User's Manual

P440 Data Sheet / User Guide DRAFT 13
Fig. 4: Signal (green), Noise (blue), and SNR (red) of a link as function of separation distance.
(Note the Fresnel cancellation and enhancement.)
2.4.2 Networking with RangeNet
Operating a system that consists of only two units is very simple. Operating with more than two units
starts to introduce significant complexity. For example:
 The number of radios in the system may vary with time. Units that enter the system need to
be discovered. Units that exit the system need to be removed from the network.
 There needs to be a way to prevent units from interfering with each other.
 Not all units need to behave the same way. Some units might initiate and respond to range
measurement requests. Some might only initiate requests. Some might only respond. Some
units might only communicate with a subset of the system.
The RangeNet API allows the user to define a network and to define the behavior of the radios in the
system. Operation of the network is controlled by the P440. In particular, the P440 is responsible for
scheduling range requests, maintaining all of the neighbors in a database, and passing data between
the Host and the network. The Host computer function is thereby limited to monitoring and
supervision, thus significantly offloading its responsibilities.
The RangeNet API provides the user with tools to define and monitor the network. For example:
 A network can be defined using two different time-sharing protocols: ALOHA (randomized)
or TDMA (Time Division Multiple Access).
 If the ALOHA protocol is used, then the average interval and the random variation of that
interval can both be defined. The average interval can be manually or automatically throttled
based on the number of units in the system. Radio behavior can be limited on a per unit basis
such that some units initiate and respond to range requests, while others initiate-only or
respond-only. In addition, some units can be instructed to limit their interactions to a subset
of the network members. While most ALOHA networks have an efficiency of 19%, the