Abstract
In this paper, we investigate the so-called noise propagation effect in a mixed radio-frequency/ free-space optical (RF/FSO) amplifying-and-forwarding (AF) relaying system that is applied for data transmission in wireless sensor networks. The noise propagation could be essentially severe when battery-charged sensor nodes have very limited transmit power. We provide an exact expression on the cumulative distribution function (CDF) of end-to-end signal-to-noise power ratio (SNR) for a dual-hop mixed RF/FSO AF relaying system. We assume a tightly power-constrained amplifying gain at the relay, which has been usually ignored in existing performance studies for the mixed RF/FSO AF system. It however should be considered to properly evaluate the noise propagation effect especially if the relaying power is not infinite or the sensor has a poor budget in transmit power. We apply the derived exact CDF to evaluate the system performances such as outage probability, average bit-error rate, and ergodic capacity. Numerical investigation is used to justify that the proposed analysis is exactly matched with the simulation and shows that the performance gap caused by the inclusion of the noise propagation effect is significant (about 2–12%) especially when the SNR per hop is in the medium- or the low-SNR ranges (i.e., at 10–20 dB).
Highlights
Increasing demand for deploying wireless sensor nodes usually raises battery and spectrum issues.An idea of reducing battery consumption in sending the sensed data is to put a relay node, which is charged, between the sensors and the data sink
Numerical investigation is used to justify that the proposed analysis is exactly matched with the simulation and shows that the performance gap caused by the inclusion of the noise propagation effect is significant especially when the signal-to-noise power ratio (SNR) per hop is in the medium- or the low-SNR
Since wireless sensors normally exchange the data through RF channels, to mitigate a spectrum burden between the relay and the data sink, free-space optical (FSO) communication is considered in this paper
Summary
Increasing demand for deploying wireless sensor nodes usually raises battery and spectrum issues. In the dual-hop AF systems, the signal from the source received at the relaying node after suffering from a fading channel is amplified with gain G. For mixed RF/FSO systems, many works have been done to provide statistical analysis of γe that mainly determines the system performance including outage probability (OP), average bit-error rate (BER) and ergodic capacity, etc. The performance evaluated with the approximate SNRs usually ignores the noise propagation effect in an AF relay system. Mixed RF/FSO AF relaying application in wireless sensor networks should be adequately evaluated by including the noise propagation effect. In [7] and [10], more generalized settings are used for modeling the fading channels but, to the best of our knowledge, no existing works have provided the exact statistical analysis of the mixed RF-FSO AF system with the power-constrained variable amplifying gain. Though the performance gap diminishes to around 1% if the SNR is greater than 30 dB, the exact analysis seems greatly important in the medium- or the low-SNR ranges
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