Smart antenna effects on soft handoff and capacity in a code division multiple access wireless communication system

As the wireless handset market expands exponentially and existing base stations reach their capacity, solutions are currently being researched in order to find an economic way to meet the demand. One of the recent developments is the implementation of digital communication systems such as Code Division Multiple Access (CDMA) in cellular and Personal Communications Services (PCS). Although a CDMA system improves the capacity, other techniques are still needed. Smart antenna arrays are becoming a popular solution to integrate with systems such as CDMA resulting in significant capacity improvements. Soft Handoffs are an important and unique feature of CDMA systems that improve the communications link reliability. With the increasing interest in smart antenna arrays because of their potential for improving cellular system capacity, the question of how these arrays affect soft handoff arises. This dissertation explores a CDMA system employing a smart antenna array. The key aspects of this dissertation are the smart antenna array impact on capacity and soft handoff. The reverse link blocking probability, upon which the reverse channel capacity is determined, is derived and compared with a conventional antenna system. The forward channel asymptotic capacity is also derived including an analysis of the forward link interference equations. It is shown that the CDMA system that employs a smart antenna array is a forward link limited system.; The major contribution of this dissertation is the soft handoff analysis of the CDMA system with a smart antenna array. Using the asymptotic capacity, this dissertation shows a method for quantifying the dependence of the forward link capacity on soft handoffs. Several cell architectures are studied and an optimum solution is shown with the best asymptotic capacity. Systems with identical array characteristics are studied as well as systems where adjacent cells have different numbers of antenna elements in the smart antenna array. A general form of the forward channel interference as well as the asymptotic capacity is derived. With the equations provided in this dissertation, one can determine the forward channel performance under any variable conditions. It is shown that the best cell architecture under uniform conditions is also the best cell architecture under variable-element smart antenna array conditions.