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* slow frequency hopping: after hopping to the new frequency, the transmitter sends several symbols before hopping to the next frequency. This gives the fastest data rate when running on hardware that takes a long time to switch to a different frequency. | * slow frequency hopping: after hopping to the new frequency, the transmitter sends several symbols before hopping to the next frequency. This gives the fastest data rate when running on hardware that takes a long time to switch to a different frequency. | ||
* fast frequency hopping: The transmitter hops to several different frequencies, sending the same symbol on each one, before transmitting the next data symbol. This is more tolerant of single-frequency interference. | * fast frequency hopping: The transmitter hops to several different frequencies, sending the same symbol on each one, before transmitting the next data symbol. This is more tolerant of single-frequency interference. | ||
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* Other places we [http://opencircuits.com/Special:Whatlinkshere/FHSS talk about FHSS on Open Circuits]. | * Other places we [http://opencircuits.com/Special:Whatlinkshere/FHSS talk about FHSS on Open Circuits]. | ||
− | == | + | == acquisition and tracking == |
When a receiver is turned on, what frequency should it listen to first, and how long should it listen before trying some other channel? | When a receiver is turned on, what frequency should it listen to first, and how long should it listen before trying some other channel? | ||
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* The receiver picks a random acquisition channel (a random point on its hop sequence) -- perhaps the quietest channel with the least noise on it -- and stays on that channel until it hears the transmitter. The transmitter always goes through the hop sequence in the standard order, sending a packet on each channel. Eventually the transmitter gets to the channel the receiver is listening on, and the receiver hears that packet, synchronizes its time, and starts hopping. | * The receiver picks a random acquisition channel (a random point on its hop sequence) -- perhaps the quietest channel with the least noise on it -- and stays on that channel until it hears the transmitter. The transmitter always goes through the hop sequence in the standard order, sending a packet on each channel. Eventually the transmitter gets to the channel the receiver is listening on, and the receiver hears that packet, synchronizes its time, and starts hopping. | ||
* The transmitter picks a random acquisition channel (a random point on its hop sequence) -- perhaps the quietest channel with the least noise on it -- and transmits its time signal over and over on that channel. The receiver goes through the hop sequence in the standard order. Eventually the receiver gets to the channel the transmitter is sending on, and the receiver hears the packet and synchronizes its time. After the transmitter has given the receiver plenty of time to sample every possible channel, both should now be synchronized, and start hopping. | * The transmitter picks a random acquisition channel (a random point on its hop sequence) -- perhaps the quietest channel with the least noise on it -- and transmits its time signal over and over on that channel. The receiver goes through the hop sequence in the standard order. Eventually the receiver gets to the channel the transmitter is sending on, and the receiver hears the packet and synchronizes its time. After the transmitter has given the receiver plenty of time to sample every possible channel, both should now be synchronized, and start hopping. | ||
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* ... | * ... | ||
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+ | == legal considerations == | ||
In addition to the physical limitations mentioned above, there are also legal considerations, such as, for example: | In addition to the physical limitations mentioned above, there are also legal considerations, such as, for example: | ||
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''... What other legal considerations and FCC policies are relevant to designing intelligent radio communication systems? ...'' | ''... What other legal considerations and FCC policies are relevant to designing intelligent radio communication systems? ...'' | ||
− | == | + | == further reading == |
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* [http://interwiki.sourceforge.net/cgi-bin/picawiki.pl/NgARN NgARN : Next Generation Amateur Radio Network] | * [http://interwiki.sourceforge.net/cgi-bin/picawiki.pl/NgARN NgARN : Next Generation Amateur Radio Network] | ||
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* [http://focus.ti.com/general/docs/techdocsabstract.tsp?abstractName=swra048 TI Application Report SWRA048: "ISM-Band and Short Range Device Regulatory Compliance Overview"] edited by Matthew Loy, Raju Karingattil, Louis Williams | * [http://focus.ti.com/general/docs/techdocsabstract.tsp?abstractName=swra048 TI Application Report SWRA048: "ISM-Band and Short Range Device Regulatory Compliance Overview"] edited by Matthew Loy, Raju Karingattil, Louis Williams | ||
* [http://focus.ti.com/lit/an/swra060/swra060.pdf "Application Note AN032", aka "swra060": "SRD regulations for license-free transceiver operation in the 2.4 GHz band"] by M. Engjom (discussing regulations on devices legally classified as a "short range device") | * [http://focus.ti.com/lit/an/swra060/swra060.pdf "Application Note AN032", aka "swra060": "SRD regulations for license-free transceiver operation in the 2.4 GHz band"] by M. Engjom (discussing regulations on devices legally classified as a "short range device") | ||
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