Realizable DS-CDMA System Occupying Nyquist Chip Bandwidth and Exhibiting Zero Direct-Current

In this paper, the realizable short-code direct sequence code-division multiple-access (DS-CDMA) system occupying Nyquist chip bandwidth and exhibiting zero direct-current (DC) is developed. By limiting the spreading waveform to exhibit zero DC and continuous bandlimited spectrum, the realizability and DC nulling constraints on spreading codewords are derived to enable such system realization. Based on both constraints, a low-complexity implementation structure in spreading and despreading is also addressed. Several frequently-adopted spreading codes are examined for realization feasibility. It is shown that Nyquist chip bandwidth and zero-DC transmission can be practically achieved for the bandlimited DS-CDMA system using two conventional even-length orthogonal spreading codes at the sacrifice of very little user capacity. A new odd-length orthogonal spreading code is also proposed to enable such system realization.