Sercel Inc 0500A ユーザーズマニュアル
Rev 30-2015
Page 9
Use the Synchro Word key to prevent connection to another Sercel network. The radio packets transmitted with a
Synchro Word key cannot be received by a Sercel network configured with another Synchro Word key.
Synchro Word key cannot be received by a Sercel network configured with another Synchro Word key.
Hop Sequence key = 1 (default),…xxx
For example :
Hop Sequence #1 = 10 15 1 6 11 16 2 7 12 3 8 13 4 9 14 0 5;
Hop Sequence #2 = 5 0 14 9 4 13 8 3 12 7 2 16 11 6 1 15 10 ;
Hop Sequence #3 = 0 5 9 14 4 15 10 1 6 11 16 2 12 7 3 13 8
Hop Sequence # = …
Synchro Word key = 1 (default),…xxx
Description of radio protocol:
The WTU-518 uses a half-duplex transmission protocol with a Frequency Hopping Spread Spectrum (FHSS) method.
A mechanism of Listen Before Talk (LBT) is implemented to avoid radio collisions inside the WTU-518 network or
with an external radio network. Moreover, two security keys are configured to secure the WTU-518 network.
A mechanism of Listen Before Talk (LBT) is implemented to avoid radio collisions inside the WTU-518 network or
with an external radio network. Moreover, two security keys are configured to secure the WTU-518 network.
Frequency Hopping Spread Spectrum (FHSS)
The FHSS operates on a set of frequencies. It will use one frequency for a fixed period of time and then switches to
another channel. The next frequency will be given by a pseudo-random sequence. In order to communicate, the
transmitter and the receiver have to use the same set of frequencies, the same frequency sequence defined by the
Frequency key. FHSS synchronization can be based on the date delivered by the internal GPS receiver or based on
the reception of packets issued from another WTU-518.
The FHSS operates on a set of frequencies. It will use one frequency for a fixed period of time and then switches to
another channel. The next frequency will be given by a pseudo-random sequence. In order to communicate, the
transmitter and the receiver have to use the same set of frequencies, the same frequency sequence defined by the
Frequency key. FHSS synchronization can be based on the date delivered by the internal GPS receiver or based on
the reception of packets issued from another WTU-518.
f1
f2
f3
f4
f5
f6
f1
f2
f3
f4
f5
f6
f1
f2
f3
f4
f5
f6
Send packet on f2
Send packet on f1
Send packet on f6
Example of FHSS based on a set of 6 frequencies
Listen Before Talk (LBT)
The LBT is based on a Channel Control Access mechanism: the WTU-518 measures the Received Signal Strength
Indication (RSSI) before beginning packet transmission. If the RSSI is too high, the media is said “busy” and the WTU-
518 postpones the transmission for a random backoff time.
Indication (RSSI) before beginning packet transmission. If the RSSI is too high, the media is said “busy” and the WTU-
518 postpones the transmission for a random backoff time.