Wireless Access Solution Overview

Doing a good job in wireless access solutions is an important part of the preliminary work. So I studied how to implement a more optimized and reasonable Wireless Access solution. I will share it with you here, I hope it will be useful to you.

1 Overview

In short-distance communication, wireless technology is widely favored, among which RF technology is favored because of its low power consumption and no direction. The GHz communication frequency band is a globally open ISM (industrial, scientific, and medical) band. users do not need to apply for a license, which brings great convenience to developers and users, it can effectively avoid interference of low frequency band signals, various types of electric sparks and household appliances. Because this band has these advantages, other applications, such as Bluetooth and WLAN, are also in this band; however, Bluetooth and WLAN are too complex and cost-effective for industrial control, medical sensors, residential buildings and building automation devices. Therefore, a low-cost, low-power, and fast application development Wireless Access solution is urgently needed to achieve wireless connection of devices.

On the other hand, after years of development, TCP/IP has become a communication protocol widely used in the Internet. In an embedded system, the TCP/IP protocol stack is implemented. Remote Data Transmission over the Internet can monitor and control the running status of remote devices. On the embedded TCP/IP platform, the wireless transceiver module with a working frequency of 2 to 4 GHz is used for short-distance point-to-point wireless communication. The wireless technology is used to solve the final 10 m communication problem, A wireless access solution is provided.

2. nRF24E1 and its communication protocol

2.1basic features of the nRF24E1 Module
NRF24E1 is a wireless transceiver module with a 8051 kernel launched by Nordic. its internal structure is shown in 1. The wireless transceiver of this module works in the 125 GHz ISM band and has up to frequency points. It can avoid interference through frequency change and frequency hopping. The integration of nRF24E1 is very high. It is integrated with enhanced 8051 kernel, 2.4GHz wireless transceiver, 9-Channel 10-bit ADC of 100ksps, UART interface, SPI interface, and PWM output, built-in RC oscillator, watchdog, wake-up timer, and special voltage regulator circuit. All the high-frequency components, including inductance and oscillator, are integrated into the chip. Therefore, the performance of the chip is stable and has little impact on the external environment.
NRF24E1 is encapsulated with 36-pin QFN (6mm × 6mm). The maximum transmission rate is 1 Mb/s, the sensitivity is 90dBm, and the maximum transmit power is OdBm. In ideal environments, the indoor transmission distance can reach 30 ~ 40 m, outdoor transmission distance up to 100 ~ 200 m; the operating voltage is 1.9 ~ 3.3 V, working temperature range: 40 ~ + 80 ℃.

2.2nRF24E1 communication protocol
Preamble is the forward guide code, which is automatically added by the hardware; ADDR is the Sending address, which is 32 ~ 40 BITs; PAYLOAD is the valid data; CRC is the CRC checksum, which is automatically added by the built-in CRC error correction hardware circuit and can be set to O, 8, or 16 bits. The total length of ADDR, PAYLOAD, and CRC is up to 256 bits. Therefore, setting a short address and verification can improve the transmission efficiency, but also reduce the reliability.

The software sets the sending and receiving modes, receiving frequency, receiving address, transmitting power, CRC checksum length, and valid data length. The wireless transceiver has two channels: Channel 1 can receive and send; Channel 2 can only receive, and channel 2 receives a total of 8 MHz higher than Channel 1. At the same time, you can set two addresses for each chip. The sending and receiving frequencies and addresses can be changed through software at any time to achieve frequency change and frequency hopping. However, the communication protocol must be used to ensure that consistent frequencies and correct addresses are the prerequisite for data transmission. Only packets with the correct address and checksum can be further processed. If one packet is incorrect, the entire packet is automatically discarded by the hardware. If the address matches the checksum, the hardware will interrupt DRl or DR2, and 8051 will receive the data to the buffer. At the same time, nRF24E1 can only be in the receiving or sending mode. Generally, the receiving mode is used as the standby mode.

3 Wireless Access Solution

The nRF24E1 host is a key part of the wireless system. It is not only an access point, but also responsible for exchanging data with the embedded TCP/IP module and communicating with other wireless modules. To achieve Internet interconnection, use the Ethernet control chip RTL8019AS and embed the TCP/IP protocol stack in the ATmegal28. In addition, ATmegal28 also implements a small and common WebServer, while the remote PC serves as the client.

The data transmission process is that the remote PC sends data over the Internet, and the RTL8019AS receives the data packet, and then the ATmegal28 processes the TCP/lP data packet to obtain the information sent by the PC, the AT-megal28 then transmits the data to the nRF24E1 host through the SPI interface. The nRF24E1 host transmits data to the corresponding nRF24E1 slave based on the internal protocol, and then the nRF24E1 slave machine communicates or controls the respective devices. The process of transferring data from a remote PC to a remote PC is reversed.

1. The development of optical fiber access networks will drive the comprehensive improvement of broadband services
2. Detailed Rules for ensuring technical security of Wireless Access Networks
3. Viewpoint: Wi-Fi and 3G convergence issues in Access Networks
4. Comprehensive introduction to WCDMA in Wireless Access Networks
5. A detailed overview of the development of broadband access networks