Wireless Roaming Between Multiple Hubs

You can install our pulsAR wireless ethernet bridge radios in your service vehicle and stay connected to a control center by automatically roaming between multiple fixed hubs.  This is ideal for applications where vehicles must move beyond the range of a single hub radio.

All the hubs are typically connected, through a backbone network, back to a central site. This backbone network can be wired or wireless.  The overall system supports the following features:

• Mobile nodes automatically attach to the strongest hub.
• As a mobile unit moves and the link to its hub fades, the mobile radio changes autonomously to attach to a stronger hub.
• Connectivity to a central site, through a backbone network, is maintained when a mobile changes hubs. Packet routing is switched over autonomously throughout the network so that packets are correctly routed immediately after the mobile radio changes hubs.
• The fixed radios can be used to support the roaming operation and also make up the backbone network by using our the WIreless Mesh tree topology (exemplified in the figure).

Roaming Operation

To support roaming operation you must configure each hub to operate on its own channel (transmit and receive), which must not overlap with the other hubs within RF range.  For large networks, after using 6 different channels you can start reusing channels in hubs that are far apart.

At a roaming radio you can specify up to 6 different receive channels. The "rf-1-setup" command accepts a list of channels separated by commas, for example:

>rf-1-setup receive-channel=11,18,23,30

At each mobile radio you configure this list to match the transmit channels assigned to the hubs. When the mobile radio powers up, it first monitors the environment, listening sequentially in each of the receive channels in its list. Once it determines the strongest hub it attaches to the network through that hub.

Once attached, a roaming radio "steals" one out of every 32 cycles (once every 640 ms) to receive in one or more of the other channels. This way the radio keeps track of all other hubs that are within range and their respective signal strengths. You can monitor this process with the command:

>monitor roaming

Each roaming radio decides on its own when to switch to another hub. If the signal strength from the current hub drops down to a point where the link performance becomes compromised, and there is a stronger signal from an alternate hub, then the mobile radio drops its current link and reattaches to the stronger hub. Once it reattaches to the network, the roaming radio broadcasts its new position so that all the equipment in the network will update their routing tables accordingly. Overall the switch-over takes less than 200 ms.

You can view a list of all radios in the network and their current topology with the command:

>show radios

Roaming License

The radios need to be licensed for this capability. When you attempt to configure multiple receive channels you may get a message indicating that the radio is not enabled for roaming. In that case, contact Afar Communications to purchase the key. You will need a key for each roaming radio and also for the hubs where roaming radios attach.