On the influence of a CDMA cellular repeater in the capacity of a donor base station

Abstract

The low cost of CDMA cellular repeaters suggests that its use may be always advantageous. However, the interference inserted by such repeaters in the CDMA system must not be neglected. The CDMA repeater inserts thermal noise in the repeated carrier, amplifies the carriers of other Base Stations, and thus can also be a source of interference for the mobile stations served by it. In this paper we perform a numerical analysis of the traffic capacity loss of a carrier in the donor Base Station. The analysis is based on real interference measurements, and the classical CDMA capacity equations. Results indicate a considerable loss in capacity. I. INTRODUCTIONOur main goal is to estimate the capacity loss in a digital cellular system based on Code Division Multiple Access (CDMA) when a cellular repeater is inserted in this system. First, we consider the capacity equations based on the total interference of the CDMA system. Then, the total interference, with and without the repeater, will be measured in a real operating network, and included in the equations to find the actual reduction in capacity.The literature is divided when it comes to the impact caused by repeaters in the capacity of CDMA networks. Many authors advocate the advantages of cellular repeaters; while others point out that its use demands a lot of care. For instance, in [1], [2] the arguments point to loss, but in [3] the arguments point to a gain in capacity.In a digital cellular system based on CDMA, the carrier in a sectored Base Station (BS) is the same for all sectors of this BS, and it is also the same for all BSs in the network. This is provided by the codification of the carrier in a sector of the CDMA BS by means of pseudonoise sequences, or PN pilots [4]. These PN are quasi-orthogonal codes [5], where the carrier information of any sector of a specific BS is isolated from the interference caused by other sectors of the same BS.In general, the main concern in the CDMA network planning is the interference in the forward link, or co-PN, in the Mobile Station (MS). However, the capacity of the CDMA system is determined by its reverse link, where cellular repeaters can cause great harm to the network through the additional interference which they insert in the donor BS.