CC BY
33
Куповых Геннадий Владимирович - e-mail: [email protected]; тел.: 89289543642; д.ф.-м.н.; профессор.
Клово Александр Георгиевич - e-mail: [email protected]; тел.: 89281221064; к.ф.-м.н.; доцент.
Svidelsky Sergey Sergeevich - Southern Federal University; e-mail: [email protected]; 44, Nekrasovsky, Taganrog, 347928, Russia; phone: +79281410341; postgraduate student.
Litvinova Valeria Sergeevna - e-mail: [email protected]; phone: +79185884396; postgraduate student.
Kupovykh Gennady Vladimirovich - e-mail: [email protected]; phone: +79289543642; dr. of phys. and math. sc.; professor.
Klovo Alexander Georgievich - e-mail: [email protected]; phone: +79281221064; cand. of phys. and math. sc.; associate professor.
УДК 621.396.94:621.376 DOI 10.18522/2311-3103-2020-5-141-149
Hussein Ahmed Mahmood, К.Е. Румянцев, Al-Karawi Hussein Shookor
ЭВОЛЮЦИЯ РАДИОСВЯЗИ ПО ОПТИЧЕСКОМУ КАНАЛУ СВЯЗИ
В СВОБОДНОМ ПРОСТРАНСТВЕ С ИСПОЛЬЗОВАНИЕМ МУЛЬТИПЛЕКСИРОВАНИЯ ПОДНЕСУЩИХ С АМПЛИТУДНОЙ
МАНИПУЛЯЦИЕЙ
В беспроводных системах и сетях отмечается высокий спрос на радиосвязь по оптическому каналу связи в свободном пространстве (RoFSO) с широкой полосой пропускания и высокой скоростью передачи данных. Такая связь обеспечивает такую же скорость передачи данных, как в волоконно-оптических системах, но при меньшей стоимости на её развёртывание. Системы RoFSO реализуются комбинированием радиосигнала (RF) с оптическим сигналом для беспроводных каналов в свободном пространстве (FSO). Предлагается моделирование системы с мультиплексированием поднесущих с амплитудной манипуляцией (SCM/ASK) для оптической связи в свободном пространстве. В системе Скорость передачи данных принята равной 1 Гбит/с. Электронный амплитудный модулятор настроен на радиосигнал 10 ГГц. К нему добавляются 100 каналов с частотным разнесением поднесущих частот на 10 МГц при рабочей частоте первого канала 60 МГц. Эти каналы поднесущих смешиваются с гармоническим радиосигналом с несущей частотой 10 ГГц в гибридном ответвителе со сдвигом фазы в 90o. Непрерывное лазерное излучение с входной мощностью 10 дБм и длиной волны 1550 нм модулируется сформированным радиосигналом в оптическом LiNb модуляторе Маха-Цендера на LiNb-кристалле. Выходной сигнал модулятора передаётся по разным оптическим линиям связи в свободном пространстве протяжённостью 300 ... 1000м под воздействием атмосферной турбулентности, определяемой структурной характеристикой флуктуаций показателя преломления. Система оценивается с точки зрения Q-добротности и частоты ошибок бит (BER) с использованием программного обеспечения Optisystem. Показано, что максимальная протяжённость связи при слабой турбулентности (С^ = 5 X 1 0 " 15 м" 2 /3) и BER=10'9 составляет 950 м, а при сильной турбулентности (С2 = 5 X 1 0 " 1 3 м "2/3 ) - 850 м.
Радиосвязь; оптический канал; свободное пространство; поднесущие составляющие; мультиплексирование; амплитудная манипуляция; оптический модулятор Маха-Цендера; частоты ошибок бит; добротность.
Hussein Ahmed Mahmood, K.Y. Rumyantsev, Al-Karawi Hussein Shookor
EVOLUTION OF RADIO OVER FREE SPACE OPTICAL COMMUNICATION UTILIZING SUBCARRIER MULTIPLEXING / AMPLITUDE SHIFT KEYING
The high demand for increased bandwidth, data rate and quality in optical communication systems in modern applications. Radio over free space optics (RoFSO) is deemed a new design methodology over wireless systems and networks. This technique has to ensure data rates like ones presented by means optical fiber communication techniques in keeping with a portion of its arrangement cost. Such systems are implemented by combined radio signal (RF) with optical signal, which containing various wireless administrations and Free Space Optics (FSO) link. In this paper, the simulation and evaluation system of Subcarrier Multiplexing/Amplitude Shift Keying (SCM/ASK) transmitter for Free Space Optical Communication is proposed. 1Gb/s data Rate given to the system. Whilst 10 GHz radio frequency signal setting in electrical amplitude modulator. Thereafter, radio signal is added with 100 subcarrier channels of 10 MHz spacing channel at operated first channel frequency of 60 MHz. These subcarrier channels with 900 combined with 10 GHz sin wave signal ( radio frequency ) at hybrid coupler, the combination of each subcarriers and radio signal are modulated by LiNb Mach-Zehnder optical modulator with 1550 nm wavelength continues wave laser signal at 10 dBm input power. The optical modulated signal (after optical modulator) is transmitted over a various free space optical link from 300m to 1km under the Atmospheric turbulence effect (the structure feature of the refractive index). The system is evaluated utilizing Opti system software with Q-factor and BER terminology. It is shown that the maximum optical distance for weak turbulence (C% = 5 X 1 0 " 1 5 m~2 /3) at BER equal to 10'9 is 950m, while the maximum optical distance for strong turbulence C^ = 5 X 1 0 " 1 3 m " 2 / 3) is 850m.
Subcarrier Multiplexing; Radio Over Free Space Optics; Amplitude Shift Keying (ASK); Mach-Zehnder optical modulator; Radio Signal (RF); Q-factor, Bit Error Rate (BER).
Introduction. There have been many advantages of free space optical communication (FSO) systems or wireless optical communication, for instance large capacity, unlicensed system, excellent protection and minimal cost-efficiency of transmitting high data rates besides radio frequency (RF) signals with the identical size as optical fiber [1-6]. Though, it's a feasible technology that corresponding with point-to-point communication. FSO communication systems effectiveness is highly vulnerable to adverse atmospheric situations caused by fluctuations in the deflective index due to temperature inhomogeneities and changes in pressure.[4]. Due to variations in the refractive index via transmission signal along the path link, atmospheric turbulence affects variations (scintillation) in both the intensity and phase of the received signal [2].
Many different mathematical models have recently been suggested to explain this variation based on atmospheric turbulence in both weak and strong fading regimes in the optical channel, such as:
1) log-normal distribution;
2) gamma-gamma distribution;
3) negative exponential dissemination [4-7].
In addition, In addition, the analysis of the malfunction probability and the median capacity of free - space channels is evaluated, derived from the closed form expression for the malfunction probability and the regular capacity of communication systems over atmospheric turbulence-induced fading channels modelled by the distribution of lognormal and gamma-gamma with regard to turbulence influences [2]. It is proposed to simulate and compare the hybrid modulation technique namely PPM-MSK-SIM based on PPM and MSK subcarrier strength modulation. Additionally, theoretical analysis of the BER performance under lognormal turbulence model for an avalanche photodetector system [8].
In Conjunction with using the SIM-DPSK modulation method over the lognormal turbulence channel, the performance review of the free space optical communication system is proposed with regard to the misalignment effects. Likewise, the formulas for the average of BER and probability have been derived [9]. For the FSO framework with avalanche photodetector receiver, it is proposed to derive theoretical representation for the average BER of the SIM-BPSK modulation format.
In addition, under the influence of the gamma-gamma atmospheric turbulence model, the magnitude fluctuation of the optical signal is regarded [10]. The simulation studies of optical communications utilized subcarrier phase shift keying intensity modulation over atmospheric turbulence conditions. The bit error rate is derived for optical system using either on/off key or subcarrier PSK intensity modulation format [11].
In relation to our knowledge, a study of the optical communication method of radio over free space using subcarrier multiplexing / Amplitude Shift Keying was not carried out in previous papers. Therefore, the assessment of radio over free space optical (FSO) transmission at different free space links from 300 m to 1 km with 10 GHz radio signal is fulfilled in this paper. It is proposed to handle all this under atmospheric turbulences conditions (weak and strong) utilizing subcarrier multiplexer/Amplitude Shift Keying (SCM/ASK) is suggested. In addition, the method of estimation is explained in terms of the BER Q-factor and value.
Theoretical analysis. This section presents a brief overview of the Amplitude Shift Keying (ASK), optical subcarrier multiplexing (SCM), optical modulation and gamma-gamma distribution model turbulence.
A. Amplitude Shift Keying (ASK)
Amplitude shift keying is a type of amplitude modulation which characterizes the binary data (0 or 1) for differences within the amplitude of a carrier wave. Fig. 1. is represented the waveform of the amplitude shift keying (ASK) signal, the transmitted ASK signal for symbol i is defined by [12].
Si(t) =
N
2E.it)
, „ , f 0 < t < Г") cosKt + 0) (, = 1.....Mj
(1)
Where the amplitude phrase j2 Ei ( t) / T will utilize M values, besides the phase term ^ is a constant value.
Fig. 1. Binary Amplitude Shift Keying (ASK)
B. Optical subcarrier multiplexing (SCM)
Optical subcarrier multiplexing (SCM) [13] is a system through it numerous signals are multiplexed in the radio frequencies domain as well as used to modulate with the light signal to be transferred through a single wavelength [14]. Furthermore, this system considers a more sensitive to noise effect and more flexible for superior data rate diffusion in the field of optical communication to increase the efficiency of the bandwidth [15]. The basic scheme of SCM is demonstrated in fig. 2.
Fig. 2. The basic scheme of Subcarrier Multiplexing (SCM) within optical system [20]
C. Optical modulation
In optical communication systems, the electrical signal is modulated onto a light source (carrier) by an optical modulator. The configuration of Dual-Arm LiNb Mach-Zehnder optical Modulator is shown in fig. 3. The electric signal is divided into two signals V1 and V2 with 900 phase shifts between them, mathematical expression for each signal as given in Eq. (1).
V1(t) = VRF cos(coRF(t) + 0(t)). (2)
Where , and correspond to the amplitude, frequency and phase of
electrical signal component correspondingly, Whereas, the yield signal of dual-arm MZM which is define in Eq. (2) [16].
exp (jn y} + exp (jn yj . (3)
Where is the light signal, V1 and V2 are the modulated electrical signals, is the voltage to offer a phase shift to each phase modulator.
Et
F = —
0 2
Fig. 3. The basic scheme Dual-Arm MZM [21] D. Gamma-Gamma dissemination model turbulence
The gamma-gamma prototype is represent mutually small-scale in addition large-scale atmospheric fluctuations besides factor the irradiance such as the result of two separate random procedures, every getting a gamma PDF, as the expression following [4, 6, 17]:
m = 2(f )(Г)/2/{(а+Ь)/2Ь1^-*(24Ш)-
Ча)1^)
Where r (.) is the Gamma function, Kn (.) is the modified Bessel function of the second kind of order n, a and b are the active numbers of small scale what is more large scale eddies of the scattering situation and characterized for spherical wave through aperture-averaged scintillation as following [4, 18, 19]
a =
exp
0.49S2
(1 + 0.18d2 + 0.56512/5)7/6
- 1
and
b =
exp
0.5152
(1 + 0.9 d2 + 0.62512/5)5/6
- 1
(5)
(6)
Where: d = j k£>2 / 4L , k = 2n/A is the optical wave number, L is the length of the optical link and D is the receiver's aperture diameter. The parameter S2 is the Rytov variance given by
S2 = 1.23C2k?/6L11/6. (7)
Through being the altitude-dependent turbulence strength and changing from
1"7 1 ^ 0
10- to 10- m- matching to the atmospheric turbulence terms.
Simulation setup. The proposed system of radio over free space optical communication utilizing subcarrier multiplexing/Amplitude Shift Keying transmitter is illustrated in fig..4. This system is simulated using optisystem software. The design simulation as well as system factors are inserted in table 1 and table 2 respectively.
Fig. 4. Block diagram of proposed SCM/ASK free space optical communication system
Table 1
Layout simulation parameters
Parameters Value
Bit rate G bit/s 1
Sequence length 64
Samples / bit 256
Central frequency (nm) 1550
System parameters Table 2
Parameters Value
ASK frequency GHz 10
Carrier generator frequency MHz 60
Sinewave generator frequency GHz 10
Optical amplifier gain dB 20
Optical amplifier power dBm 10
Optical amplifier noise figure dB 5
Free space channel attenuation dB/Km 20
APD photodiode responsivity A/W 0.9
APD photodiode dark current nA 10
Band pass Bessel filter frequency GHz 10
Bandwidth Bessel filter GHz 1
ASK demodulated frequency GHz 10
Low pass filter cutoff frequency GHz 0.6
A pseudo-random bit sequence (PRBS) initiator involves the transmitter and generates the modulation signal. The NRZ pulse generator has been utilized as low speed electrical coded. When setting the 10 GHz radio signal in the electric amplitude modulator as a baseband radio frequency converter. In this case, the frequency domain is given by the modulation format for amplitude shift keying (ASK). On the other hand, the radio frequency signal is modulated with subcarrier multiplexing, involving the setting of the carrier generator at 100 channels of the 10 MHz spacing channel at the 60 MHz first channel operated and the 10 GHz frequency of the sinewave signal generator. The 900 hybrid coupler is provided with these combined signals. A 900 hybrid coupler breaches the input signal into two output with 900 phase shift in the middle of each other. After that, the subcarrier radio signals of the hybrid coupler are came to the tow arm of LiNb Mach-Zehnder optical Modulator which modulate and adjust electrical signal to optical domain with continuous wave laser source has the yield power 10 dBm, linewidth of 10 MHz and 1550nm wavelength. In free space link, the transmitted signals are propagated over various lengths from 300m to 1km under different atmospheric turbulence conditions (gamma-gamma distribution model), weak ( and strong C2 = 5 x 1 0" 1 3 m" 2 /3 ) . Signals are processed on the receiver side of the APD photodiode used to transform optical signal to electrical signal with a 5-degree receiver gain, 0.9 A / W responsivity and 10 nA dark current. Subsequently, the subcarrier radio signal is transmitted at 10 GHz frequency and 1 GHz bandwidth through the electric band pass Bessel filter configuration. Radio signal demodulated by AM electric demodulator set to 10 GHz frequency and 0.6 GHz cut-off frequency after filter.
Results. Effects are simulated using version 10 of Opti system software. The transmission optical spectrum after the LiNb Mach-Zehnder optical modulator is shown in fig. 5. The Q-factor values vs. transmission distance are shown in fig. 6 (free space link from 300m to 1km) according to various atmospheric turbulence conditions (feeble
turbulence at C 2 = 5 x 1 0 " 1 5 m" 223 and strong turbulence at C 2 = 5 x 1 0" 1 3 m " 2 23 ) . At the same conditions, fig. 7 shown the values of bit error rate (BER) vs transmission distance. The evaluation system is depending of the special value of BER equal to 10-9.
1.5499 M 1.55 M 1.5501 м
Wavelength (m)
Fig. 5. optical spectrum at 1550nm wavelength after LiNb Mach-Zehnder optical
Modulator
11,676 il,: 244 10.715 —•—weak turbulence — — strong turbulence
9,979 8,902 9,785 —^9,133
8,3 j4 7,i 51 ^^^ 7 405 1 iridic™
s? ^Ш-4.739
.4.: tei
0,25 0,3 0,35 0,4 0,45 0,5 0,55 0,6 0,65 0,7 0,75 0,8 0,85 0,9 0,95 1 1,05
Transmission Distance Ian
Fig. 6. Q-factor vs transmission distance for (C 2 = 5x1 0 1 5 m 223) frail turbulence (Blue line) and C? = 5 x 1 0 " 1 3 m "2 23 ) sturdy turbulence (Green line).
Transmission Distance km
0,25 0,3 0,35 0,4 0,45 0,5 0,55 0,6 0,65 0,7 0,75 0,8 0,85 0,9 0,95 1 1,05
Fig. 7. BER vs transmission distance for (C^ = 5 x 1 0 1 5 m 2 23 ) frail turbulence (Blue line) and C2 = 5 x 1 0 " 1 3 m"223) sturdy turbulence (Green line)
Conclusion. We have proposed the subcarrier multiplexing/Amplitude Shift Keying transmitter system for radio over free space optical communication. Radio frequency, 10 GHz is modulated with the multiplexing portion of the subcarrier including the transporter generator and the sine wave signal. Free space optical channel under deferent atmospheric turbulence conditions weak and strong. The simulation system is reported that the maximum transmission distance for weak atmospheric turbulence is 950m at BER equal to 8.613*10-9 and Q-factor is 5.637. While the maximum transmission distance for strong atmospheric turbulence is 850m at BER equal to 2.284*10-9 and Q-factor is 5.862.
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Статью рекомендовал к опубликованию д.т.н., профессор О.И. Шелухин.
Hussein Ahmed Mahmood - Диялайский университет; e-mail: [email protected]; Дияла, Ирак; кафедра инженерных коммуникаций.
Al-Karawi Hussein Shookor - e-mail: [email protected]; кафедра инженерных коммуникаций.
Румянцев Константин Евгеньевич - Южный федеральный университет; e-mail: [email protected]; г. Таганог, Россия; тел.: 89281827209; д.т.н.; профессор.
Hussein Ahmed Mahmood - College of Engineering, University of Diyala; e-mail: [email protected]; Diyala, Iraq; the department of communications engineering.
Al-Karawi Hussein Shookor - e-mail: [email protected]; the department of communications engineering.
Rumyantsev Konstantin Yvgen'evich - Southern Federal University; e-mail: [email protected]; Taganrog, Russia; phone: +79281827209; dr. of eng. sc.; professor.
