# Research on New Drilling Downlink Communication Based on Anisotropic Magnetoresistive Technology
## 1 Introduction  
With the continuous development of the economy, oil and gas resources have become one of the most important energy sources in the world [1]. However, there are many difficulties in the exploitation of oil and gas resources, including the low accuracy of an automatic drilling system in downlink communication and the low feedback rate of bottom hole parameter information. One of the most important links in the process of oil and gas resource exploitation is to transmit the control command of the downhole automatic drilling system with low BER. If the control fails or any wrong control occurs, it will not only cause large economic losses, but also cause serious safety accidents. Due to the complex downhole environment, large noise interference, and low BER downlink communication of control commands requires high information transmission technology, which makes the control of the downhole automatic drilling system very difficult [2]. Therefore, it is of great significance to develop a high-speed and low BER downlink communication technology. The existing downhole information transmission methods mainly include cable, optical fiber, smart drill string, electromagnetic wave, acoustic wave, drilling fluid pressure wave, etc. [3]. Wired information transmission technologies such as cables, optical fibers,smart drill are generally vulnerable to extrusion and wear, resulting in high cost and great installation difficulty [4; 5; 6]. Downhole information transmission by wireless communication technology can effectively avoid problems such as wear and compression. The transmission speed of electromagnetic waves is fast and can be applied to air drilling, foam drilling, laser drilling, and other fields. However, the transmission distance of electromagnetic waves is limited, which is unsuitable for ultra-deep well construction [7]. Sound wave transmission uses the propagation of the sound wave in the medium for communication. The transmission mode is simple, and the cost is low. However, in the acoustic transmission channel, the noise is strong, the interference is large, and the attenuation is serious, which lowers the transmission accuracy [8; 9]. The drilling fluid pressure pulse transmission method uses the drilling fluid as a channel for pressure wave information transmission, which is the most widely used technology at present [10; 11]. An early measure while drilling (MWD) mud telemetry system generates a pressure pulse in the mud channel using a plunger valve and transmits downhole data with the baseband transmission pattern. The data rate is low, at approximately 3 bits per second. Now, the baseband transmission pattern has been replaced by a frequency band transmission pattern with a continuous pressure wave mud telemetry system for a relatively higher data rate up to 20 bits per second and better tolerance of normal noise sources [12]. However, the efficiency of the MWD mud telemetry system still needs to be further improved. With the rapid development of information transmission technology, various new technologies have been developed. [PERSON] proposed a method of information transmission based on radio frequency identification technology. In this way, the Radio Frequency Identification (RFID) tag carrying the command to be transmitted is put into the drill pipe at the wellhead and pumped down the tag. Then, the command is identified by the reader to realize the purpose of downlink communication. However, the RFID tag identification code used in this method is single-use, which is not easy to be modified or reused [13]. [PERSON] first applied vector orthogonal frequency division multiplexing (V-OFDM) modulation technology to downlink communication technology, and studied different synchronization timing errors and detection schemes. Then, they gave a performance analysis of different schemes [14]. The application of electric current field information transmission technology has attracted much attention due to its low production cost and simple operation.