Frequency-domain Pilot Symbols Research Articles

Data-Aided Frequency Offset Estimation for CE-OFDM Broadband Satellite Systems

In recent years, the constant-envelope orthogonal frequency-division multiplexing (CE-OFDM) has been considered as a candidate waveform in broadband satellite systems as it has a 0-dB peak-to-average power ratio (PAPR). However, the carrier frequency offset (CFO) estimation scheme for CE-OFDM broadband satellite systems directly affects system performance. In this paper, we analyze the network architecture and the propagation environment of CE-OFDM broadband satellite systems, and we propose a data-aided CFO estimation strategy based on the frequency domain pilot symbols. The Cramer–Rao bound (CRB) of our CFO estimator is given by mathematical analysis, and the effect of the number of pilot symbols on the estimation performance is analyzed. The pilot symbol-based CFO estimator is composed of a phase demodulator and a discrete Fourier transform (DFT) module, and it can obtain a large estimation range under a small pilot overhead. The simulation results show that the CE-OFDM broadband satellite systems can achieve a good bit error rate (BER) performance by using the proposed strategy to estimate and compensate the CFO.

Analytic Comparison for Channel Response Estimation Based on Time- and Frequency-Domain Pilot Signals

For the orthogonal frequency-division multiplexing (OFDM) system, one can estimate the channel responses (CRs) based on frequency-domain (FD) pilot symbols. One can also estimate the time-domain (TD) channel impulse response (CIR) by inserting a unit pulse ahead of each OFDM block. However, there is no analytic comparison between the CR estimation based on FD pilot symbols and TD unit pulses. In this paper, we first consider the 1-D blocks of CRs and give the analytic comparison of mean-squares error (MSE) for the CR estimation based on TD and FD pilot signals, respectively. For the linear minimum MSE (LMMSE) algorithm, which attains the minimum MSE for the CR estimation based on FD pilots, we derive an MSE lower bound among all possible distributions of pilot symbols. This MSE lower bound coincides with the MSE attained by the optimal CR estimation based on TD unit pulses, under the condition that both FD and TD pilot signals have the same power. Our analysis also indicates that when the number of FD pilots is smaller than the rank of correlation matrix of CRs, it results in an error floor. We further extend our analysis to 2-D blocks of CRs and show that the MSE formulas for CR estimation based on FD and TD pilot signals share the same forms and that they have close numerical values.