Power control and number of antenna elements in CDMA distributed antenna systems

Abstract

In this study the relationship between the number of antenna elements (AEs) in a CDMA distributed antenna (DA) system and the yielding reverse link SIR is investigated by taking the power control dynamic range into account. In environments hostile to propagation, perfect power control may not be realized with a central antenna (CA), because this would require an impractically high dynamic range. This situation may yield a significant decrease in capacity. In such environments, the DA system is an ideal solution, since as the number of antenna elements increases, the dynamic range of the power control decreases. It is demonstrated that by using a DA system with as small as 4 AEs, a capacity increase of almost 30% is achievable, compared to the CA type. However, in a single-cell system once there are a sufficient number of antenna elements to implement perfect power control within a reasonable dynamic range, there is no need for additional antenna elements. Also, in a multi-cell system with CAs, the occasional transmissions at very high power levels in order to maintain perfect power control cause significant intercell interference. Since with the DA such situations are almost eliminated, the intercell interference is kept at a minimal level. Therefore, the DA is an ideal antenna type for both singleand multi-cell systems employing CDMA modulation.