The effect of adjacent channel interference on capacity in a hybrid TDMA/CDMA-TDD system using UTRA-TDD parameters

The subject of this analysis is the effects of adjacent channel interference (ACI) on capacity in a hybrid TDMA/CDMA system using time division duplex (TDD). The parameters of the UTRA (UMTS terrestrial radio access) air interface were used for this investigation. A statistical approach assuming a spatially uniform user distribution was taken to investigate the capacity reduction due to ACI. The probability density function (PDF) of ACI at the base station (BS) of interest was calculated and by defining a certain outage threshold (P_out), the interference used to calculate the capacity loss was determined. A path loss model which accounts for the correlation of log normal shadowing between the useful link and interference link was adopted. The impact of the following parameters were studied: (a) BS separation, (b) adjacent channel protection (ACP), (c) load in the interfering cell and (d) frame synchronisation. It was found that there are sub-optimal BS separations due to a tradeoff between MS→BS and BS→BS interference. Moreover, it became apparent that an intelligent dynamic channel assignment (DCA) algorithm is required