There have been great advances in WLC over the years, but a number of factors have limited the applications and deployments of the technology by first-to-market companies. The information below is a brief explanation of historical drawbacks to 1st generation products and how DLI's design and application approach to WLC technology differs. For a more detailed discussion on these issues, download the White Papers from the links provided on the right side of this page.
Short all-weather distances - Heavy fog has been the greatest limiting factor to WLC and is what has limited the terrestrial applications to relatively short distances compared to microwave radio. While the technology has great clear weather distance capability and outperforms microwave in rain (up to 6 in/hr), heavy fog limits its all-weather capability to approximately 500 meters. The reason heavy fog effects WLC so adversely is because the water particles that make up fog, scatter, absorb and attenuate the wavelengths (850 nm, 1550 nm) used by most commercial WLC systems. Research based on data collected by the National Weather Service (1950-2000) indicates WLC availability between 97.78% and 99.99% at a distance of one mile for the 64 largest cities in the U.S. However, availability significantly increases by reducing the transmission distance. When operated at 500-meters or less, the expected availability for these same cities improves dramatically, ranging from 99.92% to 99.999%.
Size and cost of equipment - Most of the first-to-market players trying to produce longer range carrier-class gear over-engineered and over-sized their hardware to great expense ($30K - $200K/system) with very little fog penetration improvements. The different product offerings ranged in size from 300 pound, 9 foot tall towers, to large bulky mailboxes that were heavy (45 lbs.) and difficult to install. Some vendor’s products are still over the OSHA weight standard for one man to carry on a ladder alone, thus requiring a coordinated two man ladder effort or a small lift to get the unit to the roof. Additionally, these over-sized products demand equally over-sized, high-dollar mounts in order to stabilize them from wind loads.
Cost and complexity of installation - Due to the fact that all competitive WLC products have their opto-electronics and other sensitive components inside the outdoor unit, a 110/220 volt rooftop power connection is required to operate the unit. This means that besides the WLC installer, a certified electrician must provide the appropriate power equipment and connection which can add several thousands of dollars worth of expense per site, as well as significant time delays due to permits and security clearances for roof top access. In more recent products, competitors have created systems that use Power-Over-Ethernet (POE). Though this is a step in the right direction, most of the switches currently in use do not support POE. Lastly, some WLC systems were so complex that they required very expensive tools and training (as high as $45K). This complexity contributed to contractor installation errors that led to unnecessary failures due to improper mounting and alignment. To help alleviate these issues and other mount movement problems, many vendors produced even more expensive systems that use active alignment technology.
DLI’s design and application approach - Instead of trying to build expensive long range (2 km - 15 km) equipment that cannot reliably transmit through the atmosphere, DLI set its sights on designing a robust short range (50m - 2km), low cost, easy to install product for the enterprise market with an eye towards building dense PtMP citywide networks for service providers. After 4 years of research and development, DLI made a fundamental breakthrough in optical propagation that enabled it’s small aperture, low cost antenna to extend its reach from 350 meters to over 2 kilometers using a single light source and operate better than many competitive systems that rely on 2 and 4 light sources with large or multiple receive apertures. Secondly, for any distance over 500m, DLI has built-in Redundant Link Management (RLM) technology which provides an alternate backup path for the system. This approach coupled with DLI's patented SkyFiber® products allows the company to capitalize on all of the strengths of WLC, while eliminating the historical objections to deploying WLC mentioned above. Today, availabilities of 99.999% have been demonstrated in hundreds of DLI installations around the country, in all kinds of weather conditions, equaling the level of reliability that carriers achieve with fiber optic cabling.
