Iterative detection for frequency-asynchronous distributed Alamouti-coded (FADAC) OFDM

Bong-seok Kim, Kwonhue Choi
2017 EURASIP Journal on Wireless Communications and Networking  
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
more » ... carriers 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. fading channel by dividing the entire subcarriers into multiple subblocks. However, in the severely frequencyselective fading channels, FADAC-OFDM gets worse due to non-negligible inter-block ICI terms. Meanwhile, [5] [6] [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. Thus, a considerable number of iterations of cancelation has to be performed until the performance converges. Moreover, the converged performances are not so impressive. Although in [5] they derived the performance result close to no-CFO case, they assumed the perfect ICI cancelation which has not been justified. The schemes in [6, 7] rapidly break down as the CFO gets larger than 0.5. Moreover, they have high computation overheads because at each iteration, the required number of complex multiplications for the interference
doi:10.1186/s13638-017-0819-1 fatcat:ylid653yprgzrpbnnpcw42gcee