Portable and mobile radios typically have considerably lower transmit power levels due to size, exposure and cost considerations. This means a single repeater may not be able to receive transmissions from all radios operating in the coverage area at a sufficient signal strength to provide reliable communications.
Potential applications for Digital Voting include systems where the SL4000 or DP4000Ex are used or where there are critical talk-in gaps in the system coverage area.
For a Digital Voting system, multiple Satellite Receivers are installed to relay radio transmissions to a central Voting Repeater. The Satellite Receiver is a standard (receive-only) repeater used to extend the system’s inbound range. When a Satellite Receiver receives an acceptable signal transmitted by a radio, the signal is relayed back to the Voting Repeater over an IP link.
The Voting Repeater is a receive-and-transmit repeater with a built-in voting capability. The Voting Repeater checks the quality of the received signal from all Satellite Receivers, as well as its own internal receiver then selects the best copy of the received transmission and ignores the rest.
This selection is called the voting process and is accomplished by determining the best received signal, based on the signal-to-noise ratio of the signal or the bit error rate. The voted result is then repeated over the air by the Voting Repeater, and where applicable sent to the other sites or applications.
The digital voting feature needs to be activated in voting repeaters, but not satellite repeaters. Other features activated in a voting repeater (e.g. Capacity Plus, Linked Capacity Plus) need also to be activated in the associated satellite repeaters.
The (one way, not round trip) latency between the Voting Repeater and any of its Satellite Receivers must be less than or equal to 40ms. Additionally, the network asymmetry between the Voting Repeater and any of its Satellite Receivers must be less than or equal to 12ms.
The network asymmetry is the absolute value of the time difference for an IP packet to travel from the Voting Repeater to the Satellite Receiver, and from the Satellite Receiver to the Voting Repeater. This applies to all system configurations.
Most business grade IP networks are able to meet this 40ms per 12ms network requirement.
The maximum number of Satellite Receivers for a specific Voting Repeater depends on the number of repeater sites and Peer Data and Voice applications. The below table shows the maximum number of Satellite Receivers supported per Voting repeater in a multi-site system.
Below is an example of a conventional single site voting system with 4 Satellite Receivers (in accordance with the Satellite Receiver Consideration slide, up to 7 Satellite Receivers can be added to this system).
|Single site voting arrangement|
For an IPSC Wide Area Channel, it’s not necessary to have the same number of Satellite Receivers at each site. The following example shows a two-site IPSC voting system where each site has four Satellite Receivers.
|Two site IPSC voting arrangement|
In order to obtain the same inbound-outbound coverage, from channel to channel, in a Capacity Plus or Linked Capacity Plus system, a Satellite Receiver for each Trunked RF Channel needs to be placed at every selected Satellite Receiver location. Hence, each trunked channel requires the same number of Satellite receivers as the others.
In order to obtain the same coverage with the Data Revert Channels, a Satellite Receiver for each Data Revert channel will also need to be placed at every selected Satellite Receiver location. However, it is not essential that the Data Revert coverage is the same, therefore this is only a recommendation.
The following example shows a Capacity Plus voting system with 2 RF Channels where each RF channel has four Satellite Receivers.
|A single site LC+ or C+ Digital Voting arrangement|
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