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Dynamic CCK-OFDM - True

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So generell CCK and OFDM is off.

But what does the Line "Dynamic CCK-OFDM: True" mean?

CCK and OFDM ist switched dynamically, for the case one is better in a specific Situation?

I can't find an Answer, pleae Help.

asked 27 Jun '14, 10:03

Jan%20Hermanns's gravatar image

Jan Hermanns
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One Answer:

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I think it means "uses OFDM if it can, reverts to CCK if it can't". The Wikipedia article on 802.11g says

802.11g hardware is fully backwards compatible with 802.11b hardware. Details of making b and g work well together occupied much of the lingering technical process. In an 802.11g network, however, the presence of a legacy 802.11b participant will significantly reduce the speed of the overall 802.11g network. Some 802.11g routers employ a back-compatible mode for 802.11b clients called 54g LRS (Limited Rate Support).

The modulation scheme used in 802.11g is orthogonal frequency-division multiplexing (OFDM) copied from 802.11a with data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbit/s, and reverts to CCK (like the 802.11b standard) for 5.5 and 11 Mbit/s and DBPSK/DQPSK+DSSS for 1 and 2 Mbit/s. Even though 802.11g operates in the same frequency band as 802.11b, it can achieve higher data rates because of its heritage to 802.11a.

IEEE Std 802.11g-2003 says

For example, a BSS could operate in an ERP-OFDM-only mode, a mixed mode of ERP-OFDM and ERP-DSSS/CCK, or a mixed mode of ERP-DSSS/CCK and Non-ERP.

and "Dynamic CCK-OFDM" is probably "a mixed mode of ERP-OFDM and ERP-DSSS/CCK", whereas just "OFDM" would probably be "an ERP-OFDM-only mode" and just "CCK" would presumably be "a mixed mode of ERP-DSSS/CCK and Non-ERP".

(Note that the "channel type" field describes the channel, not the way the particular packet was transmitted.)

answered 27 Jun '14, 14:47

Guy%20Harris's gravatar image

Guy Harris ♦♦
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edited 27 Jun '14, 14:48

I got it!

As the name implies, CCK/OFDM is a hybrid. It is included as an optional part of the IEEE 802.11g Draft Proposal. As shown in Figure 7, CCK/OFDM uses CCK modulation to transmit the Preamble/Header and OFDM to transmit the Payload. Note that the CCK and OFDM modulation formats remain separate and distinct. A transition from CCK modulation to OFDM modulation is made between the Preamble/Header and the Payload.

(29 Jun '14, 10:30) Jan Hermanns