This paper presents some results of field tests for our proposed interference cancelling equalizer (ICE) to assess the feasibility of path division multiple access (PDMA). PDMA exploits the different properties of propagation paths between a desired and a co-channel interference (CCI) signal to discriminate them. The focus of this paper is on the case where the desired and CCI signals actually come from the same direction, in which case an adaptive array antenna based on space division multiple access (SDMA) cannot resolve the desired and CCI signals. The field trial results show that even in a negative range of average carrier-to-interference ratio (CIR), the ICE can achieve excellent CCI cancellation performances.

Spectrum efficiency ofM-ary PSK land-mobile radio is discussed theoretically. The spectrum efficiency ηT(erlangs/Hz·m2) is defined as spatial traffic density per system bandwidth, and is shown to be consistent with the conventional ones. The effect of multilevel modulation upon ηTis calculated. It is shown that ηTis optimal whenM=4, i.e. QPSK.

This paper is concerned with digital modulation for future mobile radio telephone services. First, the specific requirements on the digital modulation for mobile radio use are described. Then, premodulation Gaussian filtered minimum shift keying (GMSK) with coherent detection is proposed as an effective digital modulation for the present purpose, and its fundamental properties are clarified with the aid of machine computation. The constitution of modulator and demodulator is then discussed from the viewpoints of mobile radio applications. The superiority of this modulation is supported by some experimental test results.

Predetection Gaussian bandpass filtering effect on the coherent detection of minimum-shift-keying (MSK) is theoretically anlayzed on the basis of the worst signal pattern which brings the maximum intersymbol interference. The optimum 3 dB-down bandwidth (B)-bit duration (T) product of the Gaussian bandpass filter is proved theoretically to beBT = 0.5887, which degrades the requiredE_{b}/N_{0}(signal-energy-per-bit to noise-power-density ratio) only by 0.14 dB from that of antipodal coherent PSK using differential encoding. The degradations due to the phase errors of reference carrier and decision timing and the frequency drift of the received input signal are also shown. In addition, an alternative coherent detection using the reference carrier having the frequency deviated from the center frequency by the frequency deviation, which is called the deviated-frequency-locking scheme, is presented, and its error-rate performance is proved to be substantially identical with that of the conventional center-frequency-locking scheme.

In a high-speed digital radio relay system with four-phase-shift keying and coherent detection, it is very important to realize an accurate, stable, and wide-band carrier synchronizer. In this paper, the influence of time delay causing trouble for the wide-band synchronizer realization is analyzed. Then the design procedure of this synchronizer is described. Finally, the realizability of such a synchronizer is proved by the experimental results at a 1.7-GHz intermediate frequency and a 200-MHz clock frequency.