1,748 research outputs found
A Generalized Spectral Shaping Method for OFDM Signals
Orthogonal frequency division multiplexing (OFDM) signals with rectangularly
windowed pulses exhibit low spectral confinement. Two approaches usually
referred to as pulse-shaping and active interference cancellation (AIC) are
classically employed to reduce the out-of-band emission (OOBE) without
affecting the receiver. This paper proposes a spectral shaping method that
generalizes and unifies these two strategies. To this end, the OFDM carriers
are shaped with novel pulses, referred to as generalized pulses, that consist
of the ones used in conventional OFDM systems plus a series of cancellation
terms aimed at reducing the OOBE of the former. Hence, each generalized pulse
embeds all the terms required to reduce its spectrum in the desired bands. This
leads to a data-independent optimization problem that notably simplifies the
implementation complexity and allows the analytical calculation of the
resulting power spectral density (PSD), which in most methods found in the
literature can only be estimated by means of simulations. As an example of its
performance, the proposed technique allows complying with the stringent PSD
mask imposed by the EN 50561-1 with a data carrier loss lower than 4%. By
contrasts, 28% of the data carriers have to be nulled when pulse-shaping is
employed in this scenario
Pulse Shaped OFDM for 5G Systems
OFDM-based waveforms with filtering or windowing functionalities are
considered key enablers for a flexible air-interface design for multi-service
support in future 5G systems. One candidate from this category of waveforms is
pulse shaped OFDM, which follows the idea of subcarrier filtering and aims at
fully maintaining the advantages of standard OFDM systems while addressing
their drawbacks. In this paper, we elaborate on several pulse shaping design
methods, and show how pulse shapes can be exploited as an additional degree of
freedom to provide better frequency localization and more efficient spectrum
utilization under a pre-defined spectrum mask. The performance analysis and
evaluation results show that, for a practical mobile communication systems, the
application of pulse shaping is a simple and effective means to achieve a lower
out-of-band leakage for OFDM systems at virtually no costs. In fact, the
complexity increase amounts to 1-2% compared to CP-OFDM only. In addition, the
system's robustness against both time and frequency distortions is shown to be
substantially improved by a proper pulse shape design. By allowing for the
flexible configuration of physical layer parameters per sub-band according to
the diverse requirements of future 5G services, pulse shaped OFDM systems can
efficiently facilitate asynchronous transmissions and fragmented spectrum
access, rendering it beneficial for various mobile-broadband and
Internet-of-Things applications.Comment: Minor revision of abstract, introduction, section II/VI, Appendix A,
and conclusio
The PAPR Problem in OFDM Transmission: New Directions for a Long-Lasting Problem
Peak power control for multicarrier communications has been a long-lasting
problem in signal processing and communications. However, industry and academia
are confronted with new challenges regarding energy efficient system design.
Particularly, the envisioned boost in network energy efficiency (e.g. at least
by a factor of 1000 in the Green Touch consortium) will tighten the
requirements on component level so that the efficiency gap with respect to
single-carrier transmission must considerably diminish. This paper reflects
these challenges together with a unified framework and new directions in this
field. The combination of large deviation theory, de-randomization and selected
elements of Banach space geometry will offer a novel approach and will provide
ideas and concepts for researchers with a background in industry as well as
those from academia.Comment: Accepted for publication in IEEE Signal Processing Magazin
Impact of Timing and Frequency Offsets on Multicarrier Waveform Candidates for 5G
This paper presents a study of the candidate waveforms for 5G when they are
subject to timing and carrier frequency offset. These waveforms are: orthogonal
frequency division multiplexing (OFDM), generalized frequency division
multiplexing (GFDM), universal filtered multicarrier (UFMC), circular filter
bank multicarrier (C-FBMC), and linear filter bank multicarrier (FBMC). We are
particularly interested in multiple access interference (MAI) when a number of
users transmit their signals to a base station in an asynchronous or a
quasi-synchronous manner. We identify the source of MAI in these waveforms and
present some numerical analysis that confirm our findings. The goal of this
study is to answer the following question, "Which one of the 5G candidate
waveforms has more relaxed synchronization requirements?"
Precoded GFDM System to Combat Inter Carrier Interference : Performance Analysis
The expected operating scenarios of 5G pose a great challenge to orthogonal
frequency division multiplexing (OFDM) which has poor out of band (OoB)
spectral properties, stringent synchronization requirements, and large symbol
duration. Generalized frequency division multiplexing (GFDM) which is the focus
of this work, has been suggested in the literature as one of the possible
solutions to meet 5G requirements. In this work, the analytical performance
evaluation of MMSE receiver for GFDM is presented. We also proposed precoding
techniques to enhance the performance of GFDM. A simplified expression of SINR
for MMSE receiver of GFDM is derived using special properties related to the
modulation matrix of GFDM, which are described in this work. This SINR is used
to evaluate the BER performance. Precoding schemes are proposed to reduce
complexity of GFDM-MMSE receiver without compromising on the performance. Block
Inverse Discrete Fourier Transform (BIDFT) and Discrete Fourier Transform (DFT)
based precoding schemes are found to outperform GFDM-MMSE receiver due to
frequency diversity gain while having complexity similar to zero-forcing
receiver of GFDM. It is shown that both BIDFT and DFT-based precoding schemes
reduce peak to average power ratio (PAPR) significantly. Computational
complexity of different transmitters and receivers of precoded and uncoded GFDM
is also presented.Comment: accepted in IET Communicatio
Discrete-Time Ping-pong Optimized Pulse Shaping-OFDM (POPS-OFDM) Operating on Time and Frequency Dispersive Channels for 5G Systems
The Fourth Generation (4G) of mobile communication systems was optimized to
offer high data rates with high terminal mobility by ensuring strict
synchronism and perfect orthogonality. However, the trend for novel
applications, that had not been feasible a few years back, reveals major limits
of this strict synchronism and imposes new challenges and severe requirements.
But, coarse synchronization can dramatically damage the waveforms orthogonality
in the Orthogonal Frequency Division Multiplexing (OFDM) signals, which results
in oppressive Inter-Carrier Interference (ICI) and Inter-Symbol Interference
(ISI). As a consequence, the use of non-orthogonal waveforms becomes further
essential in order to meet the upcoming requirements. In this context, we
propose here a novel waveform construction, referred to Ping-pong Optimized
Pulse Shaping-OFDM (POPS-OFDM), which is believed to be an attractive candidate
for the optimization of the radio interface of next 5G mobile communication
systems. Through a maximization of the Signal to Interference plus Noise Ratio
(SINR), this approach allows optimal and straightforward waveform design for
multicarrier systems at the Transmitter (Tx) and Receiver (Rx) sides. In this
paper, we analyze several characteristics of the proposed waveforms and shed
light on relevant features, which make it a powerful candidate for the design
of 5G system radio interface waveforms
N-continuous Aided GFDM Signaling
An N-continuous-based generalized frequency division multiplexing (GFDM)
transceiver architecture is investigated, which operates with the aid of
time-domain N-continuous orthogonal frequency devision multiplexing
(TD-NC-OFDM), hence called time-domain N-continuous GFDM (TD-NC-GFDM). More
specifically, the basis signals conceived allow us to attain compact spectrum
as an explicit benefit of sidelobe suppression, which constitute the smooth
signal capable of eliminating the discontinuities imposed by the cyclic shift
GFDM filters and their high-order derivatives. The proposed N-continuous GFDM
signaling has relatively low interference through evaluating the
signal-to-interference ratio (SIR) that significantly decreases upon increasing
the number of GFDM subsymbols. Furthermore, a signal recovery algorithm for
reception is adopted by constructing a decoding matrix for eliminating the
interference caused by the smooth signal, which exhibits an explicit error
performance improvement compared to TD-NC-OFDM. It is demonstrated that
N-continuous GFDM outperforms TD-NC-OFDM in terms of sidelobe suppression,
while achieving small BER performance degradation with a small roll-off filter
compared to original OFDM.Comment: 19 pages, 9 figures, 1 tables. arXiv admin note: text overlap with
arXiv:1608.0066
Overview of MC CDMA PAPR Reduction Techniques
High Peak to Average Power Ratio (PAPR) of the transmitted signal is a
critical problem in multicarrier modulation systems (MCM) such as Orthogonal
Frequency Division Multiplexing (OFDM), and Multi-Carrier Code Division
Multiple Access (MC CDMA) systems, due to large number of subcarriers. High
PAPR leads to reduced resolution, and battery life. It also deteriorates system
performance. This paper focuses on review of different PAPR reduction
techniques with attendant technical issues as well as criteria for selection of
PAPR reduction technique. To reduce PAPR the constraints are low power
consumption, and low Bit Error Rate (BER). Spectral bandwidth is improved by
better spectral characteristics, and low complexity/cost.Comment: 14 pages, 7 figures, IJDPS March 201
Out-of-Band Radiation Comparison of GFDM, WCP-COQAM and OFDM at Equal Spectral Efficiency
GFDM and WCP-COQAM are amongst the candidate physical layer modulation
formats to be used in 5G, whose claimed lower out-of-band (OOB) emissions are
important with respect to cognitive radio based dynamic spectrum access
solutions. In this study, we compare OFDM, GFDM and WCP-COQAM in terms of OOB
emissions in a fair manner such that their spectral efficiencies are the same
and OOB emission reduction techniques are applied to all of the modulation
types. Analytical PSD expressions are also correlated with the simulation based
OOB emission results. Maintaining the same spectral efficiency, carrier
frequency offset immunities will also be compared.Comment: submitted to IEEE Signal Processing Letter
A Survey on Multicarrier Communications: Prototype Filters, Lattice Structures, and Implementation Aspects
Due to their numerous advantages, communications over multicarrier schemes
constitute an appealing approach for broadband wireless systems. Especially,
the strong penetration of orthogonal frequency division multiplexing (OFDM)
into the communications standards has triggered heavy investigation on
multicarrier systems, leading to re-consideration of different approaches as an
alternative to OFDM. The goal of the present survey is not only to provide a
unified review of waveform design options for multicarrier schemes, but also to
pave the way for the evolution of the multicarrier schemes from the current
state of the art to future technologies. In particular, a generalized framework
on multicarrier schemes is presented, based on what to transmit, i.e., symbols,
how to transmit, i.e., filters, and where/when to transmit, i.e., lattice.
Capitalizing on this framework, different variations of orthogonal,
bi-orthogonal, and nonorthogonal multicarrier schemes are discussed. In
addition, filter design for various multicarrier systems is reviewed
considering four different design perspectives: energy concentration, rapid
decay, spectrum nulling, and channel/hardware characteristics. Subsequently,
evaluation tools which may be used to compare different filters in multicarrier
schemes are studied. Finally, multicarrier schemes are evaluated from the view
of the practical implementation issues, such as lattice adaptation,
equalization, synchronization, multiple antennas, and hardware impairments.Comment: Submitted to IEEE Communications Surveys & Tutorials, 27 pages, 14
figures (main), (First Revision
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