According to the physical phenomena of atmospheric channels and wave propagation, performance of wireless communication systems can be optimized by simply adjusting its parameters. This way is more economically favorable than consuming power or using processing techniques. In this paper for the first time an optimization problem is developed on the performance of free-space optical multi-input multi-output (FSO-MIMO) communication system. Also it is the first time that the optimization of FSO is developed under saturated atmospheric turbulences. In order to get closer to the actual results, the effect of pointing error is taken into considerations. Assuming MPSK, DPSK modulation schemes, new closed-form expressions are derived for Bit Error Rate (BER) of the proposed structure. Furthermore, an optimization is developed taking into account the beam width as the variable parameter, and BER as the objective function, there is no constraint in this system. The obtained results can be a useful outcome for FSO-MIMO system designers in order to limit effects of pointing error as well as atmospheric turbulences and thus achieves optimum performance.
Deep Dive into A new optimization problem in FSO communication system.
According to the physical phenomena of atmospheric channels and wave propagation, performance of wireless communication systems can be optimized by simply adjusting its parameters. This way is more economically favorable than consuming power or using processing techniques. In this paper for the first time an optimization problem is developed on the performance of free-space optical multi-input multi-output (FSO-MIMO) communication system. Also it is the first time that the optimization of FSO is developed under saturated atmospheric turbulences. In order to get closer to the actual results, the effect of pointing error is taken into considerations. Assuming MPSK, DPSK modulation schemes, new closed-form expressions are derived for Bit Error Rate (BER) of the proposed structure. Furthermore, an optimization is developed taking into account the beam width as the variable parameter, and BER as the objective function, there is no constraint in this system. The obtained results can be a use
ue to the considerable demand for capacity and data rate in the next generation communication systems, communicating over the optical domain, the so called FSO system, with unlimited, unlicensed spectrum, has been proposed as an alternative for conventional wireless systems. FSO system hardware can support multiple Gsps, and typically uses pulse-based modulations, such as on-off-keying (OOK) or pulse position modulation (PPM) [1]. One of the well-known modulations used in FSO systems is subcarrier intensity modulation (SIM), which does not need adaptive threshold detection and is more rugged to the atmospheric turbulences and provides satisfactory performance. This modulation leverages on advances made in signal processing as well as revolution of Radio Frequency (RF) devices such as highly selective filters and stable oscillators, and permits the use of modulation techniques such as phase shift keying (PSK) and quadrature amplitude modulation (QAM) [2].
FSO system has important role in the architecture of hybrid wireless-communications, due to its feasibility in last-mile access, service acceleration, metro network extensions, enterprise connectivity, backup and backhaul links. In the urban environments, the FSO transreceiver should be mounted on high buildings to obtain a Line of Sight (LOS). The availability of a LOS is affected by transreceiver misalignment, which is called pointing error. Also intensity fluctuations caused by atmospheric turbulence, degrades FSO system performance. Mitigate the effects of pointing error and atmospheric turbulence is an important issue in design of FSO system. Which can be done by appropriately adjusting system parameters or using the efforts of multi-input multi-output (MIMO) scheme [3].
Transreceiver misalignment can be caused by winds, thermal expansions, and earthquakes. Under the influence of wind, high-rise buildings sway in three directions of along wind, across wind, and torsional. Transreceiver misalignment is a random process that affects system performance by means of the pointing error [4].
Even at clear weather, FSO system is uncounted with atmospheric turbulence. This effect is like fading in RF system and causes random fluctuations in signal intensity [5]. Following statistical models have been developed to investigate this effect; Exponential-Weibull [6], Generalized Malaga [7], Log-normal [8], Gamma-Gamma [9], and Negative Exponential [10]. Among them Negative Exponential model has high accompany with experimental results for saturated atmospheric turbulence.
Recently, some investigations were developed on the optimization of FSO system. A minimization model for transmitter power and optimization model for divergence angle in a given Bit Error Rate (BER) are developed in [4]. However, it has not provided closed-form expressions. Two optimization models for FSO systems are presented in [3] based on [4], and wavelength is taken as varying parameter. A FSO system in atmospheric turbulence and pointing error is considered in [11], beam width, pointing error variance, and detector size are taken into account; lognormal and gamma-gamma atmospheric turbulences are considered. The BER expression for an intensity-modulation/direct detection (IM/DD) FSO system in strong atmospheric turbulence and pointing error is derived in [12]. [13] assumed IM/DD in the general model of misalignment given in [11]. It did not consider any atmospheric turbulence effects.
In this paper a FSO-MIMO communication system is investigated under the effect of saturated atmospheric turbulence with pointing error. To the best of the authors’ Mohammad Ali Amirabadi, and Vahid Tabataba Vakili A new optimization problem in FSO communication system D knowledge, it is the first time an optimization model is developed over FSO-MIMO systems, also it is the first time that saturated atmospheric turbulence is considered in an FSO optimization problem. Assuming MPSK, DPSK modulation schemes, new closed-form expressions are derived for BER of the proposed structure. Furthermore, an optimization is developed taking into account the beam width as the variable parameter, and BER as the objective function, there is no constraint in this system.
Consider a FSO system with N transmit and M receive apertures, where ๐ฅ is the transmitted signal by all transmit apertures over one time slot. After optical-to-electrical conversion, the received electrical signal at ๐ -๐กโ, ๐ = 1, . . , ๐ receive aperture, becomes as follows:
where ๐ ๐ , additive white Gaussian noise (AWGN), is zero mean and ฯ 2 variance; I i,j
โฒ is irradiance of the link between the ๐ -๐กโ, ๐ = 1, . .
(
Because pointing error and atmospheric turbulence affect the LOS, received power is obtained by multiplying the transmitter power (P T ), transmitter and receiver telescope gains (G T , G R ), and losses and is given as:
where โ is the random variable indicating pointing error, ฮท T is the optical efficiency of the transmitter and ฮท R is
…(Full text truncated)…
This content is AI-processed based on ArXiv data.
