Johny Learns

What is Bluetooth?

Johny:  Dad, What are all the important points I should remember about Bluetooth?

Dad :  1)  Bluetooth is the name of a King who lived in Denmark.

          2) It uses Radio  Frequency of 2.4GHz ISM band

          3) It uses  Gaussian FSK Modulation technique ( in Version.1)

          4) It uses Fast Frequncy-Hopping Spread Spectrum (Fast FHSS).

          5) The speed  of version.1 is  1 Mbps. Version 2 has 3 Mbps speed.

          6)  Effective distance is 10 meters.

          7) Data is transmitted in packets during time slots which are of fixed duration.

          8) Security :FHSS allows only the synchronized receivers to receive the data.

              In addition, it uses 128 bit encryption of data.

          9) Using Bluetooth,you can connect a computer to a Printer,Fax,Headset,Mobile phone,Camera,Mouse,etc.

         10. It is Personal Area Network(PAN).

         11) IEEE standard is 802.15

Johny : What is Fast FHSS?

Dad : Radio Mirchi FM is trasmitting at 98.3MHz. Just imagine, after 5 minutes it changes its frequency to 99.3 MHz for next Five Minutes. Then again it switches to 98.3. What you will do to continuously listen to the program?

Johny: I will tune my receiver to 98.3 for 5 minutes, then I will change my frequency to 99.3.....

Dad : In the same way, in case of FHSS, the FREQUENCY HOPS from one frequency to the other. The receiver is  synchronized for the same pattern . So, the receiver receives data continuously without interruption. It changes its frequency 1600 times per second. It is so FAST, is it not?  Instead of using one central frequency, it can choose its pattern from 79 frequencies. So the frequency spectrum  is not narrow. It is SPREAD SPECTRUM. Hence this technique got the name Fast Frequency Hopping Spread Spectrum. The advantage of Frequency Hopping is, only the receiver knowing the  'pseudo random pattern of frequency change' will receive the data. So it is a kind of security.

Johny : What is ISM band?

Dad : ISM band means  Industrial,Scientific and Medical Frequency Band. You need not get license from the Government for using these frequencies. 2450 and 5800 MHz are commonly used ISM Band frequencies. 

Johny: What is PAN?

Dad: PAN stands for Personal Area Network. A PAN can be either a PICONET or SCATTERNET. A piconet will be having only one Master and upto 7 slaves. If there are more than 7 slaves, the rest of slaves must be PARKED. To activate a parked slave, a currently active slave should be parked.