Showing papers on "Frequency-division multiplexing published in 2017"

Line-of-Sight Millimeter-Wave Communications Using Orbital Angular Momentum Multiplexing Combined With Conventional Spatial Multiplexing

Abstract: Line-of-sight wireless communications can benefit from the simultaneous transmission of multiple independent data streams through the same medium in order to increase system capacity. A common approach is to use conventional spatial multiplexing with spatially separated transmitter/receiver antennae, for which inter-channel crosstalk is reduced by employing multiple-input-multiple-output (MIMO) signal processing at the receivers. Another fairly recent approach to transmitting multiple data streams is to use orbital-angular-momentum (OAM) multiplexing, which employs the orthogonality among OAM beams to minimize inter-channel crosstalk and enable efficient (de)multiplexing. In this paper, we explore the potential of utilizing both of these multiplexing techniques to provide system design flexibility and performance enhancement. We demonstrate a 16 Gbit/s millimeter-wave link using OAM multiplexing combined with conventional spatial multiplexing over a short link distance of 1.8 meters (shorter than Rayleigh distance). Specifically, we implement a spatial multiplexing system with a $2\times 2$ antenna aperture architecture, in which each transmitter aperture contains two multiplexed 4 Gbit/s data-carrying OAM beams. A MIMO-based signal processing is used at the receiver to mitigate channel interference. Our experimental results show performance improvements for all channels after MIMO processing, with bit-error rates of each channel below the forward error correction limit of $3.8\times 10^{-3}$ . We also simulate the capacity for both the $4\times 4$ MIMO system and the $2\times 2$ MIMO with OAM multiplexing. Our work indicates that OAM multiplexing and conventional spatial multiplexing can be simultaneously utilized to provide design flexibility. The combination of these two approaches can potentially enhance system capacity given a fixed aperture area of the transmitter/receiver (when the link distance is within a few Rayleigh distances).

Digital signal processing for fiber nonlinearities [Invited].

Abstract: This paper reviews digital signal processing techniques that compensate, mitigate, and exploit fiber nonlinearities in coherent optical fiber transmission systems.

Terahertz Wireless Data Transmission With Frequency and Polarization Division Multiplexing Using Resonant-Tunneling-Diode Oscillators

Abstract: High-capacity short-distance wireless communications in the terahertz (THz) range are anticipated and therefore have been intensively studied. Higher data rates are made possible by the introduction of frequency division multiplexing (FDM) and polarization division multiplexing (PDM) schemes in the THz range. In this paper, wireless data transmissions using 2-channel FDM in the 500 and 800 GHz ranges and PDM in the 500 GHz range are demonstrated using resonant-tunneling-diode oscillators with different frequencies and polarizations integrated into one chip. Transmissions at a data rate of 28 Gbit/s were achieved in each channel with an error rate below the forward error correction limit in both multiplexing systems. The ratios of the leakage of the transmitted signal in one channel into the other channel were about −40 and −30 dB in FDM and PDM modes, respectively.

A Novel Hybrid Beamforming Algorithm With Unified Analog Beamforming by Subspace Construction Based on Partial CSI for Massive MIMO-OFDM Systems

Abstract: Hybrid beamforming (HB) has been widely studied for reducing the number of costly radio frequency (RF) chains in massive multiple-input multiple-output (MIMO) systems. However, previous works on HB are limited to a single user equipment (UE) or a single group of UEs, employing the frequency-flat first-level analog beamforming (AB) that cannot be applied to multiple groups of UEs served in different frequency resources in an orthogonal frequency-division multiplexing (OFDM) system. In this paper, a novel HB algorithm with unified AB based on the spatial covariance matrix (SCM) knowledge of all UEs is proposed for a massive MIMO-OFDM system in order to support multiple groups of UEs. The proposed HB method with a much smaller number of RF chains can achieve more than 95% performance of full digital beamforming. In addition, a novel practical subspace construction (SC) algorithm based on partial channel state information is proposed to estimate the required SCM. The proposed SC method can offer more than 97% performance of the perfect SCM case. With the proposed methods, significant cost and power savings can be achieved without large loss in performance. Furthermore, the proposed methods can be applied to massive MIMO-OFDM systems in both time-division duplex and frequency-division duplex.

On the Road to 5G: Comparative Study of Physical Layer in MTC Context

Abstract: During the past few years, we are witnessing the emergence of 5G and its high-level performance targets. Waveform (WF) design is one of the important aspects for 5G that received considerable attention from the research community in recent years. To find an alternative to the classical orthogonal frequency division multiplexing (OFDM), several multicarrier approaches addressing different 5G technical challenges, have been proposed. In this paper, we focus on critical machine-type communications (C-MTC), which is one of the key features of the foreseen 5G system. We provide a comparative performance study of the most promising multicarrier WFs. We consider several C-MTC key performance indicators: out-of-band radiations, spectral efficiency, end-to-end physical layer latency, robustness to time and frequency synchronization errors, power fluctuation, and transceiver complexity. The investigated multicarrier WFs are classified into three groups based on their ability to keep the orthogonality: in the complex domain, e.g., most of the OFDM-inspired WFs, in the real domain like offset-quadrature amplitude modulation (QAM)-based techniques, and non-orthogonal WFs like generalized frequency division multiplexing and filter bank-based multicarrier-QAM. Finally, the performances of these WFs are thoroughly discussed in order to highlight their pros and cons and permit a better understanding of their capabilities in the context of C-MTC.

Dual-Band LFM Signal Generation by Optical Frequency Quadrupling and Polarization Multiplexing

Abstract: A photonic approach to generating dual-band linear frequency modulation (LFM) signal is proposed based on optical frequency quadrupling and polarization multiplexing. This is achieved by using an integrated polarization multiplexing dual-parallel Mach-Zehnder modulator to perform frequency quadrupling in two orthogonal polarizations independently. After optical-to-electrical conversion, two LFM signals in different frequency bands can be generated simultaneously. The proposed scheme has a very simple and compact structure. Thanks to the frequency quadrupling technique, high-frequency, and wideband LFM signals can be generated with low speed electrical devices. The central frequency, bandwidth, and temporal duration of the generated LFM signals can be easily adjusted. In the experiment, the generation of dual-band LFM signals in K-band and Ka-band (centered at 20 and 30 GHz, respectively) is demonstrated. Tunability of the central frequency, bandwidth, and time duration is also verified. The proposed signal generator is a promising candidate in dual-band multi-function radar applications.

Transmission Experiment of Bandwidth Compressed Carrier Aggregation in a Realistic Fading Channel

Abstract: In this paper, an experimental testbed is designed to evaluate the performance of a bandwidth compressed multicarrier technique, termed spectrally efficient frequency division multiplexing (SEFDM) in a carrier aggregation (CA) scenario. Unlike orthogonal frequency division multiplexing (OFDM), SEFDM is a nonorthogonal waveform which, relative to OFDM, packs more subcarriers in a given bandwidth, thereby improving spectral efficiency. CA is a long-term evolution-advanced (LTE-Advanced) featured technique that offers a higher throughput by aggregating multiple legacy radio bands. Considering the scarcity of the radio spectrum, SEFDM signals can be utilized to enhance CA performance. The combination of the two techniques results in a larger number of aggregated component carriers (CCs) and, therefore, increased data rate in a given bandwidth with no additional spectral allocation. It is experimentally shown that CA-SEFDM can aggregate up to seven CCs in a limited bandwidth, while CA-OFDM can only put five CCs in the same bandwidth. In this paper, LTE-like framed CA-SEFDM signals are generated and delivered through a realistic LTE channel. A complete experimental setup is described, together with error performance and effective spectral efficiency comparisons. Experimental results show that the measured bit error rate performance for CA-SEFDM is very close to CA-OFDM and that the effective spectral efficiency of CA-SEFDM can be substantially higher than that of CA-OFDM.

SIR Analysis of OFDM and GFDM Waveforms With Timing Offset, CFO, and Phase Noise

Abstract: In this paper, we analyze the impacts of timing offset (TO), carrier frequency offset (CFO), and phase noise in orthogonal frequency division multiplexing (OFDM) and generalized frequency division multiplexing (GFDM) waveforms. As TO can be classified into four cases depending on the direction of offset, we provide the analysis of signal-to-interference ratio (SIR) for each of the cases when phase noise and synchronization errors of the desired user occur in frequency selective channel. We also propose the receiver filter for GFDM systems that is optimized to maximize SIR with CFO in additive white Gaussian noise channel. Simulation results show that GFDM is more sensitive to CFO than OFDM. We also confirm that GFDM systems using proposed receiver filter are robust against CFO compared with conventional systems.

Why Noise and Dispersion May Seriously Hamper Nonlinear Frequency-Division Multiplexing

Abstract: The performance of optical fiber systems based on nonlinear frequency-division multiplexing (NFDM) or on more conventional transmission techniques is compared through numerical simulations. Some critical issues affecting NFDM systems—namely, the strict requirements needed to avoid burst interaction due to signal dispersion and the unfavorable dependence of performance on burst length—are investigated, highlighting their potentially disruptive effect in terms of spectral efficiency. Two digital processing techniques are finally proposed to halve the guard time between NFDM symbol bursts and reduce the size of the processing window at the receiver, increasing spectral efficiency and reducing computational complexity.

A Comparison Between Orthogonal and Non-Orthogonal Multiple Access in Cooperative Relaying Power Line Communication Systems

Abstract: Most, if not all, existing studies on power line communication (PLC) systems as well as industrial PLC standards are based on orthogonal multiple access schemes, such as orthogonal frequency-division multiplexing and code-division multiple access. In this paper, we propose non-orthogonal multiple access (NOMA) for decode-and-forward cooperative relaying PLC systems to achieve higher throughput and improve user fairness. To quantitatively characterize the proposed system performance, we also study conventional cooperative relaying (CCR) PLC systems. We evaluate the performance of the two systems in terms of the average capacity. In this respect, accurate analytical expressions for the average capacity are derived and validated with Monte Carlo simulations. The impact of several system parameters, such as the branching, impulsive noise probability, cable lengths, the power allocation coefficients, and input signal-to-noise ratio, is investigated. The results reveal that the performance of the proposed NOMA-PLC scheme is superior compared with that of the CCR-PLC system. It is also shown that the NOMA-PLC system can be more effective in reducing electromagnetic compatibility associated with PLC and that increasing the network branches can considerably degrade the performance. Moreover, optimizing the power allocation coefficients is found to be of utmost importance to maximize the performance of the proposed system.

Capacity limit for faster-than-Nyquist non-orthogonal frequency-division multiplexing signaling.

Abstract: Faster-than-Nyquist (FTN) signal achieves higher spectral efficiency and capacity compared to Nyquist signal due to its smaller pulse interval or narrower subcarrier spacing. Shannon limit typically defines the upper-limit capacity of Nyquist signal. To the best of our knowledge, the mathematical expression for the capacity limit of FTN non-orthogonal frequency-division multiplexing (NOFDM) signal is first demonstrated in this paper. The mathematical expression shows that FTN NOFDM signal has the potential to achieve a higher capacity limit compared to Nyquist signal. In this paper, we demonstrate the principle of FTN NOFDM by taking fractional cosine transform-based NOFDM (FrCT-NOFDM) for instance. FrCT-NOFDM is first proposed and implemented by both simulation and experiment. When the bandwidth compression factor α is set to 0.8 in FrCT-NOFDM, the subcarrier spacing is equal to 40% of the symbol rate per subcarrier, thus the transmission rate is about 25% faster than Nyquist rate. FTN NOFDM with higher capacity would be promising in the future communication systems, especially in the bandwidth-limited applications.

Introduction on IMT-2020 5G Trials in China

Abstract: Ultrahigh data rate, massive connectivity, ultralow latency, and high reliability, as well as ultraflexible air interface design to support diversified usage scenarios, are the major targets of 5G radio access network design To meet these targets, advanced new radio transmission technologies, including new waveform, new channel coding, non-orthogonal multiple access, as well as massive antenna techniques, have been proposed and studied worldwide in both academic and industries Most of the gains claimed in the literature are from simulations or by small scale lab testing Instead, this paper elaborates on the first hand results and analysis of the large-scale field trials carried out in China for a selection of key 5G technology components as well as some of their combinations, including filtered-orthogonal frequency division multiplexing (OFDM) (f-OFDM), polar code, sparse code multiple access, and massive multi-input multi-output (MIMO) for both uplink and downlink cellular networks Testing results verify the feasibility and benefit of each technology contributing toward the diversified 5G targets, as well as the feasibility for these technologies to work jointly for higher spectrum efficiency, larger connectivity, and lower latency

Optical transport solutions for 5G fixed wireless access [Invited]

Abstract: With the advent of 5G, fixed wireless access (FWA) has emerged as a promising candidate for rolling out fixed broadband services. By means of radio simulations, we define a 5G radio deployment scenario for FWA that can meet the service requirements of future fixed broadband access. Different transport requirements imposed by different radio access network (RAN) split options are considered and a broad range of optical transport technologies/systems to support the FWA scenario is analyzed. For higher-layer RAN split options, we find that conventional 10G passive optical networks (XG-PONs) and coarse wavelength-division multiplexing (CWDM) technologies are the most cost effective. CWDM provides improved support for low-latency services while XG-PON facilitates future migration to fiber to the home. For lower-layer RAN splits, point-to-point (PtP) fiber or PtP-WDM is required. In the considered scenario, CWDM and PtP technologies are found to be the most cost effective.

Capacity Analysis of Signaling on the Continuous Spectrum of Nonlinear Optical Fibers

Abstract: This paper investigates the capacity of signaling on the continuous spectrum (CS) of optical fibers as defined by the nonlinear Fourier transform (NFT). The channel model of such NFT-based optical fiber communication systems is studied based on the behavior of the propagated optical signal in the time domain for an asymptotically long fiber length. The derived channel model is validated using simulation for different scenarios of practical interest. An important characteristic of the channel in the nonlinear spectral domain is the strong dependence of noise to signal. A variance normalizing transform is applied as a tool to obtain an estimate on the capacity of the underlying channel. The results predict a remarkable capacity for signaling on CS, which can be utilized as an extra degree of freedom along with discrete spectrum (i.e., soliton transmission). It is further observed that the channel capacity of signaling on CS saturates at high signal power despite the linearizing capability of the NFT.

Performance Analysis of Aperture-Based Receivers for MIMO IM/DD Visible Light Communications

Abstract: Aperture-based receivers are a new form of receiver for multiple-input multiple-output (MIMO) intensity-modulated direct-detection visible light communication (VLC). These receivers provide a wide field of view and excellent angular diversity using a compact planar structure and so are ideally suited for integration in hand-held devices such as smartphones. It is shown that in typical scenarios to achieve similar performance the photodiodes in a conventional receiver based on spatial diversity would have to be separated by distances greater than 30 cm. An in-depth analysis of the performance of aperture-based receivers is presented. Expressions are derived for the channel gain between an optical transmitter and each receiving element (RE) as a function of the transmission pattern of the transmitter, the design of the RE, and the relative positions of the transmitter and receiver. It is shown that a well-designed receiver consisting of multiple REs can separate signals received from different directions with low-multistream interference and that the associated MIMO channel matrices are well conditioned. Simulations are performed for a typical indoor VLC scenario in which light-emitting diode luminaires transmit information using asymmetrically clipped optical orthogonal frequency division multiplexing. Results are presented for receivers using both linear and nonlinear equalizers and for both line of sight (LOS) and LOS plus diffuse reception. The diffuse component is shown to improve the bit error rate (BER) performance slightly. It is shown that the BER depends on the receiver position. When a zero-forcing (ZF) linear receiver is used, the BER is dominated by the most attenuated signal, so the performance degrades at the corners of the room. In contrast, the receivers with nonlinear equalizers based on ZF followed by successive interference cancelation achieve low BER throughout the scenario.

Orthogonality-Based Generalized Multicarrier Constant Envelope Multiplexing for DSSS Signals

Abstract: The new generation global navigation satellite systems will broadcast multiple direct sequence spread spectrum signals on multiple different central frequencies, with complex spreading chip waveforms. There is a strong demand for efficient and flexible multiplexing techniques to combine these signals into a constant envelope composite signal. In this paper, a high efficiency generalized multicarrier joint constant envelope multiplexing (CEM) technique for multilevel DSSS signals is proposed. The basic idea of this technique is adding an auxiliary component into the direct superposition of signals to keep the envelope of the integrated signal constant. Design principle, constraints, and optimization method of the auxiliary component are investigated. An analysis with typical case studies demonstrates the high efficiency and high flexibility of the proposed technique. Compared with existing CEM techniques, the proposed technique has much higher design flexibility in the number of subbands, the number of signal components, power ratio and phase relationship among components, and the spreading chip waveforms. It can be applied to any number of bipolar or multilevel DSSS signals with arbitrary power distribution at one or more subcarrier frequencies. Such high-level design flexibility provides system designers great room in signal scheme optimization for varied navigation applications in the future.

A Novel Hybrid CFO Estimation Scheme for UFMC-Based Systems

Abstract: In this letter, a robust hybrid carrier frequency offset (CFO) estimation scheme based on training symbols is devised for universal-filtered multi-carrier (UFMC) based systems. In this scheme, the CFO estimator based on a least square (LS) criterion is first derived to acquire a coarse frequency offset estimation with the use of a large frequency searching step. And then, the residual frequency offset is accurately estimated through the auto-correlation operation of received signals, which have been compensated. This algorithm has the features of larger estimation range as well as higher estimation precision. Through numerical simulations, it is validated that the performance of the proposed algorithm is better than that of existing algorithms.

64 × 0.5 Gbaud Nonlinear Frequency Division Multiplexed Transmissions With High Order Modulation Formats

Abstract: Nonlinear frequency division multiplexing (NFDM) with the modulation of the nonlinear Fourier spectrum (both discrete and continuous parts) has been recently considered as a promising transmission method to combat fiber nonlinearity impairments. In this paper, we experimentally demonstrate the generation, detection, and transmission performance of NFDM systems where the transmitted information is encoded directly onto the continuous part of the nonlinear spectrum using 64 overlapped 0.5 Gbaud channels with high order QAM formats (e.g., 16 QAM, 32 QAM, and 64 QAM). In comparison with the conventional orthogonal frequency division multiplexing transmission, which is the linear counterpart of NFDM transmission, clear performance advantage of NFDM systems, up to 1.3 dB, has been observed. This result indicates for the first time the performance benefit of NFDM transmission over its linear counterpart, showing the high potential of this emerging technology.

Waveform Design of Zero Head DFT Spread Spectral Efficient Frequency Division Multiplexing

Abstract: Zero head discrete Fourier transform (DFT) spread spectral efficient frequency division multiplexing (ZH-DFT-s-SEFDM) as a non-orthogonal multicarrier transmission scheme is proposed for the bandwidth compressing. A zero head DFT spread approach consists in this waveform design for reducing the peak-average-power-ratio (PAPR) and suppressing the out-of-band emissions introduced by the inter symbol interference and the inter carrier interference. Simultaneously, the corresponding receiver design is given, and a low complexity zero-forcing (ZF) detection algorithm is attached to the ZH-DFT-s-SEFDM receiver design. As the loss of orthogonality, the conventional SEFDM detector is overly complex, and however, the ZF detector as a linear detector performs well in the ZH-DFT-s-SEFDM system by adjusting the length of zero head. Simulation results show that the ZH-DFT-s-SEFDM signal achieves lower out-of-band emissions and a better PAPR performance than the conventional SEFDM signal at the same bandwidth compressing ratio. The binary error ratio (BER) performance of a ZH-DFT-s-SEFDM receiver with a ZF detector is also investigated. It performs better as the longer zero head inserted, and can achieve the better BER performance than conventional SEFDM and OFDM at the low signal-to-noise-ratio (SNR) for a particular number of zero head, and the BER performance of ZH-DFT-s-SEFDM remained the same as OFDM and traditional SEFDM at the high SNR.

Single channel 106 Gbit/s 16QAM wireless transmission in the 0.4 THz band

Abstract: We experimentally demonstrate a single channel 32-GBd 16QAM THz wireless link operating in the 0.4 THz band. Post-FEC net data rate of 106 Gbit/s is successfully achieved without any spatial/frequency multiplexing.

Orthogonal Multiband CAP Modulation Based on Offset-QAM and Advanced Filter Design in Spectral Efficient MMW RoF Systems

Abstract: In this study, to the first time, we demonstrate an offset-QAM carrier-less amplitude and phase modulation (OQAM-CAP) technique for spectral efficient multi-user radio-over-fiber systems. In comparison with traditional QAM-based CAP modulation schemes, the digital filter for each channel in OQAM-CAP can be adaptively redesigned to obtain either higher spectral efficiency or lower computational complexity. Two kinds of digital filters, namely, square-root raised-cosine (SRRC) filters and isotropic orthogonal transform algorithm (IOTA)-based filters, are studied and applied to shape the frequency window of each channel in CAP systems. We compared the performances among SRRC-OQAM CAP, IOTA-OQAM CAP, and traditional SRRC-QAM CAP. It is experimentally demonstrated that SRRC-OQAM-CAP can achieve higher spectral efficiency, IOTA-OQAM-CAP can obtain higher computational efficiency, and SRRC-QAM-CAP can be used in uplink transmission with lower interchannel interference. Bidirectional experiments are conducted with around 2-GHz nine aggregated channels on 60-GHz optical millimeter wave. Less than 7% error vector magnitudes are realized over 15-km standard single-mode fiber and 1.5-m wireless channel.

Time Lens-Based Optical Fourier Transformation for All-Optical Signal Processing of Spectrally-Efficient Data

Abstract: We review recent progress in the use of time lens-based optical Fourier transformation for advanced all-optical signal processing. A novel time lens-based complete optical Fourier transformation (OFT) technique is introduced. This complete OFT is based on two quadratic phase-modulation stages using four-wave mixing, separated by a dispersive medium, which enables time-to-frequency and frequency-to-time conversions simultaneously, thus performing an exchange between the temporal and spectral profiles of the input signal. Using the proposed complete OFT, several advanced all-optical signal processing schemes for spectrally-efficient systems and networks have been achieved, including all-optical generation, detection and format conversion of spectrally-efficient signals. The spectrally-efficient signals in this paper mainly refer to efficiently multiplexed signals with a high symbol rate per Hz, such as orthogonal frequency division multiplexing, Nyquist wavelength-division multiplexing (Nyquist-WDM), and Nyquist optical time division multiplexing (Nyquist-OTDM) signals.

A Shock Tube Experimental System for Communication Performance Evaluation Under the Time-Varying Plasma Flow Channel

Abstract: Plasma sheath can severely affect the electromagnetic waves and lead to the radio blackout problem. Existing simulation works on the influence of plasma on communications, either failed to illustrate the high dynamics of the plasma or suffered from high computational complexity. In this paper, we propose an experimental system based on a shock tube to evaluate the communication performance over the plasma channel. In order to compare the performance of different modulation modes simultaneously, we initiatively mixed frequency-shift keying (FSK), pulse-position modulation, and quadrature phase-shift keying (QPSK) together in the transmission signal. Since the duration of the plasma generated by the shock tube is short in each experiment instance, we employ the achievable rate to evaluate the communication performance. Specifically, according to our experimental results, the communication performance of FSK is the best and most stable, while the QPSK is the worst and most unstable, indicating that the plasma channel has the greatest impact on the phase domain compared with the frequency domain and the time domain. Finally, the nonstationary and high dynamic characteristics of the plasma channel are verified in our designed experiment.

IQ Imbalance Compensation for Generalized Frequency Division Multiplexing Systems

Abstract: Generalized frequency division multiplexing (GFDM) with a flexible structure is one of the promising candidates for the fifth generation wireless communication system. This letter presents a compensation scheme of in-phase and quadrature (IQ) imbalance caused by radio frequency front-end for GFDM. The motivation behind this letter is to relax the requirement on time-invariant channel in the process of estimating IQ imbalance parameters. A low computational complexity approach is proposed to directly estimate IQ imbalance parameters without any prior knowledge of channel. Meanwhile, the structure of training sequences that avoid channel estimation is derived. Simulation results confirm that the proposed method can reduce the effects of IQ imbalance and provide reliable performance even over severe IQ imbalance environment.

Efficient Hybrid Grouping Spectrum Assignment to Suppress Spectrum Fragments in Flexible Grid Optical Networks

Abstract: Flexible grid optical networks (FONs) can accommodate diverse kinds of service connections with higher networking flexibility and spectrum-utilization efficiency by employing a finer resource allocation granularity (known as frequency slot) and a more sophisticated path-routing and resource-allocation algorithm (known as routing and spectrum assignment algorithm), when compared to the traditional wavelength division multiplexing optical networks However, the continuity and the contiguity constraints in spectrum allocation may possibly introduce spectrum fragments, which cannot be utilized by the subsequent service connections and thus reduce the amount of available resources as well as the networking flexibility in FONs Therefore, many algorithms have been proposed to decrease the amount of spectrum fragments by re-optimizing the fragmented resources These algorithms are known as spectrum defragmentation algorithms, which always induce traffic disruption or require extra components In order to avoid traffic disruption and the requirement of extra components, some grouping RSA algorithms have been proposed to suppress spectrum fragments from their generation by pre-dividing the spectrum resources into several either fixed or variable groups However, since the spectrum resources in one group can only be assigned to the service connections of one specific kind, the flexibility of these grouping algorithms is always limited by the kinds of service connections In this paper, we introduce hybrid grouping mechanism into spectrum assignment and propose a hybrid-group-based RSA algorithm, most-used-first hybrid grouping (MUFHG) RSA algorithm, to suppress the spectrum fragments generated in FONs By employing hybrid grouping mechanism, the proposed MUFHG algorithm sorts the spectrum resources into several flexible groups with specified allocation starting FSs And each spectrum group can accommodate several kinds of service connections if the bandwidth requirements of these service connections have multiple relations, which guarantees that the remained or the released spectrum resources in each group can always be re-used Therefore, spectrum fragments are only generated in the spectrum bands between two adjacent flexible groups In this way, the proposed hybrid-group-based algorithm can significantly suppress spectrum fragments from their generation Besides, the proposed MUFHG algorithm helps improve the blocking performance of the network by employing the most-used-first strategy to maximize the number of less frequently used spectrum resources for subsequent service connections The simulation results indicate that the proposed MUFHG algorithm gains notable reductions in both spectrum fragments and bandwidth blocking probability with neither traffic disruption nor extra components

A Precoding-based PAPR Reduction Technique for UF-OFDM and Filtered-OFDM Modulations in 5G Systems

Abstract: The universal filtered-orthogonal frequency division multiplexing (UF-OFDM) (also called universal filtered multicar- rier (UFMC)) and the filtered-OFDM (F-OFDM) are candidates to be alternative to the OFDM modulation in the upcoming 5G systems thanks to their improved spectral occupation and resistance to the carrier frequency offset. However, like the majority of the multicarrier modulations, UF-OFDM and F- OFDM have a high peak-to-average power ratio (PAPR). This influences the operation mode of radio frequency components such as the power amplifier and the digital-to-analog converter. In this paper, a precoding-based PAPR reduction technique is proposed for both the UF-OFDM and the F-OFDM cases. A similar technique has been proposed in the literature for OFDM. The principle of this method is to transform the UF-OFDM signal to a lower order summation of single carrier signals and the F-OFDM signal to single carrier signal. The relevance of the proposed PAPR reduction technique is confirmed by simulation results. The latter show a PAPR reduction of at least 2.5 dB. Moreover, the proposed technique does not impact the bit error rate performance and lowers down the power spectral density tails at the power amplifier output.

Space-frequency to space-frequency for MIMO radio over copper

Abstract: Centralized Radio Access Network (C-RAN) architecture is considered the only viable solution to handle the complex interference scenarios generated by massive antenna and small cell deployment foreseen for next generation (5G) mobile networks. The fronthaul links used to exchange the signal between Base Band Units (BBUs) and Remote Radio Heads (RRHs) are conventionally based on optical fiber, due to its huge bandwidth. In this paper we propose the radio over copper (RoC) as a complementary technology for the fronthaul architectures leveraging on the pre-existing LAN cables that are largely deployed in buildings and enterprises. To fully exploit the capabilities of LAN cable over the last 50–200m, a joint space and frequency division multiplexing is proposed. In particular, the main contribution of the paper is to prove that a smart mapping between the radio antennas/spectrum and the copper cable space/frequency dimensions allows an efficient communication over the RRH-BBU link with performances that are comparable to those achieved by an ideal fronthauling where BBU and RRH are assumed to be co-located. Validation is on the radio-link capabilities of RoC over Cat-6 cable to meet the demand for massive MIMO technology.

A comparison of OFDM, QAM-FBMC, and OQAM-FBMC waveforms subject to phase noise

Abstract: Frequencies above 6 GHz are being considered by mobile communication industry for the deployment of future 5G networks. However in the higher carrier frequencies, especially the millimeter-wave frequencies (above 30 GHz), there can be severe degradations in the transmitted and received signals due to Phase Noise (PN) introduced by the local oscillators. In this paper, the effect of PN has been investigated for Orthogonal Frequency Division Multiplexing (OFDM), Offset QAM Filter-Bank Multi-Carrier (OQAM-FBMC) and QAM Filter-Bank Multi-Carrier (QAM-FBMC). The sources of degradation in these waveforms are quantified and closed-form expressions are derived for Signal-to-Interference Ratio (SIR). Evaluations are performed in terms of SIR and Symbol Error Rate (SER) for mm-wave frequencies using mmMAGIC PN model. The results reveal that OFDM outperforms OQAM-FBMC and QAM-FBMC and is a promising candidate for mm-wave communication.