Application of Bluetooth Mesh Ad-Hoc Network in Smart Home

The Internet of Things (IoT) smart home is a highly popular topic nowadays, but people's requirements for smart homes are by no means limited to the simple level of controlling lights with a mobile phone. We need to spread intelligence to every corner. However, how can we transmit commands to every device? In the past, we relied on WiFi technology, but WiFi technology also has many limitations. Now, with the new "Bluetooth Mesh" network, these problems have been solved.

Bluetooth technology has begun to support mesh networks, enabling more diversified IoT application scenarios. Currently, most smart home devices transmit data through WiFi modules. However, what they can do is to turn lights on and off and control home appliances with a mobile phone, and at best, allow you to give voice commands. In fact, you usually need to open an app to issue a command when controlling the lights, and then open another app to issue other commands when controlling other devices. It's not really that "smart".

However, wouldn't it be much smarter if when you open the front door, the hallway lights turn on, the sensors of the alarm system turn off, the air conditioner turns on automatically, and your favorite music plays in the living room, all happening the moment you step into the house?

Advantages of Bluetooth Mesh Network

One major drawback of WiFi modules is their limited range. Traditional wireless networks, including the one-to-one Bluetooth network in the past, are limited by the distance between two devices. For WiFi wireless technology, the effective transmission range is within 50 square meters. Unless you install intermediate devices, once you leave this area, your mobile phone becomes useless.

In addition, WiFi modules have a power consumption issue. Even if you turn off the phone screen, you still need to charge it once a day.

"Bluetooth Mesh" has found an ingenious solution. These devices connect to each other and transmit signals to another nearby device, forming an interconnected device network or grid for metadata transmission. This means that messages are transmitted from one device to another, and then to the next, in a relay manner.

The left figure shows the connection method of traditional WiFi technology, which requires a Hub to connect other devices, so there is a distance limit. The right figure shows the Bluetooth Mesh ad-hoc network method. The more devices connected to this network, the wider the range.

Through this relay transmission, a reliable network is formed that does not require a large amount of power consumption or extensive antenna deployment. Bluetooth devices can "talk" to each other without going through a Wi-Fi network. In other words, smart devices using this technology can communicate with each other within a limited range and be controlled by devices such as mobile phones.

In the past, because a Hub was needed at home to connect other devices, "voice assistants" such as Google, Apple, and Amazon emerged as control centers. However, under the Bluetooth Mesh ad-hoc network architecture, you don't need an additional "hub" and can control everything with a smartphone. The Bluetooth devices at home build their own network, and as long as the mobile phone connects to one of the Bluetooth devices, it can control all the devices in the house (the entire building) and monitor the status of these devices.

Since Mesh networks do not require complex settings, pairing, or the use of access devices such as routers, they do not impose an installation burden. In contrast, other smart home networking technologies such as ZigBee, Z-wave, or proprietary communication technologies between manufacturers often require the installation of a Gateway to ensure smooth communication between various devices.

Working Principle of Bluetooth Mesh Ad-Hoc Network Module

In the Bluetooth BLE communication protocol, the GAP layer (Generic Access Profile) is used to control and determine the scanning, broadcasting, and connection relationships of Bluetooth devices. In other words, GAP determines how a Bluetooth device connects to other devices and is discovered by other devices. Before the emergence of Bluetooth mesh networks, GAP had a typical parent-child network relationship, where the "parent" end determines all routes, and the "child" end performs assigned tasks. For example, when you connect a Bluetooth keyboard to a tablet computer, the tablet is the parent end and the keyboard is the child end.

GAP makes your device visible to other devices and determines whether and how your device can interact with other devices. For example, Beacon devices commonly used in indoor positioning only broadcast outward and do not support connections. Devices such as smart bracelets can connect to your mobile phone.

Starting from the Bluetooth 4.1 protocol, GAP has expanded the network capabilities of Bluetooth devices. Bluetooth devices can have both "parent" and "child" functions, allowing all devices to directly connect and broadcast to any other device. Bluetooth modules are therefore applicable to all devices within and outside the transmission range.

It is precisely because of this ability to directly or indirectly connect any number of Mesh-enabled devices that in theory, it is possible to build a Mesh network with a range of several kilometers. If each device in the network is within the broadcast range of at least one other device, the Mesh network can theoretically cover an infinite distance.

In this case, light bulbs may become one of the main Mesh network devices in a home. Because in a home or building, almost every corner needs to be covered by light, light bulbs are installed continuously at a certain distance. If each light bulb is a Bluetooth Mesh device, then this network can fully cover the building.

Bluetooth Mesh networks not only have low power consumption but also low bandwidth. This sounds like a disadvantage? Actually, it's not. Since Bluetooth Mesh networks are not used to transmit audio-visual data, they are mainly used to maintain connections or send commands. Sending a "turn off" or "turn on" command does not require much bandwidth. This is why although the Bluetooth Mesh network has an almost unlimited range, it cannot completely replace WiFi technology.