CDM based reference signal structure using oversampling for OFDM downlink

This paper proposes code division multiplexing (CDM) based reference signal (RS) multiplexing using oversampling for orthogonal frequency division multiplexing (OFDM) in the downlink. In the proposed RS multiplexing scheme, multiple transmission-stream-specific RSs are multiplexed using orthogonal CDM into the same original resource elements (REs) through oversampling of the fast Fourier transform (FFT) (or inverse fast Fourier transform (IFFT)). Hence, the required REs for the increased number of transmission streams, which correspond to the number of transmission antennas, can be reduced compared to that for the conventional RS multiplexing scheme that uses a combination of frequency division multiplexing (FDM) and time division multiplexing (TDM). Computer simulation results show that when the RSs for the third and fourth streams are multiplexed into the same REs as those for first and second streams using orthogonal CDM, the same block error rate performance is achieved as that for the RS multiplexing based on the Release 8 Long-Term Evolution (LTE) radio interface for 4-antenna space-frequency block code (SFBC) plus frequency switched transmit diversity (FSTD).