This letter presents a flexible signal structure supporting localization service for time domain synchronous OFDM (TDS-OFDM) in multi-service transmission applications. Localization is treated as one specific service and the corresponding data is allocated within the physical layer pipe (PLP) of the first subframe. The concept of variable sub-carrier spacing to combat Doppler spread is also introduced for the localization service. Simulation results indicate that the proposed scheme outperforms the conventional scheme and at the same time achieves high positioning accuracy.

This letter considers multicarrier CDMA systems using rectangular chip waveform, where each user's data stream is serial to parallel converted to a number of lower rate streams. Each lower rate stream is then spread by a random spreading code and a suitable chip rate before modulating orthogonal carriers. It is shown that, for a fixed system bandwidth and a given number of carriers, there exists an optimal carrier spacing that minimizes the multiple access interference. Numerical examples also show that the multicarrier DS-CDMA system previously proposed in performs very close to the muticarrier CDMA system using the optimal carrier spacing.