Band Orthogonal Frequency Division Multiplexing Research Articles

Efficiency Maximization for Battery-Powered OFDM Transmitter via Amplifier Operating Point Adjustment.

While Orthogonal Frequency Division Multiplexing (OFDM) is a dominating spectrum access technology in modern, wideband access networks, it is important to maximize its transmission efficiency considering the underlying radio front-end characteristics. A practical front-end contains nonlinear components, e.g., a Power Amplifier (PA), resulting in nonlinear distortion being injected into OFDM band deteriorating symbols detection. A PA operating point, defined here by Input Back-Off (IBO), can be adjusted to balance the wanted signal power and nonlinear distortion power. While it is the most common to maximize the spectral efficiency (SE), recently, energy efficiency (EE) maximization gained momentum. However, EE maximization requires, in addition to PA nonlinearity modeling, modeling of the power consumption of the PA and all other transmitter components. While it is commonly overlooked, if a battery is used to power the transmitter, its model should be considered as well. This paper derives mathematical expressions for EE and SE of an OFDM transmitter considering Rapp and soft-limiter models of PA nonlinearity, class A, class B, and perfect PA power consumption models, and two battery models: perfect and worst-case. While closed-form expressions cannot be obtained for most of the derived integrals, numerical methods have been used to obtain the optimal IBO value in each case. The numerical results show, in addition to optimal IBO values, the expected Signal-to-Noise and Distortion Ratios (SNDRs). It is shown that the optimal IBO value changes significantly with the wireless channel properties, utilized hardware architecture, or the utilized optimization goal. As such, the proposed optimization is an important topic for 5G and beyond transmitters.

Wideband ring mixer for band #1 of MB-OFDM systems in 180 nm CMOS technology

Abstract A wideband down conversion ring mixer is proposed for multi band orthogonal frequency division multiplexing (MB-OFDM) system in 180 nm CMOS technology. The mixer is essentially used in a heterodyne wireless receiver to enhance the selectivity of the system. Being a nonlinear system, the mixer dominates the overall performance of the system. The design of down conversion mixer is the most challenging part of a receive chain. Wideband impedance matching always remains a challenge in any radio frequency integrated circuit design. This paper presents the design of a ring mixer with high linearity, wideband impedance matching using differential resistive impedance matching and without using any DC bias. The proposed mixer is tuned for a frequency of 3.432 GHz of band 1 of the MB-OFDM system. Mixer core is based on the FET ring mixer topology. The mixer is implemented in 180 nm CMOS technology. The mixer achieves the minimum conversion loss of 10.49 dB, 1 dB compression point (P1) of 12.40 dBm, third order input intercept point (IIP3) of 12.01 dBm, a minimum SSB noise figure of 8.99 dB, and S 11 of less than -10 dB over the frequency range of 0 to 13.61 GHz . The layout of the mixer records an active area of 183.75 μm 2 .

A 5G C-RAN Optical Fronthaul Architecture for Hotspot Areas Using OFDM-Based Analog IFoF Waveforms

Analog fronthauling is currently promoted as a bandwidth and energy-efficient solution that can meet the requirements of the Fifth Generation (5G) vision for low latency, high data rates and energy efficiency. In this paper, we propose an analog optical fronthaul 5G architecture, fully aligned with the emerging Centralized-Radio Access Network (C-RAN) concept. The proposed architecture exploits the wavelength division multiplexing (WDM) technique and multicarrier intermediate-frequency-over-fiber (IFoF) signal generation per wavelength in order to satisfy the demanding needs of hotspot areas. Particularly, the fronthaul link employs photonic integrated circuit (PIC)-based WDM optical transmitters (Txs) at the baseband unit (BBU), while novel reconfigurable optical add-drop multiplexers (ROADMs) cascaded in an optical bus are used at the remote radio head (RRH) site, to facilitate reconfigurable wavelength switching functionalities up to 4 wavelengths. An aggregate capacity of 96 Gb/s has been reported by exploiting two WDM links carrying multi-IF band orthogonal frequency division multiplexing (OFDM) signals at a baud rate of 0.5 Gbd with sub-carrier (SC) modulation of 64-QAM. All signals exhibited error vector magnitude (EVM) values within the acceptable 3rd Generation Partnership Project (3GPP) limits of 8%. The longest reach to place the BBU away from the hotspot was also investigated, revealing acceptable EVM performance for fiber lengths up to 4.8 km.

140-Gb/s PS-256-QAM Transmission in an OFDM System Using Kramers–Kronig Detection

We experimentally demonstrate an orthogonal frequency-division multiplexing (OFDM) system with direct detection. Adopting Kramers–Kronig (KK) detection and probabilistic shaping (PS) technology, 140-Gb/s 256-QAM signal can be successfully transmitted over 25-km standard single-mode fiber (SSMF), which satisfies the normalized generalized mutual information (NGMI) threshold of 0.865. Based on the experimental results, the performance of single-side band (SSB) OFDM signal can be effectively improved with the aid of KK detection and can be further enhanced by the deployed PS method.

58.74-Gb/s $2\times2$ MIMO 60-GHz Optical/Wireless System With Simple Power-Detector Down-Conversion

We demonstrate a 58.74-Gb/s $V$ -band orthogonal frequency-division multiplexing (OFDM) radio-over-fiber (RoF) system employing the $2\times 2$ multiple-input-multiple-output (MIMO) technology and power detector for down-conversion for the first time. Additional radio frequency (RF) tone is generated and transmitted from central station to replace the local oscillator at wireless receiver for power detector down-conversion. To enhance spectrum efficiency, the gap mymargin between OFDM signal and RF tone is not needed. However, the down-converted signal will suffer signal-to-signal beating interference (SSBI). In this letter, we propose and successfully employ the $2\times 2$ MIMO SSBI mitigation schemes to mitigate SSBI, resulting in 45% capacity improvement.

Performance Analysis of Single Side Band Orthogonal Frequency Division Multiplexing in Radio over Fiber System with Direct and External Modulation Schemes

Abstract Radio over fiber is a technology in which the light signals at the central station are modulated by a radio frequency signal, and by using the optical fiber it is transmitted to base stations. The data stream being sent is separated into subcarrier frequencies by the technique of orthogonal frequency division multiplexing. The orthogonality between the sub-carriers is provided by FFT modulation, which avoids the demodulators from accepting other frequencies. It is possible to transmit high-data rate signals over short and long distance by implementing orthogonal frequency division multiplexing with radio over fiber system along with the optical fiber. This enhances the system with more coverage area, and without increasing the cost of the system it provides the flexibility. The proposed work is to investigate the performance analysis of single side band orthogonal frequency division multiplexing in radio over fiber system with external and direct modulations using spectral analysers and constellation visualizers. The Mach-Zender modulator is proposed for external modulation, the vertical cavity surface emitting laser is used in direct modulation. The simulations were carried out by using Optisystem Software version 15.0 with global parameters for both intensity modulation schemes.

Pilot Design for Sparse Channel Estimation in Orthogonal Frequency Division Multiplexing Systems

Orthogonal Frequency Division Multiplexing (OFDM) is a well-known technique used in modern wide band wireless communication systems. Coherent OFDM systems achieve its advantages over a multipath fading channel, if channel impulse response is estimated precisely at the receiver. Pilot-aided channel estimation in wide band OFDM systems adopts the recently explored compressive sensing technique to decrease the transmission overhead of pilot subcarriers, since it exploits the inherent sparsity of the wireless fading channel. The accuracy of compressive sensing techniques in sparse channel estimation is based on the location of pilots among OFDM subcarriers. A sufficient condition for the optimal pilot selection from Sylow subgroups is derived. A Sylow subgroup does not exist for most practical OFDM systems. Therefore, a deterministic pilot search algorithm is described to select pilot locations based on minimizing coherence, along with minimum variance. Simulation results reveal the effectiveness of the proposed algorithm in terms of bit error rate, compared to the existing solutions.

High performance mixed optical CDMA system using ZCC code and multiband OFDM

In this paper, we have proposed a high performance network design, which is based on mixed optical Code Division Multiple Access (CDMA) system using Zero Cross Correlation (ZCC) code and multiband Orthogonal Frequency Division Multiplexing (OFDM) called catenated OFDM. In addition, we also investigate the related changing parameters such as; effective power, number of user, number of band, code length and code weight. Then we theoretically analyzed the system performance comprehensively while considering up to five OFDM bands. The feasibility of the proposed system architecture is verified via the numerical analysis. The research results demonstrated that our developed modulation solution can significantly enhanced the total number of user; improving up to 80% for five catenated bands compared to traditional optical CDMA system, with the code length equals to 80, transmitted at 622 Mbps. It is also demonstrated that the BER performance strongly depends on number of weight, especially with less number of users. As the number of weight increases, the BER performance is better.

New catenated OFDM modulation scheme in zero cross correlation OCDMA at various number of user and effective power

This paper proposes an integration of optical Code Division Multiple Access (OCDMA) with new catenated Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme. This effective combination based on Zero Cross Correlation (ZCC) code can enhanced the system capacity and increased spectral efficiency by fully utilizing the available electrical bandwidth. We investigate the performance of the proposed system for various number of user, number of weight and effective power. The performance assessment is carried out by means of the signal to noise ratio (SNR) and bit error rate (BER) for up to five catenated OFDM bands transmitted simultaneously through optical link at 622 Mbps. More specifically, mathematical expressions for SNR and BER performance are derived. The corresponding numerical results are presented and compared with traditional OCDMA-ZCC system to verified the feasibility of the proposed system. The results show that with OCDMA/catenated-OFDM based on ZCC code provides 86% more number of permissible user for SNR of 15 dB. In addition, this integration provides higher receiver sensitivity; an approximately –22.5 dBm for 20 number of user with 8 number of weight. It is also found that, to accommodate more user, the system requires higher effective power at the receiver.

Suppressing the relaxation oscillation noise of injection-locked WRC-FPLD for directly modulated OFDM transmission.

By up-shifting the relaxation oscillation peak and suppressing its relative intensity noise in a weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) under intense injection-locking, the directly modulated transmission of optical 16 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) data-stream is demonstrated. The total bit rate of up to 20 Gbit/s within 5-GHz bandwidth is achieved by using the OFDM subcarrier pre-leveling technique. With increasing the injection-locking power from -12 to -3 dBm, the effective reduction on threshold current of the WRC-FPLD significantly shifts its relaxation oscillation frequency from 5 to 7.5 GHz. This concurrently induces an up-shift of the peak relative intensity noise (RIN) of the WRC-FPLD, and effectively suppresses the background RIN level to -104 dBc/Hz within the OFDM band between 3 and 6 GHz. The enhanced signal-to-noise ratio from 16 to 20 dB leads to a significant reduction of bit-error-rate (BER) of the back-to-back transmitted 16-QAM-OFDM data from 1.3 × 10(-3) to 5 × 10(-5), which slightly degrades to 1.1 × 10(-4) after 25-km single-mode fiber (SMF) transmission. However, the enlarged injection-locking power from -12 to -3 dBm inevitably declines the modulation throughput and increases its negative throughput slope from -0.8 to -1.9 dBm/GHz. After pre-leveling the peak amplitude of the OFDM subcarriers to compensate the throughput degradation of the directly modulated WRC-FPLD, the BER under 25-km SMF transmission can be further improved to 3 × 10(-5) under a receiving power of -3 dBm.

Reconfigurable LNA for MB-OFDM Receiver using Active Inductor

Low Noise Amplifier (LNA) is very much important in achieving good reception sensitivity in the wideband transceiver of Ultra Wide Band (UWB) architecture. In this paper, the LNA is designed for Multi Band-Orthogonal Frequency Division Multiplexing (MB-OFDM) receiver, which is used to transmit the information on 14 different sub bands of UWB with minimum of 528 MHz frequency in each band. The LNA comprises of three stages namely input stage, core stage and output stage. The input stage is for better Input matching and output stage contributes better Output matching by acting as a buffer. The core stage is responsible for high gain of the LNA. Different sub bands are achieved with the help of inductors at the input and the output stage. The spiral inductor at the input stage of the LNA is replaced with a suitable active inductor. The gain and Noise Figure of all the three stages depends on the Active inductor. The gain of the Active Inductor (AI) based LNA varies from 25 dB to 22 dB throughout the 14 bands of UWB. The noise figure varies from 5 dB to 6.3 dB. The input impedance lies between -7 dB to -9 dB and output impedance lies from -5 dB to -14 dB. All simulations are carried out using Advanced Design Software (ADS) 2013.

Choose Your Subcarriers Wisely: Active Interference Cancellation for Cognitive OFDM

A novel low complexity active interference cancellation (AIC) scheme for primary user (PU) protection is presented for application to cognitive orthogonal frequency division multiplexing (OFDM) systems, in which out-of-band radiation spilling over the PU protected band is to be minimized. A set of cancellation subcarriers are modulated by appropriate linear combinations of the remaining data subcarriers. The combination weights are fixed so that, in contrast with previous AIC approaches, they need not be recomputed on a symbol-by-symbol basis. Weight optimization can thus be carried out offline, drastically reducing the online computational cost. In addition, it is shown that by carefully selecting the location of cancellation subcarriers, significant performance improvements can be achieved. Given that finding the optimal location is an intractable combinatorial problem, an heuristic approach is proposed, based on a greedy search which provides a good tradeoff. The proposed scheme is shown to outperform current AIC solutions both in terms of performance and computational cost, obtaining significant improvements in terms of notch depth, with almost 50 dB depth in typical settings, to protect a narrowband PU inside the secondary user OFDM band. Further, experimental measurements from the implementation of the proposed scheme on both professional and off-the-shelf hardware platforms validate its effectiveness.

Hybrid lightwave subcarrier CATV/16-QAM/16-QAM OFDM transmission system

A hybrid lightwave subcarrier CATV/16-QAM/16-QAM orthogonal frequency-division multiplexing (OFDM) transmission system employing light injection/optoelectronic feedback techniques and photonic crystal fiber (PCF) is proposed and demonstrated. Good performance of carrier-to-noise ratio (CNR), composite second order, and composite triple beat were obtained for the CATV band, and high CNR and low bit error rate values were achieved for the 16-QAM and 16-QAM OFDM bands over a combination of 80 km single-mode fiber (SMF) and 2.86 km PCF transport.

UWB MB-OFDM 4-Parallel Radix2 FFT Performance Analysis_ ENG

The Ultra Wide-Band Multi Band-Orthogonal Frequency Division Multiplexing (UWBMB-OFDM) systemis a low power (– 41.3 dBm/MHz); short-range (less than 10 m); high speed (53.3 - 480 Mbps) wireless technology with spectral band widthfrom 3.1GHz to 10.6 GHz allocated by Federal Communications Commission (FCC) according to IEEE 802.15.3a standard. The UWB spectrum is divided into 14 subbands, each with 528 MHz bandwidth . Each OFDM symbol is transmitted / received a cross each subband using a single 128-point radix2 IFFT/FFT. In this paper a simulation software is written using Matlab version 10 to evaluate the Bit Error Rate (BER) of the system using the traditional 128-point IFFT/FFT algorithm, and the proposed 4-parallel 32-point radix2 IFFT/FFT algorithm. It has been shown that a time saving is 28.7 % , and that the BER is better off 5dB using the proposed method as compared to traditional method.

1-Tb/s WDM-OFDM-PON System With Subband Access Scheme and Flexible Subcarrier-Level Bandwidth Allocation

A novel subband access scheme for multiband high-speed orthogonal frequency division multiplexing (OFDM) passive optical network (PON) is proposed, where the granularity of the bandwidth allocation is as small as the bandwidth of just one subcarrier and the ONUs only receives the desired subcarriers according to the bandwidth allocation strategy from the whole downstream OFDM signal without band limitation. Since the ONUs do not have to receive a complete OFDM band, low-bandwidth and low-speed devices can be used to reduce ONU cost. The algorithm used in the scheme is also explained in detail, and a 1-Tb/s experimental system is successfully established to prove the feasibility of the proposed scheme.

Multi Band OFDM System Model and Its Performance Evaluation for UWB Communication

In this work multiband orthogonal frequency division multiplexing (OFDM) System is modeled and its performance evaluation is analyzed for ultra wide band (UWB) communication environment. Theoretical derivation for the average pairwise error probability (PEP) and Outage Probability are derived based on Saleh and Valenzuela fading model. In line with this, the impact of joint coding the information across subcarriers in the system performance is investigated. The link budget analysis is also computed and results are obtained in regard to the transmission range for indoor environments. Moreover, average coded bit error rate achieved from convolutional codes over the system is computed and supported with computer simulations for all UWB channel conditions.

An in-building network based on community access television integration with quadrature phase-shift keying orthogonal frequency-division multiplexing

An in-building network based on cable television (CATV) integration with quadrature phase-shift keying (QPSK) orthogonal frequency-division multiplexing (OFDM) transport over a combination of single-mode fibers (SMF) and perfluorinated graded-index plastic optical fibers (GI-POF) is proposed and experimentally demonstrated. In this system, a 1558.5 nm optical signal is directly transmitted along two fiber spans (20 km SMF + 25 m GI-POF). An optimum guard band is carefully established to ensure that no very substantial signal interference is induced between the CATV and QPSK OFDM bands. Error free transmission with sufficiently low bit error rate values was achieved for 1.25 Gbps/771.5 MHz QPSK OFDM signals; also, acceptable carrier-to-noise ratio, composite second-order, and composite triple-beat performances were obtained for CATV signals. This proposed network is significant because it is economical and convenient to install.

Design and analysis of an orthogonal frequency division multiplexing millimeter wave signal generation and distribution with dual driver Mach-Zehnder modulator and semiconductor optical amplifier

A scheme of photonic orthogonal frequency division multiplexing (OFDM) signal generation and distribution employing copolarized pumps generated by a dual driver Mach-Zehnder modulator and four-wave mixing inside an optical semiconductor amplifier (SOA) is proposed and evaluated by theoretical analysis and simulations. In this proposal, 12 times optical frequency multiplication is utilized to up-convert the intermediate frequency band OFDM signal to the millimeter wave (mm-wave) band. The system performance under various key parameters of the SOA and the input optical signal is evaluated and discussed. The results present useful insight for the practicality of photonic mm-wave signal generation and distribution in the next-generation optical-wireless access network.

121.9-Gb/s PDM-OFDM Transmission With 2-b/s/Hz Spectral Efficiency Over 1000 km of SSMF

We discuss optical multi-band orthogonal frequency division multiplexing (OFDM) and show that by using multiple parallel OFDM bands, the required bandwidth of the digital-to-analogue/ analogue-to-digital converters and the required cyclic prefix can significantly be reduced. With the help of four OFDM bands and polarization division multiplexing (PDM) we report continuously detectable transmission of 10 times121.9-Gb/s (112.6-Gb/s without OFDM overhead) at 50-GHz channel spacing over 1,000-km standard single mode fiber (SSMF) without any inline dispersion compensation. In this experiment 8 QAM subcarrier modulation is used which confines the spectrum of the 121.9 Gb/s PDM-OFDM signal within a 22.8 GHz optical bandwidth. Moreover, we propose a digital signal processing method to reduce the matching requirements for the wideband transmitter IQ mixer structures required for PDM-OFDM.

Analysis of Clipping Noise and Tone-Reservation Algorithms for Peak Reduction in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) suffers from a high peak-to-average power ratio (PAR). Tone reservation is a popular PAR reduction technique that uses a set of reserved tones to design a peak-canceling signal. In a previous paper by Krongold and Jones, an active-set approach was developed to efficiently compute the peak-canceling signal. In this paper, we consider the use of clipping noise, which is generated when the OFDM signal is clipped at a predefined threshold, to design the peak-canceling signal. To this end, the clipping noise is analyzed as a series of parabolic pulses under tone-reservation constraints. The single-pulse case and the multiple-pulse case are treated. The analysis explains peak regrowth and the constancy of the clipping noise power spectrum over the whole OFDM band. Moreover, the clipping noise at the end of several clipping and filtering iterations is shown to be approximately proportional to that generated in the first iteration. The constant of proportionality is estimated via the level-crossing theory for high clipping thresholds. Using this analysis, a constant-scaling algorithm and an adaptive-scaling algorithm are proposed for tone reservation. These algorithms scale the filtered first-iteration clipping noise to compensate for peaks that are above the threshold. The simulation results show that the proposed algorithms achieve a larger peak reduction and lower complexity than the active-set algorithm.