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Why use 11MHz chip rate when Channel Bandwidth is 22MHz

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addunw

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Hi,

Does anybody know why we use 11MHz chip rate while the channel bandwidth is 22MHz in 802.11b.

It seems like a waste of bandwidth. Is is because of the pulse shape??

Thanks
 

Hi

it is not waste of BW. As far as I can remember, it is due to CCK (complimentary code keying) and QPSK. To send 1Mbps CCK, there should be 11Mchips at 2MHz QPSK. Thus it makes 22MHz.

I guess if you search CCK, QPSK and 802.11b together, you may find some good resource for more accurate and detailed explanation why you need 22MHz BW.
 

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