Showing papers on "Frequency-division multiplexing published in 2015"

2.3 Gbit/s underwater wireless optical communications using directly modulated 520 nm laser diode.

Abstract: We experimentally demonstrate a record high-speed underwater wireless optical communication (UWOC) over 7 m distance using on-off keying non-return-to-zero (OOK-NRZ) modulation scheme. The communication link uses a commercial TO-9 packaged pigtailed 520 nm laser diode (LD) with 1.2 GHz bandwidth as the optical transmitter and an avalanche photodiode (APD) module as the receiver. At 2.3 Gbit/s transmission, the measured bit error rate of the received data is 2.23×10(-4), well below the forward error correction (FEC) threshold of 2×10(-3) required for error-free operation. The high bandwidth of the LD coupled with high sensitivity APD and optimized operating conditions is the key enabling factor in obtaining high bit rate transmission in our proposed system. To the best of our knowledge, this result presents the highest data rate ever achieved in UWOC systems thus far.

Frequency-division multiplexing in the terahertz range using a leaky-wave antenna

Abstract: Using a leaky-wave antenna, free-space-to-waveguide frequency-division multiplexing and demultiplexing are demonstrated in the terahertz range. Both the frequency and the spectral bandwidth of multiplexed channels can be independently controlled. The idea of using radiation in the 0.1–1.0 THz range as carrier waves for free-space wireless communications has attracted growing interest in recent years, due to the promise of the large available bandwidth1,2. Recent research has focused on system demonstrations3,4, as well as the exploration of new components for modulation5, beam steering6 and polarization control7. However, the multiplexing and demultiplexing of terahertz signals remains an unaddressed challenge, despite the importance of such capabilities for broadband networks. Using a leaky-wave antenna based on a metal parallel-plate waveguide, we demonstrate frequency-division multiplexing and demultiplexing over more than one octave of bandwidth. We show that this device architecture offers a unique method for controlling the spectrum allocation, by variation of the waveguide plate separation. This strategy, which is distinct from those previously employed in either the microwave8 or optical9 regimes, enables independent control of both the centre frequency and bandwidth of multiplexed terahertz channels.

Wireless Power and Data Transfer via a Common Inductive Link Using Frequency Division Multiplexing

Abstract: For wireless power transfer (WPT) systems, communication between the primary side and the pickup side is a challenge because of the large air gap and magnetic interferences. A novel method, which integrates bidirectional data communication into a high-power WPT system, is proposed in this paper. The power and data transfer share the same inductive link between coreless coils. Power/data frequency division multiplexing technique is applied, and the power and data are transmitted by employing different frequency carriers and controlled independently. The circuit model of the multiband system is provided to analyze the transmission gain of the communication channel, as well as the power delivery performance. The crosstalk interference between two carriers is discussed. In addition, the signal-to-noise ratios of the channels are also estimated, which gives a guideline for the design of mod/demod circuits. Finally, a 500-W WPT prototype has been built to demonstrate the effectiveness of the proposed WPT system.

Optical wireless transmission of 405 nm, 1.45 Gbit/s optical IM/DD-OFDM signals through a 4.8 m underwater channel.

Abstract: In this paper, we experimentally demonstrate wireless transmission of optical intensity modulation/direct detection-orthogonal frequency division multiplexing (IM/DD-OFDM) signals in an underwater channel using a field programmable gate array based real-time transmitter. The real-time transmission of a 405 nm 1.45 Gbit/s optical OFDM signal through a 4.8 m underwater channel with an error vector magnitude of approximately 10% was successfully achieved.

Frequency division multiplexing for wireless power providers

Abstract: Disclosed are various embodiments for frequency-division multiplexing for wireless power providers using guided surface waveguide probes to transmit power. Guided surface waveguide probes may transmit power on multiple frequencies with potentially overlapping service areas. Frequency-agile wireless power receivers may tune to one or more frequencies. Cost, availability, and/or other information may be provided to the wireless power receivers. Power usage may be reported by the wireless power receivers to power providers.

Network Architecture of a High-Speed Visible Light Communication Local Area Network

Abstract: A novel ultrahigh-speed LED visible light communication (VLC) local area network to provide beyond 10-Gb/s optical wireless access based on star topology architecture is proposed and experimentally demonstrated for massive users. Fiber link is used as the backbone of the bidirectional VLC network. The hybrid access protocol is utilized: 1) frequency division multiplexing for downlink and uplink fiber transmission and 2) time division multiplexing for bidirectional VLC transmission. A full-duplex VLC network for eight VLC access points (VAPs) has been successfully demonstrated with the total throughput of 8 Gb/s. Each VAP is offered 500-Mb/s downstream and 500-Mb/s upstream. The measured bit error rates of downlink and uplink for all the VAPs are under 7% FEC limit of $3.8\times 10^{-3}$ over 25-km standard single mode fiber and 65-cm free space, clearly validating the promising potential of the proposed VLC network architecture for future 40- and 100-Gb/s wireless access.

LDM Versus FDM/TDM for Unequal Error Protection in Terrestrial Broadcasting Systems: An Information-Theoretic View

Abstract: In this paper, power-based layer-division multiplexing (LDM) is studied as a means to provide unequal error protection in digital terrestrial television (DTT) systems by adopting an information-theoretic approach. LDM can potentially offer fundamental performance gains as compared to traditional time-division multiplexing (TDM) or frequency-division multiplexing due to the reuse by all information layers of all the available time-frequency resources. The main use case of LDM for terrestrial broadcasting is the simultaneous provision of fixed and mobile services in the same channel. Since most DTT networks worldwide are dimensioned for fixed rooftop reception, this paper illustrates the performance comparison between LDM and F/TDM in terms of the capacity-coverage tradeoff of the mobile service for a given reduction of the capacity of the fixed service while keeping the coverage of the fixed service constant. A mathematical formulation, and corresponding numerical results, are provided for different fading channels, including single-input single-output, single-input multiple-output, multiple-input single-output, and multiple-input multiple-output antenna systems, and accounting also for the impact of non-ideal channel coding.

Fractional Frequency Reuse in DCO-OFDM-Based Optical Attocell Networks

Abstract: In this paper a fractional frequency reuse (FFR) technique is considered in a direct-current optical orthogonal frequency-division multiplexing-based optical attocell network. An optical attocell network is proposed as a special type of visible light communication system that has the complete function of a cellular network. The cellular network is composed of many cells of extremely small size—the optical attocells. Two FFR schemes, strict fractional frequency reuse and soft frequency reuse, are considered. The signal-to-interference-plus-noise ratio (SINR) statistics and the spectral efficiency of the optical cellular system with FFR are analyzed. The performance of the systems with full frequency reuse and FFR is evaluated and compared. The results show that the FFR scheme can effectively achieve interference mitigation in an optical attocell network. The cell edge user SINR and spectral efficiency are significantly improved. Additionally, FFR provides improvements in average spectral efficiency. The effects of important parameters such as cell radius are also studied.

A Gb/s VLC Transmission Using Hardware Preequalization Circuit

Abstract: In this letter, we proposed a constant-resistance symmetrical bridged-T amplitude equalizer for high-speed visible light communication (VLC) system. Using the hardware equalizer, we successfully demonstrated a gigabit per second VLC transmission over 80-cm free space based on a RGB LED. The measured bit error rates (BERs) for the signals in 64-quadratic-amplitude modulation (64QAM) single carrier modulation at 1.05-Gb/s, 64QAM-orthogonal frequency division multiplexing (OFDM) at 1.05 Gb/s, and bit and power loading OFDM modulation at 1.42 Gb/s, are under 7% pre-forward error correction (pre-FEC) limit of $3.8\times 10^{-3}$ , clearly validating the feasibility of the proposed equalizer. Compared with the system without using the equalizer, the BER performance of the VLC systems can be improved at least by 1 order of magnitude. Moreover, the equalizer can be easily integrated into amplifier or LED because of its compact size and easy installation for just using passive component. To the best of our knowledge, it is the highest data rate with longest transmission distance using preequalization circuit.

Indoor positioning system designs using visible LED lights: performance comparison of TDM and FDM protocols

Abstract: The performance of time division multiplexing and frequency division multiplexing protocols for light emitting diode light emitting diode (IPS) designs using visible light emitting diode lights is evaluated. The impact of timing synchronisation errors on the localisation accuracy of IPS designs is also determined.

Robust WHT-GFDM for the Next Generation of Wireless Networks

Abstract: This paper presents the combination of generalized frequency division multiplexing (GFDM) with the Walsh-Hadamard transform (WHT) to achieve a scheme that is robust against frequency-selective channels (FSC). The proposed scheme is suitable for low-latency scenarios foreseen for 5G networks, specially for Tactile Internet. The paper also presents analytical approximations that can be used to estimate the bit error rate of GFDM and WHT-GFDM over frequency-selective channels in single shot transmission. Simulation results for encoded GFDM are included for further comparison.

Frequency-Shift Offset-QAM for GFDM

Abstract: This paper presents a novel perspective to apply the offset quadrature amplitude modulation (OQAM) scheme on top of the multicarrier waveform termed Generalized Frequency Division Multiplexing (GFDM). The conventional time-shift OQAM is described for GFDM and, with the introducing of the general use of unitary transform, an interesting counterpart, i.e., frequency-shift OQAM, is proposed. The conventional long prototype pulse with time-shift of one half subsymbol becomes a short prototype pulse with frequency-shift of one half subcarrier. The frequency-shift OQAM scheme offers advantages such as low out-of-band emission and low implementation complexity. The concept can be applied to the broader scope of filtered OFDM without penalties in terms of performance in time variant frequency-selective channels.

Classification of STBC Systems Over Frequency-Selective Channels

Abstract: Space–time block code (STBC) classification algorithms have recently received growing attention in academia and industry. In addition to their use in the context of military operations, these algorithms found civilian applications in reconfigurable systems, such as software-defined and cognitive radios. The previously reported single-carrier-based STBC classification algorithms are limited to frequency-flat fading channels; however, the wireless channels are typically frequency selective. This paper exploits the dispersive nature of the frequency-selective fading channels to classify Alamouti (AL) and spatial multiplexing (SM) STBCs over such channels. We show that the cross-correlation function of two different received signals for AL exhibits peaks at a particular set of time lags, whereas that for SM does not. Furthermore, we develop a maximum-likelihood classification algorithm. This requires channel knowledge, which may be unavailable in some scenarios such as radio environment awareness in cognitive radios. To avoid this requirement, we also propose a new classification algorithm based on the false alarm rate. Monte Carlo simulations are conducted to demonstrate the performance of the proposed algorithms.

Transmission designs for radio access technologies

Abstract: Technology described herein addresses symmetric uplink (UL)/downlink (DL) designs that can be applied to both uplink and downlink transmissions. A symmetric UL/DL design can define a Transmission Time Interval (TTI) format with control channels and data channels multiplexed using Frequency Division Multiplexing (FDM) or Time Division Multiplexing (TDM) to partition the control channels and the data channels within a Transmission Time Interval (TTI). A unified waveform can be applied to both UL and DL transmissions. Several Demodulation Reference Signal (DM-RS) designs are also described. A hybrid mode for UL transmissions is also described.

Blind Identification of SM and Alamouti STBC-OFDM Signals

Abstract: This paper proposes an efficient identification algorithm for spatial multiplexing (SM) and Alamouti (AL) coded orthogonal frequency-division multiplexing (OFDM) signals. The cross correlation between the received signals from different antennas is exploited to provide a discriminating feature to identify SM-OFDM and AL-OFDM signals. The proposed algorithm requires neither estimation of the channel coefficients and noise power, nor the modulation of the transmitted signal. Moreover, it does not need space–time block code or OFDM block synchronization. The effectiveness of the proposed algorithm is demonstrated through extensive simulation experiments in the presence of diverse transmission impairments, such as time and frequency offsets, Doppler frequency, and spatially correlated fading.

Polar-based OFDM and SC-FDE links toward energy-efficient Gbps transmission under IM-DD optical system constraints [Invited]

Abstract: Recent studies have investigated the use of orthogonal frequency division multiplexing (OFDM) and single carrier frequency-domain equalization (SC-FDE) for gigabyte per second (Gpbs) short-range optical wired and wireless access networks based on direct intensitymodulation with direct detection (IM-DD). OFDM systems have an inherent high peak-to-average power ratio (PAPR). SC-FDE systems have lower PAPR and thus outperform comparable OFDM systems in terms of bit-error performance under various practical considerations, mainly the limited dynamic range of operation at the transmitter. In RF-based OFDM and SC-FDE systems, the output signal is bipolar, complex, and cannot be transmitted in IM-DD systems. Therefore, several power efficient schemes, however spectrally inefficient, have been proposed to make positive OFDM and SC-FDE signals, e.g., asymmetrically clipped optical OFDM (ACO-OFDM) and repetition and clipping optical SCFDE (RCO-SCFDE). To increase the data rate, novel OFDM and SC-FDE signal formats, called polar OFDM (P-OFDM) and polar SC-FDE (P-SC-FDE), based on a polar representation of complex symbols, are proposed. The proposed format offers twice as much spectral efficiency as state-of-the art unipolar OFDM and SC-FDE formats. Moreover, using a power allocation approach on the time-domain positive samples, the PAPR is further reduced, and the numerical evaluation of the bit-error performance under optical source power and dynamic range constraints demonstrates superior results toward Gpbs transmission.

50μm multimode fibers for mode division multiplexing

Abstract: 50μm-diameter graded-index core multimode fibers can be adapted to mode-division-multiplexed transmissions that use multiple-input-multiple-output digital signal processing and selective mode multiplexing. We realize and characterize such fibers and compare them to low-differential-mode-group-delay few-mode fibers.

25-Gb/s OFDM 60-GHz Radio Over Fiber System Based on a Gain Switched Laser

Abstract: A 25-Gb/s OFDM 60-GHz radio over fiber (RoF) transmission system employing a gain switched DFB laser for millimeter-wave generation is demonstrated. Transmission performance below the 7% FEC limit is achieved over 50 km of fiber initially by employing precompensation. This precompensation overcomes phase noise caused by the optical phase decorrelation induced by chromatic dispersion on the two optical channels separated by 60 GHz. An externally injected gain switched laser is subsequently employed to eradicate the need for the precompensation, thus reducing phase noise and increasing the tolerance to the induced time delay between the optical tones. Transmission performance below the 7% limit is achieved over 25 km of fiber with 2-m wireless transmission in this case.

On capacity merits of spectrally efficient FDM

Abstract: This paper explores the potential benefit of recently proposed spectrally-efficient frequency-division multiplexing systems (SEFDM), when compared to traditional orthogonal frequency-division multiplexing (OFDM) systems. First, the considered SEFDM channel model is described, then we obtain an expression for the capacity of this channel in case of un-precoded transmission. We evaluate the channel capacity for various practical continuous-time modulation pulses. Numerical capacity results indicate that SEFDM can lead to channel capacity improvement over OFDM for some considered pulses, especially at relatively high SNR's.

5Gbps HG 0,1 and HG 0,3 optical mode division multiplexing for RoFSO

Abstract: Radio-over-free-space optics (Ro-FSO) technology harnesses the large capacity of optical fiber and the mobility native to wireless networks. To increase the capacity of Ro-FSO networks, this work introduces a new optical mode division multiplexing (MDM) scheme for Ro-FSO by incorporating optical Hermite-Gaussian modes HG 0, 1 and HG 0, 3 for transmitting two distinct 2.5 Gbps data modulated on 10 GHz radio subcarriers. Signal-to-noise ratios and biterror-rates show successful 2 × 2.5Gbps data transmission of 10GHz radio-modulated subcarriers over the two HG optical carriers through a 800m free-space channel.

Precoded generalised frequency division multiplexing system to combat inter-carrier interference: performance analysis

Abstract: The expected operating scenarios of fifth-generation (5G) pose a great challenge to orthogonal frequency division multiplexing which has poor out of band spectral properties, stringent synchronisation requirements and large symbol duration Generalised 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 study, the analytical performance evaluation of minimum mean square error (MMSE) receiver for GFDM is presented The authors also proposed precoding techniques to enhance the performance of GFDM A simplified expression of signal-to-interference and noise ratio (SINR) for MMSE receiver of GFDM is derived using special properties related to the modulation matrix of GFDM, which are described in this study This SINR is used to evaluate the bit error rate 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 significantly Computational complexities of different transmitters and receivers of precoded and uncoded GFDM are also presented

Bandwidth compressed carrier aggregation

Abstract: Carrier aggregation (CA) is a technique introduced in LTE-Advanced to achieve a higher throughput by increasing bandwidth. In this work, the spectrally efficient frequency division multiplexing (SEFDM) bandwidth compression technique is utilized to enhance CA performance. This work reports experimental demonstration of SEFDM and shows that up to 7 component carriers (CCs) can be aggregated in a given bandwidth with guaranteed bit error rate (BER), while orthogonal frequency division multiplexing (OFDM) can only pack 5 CCs in the same bandwidth. Full system description and experimental set up are given in the paper together with BER results for SEFDM and OFDM based systems using LTE-like frame and signal formats and transmitted over an LTE standard fading channel. Experimental results show the bandwidth advantages of SEFDM and confirm that the effective spectral efficiency of aggregated SEFDM is much higher than that of aggregated OFDM.

Resource Allocation for Multiuser Improved AF Cooperative Communication Scheme

Abstract: Joint power and bandwidth allocation of an improved amplify and forward (AF) cooperative communication scheme is proposed to utilize the spectrum efficiently. Each user adapts to a mixed strategy transmission using frequency division multiplexing (FDM), where part of the data is transmitted using AF relaying with diversity, and the other part is transmitted using direct transmission without diversity. The resource allocation problem aimed at maximizing the sum rate of a multi-user up-link scenario using the improved scheme is formulated. Both flat and frequency-selective fading channels are addressed. The resource allocation problem of the power and bandwidth profiles is non-convex and difficult to solve. In this sense, a two-step iterative algorithm is proposed, which alternates between solving either power allocation sub-problem for a given bandwidth profile or a bandwidth allocation sub-problem for a given power profile. The convergence and optimality of the proposed algorithm are discussed using game theory framework. Numerical simulations show the merits of the proposed improved AF cooperative communication scheme and the proposed iterative algorithm.

Discrete Fourier transform spreading-based generalised frequency division multiplexing

Abstract: Generalised frequency division multiplexing (GFDM) has gained significant importance as a contender for the fifth generation (5G) air interface. The peak-to-average power ratio (PAPR) of GFDM is high due to the use of a same pulse shaping filter per subcarrier and the addition of different subcarriers at the transmitter. Proposed is the use of discrete Fourier transform (DFT) spreading-based GFDM transmission to reduce the PAPR. It is found that DFT spreading helps to reduce the PAPR of GFDM significantly. It is also seen that the bit error rate performance, which is computed through simulation and using an analytical expression of the signal-to-interference-plus noise ratio, is not compromised by DFT spreading but rather is improved in the frequency selective fading channel.

A 5.4-mW 4-Gb/s 5-band QPSK transceiver for frequency-division multiplexing memory interface

Abstract: This paper presents a novel self-equalized and skewless frequency-division multiplexing memory interface. To prove its feasibility, we have realized a 5-band QPSK transceiver in 40 nm CMOS to transmit up to 4 Gb/s through 10 orthogonal communication channels (each with 400 Mb/s) via on-chip TSV emulator with effective loading of 1 pF or 5-cm FR-4 PCB trace. With differential current-mode signaling, the transceiver consumes only 5.4 mW and takes only 80×100 μm2. A real-time flexible BER testing platform is established to prove that the BER of the transceiver is less than 10 12.

Optical chaos and hybrid WDM/TDM based large capacity quasi-distributed sensing network with real-time fiber fault monitoring

Abstract: An optical chaos and hybrid wavelength division multiplexing/time division multiplexing (WDM/TDM) based large capacity quasi-distributed sensing network with real-time fiber fault monitoring is proposed. Chirped fiber Bragg grating (CFBG) intensity demodulation is adopted to improve the dynamic range of the measurements. Compared with the traditional sensing interrogation methods in time, radio frequency and optical wavelength domains, the measurand sensing and the precise locating of the proposed sensing network can be simultaneously interrogated by the relative amplitude change (RAC) and the time delay of the correlation peak in the cross-correlation spectrum. Assisted with the WDM/TDM technology, hundreds of sensing units could be potentially multiplexed in the multiple sensing fiber lines. Based on the proof-of-concept experiment for axial strain measurement with three sensing fiber lines, the strain sensitivity up to 0.14% RAC/μe and the precise locating of the sensors are achieved. Significantly, real-time fiber fault monitoring in the three sensing fiber lines is also implemented with a spatial resolution of 2.8 cm.

Space-Time Coding Schemes for MDL-Impaired Mode-Multiplexed Fiber Transmission Systems

Abstract: Spatial division multiplexing (SDM) holds out the prospects of increasing the capacities of optical fiber transmission links, especially with the recent achievements in the design of few-mode fibers and few-mode optical amplifiers. However, these systems are impaired by the capacity-limiting mode dependent loss (MDL) arising from imperfections in the optical fiber and inline components. Optical solutions were suggested to reduce, yet not completely remove, the accumulated MDL in the link through the use of strong coupling fibers and mode scramblers. Inspired by our previous study on mitigating polarization dependent loss (PDL), we present space-time (ST) coding schemes to mitigate MDL in mode-multiplexed optical transmission systems. We show, for the first time, that the combination of redundancy-free ST coding solutions with inline mode scrambling and optimal maximum-likelihood (ML) detection can completely absorb the SNR penalties induced by the MDL. The performance was assessed through simulations of three- and six-mode multiplexed systems where MDL levels up to 10 dB were observed. However, given the increased computational complexity of the suggested ML-decoded ST schemes, we present two reduced-complexity ST solutions offering a near-optimal performance. The first one consists in using a sub-optimal decoder and the second is a multiblock ST coding approach that can be scaled up for larger SDM systems.