A basestation power amplifier requires high linearity and stable operation for common amplification of a multiplexed wideband signal. Nonlinearity compensation techniques with the feedforward or predistorter are useful for this purpose. This paper presents a predistortion amplifier with automatic control at RF band for application at a basestation. In this method, the predistorter distorts an RF input signal by referring to a look-up table (LUT) corresponding to the input power. Out-of-band radiation power are directly monitored at IF band to determine the LUT. A DSP with an iterative algorithm updates the content of the LUT to minimize the out-of-band radiation power. Computer simulation experiment is carried out. The use of this proposed method promises a highly linear wideband and high power-efficiency amplifier.

In the multipath mobile channel, the received signal suffers from both the fluctuation in the received field intensity caused by fading and waveform distortion caused by the echo. Diversity reception using multiple spaced antennas is an effective method to compensate for fading, while echo cancellation with an adaptive array is good at compensating for waveform distortion. In this paper, an adaptive switching echo cancellation/diversity reception method to compensate for both waveform distortion and fading is proposed. The proposed switching reception monitors the impacts of channel conditions on received signal and then one of an echo canceller and a diversity receiver is selected accordingly to compensate the channel. The compensation performance of the proposed switching reception in terms of both average DUR (Desired to Undesired signal Ratio) and the probability of DUR below a threshold value is investigated with computer simulation. The results show that the adaptive switching echo cancellation/diversity reception has realized the advantages of both adaptive echo cancellation and diversity reception.

A widely used partial height ferrite circulator is analyzed. The circulator consists of ferrite post, dielectric spacers and a radial line stepped transformer, all of whose structures are assumed to be cylindrical. Eigenvalues of a circulator scattering matrix are numerically calculated, using mode matching method. Field analysis yields characteristics equations, which determine propagation constants in the partial height ferrite and dielectric structure. Calculated results of X-band circulators agreed well with experimental results. Wideband characteristics are obtained with numerical calculations.

In this paper, we propose an adaptive guard symbol insertion method for one-cell reuse TDMA cellular systems in which co-channel interference is reduced by adaptively selecting the best transmit-pulse waveform with different guard (null-) symbols according to the average error power (AEP) corresponding to signal-to-interference and noise power ratio (SINR), even though the same frequency channel is used at all base stations. Using the proposed system, current TDMA-based systems are readily extensible to one-cell reuse systems, which achieves higher spectrum efficiency. The system capacity is enhanced using the proposed method; moreover, the required qualities such as blocking probability and outage probability are retained.

A major drawback in OFDM systems is that the transmit-signal exhibits a high Peak-to-Average Power Ratio (PAPR) which causes nonlinear distortion at the output of power amplifier. To achieve high efficiency in OFDM systems, it is important to suppress PAPR of the transmit signal. In IEEE802.16e (mobile WiMAX) based systems, it is desirable to employ a simple PAPR reduction method such as clipping & filtering (C&F) or peak windowing (PW). The purpose of this paper is to evaluate PAPR reduction performance of C&F and PW and compare them in an IEEE802.16e based OFDM system. In addition, we also show a repeated PW method which reduces PAPR by repeatedly applying a smooth window function to the transmit signal. Computer simulation results show that the repeated PW can achieve almost the same PAPR reduction performance as that of the repeated C&F with significantly lower computational complexity.

Performance of multilevel FM with discriminator detection is studied for digital speech transmission in mobile radio channels. New transmit- and receive-baseband filter configurations in digital FM are considered. The low-pass filters are characterized by a square root of the raised cosine Nyquist filter. The present method is simple as an analog FM and has high immunity against fast fading. It is shown that digital speech can be transmitted with a 4-level FM and a 16 kbit/s adaptive delta modulation under a 25 kHz channel spacing, where the relative interchannel interference power is around -70 dB.

Compensation for the nonlinear systems represented by polynomials involves polynomial inverse. In this paper, a new algorithm is proposed that gives the baseband polynomial inverse with a limited order. The algorithm employs orthogonal basis that is predetermined from the distribution of input signal and finds the coefficients of the inverse polynomial to minimize the mean square error. Compared with the well established p-th order inverse method, the proposed method can suppress the distortions better including higher order distortions. It is also extended to obtain memory polynomial inverse through a feedback-configured structure. Both numerical simulations and experimental results demonstrate that the proposed algorithm can provide good performance for compensating the nonlinear systems represented by baseband polynomials.

The Fourier integrals are treated as a rigorous extension of the Fourier series expansion. The reward for this is that so called, in the Fourier integrals, singular functions that are not absolutely integrable, e.g., trigonometric functions can be discussed within a field of ordinary function giving a foundation for the delta function as distribution.

As a method to realize a high-speed communication in the home network, the power-line communication (PLC) technique is known. A problem of PLC is that leakage radiation interferes with existing systems. When OFDM is used in a PLC system, the leakage radiation is not sufficiently reduced, even if the subcarriers corresponding to the frequency-band of the existing system are never used, because the signal is not strictly band-limited. To solve this problem, each subcarrier must be band-limited. In this paper, we apply the OQAM based multi-carrier transmission (OQAM-MCT) to a high-speed PLC system, where each subcarrier is individually band-limited. We also propose a pilot-symbol sequence suitable for frequency offset estimation, symbol-timing detection and channel estimation in the OQAM-MCT system. In this method, the pilot signal-sequence consists of a repeated series of the same data symbol. With this method, the pilot sequence approximately becomes equivalent to OFDM sequence and therefore existing pilot-assisted methods for OFDM are also applicable to OQAM-MCT system. Computer simulation results show that the OQAM-MCT system achieves both good transmission rate performance and low out-of-band radiation in PLC channels. It is also shown that the proposed pilot-sequence improves frequency offset estimation, symbol-timing detection and channel estimation performance as compared with the case of using pseudo-noise sequence.

In the cellular mobile communication systems, co-channel interference and Rayleigh fading degrade the transmission performance. Adaptive Array Antenna (AAA) can suppress interference and, at the same time, can cope with multi-path fading by using a wide antenna spacing resulting in low correlation of received signals in each antenna element. A feedback-type AAA was proposed for frequency division duplexed (FDD) systems, where mobile station measures channel characteristics and feed-backs them to the base station. In this paper, we extend the system by introducing 2-branch diversity reception at a mobile station, and study the influence of antenna element spacing at the base station and control delay time on bit error rate performance under a realistic propagation model.

This paper introduces the research and development of digital modulation/demodulation techniques for mobile radio communications carried out so far in Japan. Constant envelope modulations such as GMSK, Nyquist filtered multilevel FM, PLL-QPSK and CCPSK are described. Linear modulations including π/4 shift QPSK, 16 QAM, anti-multipath modulations and nonlinearity compensated transmitter power amplifier are presented. The paper shows that Japan has made a significant contribution to the evolution of new technologies in this field.

The purpose of this paper is to improve a feedback-type adaptive array antenna (AAA) with feedback information quantized by one bit which was presented recently on TDMA system by an author of this paper. The improvement is made by using adaptive, instead of constant, update size of adaptive antenna weights control. Computer simulation results show that the performance of this system is improved to be almost equivalent to the performance of a system without quantization of the feedback information for wide range of fading speed. The results include the effect of control delay time and the maximum Doppler frequency under flat fading and frequency-selective fading.

This work is targeted to understand the operating principle of the feedback type echo canceller for use in an FM broadcasting receiver and to study its compensating features and the effects of the practical operating environment on its performance. The effects of the tap interval and the compensation performance in the presence of an echo with excess delay 0 - 15 µs are examined. The results show that the tap interval should be selected according to the observable bandwidth of the channel transfer function and the performance of a feedback type echo canceller has a wavelike curve with respect to the excess delay of the echo. To improve the performance of the feedback type echo canceller, an adaptive echo canceller operating with CM algorithm is proposed and examined with computer simulation. The results show that the compensation performance is improved.

With popularity of radio communication, voice scrambling has received increased attention for communication privacy. It has been known that pre-emphasis at the transmit side and de-emphasis at the receive side improves the received signal to noise power ratio (SNR) both for scrambled and nonscrambled signals. In this paper, optimum pre- and de-emphasis are theoretically investigated for FM and PM transmission including frequency-domain scrambling for voice security. Using a linear system model, the optimum frequency-characteristics for pre- and de-emphasis filter are given as a function of a voice signal spectrum, demodulator output noise spectrum, and the scrambling method. Comparisons of the maximum attainable SNR are made for various case including plain voice (non scrambling) and secured voice scrambled by spectrum inversion, reverberation and FFT spectrum transformation, assuming simple voice and noise spectra.

In order to exploit fully the frequency diversity benefits of multicarrier modulation (MCM), and the very nature of the frequency selective radio channel, we investigate an erasure decoded π/4 QDPSK MCM (ED-MCM) by employing simple Hamming (block) code. We propose the threshold-free criteria, i. e. relative minimum receive power test (RMRPT) and relative maximum decision error test (RMDET) for erasure generation and evaluate ED-MCM's performance by applying these tests to average received power, average decision error, instantaneous symbol/bit decision errors. At a normalized delay spread of 1/64, computer simulation results indicate a coding gains of 6.0 - 7.0 dB with ED-MCM at a BER of 10-3. RMDET/RMRPT based erasure decoding yields a 1.5 - 2.5 dB improvement over the conventional forward error correction (FEC) decoding at a BER of 10-5. The simulation results at other normalized delay spreads, i. e. , 1/32, 1/16 are also obtained. The erasure criteria (RMRPT and RMDET) applied to average values of received power/decision error yield consistently better performance over error only decoding. The results indicate that the erasure decoding based on relative (threshold-free) measures clearly promises an improved performance of the MCM system.

We propose a dynamic assignment method of radio channels using their qualities and data packet sizes. In this method, a high quality channel is assigned for long packets and a low quality channel is assigned for short packets. Assuming a packet transfer method based on PHS (Personal Handy System) procedure, the transfer speed and delay characteristics are investigated by computer simulation and compared with conventional method (i.e. random assignment). Both the transfer speed characteristics and delay performance are improved under light traffic load.

In this paper, radio propagation in the medium-scale building is investigated at 2.5GHz band. In order to predict the propagation loss in any place, four major modes of propagation are considered: low-loss in line-of-sight (LOS) wave, corridor guided wave, direct transmission wave through obstructions, and the reentered wave. Based on the measured results of attenuation characteristics, the macroscopic parameters for the above mentioned modes of wave propagation are determined. Using these parameters, signal strengths are predicted with average standard deviation of 4.5dB. The fading characteristics are studied by measuring the Rician parameter and the correlation coefficient for 2-branch diversity antennas separated by 50cm. The Rician parameters are 2 in case of the LOS propagation, and 1 in case of the no LOS propagation. The two branch correlation coefficients are less than 0.5 within coverage of 80-95% in almost all the locations.

The umbrella cell system, where the same radio system is used for microcells and overlaying macrocells, is a promising strategy for deploying microcell service to cope with the locally increased radio traffic. The interference at microcells due to macrocells can be compensated by increasing the transmit power of microcell. In this paper, a practical method to implementing a microcell system overlaid with an existing macrocell system is proposed. In order to engineer the radio resource planning for the underlaid microcells, transmit power design and application of Channel Segregation, a self-organized dynamic channel assignment, are proposed. By these techniques, the system channels are reused automatically while minimizing interference between macrocell and microcell systems, thereby communication quality of umbrella cell system can be improved. Furthermore, the prime advantage of the proposed method is that locally increased traffic is handled by the underlaid microcells without any extra effort for channel management.