Performance of a relay-assisted hybrid FSO/RF communication system

2019

IET Optoelectronics

Self Cite

One of the main problems in mobile communication systems is the degradation of Radio Frequency (RF) connection when mobile user is far from base station. One way to solve this problem is to increase the transmitter power, but the mobile transmitter is not able to supply much power. Another way is to use a relay; among relay schemes, amplify and forward is better for long range communications. Amplify and forward relay is not affordable in terms of power consumption and performance, because it consumes a lot of power inefficiently and enhances the noise. Therefore, in other cases, except in the case of long range links, other relay protocols, such as decode and forward, as well as demodulate and forward, are preferable. In this paper, a novel multi-hop hybrid Free Space Optical (FSO) / RF link is presented; it is made up of two main parts. The first part establishes the connection between the mobile user and source base station, and the second part establishes the connection between the source and the destination base stations. In the first part, a mobile user wants to connect to the source base station via a long range link; therefore, a fixed gain amplify and forward relay with multiple receive antennas is used for communication establishment. In the second part, the source and the destination base stations are connected via a multi-hop hybrid parallel FSO / RF link with demodulate and forward relaying. Considering the FSO link in Gamma-Gamma atmospheric turbulence with the effect of pointing error in moderate to strong regime and the Negative Exponential atmospheric turbulence in saturate regime, and the RF link in Rayleigh fading, new closed form exact and asymptotic expressions are derived for the Outage Probability and Bit Error Rate of the proposed structure. Derived expressions are verified with MATLAB simulations. The results show that the performance of the proposed structure does not change with changing channel conditions; therefore, this structure is reliable and does not require more processing or power consumption in order to maintain system performance in poor channel conditions. Hence, the proposed structure is particularly suitable for mobile communications with limitations in power, processing and latency. The innovations and contributions of this paper, which are first introduced in the multi-hop hybrid FSO / RF hybrid structure, include the novelty of the proposed structure, the presentation of new exact and asymptotic mathematical solutions, the use of receive diversity, Bit Error Rate analysis, using amplify and forward as well as decode and forward protocols, taking into account a wide range of atmospheric turbulences with the effect of pointing error, using opportunistic selection and selection combining schemes.The atmospheric turbulence causes the random oscillation of the received signal intensity [5]. Many statistical models have been presented to investigate the effects of atmospheric turbulence including Log-Normal [6], Gamma-Gamma [7], K [8], M [9], and Negative Exponential [10]. Am...

Section: Related Workmentioning

confidence: 99%

“…The DPSK is of the most frequently used modulation formats in hybrid FSO / RF system. The BER of DPSK modulation can be calculated from the following equation [32]:…”

Section: Bit Error Ratementioning

confidence: 99%

Performance evaluation of a novel relay‐assisted hybrid FSO/RF communication system with receive diversity

2019

IET Optoelectronics

Self Cite

“…The so called hybrid FSO / RF systems are available in singehop [3,[5][6][7][8][9][10][11][12][13][14], dual-hop [15][16][17], and multi-hop [18][19][20] structures. Single-hop structure is more preferable for short range communications.…”

Section: Introductionmentioning

confidence: 99%

A novel hybrid FSO / RF communication system with receive diversity

2019

Optik

Self Cite

In mobile communication system, due to the limitations of mobile device such as low power supply as well as small size, most of the processing should be done at the Base Station. Using multi-receive structure at the Base Station really helps better recovery of the original signal by combining different received signals. In this paper, for the first time, receive diversity is used in single-hop hybrid Free Space Optical / Radio Frequency (FSO / RF) communication system. Also it is the first time that a single-hop hybrid FSO / RF system is investigated at saturate atmospheric turbulence regime. For the first time, closed-form expression is derived for Outage Probability of the proposed system and verified through MATLAB simulation. Results indicate a significant improvement in the performance of the proposed structure compared with common FSO and RF systems with receive diversity. Therefore it can be concluded that although the proposed structure requires a complex receiver, but addition of this complexity could significantly reduce processing or power consumption required for performance maintenance of the system.

“…However, it did not provide closed-form expressions. Taken into account beam width, pointing error variance, and detector size, an optimization on FSO system in Lognormal and Gamma-Gamma [14] atmospheric turbulences with pointing error is done in [13]. The BER expression for an IM/DD FSO system in strong atmospheric turbulence and pointing error is derived in [15].…”

Section: Introductionmentioning

confidence: 99%

A New Optimization Problem in FSO Communication System

2018

IEEE Commun. Lett.

Self Cite

Performance of Free Space Optical (FSO) communication system is affected by atmospheric turbulences and pointing errors. These effects can easily be mitigated by adapting natural system parameters such as wavelength. In this paper, considering effects of pointing error and atmospheric turbulence, two optimization models are presented on FSO communication system. In Model 1, the normalized transmitter power is objective function, Bit Error Rate (BER) is equality subjective. In Model 2 normalized transmitter power is equality subjective, the BER is objective function. In both of them the normalized wavelength is variable parameter. These models were previously investigated using numerical methods; in the sense that they were solved asymptotically. From this point of view, this paper regenerated these models and solved them by a completely different analytical method, and derived a new exact solution. Comparing exact and asymptotic methods shows some interesting results; the asymptotic method achieves BER=10 −9 , but the presented new exact method achieves BER=10 −13 , which is a significant difference. It means that even at the worst case scenario such as pointing error, it is possible to have a very good performance by only the transmitting wavelength a bit. Proposed models are practical and obtained results show that this system is cost and power effective.