SUMMARYRain fades at Ka-Band degrades the link quality and performance significantly. Several rain fade mitigation techniques for Ka-band satellite systems are being investigated to improve the channel capacity. Methods such as power control and adaptive waveform techniques have been proposed for use in the uplink as they are capable of straightforward implementation. A novel down link power control technique for multi-beam Ka-band system has been proposed in this paper. It is based on the use of multi-port amplifier, which is commonly used for dynamic power sharing of the beams depending upon the traffic. Payload architecture for multi-beam coverage using multi-port amplifiers has been designed for the proposed technique. The simulation results to compensate for the rain fade attenuation of one beam by sharing the unused power from other beams have been presented
Interoperability and compatibility is the main goal for current GNSS systems. A concept of Global Navigation Satellite System (GNSS) is to use all navigation system together to provide better capabilities compared with those that would be achieved relying solely on one service or signal. Compatibility, on the other hand, assures that existing GNSS signal is not degrading each other below certain threshold. GNSS provider is concerned about their own signal as well as other signals from different service provider for coexistence. For this reason interference analysis of current GNSS signal is the most needed requirement in current scenario. India is developing its own regional navigation systems named as Indian Regional Navigation Satellite System (IRNSS).An in-house tool is developed with suitable Graphic User Interface (GUI) which provides static analysis of different type of interference parameters and indicates its compatibility with already existing signals. Using the tool, this paper analyzes the degradation in IRNSS signal performance due to various navigation signals in different bands via consideration of parameters such as Power Spectral Density, Root Mean Square (RMS) Bandwidth and Rectangular Bandwidth. A detailed interference analysis of proposed signals is also calculated. In this paper, an attempt is made to analyze & review few suitable navigation signals for IRNSS in various navigation bands.
Satellite Navigation Systems (SNS) provide Position, Velocity and Time (PVT) services. The SNS is required to maintain its own System Time with high accuracy. To set up the precise System Time, each system component should maintain its own time within a specified limit. In the SNS, the onboard Space Vehicle (SV) time generator is one of the components and it should be set and maintained with few nanoseconds accuracy. To achieve accurate time setting with minimum difference between the ground and onboard SV systems, the onboard time setting should be highly predictable and accurate. This paper proposes an approach to initialize/set the onboard SV Time. The paper also discusses the concept of synchronization of SV Time with System Time with an overall accuracy better than 1 nsec. The proposed technique requires minimum setting time and synchronization steps and there is no need to predict accurate uplink propagation delay and command execution time.
The paper presents a modified Constant Envelope Multiplexing with Intermodulation Construction (CEMIC) technique for multiplexing signals within a single frequency band. A constant envelope signal is necessary to operate a transponder at maximum efficiency. This paper proposes a novel scheme to incorporate backwards compatibility constraints into the cost function of the existing CEMIC scheme to minimize changes in the onboard navigation system and ground receivers. The proposed scheme maximizes multiplexing efficiency by optimizing signal power sharing as per system requirements. Simulation results indicate that the proposed scheme provides 0.1% to 13.7% better efficiency than the existing CEMIC scheme, depending upon the case severity. Furthermore, the power distribution and phasing of the individual intermodulation constituent signals are optimized to minimize intra-system and inter-system interference. As a result, the proposed scheme facilitates frequency coordination with GNSS service providers. The paper also discusses the hardware performance of the proposed scheme's composite signal.
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