User's Manual

30 Document Number: 0100SM1401 Issue: 12-16

Digital Collision Avoidance Example 2

This flow chart shows the C/A operation in a remote

radio with the following configuration:

• C/A: Digital

• Backoff Method: Delay Before Tx attempt

• Backoff time:

- Max Slots: 16

- Slot Time: 20ms

• Data Priority: Tx Data

Data waiting to be

transmitted

Wait a random

time

Is C/A busy

flag set?

Transmit data to

C/A master

Yes

Rx data ‘Priority’:

In PTMP/R system topologies, where the Entry Point radio is half duplex, the configuration of Rx data priority may be required.

This is particularly useful for asynchronous traffic, such as a combination of SCADA exception reporting and polling. In this

scenario, the probability that a data packet currently being receive by the Entry Point radio is for the Entry Point radio and not

for a remote, is high. Therefore, without Rx data priority, incoming packets to the Entry Point radio would be lost if priority was

given to transmitting packets.

The primary difference when compared to example 1, is that the radio applies the random wait time before any attempt is

made to check the C/A busy flag.

This collision avoidance configuration provides maximum radio channel efficiency when there is synchronous data traffic on

the radio channel (i.e. GPS timing, synchronous exception reports) .

When data is ready to be transmitted, the remote radio

waits a random time before checking the C/A busy flag

to see if it is set (i.e. is the C/A master receiver busy). If

the C/A busy flag is clear, the data is transmitted to the

C/A master. If the C/A busy flag is set, the radio repeats

the wait time and tries again.

Part D – Feature Detail