A simulation study on time-frequency localized CDMA using MMSE per carrier equalization

In this paper, a recently proposed general multi-carrier (MC) code division multiple access (CDMA) concept called time-frequency localized CDMA (TFL-CDMA) is further studied in a mobile broadband downlink environment. The known minimum mean square error (MMSE) per carrier equalization method is used as a starting point. A slightly modified MMSE per carrier equalization method is then proposed. When certain bi-directional spreading options are used, a lower frame error rate (FER) is achieved with the modified MMSE per carrier equalization method than with the known MMSE method. The simulated FER is also shown to be nearly constant with respect to the near-far effects. However, when the inter-code interference (ICI) is not a limiting factor, the results suggest that it is advantageous to use spreading only in the frequency direction with the known MMSE method.