Batboard

I have been researching the TRBO system planner for Connect Plus multisite digtial trunking and have a question for the trunking gurus...

Page 62 (for those of you who have the planner) talks about the RSSI settings that would trigger roaming and connection to a site and also talks about "balanced" coverage. I have been running several different coverage maps to plan potential site locations within our city- depicting estimated signal levels of a handheld radio talking to the Trunking site receivers and the Trunking site transmitters talking to a handheld.

For example- modeling a 9dBd gain antenna at 30 meter height with 100 watt transmitter gives outbound signal levels of -70dBm+ in the area of concern and inbound signal levels of -90dBm+ (increasing the closer you get to the site) in the area of concern. (I have estimated coverage maps available if anyone wants to see them)

Transmit and Receive will be using different antennas via combiners as we, most likely, would have 3 MTR3000 per site. The planner talks about either lowering the transmit power or changing the settings for RSSI thresholds.

For those of you that have dealt with trunking site coverage issues- how important is it for the transmit/receive signal levels to be as close to "balanced" as possible? And what issues should I be concerned with?
Anyone have thoughts on this?

Thanks in advance,
JJ

In digital LMR systems with the same signaling and coding techniques (P25/Trbo) used on both the up and downlinks balanced coverage is important as there is not much point in being able to signal to the subscriber if the subscriber responses are unable to be received.

As you know the cellular industry has long recognized this with tower mounted receiver pre-amps and diversity receiver arrangements favoring the uplink while the newest cellular standards such as LTE using a coding system that improves the detection of subscriber devices (and reduces those device PA linearity requirements).

It’s interesting to look at Tetra in this respect as while Tetra mobiles have relatively low power because of power amp (PA) linearity constraints the system ends up with mobiles and portables having similar powers (3W mobile and 1W handhelds). Whiloe Tetra base tranmitters do run more power a lot of goes channel combiner and feeder losses. Technical papers from infrastructure makes such as Nokia put the emphasis on uplink improvements as the way to improve coverage.

You may want a small advantage to the base station to aid the mobile in finding the control channels but people I know who manage a large P25 trunking system say balance is important. So much so that they have partitioned the system with portable allocated one set of low power infrastructure on UHF and mobiles to another on VHF at higher power.

Rssi level setting keeps the SU on the site till the control channel level drops bellow the Rssi set level ,then it starts the handoff process , if it can detect a different control channel at a level set higher than the set Rssi , then the handsoff take place , SU adjusts its TX power depending on what level it receives on the downlik , this is to avoid Rx amplifier overloading at the site ,and also helps to decreases SU battery discharging rate if it is close to the site ,
since SU adjusts its TX power based on the downlink signal leve that it receives , it is important to have the down and up links balanced ,
The rssi level setting depends on the proximity of the sites and the overlaps ,

Ali Abbassi wrote: ... SU adjusts its TX power depending on what level it receives on the downlik , this is to avoid Rx amplifier overloading at the site ,and also helps to decreases SU battery discharging rate if it is close to the site , ...

Is automatic power control unique to Connect Plus, or does it also occur in Capacity Plus and/or IP Site Connect modes of operation?