6.1. an introduction to preamble sampling

Nodes using preamble-sampling are not synchronized. Instead, nodes periodically listen for a very short time (called Clear-Channel-Assessment, or CCA ) to decide whether a transmission is ongoing. We call check interval ( CI ) the amount of time a node waits between two successive CCAs. The sender needs to make sure thereceiver node is awake before sending data; it prepends a (long) preamble to its data. By having the preamble at least as long as the wake-up period, the sender iscertain that the receiver will hear it and be awake for receiving the data.

The figure below is a chronograph depicting the radio state of node S and its three neighbors A , B and C . A box above/under a vertical line means the node's radio is transmitting/ receiving, respectively. No box means the radio is off. All nodes sample thechannel for Dcca seconds every CI seconds.

In this Section, you will implement a simplified version of preamble sampling:

• there is no data;
• the preamble is cut into a series of micro-frames. Each micro-frame contains a counter indicating how many micro-frames still remain. A micro-frame is sentevery Tmf seconds, and lasts for Dmf .