A Novel Carrier Loop Algorithm Based on Maximum Likelihood Estimation (MLE) and Kalman Filter (KF) for Weak TC-OFDM Signals

Abstract

Digital broadcasting signals represent a promising positioning signal for indoors applications. A novel positioning technology named Time & Code Division-Orthogonal Frequency Division Multiplexing (TC-OFDM) is mainly discussed in this paper, which is based on China mobile multimedia broadcasting (CMMB). Signal strength is an important factor that affects the carrier loop performance of the TC-OFDM receiver. In the case of weak TC-OFDM signals, the current carrier loop algorithm has large residual carrier errors, which limit the tracking sensitivity of the existing carrier loop in complex indoor environments. This paper proposes a novel carrier loop algorithm based on Maximum Likelihood Estimation (MLE) and Kalman Filter (KF) to solve the above problem. The discriminator of the current carrier loop is replaced by the MLE discriminator function in the proposed algorithm. The Levenberg-Marquardt (LM) algorithm is utilized to obtain the MLE cost function consisting of signal amplitude, residual carrier frequency and carrier phase, and the MLE discriminator function is derived from the corresponding MLE cost function. The KF is used to smooth the MLE discriminator function results, which takes the carrier phase estimation, the angular frequency estimation and the angular frequency rate as the state vector. Theoretical analysis and simulation results show that the proposed algorithm can improve the tracking sensitivity of the TC-OFDM receiver by taking full advantage of the characteristics of the carrier loop parameters. Compared with the current carrier loop algorithms, the tracking sensitivity is effectively improved by 2–4 dB, and the better performance of the proposed algorithm is verified in the real environment.

Effective Blind Frequency Offset Estimation Scheme for BST-OFDM Based HDTV Broadcast Systems

“…As reported in the literature [17][18][19], the drawback of LS estimation scheme is that its performance is strongly influenced by the noise under low signal-to-noise ratio (SNR). Since the ISDB-T system has no sufficient CPs for synchronization, it gives rise to a significant loss in estimation accuracy of (11) and (12). To overcome such a problem, an information-carrying TMCC signal can be considered as pilot symbols for the synchronization purpose.…”

“…If not accurately estimated and compensated, the CFO and SFO can destroy the orthogonality among the subcarriers, leading to performance loss at the OFDM receiver [9,10]. In the literature, several types of pilot-aided algorithms have been proposed to perform the joint estimation of CFO and SFO, including maximum likelihood (ML) and linear least-squares (LS) strategies [11][12][13][14][15][16][17][18][19][20][21][22][23]. The joint ML estimation scheme needs a two-dimensional search to obtain the exact estimation of CFO and SFO.…”

An Efficient Frequency Estimator for a Complex Exponential Signal Based on Interpolation of Selectable DTFT Samples

“…Many estimators have been proposed based on the interpolation of DFT and DTFT samples, which is an efficient way to perform fine frequency estimation [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. The interpolations of Jacobsen estimator [ 7 ], Candan estimator [ 8 , 9 ], Quinn estimator [ 10 ], parabolic interpolation estimator [ 11 , 12 ], and Fang estimator [ 13 ] are based on DFT samples.…”

Fine Frequency Acquisition Scheme in Weak Signal Environment for a Communication and Navigation Fusion System

“…In this case, the existing communication system only needs to be simply modified with a lower cost. This technique of superimposing positioning and communication signals has been used in China's mobile Multimedia Broadcasting (CMMB) system and realize fine positioning result [16][17][18][19][20]. Compared with the CMMB system, the mobile communication system has several advantages such as dense base station layout and signal coverage and is developing rapidly.…”