Capacity analysis of uplink multi-user SC-FDMA system with frequency-dependent I/Q imbalance

In this paper, we investigate the capacity of the multi-user (MU) channels with the single-carrier frequency-division-multiple-access (SC-FDMA) transceivers using widely linear equalizers (WLE) to counteract front-end I/Q imbalance (IQI) issues. When the erroneous channel knowledge is available at the equalizer, it is shown that the mutual information could be expressed as a function of the eigenvalues of the direct and image channel realization. Expressions for the error variance of the effective channel and the associated channel capacity are derived in closed form and discussed under special cases. Numerical analysis shows that the ergodic and outage capacity of WLE receivers tends to achieve a capacity region in the vicinity of an ideal system and considerably extends the coverage region of the cell. The impact of the channel correlation and the IQI on the outage probability is also investigated, which highlights the crucial role of the MU resource assignment in exploiting the spectral diversity and their optimality in the presence of IQI.