Intel researchers stretch Wi-Fi to cover 60 miles

Editor’s Note: The following article is reprinted from Network World.

Intel recently demonstrated a modified 802.11 radio link with a data rate of around 6 Mbps and a range of more than 60 miles.

Intel achieved this extraordinary range using off-the-shelf hardware, including parabolic antennas, for its project, dubbed the rural connectivity platform (RCP). The key innovation was a change, borrowed from cellular networks, to the underlying 802.11 media-access-control layer that allowed for a more efficient signal, and translates into longer reach.

RCP is one of several research projects intended to extend the Internet into rural areas, especially in developing countries. The idea is to use low-cost, low-power Wi-Fi radios to bridge between wired Internet connections in a city and wired and wireless connections in small, rural villages. RCP's unprecedented range minimizes the need for lots of wireless nodes to span those distances.

RCP has been in development by Intel Research and Intel's Emerging Markets Platform Group for about two years, and has been talked about online for about a year. There are pilot RCP deployments in a handful of countries: India, Vietnam, Panama and South Africa. Earlier this month, the chip maker demonstrated the link in operation during an open house at its Berkeley Research Lab in California. In the demonstration, users viewed a live video image streamed over a 5.8GHz RCP connection from a camera about 1.5 miles away.

Wi-Fi is being used in outdoor settings, especially in municipal wireless-mesh networks, from such companies as BelAir Networks and Firetide. Typically, these radio nodes use a combination of high-power radios and high-gain, directional antennas to enable the Wi-Fi signal to reach, at best, a mile or two. (Compare wireless mesh products.) 

As Intel notes, the 802.11 protocol becomes inefficient as the ends of the wireless connection get farther apart. In part this is because when one 802.11 radio sends data, it then waits for an acknowledgement from the receiving radio. If it doesn't hear that acknowledgement within a certain amount of time, the sending radio assumes the data was lost or dropped, and resends it. The longer the distance, the more likely the sending radio won't get the acknowledgement in time.

So, Intel researchers changed the protocol, adding a technique called time division multiple access (TDMA), which is used today in GSM cellular networks. TDMA divides the channel into time slots, then synchronizes between the sending and receiving radios. In effect, each radio sends and receives on a schedule, so there's no waiting for acknowledgements and no subsequent resending of data.

Wi-Fi vendors, such as Meru Networks and Extricom, have added a type of centralized scheduling to their 802.11 wireless LAN products, claiming it simplifies deployments (because all access points can run on one channel) and increases throughput when networks are heavily loaded.

In Intel's case, the TDMA technique translates into longer range, because it minimizes the wireless overhead and frees up more bandwidth for data transmission, giving the signal greater range. (We're waiting to hear back from Intel on more details, and will update this story when we have them.)

RCP is a line-of-sight technology: The antennas on each side of the link need to be able to "see" each other.

The RCP units can be endpoints, on each side of a link, or relay stations through which the signal can hop. Both types of RCP devices include a single-board computer with an embedded Intel IXP 425 network processor, CompactFlash storage, 10/100 Ethernet ports that support Power over Ethernet, and a "local" 802.11 access point for client connectivity. The device draws about 6 watts of power.

Intel has been using 802.11 radios for the long-distance connection (as many as three are possible), but any long-haul radio can be substituted including WiMAX radios. RCP works over the 900MHz band and the 2.4GHz and 5.8GHz bands. The Berkeley Research Lab demonstration shows an external parabolic antenna roughly two feet wide.

The hardware is encased in a compact, rugged, die-cast aluminum casing, and the units are designed to configure themselves automatically. Intel says it will start selling the devices in India later this year, apparently through deals with equipment makers to turn the Berkeley lab's reference design into a commercial product. The target price is less than US$500.

The RCP software runs on an operating systems based on the SnapGear embedded Linux distribution.  A Web GUI can be used for monitoring and for manual configuration.

In Panama, one RCP device was perched on a 15-story hotel, with an Internet connection. The other was mounted on a tall, narrow tree trunk in a village several miles away. No special tools were needed. The tree-mounted RCP unit, powered by a solar panel in the village, now provides a reliable Internet connection to the villagers, where none existed before.

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