IDAS™ Digital Simulcast
- IDAS Advantages
- Application Example
Wide Area Coverage on a Single Pair of Frequencies
The IDAS Simulcast synchronizes multiple repeater sites for seamless wide area repeater coverage using just a pair of frequencies, regardless of the number of repeater sites in the network*. Each repeater site in the system is simply composed of only a network controller, GPS antenna and repeater. No external timing reference unit, no additional modulation unit or other equipment is required.
* The maximum number of sites for an IDAS Simulcast system is 32.
Simulcast repeaters transmit a signal on the same frequency and at the same time with GPS synchronization. Using the digital signal, the IDAS simulcast system can greatly reduce signal degradation in overlapping areas. By tuning the timing of the repeater transmission, overlapping signal areas can be adjusted relatively simply.
Simulcast Selects the Best Signal
Uplink signals received by each repeater site are first collected by the Master Repeater (Controller) through the network. The best uplink signal is selected and distributed to all repeater sites to be retransmitted.
Abundant IDAS Radio Lineup
All NXDN™ compatible IDAS radio terminals can be used on the IDAS simulcast system. In addition, the radio terminals wait for a call without scanning, so the battery consumption can be reduced. It extends the operating time, when compared to a conventional multi-site system.
Scalability and Flexibility
Installation and maintenance of a simulcast system could not be easier. You can effortlessly expand the coverage area by just adding repeaters. Additional pairs of frequencies are not required. Those repeaters can be integrated into the network with simple setup (No reprogramming of radio terminals is necessary).
6.25 kHz FDMA Technology is ideal for Simulcast
In a simulcast system, there is an overlapping area where multiple signals arrive from two or more repeater sites. Delay spread means the time difference between receiving the signals, according to the distance from the respective repeater sites. Delay spread can make received audio unintelligible, similar to multipath fading, which reduces repeater coverage.
The IDAS Simulcast system sends digital voice and data in 4800 bps using 4-Level FSK, and 6.25 kHz very narrow bandwidth FDMA technology. Symbol duration is about 420 microseconds (μs). This long symbol duration affects very small Inter-Symbol Interference (ISI). As a result, the delay spread tolerance of the IDAS Simulcast system is about 60 μs. The simplicity of a non-linear transmitter and GPS synchronization enables an FDMA digital system to achieve wide repeater coverage as an analog FM simulcast system.
By comparison, the delay spread tolerance of a DMR/P25 Phase 1 system is about 30 μs, the coverage radius is reduced by a similar amount. In a P25 simulcast system, a more complex Linear Simulcast Modulation system is required to maintain a better tolerance to delay spread and for greater repeater coverage.