When Bluetooth, a standard for ad hoc wireless connectivity, was first released in 1998, the technology was billed as a cable replacement cure-all.
However, as Bluetooth-enabled gear started hitting the market, early adopters began to realize that the vision of what Bluetooth could one day do didnt match the reality of what was actually possible at the time.
Its been more than five years since Bluetooth was released, and although the Bluetooth specification and the devices based on it have grown more mature, plenty of work must still be done before the technology can fulfill its ambitious original goals.
The latest release of the Bluetooth specification, Version 1.2, became final late last year. eWEEK Labs tested a pair of Bluetooth 1.2-capable USB (Universal Serial Bus) adapters from Anycom Inc. that began shipping in May. The devices, the $50 Anycom Blue USB-240 and $40 USB-120, are the first Bluetooth 1.2-based products weve had the opportunity to test.
Although we found both of the Anycom adapters to be significant improvements over the Bluetooth 1.1-based units they replace, some tricky problems remain. The troublesome issues and areas of uncertainty we encountered in our tests are common to most products in the Bluetooth ecosystem and are the result of the complicated way that specification developers, software developers and hardware vendors interact to produce user devices.
For one thing, although the Anycom hardware that we evaluated is Bluetooth 1.2-capable, the Widcomm software stack, with which it ships, is tied to the older 1.1 standard.
Further complicating matters, Widcomm was recently purchased by Bluetooth chip-set vendor Broadcom Corp. According to Anycom officials, Broadcom has indicated that it plans to discontinue support for radios from competing Bluetooth vendors, such as the Silicon Wave hardware that powers the Anycom adapters we tested.
Nevertheless, we were able to test the latest Anycom adapters alongside an earlier 1.1-based Anycom USB adapter and thus could compare the performance of the two in various scenarios.
one of the more compelling improvements in Bluetooth 1.2 is the provision for better coexistence between Bluetooth and the other emitters in the swath of unlicensed spectrum in which Bluetooth operates. Version 1.2 makes this happen via a feature called AFH (Adaptive Frequency Hopping).
Bluetooth was designed to deal with interference from its neighbors in the 2.4GHz spectrum—among them 802.11b and 802.11g radios, microwave ovens, and certain cordless phones and baby monitors—by randomly hopping among 79 channels in the band to transmit data. Bluetooth packets lost due to interference from other devices in the band (most of which, including Wi-Fi radios, do not channel-hop) are retransmitted.
AFH improves on this scheme by detecting busy channels and enabling Bluetooth devices to avoid them altogether, thereby improving performance for Bluetooth devices and for their neighbors alike.
We couldnt confirm whether AFH was enabled in the 1.2 hardware/1.1 software configuration we tested, but certain vendors are shipping AFH-enabled gear. Apple Computer Inc., for one, brought AFH to its Bluetooth implementations two months before Bluetooth 1.2 was finalized.
The Bluetooth 1.2 specification also provides for shorter connection times between Bluetooth devices through a feature called enhanced inquiry, which cuts in half the maximum time required for devices to pair up, from 10 to 5 seconds. Enhanced inquiry is also supposed to boost the success rate for pairings from approximately 90 to nearly 100 percent.
Also notable in Bluetooth 1.2 are improvements in sound quality for products such as cell phone headsets through a feature called eSCO (Extended Synchronous Connection-Oriented) channels, which enable the retransmission of corrupted voice data.
Although the Bluetooth specification has certainly made progress, there are still fundamental pieces of functionality that the standard leaves open to individual vendors to implement as they see fit—a situation that leads to confusion for users and potential incompatibility among devices.
Scatternets are a great example of this immaturity in the specification.
The most basic unit of a Bluetooth network is the piconet—a combination of a master device and as many as seven slave devices. The slave devices depend on the master device for handling fundamental chores such as setting the hopping pattern for the piconet, and a slave device cannot have two masters.
Master and Slave
However, there are times when a Bluetooth device must function as a master and a slave. For instance, a laptop computer that connects to the Internet via a Bluetooth access point functions as a slave to the access point.
To use a Bluetooth mouse with the same laptop, the laptop must also function as a master to the mouse—which means two piconets are linked by one of their peers, thus forming a scatternet.
The same situation arises when a user wants to dial a number on a cell phone by clicking on a name in a PDA address book and placing a call with a Bluetooth headset. The PDA must be master to the cell phone, and the cell phone must be master to the headset.
As these basic-use cases illustrate, scatternets are a central part of Bluetooth. And yet, even as of Bluetooth 1.2, the specification does not directly address scatternets.
The Bluetooth Special Interest Group had planned to include specifications for scatternets in 1.2 but opted to push the specifications back to a later version.
However, there are Bluetooth devices on the market that do support scatternets, with individual vendors defining the details. In fact, support for scatternets is the most important selling point for the Anycom USB-240 and USB-120 adapters we tested. In our evaluation, we were able to use a Bluetooth mouse, keyboard and network access point, along with our test laptop, simultaneously without incident.
In a parallel test with a Bluetooth 1.1-based USB adapter, we had to disconnect our mouse to link up with the access point we were using.
With our Bluetooth 1.2 adapter, we were able to add a large file transfer to another Bluetooth-enabled laptop into the mix, but we found that the transfer saturated our Bluetooth link enough to interrupt the playback of an Internet music stream that we were listening to until the transfer was complete.
Senior Analyst Jason Brooks can be reached at [email protected]