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In the NTN scenario A, to avoid interference with other GEO commercial services, the power spectrum of the relayed OFDMA signal should be strictly limited to be within a bandwidth of 200 kHz, which results in a serious challenge on the gNB side. For example, some GEO operators specify that the band-edge attenuation at 100 kHz from the center frequency should be larger than 60 dB. Therefore, the gNB for NTN scenario A requires more sophisticated output filtering before it transmit signal is sent to the gateway and GEO.
In addition to the band-edge suppression challenge that GEO operators face, another vital requirement should be considered by network operators, whose primary goal is to maintain an acceptable link performance. During the 3GPP conformance test, transmit signal quality was evaluated in terms of the EVM of the modulation constellation. For example, for QPSK constellation to be faithfully received, the EVM should be less than 17.5%
Hence, the filtered signal may exhibit severe EVM degradation at its outermost subcarrier as a result of spectral edge suppression. In this study, we addressed this challenge to achieve an implementable filter design with a favourable tradeoff between band-edge suppression and EVM performance.
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IEEE/ICACT20230155 Slide.07
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