P440 Data Sheet / User Guide
DRAFT
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The network also takes advantage of two features available with simple ranging applications,
Echo Last Range (ELR) and Coarse Range Estimate (CRE), but which find special utility
when used in a network. ELR takes advantage of the fact that all units can receive any
transmission. Whenever a unit requests a range from a particular unit, it also transmits the
last successful range measurement and node number of the corresponding unit. This
information is effectively broadcast to all units in the area. This mechanism therefore
distributes network range information throughout the units in the system.
CREs take similar advantage of the broadcast nature of transmission. When a unit receives a
transmission it will automatically generate a waveform scan and measure the strength of the
first arriving energy. This yields a number similar to RSSI, but which is different in two
ways. First, the strength measured is proportional to the strength of the first arriving energy
and not, as in the case of RSSI, the peak strength of any signal. Second, while RSSI is rarely
if ever calibrated, the CREs are calibrated based on the last time the unit successfully
completed a TW-TOF range measurement with the target unit. While the accuracy of a CRE
does not compare with the accuracy of the TW-TOF measurement, its level of accuracy is
frequently good enough to be useful and it has the added benefit of expanding the network
knowledge without incurring any cost.
While these are all powerful network tools, the complexity inherent in this richness can make it
difficult to visualize and operate through just the API. The RangeNet GUI fills this gap. Not only
does it allow the user to configure the system, but it also provides a means for easily maintaining
different configurations, monitoring results, evaluating the performance of individual links in the
network, and monitoring the neighbor database. For example, RangeNet allows the user to:
Define all types of configuration information (including TDMA slot map, ranging
configuration details, ALOHA setup information, neighbor database characteristics),
download it to the P440, store that configuration to disk, and recover from disk any given
configuration.
Monitor the database at whatever update rate the user finds useful.
Figure 6
illustrates the
database from a 4-node system. Note the extent and volume of statistics maintained in the
database. (For details on the meaning of specific fields, refer to the RangeNet User Guide.)
Send, receive, and display data.
Display waveform scans associated with a particular link.
