Interference issues in multi-code CDMA networks

Multi-code direct-sequence code division multiple access (MC-CDMA) has been proposed as a flexible multiple access scheme for wireless packet networks that support a large variety of mobiles with different and even time-varying rates. However, the interference model typically used with conventional DS-CDMA cellular systems - a large number of low-power mobiles uniformly distributed in cells - may not hold. In MC-CDMA cellular systems, it is possible for a high-rate mobile, perhaps near the boundary of a cell, to have all the codes for high-rate transmission - therefore transmitting at high power and causing significant interference to the neighboring cell. In this study, we analyze the effects of MC-CDMA intercell interference on the reverse link (i.e., mobile to cell site) and investigate a maximum capacity power allocation (MCPA) criterion that exploits the sub-code concatenation property of MC-CDMA transmission. When the transmission rate is high, power control with MCPA criterion can significantly reduce reverse-link MC-CDMA intercell interference. However, with only four codes per mobile (e.g., as in IS-95), the reduction in intercell interference is less than 1 dB.