Murata Electronics Corporation 4 6/2/2021
2. RADIO OPERATION
2.1. Synchronization and Registration
As discussed above, frequency hopping radios periodically change the frequency at which
they transmit. In order for the other radios in the network to receive the transmission, they
must be listening to the frequency over which the current transmission is being sent. To do
this, all the radios in the net must be synchronized and must be set to the same hopping
pattern. All radios in a net must be set to the same hopping pattern before attempting to
communicate.
In point-to-point or point-to-multipoint arrangements, one radio module is designated as the
base station. All other radios are designated remotes. One of the responsibilities of the base
station is to transmit a synchronization signal to the remotes to allow them to synchronize
with the base station. Since the remotes know the hopping pattern, once they are
synchronized with the base station, they know which frequency to hop to and when. Every
time the base station hops to a different frequency, it immediately transmits a synchronizing
signal.
When a remote is powered on, it rapidly scans the frequency band for the synchronizing
signal. Since the base station is transmitting over 75 frequencies and the remote is scanning
75 frequencies, it can take several seconds for a remote to synch up with the base station.
Once a remote has synchronized with the base station, it must request registration from the
base station. The registration process identifies to the base station the remotes from which
transmissions will be received and not discarded. Registration also allows tracking of
remotes entering and leaving the network. The base station builds a table of serial numbers
of registered remotes. To improve efficiency, the 24-bit remote serial number is assigned a
6-bit “handle” number. Two of these are reserved for system use, thus each base station can
register 62 separate remotes. This handle is how user applications will know the remotes. If
necessary, the automatic handle assignment can be overridden to explicitly tie certain handles
to certain remotes. See the section on Network Commands for details on the Set Default
Handle command.
To detect if a remote has gone offline or out of range, the registration must be “renewed”
once every 256 hops. Registration is completely automatic and requires no user application
intervention. When the remote is registered, it will receive several network parameters from
the base. This allows the base to automatically update these network parameters in the
remotes over the air. Once a parameter has been changed in the base, it is automatically
changed in the remotes. The parameters automatically changed are hop duration and the
duty cycle.
At the beginning of each hop, the base station transmits a synchronizing signal. After the
synchronizing signal has been sent, the base will transmit any data in its buffer unless data
transmit delay has been set. The data transmit delay parameter allows for the transmission
of groups of continuous data in transparent mode (protocol mode 0). The amount of data that
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