“With the continuous development of urban road network construction, the number of street lights has increased. Improving the intelligent management and functional diversity of street lights has become a top priority in the construction of urban lighting systems. What wireless control schemes can be used in smart street lights?

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With the continuous development of urban road network construction, the number of street lights has increased. Improving the intelligent management and functional diversity of street lights has become a top priority in the construction of urban lighting systems. What wireless control schemes can be used in smart street lights?

In recent years, national policies have consistently promoted smart cities, and smart street lighting, as one of the most basic public facilities in the construction of smart cities, has naturally attracted attention. According to the goal of the “Thirteenth Five-Year Plan for Urban Green Lighting”, China will build 12 million LED lights at a growth rate of 46%, and renovate 50% of existing street lights, with a total scale of 29 billion yuan. The huge market has naturally attracted the attention of many companies.

Some time ago, the first batch of smart street lights in Xiong’an New District and Wuhan City attracted a lot of attention. In addition to their unique shapes, they also added video, Electronic Display, environmental monitoring, 5G, charging piles and other functions.

Unlike ordinary street lamps that only emit light on the top of the lamp, smart street lamps can emit light all over the body. The LED light strip can be adjusted to a variety of colors, just like neon flashing. At festivals or special times, the lights can “dance” and become colorful, and they can also change color as the density of traffic changes, acting as a warning.

The person in charge of the project said that the LED lights are soft, less glare, and high luminous efficiency. Each street lamp has a single lamp controller that can collect technical parameter information and adjust the power in conjunction with the flow of people and vehicles to achieve better energy-saving effects.

At the same time, the light pole can be equipped with monitoring probes of public security and traffic control to conduct video monitoring of road public safety. The large LED display on the back of the light pole can scroll and broadcast public information such as weather forecasts, as well as monitor the current PM2.5 value for screen display. To set a touch screen on the base of some of the light poles at the road junction, passers-by can directly query information about geography, tourist attractions, commercial shopping, etc. through the touch screen above, and news, warnings, public service advertisements, etc. issued by the government can also be touched The screen is displayed.

Some light poles also integrate broadcasting functions. When there are more tourists, the role of street lights can be more obvious.

While monitoring road traffic flow, pedestrian safety, and city management, while prompting information such as weather, pedestrian flow, violations, etc., it can also broadcast radio to create an urban atmosphere and stop violations. When there is a lot of people, the display screen will give an early warning, and the brightness of the street light will be increased accordingly.

There are many implementation methods for a single street light control solution. At present, it can be divided into two types: a wired solution and a wireless solution, mainly according to whether additional communication wiring is needed. The current mainstream of wired is the power line carrier communication technology, and the wireless is mainly based on technologies such as LoRa and ZigBee.

1. Power carrier

The distribution transformer has a blocking effect on the power carrier signal, so the power carrier signal can only be transmitted within the area of ​​a distribution transformer;

There is a large signal loss between the three-phase power lines (10 dB -30dB). When the communication distance is very short, the power carrier chip may receive signals between different phases. Generally, power carrier signals can only be transmitted on single-phase power lines;

Different signal coupling methods have different loss of power carrier signal. Coupling methods are wired-ground coupling and line-center coupling. Compared with the line-to-center coupling method, the line-to-ground coupling method has less power carrier signal loss by more than ten dB, but the line-to-ground coupling method is not applicable to all regional power systems;

The power line has inherent impulse interference. The AC power currently in use is 50HZ and 60HZ, and the period is 20ms and 16.7ms. In each AC cycle, there are two peaks, and the two peaks will cause two pulse interference, that is, there are fixed 100HZ or 120HZ pulses on the power line. Interference, the interference time is about 2ms, so the interference must be dealt with;

The power line causes high cuts to the carrier signal. When the load on the power line is heavy, the line impedance can reach below 1 ohm, resulting in a high reduction in the carrier signal. In practical applications, when the power line is empty, the point-to-point carrier signal can be transmitted up to several kilometers. But when the load on the power line is heavy, only tens of meters can be transmitted.

2. LoRa short frequency communication

LoRa can communicate over long distances with lower power consumption, and can be powered by batteries or other energy harvesting methods; lower data rates also extend battery life and increase network capacity. The LoRa signal also has a strong ability to diffract obstacles, which is very suitable for low-cost large-scale IoT deployment.

Figure 6 ZHIYUAN Electronics LoRa transparent transmission module

3. NB-IoT narrowband communication technology

With the emergence of NB-IoT technology, the industry is increasingly calling for NB-IoT to become the mainstream wireless control technology for the Internet of Things. In addition to the advantages of low power consumption, low cost and high stability, the biggest feature of NB-IoT is that as long as the signal can cover the place, it can quickly deploy the network without a gateway.

Moreover, a base station is expected to carry more than 200,000 terminals, which means that managing each street light becomes easy and simple. At present, many smart street light projects in China have used NB-IoT technology.

Figure 7 Zhiyuan Electronics NB-IOT IoT module

Four, ZigBee communication technology

Since ZigBee technology was born in industrial places with complex application environments, it also has the advantages of extremely high safety, reliability, low power consumption, and strong self-organizing network capabilities. It is naturally more important for intelligent lighting street lights with complex and changeable environments. reliable.

Figure 8 Zhiyuan Electronics ZM32 high-performance ZigBee module

ZM32 is a high-performance ZigBee transparent transmission module based on Silicon Labs EFR32MG1 series chips. It has five characteristics:

Extreme hardware performance, maximum communication distance:

A single chip can reach a transmit power of 19dBm, and with a receiving sensitivity of -99dBm, it can provide a line-of-sight communication distance of more than 3.3km, and it has a significant improvement in wall penetration and adjacent channel suppression performance.

Powerful Mesh networking capabilities:

Powerful networking capability, can automatically form a Mesh network with one click, and support non-polling Mesh networking of up to 200 nodes, and the self-organizing time of 100 devices does not exceed 100 seconds

A variety of communication methods can be dynamically switched:

Supports three communication methods: short address communication, modifiable MAC address communication, and a certain part of the designated data frame as address communication. The three communication methods can be dynamically switched by AT commands

Data encryption to ensure transmission security:

Support AES128 communication encryption and new device login encryption, using illegal devices to capture packets from the air can not obtain data, to ensure the safety of data transmission

Rich AT command set:

It has a wealth of built-in AT commands, supports dynamic modification of communication mode, modification of MAC address, reading of signal strength, reading of status of sub-nodes and other common AT commands, making it easier to use.