Fumio Ikegami

Propagation factors controlling mean field strength on urban streets

Calculation of mean field strength for urban mobile radio has been made on a ray-theoretical basis assuming an ideal city structure with uniform building heights. The result shows that building height, street width, and street orientation as well as mobile station antenna height are controlling propagation parameters in addition to the ordinary factors. The major theoretical characteristics agree approximately with experimental data including conventional empirical predictions. This suggests a way of theoretically predicting mean field strength in an urban area.

Causes of burst errors in multipath fading channel (mobile radio)

The so-called irreducible error due to frequency-selective fading is known to have a serious effect on mobile radio communication systems. Thus, the analysis of such errors is a prerequisite for making high-speed digital signal transmission over a fading channel feasible. The authors attempted to elucidate the physical mechanisms causing such errors using laboratory measurements of microscopic bit error rate. The results clarified some sources of burst errors in a multipath fading channel. In particular, large and rapid timing fluctuations of eye pattern due to severe delay distortion of the multipath channel was found to be the most dominant source of error. >

Fractional-bit differential detection of MSK: A scheme to avoid outages due to frequency-selective fading

A new scheme of fractional-bit differential detection of minimum shift keying (MSK) is proposed. This technique is aimed at reducing timing fluctuation of eye patterns, which is found to be a cause of abnormally long burst errors in a frequency-selective fading channel. We have confirmed in a detailed laboratory experiment that such long-burst errors can be eliminated by employing a differential delay shorter than one-bit interval, thereby yielding remarkable improvement in the measured average bit error rates. The result, in a way, highlights the influence of eye-pattern timing fluctuation on an actual digital mobile radio system.

Comparison of multipath delay characteristics with BER performance of high speed digital mobile transmission

Delay profile measurements made on urban streets using double-phase-shift keying (DSK) were compared with the bit error rate (BER) performance to analyze the cause of burst errors due to multipath propagation. Two types of correlators were used to calculate the delay profile for different purposes. Multipath delay has been observed to depend on the environmental conditions with maximum up to 5 mu s and delay spread less than 1.6 mu s. The major reflecting objects were identified that cause long delayed waves in correspondence to the measured DSK BER performance. From the comparison of delay profile measurements with BER performance of DSK, it has been found that the BERs are markedly reduced as long as the delay time does not exceed a half timeslot of DSK signal and a sufficient C/N is attainable.<<ETX>>

High bit-rate field transmission of an anti-multipath modulation technique PSK-RZ

Return-to-zero phase shift keying (PSK-RZ) is an anti-multipath modulation technique showing much improved bit error rate when the multipath delay difference is smaller than a symbol duration. Major results of high-rate transmission of an anti-multipath modulation technique PSK-RZ experiment in an urban area of Kyoto at 400 MHz band are described. The field test has proven the superior performance of PSK-RZ when the multipath delay time is smaller than a symbol duration. Measurement results are presented and compared with those of another anti-multipath modulation technique, double phase shift keying (DSK). It is confirmed that PSK-RZ shows an anti-multipath feature as long as the multipath delay time is shorter than a symbol duration, whereas DSK shows an anti-multipath feature only when multipath delay time is less than a half-bit duration.<<ETX>>

Transmission bandwidth improvement by directive antenna in urban mobile radio communication

The transmission bandwidth in urban areas determines the maximum transmission rate of digital mobile communication. A directive antenna can have an effect of broadening the transmission bandwidth by itself. The transmission bandwidth improvement of proposed antenna pattern diversity reception (APDR) is estimated by computer simulation based on the measured fading data received by directive antennas in urban areas, with two branch-switching strategies, resulting in appreciable transmission performance improvement.

An improvement effect by a hard-limiter on differential detection performance of PSK in frequency-selective fading

Differential detection of PSK after an IF hard-limiter is described. This detection scheme is well known for the reason that the receiver structure is greatly simplified with saturated amplifiers and a digital-type differential detector. In addition, it can give the improved effect of reducing eye pattern timing fluctuation which is found to be a cause of excessive errors in a frequency-selective fading channel. Error rates were measured for binary and quadrature phase-shift keying. The results show great improvement over the detection scheme employing linear amplifiers and an analog differential detector.

Fractional-bit differential detection of MSK&#8212;A new scheme for performance improvement in land mobile radio

A new scheme of fractional-bit differential detection of MSK is proposed. This technique is aimed at reducing timing fluctuation of eye patterns, which is found to be a cause of abnormally long burst errors in a frequency-selective fading channel. We have confirmed in a detailed laboratory experiment that such long burst errors can be eliminated by employing differential delay shorter than one-bit interval, thereby yielding remarkable improvement in the measured average bit error rates.