Prediction of bandwidth requirements for a digitally based WCDMA phase modulated outphasing transmitter

This paper gives an overview and predicts the bandwidth requirements for the design of a phase modulated outphasing transmitter (H. Chireix, Nov. 1935) (also known as LINC, linear amplification using nonlinear components) in two different WCDMA applications (uplink, downlink). The influence of bandwidth limitations on a digitally based LINC-transmitter for WCDMA utilization is investigated by simulations. In order to achieve a constant envelope signal, LINC uses vector decomposition and a phase modulation, having theoretically an infinite frequency bandwidth. It is found that the required bandwidth does not noticeably depend on the signal amplitude statistics (CREST) but on the ratio of the sampling frequency to the chip rate as well as on the channel spacing if two channels (downlink) are transmitted simultaneously. Furthermore the impact of the analog reconstruction filter shape is investigated. A compromise between the sampling frequency and the filter characteristics has to be made to obtain an optimal signal/distortion ratio over the entire bandwidth