Centralized vs Distributed Industrial Communications

To assess the role of distributed systems in modern industrial telecom, first of all, it is necessary to start out from the key requirements imposed to these systems in general.

The first one is a high level of reliability of the system. It means that its service life shall be decades. In this case, the system can be in the standby mode (preset readiness) if there are no emergency or out-of-schedule circumstances. But, in case of the emergency situation, the system shall be immediately activated. The reliability of industrial communication system guarantees that it will help saving human lives at the proper moment.

The second requirement is the speed of the system response – the possibility of the call initiator to contact immediately one or a group of subscribers. The connection time is the most vital in case of emergency situations when every second counts.

Simplex Calls Control in Industrial Communication Systems

The case history started in the 1940s of the last century when the European and American PA/GA and intercom paradigms originated. At the time, industrial intercom and control communication became duplex and simplex. Military application and high requirements to speech illegibility led to the creation of standards for communication in high ambient noise environment. At half-duplex (variation of duplex connection) connection, the built-in echo suppression system automatically controls the direction of the voice transmitting; in this case, communication delays happen as well as loss of speech and parts of important information. These peculiarities caused the development of simplex communication systems and technologies of simplex calls management correspondingly.

Speech Intelligibility In Industrial Communication

In accordance with the international standards, the speech intelligibility means "the degree to which speech can be understood by the recipient".

As the speech signal has some redundancy, some loss of information during transmitting is considered acceptable to provide the sufficient intelligibility. However, the allowed value of the transmitted signal loss depends significantly on ambient conditions. Because of different noise, distortions and reverberation interference, the total loss of information may be so considerable that it may lead to the impossibility of speech understanding, in other words, to decreasing of speech intelligibility level. Thus, the communication systems which provide the sufficient speech intelligibility in normal conditions may be inapplicable in case of the high-level ambient noise.

Overtones

It is commonly believed that the band of the main speech signal energy is quite narrow: about 500 Hz - 2 kHz. That is why the standard telephony systems are intended for the full operating frequency band within 300 Hz – 3,5 kHz. This band is considered sufficient for voice transmitting under normal conditions.

In fact, the human voice contains a wider frequency spectrum.