A Low-Complexity Frequency Offset Correction Scheme for Synchronization in OFDM Systems

Abstract

A new carrier frequency offset estimation scheme in the orthogonal frequency division multiplexing (OFDM) system is proposed. In non-data-aided synchronization systems, maximum likelihood estimation (MLE) is often used for carrier frequency offset acquisition but it could not correct the accumulated residue frequency offset caused by sampling clock offset and other factors. After simple comparisons at frequency domain, the proposed scheme takes correction to OFDM symbols and makes compensation for MLE algorithm. By sharing the same phase calculation block with the acquisition step, it keeps very low computational cost and reduces the implementation complexity. The system performance was investigated in additive white Gaussian noise channel.

Analysis of OFDMA receiver with carrier frequency offset and common carrier frequency offset (CCFO)

“…The OFDMA system is more affected by the CFO hence there are various techniques proposed earlier for the estimation and compensation of CCFO [8]- [15]. For simplicity for calculation only two users is considered Then the number of subcarriers ,'N' is divided between two users such that ,'N/2' for each user.…”

“…The normalized frequency offset ′ , which stands for the multiple of subcarrier spacing [15], could be divided into two parts: the integer frequency offset k and the fractional frequency offset . The first one causes the OFDM symbol to have a cyclic shift, and a phase change proportional to the OFDM symbol index n. The integer frequency offset should be corrected before demodulation and there are many schemes to make compensation for it.…”

“…From the figure 7 we infer that the interference of the first user's subcarrier interferes with the rest of the subcarriers of different users .The self-interference within the same user is low compared with the rest of the other users. In an OFDM system for the MLE scheme [15], three typical CFO of 20 × 10 , 100 × 10 and 50 × 10 caused by sampling clock offset are considered in figure 8. The BER is much the same at low SNR in the three conditions.…”

A Fast and High Efficiency Carrier Offset Estimator for OFDM

“…Orthogonal frequency division multiplexing (OFDM) is a multiple carriers transmission technique, which divides the available spectrum into many subcarriers, each one being modulated by a low data rate stream [1]. The OFDM system has two advantages over a single carrier system: to overcome multipath fading and to decrease the complexity of a channel equalizer by inserting cyclic prefix.…”