# Design and Simulation of Low-Orbit Satellite Broadcast Signal Receiving and Processing Terminal
## 1 Introduction
These advantages of digital beamforming are not available in modular beamforming and have a far-reaching impact on improving the performance of the receiver [10]. Although digital beamforming has been widely valued in the field of military radar due to its unique functions and advantages, its application is restricted by the accuracy and gain of beamforming. Therefore, as digital beamforming technology develops, how to improve its accuracy and gain has also received widespread attention at home and abroad [9; 10; 11; 12]. Narrowband interference refers to interference with a signal bandwidth much smaller than the RF signal bandwidth, including single-tone interference, multi-tone interference, narrowband random processes, and low-rate digital signals. Narrowband interference is usually defined as an interference signal with an interference frequency band no greater than one-tenth of the signal frequency band. Therefore, for any satellite signal, narrowband interference signals are widespread. Each navigation satellite transmits carrier radio signals at two L frequencies (i.e., L1 and L2) [6]. In communication confrontation scenarios, since narrowband interference (NBI) is easy to generate, the power spectrum density can be very high, and a few narrowband interferences can cover a certain width. Compared with broadband suppression interference, it is more conducive to interfering with the opponent's system and ensuring the normal operation of one's own system. Therefore, narrowband interference is very common, and the effective means of implementing anti-narrowband interference is one of the issues worthy of key research in the current field of satellite signal reception and processing [2]. The purpose of spread spectrum signal capture is to obtain a rough estimate of the carrier frequency and code phase of all visible satellites, which is the premise for the receiver tracking loop to successfully track GPS satellite signals. At present, many scholars at home and abroad have designed and used different capture methods for various scenarios, but any method has its own trade-offs between computational complexity, hardware cost, and limitations in the scope of application. Even the most commonly used PMF-FFTmethod in the current communication confrontation field can effectively combine matched filtering with frequency domain parallel capture methods, compensate for their respective disadvantages while taking into consideration the advantages of both, and greatly reduce the number of FFT operation points and complexity when using filters. It can stably capture signals in weak signal and high dynamic scenarios, but it still needs to align the symbol rate with the spread spectrum code [5]. In order to solve this problem, it is necessary to generate a spread spectrum code period interrupt and perform incoherent operations, which will cause a significant increase in the amount of calculation, making it difficult to meet the high real-time and high sensitivity requirements in the current communication confrontation scenario. How to solve the problem of aligning the symbol rate and spread spectrum code during capture under the requirements of high real-time and high sensitivity capture is of great research significance [8]. The issues studied in this paper are: (1) Aiming at the problem of determining the amplitude and phase weighting coefficients of the signals of each array element required in different directions, a digital beamforming technology is proposed while taking into account the low sidelobes and constant gain of the array beam; (2) Addressing the issue that time domain anti-interference method requires a large amount of prior information and that two transformations of frequency domain anti-interference method require a large amount of computing resources, an interference suppression technology that combines time and frequency domains is proposed [2; 5].