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Bluetooth frequency-hopping techniques

Could you please tell me where Bluetooth spread spectrum frequency-hopping techniques can be applied? Do other wireless technologies, such as 802.11 Wi-Fi, use this technique?

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Spread spectrum technology -- or at least the concept -- has been kicking around since the 1920s and was first publicly patented in the 1940s by movie actress Hedy Lamarr and composer George Antheil. The first use of the technology was to secure communications during World War II, although since then it has evolved to become the framework for nearly all wireless communications worldwide. Today, spread spectrum technology and frequency-hopping techniques not only make for more secure communications, but allow reliable communications within "noisy" and increasingly crowded wireless environments. This is more of an issue as we add multiple wireless networks and we move toward an era where nearly every device and product will be screaming out a wireless signal.

Bluetooth is but one technology that makes use of spread spectrum and frequency-hopping, by spreading its signal across 79 different frequencies at 1 MHz intervals. This allows up to seven or eight simultaneous connections per Bluetooth device without the fear of collision and corrupted signals. This means that multiple users in an office can send data to a Bluetooth-equipped printer, and groups of users at an airport can use their Bluetooth-equipped phones to access the Internet without fear of someone tapping into their signal. This provides some level of security, although most security is layered on top of this basic hardware solution.

802.11 Wi-Fi, ZigBee and other limited-area wireless networking technologies also employ spread spectrum and frequency-hopping techniques to avoid collisions and add some level of security to communications. Wide area wireless networks, like those used for cell phones, also rely on these techniques as signals are passed from tower to tower during calls and data transmissions -- although it becomes increasingly more difficult to develop frequency-hopping systems for wider-area wireless networks that are used over great distances. This is due to the time lag of frequency hopping, which is pretty negligible over short distances but could be a problem when dealing with longer-distance communications.

It is for this reason that a number of wireless vendors avoid frequency-hopping techniques when designing outdoor fixed-wireless broadband solutions. Instead, they might use direct sequence technology, which has a shorter latency time, better signal-to-noise ratio, and a longer range than frequency-hopping alternatives.

This was first published in January 2004

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