Performance of physical cell ID detection using PVS based transmit diversity for NB-IoT

The Narrowband (NB)-Internet-of-Things (IoT) radio interface by the 3rd generation partnership project (3GPP) achieves efficient low-cost transmission of IoT traffic with low power consumption for a set of user equipment (UE). Transmit diversity at a base station is effective in achieving a high detection probability for the NB primary synchronization signal (NPSS) and NB secondary synchronization signal (NSSS) without increasing computational complexity at the UE. This paper investigates the effect of precoding vector switching (PVS) based transmit diversity employing up to 8 transmitter antennas on the physical cell ID (PCID) detection probability for NB-IoT. Computer simulation results show when the fading among transmitter antennas is uncorrelated, and that the NPSS detection probability using PVS based transmit diversity with Ntx = 4 antennas is improved by approximately 14% compared to that with Ntx = 2 at the average received signal-to-noise power ratio of −5 dB. Moreover, the PCID detection probability with Ntx = 4 is improved by approximately 10% compared to that with Ntx = 2 even for a high fading correlation among transmitter antennas such as 0.6. When increasing the Ntx value to 8, the PCID detection probability increases by approximately 8% compared to that with Ntx = 4 for the large frequency offset of Af = 70 kHz. Therefore, we conclude that the PVS based transmit diversity with more antennas up to Ntx = 8 is effective in improving the PCID detection probability when considering the actual impairments including fading correlation among transmitter antennas and frequency offset due to the frequency error of the oscillator in the IoT equipment.