Estimation and reduction of CFO in OFDM system

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrier modulation scheme. OFDM is sensitive to the carrier frequency offset (CFO) which may be caused due to difference in the carrier frequencies of transmitter and receiver. A well-known problem of OFDM is its sensitivity to frequency offset which occur due to the mismatch between transmitter and receiver local oscillator. Doppler shift and frequency offset introduces inter-carrier interference (ICI) in the OFDM symbol. Inter-carrier interference (ICI) is still a major concern OFDM system. It degrades the system performance significantly in multipath fading channels. Estimation of CFO are performed by using various methods, i.e. training sequence based and using pilot symbol. In this project work, we have done the estimation of CFO using pilot based. At the receiver, after serial to parallel conversion of the received signal, the cyclic prefix is removed first and then fed to an FFT block for de-multiplexing the multi-carrier signals. Following the FFT block, the pilot signals are extracted from the demultiplexed samples. The CFO estimation at pilot subcarriers is performed by MMSE. We send a pilot signal to the receiver, the pilot transmitted to receiver is separately and it compares the phases of all subcarriers at each OFDM symbol. When pilot is send only one input is known and others are zero then CFO is estimated by using set of equations After signal demodulation at the signal demapper, the information binary data is reconstructed at the receiver output. In this project, we focused on the estimation and reduction of CFO using MMSE and ZF techniques. The result shows the implementing equalization techniques like Zeroforcing (ZF) and Minimum mean square error (MMSE) for AWGN and Rayleigh fading channels. It improves the BER performance of the AWGN and Rayleigh channel. Index Term-OrthogonalFrequency Division Multiplexing (OFDM), Carrier Frequency Offset (CFO), Zero Forcing (ZF), Minimum Mean Square Error (MMSE).

FBMC/OQAM Transceiver for Future Wireless Communication Systems: Inherent Potentials, Recent Advances, Research Challenges

“…This reduces the spectral efficiency since the Cyclic Prefix (CP) duration must be greater than the relative TO between users. Nevertheless, despite being adopted in 5G thanks to its simplicity and robustness to multipath, OFDM presents several drawbacks: high sensitivity to Carrier Frequency Offsets (CFO) coupled with a high Out-Of-Band-Power-Leakage (OOBPL) [12]- [14]. Fine synchronization and guard bands are required to avoid compromising multiple access and for the coexistence of multiple services.…”

A novel orthogonal frequency division multiplexing with index modulation waveform with carrier frequency offset resistance and low peak‐to‐average power ratio

“…[1][2][3][4] However, OFDM-based systems are relatively sensitive to the carrier frequency offset (CFO), which is caused by frequency mismatches between the transmitter and receiver or by Doppler effect. 5 To achieve reliable communication, intercarrier interference (ICI) caused by the CFO must be estimated and compensated. 6 Moreover, high peak-to-average power ratio (PAPR) at the transmitter side either limits the efficiency of high-power amplifiers (HPAs) by forcing them to operate in linear region or causes HPAs to operate in nonlinear region, disturbing the time-domain OFDM signal.…”

“…Several blind CFO estimation algorithms are given in previous studies. 5,[9][10][11][12] Although blind CFO estimation techniques do not decrease the spectral efficiency of a given system, they suffer from imprecise CFO estimations. In Mokhtar et al, 13 a semiblind CFO estimation technique is considered, which utilizes zero pilots.…”

“…Orthogonal frequency division multiplexing with index modulation (OFDM‐IM) is a highly attractive technique for high rate data transmission under multipath and frequency‐selective wireless channels due to its resistance against intersymbol interference (ISI) and improved performance compared to classical OFDM 1–4 . However, OFDM‐based systems are relatively sensitive to the carrier frequency offset (CFO), which is caused by frequency mismatches between the transmitter and receiver or by Doppler effect 5 . To achieve reliable communication, intercarrier interference (ICI) caused by the CFO must be estimated and compensated 6 .…”

“…Various methods and algorithms are proposed for the CFO estimation. Several blind CFO estimation algorithms are given in previous studies 5,9–12 . Although blind CFO estimation techniques do not decrease the spectral efficiency of a given system, they suffer from imprecise CFO estimations.…”