Bluetooth

Bluetooth is a method for data communication that uses short-range radio links to replace cables between computers and their connected units.

History of Bluetooth

Harald Bluetooth was king of Denmark in the late 900s. He managed to unite Denmark and part of Norway into a single kingdom then introduced Christianity into Denmark. He left a large monument, the Jelling rune stone, in memory of his parents. He was killed in 986 during a battle with his son, Svend Forkbeard. Choosing this name for the standard indicates how important companies from the Nordic region (nations including Denmark, Sweden, Norway and Finland) are to the communications industry.

Logo

Bluetooth is managed by the Bluetooth Special Interest Group, which has more than 15,000 member companies in the areas of telecommunication, computing, networking, and consumer electronics. It has a patent logo.

Working of Bluetooth Network

Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency of 2.45 gigahertz (between 2.402 GHz and 2.480 GHz, to be exact). This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).

One of the ways Bluetooth devices avoid interfering with other systems is by sending out very weak signals of about 1 milliwatt. By comparison, the most powerful cell phones can transmit a signal of 3 watts. The low power limits the range of a Bluetooth device to about 10 meters (32 feet), cutting the chances of interference between your computer system and your portable telephone or television. Even with the low power, Bluetooth doesn't require line of sight between communicating devices. The walls in your house won't stop a Bluetooth signal, making the standard useful for controlling several devices in different rooms.

Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter (32-foot) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it’s unlikely that two transmitters will be on the same frequency at the same time.

Bluetooth Piconet

 Piconet is an ad-hoc computer network using Bluetooth technology. Bluetooth communication always designates one of the Bluetooth devices as a main controlling unit - master unit. Other devices that follow the master unit are slave units. The devices can switch roles, by agreement, and the slave can become the master.  

Up to 8 active Bluetooth devices can form or become part of temporary small networks Piconets. Bluetooth allows wireless data connections within the Piconet to be dynamically added and removed between nearby devices. The probability of interfering (overlapping) with another Bluetooth system is less than 1.5%.

                                                                                                                 

                                                                                          

Bluetooth Scatternet

Piconets can be setup to interact with other Piconets to form larger networks called Scatternets. Scatternets allow the master in one Piconet to operate as a slave in another Piconet. While this allows Bluetooth devices in one Piconet to communicate with devices in another Piconet (cross-Piconet communication), the use of Scatternets requires synchronization (and sharing of data transmission Bandwidth) making them less efficient. (second Figure is a scatternet set up).

 

Types of Antenna

On the basis of their Structure and applications Antennas can be divided into five major parts. They are following...

1. Wire Antennas
2. Microstrip Antennas
3. Reflector Antennas
4. Travelling Wave Antennas
5. Aperture Antennas

Now Wire Antennas are also of  five different types. They are...

1. Short dipole
2. Dipole
3. Monopole  
4. Small loop
5. Half wave dipole

1) Short Dipole: It is the simplest of all antennas. It can be made of a simple wire, with a center-fed driven element. They are used as antennas, notably in traditional "rabbit ears" television antennas. Word "short" or "small" in antenna always imply "relative to a wavelength".

2) Dipole Antenna: The dipole antenna is similar to the short dipole except it is not required to be small compared to the wavelength at which antenna is operating. 

   Dipole Antenna

3) Monopole Antenna:  A monopole antenna is one half of a dipole antenna, always mounted above some ground plane. 

Monopole Antenna

One side of antenna feed line is attached to the lower end of the monopole, and the other side is attached to the ground plane, generally to the ground.

4) Loop Antenna: A small loop antenna is a loop of wire or tubing with its end connected to a transmission line. Due to radiation resistance and high reactance they are often used as receiver antennas. They have poor efficiency. 

Loop Antenna

5) Half Wave dipole: Half wave dipole is a special type of dipole antenna but is enough important to have a different type. The half wave term means that the length of this dipole antenna is half wavelength of operating frequency. 

Continued...

Antenna- Working Principle

Antenna is mostly used for Radio waves due to which it is often referred as 'Radio Antenna'. Radio waves are electromagnetic waves which carry signals through the air (or through space) at the speed of light with almost no transmission loss. The first antennas were built in 1888 by German physicist Heinrich Hertz in his pioneering experiments to prove the existence of electromagnetic waves predicted by the theory of James Clerk Maxwell.

An antenna is an Impedance matching and directing device. It is an electrical device which converts the electrical currents into radio waves or radio waves into electrical currents. Since they are directing devices they are used with transmitters and receivers. Antennas are arrangements of electrical conductors. These conductors are electrically connected to transmitters or receivers. The antenna at the receiver intercepts the small amount of EM wave and develops tiny voltage which forms small current this current is amplified at the receiver.

When a two wire transmission line is open circuited at the ends it will have a standing wave pattern with voltage maximum at the end of the line. From quarter wave from the end it will have a minimum. The transmission line looses very little amount of energy because field of each wire cancels each other. By folding that wire we form a dipole antenna. Now both fields are added.The name dipole is given due to it has to electrical poles not the physical poles.

Maximum power will be emitted from the Antenna if it follows the maximum power transfer theorem. Which is matching the impedance of an antenna system to the complex conjugate of impedance of transmitter or receiver system. ANY piece of conducting material will work as an antenna on any frequency. The  reason for building sophisticated antennas is to allow us to Control The Radiation Pattern for maximum efficiency and effectiveness.

 Antennas are basically two types according to technology: Omnidirectional and Directional (in one or two direction).

Although according to their structure and application antennas are of various types...

What is difference between CDMA and GSM

There is a lot of confusion between GSM and CDMA technologies. Both are cellular data transmission technologies used in Mobile Communication. To understand them we need a basic foundation of how a technology emerged to push over the other.

History of CDMA:  In 1940, Hollywood actress turned inventor, Hedy Lamarr, and co-inventor George Antheil, with World War II situations arising, co-patented a way for torpedoes to be controlled by sending signals over multiple radio frequencies using random patterns. But the U.S. Navy discarded their work as architecturally unfeasible.New York took up the idea, and after the Lamarr-Antheil patent expired, used it to secure communications for the U.S. during the 1962 Cuban Missile Crisis. After becoming an integral part of government security technology, the U.S. military, in the mid-80s, declassified what has now become CDMA technology, a technique based on spread-spectrum technology.

CDMA, incorporating spread-spectrum, works by digitizing multiple conversations, attaching a code known only to the sender and receiver, and then converting the signals into bits and reassembling them. Qualcomm, which was started by a MIT alumni patented CDMA in early 90's began the design of the first CDMA-based cellular base station.But was launched commercially in Hong Kong in 1995.

Advantages of CDMA:

• Increased cellular communications security.
• Simultaneous conversations.
• Increased efficiency, meaning that the carrier can serve more subscribers.
• Size of Phones became smaller.
• Low power requirements and little cell-to-cell coordination needed by operators.
• Extended reach - beneficial to rural users situated far from cells.

GSM: Just two years before CDMA's 1995 introduction in Hong Kong, European carriers and manufacturers chose to support the first available digital technology - Time Division Multiple Access (TDMA). GSM uses TDMA as its core technology. Therefore, since the majority of wireless users are in Europe and Asia, GSM has taken the worldwide lead as the technology of choice.

Advantages of GSM:

• International roaming permits subscribers to use one phone throughout Western Europe. CDMA will work in North America, but not France, Germany, the U.K. and other popular European destinations.
• GSM is mature, having started in the mid-80s. This maturity means a more stable network with robust features. CDMA is still building its network.
• GSM's maturity means engineers cut their teeth on the technology, creating an unconscious preference.
• The availability of Subscriber Identity Modules, which are smart cards that provide secure data encryption give GSM m-commerce advantages. 

        There are around  5 billion GSM users versus CDMA's not reaching even 1 billion figure. CDMA is majorly used in North America while GSM technology is mostly opted in Europe, Middle East and Africa.

Parameter to Decide Which One is Best: 

CDMA:  While using CDMA Your account information is programmed into your cellular phone. If you want to change your phone, you have to contact your carrier and have them reprogram your new phone. You will also need to re-enter your contact list and calendar information into your new phone.

GSM: Your account information along with your contact list and other personal data are stored on a SIM card (Subscriber Identity Module). It is a small chip you can freely remove from your phone. When you get a new mobile device, you can simply insert your SIM card into it and it will work with your current account information and contact list.

So here GSM is clear winner.

'Steganography'

            Word 'Steganography' is of Greek and it is made of two different words 'steagnos' means 'covered or protected' and 'graphein' means 'to write'. Combining these two word we find the Steaganography as the art of writing important messages in such a way that no one else apart from sender and receiver suspects the existence of hidden message.

            Steganograpghy was used since ancient time. First  steganography was traced back from 400 B.C. When Demaratus king of sparta send a warning about forthcoming attack on Greece by writing the message on wooden backing of the wax tablet before applying its surface.

             There are a lot of examples in history who signifies the importance of Steganography.

             Steganography consist two part in execution...

1.          Encryption
2.          Decryption                                                                                                                                                 
             Encryption is part in which the secret and highly classified information is written or hide within some carrier which should be normal and innocent. It should drag any attraction towards it for safety of the secret message.                                                                                                                                  

              Decryption is just opposite process of encryption in this the receiver decodes the encrypted message from the carrier with  the help of proper technique information about which he gets  from the sender.                 

              Decrypting the hidden message is called STEGANALYSIS.

             

For example if there is a letter written to Mr. Robertson....

Salutations, Mr. Robertson of CIS 5371.  The Florida Society of Math and Cryptography is proud to present you with an small exam for qualification into our society.   The key for passing is studying.  Cryptography is rigorous and only those with patience in themselves pass. We have an exam PO Box in Tallahassee. But please submit by 12/12.

             

The decrypted message which was hidden inside the carrier message is...

               

The Cryptography exam key is in PO Box 1212.