Reducing Delay for Analog Simulcast

With an analog IP simulcast system, the access time has increased such that the originator of a subscriber transmission may hear the conclusion of the audio after dekey in a radio-to-radio call.

The echo risk may be mitigated by adjusting user-configurable parameters in the MLC 8000 Configuration Tool. The echo period is dependent on the delay through the infrastructure and the receive qualifiers configured in the subscriber.

All of the parameters in the following table can be used to reduce overall access time.

Timing Dependencies
Parameter Default/ Range Description of Parameter Considerations
Analog Voting Sample Period 50 ms/5 ms to 10000 ms Sets the Signal Quality Measurement (SQM) sampling window length at the MLC 8000 Subsite Link Converter. During this window, the Digital Signal Processor (DSP) collects the voice stream coming from the base radio. After the window has closed, the DSP calculates the SQM value from the collected samplings. The SQM number represents the quality of the received voice. Some loss of voting quality is expected as sample time is reduced. Voting quality is commensurate with the sampling duration.
Link Delay 80 ms/80 ms to 300 ms From the first SQM value received at the voter, the voter starts the Link Delay timer and collects all SQM values in between. This is the expected maximum inbound link delay, which is a function of transport delay plus the transport delay variation. The amount of reduction is coupled to behavior of transport on the system.
Simulcast Launch Time Offset 0 ms/000 ms to 999 ms The Simulcast Launch Time compensates for the network delay variation.
  • Generally can be lowered if the network has stable (low jitter), high-speed transport.
  • Directly reduces overall access time, specifically delay, for IP simulcast systems.
  • Too low of reduction results in launch time errors which leads to audio quality issues.
Audio Truncation Enabled/[Enabled..Disabled] If checked (enabled), the default value, inbound audio samples used for calculating the SQM are discarded and the audio is played with truncation. If unchecked (disabled), the inbound audio samples used to calculate the SQM are played. If enabled, causes audio processed during the sample period to be expressed as truncation which helps mitigate echoing effect. If disabled, the sample period contributes to delay.