What is an acceptable WiFi signal strength for a specific application?
What signal strength should I try to achieve in my wireless deployment?
These common questions illustrate the somewhat confusing nature of signal strength. First, we must understand the units of measurement, and what those measurements mean when deploying, managing, or diagnosing problems in a typical WiFi environment. Only then can we understand what signal strength is needed for specific uses.
The key to any good wireless deployment is proper planning, which requires a set of goals and requirements to achieve. Determining minimum signal strength requirements in the coverage area is almost alway part of the network requirements list.
Requirements and Variables
Desired signal strength for optimum performance varies based on many factors, such as background noise in the environment, the amount of clients on the network, what the desired data rates are, and what applications will be used. For example, a VoIP or VoWiFi system may require much better coverage than a barcode scanner system in a warehouse.
Understanding Signal Strength
WiFi signal strength is tricky. The most accurate way to express it is with milliwatts (mW), but you end up with tons of decimal places due to WiFi's super-low transmit power, making it difficult to read. For example, -40 dBm is 0.0001 mW, and the zeros just get more intense the more the signal strength drops.
RSSI (Received Signal Strength Indicator) is a common measurement, but most WiFi adapter vendors handle it differently, as it isn't standardized. Some adapters use a scale of 0-60, and others 0-255.