Study On Self-adaptive Satellite Communication System Scheme And Relative Technologies

Satellite communication, as one of the supports of long distance communication, has become an indispensable communication means in modern society. But with the development of satellite communication enterprise, interference has become a serious problem. Satellite with different communication system can't communicate with each other, which has also became an obstacle for the development of satellite communication. Under these conditions, self-adaptive communication technologies are proposed in satellite communication system in this paper. The relative technologies have also been studied.The kernel of self-adaptive satellite communication technology is that, transmitter can automatically choose the transmitting frequency, symbol rate and modulation type according to the interference condition of channel in order to lower the BER (bit error rate) to the utmost, while receiver can realize signal detection, modulation recognition, interference cancellation and demodulation automatically.At first, we select SDR (software defined radio) as the system platform considering the character of self-adaptive satellite communication system, and put forth a few imaginations for the platform design. We also discussed the multiple sample rate signal processing, which is the academic base of SDR, and introduced the decimation and interpolation theory in detail.Secondly we proposed a self-adaptive modulation technology based on the analysis of interference condition in the satellite channel. This technology can not only restrain interference on the system level view, but also ensure satellite communication quality and channel utilization. The key technology in it, such as interference discrimination, self-adaptive modulation strategy and channel quality estimation are discussed in this paper particularly.In order to meet the requirement of special satellite and realize non-cooperative communication in a sense, we studied automatic detection and modulation recognition of communication signals in depth. We bring forward a new narrow band signal detection algorithm based on the analysis of CNR (carrier noise ratio) of uplink in UHF (ultra highfrequency) band and make theory deduce together with algorithm simulation. Moreover we sum up a general spread spectrum signal detection algorithm, which is fit for self-adaptive satellite communication system. Besides signal detection, modulation parameters, such as symbol rate, chip rate and PN (pseudo noise) codes are estimated in this algorithm. Automatic modulation recognition of communication signals is the precondition of self-adaptive demodulation for receiving signals. In this paper we proposed a new modulation recognition algorithm based on the decision-theoretic approach and made algorithm simulation. The simulation results express that this algorithm is very simple to be calculated on-line and it also has a good recognition rate in the low SNR (signal noise ratio) environment, furthermore the effect of symbol shape to the parameter extraction has been considered, which can satisfy the needs of engineering.In succession, according to the detection and recognition results, this paper proposed an algorithm, which can demodulate different signals. Coherent demodulation and non-coherent demodulation are introduced distinguishingly in this paper. The study emphasis is the carrier and symbol synchronization problems in coherent demodulation of PSK (phase shift keying) and 16QAM (quadrature amplitude modulation) signals. Furthermore we proposed a scheme adopting the same PLL (phase locked loop) to acquire coherent carriers of these different modulation signals, and discussed the late-early gate method for symbol synchronization.At last, the general work of this paper is summarized and the further research direction is pointed out.