An identification of the tolerable time-interleaved analog-to-digital converter timing mismatch level in high-speed orthogonal frequency division multiplexing systems

Abstract

<span>High-speed Terahertz communication systems has recently employed orthogonal frequency division multiplexing approach as it provides high spectral efficiency and avoids inter-symbol interference caused by dispersive channels. Such high-speed systems require extremely high-sampling <br /> time-interleaved analog-to-digital converters at the receiver. However, timing mismatch of time-interleaved analog-to-digital converters significantly causes system performance degradation. In this paper, to avoid such performance degradation induced by timing mismatch, we theoretically determine maximum tolerable mismatch levels for orthogonal frequency division multiplexing communication systems. To obtain these levels, we first propose an analytical method to derive the bit error rate formula for quadrature and pulse amplitude modulations in Rayleigh fading channels, assuming binary reflected gray code (BRGC) mapping. Further, from the derived bit error rate (BER) expressions, we reveal a threshold of timing mismatch level for which error floors produced by the mismatch will be smaller than a given BER. Simulation results demonstrate that if we preserve mismatch level smaller than 25% of this obtained threshold, the BER performance degradation is smaller than 0.5 dB as compared to the case without timing mismatch.</span>

Improving the performance of free space optical systems: a space-time orthogonal frequency division modulation approach

“…And one of such turbulence-mitigation solutions is the adaptation of efficient coding schemes that have hitherto been quite successful in RF systems like transmit antenna selection multiple-input multiple-output (MIMO) systems [7], turbo coded RF system [8], superorthogonal codes for Nakagami fading channels [9], binary phase-shift keying (BPSK) trellis coded orthogonal frequency division modulation (OFDM) MIMO system [10], MIMO OFDM RF systems [11] and hybrid concatenated codes with iterative decoding RF systems [12], for FSO systems. Other similar adaptable RF error mitigating techniques include concatenated low-density parity-check (LDPC) space-time codes [13], codeword diversity technique [14], and interleaving technique for high-speed OFDM systems [15], for FSO systems as reported in space-time coded FSO system as reported in [16] and space-time coded OFDM FSO system reported in [17]. Other turbulence mitigation schemes proposed so far include the exploitation of some diversity properties to enhance the quality of communication by reducing the overall error on FSO links.…”