# LR-MPIBS: A LoRa-Based Maritime Position-Indicating Beacon System
## 2 Materials and Methods
### Design and Implementation of System Hardware
#### 2.2.4 Power-Management Module of the Position-Indicating Terminal  
The design of the power-management module of the PIT focused on the power-supply and voltage-regulator circuit. The PIT integrates Beidou positioning and LoRa RF circuits. The power management module should have good ripple suppression capability to reduce the impact of power-supply-ripple interference on the stability and reliability of RF communication. The stable working current of PIT is about 50 mA, and the transient peak current of communication will reach 156 mA. A high transient current can cause a decrease in power supply voltage and lead to PIT shutdown. Therefore, we design a highly reliable power supply circuit to improve the source ripple suppression and transient response capability of the power supply.  
The selection of power supply batteries in this paper focuses on their transient response capability, output voltage, and battery capacity. Its transient peak output current should exceed three times the transient operating current of PIT. Its output voltage range is between 3.6 V and 4.2 V, meeting the working voltage requirement of 3.3 V for each module. A lithium battery has a higher energy density and longer lifespan compared to other types of battery, so we prefer lithium batteries. The voltage of a typical small lithium battery is 3.7 V, and the discharge rate (C) is 1. We can calculate based, on Formula (2), that the battery capacity needs to be greater than 486 mA, taking into account the transient response requirements of the battery.  
\[I=M\times C_{n} \tag{2}\]  
The power supply battery used in this paper is a 3.7 V lithium battery with a capacity of 1500 mAh and a discharge rate of 1C. This means that the maximum transient current the power supply can deliver is 1500 mA.  
The power-management circuit is shown in Figure 4. This circuit is used to regulate the power-supply voltage to the 3.3 V required for each functional module. The electrolytic capacitor CT112 in the ripple-filter circuit is used to absorb instantaneous current transients caused by power-supply voltage fluctuations during RF communication. The range of its capacitance value is 10-100 \(\upmu\)F. Ceramic capacitors C114 and C116 are used for the main ripple filter capacitance: C114 is a low-frequency filter with a value range of 1.0-4.7 \(\upmu\)F. C116 is a high-frequency filter with a value range of 10-100 nF. The TLV757P-3.3 regulator chip (U5) from Texas Instruments is used to regulate voltage. It has a maximum transient  
\begin{table}
\begin{tabular}{c c c c c c} \hline RF transmission line width (mil) & 6.5 & 7.5 & 10.5 & 12.5 & 21.71 \\ Simulated value of RF transmission line impedance (\(\Omega\)) & 66.91 & 64.75 & 59.8 & 57.36 & 50 \\ Communication distance (m) & 28 & 113 & 1289 & 3126 & 3631 \\ \hline \end{tabular}
\end{table}
Table 1: Relationship between transmission line impedance value and communication distance.  
load capacity of 1 A. The 1 \(\upmu\)F ceramic capacitor C115 is used to ensure that the output voltage ripple is below 45 mV.