Towards a Baltic Sea Region Strategy in Critical ... - Helsinki.fi

CRITICAL INFRASTRUCTURE PROTECTION IN THE BALTIC SEA REGION
as General Packet Radio Service (GPRS) and Enhanced Data rates for GSM
Evolution (EDGE), have enabled data services for GSM users. By contrast,
TETRA has been defined from its onset (TETRA Release 1) to handle both voice
and data traffic. Furthermore, an order of magnitude improvement in TETRA data
transfer rates will be enabled by the implementation of TETRA Enhanced Data
Service (TEDS) as part of TETRA Release 2 (ETSI EN 2007a). A comparison of
the key system characteristics of TETRA and GSM are summarized in Table 6.
The comparative advantages of TETRA include:
• Higher bandwidth utilization efficiency.
• Wider coverage possible in the frequency bands allocated for TETRA.
• Faster call setup times, essential in situations that require fast responsive
actions.
• Modulation schemes that is relatively simple to implement.
• Cost-effectiveness in serving a low subscriber density.
• Extremely versatile group call functionality.
• Possibility of creating virtual private networks (VPNs) that firmly isolate
traffic belonging to different user groups.
• Improved robustness to multipath impairments caused by signal
reflections. Diffractions and scattering in the mobile radio environment.
The primary air interfaces (that is, calling modes) specified by TETRA are the
Trunk Mode Operation (TMO) 73 and Direct Mode Operation (DMO). The TMO is
the same as in conventional cellular networks, whereby, users communicate via the
TETRA SwMI. On the hand, DMO enables TETRA users to communicate directly
or via repeaters, independent of SwMI (see Figure 12). These repeaters are
typically vehicle-mounted terminals that improve the DMO range, particularly if
the vehicle is parked in an elevated location, such as a hilltop. Furthermore, DMO
repeaters may increase range of base stations by providing a DMO link to users
that are beyond the coverage range of a base station. See Figure 12 for an
illustrative comparison of these different configurations. The use of DMO could be
considered as a fallback scheme that ensures continued local communications
(with limited features) even after failure to the SwMI.
TETRA Services and Applications
TETRA networks support a range of calling features and services crucial for
professional users (see Figure 13). This includes not only basic telephony services
similar to those provided by public networks, but also a set of supplementary
services to increase the effectiveness of teamwork within and beyond a TETRA
user group. For instance, during a fire fighting operation a fire fighter may make a
Late Entry into a group conversation with other squad members, or a Priority Call
from a critically injured fire fighter may override other calls in progress. TETRA
also supports standard data services and applications developed by third parties.
73 Also known as the TETRA Voice and Data (TETRA V+D) air interface.
106 NORDREGIO REPORT 2007:5