Mumbai University > Computer Engineering > Sem6 > Mobile Communication and Computing

Marks: 10M

Year: Dec 2015

• A typical Bluetooth device has a power of 100mW and can have a range of upto 100m.
• Having such huge power and relying on battery as its source will result in a huge wastage if the device lies idle for long time.
• Bluetooth defines several low-power states for a device. The major states present can be seen in the figure alongside.
• Standby: A device which is currently ON and not part of any piconet is in standby mode. Over here, in this low-power mode only the native-clock runs.
• Inquiry: Now the movement to the next node i.e. inquiry is based in either of two ways:
  • A device wants to establish a piconet: the user wants to scan all the devices in its range. This inquiry procedure is started by sending an Inquiry access Code (IAC) to all devices in range.
  • Device in Standby that listens periodically: a device which is in Standby may enter the Inquiry state periodically to search for IAC messages. If it finds one such, then it transfers the necessary information about itself and becomes a slave.
• Page mode: On successful enquiry, the device enters the page mode. In the page state two different roles are defined.
  • After the master finds all the devices required for a connection, it sets up a piconet.
  • The master then calculates special hopping sequences based on the device addresses received to contact each device individually
  • The slaves answer to calls by the master and synchronize their clocks accordingly.
  • In the meantime, the master may continue to page more devices to the piconet.
  • As soon as the device (slave) synchronizes to the hopping pattern of the piconet, it enters the connected state.
  • Connected: The connected state contains the active state and three low power states.
  • Active: in active state the slave participates in the piconet by listening, transmitting and receiving.
  • A master periodically synchronizes with these slaves.
  • The communication is done via ACL and SCO links.
  • Every device which is active needs to have a 3-bit Active Member Address (AMA).
  • In the active state, if the device is not transmitting, it can disconnect itself and go to standby by detach method.

• A Bluetooth also has the choice to go into either of the three low-power states which are:

  • Sniff:

    • Out of all the three low power states, this one has max. power consumption.
    • Unlike in active state where the slave listens to piconet at every slot, here it listens at a reduced rate which can be programmed as per the need.
    • The master also allocates a reduced number of slots for the slave in sniff mode.

  • Hold:

    • The device here stops all ACL link transmissions are stopped.
    • If no activity is there in the piconet, the slave reduce the power consumption or participates in another piconet.

  • Park:

    • This state has the lower duty cycle and lowest power consumption of the three.
    • It also release it 3-bit AMA address. Instead it gets a 8-bit PMA (Parked Member Access).
    • It remains a member of the piconet but gives a chance for another device to become active.