TETRA

TETRA -Terrestrial Trunked Radio - is a digital radio standard common in Europe, Asia,and Indonesia. Tetra is a concept - a set of communications standards that welcome multiple manufactuers and accessory designers. Tetra radios offer a multiple range of functions and capabilities.

Overview

TETRA is a digital radio standard, developed in Europe for the European Public Safety market in the early 1990's, with the first-generation networks deployed at the end of the 1990's. TETRA is a standard written by the European Telecommunications Standards Institute (ETSI) with co-operation from users and manufacturers. With its growing popularity, it has been adopted as the preferred standard in many parts of the world and is now used by all sectors of the market. It is very adaptable in terms of size, capacity and functionality.

TETRA uses Time Division Multiple Access (TDMA) style of transmitting 4timeslots (digital channels) on one radio frequency carrier. One of those timeslots (channels) is a Master Control Channel (MCH), leaving three other timeslots (channels) for voice (TCH) or data traffic. Other carriers may be added to a base station (repeater site or tower), allowing for more conversations to happen per unit time. Tetra radios, often called terminals, may communicate as a group with other radios through a radio site (repeater station) in trunked mode, or with each other in a direct point-to-point (PxP) mode. The point to point or individual call types can be either semi-duplex (half duplex) or full duplex (as a mobile phone).

TETRA standards support a variety of communications solutions, such as voice (group, individual, emergency & DMO), data (status, SDS, packet, circuit switch), and location information.

Features

The TETRA technology packsamount of feature capabilities, some of which are listed as follows:

Digital audio using a trunked communication path (radio -> repeater -> radio) or point-to-point (PxP) using
either semi or full duplex
Diversity receive antennas allow for less mobile and portable power levels
Terminal Gateway Mode: a trunked mobile can relay signals from the trunk system to radios that are too weak or too far away to directly participate
Multiple calling mode options: PxP Telephone Style, PxP PTT Style, and traditional group calling
Connectivity to a digital phone system, such as Asterisk, is available. Make a phone call from your radio to
your internal PBX, or an external line!
Optionally integrated GPS boards allow for tightly integrated Automatic Vehicle Tracking (AVL) options
Saftey feature - man down capability: the radio "automatically sends a message to a dispatcher"
if a worker becomes unresponsive
Saftey feature - radios check themselves against the trunk system, and warn the user if they travel out of coverage zones
Depending on radio model, they may be able to send and receive text messages (SDS)
Cellular-like handover from one tower site to another as the radio moves around the coverage area
Dynamic power control on the network to reduce terminal transmitter power which saves on battery
life and consumption
Optional dispatcher software allows for dynamic grouping of radios for a specific event, such as responding to a car crash, or servicing an airplane at the terminal gate after it lands

United States Pilot

A couple years ago, Nielson Communications' President, Rick Nielson, attended a TETRA Association presentation by Phil Kidner at an IWCE convention. Rick developed a relationship with Rohde and Schwarz (developer of infrastructure equipment) along with Sepura plc (developer of radio hardware), and began discussing the possibility of piloting this techology in the United States. In December 2010, staff from Nielson Communications went to Germany and participated in Rohde & Schwarz's CampusIP training classes, and met up with a representative from Sepura to learn how a basic TETRA System works. On January 11, 2011, radio hardware arrived in Green Bay from Europe, along with new antennas from Comprod, to integrate TETRA into our existing LTR antenna structure.

Construction of the TETRA system began in mid-January, with the preparation of three tower sites - DePere, Appleton, and Oshkosh. Each site required some antenna and filter installation. At our Green Bay office, on January 19, we made our first TETRA transmissions. On January 25 and 26, we installed the final pieces of networking components, allowing the installed base stations to fully communicate with each other. Enhancements to the system, such as the telephone interfaces, began later that week.

Testing of the radio system began in early February, where we compared driving observations against radio propogation software predictions. We began comparing the TETRA's digital signals with the analog LTR system, and found that the cover patterns were quite comparable. Similairly, we observed that when the TETRA range collapsed, the analog LTR system was very distorted and unusable as well.. The amazing thing is that TETRA is using 1/2 of the power of the LTR system on transmitting from the repeater (TETRA=50W, LTR=100W), and 1/3 of the power transmitting from the mobile radio (TETRA=10W, LTR=30W).

Coverage Plots comparing 10W TETRA radios vs. 30W Analog LTR radios

Below are links to larger images of our coverage study. The YELLOW map is a plot of the Tetra base stations receiving signals from a Tetra mobile transmitting 10W of RF power. The BLUE map is an LTR radio transmitting 30W to the same antenna that the Tetra radio is using. The BLUE-GREEN map is a mixture of the other two maps... if you see a greenish color, then both systems are operating. If you see a yellow dot or a blue dot, then that particular system "wins" over the other. As you can see, the two systems are nearly identical, and we were able to verify this with drive tests.


TETRA RX Plot - 10W	LTR RX Plot - 30W	Combined RX Plot

More information

We are keeping an active blog at http://tetrausa.blogspot.com; please check it often for updates to our system. If you have specific questions, you may also email tetra@nielsoncom.com.