Windows Phone Thoughts: Bluetooth - The Technology Buzz (Part 1)

Bluetooth is a wireless technology that is rapidly finding its way into many products either as part of a more featured device or as an accessory. This article is part of a series on all the different wireless technologies. Part 1 will describe the Bluetooth technology. Part 2 will look at the technology and its integration into Pocket PC devices – an overview of the design process. First things first, have you ever wondered how this wireless technology works? Read this article to find out all about this Bluetooth buzz.



Bluetooth, despite being a young wireless technology, promises to be extremely useful for wire replacement for both peripheral and mobile devices. A wide range of devices (headsets, printers, keyboards, mice, PDAs, cell phones, laptops, and GPS units) are already incorporating this technology and many more devices are expected to in the future. What is this wireless technology? How does it work? Are there any gotchas?

Bluetooth's Roots
In early 1998, a consortium of companies (Ericcson, IBM, Intel, Nokia, and Toshiba) formed a Special Interest Group (SIG) to develop an open, license free wireless standard. This wireless standard was designed specifically for portable and other electronic devices. The proposed wireless technology would allow consumers to replace the cables that connect peripheral devices and mobile devices to one another. The consortium code named the project “Bluetooth” after the 10th Century Viking king Harald Blatand. On July 26, 1999, the first specification for the technology was publicly released.

Bluetooth = Wire Replacement

How the Technology Works
Bluetooth operates in the 2.45GHz wireless spectrum band. This range is called the ISM band (industrial, scientific and medical). Worldwide, this spectrum range does not require the consumer to get a license (unlike a HAM radio operator) and is shared by many cordless telephones and wireless LAN products.


Figure 1: The Bluetooth wireless spectrum range relative to other popular wireless technologies.

Interference with other wireless technologies is avoided by a couple of Bluetooth technology features:

• Bluetooth is low power: a signal of up to 1 milliwatt is transmitted. Contrast this with the maximum broadcast power legally allowed for a cell phone of 3 watts. Therefore, the range of Bluetooth signals is much more localized around the signal source than cell phones, thus guaranteeing less of a chance for interference with other devices. Typically, the maximum signal range of Bluetooth is 10 meters (32.8 feet).
  
• Use of a technique called spread spectrum frequency hopping.

Bluetooth Spread Spectrum Frequency Hopping Explained
Bluetooth communicates by transmitting in the ISM spectrum range of 2.402 GHz to 2.480 GHz. This range is divided into 79 1-MHz zones for North America and Europe (Japan has a frequency spectrum of 2.472 GHz to 2.497 GHz divided into 23 1-MHz zones). Bluetooth transmits a signal 1,600 times per second, alternating between each 1 MHz band. The process is to transmit, hop to another band, transmit, hop to another band, transmit, etc.


Figure 2: Two Bluetooth wireless devices that have not established a communication link transmitting and are hopping from band to band

Once two Bluetooth devices establish communication with one another (either automatically or by user choice), they start to hop between the same 1 MHz bands in unison. Error Correcting Code (ECC) in the Bluetooth software corrects errors caused by interference. Interference can occur when another two devices have their communication hops occur in the same 1 MHz band and at the same relative time as the original two devices. However, this unlikely situation only occurs for a fraction of a second before another hop occurs.


Figure 3: Two Bluetooth wireless devices that have established a communication link. Note that both devices are synchronized as they transmit and hop.

How Bluetooth Devices Communicate
Two or more Bluetooth devices can communicate in a variety of ways. Communication can occur at half-duplex (similar to a conversation on a speaker phone) or at full-duplex (like your telephone). Bluetooth devices that are communicating with one another are said to have formed a “piconet”. Devices that have formed a piconet ignore signals from other bluetooth devices or other piconets.

A piconet can consist of one Master device, up to seven active Slave devices, and 248 devices in standby mode. Devices on a piconet share a common data channel where data is transferred in packets. Think of a letter in an addressed envelope as a single packet. The letter is the data in the packet and the addressed envelope is the header and handshaking information of the packet. The piconet channel has a capacity of one Megabit per second including the overhead of the header and handshaking information. Device to device connections have a maximum data transfer rate of 721 kilobits per second. This data rate corresponds to three voice channels.

Is it Secure?
Secure communication is achieved by meeting two objectives. First, data that is sent must be reliably received. Second, data that is sent should not be intercepted and decoded by anyone but the intended recipient. Bluetooth is secure for home or office use since it has:

• Built in security, authentication, and error correction;
  
• Fast hopping – making it difficult to eavesdrop.;
  
• Short range – adaptive transmission power designed to be just enough for the device being communicated with to receive - devices beyond this range do not receive a signal

Bluetooth still requires a strong application level security manager to ensure 100% security. Consider this example: someone picks up your Pocket PC that isn’t password protected and then connects to the Internet via your cell phone. In this example, the owner created a partnership between his Pocket PC and cell phone beforehand. However, the Bluetooth application didn't prompt for user authentication when used by an unauthorized individual. For some users this scenario is acceptable since they rarely leave their devices unattended and prefer quick, simple access to their Bluetooth resources without entering passwords. For other users the preceding example represents a security flaw. Realistically, we need to have the choice of how much security to implement. The option to lock all communication without the correct authentication. The option to require authentication prior to transmitting data. The peace of mind in knowing that we can lock a piconet preventing other devices from accessing or receiving data.

Technology Summary
Let us look at a quick summary of the key Bluetooth technology points before examining the uses of the technology.
Bluetooth is:

• wire and cable replacement technology
  
• open standard
  
• short range – typically up to 10m
  
• low bandwidth - much lower than Ethernet
  
• low component cost – less than $20 US
  
• low power – 0.3 mA standby and 30 mA maximum during data transfer
  
• user does not require a license - 2.45 GHZ ISM
  
• limited interference issues - Spread Spectrum Frequency hopping and very fast hopping between the 1-MHz bands (1,600 times/sec)
  
• secure – but requires application level support for robust security

Bluetooth Uses
Bluetooth is a very flexible technology that allows for the transmission of data in a variety of methods called “profiles”. There are four basic profiles and nine user profiles in version 1.0 of the Bluetooth specification. Version 1.1 of the specification expanded the number of user profiles. The user profiles often use and then expand on the basic profiles.
The four basic profiles are:

• SPP – Serial Port Profile used for serial port emulation
  
• GAP – Generic Access Profile used link management and device discovery
  
• GOEP – Generic Object Exchange Profile used for object push, transferring files, and synchronization
  
• SDAP – Service Discovery Application Profile used for information and service discovery

The nine user profiles in version 1.0 of the specification are:

• SP - Synchronization Profile
  
• FP - Fax Profile
  
• FTP - File Transfer Profile
  
• OPP - Object Push Profile for sending data objects between devices (e.g. business cards)
  
• HS - Headset Profile (e.g. headset and cell phone connections)
  
• DNP - Dial-up Networking Profile for modems, mobile phones (e.g. Access your ISP using Pocket PC and cell phone)
  
• IP - Intercom Profile for speaker phone type of functionality
  
• LAP - LAN Access Profile (e.g. A low bandwidth method for accessing a LAN)
  
• CTP - Cordless Telephone Profile (e.g. handset to base telephone connections)

Additional profiles defined in version 1.1 of the specification are:

• A2DP - Advanced Audio Distribution Profile
  
• AVRCP - Audio Video Remote Control Profile
  
• BIP - Basic Imaging Profile
  
• BPP - Basic Printing Profile
  
• ISDN - Common ISDN Access Profile
  
• ESDP - Extended Service Discovery Profile
  
• GAVDP - Generic Audio Video Distribution Profile
  
• HFP - Hands Free Profile
  
• HCRP - Hardcopy Cable Replacement Profile
  
• HID - Human Interface Device Profile
  
• PAN - Personal Area Networking Profile
  
• SAP - SIM Access Profile

Figure 4: The flexibility of Bluetooth communication is displayed between a laptop and a Pocket PC. Are they playing a game or exchanging business cards? (picture courtesy of the Bluetooth SIG).

Perfection? Not Quite
As the technology matures, future enhancements will be dictated by consumer use, acceptance, and misuse of the technology. Some future enhancements needed are:

• Improved interference reliability especially as we see more wireless enabled products. What happens in a room of 50 people who all have a Bluetooth enabled cell phone and Pocket PC in their possession?
  
  
• Ease of Use. It shouldn't be so difficult to form a partnership between a Pocket PC and a cell phone.
  
  
• Improved Security at the application level. The software application architect and developer need to remember to include additional security to prohibit unauthorized use of a device. Depending on the device, this could be accomplished in conjunction with the overall security plan and software included in the device. We don't want an unauthorized individual picking up our Pocket PC that is partnered to any number of devices and having the ability to transmit or even to receive information. This is entirely possible unless you password protect your Pocket PC at the device level.
  
  
• More user profiles. How about a stereo headset profile? Coming soon ...
  
  
• Alternatively, too many user profiles leads to consumer confusion and frustration when they purchase an option or Pocket PC only to find that a basic profile is not supported in the software.

Some of these enhancements will be addressed by the SIG in future releases of the technology. Other enhancements (secure, easy to use software) will have to be addressed by the OEMs. However, it will be interesting to see if the Bluetooth SIG remains true to the initial product requirements for Bluetooth like low cost, low power, short range, etc., or tries to expand the specification to include areas that will overlap with the wireless LAN specification. If this occurs, we can expect to see longer ranges and improved bandwidth but this could also have a negative impact to the low power requirements and confuse the market.

Conclusions
For the future, it appears that Bluetooth has secured a spot in the wireless market. I give the technology a big thumbs-up. However, I add the provision that we must be aware of our data security and make sure that we can control access to it.

As consumers, the use of any wireless technology should be transparent and ideally should not be part of our decision making process. The product should fulfill our needs to print, present, or be online wherever we choose. The technology should simply work without any complicated setup procedures.

Remember to check the Pocket PC Thoughts site often for Part 2 of this article. We will take a behind the scenes peek into the process and issues of integrating Bluetooth into a Pocket PC.