31 research outputs found
Generalized Fast-Convolution-based Filtered-OFDM: Techniques and Application to 5G New Radio
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.Comment: To appear in IEEE Transactions on Signal Processin
Channel Equalization in Fast-Convolution Filter Bank based Receivers for Professional Mobile Radio
Abstract-Fast convolution processing has recently been proposed as an efficient approach for implementing filter bank multicarrier systems with good spectral containment and high flexibility in adjusting the subchannel bandwidths and center frequencies. These features make fast convolution filter banks (FC-FBs) a particularly interesting choice for multicarrier transmission in challenging radio scenarios like dynamic spectrum access, cognitive radio, and fragmented spectrum use. In this contribution, the target is to compare the performance of the time-domain equalizer with the frequency-domain equalizer implemented through subcarrier processing in LTE-like multicarrier systems. It is shown that integrating the equalization functions with the FC-FB processing leads to an efficient overall implementation in terms of performance and computational complexity
Filtered Multicarrier Transmission
Orthogonal frequency‐division multiplexing (OFDM) has been adopted as the waveform of choice in the existing and emerging broadband wireless communication systems for a number of advantages it can offer. Nevertheless, investigations of more advanced multicarrier transmission schemes have continued with the aim of eliminating or mitigating its essential limitations. This article discusses multicarrier schemes with enhanced spectrum localization, which manage to reduce the spectral sidelobes of plain OFDM that are problematic in various advanced communication scenarios. These include schemes for enhancing the OFDM waveform characteristics through additional signal processing as well as filter‐bank multicarrier (FBMC) waveforms utilizing frequency‐selective filter banks instead of plain (inverse) discrete Fourier transform processing for waveform generation and demodulation.acceptedVersionPeer reviewe
Efficient Fast-Convolution-Based Waveform Processing for 5G Physical Layer
This paper investigates the application of fast-convolution (FC) filtering
schemes for flexible and effective waveform generation and processing in the
fifth generation (5G) systems. FC-based filtering is presented as a generic
multimode waveform processing engine while, following the progress of 5G new
radio standardization in the Third-Generation Partnership Project, the main
focus is on efficient generation and processing of subband-filtered cyclic
prefix orthogonal frequency-division multiplexing (CP-OFDM) signals. First, a
matrix model for analyzing FC filter processing responses is presented and used
for designing optimized multiplexing of filtered groups of CP-OFDM physical
resource blocks (PRBs) in a spectrally well-localized manner, i.e., with narrow
guardbands. Subband filtering is able to suppress interference leakage between
adjacent subbands, thus supporting independent waveform parametrization and
different numerologies for different groups of PRBs, as well as asynchronous
multiuser operation in uplink. These are central ingredients in the 5G waveform
developments, particularly at sub-6-GHz bands. The FC filter optimization
criterion is passband error vector magnitude minimization subject to a given
subband band-limitation constraint. Optimized designs with different guardband
widths, PRB group sizes, and essential design parameters are compared in terms
of interference levels and implementation complexity. Finally, extensive coded
5G radio link simulation results are presented to compare the proposed approach
with other subband-filtered CP-OFDM schemes and time-domain windowing methods,
considering cases with different numerologies or asynchronous transmissions in
adjacent subbands. Also the feasibility of using independent transmitter and
receiver processing for CP-OFDM spectrum control is demonstrated
Frequency-Domain Signal Processing for Spectrally-Enhanced CP-OFDM Waveforms in 5G New Radio
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 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. Transform
decomposition is used to simplify these computations. Very extensive set of
numerical results is also provided, in terms of radio-link performance and
associated processing complexity.Comment: This work has been submitted to the IEEE Transactions on Wireless
Communications for possible publication. Copyright may be transferred without
notice, after which this version may no longer be accessibl
Flexible fast-convolution processing for cellular radio evolution
Orthogonal frequency-division multiplexing (OFDM) has been selected as a baseline waveform for long-term evolution (LTE) and fifth-generation new radio (5G NR). Fast-convolution (FC)-based frequency-domain signal processing has been recently considered as an effective tool for transmitter and receiver side subband filtering of OFDM-based waveforms. However, for the original continuous FC-based model, the filtering can, in general, be configured in time-direction only with the granularity of half subframe, corresponding to 7, 14, or 28 symbols with 15 kHz, 30 kHz, or 60 kHz subcarrier spacing, respectively. In this paper, we present a symbol-synchronous FC-processing scheme flexibly allowing filter re-configuration with the time resolution equal to one OFDM symbol while supporting tight carrier-wise filtering for 5G NR in mixed-numerology scenarios with adjustable subcarrier spacings, center frequencies, and subband bandwidths, as well as providing co-existence with LTE. Proposed approach segments each stream of time-domain OFDM symbols into overlapping processing blocks of fixed size. Symbol synchronous processing is achieved by dynamically adjusting the overlap between the processing blocks while aligning the payload part of the processing block with the boundaries of the OFDM symbols. The proposed scheme is demonstrated to support the envisioned use cases of 5G NR and provide a flexible starting point for sixth generation (6G) development.acceptedVersionPeer reviewe
Optimized reconfigurable fast convolution based transmultiplexers for flexible radio access
Multirate fast-convolution (FC) processing can be used for realizing low-complexity filter banks (FBs) and transmultiplexers (TMUXs). The main advantage of the FC based realizations when compared with the polyphase FBs is the increased configurability, that is, the number of subchannels, their bandwidths, and the center frequencies can be adjusted independently. In general, FC based FBs are linear periodically shift-variant systems. In this paper, novel matrix representations for the FC synthesis and analysis FBs are first derived. These representations give all the shift-variant impulse responses of the FC based FBs. Then the TMUX optimization criteria are expressed using these representations. Two examples are included to demonstrate the performance of the optimized designs as well as to illustrate the flexibility of the resulting FC based TMUXs.acceptedVersionPeer reviewe