In this paper, we propose an iterative joint DA/DD channel estimation algorithm for known symbol padding (KSP) OFDM. The pilot symbols used to estimate the channel are not only located in the guard interval, but also on some of the OFDM carriers. Initially, the channel is estimated using the pilot symbols only. Next, a decision is made with respect to the transmitted data symbols. We consider both hard and soft decision of the data symbols. The decisions on the data symbols are then used to update the channel estimate in a joint DA/DD estimation algorithm. The algorithm iterates between data detection and channel estimation until convergence is reached. At high SNR, the MSE performance of the iterative estimator converges to the MSE performance of the case where all data symbols are prior known at the receiver, i.e. the all pilot DA estimator. It turns out that the MSE performance of hard decision of the data symbols reaches the MSE of the all pilot DA estimator at lower SNR than that of soft decision of the data symbols; this is caused by some approximations needed to simplify the estimation algorithm.
Abstract-In this correspondence, we propose an iterative "turbo" channel estimation algorithm for known symbol padding (KSP) orthogonal frequency-division multiplexing (OFDM), where the guard interval is filled with pilot symbols. Additional pilot symbols are transmitted on some of the OFDM carriers. The channel estimation algorithm is based on the expectation-maximization (EM) algorithm. In the initialization phase of this iterative algorithm, the received time-domain samples are first converted to the frequency domain, and the initial channel estimate is based on the observation of the pilot carriers only. Then the EM-algorithm switches back to the time-domain and updates the channel estimates until convergence is reached. The proposed estimator performs very good: the mean square error (MSE) performance of the proposed estimator is close to the Cramér-Rao lower bound (CRB) corresponding to the all pilots case, for the SNR region of practical interest, and the resulting bit error rate essentially coincides with the case of the perfectly known channel.
Abstract-In this paper we present a time delay estimation algorithm for known symbol padding (KSP) orthogonal frequency division multiplexing (OFDM) systems. The estimator exploits both the pilot symbols in the guard interval and on the pilot carriers, and takes the frequency selectivity of the fading channel into account. Our simulations indicate that the time delay estimator gives rise to only a small degradation of the bit error rate (BER) performance, as compared to a receiver with perfect synchronization.
Abstract-We propose an iterative decision-directed joint frequency offset (FO) and channel estimation algorithm in a known symbol padding (KSP) orthogonal frequency division multiplexing (OFDM) system, where the guard interval is filled with pilot symbols. Besides those time domain pilot symbols, some additional pilot symbols are transmitted on the pilot carriers. The decision-directed algorithm is initialized by pilot-aided FO estimation without channel knowledge. We propose a possible initialization algorithm that operates in the frequency domain (FD). After the initialization phase, the iterative decision-directed estimation algorithm is applied. For the channel estimation step, an existing pilot-aided channel estimation algorithm is extended to a decision-directed algorithm which uses the Fast Fourier Transform outputs at both the pilot and data carrier positions. For the uncoded case, the proposed iterative decision-directed joint FO and channel estimation algorithm reaches the bit error rate performance of a receiver with perfect synchronization and perfect channel knowledge. For a coded system, there is small loss in performance of less than 1 dB when our proposed algorithm is applied compared to a receiver with perfect knowledge about the FO and the channel.
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