AC4490 User Guide
Version 4.5
Laird Connectivity Solutions Support Center:
http://ews-support.lairdtech.com
32
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Europe: +44-1628-858-940
Hong Kong: +852 2923 0610
Figure 4: Loopback Repeater
If radios B & C in the above picture are not within range of radio A, they will not be able to receive or
respond to communications from radio A. A loopback repeater can be added between the three such that it
is in range of both radio A and radios B & C. When the repeater receives a packet from radio A, it will
transmit the packet out to radios B& C. If the repeater is set to Broadcast mode, radio A will receive a copy of
each packet that it sends. If the repeater has a specific destination address (i.e. 12 34 A2), then radio A will
not receive the packet as its MAC address will not match the specified destination address.
Time Division Multiple Access Network
For a more intelligent network, a Time Division Multiple Access Network (TDMA) system can be implemented.
In this system various radios transmit data to a SAP during an assigned time interval. The system is
synchronous so that only one radio is transmitting at a time and has full access to the SAP’s bandwidth. In a
TDMA network, each radio must store its data for the amount of time between its transmissions or bursts. A
typical format for data passing through a SAP is shown in
. A frame consists of arriving bursts from
remote radios and each frame is then divided into multiple time slots. The bursts can be of varying lengths
and can be longer for heavy-traffic stations. To prevent overlaps, guard intervals can be inserted to absorb
small timing errors in burst arrivals.
Figure 5: Quad Intervals
Example:
SAP sends broadcast packet which includes a sync pulse
Remote radios hear the sync pulse and join the session
Radio A transmits during time interval t = 1
Radio B transmits during time interval t = 2
Radio N transmits during time interval t = N – 1
