Bluetooth Bulletin

The Bluetooth spec was released 18 months ago. What has the industry learned about how it handles interference, security and interoperability?

Bluetooth, that funny-named short-range radio link, continues to be an enigma. Since the specification was released 18 months ago, the industry remains insecure about the technology's limitations or triumphs.

Tom Murphy, Sprint PCS director of media relations, said he wasn't sure whether to believe Bluetooth's panacea status when issues such as security, interoperability and reliability remain uncertain.

Ericsson is one of the five companies that founded Bluetooth. Lars Nilsson, Ericsson manager of strategic marketing, said that extensive testing has proved Bluetooth can successfully control interference, maintain secure transactions and still adhere to interoperability standards.

Too Much Interference?
Bluetooth shares the 2.45GHz band with LANs, microwave ovens and even garage-door openers. But Mike O'Neill, Conexant Systems executive director of marketing, said that Bluetooth's unique method of frequency hopping usually mitigates interference. An algorithm synchronizes the receiver and transmitter and different algorithms can be used to avoid interference by ensuring that two transmitters won't hop to the same frequency at the same time. Frequency hopping also provides security, is cost-effective and consumes less power.

By breaking the data signal into small packages that hop from frequency to frequency, Bluetooth-enabled devices can minimize interference by never sharing a frequency with other transmissions. Bluetooth's hop rate of 1,600 hops per second over 79 channels means the chance of other signals interfering is very low. Ericsson's Nilsson said that interference also is limited by Bluetooth's 30-foot range.

O'Neill said that radio-link power controls also can help keep interference to a minimum. By using only as much power as needed to reach the intended receiver, Bluetooth can provide direct delivery and eliminate interference.

Interference issues, however, become a concern over distances beyond 30 feet.

Current specifications deliver gross data rates of 1Mb/s over distances of up to 30 feet. Connections for 1-to-1 applications allow maximum data-transfer rates of 721kb/s. Throughput losses of about 10% can be expected for longer distances. However, in a multiple-device structure with 10 fully loaded, independent networks, a data rate of more than 6Mb/s can be achieved.

Bluetooth developers already are working on 2G applications that will increase data rates to 2Mb/s and off-chip amplifiers that increase the range to 100 feet and beyond.

Nevertheless, Nilsson said that Bluetooth applications with ranges beyond 100 feet don't have much market potential.

"(Bluetooth) is meant to connect a few home appliances and not an entire campus," he said. "These specifications are good for the intended applications."

Convinced that the technology is ready for market, Nilsson said it will be only a few years before all Ericsson handsets are Bluetooth-enabled. This past month at CommunicAsia 2000, Ericsson unveiled the T36 and R520 handsets, the industry's first to feature built-in Bluetooth technology.

Too Little Security?
Although there's some concern whether Bluetooth is secure enough for wireless e-commerce, Murphy said he thought electronic wallets and other security tools were a few years off.

In effect, Bluetooth 1.0 has three modes of operation, each with different levels of security:

• Non-secure, meant for routine information transportation such as sending a file to a printer.

• Service-level enforced security. In this mode, a device doesn't initiate security procedures before channel establishment. However, it does allow flexible access policies, especially when running applications with different security requirements. This mode is the most desirable from an interoperability standpoint and the mode most Bluetooth vendors will deploy.

• The link manager enforces security at a common level for all applications at the beginning of the connection. Although this mode is easier to implement than mode 2, it isn't flexible and drastically impedes interoperability.

Nathan Pedleton, Extended Systems business unit manager for mobile communications, said Bluetooth's frequency hopping creates built-in security for the interface, so add-on security is unnecessary, especially considering that U.S. military communications' preferred method of channel hopping isn't much different.

The allocation of IEEE 802-standard 128-bit encryption brings another form of built-in security to Bluetooth. Although the standard provides only for a low key encryption code, Bluetooth developers say they will be able to implement longer key encryption codes and feel that the two built-in security features of the specification make Bluetooth transactions nearly impossible to intercept or crack.

Omnidirectional and mutual device authentication are other forms of security Bluetooth uses. Access is granted only to devices marked as trusted in the master-control database. Currently, user authentication isn't part of the platform, but Pedleton said it may eventually become part of later specifications.

Iffy Interoperability?
If Bluetooth is an open standard, does that ensure interoperability?

"The specifications are really just a starting point," said Conexant's O'Neill. "Vendors then take that information and put the pieces together to make their product."

To ensure interoperability, the Bluetooth Special Interest Group has mandated testing and approval of Bluetooth-enabled products. The qualification program aims to help vendors set parameters to define a common user experience.

Part of the qualification program includes field tests. Nicknamed "Unplug Fest," the program allows developers to check their products against other Bluetooth-enabled devices to make sure they can communicate with one another. O'Neill said Unplug Fest is a guarantee for providers and consumers that vendors are working to make interoperability a reality.

"Interoperability, from a design perspective, is imperative if you want your technology to make it into future devices," he said.