Kazuhiko Seki

Improved ADPCM voice transmission for TDMA-TDD systems

Novel techniques are proposed to improve the adaptive differential pulse code modulation (ADPCM) voice signal transmission quality of time division multiple access-time division duplexing (TDMA-TDD) systems in fading environments. The proposed scheme employs an improved error detection technique with PCM signal differential detection and a cyclic redundancy code. Erroneous PCM bursts are replaced by error-free bursts. Hardware simulation results show that these techniques significantly improve ADPCM voice transmission quality in the fading environments typical of personal communication systems. The developed techniques enhance ADPCM voice transmission quality for cost effective personal communication systems.

A new fully-digitalized /spl pi//4-shift QPSK modulator for personal communication terminals

The proposed modulator consists of a digital pulse shaping filter and a baseband quadrature modulator. By employing a novel digital filter configuration, the required filter memory is reduced to just 6.25% of the conventional one. Moreover, since the proposed baseband modulation scheme does not employ analog mixers or an analog 90/spl deg/ divider, a very accurate, high-stable and compact modulator is realized. It is shown that the proposed scheme achieves excellent low power consumption characteristics and is more suitable for digital LSIC implementation of personal communication terminals than a direct RF modulation scheme and an analog IF modulation scheme.

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.

VLSI-implemented high speed digital burst modem-Applications for satellite video TDMA and wireless LAN

High speed (60 Mb/s) QPSK/OQPSK burst modem very large scale integrated circuits (VLSICs), which allow radio units to be compact, economical and maintenance-free, are introduced. These VLSICs enable modems to eliminate the analog devices such as mixers required for baseband modulation and zero-IF conversion in demodulation, an analog voltage controlled oscillator (VCO) for bit timing recovery and a voltage controlled attenuator for automatic gain control (AGC). In addition to the full-digital implementation, the demodulator VLSIC achieves fast carrier-acquisition for burst mode operation by employing a reverse modulation carrier recovery scheme capable of operating for OQPSK signals, and fast clock-acquisition by using a bit-timing recovery scheme with bit-timing estimation and interpolation coupled with a pulse-shaping filter. Results of experiment on the assumption of a video time division multiple access (TDMA) system show that the developed VLSICs perform well at the high speed (60 Mb/s) and with the short preamble words (80 symbols).<<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>>

Low-power and high-quality signal transmission baseband LSIC for personal communications

This paper presents a very low power consumption one-chip baseband large-scale integrated circuit (LSIC) for personal communication terminals. It comprises a /spl pi//4-shift QPSK modem, an adaptive differential pulse code modulation (ADPCM) codec, a time division multiple access time division duplex (TDMA-TDD) controller and a link access procedure for a digital cordless (LAPDC: Layer-2 protocol) controller. The developed LSIC meets all the specifications of the personal handy-phone system (PHS) standard. By employing a novel coherent demodulator and an ADPCM codec with a click noise suppressor, a higher quality voice transmission has been achieved in a fading environment. In addition, it has 61-kb/s data transmission capability to achieve wireless multimedia services based on PHS. Moreover, the novel circuit configurations of the modem, the ADPCM codec, the TDMA-TDD controller, and the LAPDC controller achieve significant power reduction of the baseband circuits (57.4 mW) of personal communication terminals. It enables very low power consumption wireless multimedia terminals to be achieved based on the PHS common air interface.

A wireless multimedia network on time division duplex CDMA/TDMA

A wireless multimedia network using a novel channel equalizer on a TDD CDMA/TDMA scheme is proposed. The uplink employs a CDMA scheme to transmit low speed human interface signals, and the downlink employs a TDMA scheme to transmit high speed signals including video and images. The control signals for equalization are calculated by using the output of the matched filters of the CDMA receiver. Theoretical analysis has been carried out to evaluate the BER performance. Numerical results show that a low BER of less than 10/sup -6/ is achieved for the downlink by employing the proposed channel equalizer.

/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.

Phase ambiguity resolver for coherent detection mobile wireless communication systems with a very low power consumption Viterbi decoder employing SST scheme

This paper proposes a novel phase ambiguity resolver (PAR) with a very low power consumption Viterbi decoder employing the scarce-state-transition (SST) scheme to realize mobile communication data terminals. The theoretical analyses on the false phase detection probability and the required Eb/No show that the proposed PAR correctly decides the phase of the received signal up to 7/spl times/10/sup -2/ of the bit error rate and the required Eb/No is only 13 dB under the static Rayleigh fading channels.<<ETX>>