Eisuke Fukuda

Estimating velocity using diversity reception

In mobile communication systems, the velocity of mobile terminals is important for adequate handoff control and efficient dynamic channel assignment. We can estimate the velocity of a mobile terminal in a Rayleigh fading channel, because it is proportional to the Doppler frequency. Diversity reception is the most common method of improving communication quality in faded channels, and since the switching rate of diversity branches is proportional to the Doppler frequency, the velocity is easily estimated. We derived a relationship between the switching rate of the branches N/sub BS/ (times/s), and the Doppler frequency f/sub D/ (Hz): as follows N/sub BS//spl sime/1.3 f/sub D/. We confirmed this relationship experimentally, and since our method is very simple and needs no additional equipment, it can easily be implemented in mobile terminals.<<ETX>>

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>>

Cartesian feedback amplifier with soft landing

The author describe the results of several experiments conducted on a Cartesian feedback amplifier with soft landing. This amplifier uses a new method for adaptively controlling the local signal phase in a Cartesian demodulator. They tested the soft-landing Cartesian feedback (SLCFB) method in the 900 MHz band using pi /4-shifted QPSK modulation to determine its applicability for pocket terminals in Japanese digital cellular systems. They developed a smooth loop-gain control mechanism using a variable gain amplifier with an FET and a continuous phase-shifter control circuit for digital processing in the IF band. They showed that the SL-CFB method can maintain the optimum local signal phase in the demodulator. This method therefore solves the problem at applying CFB amplifiers. They adopted circuit configurations that are easy to incorporate into LSI chips so that the amplifier can be used in compact terminals. The results show that the SL-CFB amplifier is a promising candidate for developing highly efficient linear amplifiers, which are very important in digital cellular telephone terminals.<<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.

Determination method for complex valued LTI transfer functions causing memory effect of power amplifier

This paper proposes a method to measure complex valued transfer functions of linear time-invariant (LTI) circuits by assuming a memory polynomial model for a power amplifier (PA). To preserve phase information, the method uses cross-correlation of the device under test (DUT) with another PA without memory effect. This paper has clarified possibility that all coefficients in the memory polynomials are directly determined by the impulse responses of the measured transfer functions. An iterative algorithm is described to obtain accurate estimates for the LTI transfer functions using the measured cross-correlation. Virtual data of the cross-correlations are generated for the assumed model of the PA. Validity of the method including the algorithm is examined by computer simulations where the input signal is assumed to be an orthogonal frequency-division multiplexing (OFDM) signal consisting of 200 subcarriers. It has been verified that the LTI transfer functions converge to the assumed ones within five iterations in the case of the blind start.

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>>

Design of Predistorter Using Measured Nonlinear Characteristics of Power Amplifier with Memory Effect

This paper describes a method to design a predistorter (PD) for a power amplifier (PA) with a memory effect by using nonlinear parameters extracted from measured intermodulation distortion (IMD) for a GaN-FET amplifier. To improve the computational efficiency, the updating of a cancellation signal is provided by an iterative algorithm. It is confirmed that the proposed algorithm attains computational intensity lower than half of a memory polynomial. A computer simulation has clarified that the PD improves the adjacent channel leakage power ratio (ACLR) of OFDM signals with several hundred subcarriers corresponding to 4G mobile radio communications. It has been confirmed that a fifth-order PD is effective up to a higher power level. The improvement of error vector magnitude (EVM) by the PD is also simulated for OFDM signals of which the subcarrier channels are modulated by 16 QAM.

An indoor bidirectional message paging system with a pocket-size terminal using a direct-conversion FSK modem

The authors describe an indoor bidirectional message paging system which has good frequency utilization and serviceability. The trial system adopts microcells (with a zone radius of 50 to 100 m) and half-duplex communication using the carrier-sense multiple-access with collision detection access method in the 420 MHz band with an occupied bandwidth of 12.5 kHz and a transmission power of 10 mW, according to the Japanese RCR STD-3 standard. Messages of up to 64 alphanumeric or 32 Japanese (Kanji) characters can be transmitted from a pocket-sized mobile terminal using a direct-conversion FSK (frequency-shift keying) modem. The modem enables the size of the mobile terminal to be the same as that of the conventional message pager. The basic concept of this system can also be applied to future microcell public message communication systems.<<ETX>>