Domain OFDM Research Articles

Design of high-order QAM modem algorithm

More and more attention has been paid on the issue of bandwidth utilization. Nowadays, with limited frequency spectrum resources, the capacity of traditional communication system has not been able to meet the demands of users. Quadrature Amplitude Modulation (QAM) has become a critical technical solution for broadband wireless access and wireless video communication due to its advantages of high frequency spectrum utilization and high-power spectrum density. In order to further improve the control information transmission performance of high-order QAM, we propose a high-order QAM modulation and demodulation algorithm, which is designed from the aspects of interleave between channels, leading sequence, constellation modulation, frequency domain sampling and (Orthogonal Frequency Division Multiplexing) OFDM generation, etc. The simulation results demonstrate that the algorithm can ensure the reliable reception of control information.

Dynein Adaptors Such as Drosophila Bicaudal (Dm BicD) Recognize Cargo and are Required to Activate Dynein for Processive Transport

In the absence of cargo, auto-inhibited BicD cannot recruit dynein, but the underlying mechanism of cargo-induced activation is elusive. Our single-molecule processivity assays show that auto-inhibition is abolished in the full-length Bicaudal mutant F684I, which activates dynein motility even in the absence of cargo. To investigate the structural basis for activation, we determined the X-ray structure of the C-terminal cargo-binding domain (CTD) of Dm BicD-CTD/F684I at 2.4 Å resolution. The structure revealed that the mutant has a homotypic coiled-coil registry, in which the two helices of the homodimer are aligned, whereas the wild-type structure has an asymmetric registry, in which the two chains are vertically shifted by ∼1 helical turn in a portion of the coiled-coil. In the mutant, N- terminal ∼20-residue region is disordered for one of the two chains. MD simulation and CD spectroscopy data suggested the structural flexibility of N-terminal region of Dm BicD-CTD/F684I and confirmed the intact protein is in the crystal and alpha-helical. We propose that a coiled-coil registry shift activates BicD for dynein recruitment. The registry shift could either be induced by the F684I mutation or by cargo-binding. Also, the human homolog of the BicD-CTD/F684I mutant (BicD2-CTD/F743I) showed diminished binding to its cargo Nup358. Thus, we propose that in mammalia, a coiled-coil registry shift modulates cargo selection for BicD2-dependent transport pathways, which are important for brain development and chromosome segregation. Furthermore, we investigated the mechanism for cargo recognition by BicD2. Our data from Circular Dicroism spectroscopy and small-angle X-ray scattering suggest that the BicD2 binding domain of Nup358, which is intrinsically disordered on its own, takes on a helical structure when binding to BicD2. This alpha-helix of Nup358 could be a structural feature for cargo recognition by BicD2.

Interaction between DMRT1 and PLZF protein regulates self-renewal and proliferation in male germline stem cells

Double sex and mab-3 related transcription factor 1 (DMRT1) encodes a double sex/mab-3 (DM) domain, which is the most conserved structure that involved in sex determination both in vertebrates and invertebrates. This study revealed important roles of DMRT1 in maintaining self-renewal of male germline stem cells (mGSCs). Our results showed that insufficient expression of DMRT1 in mice testes resulted in decreased number of spermatogonial cells and collapse of testicular niche in vivo. Self-renewal and proliferation of mGSCs were inhibited. Based on the bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation (co-IP) assay, it was finally revealed that the interaction between DMRT1 and promyelocytic leukemia zinc finger (PLZF) protein was essential for maintaining self-renewal of mGSCs. Moreover, BTB domain of PLZF, DM and DMRT1 domain of DMRT1 were indispensable in mGSC, which were responsible for preserving the quantity of germ cells. Our research provided a new scientific basis for studying the mechanism of self-renewal and spermatogenesis in goat mGSCs.

High competence MIMO-OFDM with generalized led index modulation

Optical communication in specific the visible light communication (VLC) is the next generation technology in the field of data transmission. This paper proposes an idea of improving the transmission rate of the data via a totally different method of channel using optical light communication. Here, the normal radio frequency waves aren’t being used at all. Simple light will give us the required channel medium to send the data over a range. The system that is being proposed separates each data signal and sends it one by one to the light emitting modulation. The real and imaginary part of the complex time domain OFDM signals are taken apart and are sent over a frequency-flat light channel. As a standard it was demonstrated that the performance of the simulation in two different configurations with various numbers of transmitting and receiving antennas.

Transmit power imbalance reduction method and nonlinear companding transform for beamforming OFDM systems

Abstract Due to large peak-to-average power ratio (PAPR) at the time domain OFDM signal, various peak signal reduction methods for OFDM systems have been proposed. However, in a transmit OFDM beamforming, multiplication of the transmit signal using the weights causes transmit power imbalance between antennas and increases peak signal. We propose two approaches to mitigate these problems. Adding the pseudo-noise to covariance matrix at the process of weight calculation can alleviate the transmit power imbalance. Furthermore, the companding transform of time domain signal can reduce the peak signals. We show details of proposed methods and evaluate PAPR and BER performance.

XOR Encryption Versus Phase Encryption, an In-Depth Analysis

Encryptions are used in almost all standards to ensure the confidentiality of the data. Encryptions can be and indeed are implemented in the different layers of a network protocol stack. Conventional encryption performs the bitwise XOR operation between one message bit and one key stream bit to generate one ciphertext bit. Huo et al. have recently proposed to provide confidentialities on the user data by performing the phase encryption on the time domain OFDM samples in LTE system. Phase encryption is performed on the modulated symbols, different from the bit level of XOR encryption, i.e., stream cipher encryption. In this paper, we extend their study. We first generalize the phase encryption to general communication systems independent of the underlying modulation scheme. Then, we formulate the mathematical models for XOR and phase encryptions. Based on our model, we compare these two encryption methods in terms of their security and encryption efficiency. We also show phase encryption can resist traffic analysis attack when implemented in the physical layer. Finally, we conduct simulations to compare the performance of these two methods in terms of their decoding symbol error rate.

Analysis and Compensation of Phase Noise in Vector OFDM Systems

Vector orthogonal frequency division multiplexing (V-OFDM) for single transmit antenna systems is a generalization of OFDM where single-carrier frequency domain equalization (SC-FDE) and OFDM are just two special cases. It has been shown to be able to collect multipath diversity and thus generally outperforms OFDM. The performance of OFDM under phase noise has been extensively studied in the literature. These effects can be summarized as introducing a common phase error (CPE) and inter carrier interference (ICI) resulting in poor performance. The performance of V-OFDM under phase noise still remains uninvestigated and in this paper it is shown that phase noise in V-OFDM systems leads to a common vector block phase error (CVBPE) as well as an inter vector block carrier interference (IVBCI) effect. An expression for the signal plus interference noise ratio (SINR) for a V-OFDM system is derived and found to agree closely with simulation results. A pilot vector CVBPE based phase noise estimation technique is derived, and then combined with the maximum likelihood (ML) and the linear minimum mean square error (LMMSE) estimators to estimate the phase noise. It turns out that compared with OFDM, V-OFDM systems can perform phase noise estimation with lower complexity. The decorrelation and cancellation techniques are then used to compensate for the phase noise impairment. Numerical results for both coded and uncoded systems with perfect and practical channel estimation are provided to validate the analysis and effectiveness of the proposed phase noise estimation and compensation methods.

Guardband Optimization for Cellular Systems Applying Raised Cosine Windowed OFDM

In this paper, we study the optimization of the guardbands between adjacent channels in OFDM-based cellular systems. It is well known that OFDM signals have strong sidelobes in spectrum, which lead to large necessary guardbands between adjacent channels to avoid severe adjacent channel interference. To reduce such guardbands and, thus, to increase the spectrum usage efficiency, we propose to apply raised cosine (RC) windowing of the time domain OFDM signals, which is a simple, efficient and effective method. In this context, an interesting tradeoff can be observed, i.e., a higher roll-off factor (ROF) of the RC-window is associated with higher signal overhead in time (in other words, longer OFDM symbol duration), but lower guardband overhead in frequency (due to better sidelobe suppression). We study this tradeoff and found out that the ROF and the guardband size can be jointly optimized, in the sense that the per-channel data rate can be maximized under adjacent channel interference constraints. Our mathematical analysis further shows that such joint optimization can be reduced to a single dimension optimization, i.e. the optimization of the ROF. Afterwards, this optimization procedure is illustrated and verified via numerical simulation, showing that large data rate increase can be achieved when using RC-windowing with an optimized ROF. Finally, practical analysis of the instantaneous per-OFDM symbol interference further verified the effectiveness of the proposed approach.

時間サンプルの復元によるＯＦＤＭ信号へのインパルス雑音の影響の軽減

In OFDM transmission, performance is degraded by the existence of time domain impulse noise because this noise has very wide bandwidth, and it affects all the carriers in the OFDM signal. Especially, the influence of impulse noise with large amplitude couse severe degradation[8]. In this paper, a scheme that reduces the influence of impulse noise is proposed. In the proposed scheme, the symbols after decision are re-modulated to generate a time domain OFDM signal to replace the samples that are degraded by the impulse noise in the time domain. The time domain OFDM signal is demodulated again after the influence of the impulse noise is reduced. This results in an improvemed of bit error rate. Moreover, the peformance of the proposed scheme can be further improved by applying it iteratively.

M -sequences for OFDM peak-to-average powerratio reduction and error correction

Li and Ritcey ~see ibid., vol.33, p.554-5, 1997 noted that the time domain OFDM samples are given by expressions evaluated at discrete values. However, it is demonstrated that their assumption, that the maximum value over these discrete values is equal to the maximum value of a continuous function over a continuous interval, does not follow.

Binding of matrix attachment regions to nuclear lamin is mediated by the rod domain and depends on the lamin polymerization state

The nuclear matrix maintains specific interactions with genomic DNA at sites known as matrix attachment regions (M/SARs). M/SARs bind in vitro to lamin polymers. We show that the polymerized α-helical rod domain of lamin Dm 0 provides by itself the specific binding to the ftz M/SAR. In contrast, unpolymerized rod domain does not bind specifically to this M/SAR. Non-specific binding to DNA is also observed with Dm 0 containing a point mutation that impairs its ability to polymerize or with the isolated tail domain. These data suggests that the specific binding of lamins to M/SARs requires the rod domain and depends on the lamin polymerization state.