Problem solve Get help with specific problems with your technologies, process and projects.

Modulation types

What are the modulation techniques in wireless networking with 802.11g, and why do we select those particular modulation...

types? The IEEE 802.11g-2003 standard defines several modulation types:

  • ERP-DSSS refers to PHYs using Direct Sequence Spread Spectrum (DSSS) modulation. DSSS was defined in the original IEEE 802.11-1999 standard to support data rates of 1 and 2 Mbps.

  • ERP-CCK refers to PHYs using Complementary Code Keying (CCK) modulation. CCK was added in the IEEE 802.11b-1999 supplement to support data rates of 5.5 and 11 Mbps.

  • ERP-PBCC refers to PHYs using extended rate Packet Binary Convolutional Coding (PBCC) modulation. PBCC was added as an option in the IEEE 802.11b-1999 supplement to support data rates of 5 and 11 Mbps. In 802.11g, ERP-PBCC option also supports data rates of 22 and 33 Mbps.

  • ERP-OFDM refers to PHYs using Orthogonal Frequency Division Multiplexing (OFDM) modulation. OFDM was added in the IEEE 802.11a-1999 supplement. In 802.11g, ERP-OFDM supports data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps.

  • DSSS-OFDM refers to PHYs using hybrid DSSS-OFDM modulation. DSSS-OFDM was added in the IEEE 802.11g-2003 standard and is an optional mode that does NOT use the Extended Rate PHY (ERP) protection mechanism. Instead, DSSS-OFDM combines the DSSS preamble and header with the OFDM payload, supporting rates similar to ERP-OFDM.

Which modulation type will used depends on the capabilities of your 802.11g AP and stations, their configuration, need to coexist with 802.11b, and environmental conditions. There's a nice comparative chart of these modulation types in this Texas Instruments 802.11g white paper (PDF).

This was last published in February 2004

Dig Deeper on Wireless LAN (WLAN)