## 1 Introduction  
Satellite communication has many advantages. It has a large communication coverage area, long communication distance, and the cost of building a station is almost independent of the communication distance. Besides this, it also has flexible networking, large communication capacity, good communication quality, strong reliability, etc. This paper focuses on the satellite communication system of UAVs and submarines, which uses a geosynchronous high orbit (GEO) satellite. It is well known that three satellites can achieve global coverage, which means only one satellite can achieve long-distance communication within 2000 km. The scenario in this paper adopts transparent forwarding and uses a custom private satellite communication protocol. We take the satellite-drone communication model as an example, as shown in Figure 1 below. The space and weight of platforms such as drones are severely limited, so a single input and a single output are usually used. Besides this, the caliber of the airborne antenna is usually less than 0.3 m. The signal frequency is in the ka/ku band. The SNR received by the airborne terminal is about 5-8 dB. Due to the influence of rain fade in the channel, the attenuation of the SNR should be considered. Therefore, in practical scenarios, reliable communication in the SNR of 3 dB should be satisfied at least. For submarine and unmanned aerial vehicle satellite communication systems, as well as submarines and unmanned aerial vehicles used as stealth combat platforms, the communication system is required to have strong concealment, anti-interference and reliability. This is especially true for satellite communication based on transparent forwarding, because the channel is open, the signal in the communication process is vulnerable to eavesdropping and interception, and there are serious security threats such as the positioning of the combat platform and the acquisition of business information by the other party. The longer the exposure time, the higher the security risk. Burst spread spectrum combines the advantages of the low spectral density of spread spectrum signals and the short duration of burst communication, which is an effective anti-interception communication technique. Therefore, most UAV and submarine satellite communication systems adopt the burst spread spectrum communication mode at present. Due to the randomness and temporality of burst spread spectrum communication, synchronization overhead is usually added to the physical layer to realize synchronization. The frame structure diagram of the physical layer of a typical burst spread spectrum signal is shown in Figure 2. A burst physical frame is usually composed of synchronous overhead and effective data, in which the effective data refer to modulation symbols after channel coding and symbol mapping. Synchronous overhead usually adopts a specific modulation symbol for a spread spectrum, which is generally composed of three parts, as follows: synchronization field 1 is used for spread spectrum code synchronization; synchronization field 2 is used for carrier frequency offset estimation and carrier initial phase estimation; synchronization field 3 is used to locate the start time of valid data. \(L\) is the total length of overhead 1, 2 and 3. \(L1\) must be at least 64 bytes, and \(L=L1+L2+L3\) must be at least 128 bytes [1;2]. The burst spread spectrum based on synchronous overhead usually adopts periodic code, and the burst spread spectrum signal is a fixed-length frame signal structure. The baseband signal processing process at the sending end (before he shaping filter) is shown  
Figure 1: Satellite communication scenario. Figure 2: Physical layer frame structure of a typical burst spread spectrum signal. in Figure 3. Here, \(N\) is the spread spectrum multiple, n is the length of effective data, and Rc is the code rate. The method based on synchronization overhead can make the process of signal synchronization simpler, but it will reduce the efficiency of information transmission.