This form of power control is provided to cut down on interference with other devices in the ISM band and obviously help prolong battery life (see Bluetooth: Goodbye Infrared). The second form of power control is on the receiver side of a Bluetooth device. To enable all classes to communicate in a Piconet without damage to the RF front ends of the lower power classes, a method for controlling Class 1 device transmitter power is required. Transmit power control is mandatory above 4 dBm, below this level i. e. all Class 2 and 3 modules it is optional.
To implement a power control link the remote device must implement a Receive Signal Strength Indicator (RSSI). For a transceiver wishing to take part in a power controlled link it must be able to measure its own receiver signal strength and determine if the transmitter on the other side of the link should increase or decrease its output power level. The RSSI makes this possible. Power control is specified is as a golden receive power, defined as a range with a low limit and a high limit. The RSSI must have a minimum dynamic range equal to this range.
The RSSI must have an absolute accuracy of ±4dB or better when the receiver signal power is 60 dBm. In addition, a minimum range of 20¦. 6 dB must be covered, starting from 60 dB and up. The instructions to alter the transmitter power are carried in the Link Manager Protocol (LMP) link (see Bluetooth: Goodbye Infrared). The last form of power control relates to the power consumption. The Hold, Sniff and Park modes are power saving modes set out in the specification aiming to preserve battery consumption.
The Hold mode is typically used when a master is establishing a link with a new device and requires the other slaves to temporarily halt their transmissions. The Sniff mode puts slaves into a low duty cycle mode of operation but is still an active member of the Piconet and the master can only transmit after a sniff interval. In Park mode slaves enters a low duty cycle mode of operation and are no longer active members of the Piconet (see Bluetooth: Goodbye Infrared). B. Applications and Profiles.
Undeniably the ideal candidate for the first wave of applications will inevitably be based on mobile cellular technology, but what other applications can be realised using Bluetooth technology? The specifications outline a wireless technology that is as cost effective as the cable it replaces and aim to balance reliability, resilience, convenience and low power. The short-range connections of data and voice could mean the emergence of applications suitable for: ?
Access points allowing mobile devices connection to services e.g. telephone network (PSTN) or LAN services. ? Mobile phone link to Laptop PCs ? Mobile phone connections to wireless headsets ? PDA, palmtop and desktop PC inter accessibility for file and data synchronisation. The Bluetooth core specification describes the protocol, but the Profiles document enhances this by setting out a number of profiles for applications and defining the way a number of services operate e. g. a file transfer profile defines how devices exchange data files.
The profile document aids applications development, describing implementation schemes and highlights parts of the core Bluetooth protocol supporting the profile. Profiles supported are outlined in Figure 6; they are depicted grouped together. Each profile is built upon the one underneath, attaining their features from the lower profiles. The result of this approach gives the profiles a similar look and feel for user recognition. Plus developers can recycle modules for speeding up development time and reducing costs (see Bluetooth Technology: What are the Applications?).
A wireless headset for a mobile phone is an application example using the profiles. It uses the Headset profile as its core specification. In Figure 6 the Headset profile is built from the Serial Port Profile (SPP) and the Generic Access Profile (GAP). The GAP being the base of all profiles, it defines the generic procedures related to device discovery and link management (see Bluetooth Technology: What are the Applications? ). Figure 6: Bluetooth Profiles.