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DNT24 Integration Guide - 10/19/11
One disadvantage of direct sequence systems is that due to design issues related to broadband transmit-
ters and receivers, they generally employ only a minimal amount of spreading, often no more than the
minimum required by the regulating agencies. For this reason, the ability of DSSS systems to overcome
fading and in-band jammers is relatively weak. By contrast, FHSS systems are capable of hopping
throughout the entire band, statistically reducing the chances that a transmission will be affected by fad-
ing or interference. This means that a FHSS system will degrade gracefully as the band gets noisier,
while a DSSS system may exhibit uneven coverage or work well until a certain point and then give out
completely.
Because it offers greater immunity to interfering signals, FHSS is often the preferred choice for co-located
systems. Since direct sequence signals are very wide, they can offer only a few non-overlapping chan-
nels, whereas multiple hoppers can interleave, minimizing interference. Frequency hopping systems do
carry some disadvantages, in that they require an initial acquisition period during which the receiver must
lock on to the moving carrier of the transmitter before any data can be sent, which typically takes several
seconds. In summary, frequency hopping systems generally feature greater coverage and channel utiliza-
tion than comparable direct sequence systems. Of course, other implementation factors such as size,
cost, power consumption and ease of implementation must also be considered before a final radio design
choice can be made.
2.0 DNT24 System Overview
A DNT24 radio can be configured to operate in one of three modes -
base, remote
or
router
. A
base
con-
trols a DNT24
system
, and interfaces to an application
host
such as a PC or Internet gateway. A
remote
functions to transmit or receive serial, digital (state) and analog data. A
router
alternates between func-
tioning as a
remote
on one hop and a
network base
on the next hop. When acting as a remote, the router
stores messages it receives from its
parent,
and then repeats the messages to its
child
radios when act-
ing as a network base. Likewise, a router will store messages received from its child radios when acting
as a base, and repeat them to its parent when acting as a remote. Any message addressed directly to a
router is processed by the router rather than being repeated.
2.1 Point-to-Point Systems
A DNT24
system
contains at least one
network
. The simplest DNT24 topology is a point-to-point system,
as shown in Figure 2.1.1. This system consists of a base and one remote forming a single network. Point-
to-point systems are often used to replace wired serial connections. Point-to-point systems are also used
to transmit switch positions or analog signals from one location to another.
Figure 2.1.1
