• Hi All, I am reading CWAP official study guide for my exam and have some confusion in the below explaination. as per this there are total 62 subcarriers, 11 are used for guard band and one center one is used for DC, so total 12 and then it should leave 50 not 52.

    This is on ch.10 page 364.

    Can anyone help me to understand this.

    Appriciate help in advance.

    802.11a and 802.11g radios use 20 MHz OFDM channels. Each 20 MHz OFDM channel
    contains 62 subcarriers. Each subcarrier is 312.5 KHz wide and can be separately modu-
    lated with part of the data stream. The frst six and last fve subcarriers are null because
    they act as a guard band for the channel. As well as the 11 guard band subcarriers, the cen-
    ter subcarrier is also null and is called the direct conversation (DC) subcarrier. This leaves
    52 subcarriers, as pictured in Figure 10.4. Forty-eight of these subcarriers transmit data,
    while four of the subcarriers are used as pilot tones for dynamic calibration between the
    transmitter and receiver. OFDM technology also employs the use of convolutional coding
    and forward error correction.

  • That should be a total of [b]64[/b] Subcarriers, not 62.

    20,000 kHz / 312.5 kHz = 64.

    "Good catch" as they say in my business.

  • Thanks wlanman, appriciate, and now I got the formula too.

  • This should probably be added to the CWAP Errata sticky topic found at:

    I assume these errata are being tracked and will be addressed in the next edition.

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