Takeshi Toda

An adaptive impedance matching system and its application to mobile antennas

An adaptive antenna impedance matching system for mobile communication terminals is proposed. The system adaptively controls two varactors of the pi-network matching circuit detecting the change in the reflection coefficient between the antenna combined with the matching circuit and the RF front end of a transceiver. This system consists mainly of analog circuits and employs only a simple algorithm for convergence, therefore does not need any complicated mathematical formulation for modeling of the system itself as well as its nonlinear control elements. Also the proposed system utilizes only simple digital circuits for timing generation. In this paper, the performance of the adaptive impedance matching system is investigated by simulation. The input impedance of three antennas is alternated assuming the change of the environment due to a human head or a hand and the performance of the impedance matching is compared with fixed capacitance matching systems. As a result, it is found that the input power to the antenna for transmission can be increased by about 2-3 dB per second compared with the fixed capacitance matching system.

Field trial of space-time equalizer and delay diversity transmission in uplink for TDMA mobile communication

Space-time (ST) equalizer and delay diversity transmission (DDT) were field tested in uplink for a time-division multiple-access mobile communication system. The ST equalizer used a cascade connection of constrained array processors and branch-metric-combining (BMC) maximum-likelihood sequence estimation which was designed to provide both space- and path-diversity gains from first-arrival and one-symbol-delay paths while suppressing excessive intersymbol interference. DDT with two antennas was used for the mobile transmitter to ensure sufficient path diversity at the ST equalizer in a small-delay-spread environment. Test results showed that the ST equalizer bit error rate (BER) was significantly better than an ST equalizer without BMC and a single array processor for both micro- and macrocell environments. Furthermore, the ST equalizer BER with DDT was better than that without DDT for the microcell environment.

Prediction and validation of propagation loss in urban micro-cell environment by using ray tracing simulation

Field test and ray tracing (RT) simulation results for an adaptive array antenna (AAA) for micro-cell environments in central Tokyo area, is presented. The radio frequency was 3.35 GHz. The AAA at the base station was installed at the height below the buildings, i.e. microcell environment was considered. The AAA element spacing was set to be eight wave-length for space diversity. The height of a transmitter antenna at a mobile was 2 m. The distance ranged from 30 to 100 m between the receiver and transmitter antennas. Propagation characteristic measurements show that maximum delay time is less than 0.5-symbol period and averaged delay spread throughout the course is less than 0.05/spl mu/ sec. So the channel is regarded as frequency-flat. RT simulation results are compared with measured ones with respect to the received power at the AAA. The RT simulation results provide good approximation in line-of-sight (LOS) sections and slightly shadowed non-line-of-sight (NLOS). Contrary, in deeply shadowed NLOS area, it gives a large error.

Field test results of space-time equalizers and delayed diversity transmission in central Tokyo area

Field test of space-time (ST) equalizers for combating intersymbol interference (ISI) at base stations, was conducted in microcell and macrocell environments in central Tokyo area. Test results indicate that the ST equalizers provide significantly better bit error rate (BER) than an array processor alone does, due to both space and path diversity while suppressing the long-delayed path. Furthermore, a delayed diversity transmission (DDT) in a small delay spread environment provides sufficient delay-spread and improves the BER of the ST equalizer.

A response-aware control method for analog adaptive array antenna

Analog device-based adaptive array antenna, such as RESAA (reactively steered adaptive array) and phased array antenna, is attractive and advantageous as a means for gain enhancement and interference suppression in wireless signal transmission/reception in terms of cost and power consumption. However, when the analog device for beamforming has a mechanical structure, a special control method is required taking into consideration its response and characteristic. This paper proposes a new beamforming method for an analog adaptive array antenna. Numerical results show that the proposed method has both good interference suppression and gain enhancement capabilities in an OFDM (orthogonal frequency division multiplexing)-based system, for instance, it can improve the SNIR (Signal to Noise plus Interference power Ratio) by 18-to-25 dB.

A hybrid RF-analog/digital approach for terminal-side array antenna systems

This paper proposes a hybrid RF-analog/digital approach for terminal-side array antenna systems, where lower power consumption is required. Assuming an orthogonal frequency division multiplexing (OFDM)-based wireless local area network standard, the bit error rate (BER) performance of two types of array antenna is discussed, such as an adaptive array antenna and a phased array antenna and the trade off is shown between the attainable BER performance and the number of control parameters. Furthermore, analog device-specific effects are also discussed such as phase shift error and phase resolution required.

Measurement of the array-antenna directional pattern and bit error rate of a space-time equalizer

Array-antenna directional patterns of a pair of constrained array processors used in a space-time (ST) equalizer and the bit error rate (BER) of the ST equalizer were measured in an anechoic chamber. One of the constrained array processors constrains the direct path and the other constrains the one-symbol delayed path. The one-symbol-spaced two-taps-Viterbi-equalizer was used in the ST equalizer for obtaining path diversity from the direct and one-symbol-delayed paths. The measurements were conducted in static multipath environments where the direct path, one-symbol, and two-symbol delayed paths with critical angles of arrival (AOA) were generated. The array-antenna directional patterns and BER of a non-constrained array-processor were also measured and compared with those of the ST equalizer. The center of the carrier frequency was 3.35 GHz and the 99%-occupied power bandwidth was 2.7 MHz. The measured results indicate that the pair of the array-antenna directional patterns of the pair of the constrained array processors provides large gains in the directions of both direct and one-symbol-delayed path. The ST equalizer thus has significantly lower BER than the non-constrained array processor. However, degradation of null-forming in the direction of the interference occurred because of the transmitted signal bandwidth.