Bluetooth Architecture (Continuation)

Bluetooth Architecture (continuation) Figure: Bluetooth Architecture Logical Link Control and Adaptation Protocol (L2CAP) This specification can view on Bluetooth's link layer. L2CAP delivers packet receivedfrom higher layer to the other end of the link. Bluetooth device can establish an L2CAPconnection as soon as they come in the range of the each other. So a client deviceneed to discover the services provided by the server device. Service Discovery Protocol (SDP) defines the means by which the client device candiscover services as well as their attributes. SDP is responsible only for discoverymechanism. It will not provide methods for accessing those devices. The RFCOMM specification defines a method of performing the RS-232 cableconnection on top of the Bluetooth air link. RFCOMM support legacy application thatuse the COM port to communicate with the peer host. Example: Point to Point protocol (PPP) expect a serial link line interface from the lower layer.Since PPP provides a packet oriented interface to the higher layers so all packet basednetwork and transport protocol including TCP/P can be supported on top of PPP. More efficient method of running IP over Bluetooth are currently under development.

Radio Front End (RF) The 2.4 GHz ISM band in which Bluetooth operates is globally available for license-freeuse. Europe and the United State allocate 83.5 MHz to this band but Spain, France &Japan allocate less. Effort are under process to make Bluetooth function worldwide forevery device. Link speed of Bluetooth is 1 Mbps, which is achieved by using simplemodulation techniques like Gaussian Frequency Shift Keying (GFSK). This GFSKprovide easy radio design and low cost but we can achieve more rate by using complexmodulation techniques. Bluetooth is a frequency hopping spread spectrum system.The costliest part of any wireless interface is Radio Front (RF) end. In any radioreceiver we need  RF filters  Oscillators  image reject mixers process input signals at high frequencies. and designing of such circuit is very expensive. As they require costly materials. So forreducing cost Bluetooth recommends shifting the input signal to a lower intermediatefrequency (around 3 MHz) which allow on-chip construction of low lower filters usingCMOS material. However, it creates further new problems like • reduced receiver sensitivity (Recommended receiver sensitivity for Bluetooth is -70dBm) and for 802.11 wireless LAN is - 90 dBm so for the same transmit power. The range forBluetooth is shorter then it is for 802.11 WLAN.