Merging DS-CDMA (with CI chip shapes) and oscillating-beam smart antenna arrays: exploiting transmit diversity, frequency diversity and directionality

We merge a smart antenna array with CI/DS-CDMA, a novel implementation of DS-CDMA where chips have a shape referred to as the CI (carrier interferometry) chip shape and are decomposable into N narrowband frequency components. In the antenna array, by applying suitable time-varying phases to the elements, we create small movement (oscillation) in the antenna array´s pattern, while steering the main lobe to the position of the intended user. The oscillating antenna pattern creates a time-varying channel with a controllable coherence time. This, in turn, provides transmit diversity in the form of a time diversity gain at the mobile receiver side. Thus, at the receiver, three stages of combining are available: 1) combining time components of the received signal within symbol duration T_S (each experiencing a different fade) to enhance performance via time diversity; 2) combining frequency components which make up the CI/DS-CDMA chip to enhance the performance via frequency diversity; 3) combining across chips to eliminate interfering users. Employing CI/DS-CDMA with the proposed smart antenna at the base station, we achieve: 1) very high capacity via the merger of SDMA (directionality of antenna array) and CDMA; 2) very high performance via the construction of receivers that exploit both transmit diversity and frequency diversity. We focus on the performance benefits of the proposed system.