Yoshimasa Daido

Performance evaluation for band-limited DS-CDMA communication system

The model uses a coherent binary phase shift keying (BPSK) modulation scheme operated in the asynchronous mode. For ease of interpretation of results, raised cosine spectra for filters is assumed. A standard Gaussian approximation is used to derive approximated error probabilities, P/sub e/, in simple form. The effect of imperfect despreading synchronization is shown.

Backoff improvement of an 800-MHz GaAs FET amplifier for a QPSK transmitter using an adaptive nonlinear distortion canceller

The use of a nonlinear distortion canceller (NLDC) with a Cartesian feedback loop to improve the output backoff of an 800 MHz GaAs FET power amplifier when a quadrature phase shift keying (QPSK) signal with a rolloff factor of 0.5 is applied is described. This amplifier module uses three GaAs FETs. The amplifiers saturated power is 31 dBm, and its maximum power-added efficiency is 50%. Excellent operation of the NLDC was confirmed within a backoff range of more than 4 dB. Within this range, the out-of-band emission was kept 55 dB below the center frequency level. Since the peak output power coincides with the saturation power at a 4 dB backoff, the NLDC improves the backoff to the theoretical limit.<<ETX>>

Simulated tolerance of loop parameters of Cartesian feedback amplifier for pi /4-shifted QPSK transmitter

Evaluates Cartesian feedback amplifier performance for a mobile terminal for a digital cellular system using pi /4-shifted QPSK. To determine the out-of-band emission, the authors calculated spectra in peak-hold mode based on RCR Standard STD-27 on Japan Digital Cellular Telecommunication System. They calculated the tolerance of the feedback amplifiers loop parameters, assuming TDMA system parameters based on the RCR specifications. Since the specifications for out-of-band emission of -45 dB at 50 kHz and -60 dB at 100 kHz from the band center were satisfied, the Cartesian feedback amplifier is applicable to a TDMA transmitter and is easily implemented for practical applications.<<ETX>>

Multilevel QAM Modulation Techniques for Digital Microwave Radios

A pilot carrier injection method is described together with feedback balance coding which reduces spectral power near the carrier. Robustness of carrier recovery using the pilot carrier injection method is theoretically estimated. The estimation suggests that recovered carrier SNR higher than 40 dB can be expected even under muitipath fading with notch depth of 45 dB located just at the carrier frequency. Signatures for multipath fading are estimated for a 64-QAM system with transversal equalizers as a countermeasure. Measured signatures agree reasonably well with the calculated ones. Dependences of signatures on modulation level, transversal equalizer tap number, and rolloff rate are also shown.

Theoretical Evalution of Signatures and CNR Penalties Caused by Modem Impairments in Multilevel QAM Digital Radio Modems

A calculation method for symbol error probability is proposed for multilevel QAM systems. Carrier-to-noise ratio penalties are estimated by this method for seven typical impairment factors, including recovered carrier phase error, timing error, receive filter residual delay, etc. The validity of the method is verified by experiments on penalties caused by recovered carrier phase error and timing error. Based on the new method of analysis, signatures of a 64 QAM modem are estimated theoretically, using a pseudo-two-ray model of multipath fading. The dependence of signatures on the above-mentioned impairment factors is investigated in detail. A qualitative deduction of impairment factors from a measured signature is demonstrated. The measured signature agrees well with a calculated one in which reasonable values of the impairment factors are assumed.

Improvement of Nonlinear Distortion in an IMPATT Stable Amplifier

More than a 40-dB third-order intermodulation product (IMP) has been achieved in a 13-GHz-band 2-stage IMPATT stable amplifier with 21-dBm output level and 11-dB gain, using a diode bias-current compensation technique. Theoretical calculations also verified the experimental data. This technique will enable the IMPATT stable amplifier to be used in a multicarrier AM transmission system.

K-Band High-Power Single-Tuned IMPATT Oscillator Stabilized by Hybrid-Coupled Cavities

A K-band high-power and highly stable power source has been developed using a cavity-stabilized IMPATT-diode oscillator followed by a one-stage high-power reflection-type IMPATT-diode amplifier. The power source shows an output power of 0.7 W, a temperature coefficient of 6x10/sup -7/ / /spl deg/C, and an FM noise level of 92-Hz rms/1-kHz BW at 100 kHz from the carrier. To achieve a highly stable oscillation, free from mode jumping, a new hybrid-coupled cavity circuit with a passivating absorber is applied to stabilize the oscillation. The high-power amplifier is designed using a measured large signal device admittance and a power-adding concept.

Experimental and Computer Simulation Analysis of a Gunn Diode

Bias voltage-and frequency-dependencies of dynamic admittance of a Gunn diode have been measured systematically in the 8 to 13GHz frequency range. We qualitatively verified the results by computer simulation.

AFC circuit with fast acquisition for a TDMA cellular mobile communication system

A novel AFC (automatic frequency control) circuit for a TDMA (time-division multiple-access) digital cellular mobile communication system with pi /4-shifted QPSK (quadrature phase-shift keying) modulation is described. The AFC circuit satisfies the two contradictory requirements of fast acquisition and stable operation even under low CNR (carrier-to-noise ratio) channel conditions, simultaneously. The performance of a 40-kb/s TDMA transmission system was measured to confirm the availability of the AFC circuit. An E/sub b//N/sub 0/ penalty of the differential demodulator is compressed to less than 0.1 dB by the AFC circuit when carrier frequency deviation is within +or-1 kHz. The results obtained show that the differential detection can be applied to a receiver of the TDMA digital cellular mobile communication system when the proposed AFC circuit is implemented.<<ETX>>

GaAs Monolithic Astable Multivibrator Type VCO Operable up to KU Band

The estimated theoretical limit to oscillation frequency predicts that the frequency of a GaAs monolithic astable multiviblator type oscillator can be increased from the maximum reported frequency of 5 GHz to 17 GHz by optimization of circuit parameters. The increase is made possible by the W-silicide self alignment process due to its precision processing and high uniformity of FETs within a wafer. This type of oscillator is suitable for use as the local oscillator in monolithic front ends because it can be coupled directly with a double balanced mixer or prescaler without any phase shift circuits. Its simultaneous production of 0° and 180° phase output has made it possible to fabricate the VCO and prescaler on one chip. The operation of this chip is confirmed up to 2 GHz which is the upper limit frequency of the prescaler.