User's Manual

14 DRAFT 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