K/Ka-band Channel Characterization for Mobile Satellite Systems

Mobile satellite systems allow truly ubiquitous wireless communications to users anywhere and anytime, NASA’s Advanced Communications Technology Satellite (ACTS) provides an ideal spacebased platform for the measurement of K/Ka-band propagation characteristics in a land mobile satellite application. Field tests for K-band propagation were conducted in three basic environments: clear line-ofsight (LOS) highways, lightly shadowed suburban, and heavily shadowed suburban. Preliminary results of these field tests indicate very little multipath for rural environments and for clear LOS links while deep fades were experienced in shadowed areas, especially those where tree canopies covered the road. INTRODUCTION & OBJECTIVES A mobile satellite system like the ACTS Mobile Terminal (AMT) is affected by shadowing and multipath propagation due to roadside obstacles and terrain conditions. The degree of shadowing depends on the intersecting path length with roadside obstacles. Many parameters affect the intersecting path, like path elevation angle, azimuth elevation to the satellite, nature and geometry of the obstacle (tree, utility pole), obstacles set back from the road, lane and direction driven, size and type of road driven (rolling/flat, straighthoad bends), etc. In addition, the antenna pattern, the environment, rural/suburban, the season, and the carrier frequency, also affect the degree of shadowing. The objectives of the K/Ka-band mobile propagation experiments are to measure and analyze fading characteristics of the K/Ka-band channel. The analysis involves examining multipath, shadowing and blockage effects and comparing them with previous results from UHF and L-band models [1]. NASAS ACTS satellite provides a stationary K/Kaband platform ideally suited to the measurement of Michael D. Rice Electrical and Computer Engineering Brigham Young University Provo, Utah 84602 Phone: (801 ) 37&4469 Fax: (801) 378-6586 e-mail: mdr@ee. byu.edu K/Ka-band propagation characteristics in a land mobile satellite application. Field tests conducted during the first seven months of 1994 using the AMT provide data which can be used to characterize the channel. This paper describes the field tests, the experimental aspects, the data analysis procedures, and the measurement results of the K/Ka-band channel characterization for Mobile Satellite Systems. EXPERIMENTAL ASPECTS JPL has developed a proof-of-concept breadboard mobile terminal system to operate in conjunction with ACTS at K/Ka-band [2]. As depicted in Figure 1, this system comprises a bent pipe propagation link connecting terminals at fixed and mobile sites. A CW signal from a tone generator at 3.373 GHz was provided at the upconverter input of the Link Evaluation Terminal (LET) at the NASA Lewis Research Center (LeRC) in Cleveland, Ohio. This resulted in an uplink signal of 29.634 GHz and a downlink transmission at 19.914 GHz using the microwave switch matrix mode (MSM) c)f ACTS. These downlink signals were received at various locations around the Pasadena, CA area using the AMT tracking antenna with an EIRP of 22 dBW. The AMT is equipped with a small (8” x 3“), highgain, reflector antenna [3], which tracks the satellite signal in azimuth for a fixed elevation angle (46° for these experiments). The antenna is mechanically steered and acquires and tracks the satellite over the entire 360° of azimuth with a pointing error of <0.2°. Vehicle turn rates of up to 45° per second can be accommodated. The antenna has a G/T of -6 dB/K over a bandwidth of 300 MHz. The 3-dB beamwidth is+ 9° in elevation and* 6° in azimuth. The antenna pointing system enables the antenna to track the satellite for all practical vehicle maneuvers.