Study On The Communication System In Picosatellites

The communication system is the most important part in a picosatellite. However, there are not many relevant technical materials and application specific integrated circuits in this area. Meanwhile, the communication system in a picosatellite is often required to be small, light and power saving. Therefore, it is quite challenging to develop the communication system independently.The main original work and valuable results in this dissertation are as follows. 1). A complete communication system for a picosatellite is designed and verified, with the specific characteristics of picosatellites and earth stations in China taken into account. The scheme is examined by several experts. All important modules of the system have been debugged and tested in lab. The results proves the feasibility of the design scheme. It is a good groundwork for further research on the picosatellite communication system.2). A demodulation method of the BPSK signal based on time measurement is presented in this dissertation. It is a noncoherent demodulation method and can be achieved by software. Moreover, a clock can be generated to synchronize output data. In practice, the demodulation process can be accomplished by a microprocessor already existing in the communication system. Thereafter, little additional hardware is needed to implement the demodulation. This is a very useful feature for a picosatellite communication system whose bulk, weight and power consumption are strictly constrained.3). The design methodology to achieve the lowest noise figure (NF) of the whole receiver is proposed and systematically studied. Given the performance of each device in the receiver, the NF and power gain of the whole receiver have some improvement using this method compared to methods aiming at the lowest NF for each stage in the receiver. For a picosatellite communication system the improvement is valuable.In addition, the relation among the loop filter of a phase locked loop, the stabilemargin of the system, the output steady-state error, the system locked time and the output phase noise is analyzed and summarized in the dissertation. Method to design the loop filter is described in detail. It is very helpful to design frequency synthesizers and carrier recovery circuits in a communication system.When a narrow band phase modulated signal is passed through a frequency divider with division ratio R, the power of the modulating signal is reduced. This dissertation gives the approximate relation between the power reduction and R. This relation is much simpler than the commonly used Bessel functions.