實作過程中，針對兩種子載波間隔的符號週期進行IFFT運算，有鑑於此，如何透過時序邏輯、控制訊號及狀態機等解決方案，來達到不中斷的方式產生符合5G 規格訊號OFDM 訊號，為本論文核心探討之問題。 ;In the fifth generation(5G) mobile technology, 3GPP adopted CP-OFDM for waveform modulation which is very similar to the usage in LTE. The difference between these two generations is that LTE only uses a fixed 15 kHz sub-carrier spacing in the physical channel while 5G NR-FR1 supports 15kHz, 30kHz, and 60kHz depending on the factor named Numerologies. Moreover, multi-subcarrier spacing is also supported in the same radio frame structure called mixed (or multi) Numerologies.
According to this feature, this paper focuses on studying the 3GPP-R16 specification of the 5G downlink physical layer and designs a downlink transmission channel with a specific configuration in the N78 operating band. The physical channel of SSB/PBCH and PDCCH/PDSCH are set up in different sub-carrier spacing to discuss the frame structure under the resource grid between two sub-carriers (30, 15 kHz). A hardware circuit is designed by Verilog programming language to generate the corresponding downlink baseband signal, and the transmitter is implemented and verified on the FPGA platform.
The solution proposed in this paper uses logic circuits to design control signals, state machines, etc., performing IFFT operations on sequences of two symbol period, and generating OFDM signals which meet 5G specifications in an uninterrupted manner is the best result in the experiment.
