How does dynamic spectrum sharing between LTE and 5G NR affect the RF design?

How does dynamic spectrum sharing between LTE and 5G NR affect the RF design? Dynamic Spectrum Sharing (DSS) allows LTE and 5G NR to coexist on the same carrier frequency, sharing the time-frequency resources dynamically based on traffic demand. From an RF perspective, DSS introduces several unique challenges: (1) Waveform coexistence: LTE uses CP-OFDM in the downlink and DFT-s-OFDM (SC-FDMA) in the uplink. 5G NR uses CP-OFDM in both DL and UL (with optional DFT-s-OFDM for UL). When DSS is active: the base station transmits LTE and NR symbols on the same carrier, interleaved in the time-frequency grid. Some subframes are LTE-only, some are NR-only, and some are shared. The PA must handle both waveforms with the same linearity requirements. (2) PA linearity: the combined LTE + NR waveform may have a higher PAPR than either waveform alone (due to the different numerologies and resource allocation patterns). The PA must meet the ACLR and EVM requirements for both LTE and NR simultaneously. DPD must be trained on the combined waveform (not on LTE or NR individually). (3) No hardware changes: DSS is primarily a software feature. The existing RF hardware (PA, filter, antenna) continues to operate on the same frequency band. The PA, filter, and antenna do not change between LTE-only and DSS modes. The only RF impact: the PA backoff may need to increase slightly (0.5-1 dB) if the DSS waveform has higher PAPR than the LTE-only waveform. (4) Capacity trade-off: DSS shares the same spectrum between LTE and NR, so neither gets the full bandwidth. Typical capacity: 70-80% of dedicated LTE + 70-80% of dedicated NR (combined, not 100% of each). DSS overhead: approximately 5-15% of the spectrum is used for LTE reference signals (CRS) that cannot be reused by NR. NR must rate-match around the LTE CRS, reducing its available resources.