Interference Analysis of Interleaved and Localized Mapping Schemes in OFDMA System with Carrier Frequency Offset Bilal Ranjha 1 , M. I. Sakib Chowdhury 2 (Student member IEEE), Mohsen Kavehrad 3 (FIEEE) 1,2,3 Center for Information and Communications Technology Research (CICTR) Department of Electrical Engineering The Pennsylvania State University, University Park, PA 16802 { 1 bar5254, 2 mqc5285, 3 mkavehrad}@psu.edu Abstract—In this paper, we analyze the effect of Carrier Frequency Offset (CFO) of multiple users on the SINR of a single user in OFDMA based uplink communication receiver. We have computed an explicit SINR expression for two types of mapping strategies used in uplink OFDMA systems namely Interleaved Frequency Division Multiple Access (IFDMA) and Localized Frequency Division Multiple Access (LFDMA). SINR expressions in case of carrier frequency offset correction are also computed. Using simulations, we have compared the total average interference due to different values of CFO’s of multiple users for both mapping schemes. Simulation results also show that the average value of Inter-Carrier Interference (ICI) for localized mapping is higher than interleaved mapping while the average value of Multiuser Interference (MUI) is higher for interleaved mapping. Moreover, the average MUI for localized mapping is minimum at the center of the band and it increases as we move towards the band edges. We also observe a flat response for ICI and MUI for interleaved mapping. Index Terms—Orthogonal Frequency Division Multiple Access (OFDMA), Carrier Frequency Offset (CFO). I. I NTRODUCTION In modern wireless communication system, Orthogonal Fre- quency Division Multiplexing (OFDM) [1] has been the most popular and dominant modulation scheme due to its resistance to Inter-Symbol Interference (ISI) caused by multipath fading channels. Because of its high spectral efficiency and ease of implementation using FFT/IFFT, OFDM is also considered as an efficient multiplexing scheme commonly known as Orthogonal Frequency Division Multiple Access (OFDMA). Because of these advantages, OFDMA system has been chosen as a multiplexing scheme for future wireless communication systems especially in 4G LTE [2]. In order to multiplex data from different users using OFDMA, several mapping strategies have been proposed. These include Interleaved and Localized mapping. In inter- leaved FDMA, each user is assigned subcarriers that are uniformly distributed across the whole bandwidth. However in the localized FDMA, each user is allocated a block of contiguous subcarriers for a given time [3]. One of the main disadvantages of OFDM system is its high sensitivity to the carrier frequency offset [4]. This is due to the fact that in OFDM, the separation between each subcar- rier’s center frequency is the minimum required to achieve orhogonality. This is where OFDMA differs with conventional multiplexing schemes. In traditional frequency multiplexing schemes, each user is assigned a separate band that is not overlapping with other bands allocated to other users. In contrast, OFDMA allocates each user different subcarriers that have overlapping spectrum except at the center frequency and the separation between the center frequencies is such that it satisfies minimum distance required for orthogonality. Due to CFO, this minimum separation is disturbed and all the subcarrier’s spectrum overlap at the subcarrier center frequencies. This causes interference and as a result degrades the SNR. This CFO can occur due to several reasons. It may be due to the relative motion of the receiver or due to the mismatch of the local oscillator frequency at the receiver. Sometimes it is possible to estimate the carrier frequency offset at the receiver and then apply it to the received signal to compensate for the offset. In this case, the interference caused by the subcarriers of the desired user will vanish but as we see in this paper, interference from other users caused by their CFO still exists. This is another disadvantage of OFDMA system where we have to pay the price for carrier frequency offsets of other users. In this paper we determine an exact SINR expression for OFDMA based system in the presence of CFO. We find analytical expressions for both IFDMA and LFDMA. SINR expression in presence of Carrier Frequecny Offset Correction (CFOC) is also found as a special case. In our derivation, we will follow the approach used in [5]. This paper is organized as follows. Section I presents the OFDMA system model and describes various system and signal parameters. Section II discusses the mapping strategies proposed for OFDMA. Section III shows the calculation of SINR in the presence of CFO. In Section IV, we show calcu- lation of SINR when we apply CFO compensation. Section V will present simulation results and discussion and will follow with section VI which gives the conclusion. 978-1-4673-3/12/$31.00 ©2013 IEEE 978-1-4673-3/12/$31.00 ©2013 IEEE