Todaythe demand for multimedia wireless communications isgrowing at an extremely rapid paceand this trend isexpected to continue in the future. The common feature ofmany current wireless standards for high-rate multimediatransmission is the adoption of a multicarrier air interfacebased on orthogonal frequency division multiplexing (OFDM).In OFDM, a set ofequally spaced subcarriers are used for parallel datatransmission.There is currently a strong interest in extending theOFDM concept to multiuser communication scenarios by employing orthogonal frequency division multiple access (OFDMA)and single carrier frequency division multiple access (SC-FDMA) technologies.A prominent example of this trend is the 3GPP Long Term Evolution (LTE) physical layer where OFDM has been adopted as the basic modulation technique that is newin cellular applications. In an OFDMA system, the available subcarriers aredivided into several mutually exclusive sets assigned to differentusers for simultaneous transmission.As in OFDMA, the transmitters in anSC-FDMA system use different orthogonal subcarriers to transmitinformation symbols. However, they transmit the subcarrierssequentially rather than in parallel. The SC-FDMA has similar throughput performance andessentially the same overall complexity as OFDMA. Furthermore, compared with OFDMA, it has low peak to average power ratio (PAPR) property.These systems inherit some disadvantages of OFDM beside its appealing features.Similar to OFDM, OFDMA and SC-FDMA are highly sensitive to carrier frequency offset (CFO)caused by oscillator instabilities and/or wireless channel effects. However, the CFO is a morechallenging issue on OFDMA and SC-FDMA uplink systems, wheredifferent users are affected by different CFOs.Mutualorthogonality among the subcarriers in the presence of CFO is lostand consequently inter-carrier interference (ICI) and multi-user interference (MUI) are introduced. In an SC-FDMA system ICI leads to inter-symbol interference (ISI).Currently OFDMA and SC-FDMA are two competing technologies for the uplink of next generationbroadband wireless systems, so the studyand comparison of these systems in different aspects are important.Although the sensitivity analysis of the OFDM system to CFO hasbeen investigated extensively in the literature, but less studies on OFDMA uplinksystem have been reported, and lessfocus has been applied to SC-FDMA uplink system. This thesis studies and compares OFDMAand SC-FDMA systems in terms of sensitivity to CFO on the uplink. In order to calculatesignal-to-interference ratio (SIR), we use a simple superpositionprinciple approach, where the effects of different users arestudied separately. We derive closed-form mathematical expressionsfor desired signal and interference terms and, consequently, SIR forboth OFDMA and SC-FDMA systems on the uplink. It is pointed outthat there is a strong relation between sensitivity analysis toCFO and subcarrier allocation schemes. We also prove that thederived expressions are reduced to very simple forms ininterleaved subcarrier allocation for both systems. In addition, thetheoretical analysis are verified using Monte Carlo simulations inblock, interleaved,and block-interleaved subcarrier allocations and upon this set ofresults the two systems are compared.Finally a review on the important CFO compensation methods on OFDMA and SC-FDMA uplink systems is presented. Keywords: SC-FDMA, OFDMA, Carrier frequency offset, Inter-carrier interference, Multi-user interference, Inter-symbol interference, SIR analysis, CFO compensation methods.