• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Proposed Different Signal Processing Tools for Efficient Optical Wireless Communications

    2022-08-24 03:29:24HendIbrahimAbeerAlgarniMahmoudAbdallaWalidElShafaiFathiAbdElSamieandNaglaaSoliman
    Computers Materials&Continua 2022年5期

    Hend Ibrahim,Abeer D.Algarni,Mahmoud Abdalla,Walid El-Shafai,F(xiàn)athi E.Abd El-Samie and Naglaa F.Soliman,2

    1Department of Electronics and Communications Engineering,F(xiàn)aculty of Engineering,Zagazig University,Zagazig,44519,Egypt

    2Department of Information Technology,College of Computer and Information Sciences,Princess Nourah Bint Abdulrahman University,Riyadh,Saudi Arabia

    3Department of Electronics and Electrical Communications Engineering,F(xiàn)aculty of Electronic Engineering,Menoufia University,Menoufia,32952,Egypt

    4 Security Engineering Lab,Computer Science Department,Prince Sultan University,Riyadh 11586,Saudi Arabia

    Abstract: Optical Wireless Communication (OWC) is a new trend in communication systems to achieve large bandwidth, high bit rate, high security,fast deployment, and low cost.The basic idea of the OWC is to transmit data on unguided media with light.This system requires multi-carrier modulation such as Orthogonal Frequency Division Multiplexing(OFDM).This paper studies optical OFDM performance based on Intensity Modulation with Direct Detection(IM/DD)system.This system requires a non-negativity constraint.The paper presents a framework for wireless optical OFDM system that comprises (IM/DD) with different forms, Direct Current biased Optical OFDM (DCO-OFDM), Asymmetrically Clipped Optical OFDM(ACO-OFDM),Asymmetrically DC-biased Optical OFDM(ADO-OFDM),and Flip-OFDM.It also considers channel coding as a tool for error control, channel equalization for reducing deterioration due to channel effects,and investigation of the turbulence effects.The evaluation results of the proposed framework reveal enhancement of performance.The performance of the IM/DD-OFDM system is investigated over different channel models such as AWGN, log-normal turbulence channel model, and ceiling bounce channel model.The simulation results show that the BER performance of the IM/DD-OFDM communication system is enhanced while the fading strength is decreased.The results reveal also that Hamming codes, BCH codes, and convolutional codes achieve better BER performance.Also, two algorithms of channel estimation and equalization are considered and compared.These algorithms include the Least Squares (LS) and the Minimum Mean Square Error(MMSE).The simulation results show that the MMSE algorithm gives better BER performance than the LS algorithm.

    Keywords: Optical communication systems; OWC; IM/DD; OFDM;MMSE; LS; ADO-OFDM; DCO-OFDM; ACO-OFDM

    1 Introduction

    Optical Wireless Communication (OWC) requires lightwave carriers such as Infra-Red (IR),visible, and Ultra-Violet (UV) light for transmitting data through unguided propagation media.Many ancient cultures use smoke, beacon fires, ship flags, and semaphore telegraph for signaling as examples of historical OWC [1].Also, sunlight was used in the past as a form of OWC.For example, ancient Greeks and Romans use the reflected sunlight on their polished shields to send information signals during their battles.In the late 19th and early 20th centuries, a heliograph was invented and developed for military communication purposes.A heliograph consists of a pair of mirrors, which reflect the incident light beam to a long distance [2].In 1880, Alexander Graham Bell invented another historical form of the OWC system:the photophone.He used the light source to modulate the received voice signals and transmit these voice signals to a distance of 200 m long [3].In 1979, Gfeller and Bapst were able to achieve a fast advancement in OWC technology.They proved the ability of OWC for high-capacity in indoor networks providing an electromagnetic spectrum with hundreds of THz bandwidths in the optical domain [4].

    The objective of any modern communication system is to provide high data rates and a wide range of services such as videophones, voice communications, and high-speed Internet access.Orthogonal Frequency Division Multiplexing (OFDM) is an attractive Multi-Carrier Modulation(MCM) technique that efficiently utilizes the available bandwidth.The OFDM systems can transmit high-speed data transmission across a noisy channel and combat multipath propagation effects.So, it is used in many applications such as Digital Audio Broadcasting (DAB) and Terrestrial Digital Video Broadcasting (DVB-T).It is also used in some of the most prominent wireless technologies, such as the IEEE 802.11 Wireless Local Area Networks (WLANs) and Long Term Evolution (LTE) technology [5–8].

    Recently, OFDM has been applied to optical communication for supporting high data rates.However, the conventional OFDM technique cannot be directly used in optical systems.In OWC systems, the IM/DD technique is a simple, common, and low-cost optical carrier modulation and demodulation technique.In general, it is known that the output of the conventional OFDM modulator is complex and bipolar.In optical systems, only the intensity of the signal is constrained to be real and positive.Therefore, as commonly used in RF communication systems, the conventional OFDM must be modified to be used in OWC systems.Many existing OFDM modulation techniques are suitable for IM/DD OWC systems, such as ACO-OFDM, DCO-OFDM, ADO-OFDM,and Flip-OFDM.These four OFDM-based schemes are discussed in this work.

    The rest of the work is organized as follows.Section 2 describes the intensity modulation direct detection (IM/DD) optical wireless communication system architecture.The general IM/DD system is described in Section 3.The channel coding method to improve the BER performance of any communication system is introduced in Section 4.Section 5 illustrates the proposed system models.Simulation results and discussions are given in Section 6.Finally, conclusions are given in Section 7.

    2 IM/DD-OWC System Architecture

    Fig.1 shows the IM/DD-OWC system [9,10].For OWC systems, an LED or an LD can be used as the optical transmitter for the intensity modulation process to convert the signal from the electrical domain to the optical domain (E/O).At the receiver, a photodiode can be used as the optical receiver for the direct detection process that can convert the signal from the optical domain to the electrical domain (O/E).The shot noise of the detector is added to the signal in the electrical domain, and it is represented by an Additive White Gaussian Noise (AWGN).

    Figure 1:The IM/DD-OWC system

    2.1 DCO-OFDM System

    In the DCO-OFDM system, data symbols are carried on all sub-carriers [11,12].In the DCOOFDM transmitter, the serial input data is converted from Serial-to-Parallel (S/P), and then the data is mapped onto complex numbers using QAM or QPSK modulation.Then, the Hermitian symmetry property is applied to the symbols before the IFFT to get a real signal from the IFFT output [13].This symmetry can be achieved by putting:

    To prevent any residual DC component or any DC shift in the signal,X0,XN/2are set to zero and do not carry any information [14], i.e.,

    whereNis the IFFT size,Xis the complex symbol, andX*is the complex conjugate of theXsymbol.

    In the case of using a large number of sub-carriersN, the OFDM amplitude signal can be approximated by a Gaussian distribution with zero mean and a variance Δ2Ddefined as,

    The DC bias level is chosen to be proportional to the root mean square (RMS) of the signal to minimize the amount of required optical power and avoid increasing DC bias [15], i.e.,

    whereBDCis the DC bias level,μis the proportionality constant, and ΔDis the root mean square of the electric power signal.After adding the DC biasBDC, the signal becomes

    Any remaining negative peaks ofxDC(t) signal are clipped at zero resulting in a clipping noisenc(BDC).The resulting unipolar DCO-OFDM signalxDCO(t) is expressed as

    2.2 ACO-OFDM System

    The ACO-OFDM technique has been explained in detail in many papers [16,17].In ACOOFDM, the data symbols are carried on the odd sub-carriers only, while the even sub-carriers form a bias signal, which guarantees that the transmitted OFDM signal achieves the nonnegativity requirements.The bipolar OFDM signal is clipped at zero levels, where all negative parts of the bipolar signal are removed.Due to the clipping process, all of the noise components fall on the even sub-carriers, and the transmitted data is transmitted on the odd sub-carriers without impairments.

    In the ACO-OFDM system, the front-end of the ACO-OFDM transmitter is like the DCOOFDM transmitter, where the output of the IFFT is first converted from P/S, and the CP is appended to it [17].Then, the resulting signal is D/A converted and low-pass filtered.The signal should be clipped at zero to ensure that the transmitted signal is positive.The LED can be used as an electrical to optical converter.The resulting optical signal is transmitted through an optical channel.Shot noise that affects the signal is modeled as AWGN and added in the electrical domain.

    The processing in the ACO-OFDM receiver is similar to that of the DCO-OFDM receiver,except that in the ACO-OFDM receiver, only odd sub-carriers that carry data are demodulated,but in DCO-OFDM, all sub-carriers are demodulated.

    2.3 ADO-OFDM System

    The ADO-OFDM considers an advanced technique that maintains the advantages and avoids the drawbacks of the two previous optical unipolar OFDM techniques.The ADO-OFDM is a hybrid structure of ACO-OFDM and DCO-OFDM, where a DC bias is added to a part of the signal and the other part of the signal is clipped at zero.Thus, ACO-OFDM symbols modulate odd sub-carriers, while DCO-OFDM symbols modulate even sub-carriers.After that, the negative values produced by ACO-OFDM and DCO-OFDM are separately clipped to zero.Then, the resultant two non-negative signals from ACO-OFDM and DCO-OFDM are added together and transmitted by a LED [18].

    2.4 Flip-OFDM System

    The concept of Flip-OFDM is inverting the polarity of the negative part of the signal.The output of the IFFT operation is a real bipolar signal that can be decomposed into [19,20]:

    wherex+(k) andx-(k) are positive and negative parts of a bipolar signal, respectively.They are given as [19]:

    wherek=0, 1, 2,...,N-1.These two components of the signal are separately transmitted over two successive OFDM symbols.The positive part of the signalx+(k) is transmitted in the first sub-frame (positive sub-frame), while the Flipped part –x-(k) is transmitted in the second subframe (negative sub-frame).After that, a cyclic prefix with lengthNCPis added to each OFDM sub-frame.The negative OFDM sub-frame is delayed by (N+NCP) and transmitted after the positive OFDM sub-frame.Finally, the frames are multiplexed with all positive real values [21].

    3 General IM/DD System

    In the IM/DD system model, the LED emits the transmitted optical powerX(t) into channel at the end of the transmitter.The channel will make changes in the transmitted signal, and then this optical signal is received.At the receiver, the photodetector generates the photocurrentY(t).The mathematical expression that describes the IM/DD system model is defined by [22]:

    whereY(t) is the photocurrent generated by the photodetector, K is the responsivity of the photodetector,h(t) is the channel impulse response, ?is the convolution symbol,X(t) is the transmitted optical power, andN(t) is the signal independent shot noise due to the ambient light and self-noise due to the information-bearing optical signal.

    3.1 Ceiling Bounce Channel Model

    The ceiling bounce model is the most used model for simulating the impulse response of the indoor OWC channel.It was proposed by Trenkwalder et al.[22].Two parameters can characterize the ceiling bounce model:the Root Mean Square Delay Spread (DRMS) and the optical path loss as given in Eqs.(10) and (11) [23].

    whereu(t) is the unit step function,

    andais a parameter that depends on the relative location of the transmitter and the receiver.It can be represented by Eq.(13), when the transmitter and the receiver are collocated.

    wherehcis the ceiling height,cis the speed of light.

    3.2 Log-Normal Turbulence Channel Model

    A weak atmospheric turbulence regime is characterized by a single scattering event and can be represented by a single scattering process (Rytov approach).The unitless Rytov variance parameterσ2las Eq.(14) accounts for the strength of turbulence for plane waves [23].C2nis the refractive index parameter which is constant for horizontal paths,Lis the propagation distance,k=2π/λis the wavenumber, andλis the wavelength.For weak fluctuationsC2n <10-14,σ2l <1.In the midst of weak atmospheric fading, it is deduced that the log-normal distribution model is the most appropriate statistical model that can represent the statistics of irradiance fluctuations.The Probability Density Function (PDF) of the log-normal turbulence is donated by:

    whereIis the field intensity (irradiance) in the medium which suffers from atmospheric turbulence,I0is the irradiance in free-space medium without any atmospheric turbulence,σ2lis the log-intensity variance or the Rytov variance, andE[l] is the mean log intensity.

    4 Channel Coding

    There are many techniques, which can be used to improve the Bit Error Rate (BER) performance of any communication system.One of these techniques is channel coding or error detection and correction.In this section, channel coding is used for enhancing the BER performance of DCO-OFDM, ACO-OFDM, ADO-OFDM, and Flip-OFDM in different optical wireless communication channels.Furthermore, hamming code, BCH code, and convolutional codes are proposed in this work to mitigate the noise effect [24,25].

    4.1 Hamming Codes

    Hamming code is a linear block code, where the encoder input is a group of bits with lengthk.Then, some procedures are performed to these input information bits for coding.The output of the encoder is a larger group of bits with lengthn.Such a block code can be represented as (n,k) Hamming code.Richard W.Hamming codes are widely used in many applications such as computer memory, telecommunications and can also be used for data compression.Many parameters can be computed for Hamming encoding and decoding process.For example, there is a binary Hamming code for each integerm≥2.This code can be denoted by (n, k, dmin)code.Hamming codes can detect all one and two-bit errors or correct only one-bit errors without detecting uncorrected errors [26].

    4.2 Bose-Chaudhary-Hocquenghem(BCH)Codes

    The BCH is the abbreviation for three names of scientists who developed these codes.BCH codes are as consider one of the most efficient codes in linear block coding techniques.They form a class of cyclic error-correcting codes that are constructed using polynomials over a finite field.

    There is a binary (n,k) BCH code for any integer value ofm>3 andt <2m-1 with the parameters:codeword length ofn=2m- 1, number of parity bits ofn–k≤mt, minimum Hamming distance ofdmin≥2t+1, and error-correction capability ofterrors.

    The BCH code can correct a number of errors equal to or less thant.So, this code is called aterror correcting BCH code.This code is also considered as a generalization of multiple error-correcting Hamming codes.Hamming single error-correcting codes can be known as BCH codes [25].

    4.3 Convolutional Codes

    Convolutional codes are different from block codes.Their construction is dependent on using many shift registers, which are used as a memory to store the previous data inputs for calculating the data outputs.The redundant bits are generated in the convolutional coder by using modulo-2 convolutions.The convolutional encoder consists of anM-stage shift register with fixed connections tonmodulo-2 adders and a multiplexer that is used to serialize the output of the adders.This code can be specified by three parameters (n,k,K), wherendefines the length of the output codeword,kdefines the length of the input message, andKdefines the constraint length.The code rate or the code efficiencyRequalsk/n[25,27].

    5 Proposed System Models

    5.1 Proposed IM/DD DCO-OFDM System Model

    The DCO-OFDM technique is simple to implement, but the added DC bias makes it inefficient in optical power.Also, this technique suffers from the clipping noise due to the hard clipping of the remaining negative part.The clipping noise may degrade the system performance, especially when low bias levels and large constellation sizes are used.

    The block diagram of the proposed DCO-OFDM system with channel coding is shown in Fig.2.At the transmitter side, the input data sequence is firstly encoded by adding redundant bits.Then, the serial data is converted to parallel data and modulated using any type of modulation technique such as QAM, BPSK, or QPSK.The modulated data is constrained to have Hermitian symmetry property before IFFT, where the positive half ofN-point IFFT contains the baseband modulated symbols, while the complex conjugate of these symbols is contained in the negative half.Thus, the resultant signal at IFFT output is real, and is denoted byxk.At the receiver side,the inverse processes are performed.

    Figure 2:The proposed DCO-OFDM system with channel coding

    5.2 Proposed IM/DD ACO-OFDM System Model

    In ACO-OFDM, no DC bias is required to convert a bipolar signal to a unipolar signal,so that the ACO-OFDM is more efficient than the DCO-OFDM.The signal is clipped at zero levels without adding any clipping noise and without missing any information.Fig.3 shows the block diagram of the proposed ACO-OFDM system with channel coding.In ACO-OFDM, the data symbols are carried on odd sub-carriers, but the even subcarriers are used to ensure nonnegativity requirements of the transmitted OFDM signals.Only half of the sub-carriers carry the transmitted signal.Consequently, the effective data rate of ACO-OFDM is decreased by a factor of two compared to the data rate of DCO-OFDM for the same modulation format.A convolutional coding technique is proposed to enhance the ACO-OFDM performance.

    Figure 3:The proposed ACO-OFDM system with channel coding

    Firstly, the input binary data is encoded by adding redundant data bits using a type of channel coding such as convolutional codes.The encoded data is serial-to-parallel conversion and mapping using (BPSK, QPSK,M-QAM).The input signal to the IFFT contains only the odd sub-carriers, as follows:

    To get a real-time valued signal from the IFFT, the input vector to the IFFT,Xmust be forced to have a Hermitian symmetry property.Therefore, the resulting time-domain signal from IFFT is real and has an odd symmetry property, as given in the following equation.

    Like the DCO-OFDM, the IFFT output signal is serially converted, and CP is appended.Then, it is D/A converted and passed through an ideal LPF, resulting inx(t).The signal,x(t), is clipped to zero to obtain the ACO-OFDM signal,xACO(t) where

    5.3 Proposed IM/DD ADO-OFDM System Model

    Fig.4 shows the block diagram of the ADO-OFDM system with channel coding, which is proposed as a technique for performance enhancement.It is shown that the proposed ADOOFDM transmitter is the same as the proposed ACO and DCO OFDM transmitter before applying the IFFT block.After that, the signal is split into two paths.The upper path generates the ACO-OFDM signal, and the lower path generates the DCO-OFDM signal.

    Figure 4:The proposed ADO-OFDM system with channel coding

    The generated ACO-OFDM signal is defined as follows:

    wherexoddis the odd components of the signal andnc,ACOis the clipping noise in the ACOOFDM.The generated DCO-OFDM signal is represented by,

    wherexevenis the even components of the signal,nc,DCOis the clipping noise in the DCO-OFDM andB′DCis the DC bias component.xACO(t) andxDCO(t) are added together, serialized, and a CP is appended to it and digital-to-analog conversion is performed, resulting inxADO(t).

    The proposed ADO-OFDM is the same as the ADO-OFDM except for the decoding process.At the end of the proposed ADO-OFDM receiver, the received ADO-OFDM signal is demodulated and decoded.

    5.4 Proposed IM/DD Flip-OFDM System Model

    Fig.5 shows the block diagram of the proposed Flip-OFDM with channel coding.Firstly,the input binary signal is encoded by adding extra bits to it.Then, the encoded signal is mapped to complex numbers using different digital modulation techniques such as BPSK, QPSK, 4-QAM,16-QAM, 64-QAM, or 256-QAM.After that, the system is the same as the Flip-OFDM except for the equalization process and the encoding process that is applied at the end of the receiver.

    Figure 5:The proposed Flip-OFDM with channel coding

    The matrix of the MMSE equalizer is given by:

    whereHHis the Hermitian of the channel matrix,σ2is the noise variance of the channel, andImatis the identity matrix with a size equal to the number of transmitting LEDs.Finally, the estimated) signal is de-mapped and decoded to get the original transmitted signal.

    6 Simulation Results

    The performance analysis of the communication system has been estimated by finding the relation between BER and SNR.The BER has been computed by finding the ratio between the number of bit errors (NERR) and the total number of transmitted bits (NTS) as:

    The number of bit errors is obtained by comparing the received bit sequence with the transmitted bit sequence.

    6.1 Simulation Results for the Proposed DCO-OFDM

    ·AWGN Channel

    The BER performance of DCO-OFDM is studied at two different values of DC biasing; 7 and 13 dB.Four cases of QAM constellation mapping are used:4, 16, 64, and 256 QAM.The simulation parameters are 600 OFDM symbols and 1024 subcarriers in each OFDM symbol and a CP length of 24.The simulation results are shown in Figs.6 and 7.For 7 dB biased DCOOFDM in Fig.6, it is noted that the BER performance decreases gradually with the increase of the constellation size.In cases of using 4 and 16 QAM, the system gives a better performance,but that performance decreases significantly in 64 and 256 QAM cases due to the clipping noise.The clipping noise can be reduced by increasing the DC bias to 13 dB, as shown in Fig.7.BER performance for 4 and 16 QAM is still better with higher electrical power.However, the BER performance for high constellation sizes of 64 and 256 QAM is improved significantly.

    Fig.8 shows that with increasing DC bias level, the remaining negative part of the signal decreases, which leads to a decrease in the clipping noise.The signal does not need any clipping for higher biased (13 dB) DCO-OFDM because there are no remaining negative parts after adding the DC bias.It is known that channel coding can be used to improve the performance of the communication system.Therefore, convolutional coding is used as a method of channel coding to improve the performance of DCO-OFDM.This simulation experiment uses convolutional coding with code rates (1/3, 1/2, and 2/3).

    Figure 6:The BER performance for 7 dB biased DCO-OFDM over AWGN channel for 4, 16, 64,and 256 QAM constellations

    Figure 7:The BER performance for 13 dB biased DCO-OFDM over AWGN channel for 4, 16,64, and 256 QAM constellations

    Figure 8:The Time domain waveforms of DCO-OFDM signal after adding different DC biases:(a) 0 dB, (b) 5 dB, (c) 7 dB, and (d) 13 dB

    In Fig.9, un-coded DCO-OFDM is compared to convolutional coded DCO-OFDM with code rates (1/3, 1/2, and 2/3).It is noted that convolutional codes improve the BER performance of the DCO-OFDM system.For example, at a BER= 10–4, convolutional codes with code rates 1/2 and 2/3 enhance the performance by approximately 5 dB.Also, a 7 dB performance enhancement is obtained in the case of the code with a rate of 1/3 at BER = 10-4.

    Figure 9:The performance enhancement of 7 dB biased DCO-OFDM (4QAM) over AWGN channel using convolutional code with the rate (1/3, 1/2, and 2/3)

    In the case of using low-bias DCO-OFDM, the clipping noise dominates for larger constellation sizes by increasing the BER, which leads to degradation in the system performance.Convolutional codes are used to eliminate clipping noise.Therefore, the BER performance enhancement is achieved.In Fig.10, a 7 dB bias is used in DCO-OFDM for 16 and 64 QAM constellation sizes.It is clear that the BER decreases significantly at the sameEb/N0in the case of using convolutional codes.For example, atEb/N0= 25 dB, un-coded DCO-OFDM for 64 QAM gives a BER ~= 0.13, and convolutional coded DCO-OFDM for 64 QAM gives a BER ~= 0.0001.

    Figure 10:The performance enhancement of 7 dB biased DCO-OFDM for 16 QAM and 64 QAM constellations over AWGN channel using convolutional coding

    ·Log-Normal Turbulence Channel

    The performance of the OWC system is sensitive to atmospheric turbulence.The DCOOFDM IM/DD system is affected by weak atmospheric turbulence when used in free space, as shown in Figs.11 and 12.From the results shown, it is deduced that the weak turbulence fading limits the BER performance of the DCO-OFDM system.As the turbulence strength increases,the BER performance decreases.

    Figure 11:The effect of weak atmospheric turbulence on BER performance of DCO-OFDM system (DC bias=3 dB, 4 QAM constellation) at different values of fading strength σ2l = (0, 0.01,0.1 and 0.3)

    Figure 12:The effect of weak atmospheric turbulence on DCO-OFDM (DC bias = 7 dB, BPSK modulation) at fading strengths σ2l = ([0, 0.001, 0.01 and 0.1)

    The effect of weak atmospheric turbulence can be mitigated by using error-correcting codes.The Hamming (7, 4) code can be used for improving the performance of the DCO-OFDM system over the log-normal turbulence channel model.The results of these simulation experiments are shown in Fig.13.It is clear from this figure that Hamming code gives a high BER performance atσ2l=0.01, and 0.001.

    Figure 13:The Performance enhancement using hamming (7, 4) code for 7 dB DCO-OFDM(BPSK modulation) system with log-normal turbulence channel model at σ2l = (0, 0.01, 0.01 and 0.1)

    6.2 Simulation Results for the Proposed ACO-OFDM

    ·AWGN Channel

    The BER performance of the ACO-OFDM is studied over the AWGN channel for QAM constellation sizes:4, 16, 32, 64, 256, and 1024.Convolutional codes with rates 1/2 and 1/3 are used for performance enhancement.The BER performance of the ACO-OFDM is investigated over the AWGN channel with varying QAM constellation sizes, as shown in Fig.14.It decreases gradually with the increase in constellation size.So that, a 4 QAM gives better BER performance for ACO-OFDM systems.

    The improvement of BER performance of 4 QAM ACO-OFDM over AWGN channel using convolutional codes with rates 1/2 and 1/3 is demonstrated in Fig.15.At BER=10-3, it is seen that convolutional codes with rates 1/2 and 1/3 give better performance by approximately 4.5 and 6 dB, respectively.

    6.3 Simulation Results for the Proposed ADO-OFDM

    ·Log-Normal Turbulence Channel Model

    This section studies the BER performance of the ADO-OFDM with BPSK modulation over log-normal turbulence channels.The effect of very weak atmospheric turbulence on the ADOOFDM system is illustrated in Fig.16.It is seen that very weak atmospheric turbulence has a great impact on ADO-OFDM performance.For example, if the fading strength increases from 0 to 0.01, the electrical power must increase by 10 dB to get a BER=10-4.

    Figure 14:The BER performance of ACO-OFDM for 4, 16, 32, 64, 128, 256, and 1024 QAM constellation sizes

    Figure 15:Convolutional codes rates 1/2 and 1/3 for BER performance enhancement of ACOOFDM with 4 QAM constellation size

    Figs.17–19 present comparisons between un-coded and coded ADO-OFDM in the presence of weak atmospheric turbulence with 0.01 and 0.001 fading strength.It is noted that Hamming codes and BCH codes give performance enhancement at fading strengthσ2l=0.001.Convolutional codes enhance the performance in cases of fading strengthσ2l=0.01, and 0.001.At BER=10-3,F(xiàn)ig.17 shows that Hamming codes improve the performance by approximately 3 dB.

    Figure 16:The effect of weak atmospheric turbulence on ADO-OFDM (BPSK modulation, DC bias=7 dB) at fading strengths σ2l = (0, 0.001, 0.01, and 0.1)

    Figure 17:The performance enhancement using hamming codes for coded ADO-OFDM over weak atmospheric turbulence with fading strength (σ2l =0.001)

    6.4 Simulation Results for the Proposed Flip-OFDM

    ·AWGN Channel

    This section shows Matlab simulation results for Flip-OFDM.First, the BER performance of Flip-OFDM is studied over the AWGN channel with different modulation types:BPSK, QPSK,and QAM, as shown in Fig.20.Next, ACO-OFDM and Flip-OFDM with different levels of QAM mapping are compared over the AWGN channel in Fig.21.It is shown that both techniques have the same BER performance.Convolutional codes with code rates of 1/3, 1/2, and 2/3 and BCH (15, 5) codes are used to improve Flip-OFDM performance.Fig.22 shows a performance comparison between un-coded Flip-OFDM and convolutional coded Flip-OFDM over the AWGN channel.It is clear that the proposed Flip-OFDM system with convolutional coding performs better than the un-coded Flip-OFDM system.For example, at BER = 10-3, the proposed Flip-OFDM with convolutional code with rate 1/2 provides improvement by approximately 3.5 dB.

    Figure 18:The performance enhancement using BCH codes for ADO-OFDM over log-normal turbulence fading channel at fading strength σ2l =0.001

    Figure 19:The Performance enhancement using convolutional code with rate 2/3 for coded ADOOFDM over log-normal turbulence channel at σ2l =0.001, and 0.01

    The BER performance of un-coded Flip-OFDM and the proposed Flip-OFDM with BCH coding for 4, and 16 QAM over AWGN channel are shown in Fig.23.It is clear from the results that BCH coded Flip-OFDM provides a performance enhancement over the un-coded system.For example, at BER=10-3, the proposed Flip-OFDM with BCH coding enhances 5 dB for 4 and 16 QAM.

    Figure 20:The BER performance of un-coded flip-OFDM over AWGN channel using different types of modulation (BPSK, QPSK, and M-QAM)

    Figure 21:The BER performance comparison of ACO-OFDM and Flip-OFDM over AWGN channel for different sizes of QAM constellations

    Figure 22:The BER performance enhancement using convolutional coding with rates 1/3, 1/2, and 2/3 for Flip-OFDM with 16 QAM constellation sizes over AWGN channel

    Figure 23:The BCH (15, 5) code for BER performance enhancement of flip-OFDM for 4 and 16 QAM over the AWGN channel

    ·Ceiling Bounce Channel Model

    Fig.24 shows the BER performance of the un-coded Flip-OFDM at different levels of QAM mapping over ceiling bounce channel model using two types of frequency-domain equalizers, LS and MMSE.The results show that the MMSE equalizer outperforms the LS equalizer at all levels of QAM.For example, at BER=10-3, the MMSE equalizer outperforms the LS equalizer by nearly 9 dB for 64 QAM Flip-OFDM.

    Figure 24:The BER performance of un-coded flip-OFDM system over ceiling bounce channel model (ceiling height hc=3.5 m) using LS, and MMSE techniques

    Figure 25:The BER performance of the proposed flip-OFDM system with convolutional coding(code rate=1/2) using LS and MMSE equalizers

    Fig.25 shows the BER performance of the proposed Flip-OFDM with convolutional coding over the ceiling bounce channel model using two types of channel estimation algorithms (LS and MMSE).From the results, it is seen that the MMSE equalizer outperforms the LS equalizer.For example, at BER=10-3, the MMSE equalizer outperforms the LS equalizer by 8 dB for 64 QAM Flip-OFDM.

    Fig.26 demonstrates the BER performance of un-coded Flip-OFDM and the proposed Flip-OFDM with convolutional coding for codes with rates 1/3, 1/2, and 2/3 using MMSE equalizer.Results show that convolutional coding with rates 1/3, 1/2, and 2/3 provides an enhancement by nearly 8, 6.5, and 5 dB at BER=10-3, respectively.

    Figure 26:The BER performance comparison of un-coded flip-OFDM and proposed Flip-OFDM with convolutional coding over ceiling bounce channel model using MMSE equalizer

    Figure 27:The effect of weak atmospheric turbulence with fading strengths σ2l = [0, 0.1, 0.3, and 0.5] on BER performance of Flip-OFDM

    Figure 28:Hamming (7, 4) code for performance enhancement of flip-OFDM with the effect of weak atmospheric turbulence with fading strengths σ2l = [0, 0.1, 0.3, and 0.5]

    Figure 29:The BER performance enhancement for flip-OFDM with (BPSK, QPSK, 4QAM) modulation type with weak atmospheric turbulence at σ2l =0.1, using convolutional code (code rate=1/2, constraint length=3)

    ·Log-Normal Turbulence Channel Model

    Fig.27 presents the effect of weak atmospheric turbulence with different fading strengthsσ2lon BER performance of Flip-OFDM.Fig.28 introduces the performance enhancement of Flip-OFDM with Hamming (7, 4) code and the effect of weak atmospheric turbulence with different fading strengths.Fig.29 shows the BER performance enhancement for Flip-OFDM with(BPSK, QPSK, 4QAM) modulation type with weak atmospheric turbulence atσ2l=0.1, using convolutional code with a code rate=1/2, and a constraint length=3.Fig.30 compares un-coded and proposed Flip-OFDM with BCH coding in the weak atmospheric turbulence fading channel at fading strengths (0, 0.1, 0.3, and 0.5).

    Figure 30:The BCH (15, 5) code for performance enhancement of flip-OFDM in the presence of weak atmospheric turbulence at fading strengths σ2l = [0, 0.1, 0.3, and 0.5]

    7 Conclusions and Future Work

    This paper studied the performance of OWC IM/DD systems based on four forms of unipolar OFDM with different communication channel models.The objective of the work presented in the thesis is to enhance the performance of these systems using different techniques.This study was divided into three parts.Firstly, the BER performance of the DCO-OFDM, ACO-OFDM,ADO-OFDM, and Flip-OFDM IM/DD system was studied over the AWGN channel.Hamming,BCH, and convolutional codes have been used for performance enhancement.The coded systems were compared with the un-coded systems, and the performance enhancement with coding was elaborated.Secondly, the BER performance of the IM/DD OFDM system was studied over the ceiling bounce channel model.Two channel estimation and equalization algorithms have been considered and compared:the LS algorithm and the MMSE algorithm.The simulation results show that the MMSE algorithm gives better BER performance than the LS algorithm.Then,convolutional code was utilized for BER performance enhancement.Finally, the effect of weak atmospheric turbulence was studied on IM/DD OFDM system by studying the BER performance of the system over the log-normal turbulence channel model.The obtained results show that the weak atmospheric turbulence gradually decreases the BER performance of the IM/DD OFDM system with an increase in fading strength.Also, Hamming, BCH, and convolutional codes were utilized to mitigate the effect of very weak atmospheric turbulence.For future work, the suggested signal processing tools could be employed in advanced 5G communication networks with different types of modulation techniques.

    Acknowledgement:The authors would like to thank the support of the Deanship of Scientific Research at Princess Nourah bint Abdulrahman University.

    Funding Statement:This research was funded by the Deanship of Scientific Research at Princess Nourah Bint Abdulrahman University through the Fast-track Research Funding Program.

    Conflicts of Interest:The authors declare that they have no conflicts of interest to report regarding the present study.

    a级毛片免费高清观看在线播放| 人人妻,人人澡人人爽秒播| 男女啪啪激烈高潮av片| 少妇丰满av| 国产一区二区三区在线臀色熟女| 男插女下体视频免费在线播放| 欧美色欧美亚洲另类二区| 国内久久婷婷六月综合欲色啪| 久久久久久久久久成人| 最好的美女福利视频网| 99九九线精品视频在线观看视频| 国产黄色视频一区二区在线观看 | 少妇裸体淫交视频免费看高清| 精品一区二区三区视频在线| 精品久久久久久久久久免费视频| 国产熟女欧美一区二区| 亚洲综合色惰| 99riav亚洲国产免费| 在线看三级毛片| 啦啦啦观看免费观看视频高清| 久久久久国产精品人妻aⅴ院| 日本五十路高清| 亚洲av成人av| 国产成人影院久久av| 欧美极品一区二区三区四区| 国产免费男女视频| 国产精品无大码| 国产一区二区亚洲精品在线观看| 一本一本综合久久| 成人欧美大片| 国产爱豆传媒在线观看| 欧美一区二区国产精品久久精品| 男人和女人高潮做爰伦理| 日本三级黄在线观看| 亚洲精华国产精华液的使用体验 | 久久久成人免费电影| 国产高清有码在线观看视频| 99热这里只有精品一区| 波野结衣二区三区在线| 国产成人91sexporn| 亚洲七黄色美女视频| 欧美色欧美亚洲另类二区| 免费一级毛片在线播放高清视频| 久久精品人妻少妇| 中国国产av一级| 国产精品美女特级片免费视频播放器| 中文字幕av在线有码专区| 国产高潮美女av| 亚洲精品色激情综合| 国模一区二区三区四区视频| 国产高清三级在线| 欧美一区二区精品小视频在线| 亚洲av免费在线观看| 一边摸一边抽搐一进一小说| 精品久久久噜噜| 国产精品久久久久久久电影| 亚洲国产欧洲综合997久久,| 精品人妻熟女av久视频| 97超碰精品成人国产| 日韩av不卡免费在线播放| 女生性感内裤真人,穿戴方法视频| 欧美色视频一区免费| 久久久精品大字幕| 亚洲精品日韩在线中文字幕 | 久久精品国产亚洲网站| 看免费成人av毛片| 亚洲av.av天堂| videossex国产| 国产精品永久免费网站| 亚洲人成网站在线播放欧美日韩| 99在线人妻在线中文字幕| 国模一区二区三区四区视频| 亚洲成a人片在线一区二区| 直男gayav资源| 亚洲在线观看片| 麻豆一二三区av精品| 日韩国内少妇激情av| 在线观看66精品国产| 老熟妇仑乱视频hdxx| 九九久久精品国产亚洲av麻豆| 淫秽高清视频在线观看| 国产精华一区二区三区| or卡值多少钱| 日产精品乱码卡一卡2卡三| 97热精品久久久久久| 精品免费久久久久久久清纯| 男人的好看免费观看在线视频| 国产真实乱freesex| 成人鲁丝片一二三区免费| 午夜久久久久精精品| 18+在线观看网站| 1000部很黄的大片| 久久精品久久久久久噜噜老黄 | 久久久久久久亚洲中文字幕| 久久精品国产鲁丝片午夜精品| 中文字幕久久专区| 日本熟妇午夜| 国产午夜福利久久久久久| 无遮挡黄片免费观看| 国产一区二区三区在线臀色熟女| 国产真实乱freesex| 精品久久久久久久久久免费视频| 在线观看av片永久免费下载| 免费观看人在逋| 极品教师在线视频| 欧美日韩一区二区视频在线观看视频在线 | 99精品在免费线老司机午夜| 欧美一区二区精品小视频在线| 亚洲无线在线观看| 亚洲欧美精品综合久久99| 婷婷亚洲欧美| 国产一区亚洲一区在线观看| 亚洲人与动物交配视频| 黄色配什么色好看| 在线免费观看的www视频| 好男人在线观看高清免费视频| 国产欧美日韩精品一区二区| av国产免费在线观看| 一区二区三区四区激情视频 | 婷婷亚洲欧美| 我的女老师完整版在线观看| 日韩 亚洲 欧美在线| 久久亚洲国产成人精品v| 亚洲精品成人久久久久久| 日日摸夜夜添夜夜爱| 高清毛片免费看| 女同久久另类99精品国产91| 九色成人免费人妻av| 秋霞在线观看毛片| 两性午夜刺激爽爽歪歪视频在线观看| 五月伊人婷婷丁香| 国产精品嫩草影院av在线观看| 成人精品一区二区免费| www日本黄色视频网| 欧美激情在线99| 人妻久久中文字幕网| 白带黄色成豆腐渣| 无遮挡黄片免费观看| 亚洲人成网站在线观看播放| 又爽又黄无遮挡网站| 成熟少妇高潮喷水视频| 国产欧美日韩精品一区二区| 日日摸夜夜添夜夜添av毛片| 日本黄大片高清| 久久久成人免费电影| 深爱激情五月婷婷| 精品一区二区三区视频在线| 国产v大片淫在线免费观看| 啦啦啦观看免费观看视频高清| 久久久久国产精品人妻aⅴ院| 欧美一区二区精品小视频在线| 色综合亚洲欧美另类图片| 欧美zozozo另类| 亚洲精品456在线播放app| 成人一区二区视频在线观看| 美女大奶头视频| 性插视频无遮挡在线免费观看| 黄色欧美视频在线观看| 国产 一区精品| 一边摸一边抽搐一进一小说| 亚洲无线观看免费| 亚洲av免费在线观看| 少妇熟女欧美另类| 亚洲专区国产一区二区| 国产av不卡久久| 99热这里只有是精品在线观看| 亚洲最大成人中文| 99在线人妻在线中文字幕| 夜夜夜夜夜久久久久| 网址你懂的国产日韩在线| 丰满人妻一区二区三区视频av| 99在线视频只有这里精品首页| 麻豆一二三区av精品| 国产一区二区在线观看日韩| 热99re8久久精品国产| 中文字幕久久专区| 国内精品美女久久久久久| 亚洲内射少妇av| 亚洲精品久久国产高清桃花| 真人做人爱边吃奶动态| 日韩制服骚丝袜av| 一级黄片播放器| 99久久九九国产精品国产免费| 日韩三级伦理在线观看| 欧美成人免费av一区二区三区| 在线观看免费视频日本深夜| 日韩强制内射视频| 观看免费一级毛片| 亚洲精品一区av在线观看| 亚洲五月天丁香| 成人一区二区视频在线观看| 3wmmmm亚洲av在线观看| 人妻少妇偷人精品九色| 欧美最新免费一区二区三区| 精品乱码久久久久久99久播| 欧美xxxx黑人xx丫x性爽| 天天躁日日操中文字幕| 亚洲精品在线观看二区| 一进一出好大好爽视频| av在线播放精品| 日本黄色片子视频| 在线国产一区二区在线| 国产乱人视频| 久久久久久久午夜电影| 非洲黑人性xxxx精品又粗又长| 国产毛片a区久久久久| 亚洲熟妇中文字幕五十中出| 人妻久久中文字幕网| 成人av一区二区三区在线看| 99热全是精品| 不卡视频在线观看欧美| 成年女人看的毛片在线观看| 老熟妇仑乱视频hdxx| 国产大屁股一区二区在线视频| 国产亚洲精品综合一区在线观看| 大香蕉久久网| 亚洲精品在线观看二区| 丰满乱子伦码专区| 亚洲欧美中文字幕日韩二区| 亚洲av成人精品一区久久| 国产视频一区二区在线看| 国产精品爽爽va在线观看网站| 日本三级黄在线观看| 国产精品久久久久久亚洲av鲁大| 毛片女人毛片| 国产黄片美女视频| 免费观看人在逋| 亚洲在线自拍视频| 草草在线视频免费看| 欧美xxxx性猛交bbbb| 亚洲,欧美,日韩| 丰满的人妻完整版| 晚上一个人看的免费电影| 亚洲欧美精品自产自拍| 天天躁日日操中文字幕| 日本熟妇午夜| 国产精品女同一区二区软件| 国产 一区 欧美 日韩| 尾随美女入室| av在线播放精品| 欧美成人a在线观看| 免费看日本二区| 搡老熟女国产l中国老女人| 国产午夜精品久久久久久一区二区三区 | 亚洲国产高清在线一区二区三| 少妇的逼好多水| 成年女人毛片免费观看观看9| 精品福利观看| 午夜亚洲福利在线播放| 国产欧美日韩精品一区二区| 亚洲自偷自拍三级| 亚洲国产精品国产精品| 搡老岳熟女国产| 男人和女人高潮做爰伦理| 日韩精品中文字幕看吧| 偷拍熟女少妇极品色| 日韩大尺度精品在线看网址| 免费av毛片视频| 麻豆av噜噜一区二区三区| 亚洲第一区二区三区不卡| 搡老妇女老女人老熟妇| 亚洲国产日韩欧美精品在线观看| 香蕉av资源在线| 91精品国产九色| 日本免费一区二区三区高清不卡| 在现免费观看毛片| 国产白丝娇喘喷水9色精品| 亚洲最大成人av| 精品一区二区三区av网在线观看| eeuss影院久久| 麻豆乱淫一区二区| 亚洲精品亚洲一区二区| 可以在线观看的亚洲视频| 在线观看66精品国产| 天美传媒精品一区二区| 午夜免费男女啪啪视频观看 | 18+在线观看网站| 精品午夜福利在线看| 亚洲久久久久久中文字幕| 亚洲精品在线观看二区| 午夜激情欧美在线| 欧美一区二区精品小视频在线| 在线观看午夜福利视频| 婷婷精品国产亚洲av| 偷拍熟女少妇极品色| 国产精品野战在线观看| 床上黄色一级片| 国产 一区 欧美 日韩| 午夜a级毛片| 亚洲成a人片在线一区二区| 日韩欧美 国产精品| 日日摸夜夜添夜夜爱| 国产午夜精品论理片| 亚洲av美国av| 国产av一区在线观看免费| 国产午夜精品久久久久久一区二区三区 | 国产成人a区在线观看| www日本黄色视频网| 国产中年淑女户外野战色| 国产精品亚洲一级av第二区| 亚洲高清免费不卡视频| 少妇熟女aⅴ在线视频| 成人特级av手机在线观看| 又黄又爽又刺激的免费视频.| av国产免费在线观看| 非洲黑人性xxxx精品又粗又长| 日本-黄色视频高清免费观看| 亚洲aⅴ乱码一区二区在线播放| 97超碰精品成人国产| 国产欧美日韩精品亚洲av| 国产乱人偷精品视频| 国产真实伦视频高清在线观看| 久久人人爽人人片av| 免费在线观看影片大全网站| 男人的好看免费观看在线视频| 亚洲精品一卡2卡三卡4卡5卡| 欧美一区二区亚洲| 午夜免费男女啪啪视频观看 | 91狼人影院| 波多野结衣高清作品| 欧美成人免费av一区二区三区| 国产三级中文精品| 国产人妻一区二区三区在| 精品不卡国产一区二区三区| 久久精品综合一区二区三区| 晚上一个人看的免费电影| 国产亚洲精品久久久久久毛片| 91av网一区二区| 两个人视频免费观看高清| 欧美国产日韩亚洲一区| av.在线天堂| 精品久久久久久久久av| 三级毛片av免费| 国产伦一二天堂av在线观看| av国产免费在线观看| 麻豆乱淫一区二区| 天天躁夜夜躁狠狠久久av| 国内精品宾馆在线| 女同久久另类99精品国产91| 欧美成人a在线观看| 看免费成人av毛片| 99久久无色码亚洲精品果冻| 日韩精品中文字幕看吧| 69av精品久久久久久| 国产精品电影一区二区三区| 少妇被粗大猛烈的视频| 国产高清视频在线播放一区| 成人国产麻豆网| 深爱激情五月婷婷| 欧美3d第一页| 一个人看的www免费观看视频| 丰满人妻一区二区三区视频av| 欧美xxxx性猛交bbbb| 婷婷亚洲欧美| 久久精品影院6| 老司机福利观看| 美女免费视频网站| 亚洲久久久久久中文字幕| 精华霜和精华液先用哪个| 免费看av在线观看网站| 97人妻精品一区二区三区麻豆| 欧美中文日本在线观看视频| 久久久久国内视频| 夜夜看夜夜爽夜夜摸| 亚洲精品国产av成人精品 | 丝袜美腿在线中文| 婷婷亚洲欧美| 一边摸一边抽搐一进一小说| 欧美三级亚洲精品| 久久久色成人| 久久精品人妻少妇| 成年免费大片在线观看| 国产 一区精品| 中出人妻视频一区二区| 日本五十路高清| 最近2019中文字幕mv第一页| 国产三级中文精品| 桃色一区二区三区在线观看| 婷婷精品国产亚洲av在线| 久久久久性生活片| 免费看a级黄色片| 三级毛片av免费| 男女啪啪激烈高潮av片| 欧美丝袜亚洲另类| 此物有八面人人有两片| 久久99热6这里只有精品| 国产午夜精品久久久久久一区二区三区 | 蜜桃久久精品国产亚洲av| 亚洲精品成人久久久久久| 91精品国产九色| av国产免费在线观看| 中文字幕免费在线视频6| 在线观看一区二区三区| 亚洲国产精品国产精品| 国产精品人妻久久久影院| 中文字幕人妻熟人妻熟丝袜美| 丰满的人妻完整版| 久久久久久久亚洲中文字幕| 精品久久久久久久久av| 中国美白少妇内射xxxbb| 欧美性猛交╳xxx乱大交人| 麻豆一二三区av精品| 色综合站精品国产| 国产免费男女视频| 亚洲av熟女| 99久久九九国产精品国产免费| 免费人成视频x8x8入口观看| av福利片在线观看| 午夜免费激情av| 免费观看在线日韩| 麻豆成人午夜福利视频| av在线观看视频网站免费| 久久99热6这里只有精品| 国产男靠女视频免费网站| 色视频www国产| 日产精品乱码卡一卡2卡三| 热99re8久久精品国产| 欧美日本亚洲视频在线播放| 欧美成人免费av一区二区三区| 亚洲成人中文字幕在线播放| 日韩欧美国产在线观看| 国产一区亚洲一区在线观看| 亚洲av中文字字幕乱码综合| 观看美女的网站| 不卡视频在线观看欧美| 欧美成人a在线观看| 欧美日韩一区二区视频在线观看视频在线 | 最新中文字幕久久久久| 日本爱情动作片www.在线观看 | 免费看美女性在线毛片视频| aaaaa片日本免费| 精品少妇黑人巨大在线播放 | 别揉我奶头 嗯啊视频| 国产高潮美女av| 性插视频无遮挡在线免费观看| 成人一区二区视频在线观看| 3wmmmm亚洲av在线观看| 一级毛片我不卡| 免费观看精品视频网站| 一级a爱片免费观看的视频| 亚洲国产精品成人久久小说 | 成人高潮视频无遮挡免费网站| 国产av不卡久久| 国产91av在线免费观看| 国产乱人视频| 国产精品久久视频播放| 97超碰精品成人国产| 国产精品三级大全| 最近最新中文字幕大全电影3| 在线观看一区二区三区| 亚洲精品影视一区二区三区av| 久久国产乱子免费精品| 老司机影院成人| 精品福利观看| 一级毛片我不卡| 日本黄色视频三级网站网址| 国产成人aa在线观看| 日韩精品青青久久久久久| 亚洲人与动物交配视频| 亚洲自拍偷在线| 精品99又大又爽又粗少妇毛片| 久久精品国产亚洲av香蕉五月| 天堂网av新在线| 精品久久国产蜜桃| 91狼人影院| 色播亚洲综合网| 国产白丝娇喘喷水9色精品| 97热精品久久久久久| 精品一区二区三区视频在线观看免费| 非洲黑人性xxxx精品又粗又长| 神马国产精品三级电影在线观看| 国产v大片淫在线免费观看| 香蕉av资源在线| 天堂网av新在线| 成年女人永久免费观看视频| 国产成人一区二区在线| 18禁裸乳无遮挡免费网站照片| av.在线天堂| 一级黄片播放器| 成人三级黄色视频| 久久久久久久久久久丰满| 天堂动漫精品| 亚洲无线观看免费| 免费搜索国产男女视频| 国产高潮美女av| 欧美3d第一页| 一进一出好大好爽视频| 在线国产一区二区在线| 亚洲av熟女| 成人特级黄色片久久久久久久| 可以在线观看的亚洲视频| 自拍偷自拍亚洲精品老妇| 内地一区二区视频在线| 国产国拍精品亚洲av在线观看| 少妇的逼水好多| 99国产精品一区二区蜜桃av| 两性午夜刺激爽爽歪歪视频在线观看| 亚洲无线在线观看| av专区在线播放| 欧美区成人在线视频| 欧美bdsm另类| 在线看三级毛片| 两个人的视频大全免费| 亚洲va在线va天堂va国产| 久久久久国产精品人妻aⅴ院| 深爱激情五月婷婷| 搡老熟女国产l中国老女人| 淫秽高清视频在线观看| 免费观看精品视频网站| 美女黄网站色视频| 亚洲第一电影网av| 国产蜜桃级精品一区二区三区| 亚洲图色成人| 亚洲美女视频黄频| 亚洲精品456在线播放app| 日本黄色视频三级网站网址| 亚洲精品成人久久久久久| 级片在线观看| 国产不卡一卡二| 久久99热6这里只有精品| 91久久精品电影网| 最近在线观看免费完整版| 日本黄色视频三级网站网址| 欧美成人a在线观看| 大香蕉久久网| 69人妻影院| 亚洲无线观看免费| 久久久精品欧美日韩精品| 中文字幕av在线有码专区| 久久久久久久午夜电影| 成人精品一区二区免费| 狂野欧美激情性xxxx在线观看| 看黄色毛片网站| 丰满乱子伦码专区| 国产欧美日韩精品一区二区| 亚洲真实伦在线观看| 听说在线观看完整版免费高清| 久久久欧美国产精品| 国产成年人精品一区二区| 久久久精品大字幕| 亚洲国产欧洲综合997久久,| 级片在线观看| 精品人妻视频免费看| 欧美3d第一页| 97人妻精品一区二区三区麻豆| 欧美3d第一页| 身体一侧抽搐| 男女视频在线观看网站免费| 搡老熟女国产l中国老女人| 美女xxoo啪啪120秒动态图| 亚洲成av人片在线播放无| 国产精品爽爽va在线观看网站| 看片在线看免费视频| 欧美一区二区国产精品久久精品| 美女被艹到高潮喷水动态| 亚洲国产欧美人成| 99久久精品一区二区三区| 精品久久国产蜜桃| 午夜免费男女啪啪视频观看 | 欧美人与善性xxx| 日韩欧美精品免费久久| 日韩精品青青久久久久久| 尤物成人国产欧美一区二区三区| 亚洲欧美成人综合另类久久久 | av黄色大香蕉| 看非洲黑人一级黄片| 亚洲一区高清亚洲精品| 亚洲真实伦在线观看| 国产人妻一区二区三区在| 中文亚洲av片在线观看爽| 国产成人a∨麻豆精品| 亚洲av五月六月丁香网| 最后的刺客免费高清国语| 久久精品91蜜桃| 精品人妻熟女av久视频| 亚洲av中文av极速乱| 午夜精品在线福利| 亚洲激情五月婷婷啪啪| 午夜激情福利司机影院| 亚洲成人av在线免费| 午夜福利视频1000在线观看| 欧美区成人在线视频| 插阴视频在线观看视频| av.在线天堂| 一本一本综合久久| 身体一侧抽搐| 国产欧美日韩一区二区精品| 在线观看av片永久免费下载| 在线看三级毛片| 少妇人妻一区二区三区视频| 晚上一个人看的免费电影| 色在线成人网| 99在线人妻在线中文字幕| 色av中文字幕| 精品国产三级普通话版| 真实男女啪啪啪动态图| 一级毛片电影观看 | 国产熟女欧美一区二区| 一进一出抽搐动态| 国产真实伦视频高清在线观看| 亚洲图色成人| 国产精品人妻久久久影院| 99久久精品一区二区三区| 精品免费久久久久久久清纯| 欧美日韩一区二区视频在线观看视频在线 | 国产成人精品久久久久久| 午夜激情欧美在线| 一a级毛片在线观看| 成人综合一区亚洲| 在线观看美女被高潮喷水网站| 免费av不卡在线播放| 日韩 亚洲 欧美在线| 男人舔女人下体高潮全视频| 国产成人a区在线观看| 在线观看美女被高潮喷水网站|