A static value of TA is chosen to
be 1.5 times the minimum value of TA.
The early sleeping problem is noticed by the TMAC authors in unidirectional
source to sink communication. Figure 6 explains this problem. Node C
is aware of node A transmission to B, however node D is not and will go to
sleep after TA seconds. When A transmission to B is over, C cannot transmit
its data to D since D is sleeping. The future request to send packet technique is
proposed to overcome the early sleeping problem. When node C overhears the
CTS packet coming from node B, it will immediately send a Future Request
To Send (FRTS) packet to inform node D to wake up when A??™s transmission
to B is finished. In oder to avoid collision at node B between the data packet
coming from node A and the FRTS packet coming from node C, node A first
transmits a Data-Send (DS) packet of size equal to the FRTS packet, but
this DS packet contains no useful information. After sending the DS packet,
node A starts transmitting its data packet to node B. The future request to
send packet technique, however, may result in more energy loss during heavy
tra?±c, which is undesirable in WSNs.
TMAC performance is compared against the performance of SMAC and
CSMA protocols using OMNeT++ simulator [14]. TMAC energy savings are
better than SMAC, however, TMAC throughput (bytes per node per second)
is less than SMAC at heavy tra?±c due to the early sleeping problem.
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