Abstract— A modiﬁcation to the Asymmetrically-Clipped Optical Orthogonal **Frequency**-**Division** **Multiplexing** (ACO- OFDM) technique is proposed through unipolar encoding. A performance analysis of the Bit Error Rate (BER) is developed and Monte Carlo simulations are carried out to verify the analysis. Results are compared to that of the corresponding ACO-OFDM system under the same bit energy and transmission rate; an improvement of 1 dB is obtained at a BER of 10— 4 . In addition, the performance of the proposed system in the presence of atmospheric turbulence is investigated using single-input multiple-output (SIMO) conﬁguration and its performance under that environment is compared to that of ACO-OFDM. Energy improvements of 4 dB and 2.2 dB are obtained at a BER of 10— 4 for SIMO systems of 1 and 2 photodetectors at the receiver for the case of strong turbulence, respectively.

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Abstract: This paper is a survey on the orthogonal **frequency** **division** **multiplexing** in the field of wireless communications. Nowadays the need for high data speed transmission of digital communication has increased, with the rapid growth in recent years. OFDM endeavor high data rates access for wireless communications and use for high speed applications as one of the efficient solutions as compared to other Technology. In OFDM, Demodulation and modulations of signal is done with the help of FFT/IFFT controller respectively. We have address basic OFDM and not only modulations, as well as specific techniques to improve the performance of OFDM, which includes channel estimation and signal detection also **frequency** and time offset estimation and correction, inter-carrier interference, multiple- input–multiple-output techniques and peak to average power ratio reduction. Applications of OFDM in current systems and standards are described.

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The origins of OFDM development started in the late 1950’s with the introduction of **Frequency** **Division** **Multiplexing** (FDM) for data communications. In 1966 [3] Chang patented the structure of OFDM and published the concept of using orthogonal overlapping multi-tone signals for data communications. In 1971 Weinstein and Ebert [4] introduced the idea of using a Discrete Fourier Transform (DFT) for implementation of the generation and reception of OFDM signals, eliminating the requirement for banks of analog subcarrier oscillators. This presented an opportunity for an easy implementation of OFDM, especially with the use of Fast Fourier Transforms (FFT), which are an efficient implementation of the DFT. This suggested that the easiest implementation of OFDM is with the use of Digital Signal Processing (DSP), which can implement FFT algorithms [5]. It is only recently that the advances in integrated circuit technology have made the implementation of OFDM cost effective. The reliance on DSP prevented the wide spread use of OFDM during the early development of OFDM. It

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Orthogonal **frequency** **division** **multiplexing** (OFDM) is a method of modulation of digital signal in which a signal is divided into many narrowband channels of different frequencies. This technology was first used in the 1960s for the research to minimize interference between channels which are near to each other with respect to **frequency**. In some points, OFDM and **Frequency** **Division** **Multiplexing** (FDM) are similar to each other. They differ from each other in modulation and demodulation technique of the signal. But in both the cases minimization of the interference, or crosstalk between the channels and symbols forming data stream is given priority and perfection of individual channels is given less importance.OFDM technology is used in European digital audio broadcast services. This technology is also used in digital television and is now being considered as a technique of receiving high-speed digital data over the same conventional telephone lines.

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Orthogonal **Frequency** **Division** **Multiplexing** is a **Frequency** **Division** **Multiplexing** (FDM) scheme used as a digital multi-carrier modulation method. A large number of closely spaced orthogonal sub-carrier signals are used to carry data on several parallel data streams or channels. Each sub-carrier is modulated with a conventional modulation scheme (such as quadrature amplitude modulation or phase-shift keying) at a low symbol rate, maintaining total data rates similar to conventional single- carrier modulation schemes in the same bandwidth[2]. Orthogonal **Frequency** **Division** **Multiplexing** is a form of signal modulation that divides a high data rate modulating stream placing them onto many slowly modulated narrowband close-spaced subcarriers, and in this way, is less sensitive to **frequency** selective fading[4].

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Wireless communication has become essential for all aspects of our lives. Multi-carrier communications helps to facilitate increased utilization of wireless spectrum. There has been a great demand for bandwidth of multicarrier communication systems .Multi-carrier transmission or modulation (MCM) uses multiple carrier signals at different frequencies. The advantages of MCM include relative immunity to fading caused by transmission over more than one path at a time (multipath fading), less susceptibility to interference caused by impulse noise than single-carrier systems, and enhanced immunity to inter-symbol interference [1]. Orthogonal **Frequency** **Division** **Multiplexing** (OFDM) has been adopted mostly in present communication systems [2].Then the Spectrally Efficient **Frequency** **Division** **Multiplexing** (SEFDM) was proposed to overcome some disadvantages of OFDM [3]. But there are number of practical implementation challenges for SEFDM systems are there, such as the area minimization and power dissipation overheads.

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________________________________________________________________________________________________________ Abstract— Orthogonal **Frequency** **Division** **Multiplexing** (OFDM) is a multi-carrier modulation technique which divides the available spectrum into many carriers. OFDM uses the spectrum efficiently compared to FDMA by spacing the channels much closer together and making all carriers orthogonal to one another to prevent interference between the closely spaced carriers. The main advantage of OFDM is their robustness to channel fading in wireless environment, but here MB-OFDM transmitter baseband is designing in order to provide high speed for application than OFDM . The objective of this project is to design and implement a baseband of MB-OFDM transmitter on FPGA hardware which provides very high speed for application. This project concentrates on developing Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT). The work also includes in designing a mapping module, serial to parallel and parallel to serial converter module. The design uses FFT and IFFT for the processing module which indicate that the processing block contain inputs data. All modules are designed using VHDL programming language and implement using Apex 20KE board. The board is connected to computer through serial port.Input and output data is displayed to computer .Software and tools which used in this project includes VHDLmg Design Entry, Altera and Altera Quartus-II Software tools are used to assist the design process and downloading process into FPGA board while Apex board is used to execute the designed module.

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Orthogonal **Frequency** **Division** **Multiplexing** (OFDM) is a techniques that involves transmitting signal information using smaller subcarriers, instead of a single large carrier. OFDM is a form of multi-carrier modulation. The basic principle of multicarrier modulation is to divide the data stream, , into parallel data streams with a reduced data rate of ; low rate data streams are then modulated on a separate narrow band subcarriers and summed together for transmission, thereby providing the same data rate as an equivalent single large carrier system[3]. At the receiver a set of filter banks separate the wide-band signal into the original narrowband subcarriers for demodulation. In other words, OFDM involves dividing the available spectrum into several narrow sub-channels/sub carriers which experience differential flat fading as they propagate; this make equalization at the receiver end simple .

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Abstract: Orthogonal **frequency**-**division** **multiplexing** (OFDM) has been proposed as an enabling technique for elastic optical networks to support heterogeneous traf ﬁ c demands by enabling rate and modulation adaptive bandwidth allocation. The authors investigate the energy ef ﬁ ciency of optical OFDM-based networks. A mixed integer linear programming model is developed to minimise the total power consumption of rate and modulation adaptive optical OFDM networks. Considering a symmetric traf ﬁ c, the results show that optical OFDM-based networks can save up to 31% of the total network power consumption compared to conventional Internet protocol over wavelength **division** **multiplexing** (WDM) networks. Considering the power consumption of the optical layer, the optical OFDM-based network saves up to 55% of the optical layer power consumption. The results also show that under an asymmetric traf ﬁ c scenario, where more traf ﬁ c is destined to or originates from popular nodes, for example data centres, the power savings achieved by the optical OFDM-based networks are limited as the higher traf ﬁ c demands to and from data centres reduce the bandwidth wastage associated with conventional WDM networks. Furthermore, the achievable power savings through data compression have been investigated, considering an optical OFDM-based network.

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Abstract — The aim of this paper is studying the Orthogonal **Frequency** **Division** **Multiplexing** (OFDM) system. The (OFDM) is a multi-transporter regulation system which is especially famous in new remote systems of IEEE standard, advanced TV, sound telecom and 4G portable correspondences. The principle advantage of OFDM over single-bearer plans is its capacity to manage many channels conditions without complex evening out channels. It has enhanced the nature of long-separation correspondence. The primary disadvantages of OFDM are its high crest to normal power proportion and its affectability to stage clamor and recurrence balance. This review gives a diagram of OFDM, its applications in different frameworks, for example, IEEE 802.11a, Digital Audio Broadcasting (DAB) and Digital Broadcast Services to Handheld Devices (DVB-H) along with its advantages and disadvantages.

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Generalized **frequency** **division** **multiplexing** (GFDM) is one of the multicarrier modulation candidates proposed for the 5th generation of wireless networks. Among GFDM linear receivers, GFDM MMSE receiver achieves the best error performance for multipath fading channels at the cost of high numerical complexity. Hence, the combination of GFDM match filter (MF) receiver and double-side successive interference cancellation (DSIC) method is used instead. However, there is a significant gap between the error performance of GFDM MMSE and DSIC/MF receivers for the case of employing modern channel coding. Recently, we have proposed a new multicarrier scheme based on GFDM architecture called generalized orthogonal **frequency** **division** **multiplexing** (GOFDM). This study derives an optimized cyclic tree-structured perfect reconstruction-quadrature mirror filter (PR-QMF) bank for GOFDM transceiver and then introduces a novel method for implementation of the optimum filter bank in the **frequency** domain. Employing such a fast and optimum filter bank provides several advantages for GOFDM transceiver. GOFDM transmitter mitigates out-of-band spectrum leak to the level of that of GFDM. In addition, choosing an appropriate configuration of filter bank yields lower peak to average power ratio in transmit signal of GOFDM compared to that of OFDM. On the other hand, while GOFDM MMSE receiver has lower numerical complexity compared with GFDM DSIC/MF receiver, its coded bit error rate curve is close to that of GFDM MMSE receiver. The aforementioned advantages envision GOFDM as a competitive candidate to be employed in the physical layer of new wireless applications.

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Orthogonal **frequency** **division** **multiplexing** is the desirable technique to achieve higher speed in data rates and better spectrum efficiency. In OFDM [1] first higher data stream has been divided into lower streams of data and after modulation these data streams are together transmitted by orthogonal subcarriers. One of the major challenges in OFDM system is high Peak to average power Ratio (PAPR), which produced non linear distortion and degrades system performance. As a consequence of increased value of PAPR, HPA starts operating in non linear region, hence transmitted data be came distorted. One of the simple approaches is clipping technique [3], in which PAPR has been diminished by clipping the higher peaks of the signal. This technique sometimes encounters with in-band and out- band interference.

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Optical wireless communication is an emerging dynamic research and development area that has generated a vast number of interesting solutions to very complicated communication challenges. The transmission power employed in optical wireless communication configurations (mainly indoors) is limited by numerous factors, including eye safety, physical device limitations and power consumption, in outdoor and free space optical systems. To overcome the attenuation due to fog, one could employ lasers with higher powers, but this is also limited by the eye safety standards. Both Quadrature amplitude modulation on discrete multitones and multilevel pulse amplitude modulation are spectrally efficient modulation schemes suitable for light emitting diode based communications, but are less power efficient. Orthogonal **frequency** **division** **multiplexing** (OFDM) transmission scheme is a type of multichannel systems. It does not use individual band limited filters and the oscillators for each sub-channel and furthermore, the spectra of subcarriers are overlapped for bandwidth efficiency. In this paper, a modulation scheme named interval shift key modulation is implemented to modulate the subcarriers in optical wireless system introduced to enhance the output signal parameters Mat Lab is used to measure the data rate, the spectral efficiency, the power efficiency and bit error rate. The Simulation results obtained indicate the efficiency of the proposed system for OFDM **multiplexing**.

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Abstract— Orthogonal **Frequency** **Division** **Multiplexing** (OFDM) is gaining popularity for high data rate communication systems. We propose the use of adaptive beamforming for interference rejection in OFDM systems, due to its advantages over equalization. An adaptive beamformer uses the concept of spatial filtering to direct the antenna beam towards the desired signal/transmitter and place a null towards the interfering signal. The Fast Fourier Transform (FFT) at the receiver end of an OFDM system enables the use of **frequency** domain beamforming to reduce narrow band interference individually across all the subcarriers. We implemented both decision directed and blind algorithms. Use of these algorithms reduced the Bit Error Rate (BER) to a great extent. The performance analysis for Least Mean Square (LMS) algorithm, Recursive Least Squares (RLS) and Constant Modulus Algorithm (CMA) for hundred OFDM symbols and five hundred and twelve subcarriers, four hundred and is provided.

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Multi- user orthogonal **frequency** **division** **multiplexing** (OFDM) has attracted much attention as an effective transceiver technique for high-speed multi- user wireless systems that can provide high spectral efficiency by incorporating various advanced technologies. When proportional fair (PF) and maximum SINR (MS) scheduling schemes are employed, the data rate can be maximized by optimizing SINR thresholds for modulation level selection in consideration of the SINR estimation error, which is caused by channel feedback delay for downlink systems. When the SIN R estimation error occurs because of the feedback delay and noise in the pilot signal, the achievable rate is analytically derived for PF scheduled OFDM systems with the assumption of the same average SINR for each user. However, it is required in practice to consider the situations where each user experiences different channel environments that include path loss, maximum Doppler spread, and delay spread, leading to non- homogeneous error statistics on SIN R estimation. An adaptive radio resource allocation (ARRA) algorithm for downlinks OFDMA/SDMA systems integrate with multimedia traffic. This radio resource allocation work is mathematically formulated into an optimization problem with an objective to maximize the system thro ughput under four designed constraints. For spectrum efficiency and QoS satisfaction, the radio resource allocated to a user has an upper bound and a lower bound, which are the result of the buffer occupation constraint and the QoS fulfillment constraint, respectively. In addition, there are weaknesses on the system such as the total power and the number of users multiplexed on the same sub-channel, and these limitations are represented by the total system power constraint and the sub-channel allocation constraint.

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Orthogonal **Frequency** **Division** **Multiplexing** (OFDM) is widely used in the tel- ecommunication industry. First introduced in 1960s, OFDM has wide applica- tion in data transmission, including radio and HDTV signal [1] [2] as well as the standard for WLAN system, which includes the widely used Wi-Fi [3]. The high bandwidth of OFDM signal gives its resistance to narrowband interference, high data rate [4] thus high spectral efficiency [5]. However, OFDM signal quality can How to cite this paper: Lin, Y.B. (2018)

Abstract The novel technique of using the indices of the active subcarriers of orthogonal **frequency** **division** **multiplexing** (OFDM) to transmit data, called index modulation-aided OFDM or OFDM-IM is a recently proposed multicarrier transmission technique for achieving high spectral and energy efficiency in the forthcoming fifth generation (5G) networks. In this paper, the principle of operation of OFDM-IM, its dual mode counterpart DM-OFDM and the OFDM with multiple constellation (OFDM-MC) schemes were firstly investigated. We review a number of the recent promising advances in these technologies. Their implementations in various applications such as visible light communication (VLC) and Asynchronous mMTC Networks etc are then introduced. Finally, their various performances are compared with each other to authenticate their ability for enhancing the energy efficiency of various physical (PHY) layer technologies. We see that, at the BER of 10 -5 , the SNR of precoded OFDM-MC is 33 dB while that of precoded DM-OFDM is 37 dB and that of precoded OFDM-IM is 38 dB, a clear 4 dB to 5 dB advantage. This advantage is due to precoded OFDM-MC diversity order of 4 compared to the two other schemes with diversity order of 2.

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