Performance Analysis of ZF Pre-Coder and Extended Joint Channel Estimation Method in Downlink CDMA with HPA

In the down link scenario of cdma systems, linear de-correlating detectors (ldds) provide satisfactory symbol error rates (sers), but they require all active users’ spreading sequences, which is impractical from privacy perspective. to overcome this impracticality, a simple matched filter receiver is considered in this paper. however, this receiver degrades the ser due to multiple access interference (mai). so, a zero force (zf) pre-coder is employed in the transmitter to improve the ser. moreover, we consider the non-linear distortion (nld) caused by the high power amplifier (hpa) of the base station (bs) due to large peak to average power ratio (papr) of the composite of cdma signals. we analyze the down link of the proposed system to derive an equation for its ser. theoretical analysis and numerical results show that the zf pre-coder increases the total degradation of the link significantly compared with that of the ldd. so, as a solution, rather than zf pre-coder, we propose a new method called extended joint channel estimation in which joint estimation of channel gains and ldd operator are used by the mobile station (ms). in this case, the bs transmits row k of ldd operator to ms k. simulation results show that the ser of this new proposed method is close to that of the ldd in additive white gaussian noise (awgn) channel with the added advantage of no need for spreading sequences of all co-users.