Optical Wireless Security

By: Lightpointe Communications

Optical Wireless Systems and Network Security

With its cost-effective and high-bandwidth qualities, optical wireless products operating in the near infrared wavelength range are an alternative transport technology to interconnect highcapacity networking segments. These optical wireless products, based on free-space optics (FSO) technology, are license-free worldwide. Optical wireless system installations are very simple, andthe equipment requires very little maintenance. These features make optical wireless solutions appealing to end-users and service providers globally. As a result, the number of optical wireless system installations to for enterprise, cellular, and metropolitan area network traffic demands has increased significantly—even during the recent telecommunications sector slowdown.

Because optical wireless systems send and receive data through the air between remote networking locations, network operators and administrators are naturally concerned about thesecurity aspects. One of the main reasons for this concern is based on the fact that wireless networking solutions is a category in which security and interference problems are very common in radio frequency (RF) or microwave-based communication systems. Such concerns are not valid for optical wireless systems.

Optical wireless systems operate in the near infrared wavelength range slightly above the visible spectrum. Therefore, the human eye cannot visibly see the transmission beam. Thewavelength range around 1 micrometer that is used in optical wireless transmission systems is actually the same wavelength range used in fiber-optic transmission systems. The wavelength range around 1 micrometer translates into frequencies of several hundred terahertz (THz). These frequencies are significantly (roughly three to four orders of magnitude) higher than the highest frequencies used in commercially available microwave communications systems operating around 40 GHz. This difference in frequency of operation is one of the main reasons whyoptical wireless systems belong into the equipment category of optical communication systems first rather than wireless, RF or microwave, transmission solutions. While typical RF and microwave antennas used to interconnect two remote networking locations in a point-to-pointarchitecture spread out the radiation over angles between 5 and 25 degrees, optical wireless systems use very narrow beams that are typically much less than 0.5 degrees. For example, aradial beam pattern of 10 degrees roughly corresponds to a beam diameter of 175 meters at a distance of 1 kilometer from the originating source, whereas a beam of 0.3 degrees divergence angle typically used in optical wireless systems corresponds to a beam diameter of 5 meters atthe same distance.1 This wide spreading of the beam in microwave systems, combined with the fact that microwave antennas launch very high power level is the primary reason for security concerns.

An outside intruder can easily intercept the beam or power reflected from the target location and pick up sensitive network information by using a “spectral scanner" tuned tothe specific RF or microwave transmission frequency. To overcome these security concerns, the microwave industry uses wireless encryption protocols (WEP) to protect the transmission path from being intercepted. Although it is extremely unlikely that it is possible to break into a sophisticated encryption code, there is always the concern that it can be done.

The interception of optical wireless systems operating with narrow beams in the infrared spectral wavelength range is far more difficult. In fact, military organizations or governmententities that rely heavily on extremely secure transmission technologies were among the earliestusers of optical wireless communication systems as a way to avoid signal interception. Therefore,it is understandable why the study of FSO technology in military labs and security agencies dates back several decades. In the early days of FSO development, the ability to transmit information at high data rates was actually a less important factor than the fact that FSO technologiesoffered one of the easiest and most secure ways to exchange information between remote locations. The small diameter of the beam of typically only a few meters in diameter at the target location is one of the reasons why it is extremely difficult to intercept the communication path of an FSO-based optical wireless system: The intruder must know the exact origination or target location of the (invisible) infrared beam and can only intercept the beam within the very narrow angleof beam propagation. Even more difficult, the intruder must have free and undisturbed access to the installation location of the optical wireless transceiver and be able to install electronic equipment without being observed. In the majority of cases, the installation location does not allow free access to a potential intruder because the installation location is part of the customerpremise such as the roof or an office (when optical wireless equipment is installed behindwindows).

The direct interception of an optical wireless beam between the two remote networking locations is basically impossible because the beam typically passes through the air at an elevation well above ground level. Due to the fact that the transmission beam is invisible and that any attempts to block the beam would occur near the optical wireless equipment terminus points, the transmission process imposes another obstacle. Picking up the signal from a location thatis not directly located within the light path by using light photons scattered from aerosol, fog, or rain particles that might be present in the atmosphere is virtually impossible because of the extremely low infrared power levels used during the optical wireless transmission process. Themain reason for excluding this possibility of intrusion is the fact that light is scattered isotropicallyand statistically in different directions from the original propagation path. This specific scattering mechanism keeps the total number of photons or the amount of radiation that can potentiallybe collected onto a detector that is not directly placed into the beam path well beyond the detector noise level

SummaryOptical wireless communication systems are among the most secure networking transmission technologies. Unlike microwave systems, it is extremely difficult to intercept the optical wireless light beam carrying networking data because the information is not spread out in space but rather kept in a very narrow cone of light. To intercept this invisible light beam, the intruder must be able to obtain direct access to the light beam. Due to the very narrow beam diameter, interception of the beam can virtually only be accomplished at the customer premise where the system is installed. At that point, it would be certainly easier for an intruder to plug directly into the network by using the existing copper-based infrastructure (e.g. unplug a CAT 5 networking cable and plug it into a laptop). Scattered light can not be used as a method of interception.Moreover, higher protocol layers can be used in conjunction with layer one optical wireless physical transport technology to encrypt sensitive network information and provide additional.

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