Howard H. Xia

Radio propagation characteristics for line-of-sight microcellular and personal communications

To acquire a knowledge of radio propagation characteristics in the microcellular environments for personal communications services (PCS), a comprehensive measurement program was conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three base station antenna heights of 3.2 m, 8.7 m, and 13.4 m and two frequencies at 900 MHz and 1900 MHz. Five test settings were chosen in urban, suburban, and rural areas in order to study propagation in a variety of environments. This paper reports the LOS measurements in different environments, all of which show variations of signal strength with distance that have distinct near and far regions separated by a break point. It was also found that the location of the break point for different frequencies and antenna heights can be calculated based on first Fresnel zone clearance. The regression analysis reveals a slope that is less than two before the break point, while it is greater than two after the break point. This break distance can be used to define the size of microcell and to design for fast hand-off. Beyond the first Fresnel zone break distance the base station antenna height gain was observed to approximately follow the square power law of antenna height. >

Path loss, delay spread, and outage models as functions of antenna height for microcellular system design

This paper presents results of wide-band path loss and delay spread measurements for five representative microcellular environments in the San Francisco Bay area at 1900 MHz. Measurements were made with a wide-band channel sounder using a 100-ns probing pulse. Base station antenna heights of 3.7 m, 8.5 m, and 13.3 m were tested with a mobile receiver antenna height of 1.7 m to emulate a typical microcellular scenario. The results presented in this paper provide insight into the statistical distributions of measured path loss by showing the validity of a double regression model with a break point at a distance that has first Fresnel zone clearance for line-of-sight topographies. The variation of delay spread as a function of path loss is also investigated, and a simple exponential overbound model is developed. The path loss and delay spread models are then applied to communication system design allowing outage probabilities, based on path loss or delay spread, to be estimated for a given microcell size. >

Unified approach to prediction of propagation over buildings for all ranges of base station antenna height

Theoretical results for the dependence on base station antenna height of the average received signal for mobiles at street level are presented. The results apply to residential and commercial sections of cities and to all ranges of antenna height from well above to below that of the surrounding buildings. Assuming all buildings to be of equal heights, the range dependence of the average signal is found by evaluating multiple forward diffraction past rows of buildings. The solution for this diffraction problem for sources near to or below the rooftops gives the dependence of the range index on antenna height and base station height gain, which are in agreement with measurements. These results will be of importance for proposed systems for personal communication services, which envision the use of base station antennas at the height of lamp posts, as well as cellular mobile radio. >

A simplified analytical model for predicting path loss in urban and suburban environments

An analytical propagation model has recently been developed to predict radio signal attenuation in urban and suburban environments. This analytical model explicates the path loss as a result of signal reduction due to free space wavefront spreading, multiple diffraction past rows of buildings, and building shadowing. It is applicable for cellular mobile services as well as personal communications services (PCS) in both macro- and microcellular environments. Good accuracy was found for this analytical model by comparing the predictions with numerous measurements made in various propagation environments. However, since the analytical model involves multiple-dimension integration to calculate the signal attenuation due to multiple diffraction past rows of buildings, the model in its original format does not lend itself to easy implementation into a radio system planning tool. A simplified version of the analytical model is developed in this paper, which can be used for three different propagation scenarios with base-station antenna above, below, and near the average rooftop level.

Microcellular propagation characteristics for personal communications in urban and suburban environments

New microcellular systems have been proposed to operate over short radio paths by using low-base station antennas, and transmitting at low power. In order to study radio propagation in the microcellular environments for future personal communications services (PCS), comprehensive radio propagation measurements were conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three transmitting antenna heights of 3.2, 8.7, and 13.4 m and two frequencies in the 900 and 1900 MHz bands. The paper reports the path loss measurements made in urban and suburban areas where the receiving mobile was driven along preselected line-of-sight (LOS), zig-zag, and staircase routes to gather information about direct propagation along streets, as well as diffraction over the roofs in suburban areas, and diffraction around the corners in urban areas. The results obtained for the three antenna heights are studied, and show the height gain that can be expected for microcells in different environments. >

Path-loss prediction model for microcells

Empirical path-loss formulas for microcells in low-rise and high-rise environments are established from measurements conducted in the San Francisco Bay area. Using the 1-km intercepts and slope indexes of the least square fit lines to the measurements at cellular and personal communication services (PCS) frequencies for three base station heights, simple analytic expressions are obtained. Separate formulas are presented for environments of low buildings and for the high-rise urban core. Following the formula development processes for individual test routes, in low-building environments, a single nonline-of-sight (non-LOS) formula that is applicable to all non-LOS routes is derived. Due to the anisotropic property of wave propagation, cell shape of microcells is no longer circular. As examples, cell shape is presented when base stations are on the street in the middle of a block and when they are placed in the backyard.

Path loss and delay spread models as functions of antenna height for microcellular system design

Results of wideband path loss and delay spread measurements for two representative microcellular environments in the San Francisco Bay area in the 1900 MHz band are presented. The results provide insight into the statistical distributions of measured path loss by showing the validity of a double regression model with a break point at a distance that has first Fresnel zone clearance for line-of-sight topographies. The variation of delay spread as a function of path loss is investigated, and a simple exponential overbound model is developed. The path loss and delay spread models are then applied to communication system design allowing outage probabilities, based on path loss or delay spread, to be estimated for a given microcell radius.<<ETX>>

Radio propagation measurements and modelling for line-of-sight microcellular systems

A knowledge of radio propagation characteristics in the microcell environment is recognized to be essential for future frequency allocation and system implementation of proposed personal communications services (PCS). A comprehensive radio propagation measurement program in the San Francisco Bay area is discussed. Measurements were performed using three transmitting antenna heights of 3.2 m, 8.7 m, and 13.4 m and two frequencies in the 900 MHz and 1900 MHz bands. Five test settings were chosen in urban, suburban, and rural areas in order to study propagation in a variety of environments. For all LOS measurements even in different environments, the variation of signal strength with distance was found to show distinct ear and far regions separated by a break point. It was also found that the location of the break point for different frequencies and antenna heights could be calculated based on first Fresnel zone clearance. The regression analysis shows a slope that is less than two before the break point, while it is greater than two after the break point. This break distance can be used to define the size of the microcell and to design for fast hand-off.<<ETX>>

Simulation results on CDMA PCS system performance

To investigate the application of spread spectrum code division multiple access (CDMA) technology to the future Personal Communications Services (PCS), a comprehensive study of CDMA PCS in the 1.8 GHz band in various radio environments has been conducted by Telesis Technologies Laboratory (TTL) in cooperation with Qualcomm Inc. in San Diego. This paper presents simulation results on CDMA PCS system performance. In this simulation, we consider interference in the reverse link introduced by users within the center cell as well as users in the first two rings of neighboring cells. Frequency reuse efficiency is simulated under various propagation conditions. The system capacity is assessed for uniform and non-uniform cell loading. The effects of imperfect power control on system capacity is also discussed.<<ETX>>

Path loss formulas for PCS microcells based on environmental parameters

Empirical path loss prediction models for emerging PCS microcells in typical residential/commercial, irregular urban and high-rise urban environments are reported. Depending on the type of route, individual path loss formulas are derived for each type of environment. Performance of the path loss formulas are evaluated by the comparisons with the measurements in Salling, Denmark and the Waltisch-Bertoni model.