Browsing by Author "Lee, I. E."

Now showing 1 - 3 of 3

Metadata only
Capacity analysis of free space optical links for a partially coherent gaussian beam over a turbulent channel with pointing errors
(IEEE, 2013) Lee, I. E.; Ghassemlooy, Z.; Ng, W. P.; Khalighi, M. A.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
In this paper, we investigate the joint effects of beam width and the spatial coherence length in a partially coherent free-space optical (FSO) link from the information theory perspective, taking into account the combined influence of atmospheric turbulence and pointing errors. In addition, the effects of aperture-averaging on the average capacity of FSO links employing partially coherent beams (PCBs) are examined. Results show that PCBs are desirable in the weak-to-moderate turbulence regime, whereas highly coherent laser sources are preferred under strong fluctuations conditions; and there exist optimality in the optical beam parameters for different atmospheric channel conditions. Near-optimal average capacity is best achieved through the introduction of a larger receiver aperture and the joint beam width and spatial coherence length optimization technique, which effectively mitigates the effects of scintillation and pointing errors.
Metadata only
Performance analysis of free space optical links over turbulence and misalignment induced fading channels
(IEEE, 2012) Lee, I. E.; Ghassemlooy, Z.; Ng, W. P.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
The performance of free-space optical (FSO) communication system is investigated from the information theory perspective, under the influence of atmospheric loss and channel fading due to the turbulence and pointing error. The outage probability and average channel capacity of the FSO link are evaluated using a combined slow-fading channel model and a Gaussian beam wave model, unlike the limiting Rytov-based scintillation model considered in earlier work. Taking into account various link design criteria, our study reveals that lower outage probability can be achieved with larger receiver aperture due to the aperture averaging effect. Optimization of the capacity metrics is best performed through proper selection of the aperture size and beam width for known laser wavelength, particularly for long-distance links and strong turbulence scenarios. Hence, findings and results from our analysis can be treated as the design benchmark for optimal planning and deployment of optical links.
Metadata only
Practical implementation and performance study of a hard-switched hybrid FSO/RF link under controlled fog environment
(IEEE, 2014) Lee, I. E.; Ghassemlooy, Z.; Ng, W. P.; Gourdel, V.; Khalighi, M. A.; Zvanovec, S.; Uysal, Murat; Electrical & Electronics Engineering; UYSAL, Murat
The availability and performance of terrestrial free-space optical (FSO) communication systems are heavily deterred by the fluctuating conditions of the atmospheric channel, particularly in the presence of visibility-limiting fog effects. In this paper, we examine the viability of deploying hybrid FSO and radio frequency (RF) links through an experimental study, which takes advantage of a dedicated laboratory atmospheric chamber to emulate the fog scenarios encountered on outdoor environment. In particular, a root mean square power detector is developed and introduced in the system under study to monitor the signal quality of the primary FSO link. The quasi-linear output voltage characteristics of the power detector device is utilized as a useful decision metric to implement hard switching in a hybrid FSO/RF link based upon the changes in the visibility. Our measurement results reveal that the selection of a desirable threshold voltage is dependent upon the intended data rate and minimum achievable bit error rate, in order to enable effective switching between the FSO and RF links.