Wireless Data

Overview
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Computer Networks


These are a few of the types of common computer networks that are used depending on their size and scale:
 * PAN (Personal Area Networks): Networks that are used mostly to communicate with devices that are close to one person; i.e. Bluetooth headsets, wireless game controllers, etc.
 * LAN (Local Area Networks): Networks that connect computers and devices in a limited geographical area such as a home, school, computer lab, or office.
 * MAN (Metropolitan Area Network): Networks that usually spans an entire city or large campus.
 * WAN (Wide Area Network): Networks that cover a large geographic area such as a city, country, or spans even intercontinental distances, using a communications channel that combines many types of media such as telephone lines, cables, and air waves.

Bluetooth


Bluetooth is a Personal Area Network technology that has been under development since 1994. It uses up to 3 Mbps of data rates in small 10 meter ranges.

Bluetooth devices are mostly designed for: Bluetooth uses an IEEE (Institution of Electrical Engineers) Standard of 802.15.1 and has 3 classes:
 * low cost
 * low power
 * small size
 * voice and data
 * worldwide market
 * Class 1: 100 Meters
 * Class 2: 10 Meters
 * Class 3: 1 Meter

Bluetooth Air Interface
Bluetooth technology uses a Master-Subordinate approach to connect to devices:
 * The master device determines the frequency hoping sequence.
 * There can be up to seven subordinate devices.
 * The devices are linked in a small area within a range, which is called a piconet.

Frequency hopping spread spectrum is done in a 2.4 GHz unlicensed band, which is the same band used in wireless LANs, portable phones, and baby monitors. The band uses 79.1 MHz channels between 2.402 and 2.480 MHz, and hops 1600 times per second.

There are two link types that are used in Bluetooth devices:


 * Synchronous Connection Oriented: used for voice, circuit-switched services, symmetric, QoS.


 * Asynchronous Connection-less: packet-based, for data.

Bluetooth Applications
Here is a list of applications used for Bluetooth technology:
 * Cordless telephony
 * Intercoms
 * Headsets
 * Dial-up networking
 * Fax
 * LAN access
 * File transfer
 * Forwarding SMS
 * Synchronization for PDAs
 * Advertising

Bluetooth Step-by-Step

 * 1) A Bluetooth device that includes hardware and software for sending radio signals at 2.4 GHz
 * 2) The device constantly sends out a message looking for other Bluetooth devices in range.
 * 3) When devices are in range, they examine each others' profile, which are coded in the hardware.
 * 4) After a connection is established, the devices can talk to one another.
 * 5) Two or more devices create a piconet, which uses spread-spectrum frequency hopping to avoid interference.
 * 6) Piconets can link to one another, and any Bluetooth device can also be apart of more than one piconet.

Wireless LANs


Wireless LANs have had many competing technologies and approaches, but has incompatibilties across venders. WLANs uses IEEE standard 802.11, which was approved in 1997.

Here are some of the benefits of WLANs:
 * Mobility
 * Ease and speed of deployment
 * Cost
 * Flexibility

WLAN Applications

 * Early years, focused on vertical markets: i.e., healthcare, retail, manufacturing, schools and universities, office environments.
 * Today: public settings: cafes and airports, homes
 * quickly evolving: multi-port "hot spot" networks.

IEEE 802 Standards
IEEE 802 refers to the family of IEEE standards that are used in both Local and Metropolitan Area Networks.



802.11
IEEE 802.11 has been the base standard since 1997 and has a rate up to 1-2 Mbps. It is apart of the Physical layer of the OSI Model and is defined by three types: FHSS, DHSS, and infrared. 802.11 is also apart of the MAC sublayer of the Datalink layer where it uses CSMA/CSA, or collision avoidance rather than collision detection. An access device converts 802.11 frames into 802.3 (Ethernet) or 802.5 (Token ring) frames.

802.11b
IEEE 802.11b has rates up to 11 Mbps and mostly operates in an unlicensed ISM (Industrial, Scientific, and Medical) band. It has signal ranges up to approx. 150 ft and has rapid uptake and low prices. 802.11b is also used in the 2.4 GHz spectrum.

802.11a
IEEE 802.11a has a max. rate of 54 Mbps, uses 5 GHz in the ISM band, uses OFDM (Orthogonal frequency-division multiplexing), and is not backwards compatible. It has 24 channels rather than 3 in 802.11b and 802.11g. Also, 802.11a has a 75 foot range, but is prone to interference. It is mostly used in business settings, and home entertainment.

802.11g
Like 802.11a, IEEE 802.11g has a max rate of 54 Mbps. It uses 2.4 GHz in the ISM band, also uses OFDM, and is backwards compatible. Using multiple channels in 802.11g increases the speed even more.

802.11n
IEEE 802.11n is backwards compatible, and covers larger distances. It has higher data rates compared to b and g, and has different uses for antennas. It has rates up to 540 MBps while 200 MBps is typical. IEEE approved the standard in July of 2007.

Picturing OFDM
OFDM splits a high-speed stream into several parallel, slower streams at different frequencies. Because data arrives at different times, receivers can decode transmissions as they arrive rather than all at one time.

Why split into different frequencies
The ISM band is a set of frequencies that are unregulated.

The most popular consumer bands:


 * 915 MHz Band (BW 26 MHz)


 * 2.45 GHz Band (BW 100 MHz)


 * 5.8 GHz Band (BW 100 MHz)

Typical RF transmitters in the ISM band include:


 * Analog Cordless Phones (900 MHz)


 * Microwave Ovens (2.45 GHz)


 * Bluetooth Devices (2.45 GHz)


 * Digital Cordless Phones (2.45 GHz or 5.8 GHz)


 * Wireless LAN (2.45 GHz or 5.8 GHz)

European Answers to 802.11
HiperLAN/2 is being developed at ETSI (European Telecommunications Standards Institute), and has speeds up to 54 Mbps. It also uses OFDM, but with TDMA rather than CSMA/CA in the MAC layer. The spectrum in the 5 GHz band is reserverd for Europe in HiperLAN/2.

Wi-Fi vs. Bluetooth
For Bluetooth: For Wi-Fi:
 * Its easier to discover devices
 * Low power, so it doesn't interfere at a distance
 * Low power, so its easier to use batteries
 * It Operates with more power, hence wider range
 * Its easier to encrypt
 * Higher data rates

WiMAX


WMAX (Worldwide Interoperability for Microwave Access) has higher rates than Wi-Fi with speeds up to 70 Mbps. It uses outdoor antennas with ranges up to 30 kilometers. WiMAX is apart of the IEEE working group 802.16 and operates between bands of 2-11 GHz and 10-66 GHz. There are new developments in both licensed and unlicensed bands. Also, new developments supports for mobile users with IEEE 802.16e. In the future there could be a new IEEE standard, 802.20.

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