How the Ubiquiti WiFi Bridge Works: Principles, Configuration, and Schematic

Establishing a wireless connection between two remote locations is a challenge faced by both system administrators of large enterprises and homeowners. When installing fiber optic or twisted pair cables is impossible, too expensive, or simply impractical, professional PtP (Point-to-Point) solutions come into play. The company's equipment is rightfully considered a leader in this segment. Ubiquiti Networks, whose devices are of the series airMAX And UniFi have become the industry standard. But what's behind the pretty web interface, and how exactly are radio waves converted into a stable data transmission channel?

The operation of any wireless bridge is based on the process of converting electrical signals into electromagnetic waves of a certain frequency. Ubiquiti WiFi Bridge It doesn't simply "distribute" the internet; it creates a virtual cable, compressing and encoding information for transmission over the air. Unlike home routers, which broadcast to multiple clients, a bridge is configured for precise synchronization with its partner, ignoring all other sources of noise. This enables incredible speeds and minimal latency, even over distances of several dozen kilometers.

Understanding the physical processes involved in data transmission is critical for proper installation and configuration of equipment. If you simply buy two "dishes" and hang them up haphazardly, you can't expect stable operation. It's important to consider Fresnel zone, antenna polarization, and the impact of precipitation. In this article, we'll take a detailed look at the architecture of modern Ubiquiti wireless systems, delve into TDMA and AirMax algorithms, and answer frequently asked questions when designing communication lines.

Point-to-Point Wireless Connection Architecture

The classic Wi-Fi we use in smartphones and laptops operates on the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) principle. Simply put, a device "listens" to the airwaves and, if there's no signal, begins transmitting data. If two devices talk at the same time, a collision occurs, and data is lost. This approach is ineffective for building long-distance communication channels, as it generates significant overhead and limits actual throughput. Ubiquiti engineers took a different approach, implementing a proprietary protocol. TDMA (Time Division Multiple Access).

TDMA technology divides transmission time into very short intervals called time slots. The base station (Master) strictly regulates when a client device (Slave) is allowed to transmit data. This eliminates collisions at the physical level. Imagine a conversation between two people on a walkie-talkie, where one says "Over" and the other waits their turn, as opposed to a crowd of people shouting simultaneously in a single room. This is precisely why Ubiquiti airMAX provides predictable latency and high throughput even when the channel is fully loaded.

It is important to note the difference between the operating modes of the equipment. In the mode Bridge Bridged devices transparently transmit Ethernet frames, creating a single broadcast domain. This means devices on both sides of the bridge will see each other as if they were connected by a single cable. However, modern Ubiquiti systems also support routing and NAT modes, allowing you to segment your network and hide a remote site's local network behind a single external IP address. The choice of mode depends on your network topology.

⚠️ Important: When designing a link, always keep in mind that the manufacturer's stated speed (e.g., 1 Gbps) is the theoretical maximum of the PHY layer. Actual throughput is always lower due to overhead, channel width, and environmental conditions. Allow for at least 10-15 dB of signal power reserve.

Modern models such as LiteBeam AC or PowerBeam 5AC, use MIMO (Multiple Input Multiple Output) technology. This means that data is transmitted simultaneously across multiple streams through different antennas. If one stream is weakened by interference, the others continue to operate, ensuring a stable connection. Dual-polarization of the antennas doubles the channel capacity by using the same frequency but with different electromagnetic wave orientations.

Frequency ranges and equipment selection

The first step to creating a reliable bridge is choosing the right frequency band. Ubiquiti equipment operates primarily in two bands: 2.4 GHz and 5 GHz (as well as 60 GHz in the airFiber series). Each band has its own physical properties that directly impact range and interference immunity. 2.4 GHz band It has better penetrating power and is less attenuated in the atmosphere, but it is extremely congested in cities due to the many home routers, microwaves, and Bluetooth devices.

For the construction of highways longer than 1-2 kilometers in urban or densely populated areas, it is strongly recommended to use 5 GHz. The airwaves are cleaner here and wider channels are available (40, 60, 80 MHz), which allows for speeds to be accelerated to gigabit values. Models of the series NanoStation 5AC or LiteBeam 5AC are the gold standard for such applications. However, it's worth remembering that high frequencies are more strongly absorbed by rain and tree foliage, so line-of-sight requirements are more stringent.

If you need ultra-high speed over short distances (up to 1-2 km) and your budget allows, you should pay attention to the series airFiber, operating in the 60 GHz band. These devices provide speeds comparable to fiber optics, but have a very narrow beam and are extremely sensitive to any obstacles, including heavy snow or hail. For long lines (10-50 km), highly directional, high-gain antennas operating in the 5 GHz band are used.

When choosing a frequency, it's also important to conduct a preliminary spectrum analysis. Built-in tools in the Ubiquiti interface allow you to see channel congestion. If all channels in the 5 GHz band are occupied by neighbors, you may need to use non-standard channel widths or switch to licensed frequencies if the equipment supports them.

Physics of radio waves and the Fresnel zone

Many beginners make the fatal mistake of assuming that simply "seeing" the receiving antenna with their eyes is enough for a WiFi bridge to work. This is incorrect. Radio waves propagate not like a narrow laser beam, but in the form of a rotating ellipsoid, known as Fresnel zoneFor a stable connection, this zone must be at least 60% clear of obstacles (trees, buildings, terrain). If trees obscure the edge of the Fresnel zone, you will experience significant signal loss and unstable ping, even if the antenna lens is visually exposed.

The size of the Fresnel zone depends on the signal frequency and the distance between the antennas. The lower the frequency and the greater the distance, the wider the zone. For example, at a frequency of 2.4 GHz and a distance of 5 km, the radius of the Fresnel zone at the widest point (the middle of the link) is approximately 10 meters. This means that there should be no objects between the antennas that interfere with this imaginary ellipse. At a frequency of 5 GHz, the requirements are slightly more relaxed, but still critical.

Additionally, signal polarization must not be ignored. Ubiquiti antennas typically have dual polarization (horizontal and vertical). When mounting, it's critical that both antennas at the ends of the link are oriented identically. If one antenna is rotated 90 degrees relative to the other, you'll lose up to 20 dB of signal, which is equivalent to a broken connection. When mounting on a mast, use a spirit level to ensure vertical alignment.

⚠️ Caution: Trees with foliage are powerful signal absorbers, especially at frequencies of 5 GHz and above. In summer, a link may be stable and reestablished in winter when the leaves fall, but in spring, when the leaves emerge, the connection may be completely lost. Always plan your trajectory above tree canopies.

Setup and installation: step-by-step instructions

The process of setting up Ubiquiti equipment is now as simple as possible thanks to the ecosystem UISP (formerly UNMS) and cloud service UI CloudHowever, basic configuration via the device's web interface remains a fundamental skill. After physical connection and power supply (PoE), the device receives a default IP address (usually 192.168.1.20). You need to assign your computer to the same subnet, for example, by assigning a static IP of 192.168.1.50.

After entering the device interface (default login/password: ubnt / ubnt), the first thing you should do is update the software (Firmware). Older firmware versions may contain security vulnerabilities or bugs that affect TDMA stability. After updating, go to the tab WirelessHere you need to select the operating mode: Access Point PtP for one side of the link and Station PtP for another. In the SSID field, enter a unique network name, and from the list of available networks, select the target one and click Connect.

The key parameter is Channel Width (Channel width). For maximum speed, choose 40 MHz or 80 MHz (if your equipment and air quality allow). However, the wider the channel, the lower the receiver sensitivity and the shorter the range. For long and complex links, it's often more cost-effective to use 20 MHz or even 10 MHz, sacrificing maximum speed for rock-solid stability and signal strength.

After setting up the logical part, the physical installation begins. Attach the antennas to the masts, roughly aligning them with each other. Then, using one as an access point and the other as a client, connect to the client via WiFi (or cable) and monitor the signal strength.Signal) in real time. Slowly rotate the antenna in azimuth and elevation, achieving maximum values. A signal in the range of -45 to -55 dBm is considered optimal. Values ​​below -65 dBm are considered marginal.

Link diagnostics and optimization

Even a perfectly configured bridge requires periodic diagnostics. Ubiquiti's interface has a built-in tool. Spectrum Analyzer, which displays the noise floor and channel occupancy in real time. If you see noise levels rising to -90 dBm or higher, or the channel is constantly occupied by other networks, consider changing the operating frequency. Also, keep an eye on this parameter. CCQ (Client Connection Quality). This is the connection quality percentage. If the CCQ falls below 80-90%, it means there is interference or multiplex reflections in the channel.

Another important indicator is VSWR (Standing Wave Ratio). It reflects the quality of the antenna-to-feeder match. Ideally, the VSWR should be close to 1.0. If the value exceeds 1.5-2.0, this may indicate cable damage, poor connector contact, or moisture ingress into the antenna. A high VSWR not only degrades communication but can also burn out the transmitter's output stage.

For in-depth diagnostics, use the command line (SSH). Once connected to the device, you can run ping with a large packet size to check stability under load. Monitoring the device's temperature is also useful. Although Ubiquiti hardware is designed to operate over a wide temperature range, overheating of the processor or radio module can lead to throttling (decreased performance) or reboots.

Secrets of stability

Use cables with thick copper conductors (not copper-clad aluminum CCA) for PoE power. Over long spans (>20m), voltage drop on thin cables can result in the antenna not having enough power to operate at full transmitter power.

If you observe periodic speed drops at certain times of day, this may be due to neighboring activity or changing atmospheric conditions (temperature inversion). In such cases, installing protective screens (shutters) on the antennas can help to block the side lobes of the antenna pattern from sources of interference.

Wireless channel security

A wireless bridge is essentially an Ethernet port on your local network sticking out into the sky. If it's not protected, anyone within range (which can be kilometers) can connect to your network. The first layer of protection is using an encryption protocol. WPA2-AES or WPA3Never leave a network open or with WEP/TKIP encryption, as they can be cracked in minutes.

The second, more secure level is management isolation. Change the standard web interface port (80/443) to a non-standard one, disable SSH access from the WAN (if not needed), or restrict access by IP address. In the settings Ubiquiti there is a function Management Access, which allows you to specify specific IP addresses from which device administration is permitted.

It is also recommended to disable unused services, such as Telnet, and use complex passwords. For corporate networks, it is a good practice to create a separate VLAN for bridge traffic to prevent an attacker from accessing the main network containing the accounting department or servers in the event of a hardware compromise.

⚠️ Note: Interfaces and menu names may vary depending on the firmware version (AirOS, EdgeOS, UniFi). Always consult the official documentation on the manufacturer's website for your specific model before making any critical settings changes.

Frequently Asked Questions (FAQ)

Is it possible to connect three points into a triangle (Point-to-Multipoint)?

Yes, this is possible. One antenna is configured in Access Point PtMP mode, and the other two in Station PtMP mode. However, the base station's bandwidth will be divided among all clients. For three points, it's better to use three directional antennas if they are spaced apart, or one omnidirectional antenna in the center, although the latter is less effective over longer distances.

Do I need a static IP address to set up a bridge?

For initial setup, yes, the computer must be on the same subnet as the device. After setup in Station (client) mode, the device can obtain an IP via DHCP from the main router. DHCP is also typically used in Access Point mode, but for ease of administration, the bridge itself is often assigned a static IP within the local network.

Why doesn't the Ubiquiti bridge see the second antenna?

Check three things: 1) Are the frequency (Channel) and channel width the same on both devices? 2) Is one configured in AP mode and the other in Station mode? 3) Are there any obstructions in the Fresnel zone? Also, make sure the antennas are polarized correctly and facing each other.

Does thunderstorm affect WiFi bridge?

A direct lightning strike will instantly disable equipment. But even nearby lightning strikes create powerful electromagnetic interference. Be sure to use lightning protection (surge arresters) on Ethernet cables and ground masts. This isn't a guarantee of survival, but it will significantly increase the equipment's chances of surviving a storm.