Z-connectable complete complementary codes and its application in CDMA systems

A code-division multiple access (CDMA) communication system achieves the maximum spectral efficiency over multipath fading channels if employed spreading sequences have ideal correlations, i.e., the ideal auto-correlation that are zero except for zero shift and the ideal cross-correlations that are zero for all shifts. Unfortunately, such sequences are known non-existent and, Suehiro and Hatori proposed a sequence family with ideal correlation sum called the complete complementary code (CCC). For (quasi-) synchronous CDMA systems, the ideal correlation sum of CCC provides an inter-channel interference (ICI)-free communication and CCC based CDMA (CCC-CDMA) improves spectral efficiency significantly. In previous work, we have proposed a general and systematic construction of the optimal CCC. However, in special cases, the proposed construction results in CCCs with extra interesting properties. In this paper, we propose a new type of CCC called the Z-connectable CCC (Z-CCC), which gives a sequence set with zero correlation zone (ZCZ) by connecting codes in its complementary codes. We also present two Z-CCCs which consist of rows of the discrete Fourier transform (DFT) and Hadamard matrices. Due to Z-CCC provides the guard-part reduced sub-packet structure, Z-CCC based CDMA (Z-CCC-CDMA) realizes higher spectral efficiency than the traditional CCC-CDMA and, intimate relationships of the present Z-CCCs and the DFT matrix or Hadamard matrix allows low implementation complexity.