Global Positioning System Technology:
Where am I? The question seems simple; the answer, historically, has proved not to be. For centuries, navigators and explorers have searched the heavens for a system that would enable them to locate their position on the globe with the accuracy necessary to avoid tragedy and to reach their intended destinations. On June 26, 1993, however, the answer became as simple as the question. On that date, the U.S. Air Force launched the 24th Navstar satellite into orbit, completing a network of 24 satellites known as the Global Positioning System, or GPS. With a GPS receiver that costs less than a few hundred dollars you can instantly learn your location on the planet--your latitude, longitude, and even altitude--to within a few hundred feet.This incredible new technology was made possible by a combination of scientific and engineering advances, particularly development of the world's most accurate timepieces: atomic clocks that are precise to within a billionth of a second. The clocks were created by physicists seeking answers to questions about the nature of the universe, with no conception that their technology would some day lead to a global system of navigation. Today, GPS is saving lives, helping society in countless other ways, and generating 100,000 jobs in a multi-billion-dollar industry.
Since then, GPS technology has moved into the civilian sector. Today, GPS is saving lives, helping society in many other ways, and generating jobs in a new multi-billion-dollar industry. Advances in integrated-circuit technology--the technology used to make computer chips--soon will lead to GPS receivers and transmitters the size of credit cards, so small and so inexpensive that virtually any vehicle can have one installed and any person can carry one.
What is Wireless Communication ?
Wireless communication is the transfer of information over a distance without the use of electrical conductors or "wires".The distances involved may be short (a few meters as in television remote control) or very long (thousands or even millions of kilometers for radio communications). When the context is clear the term is often simply shortened to "wireless". Wireless communications is generally considered to be a branch of telecommunications. Wireless Communication is upgrading quite rapidly day by day.
Wireless devices are various types of fixed, mobile, portable two way radios, cellular telephones, wireless internet, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, garage door openers and or garage doors, wireless computer mice and keyboards, satellite television and cordless telephones.
The History of Wirless Communication:
Before the ``Birth of Radio'', 1867-1896
*1867 - Maxwell predicts existence of electromagnetic (EM) waves
*1887 - Hertz proves existence of EM waves; first spark transmitter generates a spark in a receiver several meters away
*1890 - Branly develops coherer for detecting radio waves
*1896 - Guglielmo Marconi demonstrates wireless telegraph to English telegraph office
``The Birth of Radio''
*1897 - ``The Birth of Radio'' - Marconi awarded patent for wireless telegraph
*1897 - First ``Marconi station'' established on Needles island to communicate with English coast
*1898 - Marconi awarded English patent no. 7777 for tuned communication
*1898 - Wireless telegraphic connection between England and France established
Transoceanic Communication
*1901 - Marconi successfully transmits radio signal across Atlantic Ocean from Cornwall to Newfoundland
*1902 - First bidirectional communication across Atlantic
*1909 - Marconi awarded Nobel prize for physics
Voice over Radio
*1914 - First voice over radio transmission
*1920s - Mobile receivers installed in police cars in Detroit
*1930s - Mobile transmitters developed; radio equipment occupied most of police car trunk
*1935 - Frequency modulation (FM) demonstrated by Armstrong
*1940s - Majority of police systems converted to FM
Birth of Mobile Telephony
*1946 - First interconnection of mobile users to public switched telephone network (PSTN)
*1949 - FCC recognizes mobile radio as new class of service
*1940s - Number of mobile users > 50K
*1950s - Number of mobile users > 500K
*1960s - Number of mobile users > 1.4M
*1960s - Improved Mobile Telephone Service (IMTS) introduced; supports full-duplex, auto dial, auto trunking
*1976 - Bell Mobile Phone has 543 pay customers using 12 channels in the New York City area; waiting list is 3700 people; service is poor due to blocking
Cellular Mobile Telephony
*1979 - NTT/Japan deploys first cellular communication system
*1983 - Advanced Mobile Phone System (AMPS) deployed in US in 900 MHz band: supports 666 duplex channels
*1989 - Groupe Spècial Mobile defines European digital cellular standard, GSM
*1991 - US Digital Cellular phone system introduced *1993 - IS-95 code-division multiple-access (CDMA) spread- spectrum digital cellular system deployed in US
*1994 - GSM system deployed in US, relabeled ``Global System for Mobile Communications''
PCS and Beyond
*1995 - FCC auctions off frequencies in Personal Communications System (PCS) band at 1.8 GHz for mobile telephony
*1997 - Number of cellular telephone users in U.S. > 50M
2000 - Third generation cellular system standards? Bluetooth standards?
The range of wireless services :
Radio spectrum is used for a wide range of services. These can be broken into the following broad classes:
• Broadcasting services: including short wave, AM and FM radio as well as terrestrial television;
• Mobile communications of voice and data: including maritime and aeronautical mobile for communications between ships, airplanes and land; land mobile for communications between a fixed base station and moving sites such as a taxi fleet and paging services, and mobile communications either between mobile users and a fixed network or between mobile users, such as mobile telephone services;
• Fixed Services: either point to point or point to multipoint services;
• Satellite: used for broadcasting, telecommunications and internet, particularly over long distances;
• Amateur radio; and
• Other Uses: including military, radio astronomy, meteorological and scientific uses
The number of different devices using wireless communications is rising rapidly. Sensors and embedded wireless controllers are increasingly used in a variety of appliances and applications. Personal digital assistants (PDAs) and mobile computers are regularly connected to e-mail and internet services through wireless communications, and wireless local area networks for computers are becoming common in public areas like airport lounges. However, by far the most important and dramatic change in the use of wireless communications in the past twenty years has been the rise of the mobile telephone.
The rise and rise of mobile telephony
The introduction of cellular technology greatly expanded the efficiency of frequency use of mobile phones. Rather than exclusively allocating a band of frequency to one telephone call in a large geographic area, a cell telephone breaks down a geographic area into small areas or cells. Different users in different (non-adjacent) cells are able to use the same frequency for a call without interference.
Second generation (2G) mobile telephones used digital technology. The adoption of second generation technology differed substantially between the United States and Europe and reverses the earlier analogue mobile experience.
Groupe Speciale Mobile (GSM) was first developed in the 1980s and was the first 2G system. But it was only in 1990 that GSM was standardized (with the new name of Global System for Mobile communication) under the auspices of the European Technical Standards Institute. The standardized GSM could allow full international roaming, automatic location services, common encryption and relatively high quality audio. GSM is now the most widely used 2G system worldwide, in more than 130 countries, using the 900 MHz frequency range.
In contrast, a variety of incompatible 2G standards developed in the United States. These include TDMA, a close relative of GSM, and CDMA, referring to Time and Code Division Multiple Access respectively. These technologies differ in how they break down calls to allow for more efficient use of spectrum within a single cell. While there is some argument as to the ‘better’ system, the failure of the U.S. to adopt a common 2G standard, with the associated benefits in terms of roaming and switching of handsets, meant the first generation AMPS system remained the most popular mobile technology in the U.S. throughout the 1990s.
The GSM Mobile System:
The GSM system has become the most popular system for mobile communication in the world.
With GSM, systems for mobile communication reached a global scale. In the western world, it seems everyone has their own mobile phone, and GSM has taken more and more of the market. GSM allows users to roam seamlessly between networks, and separate the user identity from the phone equipment. In addition the GSM system provides the functional basis for the 3rd generation mobile system, UMTS.
The main work with the GSM took place from 1988 - 1990 and resulted in 12 series of specifications which in great detail specified the inner workings of GSM. In 1990, when phase 1 of the specifications was finished, there were three dominating automatic systems for mobile communications in the world:
• American AMPS from 1984, with networks in the US.
• British TACS from 1985, with network in Britain.
• Nordic NMT from 1981, with networks in the Nordic countries.
Operation of GSM System:
GSM networks operate in four different frequency ranges. Most GSM networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including Canada and the United States) use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency bands were already allocated.
The rarer 400 and 450 MHz frequency bands are assigned in some countries, notably Scandinavia, where these frequencies were previously used for first-generation systems.
In the 900 MHz band the uplink frequency band is 890–915 MHz, and the downlink frequency band is 935–960 MHz. This 25 MHz bandwidth is subdivided into 124 carrier frequency channels, each spaced 200 kHz apart. Time division multiplexing is used to allow eight full-rate or sixteen half-rate speech channels per radio frequency channel. There are eight radio timeslots (giving eight burst periods) grouped into what is called a TDMA frame. Half rate channels use alternate frames in the same timeslot. The channel data rate is 270.833 kbit/s, and the frame duration is 4.615 ms.
The transmission power in the handset is limited to a maximum of 2 watts in GSM850/900 and 1 watt in GSM1800/1900.
GSM has used a variety of voice codecs to squeeze 3.1 kHz audio into between 5.6 and 13 kbit/s. Originally, two codecs, named after the types of data channel they were allocated, were used, called Half Rate (5.6 kbit/s) and Full Rate(13 kbit/s). These used a system based upon linear predictive coding (LPC). In addition to being efficient with bitrates, these codecs also made it easier to identify more important parts of the audio, allowing the air interface layer to prioritize and better protect these parts of the signal.
GSM was further enhanced in 1997with the Enhanced Full Rate (EFR) codec, a 12.2 kbit/s codec that uses a full rate channel. Finally, with the development of UMTS, EFR was refactored into a variable-rate codec called AMR-Narrowband, which is high quality and robust against interference when used on full rate channels, and less robust but still relatively high quality when used in good radio conditions on half-rate channels.
Satellite Communication:
By the end of World War II, the world had had a taste of "global communications." Edward R. Murrow's radio broadcasts from London had electrified American listeners. We had, of course, been able to do transatlantic telephone calls and telegraph via underwater cables for almost 50 years. At exactly this time, however, a new phenomenon was born. The first television programs were being broadcast, but the greater amount of information required to transmit television pictures required that they operate at much higher frequencies than radio stations. For example, the very first commercial radio station (KDKA in Pittsburgh) operated ( and still does) at 1020 on the dial. This number stood for 1020 KiloHertz - the frequency at which the station transmitted. Frequency is simply the number of times that an electrical signal "wiggles" in 1 second. Frequency is measured in Hertz. One Hertz means that the signal wiggles 1 time/second. A frequency of 1020 kiloHertz means that the electrical signal from that station wiggles 1,020,000 times in one second.
By the end of World War II, the world had had a taste of "global communications." Edward R. Murrow's radio broadcasts from London had electrified American listeners. We had, of course, been able to do transatlantic telephone calls and telegraph via underwater cables for almost 50 years. At exactly this time, however, a new phenomenon was born. The first television programs were being broadcast, but the greater amount of information required to transmit television pictures required that they operate at much higher frequencies than radio stations. For example, the very first commercial radio station (KDKA in Pittsburgh) operated ( and still does) at 1020 on the dial. This number stood for 1020 KiloHertz - the frequency at which the station transmitted. Frequency is simply the number of times that an electrical signal "wiggles" in 1 second. Frequency is measured in Hertz. One Hertz means that the signal wiggles 1 time/second. A frequency of 1020 kiloHertz means that the electrical signal from that station wiggles 1,020,000 times in one second.
Television signals, however required much higher frequencies because they were transmitting much more information - namely the picture. A typical television station (channel 7 for example) would operate at a frequency of 175 MHz. As a result, television signals would not propagate the way radio signals did.Both radio and television frequency signals can propagate directly from transmitter to receiver. This is a very dependable signal, but it is more or less limited to line of sight communication. The mode of propagation employed for long distance (1000s of miles) radio communication was a signal which traveled by bouncing off the charged layers of the atmosphere (ionosphere) and returning to earth. The higher frequency television signals did not bounce off the ionosphere and as a result disappeared into space in a relatively short distance. Consequently, television reception was a "line-of-sight" phenomenon, and television broadcasts were limited to a range of 20 or 30 miles or perhaps across the continent by coaxial cable. Transatlantic broadcasts were totally out the question. If you saw European news events on television, they were probably delayed at least 12 hours, and involved the use of the fastest airplane available to carry conventional motion pictures back to the U.S. In addition, of course, the appetite for transatlantic radio and telephone was increasing rapidly. Adding this increase to the demands of the new television medium, existing communications capabilities were simply not able to handle all of the requirements. By the late 1950s the newly developed artificial satellites seemed to offer the potential for satisfying many of these needs.
The CDMA Mobile System:
CDMA2000 is a hybrid 2.5G/ 3G technology of mobile telecommunications standards that use CDMA, a multiple access scheme for digital radio, to send voice, data, and signalling data (such as a dialed telephone number) between mobile phones and cell sites. CDMA2000 is considered a 2.5G technology in 1xRTT and a 3G technology in EVDO.
CDMA2000 has a relatively long technical history, and remains compatible with the older CDMA telephony methods (such as cdmaOne) first developed by Qualcomm, a commercial company, and holder of several key international
patents on the technology.
The CDMA2000 standards CDMA2000 1xRTT, CDMA2000 EV-DO, and CDMA2000 EV-DV are approved radio interfaces for the ITU's IMT-2000 standard and a direct successor to 2G CDMA, IS-95 (cdmaOne). CDMA2000 is standardized by 3GPP2.
CDMA2000 1xRTT
CDMA2000 1xRTT, the core CDMA2000 wireless air interface standard, is also known as 1x, 1xRTT, and IS-2000. The designation "1x", meaning "1 times Radio Transmission Technology", indicates the same RF bandwidth as IS-95: a duplex pair of 1.25 MHz radio channels. This contrasts with 3xRTT, which uses channels 3 times as wide (3.75 MHz) channels. 1xRTT almost doubles the capacity of IS-95 by adding 64 more traffic channels to the forward link, orthogonal to (in quadrature with) the original set of 64. Although capable of higher data rates, most deployments are limited to a peak of 144 kbit/s. IMT-2000 also made changes to the data link layer for the greater use of data services, including medium and link access control protocols and QoS. The IS-95 data link layer only provided "best effort delivery" for data and circuit switched channel for voice (i.e., a voice frame once every 20 ms).
1xRTT officially qualifies as 3G technology, but it is considered by some to be a 2.5G (or sometimes 2.75G) technology. This allows it to be deployed in 2G spectrum in some countries that limit 3G systems to certain bands.
CDMA2000 3x
CDMA2000 3x is (also known as EV-DO Rev B) is a multi-carrier evolution of the Rev A specification. It maintains the capabilities of EVDO Rev A, and provides the following enhancements:
--Higher rates per carrier (up to 4.9 Mbit/s on the downlink per carrier). Typical deployments are expected to include 3 carriers for a peak rate of 14.7 Mbit/s
--Higher rates by bundling multiple channels together enhance the user experience and enables new services such as high definition video streaming.
--Uses statistical multiplexing across channels to further reduce latency, enhancing the experience for latency-sensitive services such as gaming, video telephony, remote console sessions and web browsing.
--Increased talk-time and standby time .Hybrid frequency re-use which reduces the interference from the adjacent sectors and improves the rates that can be offered, especially to users at the edge of the cell.
--Efficient support for services that have asymmetric download and upload requirements (i.e. different data rates required in each direction) such as file transfers, web browsing, and broadband multimedia content delivery.
GPRS System:
General Packet Radio Services (GPRS) is a packet-based wireless communication service that promises data rates from 56 up to 114 Kbps and continuous connection to the Internet for mobile phone and computer users. The higher data rates allow users to take part in video conferences and interact with multimedia Web sites and similar applications using mobile handheld devices as well as notebook computers. GPRS is based on Global System for Mobile (GSM) communication and complements existing services such circuit-switched cellular phone connections and the Short Message Service (SMS).
In theory, GPRS packet-based services cost users less than circuit-switched services since communication channels are being used on a shared-use, as-packets-are-needed basis rather than dedicated to only one user at a time. It is also easier to make applications available to mobile users because the faster data rate means that middleware currently needed to adapt applications to the slower speed of wireless systems are no longer be needed. As GPRS has become more widely available, along with other 2.5G and 3G services, mobile users of virtual private networks (VPNs) have been able to access the private network continuously over wireless rather than through a rooted dial-up connection.
EDGE (Enhanced Data rates for GSM Evolution):
is a digital mobile phone technology that allows increased data transmission rates and improved data transmission reliability. EDGE is generally classified as 2.75G, although it is part of ITU's 3G definition. EDGE has been introduced into GSM networks around the world since 2003, initially by Cingular (now AT&T) in the United States.
EDGE can be used for any packet switched application, such as an Internet connection. High-speed data applications such as video services and other multimedia benefit from EGPRS' increased data capacity. EDGE Circuit Switched is a possible future development.
WI-FI Technology:
A wireless network uses radio waves, just like cell phones, televisions and radios do. In fact, communication across a wireless network is a lot like two-way radio communication. Here's what happens:
1.
A computer's wireless adapter translates data into a radio signal and transmits it using an antenna.
2.
A wireless router receives the signal and decodes it. It sends the information to the Internet using a physical, wired Ethernet connection. The process also works in reverse, with the router receiving information from the Internet, translating it into a radio signal and sending it to the computer's wireless adapter.
The radios used for WiFi communication are very similar to the radios used for walkie-talkies, cell phones and other devices. They can transmit and receive radio waves, and they can convert 1s and 0s into radio waves and convert the radio waves back into 1s and 0s. But WiFi radios have a few notable differences from other radios:
--They transmit at frequencies of 2.4 GHz or 5GHz. This frequency is considerably higher than the frequencies used for cell phones, walkie-talkies and televisions. The higher frequency allows the signal to carry more data.
--They use 802.11 networking standards, which come in several flavors:
---802.11a transmits at 5GHz and can move up to 54 megabits of data per second. It also uses orthogonal frequency-division multiplexing (OFDM), a more efficient coding technique that splits that radio signal into several sub-signals before they reach a receiver. This greatly reduces interference.
---802.11b is the slowest and least expensive standard. For a while, its cost made it popular, but now it's becoming less common as faster standards become less expensive. 802.11b transmits in the 2.4 GHz frequency band of the radio spectrum. It can handle up to 11 megabits of data per second, and it uses complimentary code keying (CCK) coding.
---802.11g transmits at 2.4 GHz like 802.11b, but it's a lot faster -- it can handle up to 54 megabits of data per second. 802.11g is faster because it uses the same OFDM coding as 802.11a.
---802.11n is the newest standard that is widely available. This standard significantly improves speed and range. For instance, although 802.11g theoretically moves 54 megabits of data per second, it only achieves real-world speeds of about 24 megabits of data per second because of network congestion. 802.11n, however, reportedly can achieve speeds as high as 140 megabits per second.
---WiFi radios can transmit on any of three frequency bands. Or, they can "frequency hop" rapidly between the different bands. Frequency hopping helps reduce interference and lets multiple devices use the same wireless connection simultaneously.
WIMAX Technology:
WiMAX is short for Worldwide Interoperability for Microwave Access, and it also goes by the IEEEname 802.16.
WiMAX has the potential to do to broadband Internet access what cell phones have done to phone access. In the same way that many people have given up their "land lines" in favor of cell phones, WiMAX could replace cable and DSL services, providing universal Internet access just about anywhere you go. WiMAX will also be as painless as WiFi -- turning your computer on will automatically connect you to the closest available WiMAX antenna.
In practical terms, WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users. WiMAX could potentially erase the suburban and rural blackout areas that currently have no broadband Internet access because phone and cable companies have not yet run the necessary wires to those remote locations.
A WiMAX system consists of two parts:
--A WiMAX tower, similar in concept to a cell-phone tower - A single WiMAX tower can provide coverage to a very large area -- as big as 3,000 square miles (~8,000 square km).
--A WiMAX receiver - The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop the way WiFi access is today.
A WiMAX tower station can connect directly to the Internet using a high-bandwidth, wired connection (for example, a T3 line). It can also connect to another WiMAX tower using a line-of-sight, microwave link. This connection to a second tower (often referred to as a backhaul), along with the ability of a single tower to cover up to 3,000 square miles, is what allows WiMAX to provide coverage to remote rural areas.
WiFi-style access will be limited to a 4-to-6 mile radius (perhaps 25 square miles or 65 square km of coverage, which is similar in range to a cell-phone zone). Through the stronger line-of-sight antennas, the WiMAX transmitting station would send data to WiMAX-enabled computers or routers set up within the transmitter's 30-mile radius (2,800 square miles or 9,300 square km of coverage). This is what allows WiMAX to achieve its maximum range.
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