Be Cautious When Analyzing the Sampling Clock Offset in OFDM Systems

Abstract

Many studies have analyzed the effects of sampling clock offset (SCO) on orthogonal frequency-division multiplexing (OFDM) systems. The results of these studies are based on one of two discrete representations of continuous time-domain OFDM signals: (1) a subcarrier set consisting of both negative and positive frequencies, or (2) a subcarrier set comprising only positive frequencies. This paper discusses whether there is any difference between the two representations in the presence of SCO. When SCO is not considered, both representations are equivalent because of aliasing. In the presence of SCO, we derive a closed form of signal-to-interference-plus-noise ratio (SINR) expressions for both cases and compare their performances in terms of SINR by numerical analysis. The latter representation shows worse SINR performance compared to the former representation because the effect of SCO is more relevant for high frequencies and the latter representation has complex exponentials with high frequencies. Therefore, for fair comparisons of performance, caution is needed when analyzing SCO in OFDM systems.