Land mobile communications in Japan have shown remarkable progress in recent years. The total number of all types of radio stations has exceeded 750 million as of March, 1992 and more than 80% of them are used for land mobile communications. The more radio telecommunications becomes popular, the more demand for communicating at any time, at any place and with anyone, intensifies. Various new land mobile systems such as digital cellular telephones have been developed and to be introduced. These new systems are designed to promote effective frequency use in order to meet the exploding demand for it. The digitalization of land mobile communication systems will be the key technology which enable to bring the new possibility in the land mobile communications.

This paper describes voice communication connection controls in digital public land mobile networks (D-PLMNs). Voice communications in the D-PLMNs are carried at about 10 kbit/s over narrow-band TDMA channels with highly efficient cellular voice encoding schemes. Extensive research is being carried on half-rate voice encoding schemes that will effectively double radio resources. We first outline the configuration of voice communication connection between a cellular phone in the D-PLMN and a telephone in a fixed network, and we describe the optimum position for the CODECs that transform cellular voice codes to the conventional voice codes used in the fixed network, and vice versa. Then we propose a CODEC-bypassed communication control scheme that improves the quality of voice communication between cellular phones. And we propose a cellular voice code negotiation scheme in the D-PLMN which supports different cellular voice encoding schemes. We also propose an efficient channel reassignment scheme for effectively assigning TDMA channels to voice calls with two different bitrates (full-rate and half-rate), and we analyze this scheme's traffic capability. Finally, we describe a dual-tone multiple-frequency (DTMF) signal transmission scheme and estimate the number of DTMF signal senders required in the D-PLMN.

High frequency and low power 128/129 dual modulus prescaler ICs are developed for mobile communication applications, using 0.5 µm GaAs MESFET technology. Provided with an on-chip voltage regulator, a prescaler IC with an input amplifier operates in a wide frequency range from 200 MHz to 1,500 MHz at input power from -15 dBm to +17 dBm at the temperature of -30 to +120 with supply voltage of 2.7 V, 3.0 V and 5.0 V. At the same time, it demonstrated its low power characteristics consuming 3.68 mA with 3.0 V at +30 in operation, 0.16 mA while powered-off. Another prescaler IC without an input amplifier operates up to 1,650 MHz with Vdd=2.7 V, 3.0 V and 5.0 V at +30, dissipating 2.74 mA/3.0 V.

In order to provide a low profile wire antenna for mobile communication, we have developed a new type of the transmission line type antenna, which we call a Modified Transmission Line Antenna (MTLA). Analysis of a certain type of the modified transmission line antenna has revealed that the input impedance and the gain can be determined independently by appropriately choosing antenna configuration. In this paper, we first explain the fundamental characteristics of the modified transmission line antenna. We then introduce two types of MTLA, i. e. a zigzag MTLA and a double MTLA, for practical application of the MTLA to mobile communication. Their characteristics are also discussed theoretically and experimentally.

This paper analyzes the performance of the capacity controlled digital radio system, which controls the number of modulation levels according to the amount of traffic. These analyses are performed under thermal noise and co-channel interference. As a result, the throughput improvement is approximately 16 times comparing with the fixed capacity system which has the designed outage probability of 0.1%. Theoretical results are applied to the future mobile communication system which utilizes TDMA access method or burst co-dec, and it is found that the reuse distance can be improved to 1/5 times when the designed outage probability is 0.1%.

A new error rate formula for narrowband Differential Quaternary Phase Shift Keyed system in a Rayleigh fading channel is obtained in closed-form. The formula predicts a non-zero error probability for noiseless reception. As predicted, the computed error rates approach some constant or floor values as the signal-to-noise ratio is increased beyond a certain limit. In the presence of various Doppler frequency shifts, an IF filter bandwidth of about one times the symbol rate is found to lead to a minimum error probability prior to the appearence of the error rate floor.