Receiver late entry unsquelch delay, Transmitter power and encoder attack time, Receiver throughput delay – Codan Radio P25 Training Guide User Manual
Page 55: Transmitter throughput delay
P25 RADIO SYSTEMS | TRAINING GUIDE
Chapter 3: P25 Technical Information Page 47
The following defi nitions for a P25 system are as follows (from TIA-102.CAAA-A):
Receiver Late Entry Unsquelch Delay
The late entry unsquelch delay is the time it takes for a receiver to detect the frame synchronization
and network ID on a digital message and generate an audio output. The test is performed for late entry,
which means that the synchronizing preamble (Header Data Unit) is absent from the message, and the
receiver must detect frame synchronization during the middle of the message. This test applies to a
transceiver in the conventional mode of operation.
Transmitter Power and Encoder Attack Time
Transmitter power and encoder attack time is the time required for a transmitter to prepare and transmit
information on the radio channel after changing state from standby to transmit. This test applies to a
transceiver in the conventional mode of operation.
According to TIA-102.CAAB-B, a P25 system could have a maximum Receiver Unsquelch Delay of up
to 460 ms (if both talk groups and encryption is used) and a maximum Transmitter Power and Encoder
Attack Time of 100 ms (50 ms Power Attack Time; 100 ms Encoder Attack Time). Receiver Unsquelch
Delay can be reduced to a maximum of 370 ms if only the talk group OR encryption is used (not both).
If neither talk groups nor encryption is used the maximum Receiver Unsquelch Delay is 125 ms. In
most P25 systems the attack times are relatively close to these maximum values.
P25 Radio Systems also specify a Throughput Delay as follows (from TIA-102.CAAA-B):
Receiver Throughput Delay
Receiver throughput delay is the time it takes for a receiver to produce an audio output following the
introduction of a tone test pattern.
Transmitter Throughput Delay
The transmitter throughput delay is the time it takes for audio changes in the microphone to be encoded
and transmitted over the air.
Throughput delays are separate from attack times. Throughput delays assume that the equipment is
already powered and operational. TIA-603-C does not specify an audio throughput delay for analog
systems, as the throughput delay is typically negligible. P25 radio systems require much more
processing time (Digital Signal Processing, Vocoding, etc.) and typically have much greater throughput
delays than conventional analog.