Power inversion adaptive array antenna for high power interference suppression in DS-CDMA system

DS-CDMA[1] is being investigated for the next generation mobile communication system. In DS-CDMA, to distinguish one user’s transmission from another, each mobile terminal modulates the information data symbols by a pseudo-noise(PN) code and the strong point of this system is that it can easily realize the multi-rate transmission. On the other hand, the transmission power increases in proportion to bit rate, so the low bit rate signals such as voice data are greatly damaged from the high bit rate signal. Therefore, to cancel those high power interferences, it is effective to apply the adaptive array antenna to the base station in DSCDMA system. Usually, MMSE(Minimum Mean Square Error)[2] using a replica of the desired signal has been used for the control algorithm and the beamforming has been carried out for every users. This algorithm can certainly capture the desired signal and it is not impossible to process in real time taking into account the rapid device improvement in recent years. However, the system scale becomes large in proportion to the number of channels and this increases the consumption power of the system. Also, the requirement for large number of antenna elements in adaptive array could be a cause of the implementation problem. Therefore, introducing the adaptive array antenna would greatly affect the base station. It is necessary to solve these problems in order to spread the use of adaptive array. In this paper, we propose an adaptive array antenna for high power interference suppression. Power Inversion (PI) algorithm [3] is adopted as the signal-processing algorithm. By using this algorithm, the interference having the power larger than the noise power could be cancelled. Power Inversion procedure should be carried out before despreading (matched filtering), so the amount of the calculation is reduced compared to that of the conventional adaptive array system. Small size antenna can also be used as the auxiliary antenna.