Spread spectrum technology

Spread spectrum technology is a commonly used wireless communication technology, referred to as spread spectrum technology. The wireless local area network products using spread spectrum technology are based on the ISM (Industrial Scientific, and Medical) stipulated by the FCC (Federal Communications Committee). The frequency range is open in the two frequency bands of 902M~928MHz and 2.4G~2.484GHz, so there is no so-called restriction on the use of authorization.

Spread spectrum technology is mainly divided into two types: "frequency hopping technology" and "direct sequence".

Frequency Hopping Technology

Frequency Hopping Signaling (FHSS)

Frequency-hopping spread spectrum (FHSS) technology transmits signals with a specific narrowband carrier at both ends in a synchronous and simultaneous manner. For a non-specific receiver, the hopping signal generated by FHSS is only considered as pulse noise. The signal developed by FHSS can be specially designed to avoid noise or one-to-many non-repeating channels, and these frequency hopping signals must comply with FCC requirements, using more than 75 frequency hopping signals, and the maximum time interval (Dwell Time) between hopping to the next frequency is 400ms.

Direct Sequence Spread Spectrum Technology

Direct Sequence Spread Spectrum (DSSS)

Direct Sequence Spread Spectrum (DSSS) technology uses more than 10 chips to represent the original signal "1" or "0", so that the original high-power and narrow frequency becomes a low-power frequency with a wider bandwidth. The number of chips used for each bit is called Spreading chips. A higher Spreading chip can increase the resistance to noise interference, and a lower Spreading Ration can increase the number of users. Basically, the Spreading Ration of DSSS is quite small. For example, the Spreading Ration used in almost all 2.4GHz wireless LAN products is less than 20. In the IEEE802.11 standard, its Spreading Ration is about 100.