Passive WiFi: Advantages and Disadvantages

This page explores the pros and cons of Passive WiFi technology.

What is Passive WiFi?

Traditional WiFi can be a significant power drain on mobile devices, consuming around 60% of the total energy due to these reasons:

1. Idle Mode: Constantly searching for WiFi signals from routers (or Access Points) to establish a connection by exchanging messages.
2. Connected Mode (Strong Signal): Regularly sending and receiving data to maintain the connection.
3. Connected Mode (Weak Signal): Boosting its own signal strength, which requires extra power, to transmit data packets effectively.

Passive WiFi has been developed to extend battery life by reducing power consumption. This is achieved by separating the RF (Radio Frequency) and baseband portions onto different modules.

To achieve power savings, Passive WiFi design consists of two parts:

• Passive WiFi Device: Contains all the digital baseband components.
• Plugged-in Device: Houses power-consuming RF components like the RF synthesizer and PA (Power Amplifier) with a transmitter that emits a single-tone RF carrier. This device handles carrier sense and MAC (Medium Access Control) across multiple passive WiFi devices.

Advantages of Passive WiFi

Here are the benefits of using Passive WiFi:

• Lower Power Consumption: It consumes four orders of magnitude (10,000x) less power compared to existing WiFi chips, and 1000x lower power than Bluetooth LE/Zigbee.
• Decent Range: Passive WiFi covers distances of up to 30 to 100 feet in various Line-of-Sight (LOS) and through-the-wall scenarios.
• Simplified IC Design: The segregation of RF and baseband components simplifies the design of the Passive WiFi IC.
• Low Cost: Because Passive WiFi only requires digital functionalities on the IC, it facilitates the design of low-cost ICs for devices like smartphones, tablets, and laptops.
• Compatibility: It utilizes legacy WiFi routers or access points (APs) to establish the WiFi network, making it compliant with existing WiFi standards (WLAN).
• Battery Saving: All MAC functionalities, such as RF carrier sense, WiFi connection establishment, and message exchange for keeping the connection alive, are handled by the plugged-in device, which saves battery power significantly.

Disadvantages of Passive WiFi

Here are the drawbacks of using Passive WiFi:

• Requirement for Plugged-in Device: A plugged-in device housing the RF components is essential, as the passive WiFi device doesn’t contain them. This limits the use of passive WiFi in traditional WiFi environments where these plugged-in devices are not installed. Passive WiFi functionality requires devices to support these plugged-in components.