Algorithms For Automatic Modulation Recognition For Sub-Carrier Signals Of Satellite Unified Carrier TT&C System

Automatic recognition of modulation scheme is a key technique to build a universal real-time processing platform of satellite Tracking, Telemetry & telecommand (TT&C) signals. Its application is able to realize automatic configuration through software control without adding hardware requirements, which makes it attractive for both civil and military purpose. This paper will emphasize on the recognition method of Unified S Band (USB) TT&C system.In USB system TT&C signals are firstly modulated on sub-carriers and then combined and modulated on RF carrier. So the recognition procedure adopted in this paper is divided into two parts: carrier preprocessing and sub-carrier recognition.Before the recognition of sub-carrier moudulation, the orthogonal decomposition method based on the characteristic of analytic signal is applied to decompose carrier signal, which can achieve with large receiver carrier frequency error. While threshold judgment law is used to recognize the number, frequency and bandwidth of sub-carrier signals, and separate them. During the process, folding phase correction formula is utilized to correct the folding phase, and envelope fitting algorithm is proposed to eliminate the receiver carrier frequency error, and the spectrum of difference signal is adopted to avoid interference caused by phase noise.Sub-carrier recognition is a specific problem emerged with USB satellite TT&C system. The number of TT&C sub-carriers is small and the interval between them is not necessarily the same. Each sub-carrier may choose different modulation types. Though the method is aiming at satellite TT&C system, the soul of it can be applied to many other similar situations.After that, the concept of key feature statistic value is proposed, which means the maximum, the minimum and their margin of key features extracted from several successive segments. These segments are divided from an intercepted signal frame. Then pattern recognition approach based on decision criteria and Artificial Neural Networks (ANN) with Back-Propagation (BP) Learning Algorithm is used to recognize typical modulation types in unified carrier TT&C system including 2FSK (modulation index ), 4FSK, BPSK, QPSK, MSK, PM, CW. Simulation indicates that the overall success rate of BPSK, PM, CW is 100% can be obtained at the signal to noise ratio of 5dB. h≥1Finally based on the present work, improvement and further research are required.