CONCATENATED ORTHOGONAL PN SPREADING SEQUENCES AND THEIR APPLICATION TO CELLULAR DS-CDMA SYSTEMS WITH INTEGRATED TRAFFIC

In this paper, we investigate the application of the concatenated orth ogonal/PN spreading scheme for a cellular direct sequence code-divisio n multiple access (DS-CDMA) system with integrated traffic. The perfor mance of the system is evaluated in terms of user capacity. In order t o incorporate traffic with a wide range of source rates, line rates (a djusted data rates before spreading) have to be selected for transmiss ion. For traffic with source rates higher than the line rate of concer n, we propose the use of concatenated orthogonal/PN spreading sequence s to subdivide a high rate stream into parallel line rate streams. The refore, in this paper, we first analyze the properties of the concaten ated orthogonal/PN spreading sequences. The results are used to evalua te their performance for homogenous voice traffic in various cellular mobile environments with multipath fading, lognormal shadowing, and pa th loss. Our results show that the proposed spreading scheme offers a significant improvement in the forward link capacity as compared to us ing the conventional nonconcatenated long PN sequence, especially if t he multipath fading is Rician (e.g., microcellular and indoor picocell ular systems). Incorporating the notion of line rate, we then evaluate the performance of a system with integrated voice and video traffic. Special emphasis is placed on the effect of line rate selection on the overall capacity which leads to the optimal selection of line rates.