Williamson-Hadamard spreading sequences for DS-CDMA applications

Orthogonal bipolar spreading sequences are used in direct sequence code division multiple access (DS-CDMA) systems for both spectrum spreading and channel separation. The most commonly used sequences are Walsh– Hadamard sequences of lengths being an integer power of 2. A construction based on Williamson’s arrays leading to sequences of lengths N:4 (mod 8) is presented in the paper. Aperiodic correlation characteristics, for example sequence sets of lengths 12–252 are presented. The correlation properties of the sequence sets are later improved using a diagonal modification technique. Copyright # 2003 John Wiley & Sons, Ltd.