Abstract: This paper introduces the characteristics and basic principles of satellite positioning, timing, and synchronization; it elaborates on the hardware and software design concepts of modern satellite signal receiving systems and how to embed navigation satellites into system design to achieve precise object positioning, clock timing, and synchronization data acquisition and control. Keywords: LNA, RF, baseband processing, chipset, integrated module, satellite positioning, timing, and synchronization. Utilizing navigation satellites for object positioning, clock timing, and synchronization data acquisition and control can achieve a level of accuracy unattainable by traditional measurement and control methods. This satellite positioning, timing, and synchronization technology is increasingly widely used in aviation, maritime, land transportation, scientific research, polar exploration, geographical surveying, weather forecasting, equipment inspection, and system monitoring. In recent years, many manufacturers, such as Atmel, ST, Motorola, Maxim, NEC, Fijitsu, and Conexant, have successively launched many related satellite positioning, timing, and synchronization chipsets and modules, providing many effective and convenient ways to design stable, reliable, simple, and portable instruments. This paper comprehensively describes how existing satellite signal receiving chipsets or modules can be used to construct various compact, low-cost, easy-to-use, and high-performance satellite signal receiving channels, and how they can be embedded into different practical application systems to achieve precise object positioning, clock synchronization, or synchronous data acquisition and control. 1. Overview of Satellite Positioning, Timing, and Synchronization The key component in satellite positioning, timing, and synchronization technology is the artificial Earth navigation satellite system. Currently, the main navigation satellite systems include the US Global Positioning System (GPS), Russia's GLONASS (Global Navigation System), China's BeiDou Navigation Satellite System, and the European Union's Galileo Global Navigation Satellite System. The characteristics and applications of these navigation satellite systems are listed in Table 1. A satellite navigation system typically consists of three parts: navigation satellites, a ground monitoring, correction, and maintenance system, and a user receiver or transceiver. For the BeiDou local area satellite navigation system, the ground monitoring center assists the user in completing positioning and timing synchronization. This paper focuses on the embedded hardware and software application design of the user receiver or transceiver section. In civilian applications, GPS, GLONASS, and BeiDou offer meter-level positioning accuracy, millisecond-level satellite timing accuracy, and data synchronization capabilities below 1 μs. The future Galileo navigation satellite system will have civilian positioning and timing synchronization accuracy approximately 10 times that of GPS. Among these navigation satellite systems, GPS is the best capable of providing all-around, all-weather, and long-term satellite positioning and timing synchronization. Currently, the United States and Russia are jointly maintaining GLONASS, forming a GPS + GLONASS system. With the number of satellites multiplying, the accuracy, range, efficiency, and reliability of satellite positioning and timing synchronization will be further improved. 2. Basic Principles of Satellite Positioning and Timing Synchronization Satellite navigation is based on the Doppler frequency shift law of the Doppler effect: fΔ = λ/ν, where fΔ is the frequency change of the electromagnetic wave signal between moving objects, λ is the wavelength of the electromagnetic wave signal, and ν is the relative velocity. This formula shows a one-to-one correspondence between the Doppler frequency shift curve of the received satellite signal and the satellite orbit. In other words, as long as the Doppler frequency shift curve of the satellite is obtained, the satellite orbit can be determined. Conversely, given the satellite's orbit, the receiver's ground position can be determined based on the received Doppler frequency shift curve. The basic principle of global satellite navigation is as follows: satellites transmit navigation messages, including ranging accuracy factors, Kepler parameters, orbital perturbation parameters, satellite clock bias parameters νti, and atmospheric propagation delay correction parameters. Ground receivers distinguish between navigation satellites based on the characteristics of Code Division Multiple Access (CDMA) or Frequency Division Multiple Access (FDMA), receive and identify the corresponding navigation messages, measure the propagation time Δti of the transmitted signals, and gradually calculate the satellite's position (xi, yi, zi) using a series of parameters in the navigation message. Let the location of the receiver at the point to be measured be (x, y, z), and the receiver clock difference be νt0. The receiver can determine its position and clock difference as long as it receives signals from at least four satellites. Under a global navigation system, the user receiver continuously verifies its clock difference based on the satellite navigation message, achieving high clock accuracy—this is precise satellite time synchronization. Based on the regular timing characteristics of the navigation message, a high-precision synchronization pulse per second (PPS) signal can be obtained through a counter, used for synchronous operation of multi-channel data acquisition and control in the same/different locations. The basic principle of BeiDou local satellite navigation is: using two satellites with known positions as centers, each with a radius equal to the measured distance from its own satellite to the user's receiver, two spheres are formed. The ground control center provides a non-uniform sphere with the Earth's center as the center and the height from the center to the Earth's surface as the radius, provided by an electronic elevation map. The intersection of these three spheres is the user's position. The specific positioning process is as follows: First, the ground center sends a signal, which is reflected by two satellites and transmitted to the user receiver. The receiver then reflects the signal back to the ground center via the two satellites. The ground center calculates the time required for each of the two paths, t1 and t2. Let the satellite positions be (xi, yi, zi), and the distance from the ground center to the satellites be Ri. (xi, yi, zi) and Ri can be determined by the ground center. The position (x, y, z) of the target point can be calculated using the following set of equations: This series of complex calculations is performed at the user receiver side for global navigation systems; for the BeiDou local navigation system, it is performed at the ground center. After determining the user's position, the ground center transmits the positioning and clock information to the user via satellite. 3. Design of the Global Navigation Satellite Signal Receiver 3.1 Basic Components of the Satellite Signal Receiver The global navigation satellite signal receiver mainly consists of the following components: a satellite receiving antenna, a low-noise amplifier (LNA), an end-front radio frequency down-converter (EndFront RF), a signal channel correlator, a digital signal processing controller (DSP), a real-time clock (RTC), a memory, and input/output (I/O) interfaces. The entire system is shown in Figure 1. As can be seen from Figure 1, the core of the satellite signal receiver is the DSP. From determining the navigation message and satellite position, to determining the clock difference between the receiver's location and the receiver's clock, and the tuning and control of the satellite channel data, all are completed by the DSP. In practical applications, a 32-bit general-purpose digital signal processor or an ARM7 core microcontroller is often chosen to perform this series of complex calculations and controls. The receiver outputs accurate positioning/timing data results and PPS (Pulse Per Second) signals, and can also receive external communication configurations. 3.2 Selecting an Appropriate Satellite Signal Transceiver Antenna The satellite signal receiving antenna is a key component of the satellite receiver. When selecting a satellite signal receiving antenna, it is essential to consider both appropriate signal gain and its shape and size. For satellite signal receiving antennas used in fixed locations, high-gain, large-volume canopy antennas can be selected; for satellite receiving antennas in portable mobile devices, miniature planar antennas and quad-arm spiral antennas can be used. A common miniature planar antenna is the ceramic microwave antenna. Ceramic microwave antennas are economical and practical, and can be used as passive antennas directly connected to the front-end RF down-converter at close range, or combined with an LNA to form an active long-feed vehicle-mounted antenna. Quad-arm spiral antennas have better performance than planar antennas and have no azimuth requirements; however, they are expensive, have a long boom, and are not widely used. The received satellite signal is a right-hand circularly polarized wave, while the transmitted signal to the satellite must be a left-hand circularly polarized wave. Although user receivers using BeiDou local navigation satellites can obtain accurate positioning and timing results from the ground center without complex calculations, they need to both receive and transmit satellite signals. Therefore, the ideal antenna choice is a miniature, pen-shaped, passive dual-band helical satellite transceiver antenna. 3.3 Using Integrated Components to Construct the Satellite Signal Receiver By selecting a suitable CPU and its peripheral devices, and following the principle shown in Figure 1, the hardware circuit of the satellite signal receiver can be easily designed; however, due to the large amount of complex and tedious calculations involved, the CPU software design task is very heavy. Integrated components are often used to build satellite signal receivers. Optional LNA components include Atmel's ATR0610 and Maxim's MAX2641/2654/2655. Optional front-end RF downconverters include Atmel's ATR0600, Maxim's MAX2742/4/5, ST's STB5600, μNav's μN1005/8021C, NEC's μPB1029R, and Fujitsu's MB15H156. Many well-known semiconductor manufacturers integrate channel correlators, DSP operational controllers, and data memory into a single chip. This chip contains channel correlation algorithms, satellite position determination algorithms, and target point positioning and timing algorithms. It outputs positioning and timing information and PPS (pixel per second) once per second via an RS232 serial port and can receive user RS232 communication configuration information. This type of chip is called a baseband processor. Baseband processors contain 8 to 16 satellite channels, are stable and reliable, and are inexpensive. Using this type of chip eliminates the need for users to select high-speed DSP digital signal processors or ARM7 microcontrollers to build circuits and design satellite signal processing software. Common satellite signal baseband processors include Atmel's ATR0620, Sony's CXD2932, ST's ST20GP6, μNav's μN8031B, NEC's μPD77538, and Fujitsu's MB87Q2040. [align=center] Figure 1: Block diagram of a global navigation satellite signal receiver. Figure 2: Block diagram of a satellite signal receiver constructed with integrated components.[/align] Figure 2 is a block diagram of a GPS satellite signal receiver composed of ATR0610, ATR0600, and ATR0620. When constructing a satellite signal receiver using an LNA, front-end RF downconverter, and baseband processor, it is advisable to use components from the same manufacturer whenever possible; if this is not possible, mature and compatible components from different manufacturers should be selected. Table 2 lists several commonly used, stable, and reliable component combinations. [align=center]Table 2 Optimal Combinations for Integrated Satellite Signal Receiver Components[/align] Some well-known semiconductor manufacturers have further integrated these components. For example, STMicroelectronics integrates the RF downconverter and baseband processor into the multi-functional single-chip STB2056, and Motorola integrates the LNA, RF downconverter, and baseband processor into the modular multi-functional single-chip MG4000/MG4100/MG4200. Figure 3 is a block diagram of a satellite signal receiver constructed using the MG4200. The gradual increase in the functional integration of satellite signal receiver chips provides an effective shortcut for simplifying the design. 3.4 Building Satellite Signal Receivers Using integrated modules to build satellite signal receivers is simple and straightforward. However, if there is insufficient experience in RF circuit design, improper layout and routing during PCB (Print Circuit Board) fabrication can often lead to significant noise interference, causing fluctuations in satellite positioning and timing synchronization data or signals, resulting in excessive deviations. When designing a satellite signal receiver for the first time or lacking experience in RF circuit design, the best approach is to use OEM (Original Equipment Manufacturer) boards or modules. These OEM boards or modules are modular satellite signal receivers designed by well-known semiconductor design companies using integrated components. They offer stable and reliable operation, high accuracy, and standardized interfaces. Examples of OEM boards include μBlox's RCBLJ and SBRLS, Conexant's Jupiter Receiver, and Furuno's GN77. Examples of receiver modules include μBlox's TIMLP and TIMLS, Motorola's FS Oncore, Koden's GSU16, Rackwell's TU30, and TastraX's Trax02. These receiver modules are compact, many are low-power products, and are particularly suitable for embedded system design and development in portable devices. These OEM boards or modules, paired with appropriate passive or active antennas, can form a stable, portable receiver for field or vehicle use. There are also small-sized integrated receiver modules that combine the antenna and receiver module, such as μBlox's SAMLS, which are more convenient for application design. Figure 4 shows a satellite signal receiver constructed with TIMLP, which can be used directly in the field using the randomly carried passive antenna, or used while in motion with an external active vehicle-mounted antenna. 3.5 Special Design for Synchronization Using Only Satellite Signals In practical applications, if the purpose of using navigation satellite signals is only for precise synchronization of multi-channel data acquisition and control in different or the same location, such as fault recording, phase measurement, fault location, and relay protection in power systems, then expensive satellite signal receiver components, OEM boards, or receiver modules can be avoided. Instead, conventional components can be used to build the receiver circuit, and combined with software for signal identification and pulse counting, a precise synchronization PPS pulse signal can be directly obtained. Figure 5 is a typical example of this concept. In Figure 5, the shaping circuit obtains the strongest satellite signal; the shaping and clipping part captures the propagation frame header of the navigation message and starts the counter in the microcontroller to count the other shaping pulse; the microcontroller calculates and generates a precise PPS second pulse signal based on the speed characteristics of the navigation message propagation. [align=center] Figure 3 Block diagram of satellite signal receiver composed of MG4200 Figure 4 Satellite signal receiver composed of "antenna + receiver module" Figure 5 Simplified schematic diagram of satellite signal second pulse generation[/align] In Figure 5, the spread spectrum noise reduction uses NE570/571, the bandpass filter or signal amplification uses LM1450, the signal shaping or clipping uses LM311, and the microcontroller uses MCS51. 4 Application Design 4.1 Application of synchronous data acquisition and control of satellite signals The application of satellite navigation signals for precise acquisition and control of multi-channel industrial data in different or the same location mainly uses the PPS second pulse signal obtained from the satellite signal receiver or uses the PPM (Pulse Per Minute), 100PPS, PPH (Pulse Per Hour) pulse signals obtained from the PPS signal to synchronously start the multi-channel data acquisition analog-to-digital converter (ADC), digital control digital-to-analog converter, and synchronously open or close the switches of each channel; it is also used for measurement and judgment, and to create precise time stamps, such as fault location and power angle measurement in power systems. In addition to using a synchronization pulse to initiate the measurement, accurate measurement time values ​​are also required. This necessitates using a high-resolution timer to subdivide the time intervals between PPS points for CPU capture. A high-frequency cryo-crystal oscillator is also needed to obtain an accurate clk (clock) clock. This type of model is shown in Figure 6. [align=center] Figure 6: Block diagram of synchronous data acquisition and control model using satellite signals[/align] In Figure 6, the CPU can be a programmable logic device (PLD), a digital signal processor (DSP), or a microcontroller (MCU). The speed, type, and specifications of the CPU, ADC, DAC, etc., should be determined based on the actual system design. 4.2 Using Satellite Signals for Object Positioning and Clock Timing The general process for using satellite signals for object positioning and clock timing is as follows: Design a satellite signal receiver to obtain the three-dimensional position information (longitude, latitude, altitude) and Universal Coordinate Time (UTC) of the target point, store and display it, and broadcast the clock through a timing channel (RS232, RS485, CAN, etc.) or transmit the actual position of the object at that moment through wireless communication technology GSM/CDMA. The obtained positioning/clock accuracy resolution values ​​are as follows: latitude/longitude in centimeters can reach 5 decimal places, altitude in meters can reach 2 decimal places, and clock in seconds can reach 2 decimal places. Receivers designed using satellite signal receiving chipsets, OEM boards, or receiver modules typically use the NMEA183 standard from the National Marine Electronics Association (NMEA) for serial data output. The receiver transmits one PPS (Positioning Per Second) pulse and a series of positioning and clock information per second. The PPS pulse and the transmitted data have a strict time relationship; accurately reading the clock data by precisely timing the PPS pulse transitions yields a more precise clock value. During use, the obtained UTC time needs to be converted to Beijing time. The model for object positioning and clock synchronization is shown in Figure 7. [align=center] Figure 7 Block diagram of object positioning and clock synchronization model using satellite signals[/align] 4.3 Precautions (1) When the satellite signal reception synchronization design system is applied to mountainous areas, polar regions, or other areas that are not open or are easily affected by solar storms, hardware and software measures to prevent satellite signal reception synchronization should be added to the design. The specific approach is often to design a local precision PPS generation circuit and a real-time clock (RTC) circuit. When the invalid positioning/clock information is identified from the NMEA format information obtained from the receiver, the local PPS signal and RTC time are immediately activated, and the current position of the object is inferred based on the position characteristics of the object under normal conditions. When the satellite signal reception returns to normal, the satellite positioning clock is used for synchronization, and the local PPS generation counter is cleared and the RTC clock is corrected. Figure 8 shows this typical anti-synchronization scheme. [align=center] Figure 8 Synchronization/Clock Processing When Satellite Signal Monitoring Loses Sync[/align] (2) System Power Management Satellite signal positioning and timing synchronization system, especially embedded portable devices, involves different power supplies, such as 5V LCD display modules, 3.3V main systems, and 1.8V CPU cores, which need to obtain various power supply voltages from batteries of 1.2 to 4.3V. When designing power management, do not directly convert the battery voltage to obtain 1.8V, 3.3V, and 5V at the same time. Instead, first boost the voltage to obtain the maximum power supply voltage, and then gradually reduce the voltage to obtain the required power supply voltages at each level. Otherwise, the system will not work properly. The operation process is shown in Figure 9. [align=center] Figure 9 System Power Planning of Portable Satellite Signal Positioning Instrument[/align] 3) The design of the satellite signal receiving part needs to be considered in PCB board manufacturing. In order to reduce interference and obtain the best reception effect, the receiving antenna should be as close as possible to the receiving pin of the integrated chip; the microstrip line from the antenna interface to the receiving pin of the chip should be as short as possible, and the width should be twice the thickness of the PCB board. It should be cut at an angle and avoid sharp angles and right angles. Independent power and ground planes are required. Power and ground planes should be located close to the top/bottom layers, with large ground plane coverage. At the PCB edges, the power plane area should be smaller than the ground plane area. A dense ring of vias should be added around the ground plane edge, and the top layer should have numerous vias and a large ground plane area. Use a metal shield to shield the entire receiving section whenever possible. Conclusion Satellite navigation technology is becoming increasingly sophisticated, penetrating all aspects of daily production and life. Designing a stable, reliable, portable, low-power, and low-cost modern satellite signal receiving system to achieve accurate object positioning, clock synchronization, and synchronous data acquisition and control has broad prospects. References 1 Gao Chengfa. GPS Measurement. Beijing: People's Transportation Press, 2001 2 Motorola Co. GPS Products PREVIEW Instant GPS MG4200. Rev1.0. 200412 3 uBlox Co. GPS Positioning Components Catalog. Rev3. 200410