An improved design of chip waveforms for band-limited DS-CDMA systems

This paper introduces an efficient and improved design of chip waveforms to minimize the multiple access interference (MAI) in band-limited direct sequence code-division multiple access (DS-CDMA) systems. For the ease of implementation, the DS-CDMA system employs a time-limited chip waveform, whereas its band limitation is ensured by the low-pass filters at both the transmitter and the receiver ends. The design uses sinusoids to synthesize the time-limited chip waveform so that the portion of its spectrum across the specified bandwidth is as flat as possible. It is shown that using a simple series expansion (with only a few terms) the synthesized chip waveforms significantly outperforms the spreading/despreading waveforms previously proposed, particularly for large values of the chip duration-bandwidth product.