742 research outputs found
Performance analysis and optimization of DCT-based multicarrier system on frequency-selective fading channels
Regarded as one of the most promising transmission techniques for future wireless communications, the discrete cosine transform (DCT) based multicarrier modulation (MCM) system employs cosine basis as orthogonal functions for real-modulated symbols multiplexing, by which the minimum orthogonal frequency spacing can be reduced by half compared to discrete Fourier transform (DFT) based one. With a time-reversed pre-filter employed at the front of the receiver, interference-free one-tap equalization is achievable for the DCT-based systems. However, due to the correlated pre-filtering operation in time domain, the signal-to-noise ratio (SNR) is enhanced as a result at the output. This leads to reformulated detection criterion to compensate for such filtering effect, rendering minimum-mean-square-error (MMSE) and maximum likelihood (ML) detections applicable to the DCT-based multicarrier system. In this paper, following on the pre-filtering based DCT-MCM model that build in the literature work, we extend the overall system by considering both transceiver perfections and imperfections, where frequency offset, time offset and insufficient guard sequence are included. In the presence of those imperfection errors, the DCT-MCM systems are analysed in terms of desired signal power, inter-carrier interference (ICI) and inter-symbol interference (ISI). Thereafter, new detection algorithms based on zero forcing (ZF) iterative results are proposed to mitigate the imperfection effect. Numerical results show that the theoretical analysis match the simulation results, and the proposed iterative detection algorithms are able to improve the overall system performance significantly
A Comparison of CP-OFDM, PCC-OFDM and UFMC for 5G Uplink Communications
Polynomial-cancellation-coded orthogonal frequency division multiplexing
(PCC-OFDM) is a form of OFDM that has waveforms which are very well localized
in both the time and frequency domains and so it is ideally suited for use in
the 5G network. This paper analyzes the performance of PCC-OFDM in the uplink
of a multiuser system using orthogonal frequency division multiple access
(OFDMA) and compares it with conventional cyclic prefix OFDM (CP-OFDM), and
universal filtered multicarrier (UFMC). PCC-OFDM is shown to be much less
sensitive than either CP-OFDM or UFMC to time and frequency offsets. For a
given constellation size, PCC-OFDM in additive white Gaussian noise (AWGN)
requires 3dB lower signal-to-noise ratio (SNR) for a given bit-error-rate, and
the SNR advantage of PCC-OFDM increases rapidly when there are timing and/or
frequency offsets. For PCC-OFDM no frequency guard band is required between
different OFDMA users. PCC-OFDM is completely compatible with CP-OFDM and adds
negligible complexity and latency, as it uses a simple mapping of data onto
pairs of subcarriers at the transmitter, and a simple weighting-and-adding of
pairs of subcarriers at the receiver. The weighting and adding step, which has
been omitted in some of the literature, is shown to contribute substantially to
the SNR advantage of PCC-OFDM. A disadvantage of PCC-OFDM (without overlapping)
is the potential reduction in spectral efficiency because subcarriers are
modulated in pairs, but this reduction is more than regained because no guard
band or cyclic prefix is required and because, for a given channel, larger
constellations can be used
Phase noise effects on OFDM : analysis and mitigation
Orthogonal frequency division multiplexing (OFDM) is a promising technique which has high spectrum efficiency and the robustness against channel frequency selectivity. One drawback of OFDM is its sensitivity to phase noise. It has been shown that even small phase noise leads to significant performance loss of OFDM. Therefore, phase noise effects on OFDM systems need to be analyzed and methods be provided to its mitigation.
Motivated by what have been proposed in the literature, the exact signal to interference plus noise ratio (SINR) is derived in this dissertation for arbitrary phase noise levels. In a multiple access environment with multiple phase noise, the closed form of bit error rate (BER) performance is derived as a function of phase noise parameters.
Due to the detrimental effects of phase noise on OFDM, phase noise mitigation is quite necessary. Several schemes are proposed to mitigate both single and multiple phase noise. It is shown that, while outperforming conventional methods, these schemes have the performance close to no-phase-noise case. Two general approaches are presented which extend the conventional schemes proposed in the literature, making them special cases of these general approaches. Moreover, different implementation techniques are also presented. Analytical and numerical results are provided to compare the performance of these migitation approaches and implementation techniques.
Similar to OFDM, an OFDM system with multiple antennas, i.e., Multiple Input. Multiple Output (MIMO)-OFDM, also suffer severe performance degradation due to phase noise, and what have been proposed in the literature may not be applicable to MIMO-OFDM. Therefore, a new scheme is proposed to mitigate phase noise for MIMO-OFDM, which provides significant performance gains over systems without phase noise mitigation. This scheme provides a very simple structure and achieves adequate performance with high spectrum efficiency, which makes it very attractive for practical implementations
Time and frequency offsets in all optical OFDM systems
Ultra-high-speed data transmission (terabit-per-second per channel) is urgently required in
optical communication systems to fulfill the emerging demands of 3D multimedia applications,
cloud computing, and bandwidth-hungry applications. In one way by using singlecarrier
optical communication systems for the data transmission rates 1 Tb/s, we need the
high baud rate and/or the high-order modulation formats (i.e. 512-QAM, 1024-QAM). Another
way is to group the data carrying subcarriers without a guard bands (tightly spaced)
to form a superchannel which gives increase in channel capacity. In a superchannel, the
requirements of high-order modulation formats and high baud rates are relaxed. In an alloptical
orthogonal frequency division multiplexing (AO-OFDM) system, the subcarriers are
orthogonal and closely packed which gives more suitability to form superchannel. This thesis
focuses on the time and frequency offsets in AO-OFDM systems.
A theoretical model to investigate the performance of on-off-keying (OOK) modulated
AO-OFDM system is developed for analytical simulation. The analytical (statistical) model
considers the random characteristics of time and frequency offsets in adjacent subcarriers
as well as the common noise sources such as shot and thermal noises to calculate the interference
variances for evaluating the BER performance. The effects of time and frequency
offsets on the BER performance of AO-OFDM system is evaluated with the number of optical
subcarriers (NSC), receiver bandwidth (BWRX), and cyclic prefix (CP)
We further develop an analytical model to evaluate the performance of AO-OFDM system
with advanced modulation format (M-QAM) in the presence of time and frequency offsets,
and the performance is compared with numerical simulations of other emulation setups (oddand-
even subcarriers and decorrelated systems). The performance is investigated with NSC,
BWRX, and CP in AO-OFDM system. A delay-line interferometer based all-optical method
to reduce the effects of time and frequency offsets is proposed and evaluated.
Finally, performance of demultiplexed subcarriers from an optical discrete Fourier transform (O-DFT) in AO-OFDM system in the presence of chromatic dispersion and limited
modulation bandwidth is evaluated. The fiber Bragg grating (FBG) based passive device is
proposed to reduce the interference and the results are compared with existing method using
sampling gates. The proposed method using FBG for interference reduction provides a
cost-effective design of AO-OFDM system
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