ment. The NSSS is generated by element-wise multiplication between a ZC sequence and a binary scrambling sequence. The root of the ZC sequence and binary scram- bling sequence is determined by narrowband physical cell identity (NB-PCID). The cyclic shift of the ZC sequence is further determined by the frame number. NB-PCID is an addi- tional input parameter SO that it can be derived from the sequence. There are a total of 504 distinct NB-PCID values. The NSSS is transmitted in the last subframe of each Internet of Things 759 0123456789012345678901234567890123456789 Subframe Subframe 5 Slot 0 Slot 1 01234560123456 LTE CRS LTE PDCCH or Unused Unused 1=3,4, 2Nspm Figure 6.9 Structure of NPSS in time and frequency [2,25]. 0123456789012345678901234567890123456789 Subframe Subframe 9 Slot 0 Slot 1 012345601234 LTE CRS LTE PDCCH or unused Figure 6.10 Structure of NSSS in time and frequency domains [2,25]. even-numbered radio frame, as shown in Fig. 6.10. The sequence d(n) used for the NSSS is generated from a frequency domain ZC sequence according to the following: n=0,1,...,131 Ncell n' = n mod131; m=nmod128; q= 760 Chapter 6 The binary sequence bq(m) is given in [2]. The cyclic shift Of in frame number Nf is given by Of = 33/132(nf/2)mod4 [2]. 6.3.4 Narrowband Reference Signals The downlink narrowband reference signal (NRS) consists of known reference symbols inserted in the last two OFDM symbols of each slot for NB-IoT antenna ports 0 and 1, except invalid subframes and subframes transmitting NPSS or NSSS. There is one NRS transmitted per downlink NB-IoT antenna port. In addition to NRSs, the physical layer sup- ports narrowband positioning reference signals. Physical layer provides 504 unique cell identities using the NSSS. It will be indicated to the UE whether it may assume that the cell ID is identical for NB-IoT and LTE systems. In the case where the cell IDs are identical, UE may use the downlink cell-specific reference signals for demodulation and/or measure- ments when the number of NB-IoT antenna ports is th