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P440 Data Sheet / User Guide
efficiency of this ALOHA network is approximately 38%, making it equivalent to the
performance of a Slotted ALOHA system.
If the TDMA protocol is used, then the user can define a slot map that provides each radio
with an indication of when and to whom and with what parameters it should communicate.
An example slot map is shown below in
Figure 5
. The slot map shown is for a system of 4
nodes (100, 101, 102, and 103) in which 100 and 101 range to each of the other three and 102
ranges to 100 and 101.
Fig. 5: Representative RangeNet slot map
Maintaining system synchronization is the responsibility of the P440 processor and it does so
with an accuracy of 1 μs.
Because the P440 supports multiple communications channels, it is possible to operate either
the ALOHA or TDMA protocol with a CDMA overlay.
Because the P440 network schedules range requests, it avoids the overhead of Host to P440
communications and can therefore run at a higher ranging rate.
The P440 network maintains a neighbor database. Besides noting all of the members of the
network and their ranges, this database also contains a large body of statistics and other
useful information. For example, the database includes SNR, approach velocity, effective
ranging rate, and signal quality.
TDMA Slotmap
