Alternative solutions for joint detection in TD/CDMA multiple access scheme for UMTS

Abstract

In the TD/CDMA multiple access scheme for UMTS, the most critical step in term of complexity is joint detection. Even the simplest way to achieve it, i.e. zero-forcing block-linear-equalizer (ZF-BLE), leads to more than 100 MOPS in some cases. In this paper, two ways to reduce this complexity are investigated. First, an approximation based on the convergence of the Cholesky decomposition performed within ZF-BLE is studied. Then, by inverting one row of a small part of the matrix equation, a filter for each CDMA code is constructed. Since size and energy consumption are more critical at the mobile than at the base station, all complexity evaluations within this paper are done in the downlink, using for digital applications the current set of parameters of the ETSI proposal.