A signal design without co-channel interference for approximately synchronized CDMA systems

Optimal Polyphase Asymmetric ZCZ Sequence Sets Including Uncorrelated Sequences

“…Let Z be a sequence set with M sequences of period P. Then, Z can be represented as Z={Z. 1OsmsM-1} z.=(.6m),.iM),...,.Sm),...,,Sm-),) (1) where Zm and zSM) represent a sequence and a sequence element, respectively. Let Rzm,,zm, (T) be the periodic correlation function between Zm, and Zm,• For the sake of simplicity, the modulo operator is ,represented as %, i.e., x%p d=ef x mod p (2) 488 Then, Rz.,,z., (T) is defined as P-1 Rz.,,zm, (T) d=ef 2 zSMo)zEpMpt;%p (3) p=o where the symbol * denotes complex conjugation.…”

“…In such AS-CDMA systems, zero-correlation zone (ZCZ) sequence sets are used as spreading sequences in order to realize this advantage [1]- [15]. Generally, a ZCZ sequence set is characterized by the sequence period, the number of sequences, the ZCZ length, and the number of phases of the sequence elements.…”

“…The ZCZ length is restricted by a mathematical upper bound [6], [16], and ZCZ sequence sets that satisfy this mathematical upper bound are referred to as optimal ZCZ sequence sets. A number of studies have evaluated optimal ZCZ sequence sets [1], [6], [11], [14], [15]. On the other hand, quasi-optimal ZCZ sequence sets' have a ZCZ length that is equal to one less than the mathematical upper bound.…”

Time-Hopping Correlation Property and Its Effects on THSS-UWB System

“…As a result, orthogonal communications can be realized while the need of accurate synchronism in whole system is reduced. The idea of approximate synchronization and ZCZ was firstly proposed for direct sequence (DS) in code division multiple access (CDMA) (Suehiro, 1994), and a lot of DSs with ZCZ had been constructed (Fan, 1999;Hayashi, 2009;Hu & Gong, 2010). As for TH sequences with ZCZ, the corresponding studies were also presented (Guvene & Arslan, 2004a;Guvene & Arslan, 2004b;Zeng et al, 2011).…”

Multiple-access interference reduction for QS-CDMA systems with a novel class of polyphase sequences

“…Among the other disadvantages are that there exists some nonzero crosscorrelation among the sequences and that the sequence is useful only for synchronous channels. Another polyphase pseudoperiodic sequence is suggested in [10], [11]: since the periodic correlation of the sequence is , the system using this sequence exhibits no interuser interference. This sequence, however, is not useful in selective fading channels and is also difficult to generate.…”