Evolution of CDMA from interference-limited to noise-limited

• Authors: Hsiao-Hwa Chen
• Venue: Wireless communications systems and networks
• Year: 2004

This chapter will use descriptive language to address the issues on CDMA technological evolution, starting with the very basics of CDMA technologies, including various primary CDMA technologies and their core: spreading codes or sequences, such as M-sequences, Gold codes, Kasami codes, Walsh-Hadamard Sequences, OVSF Codes and complementary codes and their correlation statistical information, reflected in their auto-correlation functions (ACFs) and cross-correlation functions (CCFs), whose characteristics play a pivotal role in determining the overall performance of a CDMA system. Then, the cause of multiple access interference (MAI) and multipath interference (MI) in a CDMA-based wireless system will be addressed from the perspectives of spreading codes and system operation modes, followed by discussion on different methods to mitigate MAI and MI in a conventional CDMA system, such as open-loop and closed-loop power control, multi-user detection, RAKE receiver, antenna-array techniques, pilot-aided CDMA signal detection and up-link synchronization control, etc. The discussions on various features of state-of-the-arts CDMA technologies lead to the introduction of a new concept on isotropic CDMA air-link technology, which consists of two related sectors: isotropic spreading codes and isotropic spreading modulation, which can offer an homogenous performance in both synchronous and asynchronous CDMA channels. A novel CDMA architecture based on complete complementary codes, namely CC-CDMA, is presented as an example of the CDMA system using the isotropic spreading technology, characterized by its attractive isotropic MAI-free property. The lack of isotropic MI-free property in the CC-CDMA system motivates us to work out an even more desirable CDMA system, CC/DS-CDMA, which is designed based on combinational use of complementary codes and traditional direct-sequence spreading technique and can offer a truly interference-free operation in both up-link and down-link channels. With the help of such a superior isotropic MAI-free and isotropic MI-free property, the CC/DS-CDMA can operate virtually in an interference-free environment, ensuring a performance limited only by AWGN, no longer by interferences. A list of complementary codes with different PG values (from 8 to 512) is also given in Appendix at the end of this chapter. Based on the discussion on conventional CDMA technologies and introduction of two novel CDMA architectures, it is concluded in this chapter that the evolution of CDMA technologies will eventually make it happen that a CDMA system could offer a noise-limited performance.Apart from the inclusion of two innovative CDMA architectures, this chapter covers also various new CDMA based wireless standards seldom reported elsewhere in the open literature, such as TD-SCDMA and LAS-CDMA, etc., together with a wide collection of reference sources associated with them, as well as those on other commonly referred CDMA based standards, such as IS-95A/B, cdma2000, UMTS-UTRA, W-CDMA, etc., providing a rather comprehensive coverage about the evolution of CDMA technologies from interference-limited to noise-limited.