WLAN Technologies: IR vs. Spread Spectrum vs. Radio Frequency

Wireless LANs (WLANs) can be categorized based on their transmission techniques. The three major types are Infrared (IR) LAN, Spread Spectrum (SS) LAN, and Microwave Radio Frequency (RF) LAN.

This document outlines the differences between these three WLAN types: Infrared, Spread Spectrum, and RF.

Infrared (IR) WLAN

Infrared light can’t penetrate walls, so an IR WLAN cell is typically confined to a single room.

There are two main types of IR Wireless LAN:

• Diffused Infrared: Signals are reflected off surfaces.
• Directed Beam Infrared: Requires a direct line-of-sight connection.

Here’s a breakdown of IR WLAN features:

• Data Rate: 1-4 Mbps (Diffused IR), 1-10 Mbps (Directed beam IR)
• Mobility Support: Stationary and mobile (Diffused IR), Stationary with Line-of-Sight (Directed beam IR)
• Coverage Range: 15 to 60 meters (Diffused IR), 25 meters (Directed beam IR)
• Wavelength: 800 to 900 nm
• Modulation Type: ASK (Amplitude Shift Keying)
• Access Method: CSMA (Carrier Sense Multiple Access) for Diffused IR, Token Ring and CSMA for Directed Beam IR

Spread Spectrum (SS) WLAN

This type of WLAN operates in the ISM (Industrial, Scientific, and Medical) bands, so no licensing is required.

There are two types of SS Wireless LAN:

• Frequency Hopping (FH): Rapidly switches between frequencies.
• Direct Sequence (DS): Spreads the signal across a wider bandwidth.

Here’s a breakdown of SS WLAN features:

• Data Rate: 1 to 3 Mbps (FH), 2 to 20 Mbps (DS)
• Mobility: Full mobility (FH), Stationary/Mobile (DS)
• Coverage Range: 30 to 100 meters (FH), 30 to 250 meters (DS)
• Frequency Support: 902 to 928 MHz, 2.4 to 2.4835 GHz, 5.725 to 5.85 GHz
• Modulation Type: FSK (Frequency Shift Keying) in FH, QPSK (Quadrature Phase Shift Keying) in DS
• Device Radiated Power: Less than 1 Watt
• Access Method: CSMA

Microwave Radio Frequency (RF) WLAN

This type of RF-based Wireless LAN operates in both licensed and unlicensed frequency bands.

Here’s a breakdown of RF WLAN features:

• Data Rate: 10 - 20 Mbps
• Mobility Support: Supports both stationary and mobile modes
• Coverage Range: 10 - 40 meters
• Frequency Range: 902-928MHz, 5.2-5.775GHz, 18.825-19.205GHz
• Modulation Type: FS/QPSK (Likely a typo, should be FSK or QPSK)
• Device Radiated Power: Typically about 25mWatt
• Access Method: Reservation ALOHA and CSMA