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Digital SimplexRepeaters
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Digital Simplex Repeaters• Intended to provide indoor coverage extension to radio equipment operating in
SIMPLEX mode.
• Channel selective operation that allows the handling of specific channels, up to 12 simultaneously.
• Solution based on Digital Signal Processing, FPGA based, which allows a more precise operation compared with traditional analog systems.
• Digital Simplex Repeaters (DSR) are equipped with 4 antenna ports: Inbound in, Inbound out, Outgoing in, Outgoing out.
• The sensitivity is user programmable per channel and per direction.
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Overall Specifications• Fully digital repeater, FPGA based.
• Available for VHF, UHF, 700 and 800MHz.
• Compatible with P25 (Ph1 & 2), TETRA, TETRAPOL, DMR, NXDN and Conventional systems
• Channel Selective (12 channels), software programmable.
• Several filter masks available. Different group delays.
• Auto diagnostic capability.
• Built-in spectrum analyzer, no need of additional test instruments for setup.
• Adjustable squelch, programmable per channel and per direction.
• User adjustable gain control, per channel, per direction.
• Automatic Gain Control, per channel, per direction.
• Local and remote connectivity: USB, Web Browser, SNMP.
• Weatherproof enclosure, IP67/NEMA4X
• NFPA compliant.
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How Digital Simplex Rep. works?• The following diagram shows the actual topology of the Digital Simplex Repeater (DSR)
solution:
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How Digital Simplex Rep. works?• To make it simple to understand, let’s focus on how a single channel works. The
following diagram shows just a DSR single channel. This single channel topology is multiplied by 12 inside the DSR to provide multiple channel operation.
• The heart of the DSR is its FPGA module, that constantly converts RF signals from the analog to the digital world, process them, and reconverts back to the analog world in order to be retransmitted.
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How Digital Simplex Rep. works?• When no carriers are present (IDLE state), the DSR is “listening” in both directions.
• While in IDLE state, there is no amplification and outputs are “disconnected”, so no feedback loops are possible.
• FPGA Control Unit (CU) is constantly measuring the received signals strengths per channel, simultaneously in both directions. Comparison is made in the digital world (“0” and “1”).
• Being in the digital world, the measuring is done sample by sample, both directions at the same time, which allows for a precise comparison of the received signals in both directions.
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How Digital Simplex Rep. works?• When a received signal strength from one of the directions is above the user defined
sensitivity level, then the CU understands that there is a communication trying to be established in that particular direction (working direction), so the following steps are exectued by CU of DSR:
– CU will not “hear” the opposite direction, for that specific filter, while the received signal strength of the working direction is still above the sensitivity value.
– CU will connect the “output switch” of the channel on the working direction.
– CU will keep disconnected the “output switch” of the channel on the opposite direction.
– The amplification of the working direction is done while CU determines that the received signal strength is still above the sensitivity level.
– When the CU determines that the received signal strength of the working direction falls below the sensitivity level, the entire channel returns to the IDLE state.
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Q & A• How fast is the switching to avoid creating a feedback loop?
• Since the measuring, comparison and actuation is made sample by sample in the digital world, there is no amplification (or connection) of a working direction without being previously disconnected in the opposite direction. Digital signal processing does not allows the existence of any transitory state that is so often seen in the analog world.
• How the system is protected against false actuations?
• Actuations are only produced when a received signal is above the user defined sensitivity level for a particular channel and a particular direction. Measuring is made after the channel filter, which allows for a measuring only of the channel signals. So, if the sensitivity level is properly adjusted and the filter type is properly chosen, system will only actuate when desired signals are present at the DSR inputs.
• How do I choose the proper filter type?
• There is a basic rule (physics law) that says that the narrowest the channel and the highest the adjacent channel rejection, the highest the group delay. Group delay is a measuring of how much time takes to the signal to pass thru the DSR, which is a certain limitation for some TDMA systems like TETRA, P25 Ph2 and DMR. The best way to determine the type of filter is to analyze how much rejection should / can I apply to the adjacent channel and … (cont)
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Q & A• (cont) … to understand how the group delay affects the communications system
performance. Analog systems (NBFM) are not affected by the maximum group delay of the narrowest available filters. For DMR, TETRA or P25 Ph2, the maximum talk around time must be analyzed to determine which is the narrowest filter that can be used.
• How many filter types are available?
• DSR are equipped with several filter types, each filter type is determined by its operational BW: 12.5KHz, 25KHz, 30KHz, 45KHz and 90KHz. Custom made filter types area available and can be downloaded to the DSR.
• What happens with adjacent carriers?
• Adjacent carriers are first rejected by the channel filter before they can reach the signal strength measuring stage, which drastically reduces the possibility than an adjacent carrier may produce a false actuation of the DSR. Besides this the SDR is equipped with a user programmable adjacent carrier alarm level, which can report any dangerous adjacent channel carrier level.
• What are the design or installation constraints?
• A proper indoor coverage extension design must be done, starting by a coverage prediction (iBWave or similar). DSR is equipped with 4 antenna …. (cont)
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Q & A• (cont) … ports, one for the Inbound input antenna, a second one for the Outgoing
output antenna, a third one for Inbound output antenna (or antenna network, for the indoor), and a forth one for the Outgoing input antenna (or antenna network, also for the indoor). The calculated and measured “antenna-to-antenna” isolation at the DSR ports must be 70dB min.
• What happens if for the same channel, two communications are being established at the same time (someone at the outdoor and someone at the indoor pushing the PTT at the same time over the same channel)?
• That collision case is solved by defining the “priority” of the amplification. Priority is user defined channel by channel, and can be “Outgoing priority” or “Ingoing priority”. Factory default is “Outgoing priority”.
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Built-in Spectrum Analyzer
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Simplex Repeater cabinet
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NFPA Alarms
BDA
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Connectivity Types
Local
Ethernet Web Browser
USB pFOMS
Remote
Ethernet Web Browser (Requires static IP)
Ethernet FOMS / NMS (SNMP)
Wireless Modem FOMS / NMS (SNMP)
BDA
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Fiplex Communications, Inc.
Headquarters & Distribution Center7331 N.W. 54th Street. Miami, FL 33166. US
Ph: +1 305 884 8991
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