Double chip waveforms for asynchronous DS-CDMA systems with random signature sequences

In an asynchronous DS-CDMA system using random signature sequences and correlation receivers, the signal-to-interference-plus-noise ratio (SINR) at the output of each correlation receiver depends on the shape of the chip waveform employed. The use of double chip waveforms instead of a single chip waveform is investigated, in order to increase the SINR performance. An analytical expression for the SINR when double chip waveforms are used is obtained. To evaluate the performance of the proposed technique, an extension to Holtzman's approximation of the error probability for the case of double chip waveforms and signalling over an additive white Gausian noise channel is derived. Numerous numerical examples are given to demonstrate the advantage of using double chip waveforms over the single chip waveform. Moreover, the advantage of using double chip waveforms for improving the SINR performance over a multipath Rayleigh fading channel is also demonstrated.