Using Bluetooth 3-3
Introduction
Bluetooth-equipped devices can communicate without wires, using frequency-hopping spread spectrum (FHSS) RF to transmit and
receive data in the 2.4 GHz Industry Scientific and Medical (ISM) band (802.15.1). Bluetooth wireless technology is specifically
designed for short-range (30 feet/10 meters) communications and low power consumption.
Mobile computers with Bluetooth capabilities can exchange information (e.g., files, appointments and tasks) with other Bluetooth
enabled devices such as phones, printers, access points and other mobile computers. In addition, a dial-up modem connection can be
created between the Bluetooth mobile computer and a Bluetooth enabled phone. The Bluetooth phone can then be used as a modem.
Symbol mobile computers with Bluetooth technology use the StoneStreet One Bluetooth stack. To program Bluetooth within the
mobile computer refer to the StoneStreet One SDK.
Adaptive Frequency Hopping
Adaptive Frequency Hopping (AFH) is a method of avoiding fixed frequency interferers. AFH can be used with Bluetooth voice. All
devices in the piconet (Bluetooth network) must be AFH-capable in order for AFH to work. There is no AFH when connecting and
discovering devices. Avoid making Bluetooth connections and discoveries during critical 802.11b communications. AFH for Bluetooth
can be broken-down into four main sections:
• Channel Classification - A method of detecting an interference on a channel-by-channel basis, or pre-defined channel mask.
• Link Management - Coordinates and distributes the AFH information to the rest of the Bluetooth network.
• Hop Sequence Modification - Avoids the interference by selectively reducing the number of hopping channels.
• Channel Maintenance - A method for periodically re-evaluating the channels.
When AFH is enabled, the Bluetooth radio “hops-around” (instead of through) the 802.11b high-rate channels. AFH coexistence
allows Symbol mobile computers to operate in any infrastructure. AFH is always enabled in the MC3000.
The Bluetooth radio in this mobile computer operates as a Class 2 device power class. The maximum output power is 2.5mW and the
expected range is up to 32.8 feet (10 meters). A definitive definition of ranges based on power class is difficult to obtain due to power
and device differences, and whether one measures open space or closed office space.
It is not recommended to perform Bluetooth wireless technology inquiry when high rate 802.11b operation is
required.
Security
The current Bluetooth specification defines security at the link level. Application-level security is not specified. This allows
application developers to define security mechanisms tailored to their specific need. Link-level security is really between devices not
users, while application-level security can be implemented on a per-user basis. The Bluetooth specification defines security
algorithms and procedures needed to authenticate devices, and if needed, encrypt the data flowing on the link between the devices.
Device authentication is a mandatory feature of Bluetooth while link encryption is optional.
Pairing of Bluetooth devices is accomplished by creating an initialization key that is used to authenticate the devices and create a link
key for them. Entering a common PIN number in the devices being paired generates the initialization key. The PIN number is never
sent over the air. By default, the Bluetooth stack responds with no key when a key is requested (it is up to user to respond to the key
request event). Authentication of Bluetooth devices is based-upon a challenge-response transaction. Bluetooth allows for a PIN
number or passkey that is used to create other 128-bit keys used for security and encryption. The encryption key is derived from the
link key used to authenticate the pairing devices. Also worthy of note is the limited range and fast frequency hopping of the Bluetooth
radios that makes long-distance eavesdropping difficult.