Since there were the first portable radio facilities appeared, researchers struggling to create effective methods for the quantitive evaluation of this quality The slow progress in this field is conditioned, foremost, by difficulty and many-sided nature of such task. If the mechanism of the voice production is more or less studied, perception by the man of sounds   is   unstudied. In addition, the effect of habituation listener is known, when the sound of any codec, what eyes are playing tricks on him at the first collision with him  can be by unacceptable, eventually becomes so familiar and comfortable, that the change to a better quality may cause  protest and discontent.

On the other hand, if the transmission of digitized voice is performed without subjecting it to any treatment, to preserve the "telephone" sound quality the carrying capacity of channel is required at the level of 64 kbit /s, i.e. it is  required the too large carrying capacity of network. Therefore the compression of voice and its treatment is made. Traditionally devices, realizing such compression, are named as vocoders or speech codecs. In the cellular systems as a device of the voice production are used the speech codec  RPE-LTP with regular pulse excitation and speed of the  voice conversion 13 kbit / s.

To reduce computing costs and increase the efficiency of the use of communication channel in the codec of connection discontinuous transmission of speech DTX (Discontinuous Transmission) is used also, which provides including of transmitter only then, when an user starts the conversation, turns off it during pauses and at the end of the conversation. In addition, the DTX system controls the voice activity detection VAD (Voice Activity Detection),  which provides a discovery and selection of intervals speech and noise without speech, even in cases where the noise level is comparable to the level of speech.

However, to produce a compression vocoder requires at some time in the data buffer for analysis of speech and thus there is the so-called algorithmic delay. In addition, the vocoder adds further delay in carrying out the actual calculation of speech compression - the so-called latency compression.

Because of this, the actual quality of reproduced speech in digital radio systems depends on many factors and can vary within wide limits depending on the client software and hardware (such as a mobile terminal), the gateway (switching) hardware, bandwidth, and network utilization. All this affects the transmission of technical data as a delay, the proportion of lost information (letters, words).

In addition to the pauses in conversation delay causes such as "echo of transmitted speech" and imposition of voices. One reason for this inconsistency may be resistance at the transition from two to four pairs in the telephone network.

Given the difficulty of assessing voice quality in the mid-90's Telecommunication Standardization Sector of the International Telecommunication Union (ITU-T) recommendation finalized R.800 "Methods for the subjective assessment of the quality of voice communication," which is today the most recognized methodology for assessing transmission systems speech. It describes the conditions of conducting tests, the content audio samples, system assessments and data analysis techniques. The most common method of R.800 are used to calculate the average subjective evaluation of speech quality on a scale..

But the main problem R.800 an approach is that it is far from practical life: Manufacturers tend to test their systems in the "comfort" under controlled conditions, but the real mobile radio telecommunications are far from it, and especially domestic radio transmissions.

To evaluate the transmission quality of voice data with modern digital radio equipment in the department of radio technologies were tested professional radio MotorolaTLKRT80 / T80 Extreme Radio evaluation speech at the existing radio communications in a building with reinforced concrete walls and basement. For this type of buildings the choice of method of such an assessment, was not easy. The main factors that influenced this process are:

Very strong influence on distribution of radio waves is rendered by obstacles, especially different metallic constructions, including armature of buildings and buildings.  Therefore descriptions of distribution into an apartment depend on reflecting properties of build materials and penetration of signal through them (to the complex inductivity of materials). Of course, that in the models of prognostication of distribution many researchers, taking into account the specific of place, as basic initial information took information about the complex inductivity of build materials, and also about the structure of building.

Measuring consisted in: a transmission, reception, record and subsequent collation of the special verbal articulators tables. The measure of quality of examinee line of radio contact in this case is a percent of the correctly accepted words in relation to the incurrence of passed. The accepted words were written on proof-of-concept forms. Testing was conducted in critical areas (basement apartment of central building and basement apartment of nearby building, in the distance 500 m). Generally, examinee radio facilities were rationed by good results for the purpose their verbal legibility in the indicated areas.