2020/08/03 by Juha Yli‐Kaakinen, AlaaEddin Loulou, Yli-Kaakinen, Juha +11
Engineering · Computer Science · #PAPR reduction in OFDM #Digital Filter Design and Implementation #Advanced Wireless Communication Techniques
paper · pdf · doi:10.48550/arxiv.2008.00672
Orthogonal frequency-division multiplexing (OFDM) has been selected as the\nbasis for the fifth-generation new radio (5G-NR) waveform developments.\nHowever, effective signal processing tools are needed for enhancing the OFDM\nspectrum in various advanced transmission scenarios. In earlier work, we have\nshown that fast-convolution (FC) processing is a very flexible and efficient\ntool for filtered-OFDM signal generation and receiver-side subband filtering,≠.g., for the mixed-numerology scenarios of the 5G-NR. FC filtering\napproximates linear convolution through effective fast Fourier transform\n(FFT)-based circular convolutions using partly overlapping processing blocks.\nHowever, with the continuous overlap-and-save and overlap-and-add processing\nmodels with fixed block-size and fixed overlap, the FC-processing blocks cannot\nbe aligned with all OFDM symbols of a transmission frame. Furthermore, 5G-NR\nnumerology does not allow to use transform lengths shorter than 128 because\nthis would lead to non-integer cyclic prefix (CP) lengths. In this article, we\npresent new FC-processing schemes which solve the mentioned limitations. These\nschemes are based on dynamically adjusting the overlap periods and\nextrapolating the CP samples, which make it possible to align the FC blocks\nwith each OFDM symbol, even in case of variable CP lengths. This reduces\ncomplexity and latency, e.g., in mini-slot transmissions and, as an example,\nallows to use 16-point transforms in case of a 12-subcarrier-wide subband\nallocation, greatly reducing the implementation complexity. On the receiver\nside, the proposed scheme makes it possible to effectively combine cascaded\ninverse and forward FFT units in FC-filtered OFDM processing. Transform\ndecomposition is used to simplify these computations. Very extensive set of\nnumerical results is also provided, in terms of radio-link performance and\nassociated processing complexity.\n