Download A Spatial Computing Aproach to Programming Large Scale Wireless

Time (us)
Evaluate Message Time
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Figure 6.14: Variation of time to evaluate a received message.
V M T ime + 0.17 (in ms) – the constants are the worst case execution
times for message evaluation and prepare message
• The following condition must be satisfied: W orstCaseExecutionT ime <
F rameT ime
6.4
Throughput
In section 5.2 we have described a number of Myria–Proto operating modes
implemented to enable the execution of the Proto virtual machine on a low
throughput communication wireless sensor network. However, the communication throughput can also be improved by modifying various gMac parameters or the TDMA scheduling algorithm. For example, for a small–scale
network a simple TDMA scheduling is preferable. Figure 6.15 depicts the
average number of messages received by a node in a network composed of 7
nodes that use the simple TDMA scheduling protocol (a fixed TDMA slot is
assigned for each node in the network). The nodes run an application that
generates a broadcast message each round. We observe that, on average, a
node receives messages from 85% of its neighbors. However, the scheduling
is not scalable and the number of TDMA slots increases proportionally with
the number of neighbor nodes. The gMac active period increases and consequently the radio is active for a longer period and the node becomes less
energy efficient.
The usual scheduling algorithm used in MyriaNed application development is distributed Aloha, an extension of the Aloha protocol with a dynamic behavior dependent on the number of neighbors [38]. Aloha provides
35% throughput at maximum network load. In the distributed Aloha version the maximum network load is attained when the number of virtual slots
multiplied by the number of TDMA active slots is equal to the number of
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