# Design of Tracking, Telemetry, Command (TT&C) and Data Transmission Integrated Signal in TDD Mode
## 1 Introduction
The BOC signal can free the bandwidth of the center frequency according to the characteristics, and it can be used as the TT&C signal when the data transmission signal is transmitted at the same frequency. To inherit the advantages of the TDD mode, we must guarantee TT&C performance. In [20], the nodes are measured by the ground station, and the results are sent to each node. However, this method increases the ground station's burden and can synchronize with the ground station only when there is a link between the node and station. The measurement and control system in [21] records telemetry data and plays back the data to realize non-real-time TT&C functions after the communication link is interrupted. Since the tracking loop is interrupted and retracked continuously, the measurement accuracy cannot be high enough. In the paper, we propose a method that can achieve high measurement accuracy by exploring the tracking loop. Although the tracking error is increased as the extrapolation time increases, the method can ensure the TDD's stable tracking. For data transmission services, phase-shift keying (PSK) modulation system has a characteristic such as constant envelope, easy implementation and the robustness against channel effects, but its spectrum utilization is not suitable for high data transmission services [22]. Quadrature Amplitude Modulation (QAM) modulation system has high spectrum utilization, but the strong effect of nonlinearity and complex implementation limits its application to satellite [23]. Combining the advantages of both, APSK modulation mode is adopted in the paper. The APSK has advantages as follows. (1) High spectrum utilization;  
(2) Small amplitude fluctuation which can effectively resist nonlinear distortion;The constellation is circular, which requires less power;
4. It is easy to realize variable rate modulation and meet the hierarchical transmission requirements of satellite communication. At present, 16 APSK and 32 APSK have been selected into DVB-S2 standard, and are widely used in European remote sensing satellite and other military and civil satellite communication systems [24]. Considering those advantages, we adopt 16 APSK as the modulation mode of the data transmission signal. The major contributions of this article are as follows:  
1. Considering the lack of spectrum resources, this paper proposes the BOCcos and APSK integrated signal to achieve TT&C and data transmission services. 2. Considering the shortage of frequency resources in the case of large numbers of nodes, we propose the high precision measurement method for the TDD mode. The outline of the remainder of this paper is as follows. First, the BOCcos and APSK integrated signals are designed in Section 2. The design of the acquisition and tracking algorithm in the TDD mode is described in Section 3. The application scenarios and performance analysis of the measurement system are given in Section 4. Section 5 provides the discussion on the measurement and data transmission performance of integrated signals. Besides, it also gives the method to improve performance. In Section 6, we provide a conclusion and propose future work.