This paper proposes a method for measuring the rapidly varying parameters of a power amplifier (PA) characterized by a memory polynomial model in less time than in the symbol period of the orthogonal frequency-division multiplexing (OFDM) signal of a long-term evolution-advanced (LTE-Advanced) system. The method fulfills the dual-updating scheme that we proposed in our previous papers, which described a method of determining slowly varying parameters. We used the dependence of bandwidth on the order of nonlinearity to distinguish the contributions from different orders of nonlinearities in the frequency domain. We assumed that fast Fourier transforms (FFTs) with shorter fundamental periods than the symbol period attain shorter measuring times. We conducted a computer simulation to confirm the applicable range of the described method for varying the speed of the model parameters. We assumed sinusoidal variations for the parameters of the PA, and used the proposed method to trace the varying parameters and used the traced results in a predistorter (PD). We estimated the improved spectrum for the PD to confirm the accuracy of the determined coefficients. The simulation shows that our method traces changes accurately up to a variation in amplitude of 20%. We also confirmed that the method can trace the sinusoidal variation frequency up to half of the symbol period.

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.

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.>

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.>

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.

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.