Zadoff-Chu sequence based time-domain SNR estimation for OFDM systems

Abstract

The optimization of wireless orthogonal frequency division multiplexing (OFDM) systems is based on the knowledge of the signal-to-noise ratio (SNR). Most of the existing methods for the SNR estimation operates in the frequency-domain and assumes perfect carrier frequency offset (CFO) synchronization. However, it has been shown that in real systems in the presence of the residual CFO this estimators are prone to performance degradation. This problem can be avoided by estimating the SNR in the time-domain. In this paper, a novel low-complexity time-domain SNR estimator based on time periodic Zadoff-Chu (ZC) sequence, named TDZCE, is proposed. When applied to the time periodic synchronization preamble, commonly used in packed based OFDM systems, the special property of a ZC sequence preserves the considered comb-type structure both in the frequency and time-domain. This allows for easy adaptation of previously proposed moment-based SNR estimator to be applied to the time-domain samples. The TDZCE outperforms the existing time-domain SNR estimators in frequency-flat channels in the presence of the CFO, and approaches the Cramer-Rao bound (CRB) as the number of periodic parts of the proposed preamble increases. Additionally, it offers considerable computational savings compared to the existing time-domain SNR estimators.

Pilot-Based Time Domain SNR Estimation for Broadcasting OFDM Systems

“…In this section, the computational complexity of the PTD scheme is evaluated and compared with the conventional Zadoff-Chu preamble-based time domain method [25], considering the floating point operations per second (FLOPs) as a complexity metric. In general, FLOPs means the number of complex additions and multiplications required to perform one SNR estimate.…”

“…On the other hand, the Zadoff-Chu sequence SNR estimator involves 4N FFT + 2 number of FLOPs, as given in Table 1 of [25]. Hence, the PTD SNR estimator provides the computational saving of approximately 45% (for Q � 16) compared to the conventional Zadoff-Chu sequence estimator.…”

“…ese techniques can be extended to average SNR estimation schemes. Another way to overcome the limitation, due to frequency-selective channel, is to improve the structure and design of the preamble symbol, as shown in [22][23][24][25]. In [22], the whole band (total number of subcarriers) is divided into subbands (set of subcarriers).…”

“…It uses the correlation of the received preambles to estimate signal power while noise power is estimated by subtracting the estimated signal power from the total received symbol power. Yet another time domain preamble-based approach is presented in [25], where the comb-type pilot structure is designed by using the Zado -Chu (ZC) sequence, which outperforms the conventional time domain SNR estimators in terms of computational complexity due to perfect autocorrelation of the ZC sequence.…”

“…By reviewing these studies, it is found that the majority of the schemes utilize the preamble-based structure for the frequencyselective fading channel [22][23][24][25]. In the fast-changing environment, the variation of noise is not same in all OFDM symbols of the frame.…”