A laboratory system for the investigation of rain fade compensation techniques for Ka-band satellites

James Svoboda, Brian Kachmar
1994 15th International Communicatons Satellite Systems Conference and Exhibit   unpublished
The design and performance of a rain fade simulation! counteraction system on a laboratory simulated 30/20 GHz, time division multiple access (IDMA) satellite communications testbed is evaluated. Severe rain attenuation of electromagnetic radiation at 30/20 GHz occurs due to the carrier wavelength approaching the water droplet size. Rain in the downlink path lowers the signal power present at the receiver, resulting in a higher number of bit errors induced in the digital ground terminal. The
more » ... nd terminal. The laboratory simulation performed at NASA Lewis Research Center uses a programmable PIN diode attenuator to simulate 20 GHz satellite downlink geographic rain fade profiles. A computer based network control system monitors the downlink power and informs the network of any power threshold violations, which then prompts the network to issue commands that temporaril y increase the gain of the satellite based traveling wave tube (TW1) amplifier. After the rain subsides, the network returns the TWT to the normal energy conserving power mode. Bit error rate (BER) data taken at the receiving ground terminal serves as a measure of the severity of rain degradation, and also evaluates the extent to which the network can improve the faded channel. Introduction Modem communication satellite designs employ many techniques aimed at increasing the efficiency of data throughput Raising the carrier frequencies and increasing spectral bandwidth is one technique implemented in the design of modem communication satellites, such as in NASA's Advanced Communications Technology Satellite (ACTS), that increases data throughput but creates additional design considerations. Raising the uplink and downlink carrier frequencies to a less congested frequency band enables greater data throughput since more spectral bandwidth is available at these higherfrequencies. This increase in data throughput does not come without a price, and many system design tradeoffs and problems must beconsidered. One major problem deals with the transmission of electromagnetic RF energy at high frequencies which creates additional fading problems that can lower the received power to unacceptable levels. RF energy at 30120 GHz experiences atmospheric losses much greater than signals transmitted through the atmosphere at lower frequencies. Water vapor and oxygen present in the atmosphere attenuates, scatters, and radiates electromagnetic energy at different frequency dependent levels. Water vapor is particularly detrimental to the 30/20 GHz band, and this problem is further compounded when rain resides in the transmission path. Abstract The design and performance of a rain fade simulation! counteraction system on a laboratory simulated 30/20 GHz, time division multiple access (IDMA) satellite communications testbed is evaluated. Severe rain attenuation of electromagnetic radiation at 30/20 GHz occurs due to the carrier wavelength approaching the water droplet size. Rain in the downlink path lowers the signal power present at the receiver, resulting in a higher number of bit errors induced in the digital ground terminal. The laboratory simulation performed at NASA Lewis Research Center uses a programmable PIN diode attenuator to simulate 20 GHz satellite downlink geographic rain fade profiles. A computer based network control system monitors the downlink power and informs the network of any power threshold violations, which then prompts the network to issue commands that temporaril y increase the gain of the satellite based traveling wave tube (TW1) amplifier. After the rain subsides, the network returns the TWT to the normal energy conserving power mode. Bit error rate (BER) data taken at the receiving ground terminal serves as a measure of the severity of rain degradation, and also evaluates the extent to which the network can improve the faded channel. OF REPORT OFTHIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified NSN 7540-01-280-5500 Sta ndard Fo rm 298 (Rev . 2-8 9) Prescribed by ANSI Std. Z39-18 298-1 0 2 OF REPORT OFTHIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified NSN 7540-01-280-5500 Sta ndard Fo rm 298 (Rev . 2-8 9) Prescribed by ANSI Std. Z39-18 298-1 0 2
doi:10.2514/6.1994-917 fatcat:5va6g4hsfjbmjcubgiroccxvyu