This chapter addresses the issues on the architecture of next generation CDMA (NG-CDMA) systems, which should offer a much better performance in terms of its capacity and transmission rate, etc., than that possible in all current 2-3G systems based on CDMA technology. The ultimate goal is to engineer a CDMA system, whose performance will no longer be interference-limited, for its application in futuristic wireless communications. To achieve this, many challenging issues should be tackled, such as innovated design approaches for CDMA codes, multi-dimensional spreading techniques, suitable CDMA signaling format for high-speed bursty traffic, and so forth. This chapter will review the author’s ongoing research activities on the NG-CDMA technology, which can offer a performance never inferior to that of orthogonal frequency division multiple access (OFDMA) technology. In particular, the author will briefly introduce a new CDMA code design method, called Real Environment Adapted Linearization (REAL) approach, which can be used to generate CDMA code sets with inherent immunity against multipath interference and multiple access interference for both uplink and downlink transmissions. The chapter will also illustrate that an interference-free CDMA can only be made possible with the application of orthogonal complementary codes (OCCs). The use of traditional CDMA codes, such as Gold, Kasami, Walsh-Hadamard and OVSF codes, all working on an one-code-per-channel basis, will never help in this sense. Several other topics related to the NG-CDMA technology will also be addressed, such as system performance issues, other properties of the NG-CDMA technology, and so on.
Is NOMA Efficient in Multi-Antenna Networks? A Critical Look at Next Generation Multiple Access Techniques
