An optimization problem on the performance of FSO communication system

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

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

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

Performance analysis of a novel hybrid FSO / RF communication system

In this paper, a novel dual-hop relay-assisted hybrid Free Space Optical / Radio Frequency (FSO / RF) communication system is presented. In this structure an access point connects users within the building to the Base Station via a hybrid parallel FSO / RF link, this link is proposed firstly. Parallel combination of FSO and RF links and use of an access point, will increase capacity, reliability and data rate of the system. It is the first time that the effect of number of users on the performance of a dual-hop relay-assisted hybrid parallel FSO / RF system is investigated. FSO link is considered in Gamma-Gamma atmospheric turbulence with the effect of pointing error and RF link is considered in Rayleigh fading. For the first time, closed-form expressions are derived for Bit Error Rate (BER) and Outage Probability (P_out) of the proposed system. Derived expressions are verified through MATLAB simulations. It is shown that the performance of the proposed system is almost independent of atmospheric turbulence intensity, thereby when atmospheric turbulence strengthens, low power consumption is required for maintenance of the system performance. Hence the proposed structure is particularly suitable for mobile communication systems in which a small mobile battery supplies transmitter power. Also the proposed system performance of the system is preferable even at low signal to noise ratio (SNR). Therefore, proposed structure significantly reduces power consumption while maintaining performance of the system.Comment: 8 pages, 5figue

Performance of a Relay-Assisted Hybrid FSO/RF Communication System

This paper investigates performance of a relay assisted hybrid Free Space Optical / Radio Frequency (FSO/RF) communication system. The proposed structure is particularly recommended anywhere that direct RF communication between mobile users and base station is not possible due to atmospheric conditions. In this system, a multiuser RF link connects mobile users to relay and a FSO link connects relay to the base station. It is the first time that effect of number of users within the cell, on the performance of such structure, is investigated. Also it is the first time that performance of a dual hop hybrid FSO / RF system is investigated in Negative Exponential atmospheric turbulence. Considering wide range of atmospheric turbulence regimes, from moderate to saturated, for the first time, closed-form expressions are derived for Bit Error Rate (BER) and outage probability (P_out) of the proposed structure. MATLAB simulations verified accuracy of the derived expressions. Considering fixed and adaptive gain amplify and forward protocols at relay, it is shown that adaptive gain relay is less sensitive to the number of users within the cell. It is also shown that fixed gain relay, despite its low complexity, has better performance; because its gain is adjusted such that the performance be favorable even at the worst case scenario

Performance Comparison of two novel Relay-Assisted Hybrid FSO / RF Communication Systems

In this manuscript, two novel multi-hop relay-assisted hybrid Free Space Optical / Radio Frequency (FSO / RF) communication systems are presented and compared. In these structures, RF and FSO links, at each hop, are parallel and send data simultaneously. This is the first time that in a multihop hybrid FSO / RF structure, Detect and Forward protocol is used. In the first structure, at each hop, received signals with higher Signal to Noise Ratio (SNR) is selected. But in the second structure, at each hop, received FSO and RF signals are separately detected and forwarded and selection is done only at the last hop. Considering FSO link in Negative Exponential atmospheric turbulence and RF link in Rayleigh fading, for the first time, closed-form expressions are derived for Outage Probability (P_out) and Bit Error Rate (BER) of the proposed structures. MATLAB simulations are provided to verify derived expressions. The main motivation of this work is to answer this question that how much is the difference of selection at each hop and selection at the last hop. Results indicate that the structure with selection at each hop has better performance than the structure with selection at the last hop. At different target Outage Probability, selection at the last hop consumes about two times (~3dB) more power than selection at each hop. Both structures are particularly suitable for long-range communications. However, selection at each hop, in the cost of more complexity, is recommended for applications which have problem with supplying the required power for communication

New expressions on the performance of a novel multi-hop relay-assisted hybrid FSO / RF communication system with receive diversity

In this paper a novel multi-hop relay-assisted hybrid Free Space Optical / Radio Frequency (FSO / RF) communication system is presented, in which a mobile user is connected to the Base Station via a multi-hop relay-assisted hybrid FSO / RF link with receive diversity. In this structure, received signal at each relay is demodulated and forwarded. This is the first time that in a multi-hop hybrid FSO / RF system, receive diversity is used. Bit Error Rate (BER) and Outage Probability (P_out) are investigated as system performance criteria. New exact and asymptotic expressions are derived for these criteria, and MATLAB simulations are provided to verify the obtained results. For the first time impact of number of receive antennas and number of relays on the performance of such a structure is investigated. Results indicate that proposed structure has low dependence on number of receive antennas; therefore, in the proposed structure use of single receive antenna has the same performance as the multi-antenna, while low complexity and power consumption. The proposed structure shows independent performance at moderate and strong atmospheric turbulence regimes. Hence, it does not require adaptive processing to match itself according to atmospheric turbulence condition, therefore is cost effective and particularly suitable for urban areas that encounter frequent changes in atmospheric turbulence.Comment: arXiv admin note: text overlap with arXiv:1806.02597, arXiv:1806.0226

Performance analysis of hybrid FSO/RF communication systems with Alamouti Coding or Antenna Selection

In this work a novel dual-hop relay-assisted hybrid Free Space Optical / Radio Frequency (FSO / RF) communication system is presented. In this system, RF signal is transmitted from two antennas, and then forwarded by a single antenna relay through FSO channel. This is the first time that performance of using Alamouti Coding (AC) or Antenna Selection (AS) at the transmitter of a hybrid FSO / RF system is investigated. FSO link has Gamma-Gamma atmospheric turbulence, and in order to get closer to the actual results, the effect of pointing error is also considered. For the first time closed-form expressions are derived for Bit Error Rate (BER) and Outage Probability of the proposed system and validated through MATLAB simulations. Results indicate that in this structure, there is slight performance difference between AC and AS schemes. Hence due to more complexity, power consumption and latency of AC, AS is recommended. Dual-hop, hybrid FSO / RF system significantly improves performance and reliability of the system, and is particularly suitable for long-range applications that direct RF communication between source and destination is not possible. Considering these advantages this structure is particularly suitable for mobile communications which has power and processing limitations

New expression on the performance of a novel multi-hop relay-assisted hybrid FSO / RF communication system

In this paper a novel multi-hop relay-assisted hybrid FSO / RF system is presented. It is assumed that direct RF connection between mobile users and source Base Station is impossible, therefore a relay connects RF users to the source Base Station via a FSO link. Source and destination Base Stations are connected via a multi-hop relay-assisted hybrid FSO / RF link. FSO link is investigated over moderate to saturate regimes of atmospheric turbulence. Also RF link is assumed to have Rayleigh fading. For the first time, new exact and asymptotic expressions are derived in closed-form for Bit Error Rate (BER) and the Outage Probability (P_out), of the proposed system. MATLAB simulations are performed to validate obtained analytical results. Results indicate that the proposed structure has low dependence on the number of users, therefore, the proposed structure is suitable for cells which encounter different populations during a day, because there is little performance difference between systems with different number of users. Also the proposed structure, at Negative exponential atmospheric turbulence has small dependence on the number of relays, but this dependence is a bit more for Gamma-Gamma atmospheric turbulence. Therefore, the proposed structure increases capacity whereas maintaining performance of the system

A new fast approach for an EEG-based Motor Imagery BCI classification

Nowadays, Brain Computer Interface has an important role in the life quality of parallelized people. However, this technique is mainly affected by the quality of the recorded signal in each trial. This problem could be solved by rejecting low-quality trials. But developing the processing based on the recorded signal from the brain, which is a mixture of the target signal plus noise and artifact, would not be favorable in situations that all trials have low quality. This paper solves this problem by presenting a new fast algorithm for separating recorded source signals. Results indicate the improvement in classification accuracy of the proposed method compared with the classification accuracy of processing on the recorded mixture signal

On the Performance of a Relay-Assisted Multi-Hop Asymmetric FSO/RF Communication System over Negative Exponential atmospheric turbulence with the effect of pointing error

In this paper, a multi-user multi-hop hybrid FSO / RF system is presented. This structure is consisted of two main parts. The main motivation of presenting this structure is communication in long-range impassable links or some specific atmospheric conditions under which RF connection becomes easily disrupted. Although these effects could be mitigated by consuming more power or adding processing complexity, but a small user mobile phone cannot deserve more complexity or power supply. The fact that FSO and RF links are complementary of each other brings a new solution in mind; an access point that amplifies received signal via short-range RF link and forwards it to via long-range FSO link, could solve the mentioned problem. This scenario is exactly implemented at the first part of the proposed structure. At the second part, a multi-hop hybrid parallel FSO / RF link is implemented to connect source and destination Base Stations. It is the first time that in a multi-hop FSO / RF system, multi-user scheme, signal selection at each hop, known and un-known CSI in amplify and forward relaying, and saturate atmospheric turbulence with the effect of pointing error are considered. New expressions are derived in closed-form for Bit Error Rate (BER) and Outage Probability of the proposed structure and verified by MATLAB simulations. The proposed structure has advantages of FSO, RF, relay-assisted, and multi-user systems at the same time. Results indicate that it has low dependence on number of users and number of relays. Therefore, it is suitable for areas with varying population and long-range links. This structure offers independent performance without additional power consumption, processing latency, and complexity.Comment: arXiv admin note: substantial text overlap with arXiv:1806.0226