPC scheme is analyzed. The simulation results for the prototype TXPC scheme show that a maximum residual control error of +or-2.5 dB is achievable with an optimum control period of about 2 s.<<ETX>>

A very low power consumption ADPCM voice codec LSIC for personal communication systems

This paper proposes a very low power consumption ADPCM voice codec LSIC. The developed LSIC satisfies CCITT recommendation G.721 completely and is suitable for realizing the high-quality voice signal transmission expected from personal communication systems in fading environments. By employing a time sharing signal processing, a very low power consumption (only 500 /spl mu/W) for ADPCM codec core has been achieved. Moreover, the LSIC has a novel click noise detection function and erroneous received signals are suppressed digitally according to the click noise detection information. This makes it possible to improve the voice transmission quality significantly in fading environments, for instance, the MOS (mean opinion score) evaluation is improved by 0.5 points compared with that of the conventional scheme.

A very low power and high-quality signal transmission baseband LSIC for personal communications-advanced signal processing and one-channel integration

This paper proposes a very low power consumption (2V operation) one-chip baseband LSIC for personal communication terminals. It is composed of a /spl pi//4 QPSK modem, a TDMA-TDD controller, an ADPCM codec and a LAPDC controller. The developed CMOS LSIC completely meets the PHS (Personal Handy Phone System) standard. By employing a novel coherent demodulator and an ADPCM codec with a click noise suppressor, 6dB higher-quality voice transmission has been realized in fading environments. Moreover, the novel circuit configurations of the modem, the ADPCM codec, the TDMA-TDD controller and the LAPDC controller make it possible to reduce significantly the power consumption of the baseband circuits of personal communication terminals.

Semi-autonomous synchronization for TDMA-TDD communication systems

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 phase control, and compensates propagation delay between base stations by using geographical data. This autonomously synchronizes all base stations to each other. Computer simulation results confirm the accurate and stable TDMA frame synchronization of all base stations under the fading environments.<<ETX>>

Universal-coding-rate scarce-state-transition Viterbi decoder

The authors propose a universal-coding-rate scarce-state-transition Viterbi decoder that permits the realization of a high-speed high-coding-rate one-chip forward error correction CMOS LSIC. To reduce the power consumption of high-coding-rate Viterbi decoders, the proposed decoder expands the scarce-state-transition (SST) Viterbi decoding scheme from a coding rate of one-half to any higher coding rate. To employ the SST Viterbi decoding scheme for high-coding-rate convolutional codes, a universal predecoding scheme for convolutional codes is introduced. Computer simulations showed a drastic reduction in CMOS gate on-off switching. A low-power-consumption path memory is proposed to reduce the power consumption. A pilot chip was fabricated and its total power consumption was reduced by 27% for rate three-fourths coding rate Viterbi decoding.<<ETX>>

Superposed transmission of high speed QPSK signals and SSMA-QPSK signals in non-linear channels

Spread-spectrum multiaccess quadrature phase-shift keying (SSMA-QPSK) signal transmission superposed over high-speed QPSK modulated signals is proposed and analyzed experimentally. Experimental results show that when the SSMA-QPSK signal power to QPSK signal power ratio equals -30 dB, the scheme can transmit 20 SSMA-QPSK channels and a high-speed QPSK channel over the same transponder simultaneously and realize 1.530 b/s/Hz of frequency utilization efficiency (superposed transmission of 60-Mb/s QPSK signals and 20 32-kb/s SSMA-QPSK signals over a 36-MHz transponder).<<ETX>>

A full digital modem for offset type modulation schemes

This paper proposes a full digital modem employing a reverse-modulation type carrier recovery scheme for offset type modulation schemes. The full digital modem employs a wave forming filter for reverse-modulation of offset type modulated signals to increase the extracted carrier signal-to-noise ratio. The proposed modem achieves both high speed carrier acquisition and low carrier slipping rate simultaneously which other methods cannot achieve. Computer simulation results show that the proposed modem applied to OQPSK systems achieves a low carrier slipping rate performance of less than 1.0*10/sup -7/ event/symbol at an Eb/No of 4 dB with negligible bit error rate degradation. The proposed modem can be implemented in all-digital circuits and suitable for LSI implementation.<<ETX>>

High-quality signal transmission techniques for personal communication systems-novel coherent demodulation and ADPCM voice transmission with click noise processing

The paper proposes high-quality signal transmission techniques for personal communication systems. A novel coherent demodulator-variable carrier filter and hang-up free clock recovery coherent demodulator (VCHACE)-is proposed. The carrier recovery circuit uses a reverse-modulation scheme with variable bandwidth carrier filter. By employing the proposed scheme, the FER (frame error rate) performance is improved by 2 dB compared with the differential detection scheme in typical Rayleigh fading environments. An ADPCM voice transmission scheme that employs a click noise suppressor is also proposed. It achieves a voice quality improvement of 0.5 points in an MOS evaluation (3 dB improvement in required Eb/No) compared with conventional muting schemes in fading environments.

/spl pi//4-shift QPSK digital modulator LSIC for personal communication terminals

A /spl pi//4-shift QPSK digital modulator LSIC consisting of a digital pulse shaping filter and a baseband quadrature modulator is newly developed. By employing a novel digital filter configuration, the required filter memory is reduced to just 1/2048th that of the conventional modulator. Moreover, since the proposed baseband modulation scheme does not employ a complex multiplier or a quadrature modulator with multipliers, a compact and low power consumption modulator is realized.