On the Capacity of Hybrid FSO/RF Links

Abstract

Hybrid Free Space Optics (FSO)/Radio Frequency (RF) communication systems have emerged as a way to improve network performance by providing enhanced availability and reliability. In an effort to mitigate individual drawbacks in the optical link during adverse weather conditions, network traffic flows simultaneously between channels. Based on the Shannon-Hartley theorem, channel capacity is dependent, among others, on both the signal to noise ratio (SNR) and channel bandwidth. As such, combined link throughput may be affected by channel state conditions. Because atmosphere turbulence can be modeled as a time-varying fading channel, capacity analysis can be investigated. In this paper, authors apply various availability scenarios of channel state information (CSI) on the optical link to derive closed-form expressions for combined link capacity. Numerical simulation provides a comparison to the results.Keywords-Hybrid FSO/RF link, channel capacity, channel state information (CSI), reconfiguration, and lognormal fading.

Outage Performance of Hybrid FSO/RF System with Low-Complexity Power Adaptation

“…At the RF transmitter, the frequency of the digitally modulated electrical signal is up-converted using 60 GHz RF carrier 5 . The up-converted RF signal is transmitted and received using L branches RF transmission/reception scheme.…”

“…Power adaptation offers a simple and effective solution to improve link reliability and data throughput. Previous work on hybrid FSO/RF systems with power adaptation includes [5] and [6]. Particularly, [5] considers a hybrid FSO/RF system, in which the system switches to the reliable RF link to maintain communication in case that FSO link is obscured and applies water-filling power adaptation scheme on the FSO link only.…”

“…Previous work on hybrid FSO/RF systems with power adaptation includes [5] and [6]. Particularly, [5] considers a hybrid FSO/RF system, in which the system switches to the reliable RF link to maintain communication in case that FSO link is obscured and applies water-filling power adaptation scheme on the FSO link only. In [6], power adaptation has been applied on both FSO and RF links of the hybrid FSO/RF system, assuming that both links are active all the time, but transmitting with different rates.…”

“…(24)] is given byE[I] = ξ 2 A 0 h L /(ξ 2 + 1). For IM/DD FSO detection,γ F SO 2 = (ηeE[I]) 2 /N 0[15] 5. In case of using coherent RF subsystem in conjunction with coherent/heterodyne FSO subsystem, 60 GHZ carrier frequency is produced by an RF local oscillator which has excellent coherency.…”

Optical power allocation for adaptive transmissions in wavelength-division multiplexing free space optical networks

“…With negligible effect on data rates, a small portion of the bandwidth can be used for feedback of channel state information (CSI). In some hybrid RF/FSO systems, the RF channel can be used for CSI feedback [9]. Thus reliable CSI could be available in FSO systems, which will be highly useful for designing adaptive transmission schemes.…”