Orthogonal Carriers Research Articles

Direct detection of polarization multiplexed single sideband signals with orthogonal offset carriers.

We propose a novel direct detection (DD) scheme for polarization division multiplexed (PDM) single sideband (SSB) signals with two orthogonal carriers located at the opposite sides. Polarization diversity is realized with a pair of optical filters that are used to suppress the unwanted orthogonal carrier component. A PDM-SSB DD receiver is thus constructed without polarization de-rotation. The intra-polarization signal-signal beat interference (SSBI) can be mitigated by Kramers-Kronig detection or iterative SSBI cancellation. For inter-polarization SSBI mitigation, we propose a joint iterative SSBI cancellation method. The proposed PDM-SSB DD scheme is validated with a principle experiment of 40Gbaud PDM-SSB 16-ary quadrature amplitude modulation (16-QAM) signals. After 80km standard single-mode fiber (SSMF) transmission, the bit-error rates (BERs) achieve 20% hard-decision forward error correction (HD-FEC) threshold of 1.5 × 10-2. The performance of iterative SSBI cancellation, Kramers-Kronig detection, and joint iterative SSBI cancellation are evaluated for PDM-SSB signals with different carrier-to-signal ratios (CSPRs) through numerical simulations. Moreover, a multi-input-multi-output (MIMO) equalization scheme is proposed and validated with numerical simulation, which can suppress the linear inter-polarization crosstalk and relax the sharpness requirement of optical filter edges.

Cooperative Ambient Backscatter Communications for Green Internet-of-Things

Ambient backscatter communication (AmBC) enables a passive backscatter device to transmit information to a reader using ambient RF signals, and has emerged as a promising solution to green Internet-of-Things (IoT). Conventional AmBC receivers are interested in recovering the information from the ambient backscatter device (A-BD) only. In this paper, we propose a cooperative AmBC (CABC) system in which the reader recovers information not only from the A-BD, but also from the RF source. We first establish the system model for the CABC system from spread spectrum and spectrum sharing perspectives. Then, for flat fading channels, we derive the optimal maximum-likelihood (ML) detector, suboptimal linear detectors as well as successive interference-cancellation (SIC) based detectors. For frequency-selective fading channels, the system model for the CABC system over ambient orthogonal frequency division multiplexing carriers is proposed, upon which a low-complexity optimal ML detector is derived. For both kinds of channels, the bit-error-rate expressions for the proposed detectors are derived in closed forms. Finally, extensive numerical results have shown that, when the A-BD signal and the RF-source signal have equal symbol period, the proposed SIC-based detectors can achieve near-ML detection performance for typical application scenarios, and when the A-BD symbol period is longer than the RF-source symbol period, the existence of backscattered signal in the CABC system can enhance the ML detection performance of the RF-source signal, thanks to the beneficial effect of the backscatter link when the A-BD transmits at a lower rate than the RF source.

Interference Evaluation in Cellular Networks

Interference in cellular networks is one of the most common problems in the radio access network. In fact, it is the major issue in cellular networks that affects performances and quality of service. Indeed, interference can be caused by a call on the same frequency from neighboring cell, or a call on an adjacent channel in the same or in neighboring cell. So, we can classify interference on intra-cell interference and inter-cell interference. In 4G, thanks to the use of orthogonal frequency division multiple access and single carrier frequency division multiple access as access techniques in downlink and uplink respectively, intra-cell interference is reduced compared to the inter cell one which caused by the frequency reuse one mechanism and the femto cells deployment. In this work, we will evaluate the interference in different cellular network standards from 2G to 4G.

Performance analysis of V‐OFDM for acoustic communication along drill strings

To achieve real-time and high-speed communication between the surface and the bottom hole, acoustic communication along drill strings has become the most promising method for the efficient utilisation of oil fields. Vector orthogonal frequency division multiplexing (V-OFDM) is a general transmission scheme that has two special forms, orthogonal frequency division multiplexing and single carrier frequency domain equalisation. Owing to its flexibility regarding the size of the vector block, it can be adapted to meet different requirements. In this study, the authors first employ V-OFDM modulation in uplink and downlink acoustic communication. Aiming for mass-data transmission and a simple transmitter in the uplink, small-data transmission and a simple receiver in the downlink, and strong noise interference, they investigate the transmission performance with different synchronisation timing errors and detection schemes, zero-forcing and the minimum mean square error. Simulation and circuit test results are presented to demonstrate the effectiveness of the proposed different transmission schemes and the corresponding performance analysis.

FBMC vs OFDM Waveform Contenders for 5G Wireless Communication System

The multicarrier transmission techniques have been the most beguiling one for the development of wireless communication systems like 4G, Long Term evolution and now the successor 5G. For 5G or fifth generation wireless communication, Orthogonal Frequency Division Multiplexing (OFDM) and Filter Bank Multi carrier modulation (FBMC) are the dominant waveform contenders. In this research paper, the disadvantages of OFDM have been addressed and it has shown that filter bank multicarrier (FBMC) could be a more effective solution. The comparative analysis of FBMC and OFDM has been performed based on Power Spectral Densities, sub channels, computational complexity and prototype filter comparison simulated using MATLAB.

Joint virtual time reversal communications with an orthogonal chirp spread spectrum over underwater acoustic channel

In this paper, a mathematical derivation was performed to prove that there are three characteristics of chirp signals, self-compression, cyclic shift and chirp rate orthogonality. Based on these three features, a new method is proposed to improve the spectrum efficiency by joining virtual time reversal together with an orthogonal carrier. The advantages of the method can be summarized as follows. (1) By using the self-compression feature of a chirp signal, it is easy to obtain the spread gain by increasing the production of the time and bandwidth, instead of designing a complex pseudo random code. (2) The bit rate can be improved by taking the cyclic-shift feature into account and designing the M-ary modulation for the chirp carrier. (3) Chirp carriers have a certain orthogonality if they are under the considered design, that is, it is possible to use multi-carriers to improve the bit rate and spectrum efficiency. (4) Furthermore, by using the VTRM (Virtual Time Reversal Mirror) technique, the ISI (Inter Symbol Interference) of the Chirp carrier can be decreased and the robustness can be increased. Simulations, pool and sea experiments verified its feasibility and performance. Outfield experiments demonstrated that the BER (Bit Error Rate) of the method can be stabilized at a magnitude of 10−3 without the channel code, while the bit rate can reach 1kbps by using a 2kHz bandwidth. Thus, the spectrum efficiency can be over 0.5b/s/Hz and can be useful in reality.

Frequency-translated differential chaos shift keying for chaos-based communications

In this paper, an efficient, differential chaos shift keying (DCSK) method, known as frequency-translated DCSK (FT-DCSK), is proposed. Ordinary DCSK is difficult to incorporate using CMOS integrated circuits because of the long wideband delay line that is required to separate reference and data chaotic sequences into two time-shifted slots of each frame. Another disadvantage of DCSK is the repetition of chaotic sequence in reference and data slots, which decreases data security and bandwidth efficiency. In the proposed method, the usage of a delay line is avoided by frequency translation of the reference chaotic sequence over the frame time. Frequency translation is achieved by amplitude modulation of two orthogonal sine carriers with reference chaotic sequences. As a result, the FT-DCSK scheme avoids the usage of wideband delay lines and increases the bandwidth efficiency. The analytical expression for bit error rate (BER) performance is derived and compared with simulation results. Finally, the obtained performance results are compared with similar modulation schemes. The proposed FT-DCSK scheme exhibits promising performance based on BER results.

Design and Simulation of High-Precision Position System Using 60 GHz Pulse

60[Formula: see text]GHz communication technology is a type of short-range and high-speed wireless communication technology, which is currently considered the most promising one because it has a very high time and multi-path resolution. Therefore, it has the potential to achieve high-precision ranging and positioning. At present, carrier communication system like orthogonal frequency division multiplexing (OFDM) or single carrier techniques using frequency domain equalization (SC-FDE), etc., are mostly used in 60[Formula: see text]GHz communication system. Furthermore, accurate wireless positioning systems is mostly based on impulse radio. We propose a pulse positioning system in 60[Formula: see text]GHz band to meet the requirements of high-precision positioning. A pulse waveform suitable for 60[Formula: see text]GHz positioning is presented, meanwhile the positioning process of pulse transmitting, channel transmission, pulse receiving and coordinates calculation using positioning algorithm is also designed and simulated. The results show that the 60[Formula: see text]GHz pulse system has millimeter-level ranging accuracy and centimeter-level positioning accuracy in line-of-sight (LOS) channel, in addition the accuracy is much higher than that in ultra-wide band (UWB) pulse system.

Anodically Grown TiO2 Nanotube Arrays Used As Substrates for Thermal Dewetting of Pt Show Significantly Enhanced Photocatalytic H2 Generation with Minimal Co-Catalyst Amounts

TiO2 nanostructures have recently attracted much attention due to their wide range of applications, such as photocatalysis, photovoltaics (dye-sensitized solar cell, photo-electrochemistry) and gas sensing. Particularly, electrochemically formed TiO2 nanotube arrays were shown to exhibit improved photocatalytic activity compared to other TiO2 nanostructures, this being ascribed to their directional electron transport and orthogonal charge carrier separation.1 The advantage of an electrochemical growth of the TiO2 nanotube layers is not only the simplicity of the process, but also the possibility of controlling the tube geometry (length, diameter, wall thickness) by selecting suitable anodization parameters (applied voltage, anodization time, temperature, fluoride concentration). Nevertheless, TiO2 alone is not effective in photocatalytic H2 generation: it requires the presence of noble metal co-catalysts (Pt, Au, Pd).2,3 Among the various noble metals, Pt is the most effective co-catalyst: it enables an efficient electron transfer at the semiconductor interface by providing a favorable solid state junction to TiO2 and it enhances the hydrogen recombination reaction. There are several well explored methods to decorate Pt onto TiO2 nanotubes, mostly leading to a decoration of the full tube length with nanoparticles (the most frequently used up to date is photodeposition). With our contribution we show a different approach: we decorate only the outermost surface of anodic TiO2 nanotubes with very thin Pt films (nominally few nm-thick) by using a simple plasma sputtering technique.4 Then, by a controlled thermal treatment, the Pt films are dewetted at the mouth of the tubes into arrays of Pt nanoparticles that are as small as of few nm. This site-selective deposition (only at the tubes top) allows for minimizing the amounts of costly noble metal co-catalyst, while at the same time leads to a significantly enhanced photocatalytic H2 generation compared to tubes that carry along their full length a classic Pt nanoparticle decoration. [1] K. Lee, A. Mazare, P. Schmuki, Chem. Rev. 2014, 114, 9385–9454.[2] N. T. Nguyen, J. Yoo, M. Altomare, P. Schmuki, Chem. Commun. 2014, 50, 9653–9656.[3] N. T. Nguyen, M. Altomare, J. Yoo, P. Schmuki, Adv. Mater. 2015, 27, 3208–3215.[4] N. T. Nguyen, M. Altomare, J. E. Yoo, N. Taccardi, P. Schmuki, Adv. Energy Mater. 2015, doi: 10.1002/aenm.201501926. Figure 1

Broadband linearized analog intersatellite microwave photonic link using a polarization modulator in a Sagnac loop.

A novel orthogonal polarization optical carrier suppression with carrier (OCS+C) modulation and a coherent balanced detection intersatellite microwave photonic link with improved signal-to-noise and distortion ratio (SNDR) is proposed. By bidirectional use of a polarization modulator in a Sagnac loop in conjunction with a polarization beam splitter and two polarization controllers, only the light wave along the clockwise direction is effectively modulated while the counterclockwise light wave is not modulated due to the velocity mismatch, which generates the orthogonal polarization OCS+C modulation signal to mitigate the third-order intermodulation distortion (IMD3) and the signal-amplifier spontaneous emission beating noise. By demultiplexing and adjusting the polarization of the orthogonal polarization OCS+C modulation signal, coherent balanced detection can be realized without a local oscillator signal in the receiver, which suppresses the second-order distortions. Thus, a broadband linearized intersatellite microwave photonic link with high SNDR is achieved. Simulation results show that the maximum SNDR of 36.2 dB can be obtained when the optimum modulation index is 0.26, which is 8 dB higher than our previously proposed intersatellite microwave photonic link with an optical preamplifier.

A Novel Architecture for OFDM with LDPC CODED NCO

Technological developments in power line communication leads to communication systems operating at data rates greater than200Mbps.OFDM architecture forms the physical layer is of utmost importance. One of the major concerns in a PLC is noise and low speed architectures. In this article, a novel NCO based architecture with LDPC codes for OFDM is proposed. The NCO architecture is aparallelized architecture that generates orthogonal carriers for modulation. The NCO architecture is designed to minimize harmonics in orthogonal carriers and hence reduces PLC noise. Soft errors are detected and corrected using error detection unit using LDPC codes. A Software reference model is developed in Simulink to validate the NCO architecture and OFDM model. HDL code is developed for the proposed architecture and is synthesized using Xilinx ISE targeting Virtex-5 FPGA

An auto synchronization technique of unipolar MPAM signals in OFDM and its application for optical wireless communication systems

Optical wireless systems have attracted attention, because they allow high-speed transmission without electromagnetic interference. Orthogonal frequency division multiplexing (OFDM) can send multiple high speed signals by using orthogonal carrier frequencies. Recently, studies have been focused on the optimal OFDM technique for optical wireless systems. When using OFDM, one important issue is determining the cyclic prefix and removing it from the frame before the receiver detects signals. In this paper, we propose a new auto synchronization technique of unipolar MPAM signals. It can remove the cyclic prefix in any sample of the OFDM frame using unipolar MPAM. It is a candidate for wideband systems and using 2-PAM or 4-PAM. The results of mathematical analysis and simulations show that it can be used for optical wireless systems.

A wideband photonic microwave phase shifter using polarization-dependent intensity modulation

We present a tunable and wideband microwave photonic phase shifter based on polarization-dependence of the LiNbO3 Mach–Zehender modulator (MZM). In the proposed device, an orthogonal single sideband modulation is implemented by using a MZM and an optical band-pass filter. With the polarizer to synthesize the polarization orthogonal optical carrier and sideband, the phase of the optical microwave signal output from the polarizer can be tuned from 0 to 360° by simply adjusting the polarization direction of the lights whereas the amplitude keeps constant. A full range tunable phase shifting in the frequency range of 10–35GHz is achieved.

Features of equalization in LTE technology with MIMO and SC-FDMA

The Long Term Evolution (LTE) is one of communication standards for next-generation mobile phones, which has evolved the high-speed data communication standard HSDPA for the mainstream 3G (third generation) mobile phone system W-CDMA at present. Data communication volume of mobile phones is rapidly increasing at present due to dissemination of smart phones and mobile communication. Therefore, expansion of communication band (capacity) is a critical issue for communication carriers. Because the LTE that allows high-speed data communication with low delay is superior in terms of the radio wave use efficiency, many of major communication carriers in the world have indicated a policy of adopting the LTE. The rapid dissemination of the LTE in the future is expected. In this report we overview the fundamental techniques of equalization in LTE technology with MIMO and SC-FDMA in channels where the maximum delay exceeds the length of the Guard Interval. The goal of employing narrow band subcarriers is to obtain a channel that is roughly constant over each given sub band, which makes equalization much simpler at the receiver. There are considering advantage and disadvantage three types equalization techniques: time domain, frequency domain and turbo equalization. On base of these compeering are giving practical recommendation for choice method of equalization. To enhance this frequency use efficiency, antenna technologies, including Multi Input Multi Output (MIMO) that allows transmission/reception with multiple antennas and Space Division Multiple Access (SDMA) that allows multiple access between base stations, have been introduced. Furthermore, Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier Frequency Division Multiple Access (SC-FDMA) are used as multiplexing systems.

A COMPREHENSIVE REVIEW OF MODULATION TECHNIQUES USED IN LONG TERM EVOLUTION

rd generation Partnership Project (3gPP) has come up with a technology called Long Term Evolution (LTE) to attain a new high speed radio access in the field of mobile communications. Design of wireless communication system has been an important and challenging problem due to the nature of wireless channel. There are number of factors involved in the performance of a LTE system. Orthogonal Frequency Division multiple access (OFDma) and Single Carrier Frequency Division multiple access (SC-FDma) are a dominant part of future mobile communication. This paper describes about LTE physical layer, OFDma and SC-FDma receiver and transmitter structures, draw attention on the factor that influences the performance and improvement of multiple access techniques. The substantial use of the adaptive modulation in LTE is the main highlight of the paper. The selection of modulation techniques on the basis of BEr, Error probability and SNr are computed.

Flexible compensation of dispersion-induced power fading for multi-service RoF links based on a phase-coherent orthogonal lightwave generator.

A novel technique to simultaneously compensate dispersion-induced power fading for multi-service radio-over-fiber (RoF) links is proposed. At the central office (CO), a phase-coherent orthogonal lightwave generator (POLG) consisting of a polarization rotator (PR) and a single-driver Mach-Zehnder modulator (MZM) is used. By adjusting a polarization controller (PC) in the base station (BS), the phase difference between the orthogonal polarization carrier and two sidebands can be controlled, and the frequency response can be flexibly shifted for individual radio frequency (RF) service. We experimentally shift the destructive interference to the constructive interference at various frequencies for 25 km and 30 km fiber links. The performances of two services carrying 1 Gb/s on-off keying (OOK) data at 9 GHz and 16.6 GHz over a 30 km fiber in the proposed system show receiver sensitivity improvement of ∼12 dB at the bit error rate (BER) of 10(-3) compared with the conventional double sideband (DSB) modulation case.

Two orthogonal carriers assisted 101-Gb/s dual-band DDO-OFDM transmission over 320-km SSMF.

We propose a novel fading-free direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) scheme for 100-Gb/s medium-reach transmission. In the proposed scheme, we adopts two bands spaced at 100-GHz to accommodate the same complex-valued OFDM signal. However, the signals are coupled with a pair of orthogonal optical carriers. By doing so, real and imaginary parts of the complex-valued OFDM signal can be recovered from the two bands, respectively. We also propose a cost-effective scheme to generate such DDO-OFDM signal using an optical 90-degree hybrid and an optical I/Q modulator. The advantage of the proposed method is that it is fading-free, and the electrical spectral efficiency (SE) is doubled compared to traditional direct-detection method. Finally, we experimentally demonstrated a 101-Gb/s dual-band transmission over 320-km SSMF within only 30-GHz electrical bandwidth, which is highly competitive in both capacity and cost.

Investigation of magnetotransistors with new topology

Sensitivity of a lateral magnetotransistor with orthogonal charge carrier flows is investigated by means of device-technological simulation. The comparison of the simulation results for parallel carrier flows shows the change of the sensitivity sign in a magnetotransistor with the base in the form of a diffusion well. In a planar magnetotransistor, the initial offset of collector voltages is shown by experiments to depend on the topology of emitter electrodes, collectors, and the heavily-doped base contact. The investigated topologies of the lateral and planar magnetotransistors allow one to create a low initial offset of collector voltages and increase the sensitivity.

Phase-Separated DCSK: A Simple Delay-Component-Free Solution for Chaotic Communications

In this brief, a phase-separated differential chaos shift keying (PS-DCSK) modulation scheme is proposed as a simple delay-component-free version of DCSK modulation. Separated by orthogonal sinusoidal carriers rather than time delay, the reference and information-bearing signals in DCSK are transmitted simultaneously and parallel in the proposed system. As a result, PS-DCSK not only can avoid the difficult-to-implement radio-frequency delay line problem but also can achieve a doubled attainable data rate, enhanced communication security, and equivalent bit-error-rate (BER) performance with respect to DCSK. Finally, analytical expressions for the BER performance of the proposed system are derived and verified by computer simulation results over additive Gaussian white noise and Rayleigh fading channels.

Binary phase shift keying on orthogonal carriers for multi-channel CO2 absorption measurements in the presence of thin clouds.

A new modulation technique for Continuous Wave (CW) Lidar is presented based on Binary Phase Shift Keying (BPSK) using orthogonal carriers closely spaced in frequency, modulated by Maximum Length (ML) sequences, which have a theoretical autocorrelation function with no sidelobes. This makes it possible to conduct multi-channel atmospheric differential absorption measurements in the presence of thin clouds without the need for further processing to remove errors caused by sidelobe interference while sharing the same modulation bandwidth. Flight tests were performed and data were collected using both BPSK and linear swept frequency modulation. This research shows there is minimal or no sidelobe interference in the presence of thin clouds for BPSK compared to linear swept frequency with significant sidelobe levels. Comparisons between of CO(2) optical depth Signal to Noise (SNR) between the BPSK and linear swept frequency cases indicate a 21% drop in SNR for BPSK experimentally using the instrument under consideration.