Walsh-LS CDMA systems

Due to the existence of an Interference-Free-Window (IFW) or Zero-Correlation-Zone (ZCZ), a Large Area Synchronous-CDMA (LAS-CDMA) system can have a much higher system capacity and spectral efficiency than traditional CDMA. The more multi-path spreads falling in the ZCZ the greater the reduction of Inter-symbol Interference (ISI) and multiple access interference (MAI). In this paper an introduction to a CDMA forward link concept employing loosely synchronous (LS) codes and Walsh codes is presented. The LS codes are used for distinguishing cells and sectors while the individual users are separated using Walsh codes. The resulting correlation functions exhibit a ZCZ. The proposed design allows for a ZCZ that can be more easily and dynamically adjusted to cover the majority or all of the multi-path spread. The use of Walsh to separate the users places less stress on finding large family sizes of LS codes. This paper is organised as follows, a section on construction and properties of Walsh-LS spreading codes, a section on the system simulation model and the simulation results followed lastly by a conclusion.