1. Introduction Wireless sensor networks (WSNs) are a novel information acquisition and processing technology that is increasingly widely used in real life. With the development of communication technology, embedded technology, and sensor technology, sensors are gradually evolving towards intelligence, miniaturization, and wireless networking. Currently, domestic and international research mainly focuses on low-power hardware platform design, topology control and network protocols, and positioning technology for WSN nodes. This design uses a sensor that detects ultrasonic intensity as an example to implement a wireless sensor network. Based on the intensity of the ultrasonic waves detected by the sensor, it determines whether parking space indicator lights are turned on or off, thereby determining whether a vehicle has entered the detection area. This sensor network integrates embedded technology, sensor technology, and short-range wireless communication technology, and has wide applications. The system requires no modification to the field structure, does not require any existing fixed network support, can be quickly deployed, is easy to adjust, and has excellent maintainability and scalability. 2. IEEE 802.15.4 Standard The IEEE 802.15.4 standard is suitable for wireless personal area networks (WPANs) with low data rate, low power consumption, low complexity, and short-range data transmission. During wireless transmission within the network, a carrier sense multiple access mechanism with collision avoidance (CSMA/CA) is employed, supporting superframe structures and guaranteed time slots (GTS). The network topology can be a star network or a point-to-point peer-to-peer network. This standard defines three data transmission frequencies: 868MHz, 915MHz, and 2.4GHz. The first two frequencies use BPSK modulation, while the latter uses O-OPSK modulation. Each frequency supports wireless data transmission rates of 20 kbit/s, 40 kbit/s, and 250 kbit/s, respectively, with transmission distances ranging from 0m to 70m. This paper uses a 2.4GHz wireless transmitter module. 3. Implementation of Wireless Sensor Networks 3.1 Network Platform Construction The wireless sensor network platform consists of three parts: an ultrasonic sensor module, a microprocessor module, and a wireless transmitter module, as shown in Figure 1. The microprocessor module and the wireless transmitter module are integrated on a single board, while the ultrasonic sensor module is connected to the microprocessor via an interface. This allows for application in various scenarios by replacing different sensor modules. 3.1.1 Ultrasonic Sensor Module Due to the strong directivity of ultrasound, it can travel a long distance in a medium, making it frequently used for distance measurement, such as in rangefinders and level gauges. Ultrasonic detection is often rapid, convenient, computationally simple, and easy to implement in real-time control, while also meeting industrial accuracy requirements. To enable vehicles to automatically avoid obstacles, a ranging system is necessary to obtain timely distance information (distance and direction) to obstacles. The three-direction (front, left, right) ultrasonic ranging system introduced in this paper provides motion distance information for back-end personnel to understand the environment in front, to the left, and to the right. [align=center] Figure 1 Wireless Sensor Network Node Structure[/align] [align=center] Figure 2 Wireless Sensor Network Node Communication Topology[/align] The SL-SRF-25 ultrasonic sensor, when connected to a power source, can be used independently for ultrasonic ranging. The obstacle distance is displayed by a 3-digit LED display. The 3-digit LED display uses a modular assembly method, facilitating debugging, inspection, and use in different situations. The measurement range is 10cm-250cm. When the distance is less than 100cm, the error is 1-2cm; when the distance is greater than 100cm, the error is 4-5cm. The SL-SRF-25 ultrasonic sensor can also be specified to output segmented distance detection signals from the microcontroller's I/O port. 3.1.2 Microprocessor Module The processor module uses the Mica2 model node from the University of California, Berkeley. The node board provides the following functions: a 433MHz center frequency wireless communication interface, which can be customized through programming to provide various communication powers from -20dB to 10dB; multiple transmission rates from 0.3kbps to 38.4kbps in Manchester encoding; and multiple communication frequencies can be set around 433MHz with a frequency interval of 76kHz. Its high speed and large-capacity RAM facilitate data packet processing. 3.1.3 Wireless Transmission Module The wireless transmission module uses the SRWF-501 low-power wireless module RF transceiver from Sunray Electronics Technology Co., Ltd. This chip requires very few external components, boasts stable performance, and extremely low power consumption. The transceiver provides three serial ports with three interface modes: COM1 is a TTL level UART interface, COM2 is a standard RS-232 interface, and a standard RS-485 interface. It features crystal frequency stabilization, a built-in digital phase-locked loop, and the frequency can be flexibly set within the range of 300-1000MHz according to user needs. Automatic noise filtering simplifies user interface programming, making it as convenient as wired connections. Automatic "receive" and "transmit" switching eliminates the need for dedicated transmit/receive control lines; it is in normal "receive" mode when not transmitting data and automatically switches to "transmit" mode when transmitting data, returning to "receive" mode after transmission is complete. It has a low transmit power: a maximum transmit power of 10mW. The SRWF-501's selectivity and sensitivity exceed the requirements of the IEEE 802.15.4 standard, ensuring the effectiveness and reliability of short-range communication. 3.2 The system software platform uses the TinyOS system development environment developed by the University of California, Berkeley. TinyDB is the query processing system of TinyOS, capable of extracting data and information from sensor nodes in a wireless network. TinyOS provides TinyDB with a visual JAVA API window for real-time queries. 3.3 Network Type In this paper, the wireless sensor network adopts a star topology (as shown in Figure 2), with a network coordinator as the central node, capable of communicating with any ordinary node. Ordinary nodes contain ultrasonic sensors that measure and sample the ultrasonic signal intensity parameters in the surrounding environment, sending the collected data to the central node. They can also analyze and process the data and commands sent by the central node to complete corresponding operations. Data transmission between two ordinary nodes must go through the central node, which then transmits the data to the corresponding node. 3.4 Networking Process A wireless sensor network is a self-organizing network. If a fully functional node is activated, it can establish a network and set itself as the network coordinator, allowing other ordinary nodes to apply to join. This creates a wireless sensor network with a star topology. The wireless sensor network in this paper supports a superframe structure. After energy scanning and active channel scanning, the network coordinator periodically sends beacon frames according to the set parameters. Ordinary nodes first undergo energy scanning and passive channel scanning to obtain parameters containing network characteristics in the beacon frame, such as beacon sequence number, superframe sequence number, and network label. They synchronize with the network coordinator through a synchronization request and then associate with the network coordinator through a matching request. During the association process with the network coordinator, the network coordinator assigns a 16-bit short address to each ordinary node requesting association. In this way, communication can be carried out using the short address in subsequent data transmission, improving communication efficiency, reducing energy consumption during transmission, and thus extending the lifespan of the network. 3.5 Data transmission mechanism 3.5.1 Data format The IEEE 802.15.4 standard defines four types of frames: beacon frame, data frame, command frame, and acknowledgment frame. (1) Beacon frame: The network coordinator broadcasts a beacon to its neighboring nodes in the first time slot supporting the superframe structure. When a nearby node receives the beacon frame, it can apply to join the network. Since the wireless sensor network system in this paper adopts a relatively simple star topology, the structure of the beacon frame is different from that of the IEEE 802.15.4 standard: the address field of the beacon frame only contains the network label and short address of the source node, and does not contain the destination node information (because it is sent by broadcast). (2) Data frame: used to transmit data containing ultrasonic intensity information. The address field contains the network label and short address of the source node and the destination node. Since there are two transmission directions for data frames: from ordinary nodes to the central node and from the central node to ordinary nodes. (3) Command frame: used to build wireless sensor networks, transmit synchronization data, etc. The format of the command frame is not much different from other types of frames. (4) Acknowledgment frame: used to confirm that the target node has successfully received the data frame or command frame. When the target node successfully receives the data frame or command frame, it sends an acknowledgment frame to the sender. The sender receiving this acknowledgment frame indicates that the transmission was successful. If no acknowledgment frame is received within the specified time, the data frame or command frame is retransmitted. The frame type is defined as acknowledgment frame in the frame control field. The sequence number of the acknowledgment frame must be the same as the acknowledgment frame, and the payload length must be zero. The acknowledgment frame is sent immediately after the acknowledgment frame, without needing to use the CSMA-CA mechanism to compete for the channel. 3.5.2 Transmission Process In the entire wireless sensor network, ordinary nodes periodically read the ultrasonic data from their sensors and send the ultrasonic data to the central node. The central node processes the received data and then transmits it to the corresponding node to control the parking space positioning flags on it. First, the network coordinator checks the received data frame. In Figure 2, the central node determines whether the data is sensor data from a designated node. If the received data is data from a designated node, it compares the data with an ultrasonic intensity threshold to set a control variable (used to control the opening and closing state of the parking space). Otherwise, no transmission operation is performed. Then, it checks whether any idle nodes have joined the network. If an idle node is found in the network, the central node sends the control variable as the payload of the data frame to it. Otherwise, no data frame with the control variable is sent. Conclusion In our designed wireless sensor network parking control system, ordinary nodes send the ultrasonic data they collect to the network coordinator. The network coordinator sends data frames containing control variables to nodes with parking space occupancy indicators, and simultaneously transmits the ultrasonic data to a computer via serial port. The background software on the computer can monitor changes in the ultrasonic signal. The occupancy status of parking spaces can be determined from the ultrasonic sensors. This paper discusses the design and implementation of the wireless sensor network from several aspects, including the formulation of wireless transmission protocols and transmission process control. In practical applications, by simply replacing the specific sensors, it can be applied to various sensor networks. Due to the flexible networking and modular design of the wireless sensor system, it has excellent portability and scalability. With the improvement of people's living standards, this system has broad application prospects in the future traffic monitoring field. It also has broad prospects in future traffic monitoring, smart home appliances, and intelligent adjustment of the home environment.