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Given the geographical diversity of India, last-mile connectivity has always been a pain point for telecom operators. In the case of business centers, laying down fiber and wiring up old buildings is a herculean task. All this, coupled with the approvals required for digging and laying down fiber or copper, makes it difficult to provide high-bandwidth, reliable connectivity. And, after the broadband policy failed to unbundle the copper loops of BSNL/MTNL, private operators have been aggressively pursuing the fiber and wireless routes to deliver high-speed connectivity.

Free space optics (FSO) promises to solve the last-mile woes and is also being promoted as a reliable backhaul technology for the carriers.

FSO as a technology was initially used in defense (primarily in naval ship-to-ship communications) and secure aerospace applications. It is now also an alternative to fiber optic–based solutions in the commercial market space.

According to industry estimates, the worldwide FSO market at present is about $100 mn. The potential, however, is of more than $1 bn. "FSO has been popular in USA with almost 50% of the market. It is followed by EMEA with 30% share and Asia-Pacific contributes 20%," says Jeff Bean, director global marketing, LightPointe. According to statistics, there are 750,000 large business buildings in the US, of which only five% are connected to fiber, but over 70% of which are within one mile of at least one of the buildings that is connected to fiber.

In India, though pilots and testings have been carried out, deployments have been few. On the enterprise side, Krone has deployed this technology from Optical Access, an Israel-based company, at its Chennai-based Orchid Chemicals and Pharmaceuticals. Bharti is said to have tested and deployed this for its backhaul. The technology for this was provided from SONAbeam, through Netware Technologies India. "The installations are primarily for mobile wireless backhaul. However, enterprise building-to-building opportunities are starting to emerge," adds Bean.

The Tech Side
Free Space Optics, also called free space photonics (FSP) or optical wireless, refers to the transmission of modulated visible or infrared (IR) beams through the atmosphere, to obtain optical communications. Like fiber, FSO uses lasers to transmit data, but instead of enclosing the data stream in an optical fiber, the data is transmitted through the air.

FSO transmits invisible, eye-safe light beams from one 'telescope' to another, using low-power infrared lasers in the terahertz spectrum. The beams of light in FSO systems are transmitted by laser beacons towards highly sensitive photon-detector receivers. These receivers are telescopic lenses capable of collecting the photon stream and transmitting digital data containing a mix of Internet messages, video images, radio signals, or computer files. Commercially available systems offer capacities in the range of 100 Mbps to 2.5 Gbps, and demonstration systems report data rates as high as 160 Gbps.

Will It Replace Fiber Optics?
FSO, as a technology, has all the potential to compete with the optic-fiber cable. FSO is easy and fast to deploy, cost of deployment is less, apart from that, no spectrum clearances, charges, or permission is is a hinderance. An estimate by LightPointe says (according to a media reports), in India, the 10 km range connectivity in STM 1 mode, which provides 155 Mbps of bandwidth over fiber optic connectivity, will cost around Rs 75 lakh; while FSO connectivity for that will cost around Rs 25 lakh.

Despite the benefits, FSO is not seen to be on its way to completely wipe out the optical fiber. Rather, both the solutions are seen as complementary to each other. FSO works well for connecting buildings within a limited area, typically within a 4 km radius.

Similarly, for the carriers this works well where line of sight is available but other options like digging for cables are not viable. In fact, VSATs give it strong competition, when it comes to wide-area connectivity.

Lest One Forgets
The biggest drawback for FSO is that the performance goes down in extreme weather conditions. Being a line-of-sight technology, interference of any kind (like water, snow, radiation) can pose problems. Under foggy conditions, its efficiency levels become doubtful. FSO systems can transfer high-speed data and have common link for distances within 1–2 km, but inclement weather can reduce this to 500–1000 meters. The laser beam that carries data for an FSO link is adversely scattered by the water droplets in fog, and cannot reach a remote terminal more than about 200 meters away. India has a tropical climate, with weather conditions varying from extreme heat to heavy rains and thick fog. All this casts a shadow on FSO adoption rate here.

Also, it is a very high-cost technology and systems for one deployment cost around $7000, as a one-time capital investment. Companies promoting this technology say, a comparison with low-bandwidth wireless options makes it appear costly but the actual cost-per-bit analysis shows it to be less expensive. "It's a matter of supply and demand. If you demand high bandwidth, but can't find a supply, you're sunk. We supply high-bandwidth (on a par with optical fiber cable) that no other low-bandwidth or licensed wireless can remotely match it," says Bean. To overcome the cost factor, companies are working to launch low-cost entry-level systems by 2006.

Free Space Optic Security
Wireless, by its nature, is perceived to be insecure. FSO emits infrared (IR) beams for communications. To intrude these, beams have to be tapped. But, being a duplex technology, it would require tapping devices to be on both ends, increasing the chances of the intrusion being detected. Determining the size of the beams and putting nonreflective surfaces around the equipment reduces chances of these being tapped. Also, the time-tested method of encrypting the data traveling over FSO ensures greater security.

Another concern in the case of beam-based technologies is that the beams may miss the target equipment or spill beyond them.

FSO has all the properties needed to fulfill the rising demand for higher bandwidth solutions to meet the needs of corporations and individuals. If minor irritants are removed, it can augment the legacy WAN technologies in providing secure, redundant links between corporate resources, the Internet, and the telcos.

Anurag Prasad