LTE-NB : NPSS (Narrow Band Primay Synchronization Signal)
As in normal LTE, NPSS is also using a Zad-off Chu signal. I put the NPSS(LTE-NB) generation formula and PSS(LTE) formula toghether for comparision. As I mentioned, they are both Zadoff Chu form, but slight difference in denominator and NPSS has another term labeled S(l).
The biggest difference between PSS and NPSS lies with resource allocation (RE mapping). In LTE, you can have 6 RB width (72 resource elements) in single OFDM symbol to accommodate a long sequence made of 62 symbols, but in LTE-NB you have only one RB width (12 resource elements) in on OFDM symbol. So you can accommodate only a small number of data in single OFDM symbol. With such a small number of data, it would be difficult to achieve a good correlation required for NPSS detection. So, they use multiple OFDM symbols (11 OFDM Symbols) to accomodate the sync signal which is long enough to achieve good correlation. Basically, a whole RB is used to carry the NPSS. Also, the subframe that carries the NPSS is a little different comparing to LTE case.