Theoretical study on the intermodulation interference between wide-band mobile radio systems and narrow-band mobile radio systems

At starting of the service operation of 2 GHz band IMT-2000 system in Japan, it is important to make clear the mutual interference problem which may occur between IMT-2000 mobile radio systems and existing mobile radio systems, etc. Concerning about this study, Japanese Association of Radio Industries and Businesses established an investigation and examination meeting from fiscal year 1998 to 2001. After this meeting, especially about nonlinear interference that will occur when interfering wave is very high and nonlinearity of interfered receiver amplifier becomes important, specialist team of nonlinear interference is continuing to study this problem. This paper describes the theoretical study result on intermodulation (IM) spectrum generated by a wideband continuous modulation wave and generation of interfering wave caused by IM, on the nonlinear interference by which a narrowband mobile radio system (NBMR) is disturbed by a wideband mobile radio system (WBMR). In this study, the N-modulation waves model and the 3rd order intercept point input level method (IIP3) in [RC Sagers (1983)] was applied by using parameters of direct spread code division multiple access (DS-CDMA) system as WBMR and personal handyphone system (PHS) as a typical NBMR. The bit error rate characteristics (BER) of PHS receiver were estimated through comparison of measured data and theoretical analysis result of the desired signal and undesired signal ratio (D/U) to BER. The comparison result of estimated and measured BER of a NBWR receiver was reported by using a guard band between WBMR and NBWR system receiver as a parameter.