A Blind Frequency Offset Estimator for Coherent M-PSK System in Autonomous Radio
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A Blind Frequency Offset Estimator for Coherent M-PSK System in Autonomous Radio Le Wang · Zhugang Wang · Weiming Xiong
Received: 21 June 2012 / Revised: 5 September 2012 © Springer Science+Business Media, LLC 2012
Abstract This paper presents a novel blind frequency offset estimator for coherent M-PSK systems in an autonomous radio. The proposed estimator is based on the spectrum of the signal’s argument. A data removal block is developed. We derive the distribution of the instantaneous phase, which is applied to indicate that the proposed estimator can be considered as a class of nonlinear least-squares estimator. We provide a method to analyze the asymptotic performance of the proposed estimator. This enable us to predict the mean-square error on frequency offset estimation for all signal-to-noise ratio (SNR) values. Computer simulations indicate that the proposed estimator achieves better performance than the original estimator. The performance of the proposed estimator as a blind estimator is also illustrated. Keywords Instantaneous phase · Data removal · Nonlinear least-squares estimator · Blind estimation
1 Introduction The steady march of radio receiver technology over the decades has enabled smaller and increasingly capable radio terminals. With all operations done digitally, radios began to become more flexible as well, and the natural next step in the evolution of radio is the development of techniques for autonomous or cognitive software-defined L. Wang () · Z. Wang · W. Xiong Center for space science and applied research, Chinese Academy of Sciences, Beijing 100190, China e-mail: [email protected] Z. Wang e-mail: [email protected] W. Xiong e-mail: [email protected]
Circuits Syst Signal Process Fig. 1 The order of estimation in the autonomous radio
radio (SDR) receivers for whatever type of signal received [20]. The autonomous radio and cognitive radio have some aspects in common. For instance, spectrum sensing in cognitive radios is used to estimate the frequency and bandwidth, which is equally important for the autonomous radio. In [12], the order of estimation in the autonomous radio indicates that the first two parameters to be estimated are the modulation index and the frequency, shown in Fig. 1. It means that these two parameters are obtained without information on the symbol rate, symbol synchronization, and modulation type. The estimators about these two parameters are independent of other parameters estimation. Thus, a blind estimator of the frequency offset is required in autonomous radio systems. The estimation of modulation index helps decide whether the modulation of the received signal is residual-carrier phase shift keying (PSK), or suppressed-carrier PSK. There are many efficient estimators of single tone frequency in residual-carrier systems via detecting the residual carrier. In suppressed-carrier PSK systems, the frequency estimators can be grouped into two classes: the data-aided estimators and nondata-aided estimators. The data-aided estimators remove the data with the training
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