Tetsu Sakata

A simple adaptive channel estimation scheme for OFDM systems

This paper proposes a simple adaptive channel estimation scheme for orthogonal frequency division multiplexing (OFDM) in order to realize high-rate wireless local area networks (LANs). The proposed estimator consists of simple frequency-domain FIR filters, which are adaptively selected according to the difference vector between adjacent subcarriers and channel amplitude of the subcarrier. Computer simulations show that the proposed scheme offers superior packet error rate (PER) performance to the least-squares scheme, by 1.1 dB in terms of required E/sub b//N/sub 0/ at a PER=0.1 in AWGN channels. They also show, for the same criterion, a 0.7 dB improvement for a frequency selective fading channel with a delay spread value of 100 ns.

A new simple adaptive phase tracking scheme employing phase noise estimation for OFDM signals

An adaptive phase tracking scheme for orthogonal frequency division multiplexing (OFDM) signals can provide superior PER performance in channels that exhibit a variety of phase noise power. It is an effective technique with which to achieve high-rate and high quality wireless transmission. This paper proposes a new simple adaptive phase tracking scheme for OFDM in order to realize high-rate wireless local area networks (LANs). The proposed scheme measures the integrated phase rotation in order to set appropriately the properties of the FIR filter in the phase tracking circuits. This scheme is based on the fact that the integrated phase rotation is correlated to the phase noise power. Assuming an RMS delay spread of 100 ns, computer simulations show that the proposed scheme offers superior required E/sub b//N/sub 0/ performance (versus the phase noise power) compared to the conventional fixed-tap scheme, where the phase-noise-to-signal power ratios are lower than -18 dB. It also offers excellent PER performance at the packet length of 1000 bytes, unlike the conventional schemes which suffer degraded PER performance.

Study of Power Saving Scheme Suitable for Wireless LAN in Multimedia Communication

Wireless LAN access is now being offered by small personal terminals in addition to laptops. Since these terminals have very limited battery capacity, wireless LAN interfaces that offer some form of power saving are essential. IEEE802.11. specifies PSM (Power save management); it reduces power consumption by suspending some communications functions. However, since Multicasting and Broadcasting are invariably received by all terminals regardless of PSM, the terminals unnecessarily consume electric power even if the terminal is not engaged in multicasting. This paper clarifies this problem, and proposes a scheme for reducing power consumption and the results of an experiment confirm its excellent performance.

MAC protocol for fair two-way communications in wireless LANs

This paper proposes a novel MAC protocol for fair two-way communications. Our protocol achieves fairness in the throughput between the uplink and downlink under high offered traffic conditions, but the fairness cannot be achieved when using the conventional wireless LAN scheme, CSMA/CA, as the access control method. The proposed scheme introduces a release delay, which is the waiting time to attempt the transmission of the next scheduled packet in the transmission queue. The proposed protocol is evaluated by computer simulation. The results of the simulations that consider high offered traffic verify that the throughput at a station between the uplink and downlink is fair and that the throughput between stations is fair.

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 new vector error measurement scheme for transmit modulation accuracy of OFDM systems

This paper proposes a new vector error measurement scheme for orthogonal frequency division multiplexing (OFDM) systems that is used to define transmit modulation accuracy. The transmit modulation accuracy is defined to guarantee inter-operability among wireless terminals. In OFDM systems, the transmit modulation accuracy measured by the conventional vector error measurement scheme can not guarantee inter-operability due to the effect of phase noise. To overcome this problem, the proposed vector error measurement scheme utilizes pilot signals in multiple OFDM symbols to compensate the phase rotation caused by the phase noise. The proposed vector error measurement scheme makes it possible to define the transmit modulation accuracy and so guarantee inter-operability among wireless terminals.

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.

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.