Abstract
In wireless communications, higher transmission power enables higher coverage or higher data rate. However, due to hardware limitations, achieving high power efficiency becomes challenging. The main issue is that at high power region close to power amplifier (PA) saturation point the highly non-linear response of the PA leads to significant spectral regrowth. In such a case, waveforms with inherently good spectral containment allow for more spectral degradation and can be seen as the most effective solution for the problem. In this study, a fifth-generation new radio (5G NR) user equipment (UE) transmit power is improved by utilizing fast-convolution filtered orthogonal-frequency-division-multiplexing (FC-F-OFDM) waveform, which has an excellent spectral containment performance. A novel method is proposed for improving the peak-to-average-power ratio (PAPR) of FC-F-OFDM waveform, based on applying clipping before FC processing and allocating the clipping noise that stems from the applied clipping, over not only on active band, but a wider band consisting of both the in-band and guard-band regions. An accurate transmitter chain simulator including a measured memory-polynomial model of a practical PA is used to evaluate a wide set of different subcarrier spacings and channel bandwidths. Then, to validate the numerical results, a software-defined radio (SDR) based testbed is created and the modeled PA is used in this testbed. Weighted overlap-and-add (WOLA) based OFDM, also with clipping, is used as a reference in both the numerical evaluations and in measurements. For both waveforms, the transmitted signal quality, out-of-band emissions, and maximum PA output powers are measured under 5G NR specifications and results for different subcarrier spacings and channel bandwidths are provided to prove the benefits and robustness of the presented FC-F-OFDM approach.
Highlights
The fifth-generation New Radio (5G NR) mobile communication systems offer dramatic improvements in data rate thanks to the utilization of significantly wider channel bandwidths and new carrier frequencies [1]–[3]
We provide comprehensive performance evaluation over all subcarrier spacings supported by 5G NR with selected channel bandwidths representing low, medium, and high-performance user equipment (UE) devices
SIMULATION AND TESTBED MEASUREMENT RESULTS In order to characterize the maximum transmission power levels that can be obtained with fast convolution (FC)-F-orthogonal frequency-division multiplexing (OFDM) and WOLAOFDM, different cases are numerically evaluated by using the created simulator and obtained results are compared with measurement results
Summary
The fifth-generation New Radio (5G NR) mobile communication systems offer dramatic improvements in data rate thanks to the utilization of significantly wider channel bandwidths and new carrier frequencies [1]–[3]. As FC-F-OFDM allows to use very narrow guard bands, the passband of the channel filter is increased to allow wider clipping noise response, without violating the OOB requirements As it will be shown with measurement and simulation results, FC-F-OFDM supports very low PAPR levels because it can effectively attenuate the OOB emission caused by clipping and it provides higher transmission power than WOLA-OFDM, which confirms the discussion presented in [24]. B. FILTER PASSBAND EXTENSION Clipping operation that is applied in ‘‘OFDM TX processing’’ module shown in Fig. 1 reduces the PAPR level effectively, but causes an increase in OOB emissions that should be limited to achieve good spectral containment performance. The simulator and measurement based performance evaluation are preferred to analyze the possible transmission power gains that can be obtained with FC filter and as it will be shown with different results, FC filter can support quite high transmission power levels
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