AC4868 868 MHz Transceiver
User’s Manual
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Laird Technologies
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www.lairdtech.com/ramp
System Timing and Latency
Care should be taken when selecting transceiver architecture, as it can have serious effects on data rates,
latency, and overall system throughput. The importance of these three characteristics will vary from system to
system and should be a strong consideration when designing the system.
Engineer’s Tip: In High-density applications, what amount of latency should be expected?
It is not easy to predict the exact amount of latency in high-density applications. There are
many variables that affect system latency. The three variables that most affect the latency
are the network load, the distance between transceivers, and whether the transceivers are
operating in a broadcast or addressed mode. There is no fixed answer as to how much
latency will be introduced in the system when considering high-density applications. In
these cases we can just offer qualitative analysis of the latency in high-density applications.
As the network load increases, then the number of collisions that will occur increases. As
the number of collisions increase, then the system latency increases. As the distance
between the transceivers increases, so to does the system latency. Finally, when
transceivers operate in addressed mode they will retry sending a packet up to the number
of time specified in the transmit retry parameter specified in the EEPROM. As the number
of retries increases, the system latency will increase also.
System Throughput
When operating as shown below, an AC4868-250 transceiver is capable of achieving the listed throughput.
However, in the presence of interference or at longer ranges, the transceiver may be unable to meet the
specified throughput.
Table 8: Maximum system throughput
RF Mode
RF Baud (determined by
interface baud)
Half Duplex Throughput
(bps)
Full Duplex Throughput
(bps) each way
Addressed
28800
15k
7.5k
Addressed
19200
6.8k
3.4k
Addressed
28800
18k
9k
Addressed
19200
12k
6k
