Linx Technologies HUM-xxx-DT - Manual (Page 10)

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Frequency Agility
In frequency agile mode, the module transmits the same data packet on up
to four channels in turn, then loops around and sends the next data packet
on each channel. This continues until all of the data has been sent. The
number and selection of which channels are used are configured through
serial commands using the module’s Command Data Interface.
The receiver measures the RSSI of each channel, picks the quietest one
and waits on that channel for transmitted data. It re-checks all of the
channels about every 30 seconds and moves to a new channel if needed.
In normal operation, modules sit in receive mode listening for incoming
packets. When data to be transmitted is input into the module’s UART, the
module automatically switches to the transmit mode and sends the data.
All protocol functions like creating the data packet, changing channels and
validating the received packet are handled automatically.
This method is considered narrowband operation and does not qualify
for the higher transmitter output power of frequency hopping systems.
However, the data throughput can be much faster since there is no
hopping algorithm that needs to be maintained. This is especially true if
only one or two channels are used.
The commands for configuring the channels are outlined in the Command
Data Interface section. The available channels are shown in Figure 16.
Channel Frequencies
Channel Number HUM-900-DT
Frequency (MHz)
0 904.5
1 911.5
2 918.5
3 925.5
Figure 16: HumDT TM Series Transceiver Frequency Agile RF Channel Frequencies
Networking
Each module can be configured as one of three device types; Access Point
(AP), Range Extender (RE), and End Device (ED). These device types play a
specific role in creating a star network.
The AP acts as the hub in a star network. It is an always-on device and
only one AP is permitted per network. It receives all packets within its range
and is capable of relaying messages from one ED to another.
The REs are always-on devices that extend the radio range on a network.
They retransmit all received messages from devices in its network that
are within range. This relaying of data extends the range of the network.
Networks are limited to a maximum of four REs.
EDs are the simplest devices. They perform the actions in the network,
such as remote control handhelds, sensors and actuators. The EDs may
be battery powered and can be put into a low power mode to save current
consumption.
There can be a maximum of 50 EDs in each network, with 1 AP and up to
4 REs.
Each ED communicates with the AP either directly or through an RE. The
AP can output the received data from the ED or forward the data on to
another ED, depending on the addressing in the packet.
The AP sends out a beacon message about every 30 seconds to maintain
the network. This is an automatic message and is not output by the
module, though the MODE_IND line indicates the activity.
Message to Access Point
Message repeated through Range Extender
AP RE RE
ED ED ED ED ED
ED
ED ED ED ED ED
ED
Figure 17: HumDT TM Series Transceiver Star Network