Adaptive control of a reflective satellite communication system

Abstract

I n t r d u c t i o nThe system considered i n t h i s p a p e r i s a twoway comunication link using ground based transmitter-receiver pairs and a passive reflective s a t e l l i t e , This configuration allms comunications at reasonable pmer levels over distances well beyond the normal l i n e of s i g h t range of high frequency equipment.Maximum power i s d e l i v e r e d by each transmitter (Tx) whenever it i s i n operation, so the signal pmer delivered t 3 the receiver (Rx) i s maximum when the distance travelled by the signal i s minimum, o r when t h e s a t e l l i t e i s most nearly over the geometric center of the two ground s t a t i o n s . Minimum p m e r i s r e c e i v e d when the s a t e l l i t e i s j u s t above the horizon from one o r both of the ground s t a t i o n s . A typical received pmer vs. time curve i s as shown i n Fig. 1, where T denotes the time interval over which the s a t e l l i t e i s i n l i n e of s i g h t view f r m both stat i o n s . It i s not unusual for the received pmer t o vary as much as 1OOO:l during a transmission i n t e r v a l , which may vary f r m s e v e r a l minutes t o twenty minutes o r so, depending upon several factors including the distance between ground s t at i o n s , s a t e l l i t e h e i g h t , and hm nearly the satell i t e passes directly overhead. The system under consideration uses a wideband form of frequency modulation (FN) , and a phase locked loop (PLL) Rx i s used t o t r a c k t h e Doppler frequency s h i f t s caused by s a t e l l i t e motion, follow the instantaneous phase mdulation of the carrier signal, and provide the desired demdulated output signal. This type of Rx performs well as long as the signal t o noise pmer r a t i o , denoted by S/N, i s above the threshold level required t o maintain a phase locked condition. Since the noise pmer is apprsimately uniformly distributed in the frequency range about the received signal, N i s d i r e c t l y r e l a t e d t o the Rx BW. Thus, when S i s small, performance above Rx threshold requires narrm Rx BW. The Ibc BW may be increased as the satellite passes overhead and S increases, but m u s t be reduced as the s a t e l l i t e approaches the opposite horizon and S decreases again. The maximum information rate of the communication system i s d i r e c t l y r e l a t e d t o the Rx BW, s o i t i s desirable t o use maximum instantaneous Rx BW as the performance c r i t e r i o n i n developing an adaptive cmunication link. The remainder of t h i s paper i s devoted to a discussion of the general characteristics of an adaptive control system designed to maximize the information transmission capability of the cmmunication link introduced in the previous paragraphs per satellite pass. Only a minimum of detail regarding the comunication system i s provided, and emphasis i s placed throughout upon the adaptive controller, although an effort i s made to indicate the general operating characteri s t i c s of the ?Ix and Rx, p a r t i c u l a r l y t h e l a t t e r . It w ...

Robust Cascade MRAC for a Hybrid Grid-Connected Renewable Energy System

“…Adaptive control interest grew in the 1950s, as described in the survey [35] and book [36]. In 1958 [35], described and characterized several adaptive techniques already used to ensure robustness despite plant parameters, structure, inputs, and others changes.…”

“…In 1958 [35], described and characterized several adaptive techniques already used to ensure robustness despite plant parameters, structure, inputs, and others changes. Later, the book [36] deeper describes some of these techniques. MRAC is one of the adaptive control central techniques, significantly developed during the 1980s, as detailed in the book [34].…”