# Blind Recognition of Forward Error Correction Codes Based on a Depth Distribution Algorithm
## 1 Introduction  
FEC codes are a vital encoding and encryption method in modern communication systems, whose characteristics of mathematics ensure that the receivers correct errors which have occurred during the process of transmission, which improve the quality of communication systems. The FEC coding types are widely used in non-cooperative communication fields such as adaptive modulation coding (AMC), cognitive radio and remote sensing communication [1]. In the field of information countermeasures, the type of error correction codes of the detected link must be recognized correctly, so as to obtain an effective information payload and finally to decipher the message of the sender. However, based on information asymmetry in the context of non-cooperative communication, there is no prior knowledge of the FEC coding types adopted on the detection link. Therefore, it must be identified by the corresponding data analysis methods. This is the core content of the paper--the blind identification of FEC coding types. With the development of communication technology, channel coding blind identification technology is widely used in the field of intelligent communication, multi-point broadcast communication and non-cooperative communication, and has become one of the research hotspots at homeand abroad [2; 3; 4; 5]. Blind recognition of error-correcting code types is also of great significance to improve the accuracy and efficiency of code parameter recognition in asymmetry communication systems. At present, the recognition of FEC coding types can be divided into two types: full blind recognition and half blind recognition. The full blind recognition is the forward error correction coding type recognition analysis under the condition that the access signal information is completely unknown. However, in some special cases, it is possible to obtain a set of forward error correction coding types that the sender may adopt through some prior knowledge. Then, using the intercepted data flow, the forward error correction coding method with the largest matching degree is searched for from the alternative set as the estimation of the coding types used in the detection link, which is the basic feature of semi-blind recognition. At present, there are extensive researches on parameter estimation technologies such as linear block codes [6; 7; 8], convolutional codes [9; 10; 11] and Turbo codes [12]. However, these algorithms are based on a known coding type, solving its generation matrix and generation polynomial to realize parameter identification. Under the condition of non-cooperative communication, the unknown encoding type of the receiver will make it hard to recognize specific parameters. Therefore, it is crucial to study the recognition of types. At present, the recognition of FEC encoding types is mainly accomplished by mathematical methods according to the large amount of data received. In [13], the author proposed a type recognition algorithm based on rank criterion by using rank characteristics of receiving code words. However, the algorithm only analyzed the rank characteristics of each type separately, and did not comprehensively analyze and identify them. In [14], a type recognition algorithm for linear block codes and convolutional codes based on run-length features was proposed. This algorithm could recognize linear block codes and convolutional codes well, but it failed to recognize other encoding types. In [15], a coding system identification strategy for error-correcting codes with unknown coding sequences was proposed, which could provide a basic identification process for type recognition. However, it did not study and analyze the coding type identification under the condition of bit error, and failed to meet the basic requirements of engineering practice. In [16], the author proposed a general linear block code recognition and analysis method, which had a certain engineering practicability and succeeded in improving the recognition efficiency to a certain extent.