Abstract
We propose a near intercarrier interference (ICI)-free and very low complexity iterative detector for frequency-asynchronous distributed Alamouti-coded (FADAC) orthogonal frequency division multiplexing (OFDM). In the previous cancelation schemes, the entire subcarrier signals from one transmit (TX) antenna are estimated and canceled in the received signal from the other TX antenna and vice versa. However, the reliability of the estimated symbols are revealed to significantly vary across the subcarriers and thus, the poorly estimated symbols lead to the incorrect cancelation. Motivated from this, we first propose a scheme which does not cancel the interfering subcarrier(s) at the half band edges which undergo very high interference in FADAC-OFDM. For further improvement, we propose a so-called selective scheme which instantly measures the reliability of the detected symbols at each iteration and then exclude the unreliable symbols in the estimated interference generation.Moreover, the proposed scheme has a drastically reduced complexity by converting the cancelation process from the subcarrier domain to the time domain. In accordance with the analysis on the considered reliability measures, the numerical results show that the proposed scheme achieves the near ICI-free level only within three or four iterations for wide ranges of SNR, frequency offset, and delay spread.
Highlights
Several studies on Alamouti-coded orthogonal frequency division multiplexing (OFDM) for cooperative systems have been reported
In contrast to the conventional distributed Alamouti-coded OFDM, frequency-asynchronous distributed Alamouti-coded (FADAC)-OFDM is free from intercarrier interference (ICI) terms from the near subcarriers due to its ICI self-cancelation property only by simple Alamouti-decoding process
3.2 The proposed iterative ICI cancelation schemes In the previous section, we addressed the issue of the previous iterative ICI cancelation in [10], i.e., the drawback of using the entire detection symbols for ICI reconstruction and cancelation
Summary
Several studies on Alamouti-coded OFDM (orthogonal frequency division multiplexing) for cooperative systems have been reported. In [5–7], typical types of iterative ICI cancelation schemes for the conventional Alamouti-coded OFDM with the distributed antennas have been proposed. Since the conventional Alamouti-coded OFDM [9] has no ICI self-cancelation property for frequency and timing asynchronous distributed antennas, the accuracy of the initial detection is poor. We achieved better performance compared with [5] even with low complexity due to better initial detection performance of FADAC-OFDM compared to the conventional Alamouti-coded OFDM This scheme uses all the detected symbols in the interference reconstruction step without any consideration of reliability of detection symbols.
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