Analysis and Mitigation of Tropospheric Effects on Ka Band Satellite Signals and Estimation of Ergodic Capacity and Outage Probability for Terrestrial Links (2012)

The first part of this work covers the effect of the troposphere onKa band (20-30 GHz) satellite signals. The second part deals withthe estimation of the capacity and outage probability forterrestrial links when constrained to quadrature amplitudemodulations.The desire for higher data rates and the need for availablebandwidth has pushed satellite communications into the Ka band(20-30 GHz). At these higher carrier frequencies the effects ofscintillation and rain attenuation are increased. In regards to theeffects of scintillation, the first part of this work quantifies,through the use of a multiple phase screen simulation model, thebenefits of using two receive antennas to mitigatetropospheric-induced scintillation on Ka band satellite downlinks.Two representative turbulence profiles are considered, andcumulative distribution curves for scintillation-induced attenuationare generated for selection and maximal ratio combining schemes andcompared to those for a single antenna. The results indicate thatthere can be significant diversity gains achieved by combining twoantennas separated by only a short distance. Also, a comparison ofsimulation results with the results predicted by the \\emph{basicRytov} approximation shows that at elevation angles greater than 10degrees, Rytov theory can accurately predict performance benefits ofantenna combining, but at elevation angles less than 10 degrees itis better to use multiple phase screen simulations to makeperformance predictions. In addition, the effects ofscintillation-induced phase perturbations on the output power oflarge aperture antennas is examined. It is found that the outputpower degradation due to scintillation-induced phase perturbationsis generally negligible and can be countered by the simple means ofantenna tracking if necessary.In regards to rain attenuation, this work developed simple methodsfor estimating the outage probability and outage capacity andergodic capacity of satellite links due to rain fades. Therain-induced fades of a satellite link are often modeled with alog-log-normal distribution. Researchers have determined methods forcalculating the outage probability for Shannon capacity forlog-log-normal channels. However, in practical communicationssystems, the input signal is constrained to a discrete signallingset such as finite-size quadrature amplitude modulations. Underthese conditions the outage probability with regards to theconstrained capacity is a more accurate measure. A method isdetailed in this work for tightly estimating the outage probabilityand outage capacity of satellite links with quadrature amplitudemodulations. In addition this work derives a lower bound for theergodic constrained capacity of log-log-normal channels. To date, noother method for calculating the outage probability, outagecapacity, or a lower bound for the ergodic capacity for alog-log-normal channel with a finite-size quadrature amplitudemodulation has been published. Also, this portion of the workquantifies the benefit of using receive diversity to mitigate rainfades, providing the gains in outage capacity due to the use ofdiversity for a tropical region and a fairly dry region under theconstraint that practical constellations are transmitted. The aboveinformation and analysis methods provide useful tools for satellitesystem planners.The second part of this work examines terrestrial communicationlinks, which can suffer greatly from channel fading or shadowing.Two common statistical models for channels are the Rayleighdistribution and the log-normal distribution. The goal of thissecond part of the work was to develop a simple method for tightlyestimating the ergodic capacity and outage probability of these twochannel types when used with quadrature amplitude modulatedsignalling sets. Specifically an innovative method was developed forestimating the ergodic constrained capacity for Rayleigh andlog-normal channels with and without antenna combining. Theexpressions facilitate straightforward computation of outageprobability as well. Researchers have determined methods forcalculating the ergodic Shannon capacity for log-normal and Rayleighchannels for single and multiple receive antenna systems. However,in practical communications systems, the input signal is constrainedto a discrete signalling set such as finite-size quadratureamplitude modulation constellations. Under these conditions theergodic constrained capacity is a more accurate measure. The methoddetailed in this work provides a uniform expression for computingthe ergodic capacity, both Shannon and constrained, of Rayleigh andlog-normal channels with and without antenna combining. Theexpressions facilitate straightforward computation of outageprobability as well. Both the noise-limited andinterference-limited cases are studied. To date, no other methodfor estimating the outage probabilities for the constrained capacityof Rayleigh or log-normal channels has been published for either thenoise-limited case or interference-limited case. Also, no methodfor estimating the ergodic constrained capacity of a log-normalchannel or of an interference-limited Rayleigh channel has appearedin the literature. The analysis methods and information forterrestrial links developed in the second part of this work provideuseful tools for the designers of wireless communication systems ingeneral and have particular application to cellular mobile andultra-wideband systems.