In-depth

Bluetooth

uses a short range (10 meters) radio link. The range can be increased to about

100 meters with boosters, which increase the power of the signals. Bluetooth

uses the unlicensed ISM band (2.4 GHz). This makes Bluetooth-enabled products

workable across the globe, eradicating compatibility issues. Bluetooth devices

can communicate through non-metallic barriers like concrete walls too. To make

two (or more) Bluetooth devices talk, you don’t need to aim them at each

other. They emit omni-directional radio waves, which can be caught by other

Bluetooth devices located wherever and in whatever position, but within the

range.

One major problem in wireless communication is noise

induction. Radio waves can pick up noise from nearby devices like microwave

ovens. You can’t afford to lose data if that happens. This is where a

technique called "frequency hopping" comes into the picture. What is

transferred during a Bluetooth communication are packets. With frequency

hopping, after the transmission or reception of a packet, the Bluetooth device

hops or changes to a different frequency. The signal frequency changes about

1,600 times per second. In addition, it uses smaller packets and FEC (Forward

Error Correction) to further minimize the impact of interferences.

Bluetooth defines a protocol stack which essentially consists

of following layers:

• Radio : The Bluetooth radio layer is the lowest layer,
  
  and defines the frequency, transmitter and receiver characteristics.

• Baseband : This forms the physical layer and provides :

• Link control (asynchronous or synchronous)

• Error correction

• Frequency selection for frequency hopping

• Security

• LMP (Link Manager Protocol): This performs link setup,
  
  link configuration, and authentication

• HCI (Host Controller Interface): This provides access to
  
  the Bluetooth Baseband, hardware status, and control registers

• L2CAP (Logical Link Control and Adaptation Protocol):
  
  This forms the data link layer. It provides connectionless and
  
  connection-oriented data services to applications. Two link types are
  
  supported for the Baseband layer–SCO (Synchronous Connection-Oriented) and
  
  ACL (Asynchronous Connection-Less )

• RFCOMM : This provides emulation for serial ports (RS232)
  
  on the L2CAP layer

• SDP (Service Discovery Protocol) : It provides a means for applications to
  
  determine the available services and their characteristics.