Yukio Takeda

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.

A data tablet using electromagnetic induction

A new data tablet using electromagnetic 1 induction is described. The position on the i tablet is detected by the sensor in the pen holder which is coupled with the rotating magnetic field whose phase varies linearly with the position of the pen on the tablet. In this method, the sensor height “h” and the phase change factor “a” of the generated magnetic field are selected as ah ± 1 so that the positional error caused by the pen inclination is readily compensated. The phase change factor of the magnetic field, in addition, is made so large that the reading accuracy is improved. As practical examples, an electromagnetic white hoard (size: 1.4 m x 1.06 m) and a tablet unified with a plasma display panel for teleconferencing equipment are described.

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>>

GaAs Monolithic 1 GHz Video Amplifier using Ti/W Silictde Gate Technology

A GaAs monolithic video amplifier is designed with the aid of computer simulation where FET parameters are determined by the dc and low frequency responses. GaAs monolithic IC chips are fabricated by self-aligned Ti/W silicide gate technology. The amplifier composed of FETs with 2 ¿m gate length has a gain of 12 dB with a bandwidth of 0.8 GHz which agree well with the computer simulation. Gain of 13 dB and bandwidth of 3 GHz can be expected using FETs with a gate length of 1 ¿m, as suggested by computer simulation.