WLL (Wireless Local Loop) Basics Tutorial

The demand for internet access is constantly growing worldwide. This drives the need to provide broadband internet to users in offices and residential locations alike.

There are several ways to deliver internet service, including fiber optic cables, DSL lines, and wireless connections.

Providing a fixed wireless connection for broadband internet is known as WLL, or Wireless Local Loop. Microwave frequencies are utilized to establish this wireless broadband connection.

The local loop is often called the “last mile” of the telecom network, representing the segment between the Central Office (CO) and the user’s location. The following diagram illustrates this:

Benefits of WLL

Here are some advantages of using WLL services:

• The channel between the transmitter and receiver remains relatively stable, requiring less complex algorithms in the WLL network.
• Frequencies used are significantly higher (10 times or more) than cellular mobile systems, allowing for greater bandwidth and the use of high-gain antennas. These antennas act as spatial filters, helping to reject non-line-of-sight multipath signals.
• Cable installation can be time-consuming and expensive in many countries. WLL installation, on the other hand, is typically quicker and less costly, often completed within hours.
• Users or subscribers may not need to pay monthly fees, unlike traditional cable service providers.

WLL Frequency Bands

Millimeter wave frequencies, ranging from above 10 GHz to 300 GHz, are commonly employed for WLL.

In the US, the FCC has allocated approximately 15 bands for commercial fixed wireless services, spanning from 2 GHz to 40 GHz. However, using these millimeter wave frequencies introduces some challenges:

• Free space loss increases with the square of the frequency, making it higher at these frequencies. $$\text{Free Space Loss} \propto f^2$$
• Above 10 GHz, attenuation due to rainfall and atmospheric conditions becomes more significant, in addition to multipath losses.

These drawbacks typically limit the coverage of WLL systems to a few kilometers.