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.

This paper describes error probability of the second-ordered BAM in the presence of noise bits in initial input. A calculation method is proposed to estimate the error probability at the second iteration to retrieve a library pair. Theoretical estimation suggests that the BAM with a larger number of neurons are more robust for the noise bits: the error probability of 10/sup -6/ is obtained for the BAM with 500 neurons in a layer even the initial input has 90 noise bits (15% of numbers of neurons). Dependence of number of library pairs on number of neuron is estimated for the various error probabilities by assuming 15% noise bits. If the error rate of 10/sup -6/ is permitted, capacity of the BAM can be increase by about 40%.

This paper describes the theoretical performance of a frequency-hopping system using Gaussian-filtered FSK (GFSK), which is a promising candidate for 2.4-GHz wireless local area networks (WLAN). We have improved previous methods to calculate the bit-error rate (BER) performance of the GFSK system by considering the effect of a postdetection filter in the first-order approximation. The improved method is applicable when the single-sided bandwidth of the postdetection filter is wider than the bandwidth containing 99% of the GFSK signal energy. It is used to calculate the BER performance as well as the dependence of the BER on the level of interchannel interference. The calculated performance of the GFSK system suggests that the postdetection filter is very effective in reducing interchannel interference. The feasibility of a GFSK system with a 1-Mbd symbol rate and 0.32 modulation index is confirmed by the combination of a predetection filter with a 0.85-MHz bandwidth and a postdetection filter with a 0.8-MHz single-sided bandwidth.

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.