A model that combines free-space loss (proportional to the square of distance d) and excess loss has been known to assess the microwave line-of-sight (LOS) path loss in street microcell environments. The excess loss represents the effects of shadowing obstacles. We measure the path loss at the 3.35, 8.45, and 15.75 GHz frequencies in an urban environment, and analyze the distance characteristics of the pass loss for mobile antenna heights of 2.7, 1.6, and 0.5 m. Results show that using a new model that bases on a dα formula instead of d2 in the conventional model produced a better fit to the measured data. They also show that lowering the mobile antenna to a height of 0. 5 m made it possible to virtually ignore the excess loss factor and, instead, use the dα formula to assess the path loss characteristics.

Measurements of delay spread were performed at microwave frequencies of 3.35, 8.45 and 15.75 GHz along quasi line-of-sight streets in metropolitan Tokyo. It is found that the delay spreads increase with the measurement distance and reach around 600 ns up to 1 km. It is also confirmed that a cumulative probability of the delay spreads follows a log-normal distribution. The gradients of delay spreads against the distance are greater for a lower mobile antenna height hm = 1.6 m than for hm = 2.7 m in these measurements because of blocking effect by the traffic of vehicles and pedestrians on the road. When the mobile antenna height is 2.7 m, the delay spreads within the range before the break points are observed relatively small: 90 ns (3.35 GHz), 140 ns (8.45 GHz) and 150 ns (15.75 GHz) at the cumulative probability of 90%. The gradients of delay spreads against the distance are greater for wider streets in our measurements.

This paper discusses microwave path-loss characteristics as a function of mobile antenna height in an urban line-of-sight environment. Measurements were made in metropolitan Tokyo with high-density buildings, using base station antenna heights of 4 and 8 m. We describe the path-loss characteristics of vehicle-mounted mode (mobile antenna height is 2.7 m) and portable mode (mobile antenna heights are 1.6 and 0.5 m). Dependence of path loss on the distance between base and mobile stations was analyzed. This reveals that the break points shift to the near side in the vehicle-mounted mode. This phenomenon can be interpreted by the existence of an effective height h of the road. The typical value of h was found approximately 1.4 m. In the portable mode, on the other hand, break points were not observed. The mobile antenna heights (1.6 and 0.5 m) in this mode are close to or less than the average height (1-2 m) of pedestrians on the sidewalk; and the received waves at the mobile station are often disturbed by pedestrians. This explains the nonexistence of break points in portable mode. The average attenuation coefficients is observed 3.2 in this mode. The attenuation coefficients tend to be larger at lower base station antenna heights and narrower road widths.

This paper describes a method of predicting transmission performance to be obtained by applying RAKE reception and parallel transmission in realistic urban multipath environments. Delay profiles measured in metropolitan Tokyo at microwave frequencies were used to obtain the impulse responses of radio channels, and the closed-form equations corresponding to the performance of these anti-multipath techniques were derived, by means of the characteristic function method, under the assumption that the phases of the impulse responses are uniformly distributed. Results show that RAKE reception provides bit error rates 100 times lower than bare transmission does, whereas the improvement obtained by using parallel transmission should be especially valuable in broadband communication systems, such as those operating at data rates above 10 Mb/s.

There is currently a need for development of a new frequency band to enable creation of next-generation mobile communication systems. Of the potential bands, the 3 GHz and over microwave band holds the greatest promise. Experimental studies on the delay characteristics of multipath propagation must be conducted in order to achieve high-speed transmission in the microwave band. We have developed a system for measuring the microwave broadband propagation delay profile over 100 MHz spread bandwidths in the 3, 8 and 15 GHz bands. Our experiments confirmed system performances of 20-ns resolution, 40-µs maximum measurable delay, relative amplitude error of within 3 dB and dynamic range of over 60 dB. We used our system to measure delay profiles on an urban area with line of sight, particularly, in terms of the effects of mobile antenna height. Typical examples are presented. Analysis showed that delay spreads increased with transmit/receive distance and decreased with the higher antenna height.