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Article

Telephone companies have long supplied telephone service over a twisted pair of wires known as POTS (Plain Old Telephone Service) lines.  As technologies grow and advanced capabilities bring new innovations, the high-tech capabilities of the past, such as T1 lines, POTS lines, and RT (Radio Tie) lines, are heading towards obsolescence.  They are disappearing at an ever-faster pace as technologies advance and move into newer and faster capabilities.

So, you ask, why do I care that POTS and RT lines are going away?

Because their replacement is IP packet-based information transfer.  This has great benefits for most communications, but the fact that IP makes sure that data reaches its destination, but does not care about how long it takes to get there, made IP incompatible with analog voting – until now.

Analog voters need time-synced audio from all unsquelched voting receivers for two reasons:

  1. The signal quality measurement is based on the FM noise component of the RX audio, as the lowest FM noise is an excellent indicator of audio clarity and signal strength. Speech is also available at the same frequencies, so the total measurement varies as speech varies – but the speech component cancels out with synchronized signals.
  2. The voted site may need to change during individual transmissions from a user in the field as signal conditions change. When moving among buildings in an urban environment, the voted site – that voting receiver with the best audio – can sometimes change many times during even a short field transmission.  The voter cannot seamlessly switch between sites unless all audio inputs are time synchronized.

There is yet another concern with the use of IP to transfer RX audio from a voting receiver site to an analog voter: The vocoders used to digitize the receiver audio are not designed to faithfully reproduce the FM noise that’s required to perform an accurate signal quality measurement.

The Basic Problem, Simply Stated:

Many JPS customers use microwave T1’s, telco T1’s, or the twisted copper leased lines of the phone companies to synchronously transfer TX and Rx audio between remote voting receiver sites and an analog voter.  Due to reduced requirements for analog circuits, the phone companies are raising prices on leased lines, if you can even find them.  Packet-based IP networks are now often available, but the accompanying lack of time-synchronization – the “jitter” of IP networks, has prevented them from being viable replacements for audio transfer within analog voting systems.

The JPS Solution, Simply Stated:

JPS has created new hardware and software that allow the use of IP networks for audio transfer between the SNV-12 and remote RX/TX sites or to Dispatch.  It does this by making the Signal Quality measurement prior to the A/D digitization, and adding various provisions that time-synchronize the voting receiver audio, despite the network jitter.

The solution includes the new QMT-1 (Quality Measurement & Transport) unit at the voting receiver sites and new SVM-3 modules at the SNV-12 voter.  The QMT-1 does the signal quality measurement, digitizes the audio, and adds a time stamp.  The SVM-3 modules interface the signals from the QMT-1 to the voter.  They can coexist with SVM-2 modules installed in the same chassis, and can be plugged into existing SNV-12.  The only change required is to update the software in the SNV-12’s Control Processor Module.

SNV12-IP

SNV-12 Voter for Receive Audio with Backhaul over IP, and Traditional Analog Audio

For more information, go to http://www.jpsinterop.com/products/voter/

© 2018 JPS Interoperability Solutions, Inc. All rights reserved.

5800 Departure Drive | Raleigh, NC 27616 | 919.790.1011 | sales@jpsinterop.com

Radio Interoperability

Radio Interoperability Gateway

Radio over IP

RoIP

Voter Comparator

Receiver

Voting

Push To Talk Over Cellular