Rajat Acharya

Satellite link performance

This chapter takes up the practical aspects of a satellite system. It first illustrates the different facets of establishing a satellite link, describes the factors that are needed to be considered for the same and explains the link budget. Then it focuses on the performance of the link. The elements of long-term performance are first described and it is connected to the satellite fixed link margin and the risk factors associated with it are numerically presented. Later, the adaptive mitigation of the link fades is discussed and methods like ULPC and ACM are mainly explained with relevant problems and Matlab-based worked out solutions.

Interaction of waves with medium

This chapter is an extension of the previous chapter where the physics of the propagation of the wave is explained. Starting with the electrical polarization created within the material as a result of the incident electric field, this chapter derives the relation between different related parameters. It states the definition of a perfect dielectric. Further, it also considers a practical dielectric with finite conductivity and sets the conditions for which it behaves as a conductor or as a dielectric. The dispersive nature of the electric parameters of the material medium is also described to finally demonstrate their relation to the causes of the propagation impairments. At the end, the Rayleigh and Mie scattering and diffraction is discussed.

Chapter 6 – Tropospheric propagation and impairments

This chapter introduces the tropospheric impairments experienced by the satellite signals. It begins with a brief description of the standard reference atmosphere, including the tropospheric structure, which is a prerequisite for further discussions. Then, upon mentioning how the tropospheric propagation differs from that in free space, the impairing factors are identified and described sequentially. It starts with explaining the clear air components, then, after describing the different types of clouds pertinent for the purpose of propagation, finally illustrates the major aspects of rain. To each of these factors, the key parameters influencing the propagation are identified and the corresponding impairing effects are described in details.

Tropospheric impairments: Measurements and mitigation

This chapter has two major sections. The first section deals with the measurements and models of the tropospheric impairments experienced by the satellite signals. It begins with a brief description of the standard measuring instruments. Then it discusses the different impairment models, starting from the gaseous absorption in the clear sky condition, followed by the cloud attenuation and finally the rain attenuation. The models are described mentioning briefly its relevant basis. Particularly, two popular rain attenuation models are thoroughly explained with every aspect and factors of the model elaborated in the light of their contribution. Especially how the Mie scattering is used on rain drop sizes leading to the specific attenuation is illustrated at length. It is followed by the depolarization model and frequency scaling models. How these individual model values are to be combined is also mentioned. In focus of the next section are the methods of fade mitigation. Different fade mitigation techniques, from both compensation type and avoidance type are described after explaining the relevant terms associated with them.

Ionospheric impairments: Measurement and mitigation

This chapter deals with the ionospheric impairments and is a logical extension of the previous chapter. In this chapter, the methods of measuring the impairment parameters including the respective suitable instruments, corresponding models and methods of mitigating the impairments are explained. Both the direct and derived methods of estimating the ionospheric delay and scintillation are described. Two important models, viz. the Nequick and the Klobuchar model, for the delay and WBMOD for the scintillation are illustrated. The basic approach of mitigating these impairments is also elucidated in this chapter. Finally, the applications of these impairment data have been mentioned and the technique of tomographic estimation has been elaborated.

Chapter 2 – Maxwell's equation and EM waves

This chapter deals with the Maxwells equations. This is the basic technical prerequisite for the rest of the book. It starts with the statement of the equations and explains the significance of each with different forms that these equations can take. Using these equations and imposing definite conditions, both the static, electric and magnetic fields are derived and discussed to explain different aspects of them. Then the dynamic case of generation of electromagnetic fields and waves is addressed. Both the electric and magnetic field component of the wave and the scalar and vector potentials are thoroughly discussed. Finally, the Poynting theorem is explained and the Poynting vector is defined.

Chapter 4 – Ionosphere and ionospheric impairments

This chapter contains the descriptions of the ionosphere. It describes the basic structure of the ionosphere and details the salient features of each of the equatorial, mid-latitude and polar region. It also derives the Chapmans model for ionosphere and illustrates the methods by which the electron density is maintained. The propagation effects of the free electrons in the ionosphere are also explained with simple mathematics including ionospheric reflection of waves and formation of evanescent waves. It also shows how this leads to variations in the refractive index, resulting in different phase and group velocities. The effects of the ionospheric propagations, like group delay and scintillation, are described. Scintillation is substantiated with the mathematics of phase screen model. Finally, their effects on ground receivers are elaborated.

Chapter 8 – Noise, multipath and interference

This chapter can be considered as the foundation chapter for Chapter 9 . It deals with three major aspects of the signal condition at the receiver and performance. These are noise, multipath and interference. The first section is a brief treatise on noise. It explains both components of the system noise, viz. the antenna noise and the thermal noise of the system hardware. The foundation of the antenna noise model has been established from the basic radiation physics, however, with a simplistic approach. Multipath is then described, with emphasis on the effects like the fading and their mitigation techniques. Finally, the interference is explained. Different types of interference are mentioned and each of them is discussed in brief, illustrating the factors and effects associated to each of them.