Abstract
In this paper, the simulative analysis of an inter-aircraft optical wireless communication (IaOWC) system has been presented using different system parameters and the performance of the system has been enhanced by the application of EDFA amplifier at the receiver end. A link range of 110 km at 2.5 Gbps has been achieved with same BER performance resulting in the performance enhancement of 47 % when compared to previous detection mechanism.
1 Introduction
The traditional inter-aircraft communication system makes use of microwave communication technology for the purpose of space to ground communication. But in the future, though the space to ground links would keep using microwave communication technology, the inter-aircraft communication would be implemented by optical wireless communication (OWC) links [1]. OWC technology has the capability of transmitting the information data at very high speeds of the order of Gbps and at a link distance of thousands of miles. These achievements have resulted in the development of the idea of implementing OWC technology in aircraft communication. As a result, inter-aircraft optical wireless communication (IaOWC) technology has been developed. OWC technology requires clear line-of-sight (LOS) between the transmitter and the receiver [2]. Due to the high probability of blocking the LOS due to the presence of clouds, it is desired to have multiple redundant information transmission pathways for a reliable information transmission system. The introduction to the building blocks of an OWC system with high channel bandwidth capacity namely, the optical communication terminals for airborne application have been introduced in Ref. [3]. In Ref. [4], the plan for development and implementation of optical wireless technique with high data transmission speeds from satellite/aircraft is presented. A brief introduction to the present communication technology in military application and the importance of terrestrial OWC links is presented in Ref. [5]. The performance enhancement of inter-satellite OWC links using EDFA amplifier has been presented in Ref. [6]. Rest of the paper is organized as follows. In Section 2, the system description and simulation parameters are presented. Results are presented and discussed in Section 3. The final conclusion is drawn in Section 4.
2 System design and description
The IaOWC communication system consists of three main sections: the transmitter section, the propagation channel and the receiver section as presented in Figure 1, where the first aircraft acts as a transmitter and the second aircraft acts a receiver. The propagation medium for information signal between the two aircrafts is the free air/space. The information from the aircraft air traffic control system (ATC) is directed toward the aircraft transmitter. The electrical signal produced by the ATC system is then modulated with the continuous wave optical signal from CW laser operating at 1,550 nm wavelength using Mach–Zehnder Modulator (MZM) and is finally transmitted in the free air. The information signal in the form of light pulses travels through the free air and is then received by the second aircraft antenna using coupling optics. The signal is then coupled to an EDFA amplifier which amplifies the received signal and is then directed toward APD which converts the optical signal to electrical signal and is then followed by LPF to remove high-frequency noise. Simulation parameters are presented in Table 1.
A model of inter-aircraft optical wireless communication system.
Simulation parameters.
| Serial No. | Parameter | Value |
|---|---|---|
| 1. | Transmission length (km) | 80 |
| 2. | Operating wavelength (nm) | 1,550 |
| 3. | Transmitting power (mW) | 60–100 |
| 4. | Aperture diameter (cm) | 15 |
| 5. | Beam divergence (mrad) | 0.25 |
| 6. | Attenuation (dB/km) | 0.4–0.8 |
| 7. | Transmitting pointing error (urad) | 1 |
| 8. | Additional losses (dB) | 1 |
3 Results and discussion
In this paper, simulative analysis of an IaOWC system has been performed using different simulation parameters such as transmitting power levels, attenuation levels, and transmitting pointing error. Also, performance enhancement of IaOWC system has been shown using EDFA amplifier at the receiver end.
3.1 Simulative analysis of IaOWC communication system
Figure 2(a) and 2(b) shows the SNR and total power of received signal for varying link distances using different transmission power levels respectively. From Figure 2(a) and 2(b) it is observed that SNR value of received signal at second aircraft reduces from 77 dB to 10 dB and total received power reduces from –12 dBm to –80 dBm in the range of link distance 20–75 km between the two aircrafts when the transmission power level is 100 mW. Also, SNR value reduces from 75 dB to 10 dB and total received power reduces from –15 dBm to –80 dBm in the range of link distance 20–70 km between the two aircrafts when the transmission power level is 60 mW. Alternatively, SNR value reduces from 65 dB to 10 dB and total received power reduces from –25 dBm to –80 dBm in the range of link distance 20–65 km between the two aircrafts when the transmission power level is 20 mW. This shows that as the transmission power level in an IaOWC system is increased, the link range between the two aircrafts increases.
(a) SNR v/s range for different values of transmission power levels, (b) Received Power v/s range for different values of transmission power levels.
Figure 3(a) and 3(b) shows the SNR and total power of received signal for varying link distances using different attenuation levels respectively. From Figure 3(a) and 3(b) it is observed that SNR value of received signal at second aircraft reduces from 72 dB to 10 dB and total received power reduces from –14 dBm to –80 dBm in the range of link distance 20–75 km between the two aircrafts when the attenuation level is 0.4 dB/km. Also, SNR value reduces from 64 dB to 10 dB and total received power reduces from –25 dBm to –80 dBm in the range of link distance 20–55 km between the two aircrafts when the attenuation level is 0.6 dB/km. Alternatively, SNR value reduces from 58 dB to 10 dB and total received power reduces from –32 dBm to –80 dBm in the range of link distance 20–40 km between the two aircrafts when the attenuation level is 0.8 dB/km. This shows that as the attenuation level in an IaOWC system is increased, the link range between the two aircrafts decreases.
(a) SNR v/s range for different attenuation values, (b) Received power v/s range for different attenuation values.
Figure 4(a) and 4(b) shows the SNR and total power of received signal for varying link distances using different transmitter pointing error respectively. From Figure 4(a) and 4(b) it is observed that SNR value of received signal at second aircraft reduces from 76 dB to 10 dB and total received power reduces from –15 dBm to –80 dBm in the range of link distance 20–75 km between the two aircrafts when the transmitter pointing error is 1 urad. Also, SNR value reduces from 64 dB to 10dB and total received power reduces from –27 dBm to –80 dBm in the range of link distance 20–70 km between the two aircrafts when the transmitter pointing error is 3 urad. Alternatively, SNR value reduces from 55 dB to 10 dB and total received power reduces from –35 dBm to –80 dBm in the range of link distance 20–55 km between the two aircrafts when the transmitter pointing error is 5 urad. This shows that as the transmitting pointing error in an IaOWC system is increased, the link range between the two aircrafts decreases.
(a) SNR v/s range for different transmitter pointing error, (b) Received power v/s range for different transmitter pointing error.
3.2 Enhanced performance analysis of IaOWC communication system
In this paper, the performance of an IaOWC system has been enhanced using EDFA as a pre-amplifier at receiver end in order to increase the link range between the two aircrafts. In Figures 5 and 6 the SNR and total power of the received signal in an IaOWC communication system for varying transmission range are plotted respectively.
SNR v/s range with and without EDFA amplifier.
Received power v/s range with and without EDFA amplifier.
From Figure 5 it can be seen that the SNR value of received signal lies in the range 75 dB to 10 dB in the range of 20–110 km with implementation of EDFA amplifier at the receiver end. Alternatively, the SNR value of received signal lies in the range of 72 dB to 10 dB and in the range of 20–70 km without the implementation of EDFA amplifier. Also from Figure 6 it can be seen that the total power of the received signal reduces from –16 dBm to –84 dBm for link distance varying from 20 to 120 km without the implementation of EDFA amplifier. Alternatively, the total power of the received signal reduces from 19 dBm to –54 dBm for a link distance varying from 20 to 120 km with the implementation of EDFA amplifier at the receiver end. The above results show that by using EDFA amplifier, the performance of IaOWC system is improved which further helps in increasing the link distance between the two aircrafts in an IaOWC communication system. Figure 7 depicts the eye diagram of received signal in an IaOWC communication system without amplifier having a Q-factor of 5.74 and BER value of 4.51 e-009 at a bit rate of 2.5 Gbps for 75 km transmission distance. Figure 8 depicts the eye diagram of received signal with EDFA amplifier having a Q-factor of 5.11 and BER value of 1.34 e-009 at a bit rate of 2.5 Gbps for 110 km transmission distance.
Eye diagram of received signal in an IaOWC system at 75 km without EDFA amplifier.
Eye diagram of received signal in an IaOWC system at 110 km with EDFA amplifier.
4 Conclusion
In this paper, the modeling of an IaOWC system with and without EDFA amplifier at receiver end has been done and simulative analysis of IaOWC system has been performed using different system parameters and enhanced performance of the system has been reported by implementing EDFA as a pre-amplifier at the receiver end of an IaOWC system at 2.5 Gbps data rate. Hence by using EDFA amplifier, enhancement in the performance of IaOWC system can be achieved which further helps in increasing the link distance between the two aircrafts.
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