User's Manual

pulsAR radio Operator’s Manual

2-6

Control center

branch

root-1

Figure 2.3– Roaming vehicles attaching to any of three access points

Each roaming radio decides on its own when to switch to another access point. If the signal strength

from the current parent drops down to a point where the link performance becomes compromised,

and there is a stronger signal from an alternate access point, then the mobile radio drops its current

link and reattaches to a stronger parent. 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 250 ms.

Redundant hub operation: In a point-to-multipoint deployment it is often desirable to deploy the hub

site with two redundant radios. You can use the roaming feature to achieve this result. Configure the

two hubs to different non-overlapping channels. Configure all the remotes to roam between the two

hub channels. If one of the hub radios fail, or if there is interference in one of the channels, the

remote radios will automatically attach to the other hub.

In this application, since you would be co-locating the two hub radios, you need to pay attention to

the possibility of self-interference. Section 2.4 describes this issue and what you need to do to avoid

it.

2.3 Time Division Duplex

2.3.1 Fixed and variable cycle split

The PulsAR radio operates in Time Division Duplex (TDD) mode meaning that the radio switches

between transmit and receive over RF. In a point-to-multipoint topology this cycle consists of one

phase used for outbound transmissions (from parent to children) and a separate phase for inbound

transmissions (from the children to the parent). In the tree topology the cycle includes four phases: a

branch node first communicates with its children (transmit and then receive) and then with its

parent(receive and then transmit).

The radio provides two parameters that let you configure the TDD operation to best suit your

application. You can select the total cycle period between 20 and 40 ms and you can control the

cycle split to favor either outbound or inbound traffic. You only need to set these two parameters at

the hub or root node: all the children will pick up these TDD values from their parents.