**Xiong Zha \*, Hua Peng, Xin Qin, Guang Li and Sihan Yang**

PLA Strategic Support Force Information Engineering University, Zhengzhou 450001, Henan, China; Peng\_hua@outlook.com (H.P.); qinxin\_0920@163.com (X.Q.); GL\_for\_study@outlook.com (G.L.); courage32@163.com (S.Y.)

**\*** Correspondence: mici0928@163.com

Received: 20 July 2019; Accepted: 16 September 2019; Published: 19 September 2019

**Abstract:** Deep learning (DL) is a powerful technique which has achieved great success in many applications. However, its usage in communication systems has not been well explored. This paper investigates algorithms for multi-signals detection and modulation classification, which are significant in many communication systems. In this work, a DL framework for multi-signals detection and modulation recognition is proposed. Compared to some existing methods, the signal modulation format, center frequency, and start-stop time can be obtained from the proposed scheme. Furthermore, two types of networks are built: (1) Single shot multibox detector (SSD) networks for signal detection and (2) multi-inputs convolutional neural networks (CNNs) for modulation recognition. Additionally, the importance of signal representation to different tasks is investigated. Experimental results demonstrate that the DL framework is capable of detecting and recognizing signals. And compared to the traditional methods and other deep network techniques, the current built DL framework can achieve better performance.

**Keywords:** deep learning; signal detection; modulation classification; the single shot multibox detector networks; the multi-inputs convolutional neural networks
