DMR is a new radio communication standard.

DMR is a new radio communication standard.

CHIVILEV Sergey Vladimirovich,
Candidate of Technical Sciences

DMR is a new radio communication standard.

Source: «Special Equipment» magazine. No. 2 2008

The main consumers of DMR-based systems, as well as conventional (analog) radio communication systems, are enterprises of the lower and middle sectors of the economy, where the need for professional radio communication is obvious and does not require justification. These include enterprises in the security industry (security), construction organizations, transport services (taxis), as well as law enforcement and protection services (with low subscriber density and a small specific number of connections). DMR technology in the professional communications sector is comparable to the advent of compact discs in the recording industry. The growing demands of consumers for communications are no longer limited to their reliability, but are explained by the need to:

• ensure protection of radio broadcasts from eavesdropping;
• organize the transmission of text messages along with voice;
• increase speech intelligibility in the presence of strong ambient acoustic interference;
• increase the life of continuous operation of batteries, etc.

All these requirements are met by the new standard of conventional professional radio communication — DMR (Digital Mobile Radio), developed by the European Telecommunications Standards Institute (ETSI) as a single pan-European standard for digital radio communication. The DMR standard is positioned as an open standard, i.e. it is assumed that equipment from different manufacturers will be compatible. At the moment, only one company (Motorola) has presented a solution within the DMR standard — the MotoTRBO equipment line.

A little history

In April 2005, the first release of the DMR-ETSI TS 102 361 standard was released, describing the radio interface (part 1), as well as the voice and basic functional features of the standard (part 2). In January 2006, the third part of the DMR standard was added, describing the packet data transmission protocol.

DMR technology is based on TDMA (Time Division Multiple Access — multiple access with time division of channels), which allows two time intervals to be placed on one frequency carrier with a frequency grid of 12.5 kHz.

DMR Radio Interface

Fig. 1. The structure of the DMR standard radio interface

As already mentioned, two independent logical channels are implemented on one frequency channel (12.5 kHz). It is expected that DMR standard solutions will be implemented not only in the classic ranges of 136 — 174 MHz and 403 — 470 MHz, but also in the range of 450 — 527 MHz.

Fig. 1 shows the structure of the DMR standard radio interface.

As can be seen from Fig. 2, in accordance with the time-division multiplexing technology, two logical channels are organized on one frequency channel. It should be noted that from the point of view of system planning, only one logical channel out of two available is currently used in the direct communication mode (without using a repeater). In this case, the direct mode will not have an advantage over the analog mode in terms of increasing the channel capacity. Within the DMR standard, two modes are supposed to be implemented:

1. Direct mode — simplex communication;
2. Repeater mode (Fig. 2) — with support for dual-frequency simplex technology with duplex spacing, FDD (Frequency Division Duplex); in this mode, two simultaneous independent voice connections are possible.

Figure 2 shows a diagram of the organization of communication using a repeater. In this case, both logical channels are used, which allows two independent connections.

Fig. 2. Principles of communication organization
using a repeater

Speech transmission quality

The ACELP (algebraic codebook excited linear prediction) vocoder is particularly suitable for use in conditions of strong acoustic interference. Forward Error Correction (FEC) technology is used to detect errors in the radio channel and correct them during channel coding.
Fig. 3 shows a comparative graph of communication degradation for systems with analog and DMR technologies. Speaking about the communication range, it is worth mentioning that the achieved results depend not only on the presence of natural obstacles, but also on the surrounding electromagnetic environment.

Fig. 3. Comparative graph of communication degradation
 for systems based on analog and DMR technologies

Main capabilities of DMR

The DMR standard is constantly being improved, implementing a functional set that was previously not typical for the conventional radio communications sector.

The main functional capabilities of the digital DMR standard include:

• digital signal processing;
• battery management;
• priority emergency call;
• improved hands-free mode;
• built-in GPS signal receiver for implementing location monitoring applications;
• remote control;
• optional encryption;
• full-duplex call (in development);
• simultaneous transmission of voice and data (including packet data);
• operation in analog mode, which is especially important during the gradual migration of analog conventional systems.
• Types of calls implemented within the DMR standard:
• individual call «radio station — radio station»;
• group call «radio station — group of radio stations»;
• group call «radio station — all radio stations»;
• packet data transmission with a channel rate of 2 kbps.

Table 1. Call types and associated services