This paper proposes a generalized model and methods for fast-convolution (FC)-based waveform generation and processing with specific applications to fifth generation new radio (5G-NR). Following the progress of 5G-NR standardization in 3rd generation partnership project (3GPP), the main focus is on subband-filtered cyclic prefix (CP) orthogonal frequency-division multiplexing (OFDM) processing with specific emphasis on spectrally well localized transmitter processing. Subband filtering is able to suppress the interference leakage between adjacent subbands, thus supporting different numerologies for so-called bandwidth parts as well as asynchronous multiple access. The proposed generalized FC scheme effectively combines overlapped block processing with time-and frequency-domain windowing to provide highly selective subband filtering with very low intrinsic interference level. Jointly optimized multi-window designs with different allocation sizes and design parameters are compared in terms of interference levels and implementation complexity. The proposed methods are shown to clearly outperform the existing state-of-the-art windowing and filtering-based methods.
Orthogonal frequency-division multiplexing (OFDM) has been selected as the basis for the fifth-generation new radio (5G NR) waveform developments. However, effective signal processing tools are needed for enhancing the OFDM spectrum in various advanced transmission scenarios. In earlier work, we have shown that fast-convolution (FC) processing is a very flexible and efficient tool for filtered-OFDM signal generation and receiver-side subband filtering, e.g., for the mixed-numerology scenarios of the 5G NR. FC filtering approximates linear convolution through effective fast Fourier transform (FFT)-based circular convolutions using partly overlapping processing blocks. However, with the continuous overlap-and-save and overlap-and-add processing models with fixed block-size and fixed overlap, the FC-processing blocks cannot be aligned with all OFDM symbols of a transmission frame. Furthermore, 5G NR numerology does not allow to use transform lengths shorter than 128 because this would lead to non-integer cyclic prefix (CP) lengths. In this article, we present new FC-processing schemes which solve or avoid the mentioned limitations. These schemes are based on dynamically adjusting the overlap periods and extrapolating the CP samples, which make it possible to align the FC blocks with each OFDM symbol, even in case of variable CP lengths. This reduces complexity and latency, e.g., in mini-slot transmissions and, as an example, allows to use 16-point transforms in case of a 12-subcarrier-wide subband allocation, greatly reducing the implementation complexity. On the receiver side, the proposed scheme makes it possible to effectively combine cascaded inverse and forward FFT units in FC-filtered OFDM processing.
In this paper, new symbol synchronization method for OFDM-system is presented. This method is based on double correlation structure. Also the method that will compensate the effect of inaccurate FF"T position is presented. The presented methods will improve the accuracy of the symbol synchronization in channels that have long and strong echoes, as can be the case with Single Frequency Network (SFN). However, they are also usable in Ricean and Rayleigb type of channels. Furthermore, when presented symbol synchronization method is combined with the compensator that corrects the inaccurate FFT position, there is no need for fine synchronization.Specification ETS 300 744, Digital broadcasting system for television, sound and data s e n -ices; Framing structure, channel coding and modulation for digital terrestrial television, February, 1997.
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. INDEX TERMS Fifth-generation new radio (5G-NR), fast convolution (FC), filtered OFDM, physical layer, prototype, software-defined radio (SDR), power amplifier (PA), weighted overlap-and-add (WOLA), peakto-average-power ratio (PAPR).
The presented approach addresses the problem of query and persistent query (subscription) resolution, taking into consideration distribution across multi-domains, network infrastructure and content management. This approach is particularly suitable for information-centric and cloud computing applications based around a mobile-device infrastructure.
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