Digital Signal Processing Reference
In-Depth Information
Fig. 6.12
The resulting Energy-TXOP Pareto-optimal trade-off curves to be combined at run-time
to achieve the network optimum
Fig. 6.13
MAC with two-frame buffering in the Scheduler Buffer to remove data dependencies
and maximize sleep durations. By the third period of the single flow shown, frames 1 and 2 are
buffered and frame 1 begins service. As the transmission duration of frame 2 is known at this time,
the sleep duration between completion of frame 1 until the start of service of frame 2 is appended
in the MAC header
scheme described in Sect.
6.3.2
. The scheduler requires feedback on the state of
each user and then communicates the decisions to the users. In order to instruct a
node to sleep for a particular duration, the AP needs to know when to schedule the
next packet. Waking a node earlier than the schedule instance will waste energy.
Buffering just two frames informs the AP of the current and also the next traffic de-
mand, allowing a timely scheduling and communication of the next period TXOP. In
the ACK, the AP instructs the node to sleep until the time of the next TXOP mean-
while also communicates the required configuration. The AP now communicates
with each node only at scheduling instances (Fig.
6.13
). As the real-time packets
are periodic, we eliminate by doing so all idle time between transmission instances.
When a node joins a network, it sends its cost, resource and quality curves (stored in
its driver) to the AP during the association phase. The AP then stores this and refers
to it during each scheduling instance. By adding just three bytes in the MAC header
for the current channel state and the two buffered frame sizes, each node updates the
AP of its current requirement in every transmission. Protocols such as 802.11e pro-
vide support for this communication and therefore require only minor modifications.
The AP then fetches the predetermined set for the current state from memory. In the
