RADAR is the world's first Wi-Fi signal-strength based indoor positioning system. RADAR proves that RF fingerprinting and environmental profiling with commodity wireless LAN hardware can be used to determine user and machine location inside buildings, thereby enabling indoor location-aware applications (think - "Indoor-GPS")

Wherever You Go, There Is Connectivity
by Suzanne Ross

Victor Bahl, a researcher with the Systems and Networking group, says his kid doesn't get too excited about his work. "He's seen too many Star Trek shows," he says. If the characters in science-fiction shows can beam their body parts around the galaxy, what's so cool about a system that will guide you through the tricky look-alike hallways of the Microsoft campus?

Bahl's two cool projects, code named RADAR and CHOICE, will keep you from getting lost in strange places, and give you high speed Internet access from your mobile device at almost any place, at any time. And in spite of Hollywood movie hype, this hasn't been done yet.

Wireless networks explained
There are four types of wireless networks, classified by the amount of coverage they provide. A cell-phone network is a wide-area network (WAN) and a business or home wireless network is a local area network (LAN). A smaller network, such as one connecting a printer and a handheld computer, is a personal area network (PAN), and a network between sensors placed around the different parts of a human body is a body area network (BAN).

The communication technologies underlying these networks include: radio frequency (RF), infrared (IR), ultrasound, and electromagnetic communications. Each of these technologies has its pros and cons. IR based networks are inexpensive and mostly secure, but require line-of-sight between the transmitter and the receiver for efficient operation. In addition, they have a limited range and don't work very well in direct sunlight. Ultrasound and electromagnetic wireless networks are useful for some applications, such as determining location, but don't provide data networking, and like their IR counterparts have limited range, higher installation and maintenance costs and scale poorly.

An RF network offers several advantages. It supports the ability to send data at a faster rate, has a large range, is low maintenance, and is omni directional. An omni directional system does not require line-of-sight, so it can operate through walls. Unfortunately, the RF spectrum is a limited and regulated resource; it is therefore an expensive resource prone to congestion and interference. Also, since RF signals are not restricted to well-defined boundaries, RF transmission can be picked up by anyone within range of the transmitter, making it difficult to secure.

Bahl's current research is on wireless RF LANs and PANs. His goal is to make these networks more efficient so that they can become ubiquitous.

How RF-based networks work
An RF network consists of a hardware module that is plugged or built into a mobile device carried by the user. This module converts the user's data into RF signals and transmits them over the air to another network device called an access point (or base station). An access point (AP) is a piece of hardware that bridges the wireless network and the wired networks by converting the RF signals (wireless data packets) into electronic signals (wired data packets) and then transmitting them on the wired network. This type of network configuration is called an infrastructure-based wireless network, of which a cell-phone network is an example.

Finding your way
Infrastructure-based wireless RF LANs have traditionally been used for data connectivity only. Bahl and his colleague, Venkat Padmanabhan, have instead developed algorithms that let you use these networks for tracking and locating mobile users as well.

Bahl and Padmanabhan noticed that the signal strength varies as a user walks about the building. Not surprisingly, the signal received at the mobile device is strongest when the receiver is close to the AP and weakest when further away. This trend is exploited by RADAR to estimate the mobile device's location inside a building.

The RADAR system works using a radio map. A radio map is a lookup table that holds collections of packet signal strengths and the building locations where these signals were measured. To locate the user's position, the user's wireless device measures the signal strength from the APs within its range and then searches the radio map to determine the signal strength entry that best matches the measured signal strength. To improve its estimate, RADAR takes into account the recent movement history of the user and dynamic changes such as temperature, the number of people present, and any other environmental factors which will effect the radio map.

RADAR can use the information about the user's location to find the necessary computing resources closest to the user. These resources can be stored in a directory such as Active Directory™, which is part of the Windows® 2000 network architecture. Active Directory is useful because it provides a secure directory service to let the people in an organizations share and manage information about applications, files, printers, and people. So if you're visiting a client or co-worker in another building, you could use RADAR to find the nearest printer, or use it to guide you through unfamiliar halls.

It's your choice
Bahl's second project, CHOICE, is about giving individuals more control on how and where they access the Internet. In an increasingly fast-paced mobile society we invariably find ourselves spending a considerable amount of time in public places such as airports, hotels, libraries, and shopping malls; and at public events such as conferences, meetings, and lectures. Internet access is not typically provided in these settings. When it is provided it is generally in the form of inconvenient fixed kiosks or through wide-area wireless data networks that are excruciatingly slow. CHOICE is about providing people with high-speed wireless Internet access in public places. Built over widely available standards-based wireless LAN technology, it provides Internet access to users at speeds that are 25X greater than the emerging third-generation WANs.

With his colleagues in research and products groups, Bahl has created a pilot program, code named MallNet, which will provide wireless Internet connectivity at a popular local mall, initially to Microsoft employees and then to everyone. Users will be able to hang out at the food court while they read their email and check on the status of their web sites.

CHOICE is also about which ISP an individual chooses to use. Pay phones allow you to choose a telephone company connection, and Bahl believes that when wireless networking becomes ubiquitous, you should be able to connect through any ISP, whether it's the one you use at home, or one that offers cheaper rates that day. CHOICE will provide its users with a higher level of network service than is currently available. If you are at the airport and you want to download an important file from your company network to work on during the flight, you need network connectivity with a level of service that gives you higher bandwidth to carry out your transaction quickly. If you are willing to pay for it, CHOICE will give you more bandwidth than usual. CHOICE is also about security and user privacy; each user session is encrypted with a per-user key so that other people can't eavesdrop on your communications.

CHOICE allows users to check prices while they're getting ready to purchase an item in a store. You could connect to the network and go online to find out if the orange juice glasses shaped like chickens are cheaper at another store, or at an online housewares site. It will also allow users to locate their friends who are in the same place and carrying mobile devices.

In the future, RADAR, combined with CHOICE, could help you find your way inside any building. Have you ever stared at a "you are here " dot on a shopping center directory and wondered if you're here facing there or there facing here? You could pull out your wireless device, connect to CHOICE Network, and click on the center's directory. The network, using RADAR, already knows where you are, because your device communicated this information. A pleasant sounding computer voice will then tell you how to get to your chosen destination -- go past the donut shop, turn right at the bookstore, and take three baby steps into the Lots of Lollipops store.

Wireless for everyone
While there's a lot of interest in enterprise wireless networks that serve business customers, wireless for consumers is just beginning to take off. Bahl's research focuses on providing wireless for everyone. His vision is for a wireless Paradise, where you can be connected anyplace, at any time. So if you're sipping a latte at the coffee shop, you can purchase tickets to a Gorge concert, check to see if your Mom's plane is arriving on schedule, check on the status of your favorite sports team, get in on the latest hot stock deal, and read your email at the office. Ah, working hard, aren't you?

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