Enhanced RSTD for scalable bandwidth of OTDOA positioning in 3GPP LTE

We study the reference signal time difference (RSTD) performance and implementation of scalable positioning reference signal (PRS) bandwidth in long term evolution (LTE). Limited number of reference signal symbols for performing RSTD measurements reduces the quality of the timing and position estimations. To overcome this limitation, we propose to share the PRS transmit port with one of the cell-specific reference signals (CRS) transmit ports, named C-PRS scheme. To get over 10% performance enhancements for small bandwidth cases, we pay an extra complexity from 3 CRS symbols. In order to reduce the overhead of large PRS bandwidth subframes, PRSs keep only in odd slots and data can be transmitted in even slots. The C-PRS scheme may transmit extra 3~4 symbols per one PRS subframe with the negligible losses of performance in the large PRS bandwidth cases. We also discuss the implementation of RSTD measurements which compute the cross-correlation of scalable bandwidth signals by dynamic or fixed FFT/IFFT size algorithms. The fixed FFT/IFFT size algorithm can balance the computation efficiency and the size of local memories.