Abstract
This letter reports on a critical issue with the application of OFDM to a full-duplex (FD) cellular system. With small frequency offsets of uplink signals, the downlink BER increases considerably. This is attributed to the high spectral-leakage-interference from the OFDM waveforms of geographically nearby uplink users. As an alternative, we propose applying the FBMC waveform to the same FD cellular system scenario. We calculate the precise spectral-leakage-interference for OFDM and FBMC, based on which, we set up a semi-analytic BER simulation framework. Analysis and numerical results confirm that spectral leakage interference from uplink signals is the critical performance limiting factor. Even with tiny frequency offsets among the users, the performance of FD with OFDM is severely degraded. Although the FDs with the other multicarrier waveforms having lower spectral leakage such as GFDM, UFMC, and f-OFDM overcome this issue to a certain extent, the degradations remain substantial. However, the FBMC-based FD cellular system achieves almost spectral-leakage-interference-free performance, and thus, it substantially outperforms the counterparts with other waveforms.
Highlights
I F WE employ in-band-full-duplexing of the downlink signal over uplink subbands (SBs), the downlink signal is interfered by its own SB uplink signal and by the spectral leakage of uplink signals of other user equipments (UEs) at the other SBs
We present a critical issue that multicarrier-based FD cellular systems undergo a new type of interference named “up-to-down inter-UE inter-SB interference” (U2D-IUISBI)
Through intensive comparisons in various scenarios, we show that FD-FBMC is the most suitable solution to the U2D-IU-ISBI in FD cellular systems, if the SI cancellation gain is sufficiently large
Summary
I F WE employ in-band-full-duplexing of the downlink signal over uplink subbands (SBs), the downlink signal is interfered by its own SB uplink signal and by the spectral leakage of uplink signals of other user equipments (UEs) at the other SBs. For the OFDM waveform, the U2D-IU-ISBI is critical because the OFDM waveform has a large spectral leakage when the inter-carrier orthogonality is broken by the frequency offsets (FOs). The studies in [3], [4] considered FOs in OFDM-based FD. We present a critical issue that multicarrier-based FD cellular systems undergo a new type of interference named “up-to-down inter-UE inter-SB interference” (U2D-IUISBI). In existing studies on FD cellular systems, only intra SB interference has been considered. For a comprehensive comparison, the BERs for FD systems with the other filter-based multicarrier waveforms, i.e., GFDM, UFMC, and f-OFDM, are evaluated by waveform-level simulation. Through intensive comparisons in various scenarios, we show that FD-FBMC is the most suitable solution to the U2D-IU-ISBI in FD cellular systems, if the SI cancellation gain is sufficiently large
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