233 research outputs found
INTER CARRIER INTERFERENCE AND SIGNAL TO INTERFERENCE RATIO OF VARIOUS PULSE SHAPING FUNCTIONS USED IN OFDM SYSTEM WITH CARRIER FREQUENCY OFFSET
Orthogonal Frequency Division Multiplexing (OFDM) is the important modulation of choice for fourthgeneration broadband multimedia wireless systems. This paper is focused on the problem of reducing the intercarrierinterference (ICI) and signal to noise ratio in the transmission over OFDM using various pulse shaping methods. Here we have performed a detailed performance comparison of various pulse shaping functions used in OFDM System with Carrier Frequency Offset. They appear to be suitable for transmission in OFDM systems with carrier frequency offset. The results obtained by analysis show that the performance improvement over conventional pulse shapes, are significant for reducing average intercarrier-interference (ICI) power and increased ratio of average signal power to average ICI power (SIR)
Extensionless Adaptive Transmitter and Receiver Windowing of Beyond 5G Frames
Newer cellular communication generations are planned to allow asynchronous
transmission of multiple numerologies (waveforms with different parameters) in
adjacent bands, creating unavoidable adjacent channel interference. Most prior
work on windowing assume additional extensions reserved for windowing, which
does not comply with standards. Whether windowing should be applied at the
transmitter or the receiver was not questioned. In this work, we propose two
independent algorithms that are implemented at the transmitter and receiver,
respectively. These algorithms estimate the transmitter and receiver windowing
duration of each resource element (RE) with an aim to improve fair proportional
network throughput. While doing so, we solely utilize the available extension
that was defined in the standard and present standard-compliant algorithms that
also do not require any modifications on the counterparts or control signaling.
Furthermore, computationally efficient techniques to apply per-RE transmitter
and receiver windowing to signals synthesized and analyzed using conventional
cyclic prefix orthogonal frequency division multiplexing are derived and their
computational complexities are analyzed. The spectrotemporal relations between
optimum window durations at either side, as well as functions of the excess
signal to noise ratios, the subcarrier spacings and the throughput gains
provided over previous similar techniques are numerically verified.Comment: 15 pages, 2 algorithms, 3 tables, 11 figures (1 of which includes 3
subfigures) and 3 author biographies. Final version accepted for publication
in IEEE Transactions on Vehicular Technolog
Orthogonal Frequency Division Multiplexing modulation and inter-carrier interference cancellation
The Orthogonal Frequency Division Multiplexing (OFDM) technique, wireless channel models, and a pair of new intercarrier interference self-cancellation methods are investigated in this thesis. The first chapter addresses the history of OFDM, along with its principles and applications. Chapter two consists of three parts: the principal, the modern OFDM models, and the Peak to Average Power Ratio (PAPR) problem. Chapter two also summarizes possible PAPR solutions. Chapter three discusses a series of well-known wireless channel models, as well as the general formula for wireless channels. In Chapter four, ICI problem has been discussed, along with its existing solutions. Chapter five focuses on two new ICI self-cancellation schemes, namely the clustering method and the multi-codebook method. These two new methods show promising results through the simulations. A summary of this thesis and the discussion of future research are also provided in Chapter five
Waveform Advancements and Synchronization Techniques for Generalized Frequency Division Multiplexing
To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation.
This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation framework, the problem of symbol time offset (STO) and carrier frequency offset (CFO) estimation is investigated and synchronization approaches, which can operate in burst and continuous transmissions, are designed.
The first part of this work presents the modulation principles of prominent 5G candidate waveforms and then focuses on the GFDM basic and advanced attributes. The GFDM concept is extended towards the use of OQAM, introducing the novel frequency-shift OQAM-GFDM, and a new low complexity model based on signal processing carried out in the time domain. A new prototype filter proposal highlights the benefits obtained in terms of a reduced out-of-band (OOB) radiation and more attractive hardware implementation cost. With proper parameterization of the advanced GFDM, the achieved gains are applicable to other filtered OFDM waveforms.
In the second part, a search approach for estimating STO and CFO in GFDM is evaluated. A self-interference metric is proposed to quantify the effective SNR penalty caused by the residual time and frequency misalignment or intrinsic inter-symbol interference (ISI) and inter-carrier interference (ICI) for arbitrary pulse shape design in GFDM. In particular, the ICI can be used as a non-data aided approach for frequency estimation. Then, GFDM training sequences, defined either as an isolated preamble or embedded as a midamble or pseudo-circular pre/post-amble, are designed. Simulations show better OOB emission and good estimation results, either comparable or superior, to state-of-the-art OFDM system in wireless channels
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
Intersymbol and Intercarrier Interference in OFDM Systems: Unified Formulation and Analysis
A unified matrix formulation is presented for the analysis of intersymbol and
intercarrier interference in orthogonal frequency-division multiplexing (OFDM)
systems. The proposed formulation relies on six parameters and allows studying
various schemes, including those with windowing in the transmitter and/or in
the receiver (called windowed OFDM systems), which may add cyclic suffix and/or
cyclic prefix (CP), besides the conventional CP-OFDM. The proposed framework
encompasses seven different OFDM systems. It considers the overlap-and-add
procedure performed in the transmitter of windowed OFDM systems, being jointly
formulated with the channel convolution. The intersymbol and intercarrier
interference, caused when the order of the channel impulse response is higher
than the number of CP samples, is characterized. A new equivalent channel
matrix that is useful for calculating both the received signal and the
interference power is defined and characterized. Unlike previous works, this
new channel matrix has no restrictions on the length of the channel impulse
response, which means that the study is not constrained to the particular case
of two or three data blocks interfering in the received signal. Theoretical
expressions for the powers of three different kinds of interference are
derived. These expressions allow calculating the
signal-to-interference-plus-noise ratio, useful for computing the data rate of
each OFDM system. The proposed formulation is applied to realistic examples,
showing its effectiveness through comparisons based on numerical performance
assessments of the considered OFDM systems
The First 15 Years of SEFDM: A Brief Survey
Spectrally efficient frequency division multiplexing
(SEFDM) is a multi-carrier signal waveform, which achieves
higher spectral efficiency, relative to conventional orthogonal
frequency division multiplexing (OFDM), by violating the orthogonality
of its sub-carriers. This survey provides the history
of SEFDM development since its inception in 2003, covering
fundamentals and concepts, wireless and optical communications
applications, circuit design and experimental testbeds. We focus
on work done at UCL and outline work done other universities
and research laboratories worldwide. We outline techniques to
improve the performance of SEFDM and its practical utility with
focus on signal generation, detection and channel estimation
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