Title :
Spreading code selection for multiple chip rate DS-CDMA systems
Author :
Lyu, Dug-In ; Schober, Robert
Author_Institution :
Dept. of Electr. & Comput. Eng., Univ. of British Columbia, Vancouver, Canada
fDate :
5/1/2005 12:00:00 AM
Abstract :
In this paper, we analyze the interuser interference (IUI) in multiple chip rate (MCR) direct-sequence code-division multiple-access (DS-CDMA) systems employing realistic chip waveforms. In MCR DS-CDMA systems, different users may have different chip rates, which makes IUI unavoidable even if the employed spreading codes are orthogonal. Here, we consider orthogonal variable spreading factor (OVSF) codes and random spreading codes. We find that the spreading code of the low chip rate user does not affect the IUI at all. The IUI depends only on the bit patterns of the high chip rate user corresponding to one chip duration of the low chip rate user and on the carrier frequency separation of the users. We provide a closed-form equation for the IUI power of random codes, and we show that a judicious choice of the spreading codes can reduce the IUI significantly for OVSF codes.
Keywords :
3G mobile communication; cellular radio; code division multiple access; radiofrequency interference; random codes; spread spectrum communication; DS-CDMA system; OVSF; carrier frequency separation; direct-sequence code-division multiple-access system; interuser interference; multiple chip rate; orthogonal variable spreading factor; random spreading codes; spreading code selection; Code standards; Convolution; Equations; Frequency; Matched filters; Multiaccess communication; Multiple access interference; Performance analysis; RF signals; Shape; Chip waveforms; interuser interference (IUI); multiple chip rate direct-sequence code-division multiple-access (DS-CDMA); orthogonal codes;
Journal_Title :
Vehicular Technology, IEEE Transactions on
DOI :
10.1109/TVT.2005.844644