825 research outputs found
PAR-Aware Large-Scale Multi-User MIMO-OFDM Downlink
We investigate an orthogonal frequency-division multiplexing (OFDM)-based
downlink transmission scheme for large-scale multi-user (MU) multiple-input
multiple-output (MIMO) wireless systems. The use of OFDM causes a high
peak-to-average (power) ratio (PAR), which necessitates expensive and
power-inefficient radio-frequency (RF) components at the base station. In this
paper, we present a novel downlink transmission scheme, which exploits the
massive degrees-of-freedom available in large-scale MU-MIMO-OFDM systems to
achieve low PAR. Specifically, we propose to jointly perform MU precoding, OFDM
modulation, and PAR reduction by solving a convex optimization problem. We
develop a corresponding fast iterative truncation algorithm (FITRA) and show
numerical results to demonstrate tremendous PAR-reduction capabilities. The
significantly reduced linearity requirements eventually enable the use of
low-cost RF components for the large-scale MU-MIMO-OFDM downlink.Comment: To appear in IEEE Journal on Selected Areas in Communication
PAPR Reduction Method based on In-phase/Quadrature Data Symbol Components in MIMO-OFDM Systems
To overcome unpredictable spikes in the peak-toaverage power ratio (PAPR) in the presence of an orthogonal frequency-division multiplexing (OFDM) for multi-input-multioutput (MIMO) systems, implementation of a new SLM scheme is presented in this paper, which is extended from our previous study of IQ-SLM in SISO-OFDM system. In each transmit antenna, both real and imaginary parts of the base-band data symbol were modified independently using a corresponding phase element within a commonly generated phase vector, instead of modifying the complex data symbol as a single component. After applying an inverse fast Fourier transform (IFFT) for the real, imaginary, and original base-band vectors, the minimum PAPR component was observed. Therefore, the phase vector that introduced the minimal PAPR was considered to convert the original data block for transmission. This technique is called the In-phase/Quadrature-SLM (IQ-SLM) scheme. In this proposal, only U phase vectors were generated to treat all Nt data blocks, simultaneously, unlike the conventional MIMO-SLM techniques which generate UNt candidate phase blocks. The thing which, in turn, can be considered as a further computational complexity reduction, specifically in data-phase conversion stages. As a result, in terms of the complementary cumulative distribution function of PAPR performance(CCDF-PAPR), the proposal achieved a greater decibel reduction than conventional SLM methods such as dSLM, oSLM, and sSLM, at different subcarrier lengths N, candidate phase vectors U, transmit antennas Nt. Also, it shows a comparable BER performances over the dSLM scheme referencing to the theoretical curves, in the case where Nt ≤ Nr for both zero-forcing (ZF) and ZF with vertical Bell laboratories layered space-time (V-BLAST) detector
Peak to average power ratio reduction and error control in MIMO-OFDM HARQ System
Currently, multiple-input multiple-output orthogonal frequency division multiplexing (MIMOOFDM) systems underlie crucial wireless communication systems such as commercial 4G and 5G networks, tactical communication, and interoperable Public Safety communications. However, one drawback arising from OFDM modulation is its resulting high peak-to-average power ratio (PAPR). This problem increases with an increase in the number of transmit antennas.
In this work, a new hybrid PAPR reduction technique is proposed for space-time block coding (STBC) MIMO-OFDM systems that combine the coding capabilities to PAPR reduction methods, while leveraging the new degree of freedom provided by the presence of multiple transmit chairs (MIMO).
In the first part, we presented an extensive literature review of PAPR reduction techniques for OFDM and MIMO-OFDM systems. The work developed a PAPR reduction technique taxonomy, and analyzed the motivations for reducing the PAPR in current communication systems, emphasizing two important motivations such as power savings and coverage gain. In the tax onomy presented here, we include a new category, namely, hybrid techniques. Additionally, we drew a conclusion regarding the importance of hybrid PAPR reduction techniques.
In the second part, we studied the effect of forward error correction (FEC) codes on the PAPR for the coded OFDM (COFDM) system. We simulated and compared the CCDF of the PAPR and its relationship with the autocorrelation of the COFDM signal before the inverse fast Fourier transform (IFFT) block. This allows to conclude on the main characteristics of the codes that generate high peaks in the COFDM signal, and therefore, the optimal parameters in order to reduce PAPR. We emphasize our study in FEC codes as linear block codes, and convolutional codes.
Finally, we proposed a new hybrid PAPR reduction technique for an STBC MIMO-OFDM system, in which the convolutional code is optimized to avoid PAPR degradation, which also combines successive suboptimal cross-antenna rotation and inversion (SS-CARI) and iterative modified companding and filtering schemes. The new method permits to obtain a significant net gain for the system, i.e., considerable PAPR reduction, bit error rate (BER) gain as compared to the basic MIMO-OFDM system, low complexity, and reduced spectral splatter. The new hybrid technique was extensively evaluated by simulation, and the complementary cumulative distribution function (CCDF), the BER, and the power spectral density (PSD) were compared to the original STBC MIMO-OFDM signal
Modulation options for OFDM-based waveforms: classification, comparison, and future directions
This paper provides a comparative study on the performance of different modulation options
for orthogonal frequency division multiplexing (OFDM) in terms of their spectral efficiency, reliability,
peak-to-average power ratio, power efficiency, out-of-band emission, and computational complexity. The
modulation candidates are classified into two main categories based on the signal plane dimension they
exploit. These categories are: 1) 2-D signal plane category including conventional OFDM with classical
fixed or adaptive QAM modulation and OFDM with differential modulation, where information is conveyed
in changes between two successive symbols in the same subcarrier or between two consecutive subcarriers in
the same OFDM symbol and 2) 3-D signal plane category encompassing: a) index-based OFDM modulation
schemes which include: i) spatial modulation OFDM, where information is sent by the indices of antennas
along with conventional modulated symbols and ii) OFDM with index modulation, where the subcarriers’
indices are used to send additional information; b) number-based OFDM modulation schemes which
include OFDM with subcarrier number modulation, in which number of subcarriers is exploited to convey
additional information; and c) shape-based OFDM modulation schemes which include OFDM with pulse
superposition modulation, where the shape of pulses is introduced as a third new dimension to convey
additional information. Based on the provided comparative study, the relationship and interaction between
these different modulation options and the requirements of future 5G networks are discussed and explained.
This paper is then concluded with some recommendations and future research directions.This work was supported in part by the Scientific and Technological Research Council of Turkey (TUBITAK), under Grant 215E316
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