Channel estimation and multiuser detection in long-code DS/CDMAsystems

摘要

The problems of channel estimation and multiuser detection forndirect sequence code division multiple access (DS/CDMA) systemsnemploying long spreading codes are considered. With regard to channelnestimation, several procedures are proposed based on the least-squaresnapproach, relying on the transmission of known training symbols but notnrequiring any timing synchronization. In particular, algorithms suitednfor the forward and reverse links of a single-rate DS/CDMA cellularnsystem are developed, and the case of a multirate/multicode system,nwherein high-rate users are split into multiple virtual low-rate users,nis also considered. All of the proposed procedures are recursivelynimplementable with a computational complexity that is quadratic in thenprocessing gain, with regard to the issue of multiuser detection, annadaptive serial interference cancellation (SIC) receiver is considered,nwhere the adaptivity stems from the fact that it is built upon thenchannel estimates provided by the estimation algorithm. Simulationnresults show that coupling the proposed estimation algorithms with a SICnreceiver may yield, with a much lower computational complexity,nperformance levels close to those of the ideal linear minimum meannsquare error (MMSE) receiver, which assumes perfect knowledge of thenchannels for all of the users and which (in a long-code scenario) has ancomputational complexity per symbol interval proportional to the thirdnpower of the processing gain