This post covers WIRELESS COMMUNICATIONS AND NETWORKS by William Stallings.

Basic Ideas

• Bluetooth is an always-on, short-range radio hookup that resides on a microchip.

• The concept behind Bluetooth is to provide a universal short-range wireless capability.

• Using the 2.4-GHz band, available globally for unlicensed low-power uses, two Bluetooth devices within 10 m of each other can share ur to 720 kbps of capacity.

• Bluetooth is intended to support an open-ended list of applications, including data (e.g., schedules and telephone numbers), audio, graphics, and even video. For example, audio devices can include headsets, cordless and standard phones, home stereos, and digital MP3 players.

• The following are examples of some of the capability Bluetooth can provide consumers:

• Make calls from a wireless headset connected remotly to a cell phone.

• Eliminate cables linking computers to printers, keyboards, and the mouse.

• Hook up MP3 players wirelessly to other machines to download music.

• Set up home networks so that a couch potato can remotely monitor air conditioning, the oven, and childrens’ Internet surfing.

• Call home from a remote location to turn appliances on and off, set the alarm, and monitor activity.

• Bluetooth is designed to operate in an environment of many users. Up to eight devices can communicate in a small network called a piconet.

• Ten of these piconets can coexist in the same coverage range of the Bluetooth radio. To provide security, each link is encoded and protected against eavesdropping and interference.

• As was mentioned, the basic unit of networking in Bluetooth ‘s a piconet, consisting of a master and from one to seven active slave devices. The radio designated as the master makes the determination of the channel (frequency hopping sequence) and phase (timing offset, i.e., when to transmit) that shall be used by all devices on this piconet.

• Bluetooth provides support for three general application are using shortrange

  wireless connectivity:

• Data and voice access points: Bluetooth facilitates real-time voice and data transmissions by providing effortless wireless connection of portable and stationary communications devices.

• Cable replacement: Bluetooth eliminates the need for numerous, often proprietary, cable attachments for connection of practically any kind of communication device. Connections are instant and are maintained even when devices are not within line of sight. The range of each radio is approximately 10m but can be extended to 100 m with an optional amplifier.

• Ad hoc networking: A device equipped with a Bluetooth radio can establish instant connection to another Bluetooth radio as soon as it comes into range.

• Protocol Architecture Bluetooth is defined as a layered protocol architecture consisting of core protocols, cable replacement and telephony control protocol, and adopted protocols.

  • The core protocols form a five-layer stack consisting of the following elements:
  • Radio: Specifies details of the air interface, including. requency, the use of frequency hopping, modulation scheme, and transmit power.
  • Baseband: Concerned with connection establishment’ ithin a piconet, addressing, packet format, timing, and power control
  • Link manager protocol (LMP): Responsible for Iink setup between Bluetooth devices and ongoing link management. This includes security aspects such as authentication and encryption, plus the control and negotiation of baseband packet sizes.
  • Logical link control and adaptation protocol (L2CAP): Adapts upper-layer protocols to the baseband layer. L2CAP provides oth connectionless and connection-oriented services.
  • Service discovery protocol (SDP): Device information, services, and the characteristics of the services can be queried to enable the establishment of a connection between two or more Bluetooth devices.

• Piconets and Scatternets

  

• The radio designated as master makes this determination using its own device address as a parameter, while the slave devices must tune to the same channel and phase.

  

• A slave may only communicate with the master and may only communicate when granted permission by the master.

• A device in one piconet may also exist as part of another piconet and may function as either a slave or master in each piconet.

• This form of overlapping is called a scatternet. Below figure is based on contrasts the piconet/scatternet architecture with other forms of wireless networks.

• The advantage of the piconet/scatternet scheme is that it allows many devices to share the same physical area and make efficient use of the bandwidth.

• A Bluetooth system uses a frequency-hopping scheme with a carrier spacing of 1 MHz.

• Typically, up to 80 different frequencies are used for a total bandwidth of 80 MHz. If frequency hopping were not used, then a single channel would corresponed to a single 1-MHz band.

• With frequency hopping a logical channel is defined by the frequency-hopping sequence.

• At any give time, the bandwidth available is 1 MHz, with a maximum of eight devices sharing the bandwidth. Different logical channels (different hopping sequences) can simultaneously share the same 80-MHz bandwidth. Collisions will occur when devices in different piconets, on different logical channels, happen to use the same hop frequency at the same time.

• As the number of piconets in an area increases, the number of collisions increases, and performance degrades. In summary, the physical area and total bandwidth are shared by the scatternet. The logical channel and data transfer are shared by a piconet.