Adjacent Channel Interference Analyses in TETRA Direct Mode Operation

The present paper analyzes adjacent channel interference in TETRA Direct Mode Operation (DMO) for indoor and outdoor environments. To determine minimal stay-away distance and interference area propagation model is used. Thus, a brief overview of free space, Bacon and CEPT SE21 propagation models, mentioned in the TETRA DMO standard is given and two-ray and multi-wall models are described and evaluated by field measurements. We found out, that the two-ray model is suitable for fast estimation of the TETRA DMO signal coverage in open flat area while the multi-wall model, taking into account the attenuation of walls between transmitter and receiver, gives good estimate of the signal levels for indoor applications. Those two models were used for the interference analyses. According to the calculated results two-ray model gives rather pessimistic values of the stayaway distance and interference area in open flat areas while multi-wall model is appropriate for the interference calculation inside buildings that are not surrounded with the high structures causing additional ray reflections back into the interior of the analyzed building. Key-Words: interference, propagation, path loss, TETRA Direct Mode Operation, two-ray model, multi-wall model, radio signal coverage, stay-away distance