OFDM Modulation Research Articles

차량 통신 기술을 위한 OFDM 모듈레이션의 64-비트 스크램블러 설계

WAVE 시스템은 IEEE 802.11p표준으로 지능형 교통시스템 서비스에 응용되는 새로운 개념 및 차량 통신 기술이다. 또한 WAVE 시스템은 도로상의 트래픽의 효율과 안전을 높인다. 그러나 WAVE 시스템의 OFDM 모듈레이션에서 스크램블러 비트 연산 알고리즘은 하드웨어나 소프트웨어 측면에서 병렬 처리가 불가능하므로 효율성이 떨어지게 된다. 본 논문에서는 스크램블러의 비트 연산으로 64비트 행렬 테이블을 구성하는 알고리즘과 64비트 행렬 테이블과 입력 데이터를 병렬 연산하는 알고리즘을 제안하였다. 제안한 알고리즘은 64비트 행렬 테이블을 적용하여 실행한 결과 비트연산 스크램블러보다 1회와 10000회 처리 속도는 약 40.08%-40.27%가 향상되고, 초당 처리 횟수는 468.35회 더 수행할 수 있고, 32비트 스크램블러보다 1회와 10000회 처리 속도는 약 7.53%-7.84%가 향상되고, 초당 처리 횟수는 91.44회 더 수행할 수 있다. 따라서 64비트로 연산하는 스크램블러 알고리즘은 64비트를 처리할 수 있는 CPU를 사용한다면 32비트 스크램블러보다 40% 이상 성능을 향상시킬 수 있다. WAVE(Wireless Access for Vehicular Environment) is new concepts and Vehicles communications technology using for ITS(Intelligent Transportation Systems) service by IEEE standard 802.11p. Also it increases the efficiency and safety of the traffic on the road. However, the efficiency of Scrambler bit computational algorithms of OFDM modulation in WAVE systems will fall as it is not able to process in parallel in terms of hardware and software. This paper proposes an algorithm to configure 64-bits matrix table in scambler bit computation as well as an algorithm to compute 64-bits matrix table and input data in parallel. The proposed algorithm on this thesis is executed using 64-bits matrix table. In the result, the processing speed for 1 and 1000 times is improved about 40.08% ~ 40.27% and processing rate per sec is performed more than 468.35 compared to bit operation scramble. And processing speed for 1 and 1000 times is improved about 7.53% ~ 7.84% and processing rate per sec is performed more than 91.44 compared to 32-bits operation scramble. Therefore, if the 64 bit-CPU is used for 64-bits executable scramble algorithm, it is improved more than 40% compare to 32-bits scrambler.

Complexity-reduced digital predistortion for subcarrier multiplexed radio over fiber systems transmitting sparse multi-band RF signals

A novel multi-band digital predistortion (DPD) technique is proposed to linearize the subcarrier multiplexed radio-over-fiber (SCM-RoF) system transmitting sparse multi-band RF signal with large blank spectra between the constituent RF bands. DPD performs on the baseband signal of each individual RF band before up-conversion and RF combination. By disregarding the blank spectra, the processing bandwidth of the proposed DPD technique is greatly reduced, which is only determined by the baseband signal bandwidth of each individual RF band, rather than the entire bandwidth of the combined multi-band RF signal. Experimental demonstration is performed in a directly modulated SCM-RoF system transmitting two 64QAM modulated OFDM signals on 2.4GHz band and 3.6GHz band. Results show that the adjacent channel power (ACP) is suppressed by 15dB leading to significant improvement of the EVM performances of the signals on both of the two bands.

Simulation of the ofdm technique for the transmission of digital radio

The present project is motivated by the necessity of analyzing the technique of OFDM modulation and its performance, focused to the Transmission of Digital Radio. Traditionally all the radio programs are transmitted by FM, and AM modulations, and the radio should be tuned to each one of these frequencies; this used a wide range of the spectrum for a relatively short range of stations, limiting the experience of listening. In this project, a modulation system for Digital Radio Transmission is pretended, in order to combine multiple streams of audio in a relatively narrow frequency band, centered in a defi nite transmission frequency.

Hybrid WDM‐OFDMA‐PON utilising tunable generation of flat optical comb

Proposed is a wavelength-division multiplexed orthogonal frequency-division multiple access passive optical network (WDM-OFDMA-PON) for both wired and wireless OFDM signal access, by using a tunable generation scheme of a flat optical comb. 17 comb lines with 30 GHz space and no more than 0.5 dB flatness are obtained theoretically and experimentally. The obtained flat optical comb is used as the optical source for 17 WDM channels in the proposed WDM-OFDMA-PON. A 16-quadrature amplitude modulation OFDM signal achieving 10.85 Gbit/s traffic data is modulated onto each channel with double sideband modulation and the transmission for both wired and wireless access has been successfully demonstrated by experiment.

Throughput and Error State Performance of AMC Scheme in 3G Wireless Systems

In this paper, Adaptive Modulation and Coding technique for OFDM is proposed. In this technique it is possible to switch the modulation order and coding rate in order to better match the channel conditions. The use of adaptive modulation allows higher throughputs and covering long distances. The aim of this paper is to increase the transmission data rate which the high order modulation scheme with low coding redundancy is used. Numerical results are presented showing that the better performance both in terms of error probability and data throughput. Index terms: OFDMA, adaptive modulation and coding, IEEE 802.16, broadband wireless access, WiMAX.

An Efficient Performance of Mimo - Ofdm Based Cognitieve Radio System for Arrays Signal Processing

The wireless channel is central within this context, thus estimating the channel is the key to make CR operational, taking in consideration that the transmission-reception technology is available. In this thesis, we design a MIMO system using OFDM modulation technology to transmit and receive two signals over the mobile wireless channel. First formulate the pilot design as a new optimization problem. We use MIMO concept to enhance system capacity and robustness of the wireless transmission. In Multi-Input Multi-Output (MIMO) based cognitive radio (CR) systems, with the increasing demand for data rate and reliability in Wireless communicationsand devices, several issues become very important like bandwidth efficiency, quality of service and radio coverage. In this new scheme, adaptive arrays are group-selected in the spatial domain. Simulation shows that the proposed system can get significant performance improvements over the conventional array based OFDM systems over frequency-selective multipath fading channels with cognitive radio (CR) system. Keywords: Cognitive radios, MIMO, OFDM, and Joint transmit and receive group selected arrays.

Digital multicarrier modulation techniques for high data rates multimedia applications in present and future wireless communication systems

To accommodate high performance and high bit rates for multimedia applications in present and future wireless communication systems, it is essential that modulation techniques applied in this scenario are able to support high data rates upto and above 200 Mbps. To meet the increased demand of higher bit rates, the wireless systems are incorporating the multi-carrier modulation techniques ,such as FFT based MCM which is also known as conventional OFDM and wavelet transform based MCM. Wireless multicarrier modulation is a technique of transmitting data by dividing the input data stream into parallel sub-streams that are each modulated and multiplexed onto the channel at different carrier frequencies. In this paper, we studied the performance of DWT based MC-CDMA and FFT based MC- CDMA modulations for transmission over wireless fading channels. This scheme is shown to be overall quite similar to FFT based OFDM modulation, but with some interesting additional features and improved characteristics. Results shows that DWT based MC- CDMA modulation has better bit error rate (BER) performance than conventional FFT based CDMA without cyclic prefix (CP) for all signal-to-noise ratios and also outperforms FFT based CDMA for low signal-to-noise ratio values.

Optimization and Implementation for the Modified DFT Filter Bank Multicarrier Modulation System

The modified Discrete Fourier Transform (MDFT) filter bank is a Nearly Perfect Reconstruction (NPR) system based on pseudo-QMF filter bank. In this paper, we introduce an optimized algorithm to implement the MDFT filter bank based multicarrier modulation system. The system based on this optimization algorithm has the low error rate and system delay. To verify the designed system we have compared the MDFT multicarrier modulation system with the OFDM modulation system. The results show that at high speed communication the data error rate in the MDFT filter bank multicarrier modulation system is clear improved in comparison with OFDM systems.  Index Terms—MDFT filter bank, NPR, Error rate, Optimization algorithm

Reduced VHO latency using EVM measurement and ad hoc cooperation for heterogeneous ubiquitous networks

Future heterogeneous network HetNet will allow mobile ad hoc network MANET to interoperate with WiMAX/LTE/WCDMA/CRN, etc. and will prefer OFDM modulation scheme for better spectrum efficiency. The RF parts of these standards have to face major challenges viz. channel estimation under very strict low power transmission viz. MANET. To exploit the ubiquitous diversity of HetNet, mobile node MN of MANET will prefer to perform vertical handover VHO across the HetNet for better guaranteed QoS and optimal resource utilisation. Considering these design challenges, paper proposes an optimal VHO model to associate a neighbouring ad hoc node CoN to cooperate and perform some parts of the VHO procedure requiring large latencies, such as authentication L1/L2 and IP registration procedures L3 which are based on measurement of error vector magnitude EVM. Performance of proposed VHO architecture is compared with conventional VHO schemes in terms of VHO latency, average service disruption time and reject rate. Proposed algorithm significantly reduces overall VHO latency.

Adaptive Modulation Using Neuro-Fuzzy (N-F) Controller for OFDM System

As demand for high quality transmission increases, improving spectrum efficiency and error performance in wireless communication systems are important. OFDM is a multi-carrier modulation technique with densely spaced sub-carriers that has gained a lot of popularity among the broadband community in the last few years. One of the promising approaches to next generation communication systems are adaptive OFDM (AOFDM). Fixed modulation systems uses only one type of modulation scheme (or order), so that either performance or capacity should be compromised but in adaptive modulated systems change modulation scheme (or order) depending on instantaneous Signal to Noise Ratio (SNR) to attain superior performance and capacity compared to fixed modulated systems. Neuro-fuzzy controller combines advantages of fuzzy logic and neural networks. Neuro-fuzzy controller provides automatic adaption procedure to fuzzy logic controller. Neural networks requires sufficient prior knowledge to be initialized but neuro-fuzzy systems doesn't requires any prior knowledge to be initialized and is efficient compared to fuzzy logic and neural networks. In this paper we propose an adaptive modulated OFDM system using neuro-fuzzy controller. The proposed system is simulated in MATLAB and compared with existing systems, simulation results shown significant improvement in systems performance.  Index Terms—Adaptive modulation, OFDM, Neuro-Fuzzy controller

Spectrally efficient localized carrier distribution scheme for multiple-user DFT-S OFDM RoF- PON wireless access systems

We propose a modified localized carrier distribution scheme based on multi-tone generation to generate 60 GHz mm-wave for different wireless users and it improves the carrier utilization efficiency by 33.3%. The principle of multiple-user discrete Fourier transform spread optical orthogonal frequency-division multiplexing (DFT-S OFDM) Radio-over-fiber (RoF) system is presented. This multiple-user system is applicable to passive optical network (PON). Then we demonstrate a 8 x 4.65 Gb/s multiple-user DFT-S OFDM RoF-PON wireless access system over 40 km fiber link and 60 GHz wireless link using two localized carrier distribution scheme with different spectral efficiency. Compared to conventional OFDM, 2.3 dB reduction of receiver power using DFT-S OFDM modulation scheme and the calculated BER performance for 8 wireless users clearly demonstrates the feasibility of this spectrally efficient multiple-user RoF-PON scheme.

PAPR Analysis of FFT and Wavelet based OFDM Systems for Wireless Communications

is an efficient modulation technique for wideband digital communication and adopted in many wireless standards. A major drawback of OFDM modulation is the high Peak-to-Average Power Ratio (PAPR) of the transmitted signal which limits its applications in communication systems. Traditionally, OFDM is implemented using FFT. On the other hand, OFDM can be implemented using orthogonal wavelets. We can have all the benefits of OFDM if we replace traditional sinusoid carriers of the Fourier based OFDM with suitable wavelets, in addition to that, PAPR can be greatly reduced in wavelet based OFDM systems. This article examines the PAPR performances of wavelet based OFDM system and classical FFT based OFDM system. Extensive computer simulations show that the Complementary Cumulative Distribution Function (CCDF) of PAPR for the wavelet based OFDM signal achieves about 7dB improvement in PAPR over the traditional OFDM signals at 10 -3 of CCDF.

The robustness of subcarrier-index modulation in 16-QAM CO-OFDM system with 1024-point FFT

We present in numerical simulations the robustness of subcarrier index modulation (SIM) OFDM to combat laser phase noise. The ability of using DFB lasers with SIM-OFDM in 16-QAM CO-OFDM system with 1024-point FFT has been verified. Although SIM-OFDM has lower spectral efficiency compared to the conventional CO-OFDM system, it is a good candidate for 16-QAM CO-OFDM system with 1024-point FFT which uses a DFB laser of 1 MHz linewidth. In addition, we show the tolerance of SIM-OFDM for mitigation of fiber nonlinearities in long-haul CO-OFDM system. The simulation results show a significant penalty reduction, essentially that due to SPM.

Space-Division Multiplexed High-Speed Superchannel Transmission Over Few-Mode Fiber

Space-division multiplexed (SDM) transmission based on multi-core (MCF) or multi-mode fiber (MMF) emerges as one of the most promising solutions for overcoming the capacity limit of standard single mode fiber (SSMF). This paper places a focus on the MMF transmission for which a data rate of 100-Gb/s and beyond has been recently demonstrated through coherent-optical OFDM (CO-OFDM) and single-carrier (SC) superchannel transmission based on specially-designed few-mode fibers (FMF). However, to unleash the full potential of the high data rate SDM transmission requires brand-new research from device to system level. In this paper, we elucidate the overall system architecture, critical components and sub-system modules for SDM transmission and report the up-to-date demonstration of SDM superchannel transmission. We envisage that the combination of SDM and OFDM modulation could be a potential key route to the future Tb/s and beyond optical transports.

Direct modulation of a tuneable slotted Fabry-Pérot laser with adaptive modulation OFDM

Next generation optical access networks will require low cost lasers in conjunction with network flexibility and higher data rates. This work presents the direct modulation of a low cost tuneable slotted Fabry-Pérot laser (tuneable over 14 nm) with AM-OFDM. Characteristics of this dual section laser are presented and transmission of 10 Gb/s over 50 km is achieved with this device.

Energy-efficient optical line terminal for WDM-OFDM-PON based on two-dimensional subcarrier and layer allocation

We propose and experimentally demonstrate a scheme to reduce the energy consumption of optical line terminal (OLT) in wavelength division multiplexing - orthogonal frequency division multiplexing - passive optical networks (WDM-OFDM-PONs). In our scheme, a wireless communication technique, termed layered modulation, is introduced to maximize the transmission capacity of OFDM modulation module in the OLT by multiplexing data from different ONU groups with signal-to-noise ratio (SNR) margins onto the same subcarriers. With adaptive and dynamic subcarrier and layer allocation, several ONU groups with low traffic demands can share one OFDM modulation module to deliver their data during non-peak hours of a day, thus greatly reducing the number of running devices and minimizing the energy consumption of the OLT. Numerical calculation shows that an energy efficiency improvement of 28.3% in the OLT can be achieved by using proposed scheme compared to the conventional WDM-OFDM-PON.

Performance Evaluation of DWT-OFDM and FFT-OFDM for Multicarrier Communications Systems using Time Domain Zero Forcing Equalization

Other than the conventional fast Fourier transform (FFT) for multicarrier modulation, a new approach for multicarrier modulation (MCM) has been known. Meanwhile, multicarrier modulation involves dividing the broadband channel into many orthogonal but overlapping narrowband carriers. In an OFDM modulation based multicarrier system using the FFT, a cyclic prefix (CP) is inserted after each symbol frame to combat the effects of inter symbol interference (ISI). By inserting the CP, which results in spectral inefficiency OFDM schemes trades up to 25% of the transmit bandwidth. A new MCM approach that is void of the expense is the wavelet transform-based systems. These systems also have very suppressed side-lobes and exhibit improved BER performance. In wavelet based systems, the latest challenge in its implementation is in the channel estimation. In this work we have studied the performance of the FFT based OFDM system against wavelet transform (WT) based multicarrier system using a simple zero forcing (ZF) equalization in time domain. The studied system shows some improved BER performance.

FPGA Synthesis of VHDL OFDM System

This paper presents a novel Field Programmable Gate Array (FPGA) technique to gain approach in the problem of OFDM system implementation. The actual and next communication schemes tend to use OFDM systems in order to provide high baud rates, less intercarrier interference (IC), and less intersymbol interference (ISI). Some examples are IEEE-802.11, IEEE-802.15, IEEE-802.16, 3GPP, MC-CDMA, digital video broadcasting (DVB), wireless USB, and/or wireless firewire among others. Trying to provide a solution to the new devices emerging, slow standard adoption, poor spectrum use, etc. This work presents an FPGA design; validation, and implementation of an OFDM modulator for IEEE-802.16e using a high level design tool, also reports the resources requirements for the presented system. The proposed design is synthesized using high level design tools. The design flow is optimized for fast prototyping which is implemented on the latest generation of FPGA chips. Such an FPGA implementation has the added advantage to modify for changes and improved system performance, e.g. reducing propagation delay.

APSK Modulated CO-OFDM System With Increased Tolerance Toward Fiber Nonlinearity

An amplitude and phase-shift keying (APSK) modulated coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) system is proposed, with increased tolerance toward fiber nonlinearity. Numerical simulation results, based on 30.2-Gb/s single-channel and 5×30.2-Gb/s wavelength-division-multiplexing (WDM) single-polarization CO-OFDM systems, show that compared with conventional 16 quadrature amplitude modulation (QAM) modulated optical OFDM signal, the 16 APSK modulated optical OFDM signal has a higher tolerance toward fiber nonlinearity, such as self-phase modulation and cross-phase modulation. The optimal launch power and the corresponding Q2 factor are, respectively, 2 and 0.5 dB higher than 16 QAM modulated optical OFDM signal after 640-km transmission, both in single-channel and WDM CO-OFDM systems.

Joint Compensation of Transmitter and Receiver IQ Imbalance for MIMO-OFDM Over Doubly Selective Channels

Multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM), as a viable technique, is being widely considered for high data rate and bandwidth efficient wireless communications. However, analog impairments like in-phase/quadrature (IQ) imbalance decrease the performance of this technique. Furthermore, time variations of a doubly selective channel cause intercarrier interference (ICI) which again degrades the performance. In this paper, the digital compensation of both the transmitter and the receiver IQ imbalances in MIMO-OFDM transmission over doubly selective channels is studied. In particular, basis expansion model is employed to develop a novel IQ formulation for a time-varying channel. Using this formulation, two receiver schemes are suggested to jointly mitigate the IQ imbalance and channel time variation effects. In deriving one of these schemes, the general case of an insufficient cyclic prefix (CP) for OFDM modulation is also considered. An insufficient CP results in interblock interference (IBI). The proposed approach for insufficient CP case, unifies several existing methods for IQ imbalance compensation and IBI/ICI cancellation. Simulation results show that this approach considerably improves the achievable bit-error-rate performance.