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Direct Sequence Physical Layer

The Direct Sequence Physical Layer utilizes spread spectrum technology to transmit the signal over a much wider frequency band. This process entails spreading a narrow band signal over a wider frequency band. To a narrow band receiver, the transmitted signal is impossible to detect as it appears as low level noise. However, a wide band receiver can monitor the whole frequency band and detect changes. The original signal can then be recovered by a correlator which reverses the spreading process. This process gives a significant degree of protection to direct sequence transmissions as noise tends to be narrow in terms of frequency and thus does not affect the entire frequency band. To support the DS PHY, the 2.4GHz ISM (Industrial Scientific and Medical) band is divided into 14 channels, each separated by 5GHz. Unfortunately these channels may not all be available, as different regulatory bodies have allocated different portions of the ISM band.

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