Blind estimation of symbol timing and carrier frequency offset in pulse shaping OFDM systems

Abstract

We introduce a blind algorithm for the joint estimation of s mbol timing and carrier frequency offset in pulse shaping 6FDM systems. The proposed estimator exploits the cyclostationarity of the received OFDM signal and can be seen as an extension of the Gini-Giannakis estimator (11 for single-carrier systems. An important feature of our method is the capability to perform a carrier frequency acquisition over the entire bandwidth of the OFDM signal. Furthermore, our estimator can be applied even if no cyclic prefix is used. We rovide simulation results demonstrating the performance orthe new estimator. I N T R O D U C T I O N A N D O U T L I N EOrthogonal frequency division multiplexing (OFDM) systems [2]-[6 are in general more sensitive to symbol timing errors ana carrier frequency offsets than sin5le-carrier systems (71. In an OFDM system synchronization errors cause both intersymbol-interference (ISI) and intercarrierinterference (ICI). Most OFDM time-frequency offset estimators proposed in the literature require pilot symbols (e.g.[8, 91). However, the use of pilot symbols lowers the data rate. Therefore, methods that do not need pilot symbols are desirable. Such estimators [lo, 111 make use of the redundancy introduced by the cyclic prefix (CP).In this paper, we present a blind algorithm' for the joint estimation of symbol timing and carrier frequency offset in pulse shaping OFDM systems. Our estimator exploits the cyclostationarity of the received OFDM signal and can be viewed as an extension of the Gini-Giannakis estimator [ I ] for single-carrier systems. We shall next summarize important novel features of the proposed method:it applies to pulse shaping OFDM systems with arbitrary pulse shapes. it can be used in OFDM systems employing arbitrary time-frequency guard regions. it is capable of performing a carrier frequency acquisition over the entire bandwidth of the OFDM signal.it applies to time-dispersive environments. it does not need a CP (in this case the estimators proposed in [ l o , 111 would break down). it is FFT-based and hence computationally efficient. The paper is organized as follows. In Section 2 we briefly describe OFDM systems employing a time-frequency guard region [12, 131. Section 3 introduces the new estimator and discusses its properties. Section 4 presents simulation results, and finally Section 5 concludes the paper. lThe algorithm is blind because it does not need pilot symbols. In fact, it does not even need a CP.Time-frequency g u a r d region. The baseband equivalent of a pulse shaping OFDM system is given by N--1 m where T is the symbol duration, F denotes the subcarrier spacin , N is the number of carriers, g ( t ) is the transmitter pulse s%aping filter, and ck,l denotes the data symbols. The reconstructed symbols &,I are obtained as &,I = ( I , hk,!), where hk, l(t) = h(t-ZT)eJZ"kFF(t-'T) with the receiver pulse shaping filter h(t). In an OFDM system employing a CP [3] g ( t ) is a rectangular pulse of duration T , h(t) is a rectan-gular pulse of duration T -T, with T, denot...

A Fine Blind Frequency Offset Estimator for OFDM/OQAM Systems

“…A natural extension of the estimator [14], which has been designed in the context of a standard OFDM system, to an OFDM/OQAM type system is proposed in [17]. One can observe that the performance and the properties of these two estimators are close.…”

“…However, simulation experiments show that the ML-based estimator is not quite robust to ISI-channel effects. In [14], a new blind frequency estimator is proposed by exploiting the second-order cyclostationary statistics of the oversampled received signal. This estimator represents an extension of the approach proposed in [15] to the OFDM framework and is specifically designed only for flat-fading channels [14].…”

A New Carrier Frequency Offset Estimation Using CP-ICA Scheme in OFDM Systems

“…However, the algorithm relies on virtual subcarriers, which also lowers the bandwidth efficiency. For more realistic synchronization, some methods have been proposed for blind estimation of timing offset as well as frequency offset [9,10,11,12]. These algorithms mainly utilize the cyclic prefix, and some methods [11] require the OFDM signal to be cyclostationary.…”

“…For more realistic synchronization, some methods have been proposed for blind estimation of timing offset as well as frequency offset [9,10,11,12]. These algorithms mainly utilize the cyclic prefix, and some methods [11] require the OFDM signal to be cyclostationary. In addition, statistical separation approaches have also been explored to do a blind source separation [13,14,15].…”

Preamble-based frequency-domain joint CFO and STO estimation for OQAM-based filter bank multicarrier

“…The literature focused on blind estimation methods initially. In [2], a blind joint CFO and STO estimation has been presented based on the cyclostationarity of the FBMC/OQAM signal. In [3], the CFO estimation is further improved by using the conjugate second-order cyclostationarity statistics.…”