In this article the performances of grouped frequency division multiple access (GFDMA) and single-carrier frequency division multiple access (SC-FDMA) techniques using null-subcarriers based carrier frequency offset (CFO) synchronization are compared with respect to various parameters. GFDMA, is a new emerging technique, which uses multiuser interference cancellation to separate the users sharing the same sub-carrier sets. It also uses the iterative scheme in order to update the estimates and reduce errors iteration by iteration. However, just like SC-FDMA, GFDMA also suffers from carrier frequency offset (CFO), which is formed by multiple access interference (MAI) and inter-carrier interference (ICI). Also, due to the multiple signals, having different CFO values, combining at the receiver, CFO synchronization is much more difficult than that in single-user systems. This paper proposes a null subcarrier-based CFO synchronization method for the uplink of GFDMA and SC-FDMA systems, adopting sub-band based subcarrier assignment scheme. Performances of both techniques are compared under various parameters by simulations.