Simulcast, multicast or hybrid?
|One channel at each of the simulcasting sites transmits the same signal simultaneously at the same frequency||One channel at each of the participating sites transmits the same signal simultaneously at different frequency|
|Requires high level of signal control in any overlap area||No comparable requirement|
|Ease of roaming||Roaming manual or requiring advanced technology|
|Requires complex system failure scenarios planning||No comparable requirement|
|Frequency efficient||Frequency consuming|
|Requires identical number of repeaters at each site, even where traffic loading is low||Equipment (repeater) efficient, allows different number of repeaters at each site|
|Requires voting||Conventional multicast may require voting, trunked multicast does not|
Each approach has distinct advantages and disadvantages, but, in practice, in majority of Public Safety applications, the advantages of simulcast (ease of use and spectrum efficiency) will outweigh its disadvantages (typically higher costs and higher maintenance requirements). A complete and comprehensive analysis of pros and cons of simulcast vs. multicast is complex, and the outcome will depend on your particular circumstances.
It is possible and indeed common to combine simulcast and multicast into a hybrid architecture. This is most advantageous where the system needs to cover both high density urban areas with a large number of users and high number of channels, as well as larger areas with low density and subsequent limited need for channels.
Network capacity engineering is relatively simple for single site systems or for pure simulcast systems, where one frequency pair = one channel. But quickly becomes very complex for multicast or hybrid systems. Your capacity needs will determine the number and location of repeaters. While network capacity engineering can be complex, you can start by applying this simple rule of thumb: about 70 users per working channel.
Keep in mind that in a trunked P25 system, one channel per site acts as a control channel so is unavailable for voice traffic.
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