Hybrid Microwave and Free Space Optics Network for Mobile Backhaul Capacity and Availability Improvement
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Date
2023-06
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Addis Ababa University
Abstract
With the growing demand for high speed mobile data and the increasing use of smart devices, the existing microwave (MW) or radio frequency (RF) backhaul network is going to be a bottleneck for end users data volume requirements. Additionally, the performance of the MW link is significantly degraded by bad weather conditions, such as rain. To mitigate these limitations, free space optics (FSO) becomes a promising backhaul technology due to its large bandwidth and use of a different carrier frequency that is not impacted by rain. However, FSO is exposed to link loss or failure under foggy weather conditions, whereas MW links are prone to fog. Having this complementary advantage of FSO and RF, using hybrid FSO/RF networks is a preferred solution to improve the availability of the link and the capacity of backhaul networks.
In this paper, an adaptive switching hybrid FSO/RF system is used to improve the performance of the hard switching scheme, which is exposed to link flapping due to short-term changes in weather conditions. The switching threshold of the FSO and RF links and multi-rate switching on each link are determined, and the availability and capacity performance of the hybrid system are investigated based on received signal-to-noise ratio (SNR) values. To meet the objective, the methodology followed includes data collection, system and channel modeling, and RF, FSO, and hybrid performance comparison. The system used gamma gamma distribution for the FSO channel and the Rician model for the RF channel model.
Simulation results are obtained using the Matlab tool. The effects of rain and fog on the RF and FSO links are simulated and discussed, respectively. The availability of the system in terms of outage probability shows that the hybrid system significantly reduces the SNR value to 14 dB to achieve 99.99% link availability, which is not achieved by an RF-only or FSO-only link. The result also shows that adaptive switching mode has a better bit error rate (BER) than hard switching mode since the switching of links between FSO and RF and switching between multi rates on each link is based on maintaining target BER. To maintain good quality of service (QoS), the target BER of the system is set, and the system gradually lowers its modulation order to the maximum possible data rate based on received SNR values.
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Keywords
FSO, RF, Hybrid FSO/RF, Adaptive Switching, Backhaul Network, Outage Probability, BER, Rician distribution, Gamma Gamma distribution