Telesat

About: Telesat is a based out in . It is known for research contribution in the topics: Communications satellite & Satellite. The organization has 91 authors who have published 75 publications receiving 524 citations.

Spread slotted ALOHA techniques for mobile and personal satellite communication systems

Abstract: The objective is to develop a general theoretical framework for a class of spread slotted ALOHA (SSA) systems. The contributions include: modeling of a generalized spread slotted ALOHA (SSA) system; derivation of computationally efficient closed form expressions for the SSA system throughput and delay taking into account receiver complexity; and presentation of numerical results to validate the derivation as well as to substantiate the superior performance of the proposed scheme. The results demonstrate that SSA schemes offer significant improvements in terms of throughput, delay, and network stability against excessive loading at very acceptable levels of receiver implementation complexities. Also, SSA is found to be highly robust to errors in the time of arrivals and eliminates the need for a guard time. >

Triple-Band Cavity Bandpass Filters

Abstract: This paper presents a new class of cavity-based triple-band filters employing resonators that support three operation modes. The proposed triple-band filters do not require junctions and can achieve an equivalent Chebyshev performance with fewer cavities, thus significantly reducing the footprint when compared to traditional approaches. The filter facilitates a systematic design approach starting from the coupling-matrix generation to the overall response optimization. The concept is potentially applicable to most triple-mode resonators and is demonstrated in this paper using waveguide and dielectric resonators. The first design is an inline structure employing elliptical waveguide cavities, whereas the second design is a folded structure using rectangular waveguide cavities. The third design is implemented by dielectric loaded cavity resonators. All the proposed triple-band filter designs offer high Q and allow for independent control of each frequency and coupling parameter. To verify the concept, three triple-band filter examples with different realizations are designed, manufactured, and tested to allow comparisons.

Multiple differential detection of continuous phase modulation signals

Abstract: A sequence estimation algorithm for the differential detection of the continuous phase modulation (CPM) signals, yielding significant gains in BER performance and with considerable resistivity to fading, is introduced. These advantages, along with the reduced hardware complexity, low cost, and fast synchronization which characterize the differential detector, make the proposed receiver useful for land mobile radio and mobile-satellite communications. The new receiver is based on multiple differential detection. The multiple differential detection strategy provides the decoder with more information regarding the transmitted data and applies a noise decorrelation process on the received signal, useful to the sequence estimation. The algorithm is derived in a general form, and can be applied on any CPM scheme, with any degree of complexity. The authors have evaluated the receiver for two of the most popular CPM schemes, the tamed frequency modulation (TFM) and Gaussian minimum-shift keying (GMSK) (with B/sub 1/T=0.25), in the presence of additive white Gaussian noise (AWGN) and Rician fading. The BER performance evaluation results indicated significant gains and considerable reduction of error floors. In AWGN improvements close to 9 dB have been verified. >

Anik-E1 and E2 satellite failures of January 1994 revisited

Abstract: [1] The consecutive failures of the geosynchronous Anik-E1 communication satellite on January 20, 1994, and Anik-E2 about nine hours later on January 21 (both incidents occurred on January 20 local time) received considerable publicity because the malfunctions of the satellites disrupted television and computer data transmissions across Canada, as well as telephone services to remote northern communities for hours This often-cited event is revisited here with materials not covered before Using publicly available information, Anik-E failure details, media coverage, recovery effort and cost incurred are first presented This is then followed by scrutiny of space weather conditions pertinent to the occurrences of the Anik-E upsets We trace the space weather episode's inception on the Sun, propagation through interplanetary medium, and manifestation in magnetic field variations as well as in energetic electron flux increases, and its eventual impact on the Anik-Es The genesis of the energetic electron enhancements that have been blamed for the satellite malfunctions is thus traceable via high-speed solar wind stream with Alfven wave fluctuations to a longitudinally wide coronal hole on the Sun Furthermore, strong magnetic pulsations preceding electron flux peaks indicate Pc5 ULF (Ultra Low Frequency) waves as a probable acceleration mechanism for the energetic electron flux enhancement that resulted in the internal charging of the Anik-Es The magnetic fluctuations may even be possible triggers for the subsequent discharge that caused the satellites to malfunction This incident illustrates that satellite operators should be on alert for elevated high-energy electron environment that is above established thresholds, as specifications in satellite design may not render a satellite immune from internal charging