It is difficult to estimate path loss for land mobile radio using a single path loss model such as diffraction model or Okumura model individually when mobile radio is utilized in widespread area. Furthermore, high accuracy of the path loss estimation is needed when the radio system is digitized because degradation of CNR due to interference deteriorates communications.
In this paper, conventional path loss models, i.e. the diffraction model, Okumura model and two-ray model, were evaluated with 400 MHz land mobile radio field measurements, and a method of improving path loss estimation by using each of these conventional models selectively was proposed. The ratio of error between -10 dB and +10 dB for the method applying the correction factors derived from our field measurements was 71.41 %, while the ratios for the conventional diffraction and Okumura models without any correction factors were 26.71 % and 49.42 %, respectively.