Using bluetooth, Introduction, Adaptive frequency hopping – Motorola VC5090 User Manual
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Chapter 5 Using Bluetooth
Introduction
Bluetooth-equipped devices can communicate wirelessly, 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.
Vehicle computers with Bluetooth capabilities can exchange information (e.g., files and tasks) with other Bluetooth
enabled devices such as scanners and printers.
Vehicle computers with Bluetooth technology use the StoneStreet One Bluetooth stack. To program Bluetooth
within the vehicle 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 vehicle computers to operate in any infrastructure. AFH is always enabled in the VC5090.
The Bluetooth radio in this vehicle 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.