Biometrics information resource
Biometrics information resource
|
|
|
|
Wireless technologies
The most modern telephone is the cellular telephone, or commonly called a cell phone. A cellular telephone is designed to give the user maximum freedom of movement while using a telephone.
Mobile communications is a hot topic. The number of mobile communication devices users is growing very fast. The number of mobiles (cellular phones) is now exceeding the number of fixed lines in many countries (Finland, Japan etc.).
Cellular/mobile phones are everywhere and their utility is growing. A cell phone is a radio telephone, that may be used wherever "cell" coverage is provided. The role of cellular phones has risen with improvement in services, reduction in service costs and the ever increasing services available through cell phones.
Mobile Internet access is a global phenomenon with even great implications. Leading phone manufacturers such as Ericsson, Matsushita (Panasonic), Motorola, and Nokia have put a great deal of marketing effort behind the mobile Internet phenomenon, recognizing that adoption is a complex business proposition. In Europe, WAP is has generated widespread interest because of lots of marketing and expectations put to it. In Japan NTTDoCoMo's mobile Internet service is based on a service called iMode that uses Compact HTML (CHTML) microbrowsers in the phone. There are also products on the market which combine a PDA, a real web-browser and some communication interface (cellular phone, WLAN etc.) into one smart communication device. A the generic phone may soon acquire a browser. And mobile phones will morph into PDAs or organizers. The markets will show what customers will buy and use. The handsets sold over the next few years are likely to operate much differently than those of today. Mobile terminals are complex embedded systems, with stringent real-time requirements for signaling and voice processing. Now Web browsing, multimedia, and connectivity requirements are added to the list.
There are many technical challenges to be solved to make all this to work. Ubiquity is a pinnacle that the cellular communication sector has hoped to reach for the past five years. To reach this goal, a series of networks must be built that allow consumers to use their phone anytime, anywhere. The truth is ubiquity is far from becoming a reality. Across the world cellular carriers can't seem to agree on a single air interface for wireless operation. But, despite battles on the standards front, the wireless community has pushed forward in its efforts to build mobile networks and phones that deliver worldwide coverage. To make this happen, they have focused their attention on developing multimode systems that can support CDMA, TDMA, GSM, GPRS, wideband CDMA (W-CDMA), and a host of other air interfaces in the same box.
|
|
|
|
Nowadays the mobile communication technology seems to be divided to differente generations of technologies. A short description those generations are the following:
In mobile communication there are three sectors on the field: telecom companies who operate the networks, cellular phone makes who make the phones and companies which make the devices for the cellular phone networks. All of these businesses are big. For example around 400-600 million ceullar phones are sold in one year in the world. Some of the largest companies in the field (for example Nokia and Ericsson) make both networks and cellular phones.
Today Mobile Internet is a hot topic. Mobile Internet benefits from the creativity and enthusiasm of entrepreneurs to bring life to the market. It is not only the technology, but a multitude of consumer and business issues, which will decide how quickly and widely next-generation wireless services are deployed. The first version of WAP was a dissappointment to users, because it was not real Internet, but some poor imitation of it. The first users got a very strong dissappointment on the services, and the service market has not got any gib business although most new cellular phones have WAP capabilities in them, but hardly anyone uses them in most countries. Instead of WAP, most users use SMS to access simple mobile services.
In Japan, mobile Internet is getting a warm reception for various reasons in busines, technology and marketing. Third Generation wireless services are being boosted by a combination of positive factors in Japan. The Japan government is now pushing for third generation (3G) services, both to provide increased mobile capacity at home, and to ensure that Japanese companies are well positioned in the competition for the next generation of wireless equipment around the world.
Before 3G there could be 2.5G. In Europe, deployment of modified second generation services (called 2.5G products) such as General Packet Radio Service (GPRS) will boost bandwidth and provide always-on capability that should make the mobile Internet take off. GPRS is an attractive solution to operators, because it does not require the same degree of investment as UMTS. In Europe licenses for operators for third generation (3G) services have been sold in many countries at very high prices to operators, and not operators have some hard time in figuring out how to get the money from user to play for the ghigh licensing fees and high cost of building 3G network.
In North America, recently announced wireless data services (such as Sprint's HDML based web browsers) are creating U.S. market awareness. America is well behind Europe and Asia in mobile adoption, let alone wireless data services. Size and wealth make the U.S. a very attractive target, but the hyper-competitive business environment has actually held U.S. adoption back.
|
|
|
|
The origins of radio communications are in the 19th century.
At the beginning of our century, e.g. the police forces in Europe and in the US were using radio telephony equipment. During the 50’s and 60’s, first radio telephone networks were introduced for public customers in the US.
As the radio telephony services became more popular, the insufficient availability of radio frequencies became obvious. At the 60’s and 70’s, new technologies like dynamic channel allocation and cell-based networks were developed in order to decrease the congestion in the radio frequencies. The increasing lack of frequencies in the radio telephone services led to the development of cellular networks in the 70’s. The Bell Telephone company (US) introduced the first cellular public network AMPS (Advanced Mobile Phone Service) in 1978. It became a single standard for North America in 1982.
The idea behind cellular networks is the sub-division of a geographical area covered by a network into a number of smaller areas called cells. The frequencies allocated to one cell can be reused in other cells that are far enough not to disturb. A fixed radio station called as a base station within each cell acts as a transmitter/receiver serving all the mobile stations inside the cell area. A base station controls a group of transmitting/receiving frequencies allocated by the network to that cell.
In the 80’s, several analogue cellular radio networks entered to service around the world. Each country has proceeded in its own way in adopting standards for these networks. These standards are not mutually incompatible.
Later international standards, like GSM, were introduced.
The generations of different cellular technologies were introduced after each other.
The vast majority of today's voice-only (2G) wireless communications devices were originally based on a dual-processor architecture. A digital signal processor (DSP) handled many of the communications tasks, such as modulating and demodulating the bit stream, coding and decoding to maintain the robustness of the communications link despite transmission bit errors. In addition DSP part usually handles encrypting and decrypting for security, and compressing and decompressing the signal. The second processor was a general-purpose processor, which processed the user interface and the upper layers of the communication protocol stack.
The basic dual-processor architecture of 2G will migrate to data-centric 2.5 and 3G devices, but needs to be enhanced. New 2.5 and 3G applications, such as streaming video and others, will change the nature of wireless communication devices. Designers of wireless platforms should be concerned about maintaining a high degree of flexibility.
The impairments in radio transmission are difficult to model dynamically because of their unpredictable nature. Typical impairments are:
Antennas are critical links in the wireless signal chain. Right antenna for the application yields a good signal coverage, increased S/N ratio, reduced bit error rate, and lower power consumption all at very low cost. As cellular telephones have evolved over the years, so have their components, particularly the antennas. Cellular phone used to have large external antennas, but nowadays most cellular phones use an internal antenna.
Consumers do not (and should not have to) understand antenna theory, but design engineers needs to understand it. . An antenna is fundamentally a transmission line that transforms information from electrical energy (current and voltage) into electromagnetic energy (RF waves). The length of this line is inversely proportional to the frequency of transmission. Therefore, as new wireless applications in the past moved up in the frequency spectrum (Commercial Radio, Broadcast Television, Analog Cellular, Digital PCS, Wireless Data), their antennas correspondingly decreased in size. As an example, a 1/4-wave 4-inch analog cellular "whip" antenna at 800 MHz becomes a 1.5-inch digital PCS "stubby" antenna at 1900 MHz.
Old cellular used monopole used retractable antennas (stubby antennas). This kind of monopole antennas are implemented using lambda/4 length. They are the antennas of choice for wireless device designers implementing an external antenna.
Typical antennas you will see in more modern cellular is a helix radiator using 1/4-wave or 1/2-wave resonances. The cellular phone antenna radiator is mounted on a plastic carrier, the antenna is a solid and compact unit. On dual band antennas usually 1/4-wave is used for GSM and 1/2-wave for DCS/PCS. Those antennas are generally matched for 50 ohm impedance.
A rapid growing market for wireless communication has create a remarkable trend towards the development of integrated antennas for mobile phones. Many modern small cellular do not use external antennas anymore. Those cellular phones use a tiny planar or otherwise miniature special antenna which can be embedded into the phone plastic case. Antennas are slowly becoming more integral as new antenna technology becomes available. Today there are four leading antenna architectures that are commonly used in embedded applications: microstrip, patch, Planar Inverted 'F' Antenna (PIFA) and Meander Line Antenna (MLA).
Microstrip lines are an extension of the monopole. They can be easily fabricated by etching a copper strip of 1/2- or 1/4-wavelength onto the radio circuit board. While very inexpensive to make, its performance is limited by surrounding electronics on the circuit board. Microstrip is also only a single-frequency solution.
Patch antennas are a good choice for a system that requires a beam pattern focused in a certain direction. Patches are fabricated out of square or round copper clad on the top surface of a circuit board. Their radiation beam is normal to the surface of the board.
One antenna type becoming increasingly popular is PIFA (planar inverted-F antenna). The PIFA antenna literally looks like the letter 'F' lying on its side with the two shorter sections providing feed and ground points and the 'tail' providing the radiating surface. PIFAs make good embedded antennas in that they exhibit a somewhat omnidirectional pattern and can be made to radiate in more than one frequency band. PIFA has a low profile, and it can easily be incorporated into wireless handsets. PIFA antennas are generally used with a ground plane, which is generally the cellular phone circuit board ground plane.
The MLA (Meander Line Antenna) is a new type of radiating element, made from a combination of a loop antenna and frequency tuning meander lines. The electrical length of the MLA is made up mostly by the delay characteristic of the meanderline rather than the length of the radiating structure itself. MLAs can be designed to exhibit broadband capabilities that allow operation on several frequency bands.
For the base stations classical dipoles are very common. The common dipole has long been recognized as an efficient radiator when cut to the appropriate frequency length. It is made from bending the end of an open circuit two-wire transmission line into a 'T' shape, where the top of the 'T' is the radiating section of the antenna. The length of the top is lambda, the wavelength of the signal. In some applications also monopole antennas with lambda/2 or lanbda/4 length mounted over ground plane are used.
The idea behind cellular networks is the sub-division of a geographical area covered by a network into a number of smaller areas called cells. The frequencies allocated to one cell can be reused in other cells that are far enough not to disturb.
A fixed radio station called as a base station within each cell acts as a transmitter/receiver serving all the mobile stations inside the cell area. A base station controls a group of transmitting/receiving frequencies allocated by the network to that cell. The base station has also the control over subscribers that are currently in the cell area.
When a subscriber wants to make a call, the base station allocates a transmitting frequency which is then used between the subscriber and the base station. When the subscriber moves into another cell, a handover takes place, and a new base station takes over the control of the call and assigns a new frequency that is different from the first. The original frequency used in the first cell is released.
The cellular concept enables the following features:
The Holy Grail of wireless communications is ubiquitous wireless video. Hype has quickly been building around wireless video for the past few years. With 2.5G and 3G systems on the way, many have started to view the delivery of video content to mobile phones as one of the killer apps. The challenge, however, is making this work. Streaming video to a mobile phone places huge strains on the processing engine within these systems.
The processing involved in streaming video applications can be divided into roughly two types of functions: control and transport (CT) and media decode (MD). The CT and MD functions have different processing requirements. CT is not computationally intense and mainly involves string parsing, data packet manipulation, and finite state machine implementation (suitable for normal microprocessors). The CTR functionality usually used protocols like real-time streaming protocol (RTSP) session control and real-time transport protocol (RTP) media transport. The MD functionality is much more computationally intense because of the sophisticated signal processing required by audio and video coding algorithms (suitable for DSPs or microprocessor with special multimedia instructions).
In the next three years we will see wireless communication speeds go from the existing and rather pathetic 9600 bps to an impressive 384 kbps. This will come about with the implementation of Third Generation mobile networks or UMTS (Universal Mobile Telephony Services).
In 1993, Apple Computers vowed to reinvent portable computing. The company promised an "all-being, all-knowing, all-doing" electronic device. It would serve as an address book, day planner, notepad, fax machine, pager. It was designed to be an easy to use electronic device in the palm of a human hand. Apple even devised a catchy, hi-tech name for this miracle machine- the Personal Digital Assistant, or PDA for short. After long waiting Apple released the world's first PDA, the Newton. The Apple Newton grabbed people's imaginations, but did not capture their wallets.
Since then hordes of other companies attempted to take advantage of Apple's failure. Each one of them released their own version of what they think is the perfect PDA. Nowadays there are still many different PDA product from different companies available. Simplest are only like electroni calendars and notebooks, while most powerful ones have lots of processing power (like Compaq iPaq) and possibly communication functions in them (like Nokia Communicator).
Generally you can't use normal modem communications through celluar networks, but generally they have some way to offer a similar service. Normal telephone line modems do not work in most cellular teleohone systems in any acceptable way. Generally the radio noise in unaccpetable on analogue cellular systems. And digital cellular phones use speech codecs which compress speech to somewhat working soundgin speecs, but cause quite weird thigns to some non-speech signals. For transferring data on digital cellular systems (like GSM) the designers of networks have designed special data service modes to carry data on the cellular network.
For example GSM network can carry data normally up to 9600 bps (there are aalso higher speed high speed modes available with some operators and equipments). The data interfaces on many cellular phones make the phone appear to applications like it were a normal 9600 bps modem.
Cellular phones are electronic devices that commununicate with the ceullar system base station usign radio communications. This means that they contain both radio receiver and transmitter. The transmitter cause RF field around the cellular phone.
RF fields are non-ionizing radiations (NIR). ). Unlike X-rays and gamma rays, they are much too weak to break the bonds that hold molecules in cells together and, therefore, produce ionization. RF fields may, however, produce different effects on biological systems such as cells, plants, animals, or human beings. These effects depend on frequency and intensity of the RF field. By no means, will all of these effects result in adverse health effects. RF fields between 1 MHz and 10 GHz penetrate exposed tissues and produce heating due to energy absorption in these tissues. The depth of penetration of the RF field into the tissue depends on the frequency of the field and is greater for lower frequencies. Energy absorption from RF fields in tissues is measured as a specific absorption rate (SAR) within a given tissue mass. The unit of SAR is watts per kilogram (W/kg). An SAR of at least 4 W/kg is needed to produce adverse health effects in people exposed to RF fields in this frequency range. Most adverse health effects that could occur from exposure to RF fields between 1 MHz and 10 GHz are consistent with responses to induced heating, resulting in rises in tissue or body temperatures higher than 1C.
Current mobile phone systems operate at frequencies between 800 and 1800 MHz. RF fields penetrate exposed tissues to depths that depend on the frequency - up to a centimetre at the frequencies used by mobile phones. RF energy is absorbed in the body and produces heat, but the body's normal thermoregulatory processes carry this heat away. All established health effects of RF exposure are clearly related to heating. While RF energy can interact with body tissues at levels too low to cause any significant heating, no study has shown adverse health effects at exposure levels below international guideline limits
Current scientific evidence indicates that exposure to RF fields is unlikely to induce or promote cancers. Exposure to low-levels of RF fields, too low to produce heating, has been reported to alter the electrical activity of the brain in cats and rabbits by changing calcium ion mobility. However, these effects are not well established, nor are their implications for human health sufficiently well understood to provide a basis for restricting human exposure. Scientists have reported other effects of using mobile phones including changes in brain activity, reaction times, and sleep patterns. These effects are small and have no apparent health significance. More studies are in progress to try to confirm these findings.
The human exposure limits for mobile phones set by national organizations usually within international guidelines developed by the International Commission on Non-Ionizing Radiation Protection. These are based on a careful analysis of all scientific literature (both thermal and non-thermal effects) and offer protection against all identified hazards of radiofrequency energy with large safety margins. Rather than emission limits, the standard specifies exposure limits to radiofrequency EMR that regulate the rate at which the mobile phone user absorbs energy from the handset. This is known as the specific absorption rate (SAR). The SAR limit for all mobile, cordless and satellite phone handsets for sale in Australia is 1.6 watts per kilogram of tissue (averaged over 1 gram).
There are differences in SAR levels between different mobile phone models. The SAR rating published by the manufacturer is the result of tests conducted at worst case scenario. The energy you absorb from your phone cannot exceed that level. In practice, the energy you absorb in daily use of your phone will vary and in many instances will be much less that the published SAR. This is because the phone only uses as much energy as is needed to communicate with a base station. If the base station is nearby, the phone will only use as much energy as is efficient to communicate with the base station.
Mobile phone handsets and base stations present quite different exposure situations. RF exposure to a user of a mobile phone is far higher than to a person living near a cellular base station. However, apart from infrequent signals used to maintain links with nearby base stations, the handset transmits RF energy only while a call is being made, whereas base stations are continuously transmitting signals.
Handsets: Mobile phone handsets are low-powered RF transmitters, emitting maximum powers in the range of 0.2 to 0.6 watts. The RF field strength (and hence RF exposure to a user) falls off rapidly with distance from the handset. Therefore, the RF exposure to a user of a mobile phone located 10s of centimetres from the head (using a "hands free" appliance) is far lower than to a user who places the headset against the head. RF exposures to nearby people are very low. RF exposure levels to a user from mobile handsets are below international guidelines. If you are concerned about radiofrequency electromagnetic radiadion (EMR) while using your mobile phone you may choose to use a portable hands-free device. These are sold as an accessory to your mobile phone.
Base stations: Base stations transmit power levels from a few watts to 100 watts or more, depending on the size of the region or "cell" that they are designed to service. Base station antennae are typically about 20-30 cm in width and a metre in length, mounted on buildings or towers at a height of from 15 to 50 metres above ground. These antennae emit RF beams that are typically very narrow in the vertical direction but quite broad in the horizontal direction. Because of the narrow vertical spread of the beam, the RF field intensity at the ground directly below the antenna is low. The RF field intensity increases slightly as one moves away from the base station and then decreases at greater distances from the antenna. Both measurements and calculations show that RF signal levels in areas of public access from base stations are far below international guidelines, typically by a factor of 100 or more.
Electromagnetic interference and other effects: Mobile telephones, as well as many other electronic devices in common use, can cause electromagnetic interference in other electrical equipment. Therefore, caution should be exercised when using mobile telephones around sensitive electromedical equipment used in hospital intensive care units. Mobile telephones can, in rare instances, also cause interference in certain other medical devices, such as cardiac pacemakers and hearing aids. Individuals using such devices should contact their doctor to determine the susceptibility of their products to these effects.
Other risks of using cellular phone: Research has clearly shown an increased risk of traffic accidents when mobile phones (either handheld or with a "hands-free" kit) are used while driving.
Technical electronics safety: Cellular phones operate at low voltage (typically at 3-6V voltage) so the voltages in them are not dangerous. Cellular phones contain rechargeable batteries, which include several potential electrical risks. The batteries in cellular phones are lov voltsge devices, but are capble of generating high current if short circuited. Such high currents can cause lots of heat to the batteyr set itself and to electronics device conneced to it if the short circuit happens there. The energy in cellular phone battery is enough to cause fire on severe short circuit situation. For this reason most barries include internal protection circuitry to avoid this. Nowadays Lithium Ion (Li-ion) is the fastest growing battery system, because it has high energy density and is lightweigh. Li-ion technology is fragile (the contents of battery is flammable) and a protection circuit is required to assure safety. There has been some reports that damaged Li-ion batteries have cought in some case fire and even cause small "explosions". The number of this kind of accidents has been very low compared to the number of batteries in use. So there is a risk, but is low. To be safe be careful when handling the battery pack and do not use damaged battery packs.
Movie theaters today just ask you to silence your cell phone. Cell phones are asked to be turned off in the aeroplanes and hospitals for safety reasons (they can interfere with plane or medical electronics).
First generation wide area wireless communication systems are characterized as analog radio systems and designed for voice transfer. 1G Techologies used frequency dividision multiple access (FDMA) to communicate, meaning simply that every call in one are uses their own channels for voice communication. This kind of systems were resiged and used in 1970s and 1980s. Examples of this kind of systems include AMPS, TACS, and NMT. Here is some more information on those systems.
Analogue 1G systems use frequency modulation (FM) for speech transmission. The history of 1G systems is the following:
Analogue systems created the critical mass of mobile users. Analogue technology has small subscriber and traffic capacities, and the use of radio spectrum is profuse. The limitations of analogue radio network technology became, however, clear as the number of subscribers increased.
The need for more advanced solutions was urgent especially in Europe, where numerous standards in a relatively small region caused cumulative problems due to increased mobility of radio telephone users.
Second generation (2G) cellular phone system use digital communication methods. They are capable of providing voice, data and other services. Digital technology combined with harmonized standardization has made it possible to make calls at any time, anywhere, and both speech and data can be transmitted and received.
Examples of this series of systems include GSM, D-AMPS (TDMA/IS-136) and CDMA IS-95-A. Here is some more informatiom on those system.
The Europeans realized rapid growth of cellular communications early on, and in 1982 the Conference of European Posts and Telegraphs (CEPT) formed a study group called the Groupe Spécial Mobile (GSM) to study and develop a panEuropean public land mobile system. In 1989, GSM responsibility was transferred to the European Telecommunication Standards Institute (ETSI), and phase I of the GSM specifications were published in 1990. Commercial service was started in mid1991, and by 1993 there were 36 GSM networks in 22 countries.
The most basic teleservice supported by GSM is telephony. From the beginning, the planners of GSM wanted ISDN compatibility in services offered and control signalling used. The digital nature of GSM allows data, both synchronous and asynchronous, to be transported as a bearer service to or from an ISDN terminal. The data rates supported by GSM are 300 bps, 600 bps, 1200 bps, 2400 bps, and 9600 bps (14400 bps was added later). Group 3 fax, an analog method described in ITUT recommendation T.30 is also supported by use of an appropriate fax adaptor.
GSM features:
A unique feature of GSM compared to older analog systems is the Short Message Service (SMS). SMS is a bidirectional service for sending short alphanumeric (up to 160 bytes) messages in a storeandforward fashion. For pointtopoint SMS, a message can be sent to another subscriber to the service, and an acknowledgement of receipt is provided to the sender. SMS can also be used in a cellbroadcast mode, for sending messages such as traffic updates or news updates.
GSM History:
Network operators in most of the world use the original GSM spectrum allocation at 900 MHz. The frequency range allocated for ceullar telephy purposes (used now by GSM) in the 1978 World Administrative Radio Conference (WARC) was 890-915 MHz for transmissions from mobile stations and 935-960 MHz for transmissions from fixed stations.
Additional spectrum at 1,800 MHz is used for the GSM derivative called DCS-1800, and this band is used in many countries. Some countries with cellular allocations at 450 MHz may begin deploying GSM in that band as well to replace old analog networks. In many areas of the United States, there are GSM systems operating in the 1,900- MHz PCS frequency band. There are also plans to make GSM standards for operation at 400 MHz and 800 MHz bands.
Considering the many options available, dual-band GSM phones are quite commonplace now. A few tri-band (900/1,800/1,900 MHz) phones are also available, allowing a GSM subscriber to use the same phone almost anywhere in the world.
Circuit-switched voice calls are still the most commonly used services in GSM networks.
Users use also data services. Current datacom services over GSM generally allows transferring files or data and sending faxes at 9.6 kbps. This current data communication in GSM network is circuit switched.
There are two basic modes of data access over a wireless network: circuit switched and packet switched. In circuit switched system connection is a dedicated connection, and the user is billed, using the same method as that used for a voice call, by the minutes of usage. Current datacom services over GSM generally allows transferring files or data and sending faxes at 9.6 kbps. This current data communication in GSM network is circuit switched. The existing GSM network provides data access at speeds up to 14.4 kbps. This was considered a reasonable speed when the system was developed.
In packet switching data streams are broken up into packets, each packet is then quickly routed to its destination over a shared medium. Billing is done on a cents-per-packet basis, independent of the time spent online.
Enhanced GSM data technologies promise more transfer speed and also packet mode transmission.
GPRS is an extension of the GSM system, and uses the same channels, the same modulation, and the same network backbone as the existing GSM network.
High Speed Circuit Switched Data (HSCSD) is a new high speed implementation of GSM data techniques. HSCSD allows wireless data to be transmitted at 38.4 kilobits per second or even faster over GSM networks by allocating up to eight time slots to a single user.
SMS is a bidirectional service for sending short alphanumeric (up to 160 bytes) messages in a storeandforward fashion. For pointtopoint SMS, a message can be sent to another subscriber to the service, and an acknowledgement of receipt is provided to the sender. SMS can also be used in a cellbroadcast mode, for sending messages such as traffic updates or news updates.
Short messsage service (SMS) is a messaging method included in GSM system which allows sensing short messages from one cellular phone to another. GSM Short Messages have a maximum length of 160 characters (from the SMS character set), or 140 octets. However, Short Messages can be concatenated to form longer messages. Besides normal text based user to user messaging SMS system has been used to impement interfaces to on-line services and for carrying other kind of data (like alarm tones and logos to certain GSM phones). Short message service (SMS) is a globally accepted wireless service that enables the transmission of alphanumeric messages between mobile subscribers and external systems such as electronic mail, paging, and voice mail systems. SMS has also been used for tranporting data like cellular phone ring tones and screen logos (for example in Nokia Smart Messaging system).
On-line sites which provideo free SMS messaging services.
Multimedia Messaging is just around the corner. Multimedia Messaging Service (MMS) is a new prominent wireless standard for multimedia. The idea behind MMS is to enhance SMS type messagging to carry larger messages which can contain more text, images, sound and possibly animation. MMS is expected to become a very popular messaging service in the future in both today's GSM networks and 3G networks in the future. In GSM networks the MMS service is generally implemented with the aid of GPRS service with is used to transport the actual messages to GSM phone.
To be able to used the new MMS services, the consumers need net MMS capable cellular phones and GSM operator need to update their networks with new features to suport this service. Operators need for example Multimedia Messaging Service Centers (MMSC) to handle the delivery of the Multimedia Messages (the operation of MMSC is roughtly equivalent to what SMS center does to SMS messages). The key factors to make the MMS a success story is the interoperability, interworking and the availability of the types of handheld devices necessary to make widespread consumer and enterprise mobile multimedia messaging a reality.
The MMS messgae itself consists of the message header and the contents of the message (message body). The message body can consist of one or more part (like files). The message body is coded as MIME type application/vnd.wap.mms. Basically the information contained in the message can be in any format supported by the devices. The standard information presentation formats are SMIL and WAP, but the device manufacturers have agreed that the supported standard presentation language is SMIL. The typical size of MMS messages is expeced to be around 6-30 kilobyes.
When messages are transported form application to the Multimedia Messaging System, they are generally transporte dusing HTTP or SMTP protocols.3gpp Release 5 defines a SOAP based interface to MMS.
There are also other 2G systems than GSM, Those systems are generally used in more limited areas (usually country or area specific systems).
Code Division Multiple Access (CDMA) is a digital wireless technology that was pioneered and commercially developed by QUALCOMM. CDMA works by converting speech into digital information, which is then transmitted as a radio signal over a wireless network. Using a unique code to distinguish each different call, CDMA enables many more people to share the airwaves at the same time - without static, cross-talk or interference.
CDMA was adopted by the Telecommunications Industry Association (TIA) in 1993. CDMA wireless was commercially introduced in 1995. CDMA is very fas growing wireless technology. Code Division Multiple Access, a cellular technology orginally known as IS-95, competes with GSM technology for dominance in the cellular world. There are now different variations, but the original CDMA is now known as cdmaOne. A newer version of this with more speed is now known as cdma20000.
In 1999, the International Telecommunications Union selected CDMA as the industry standard for new "third-generation" (3G) wireless systems. The selected technology variation are called W-CDMA (wideband CDMA) and TD-SCDMA. wideband CDMA forms the basis of UMTS 3G networks. Many leading wireless carriers are now building or upgrading to 3G CDMA networks.
May 2001 there were 35 million subscribers on cdmaOne systems worldwide. At year 2003 over 100 million consumers worldwide rely on CDMA communications.
Third generation mobile communciation systems often called with names 3G, UMTS and W-CDMA promise to boost the mobile communications to new speed limits. The promises of third generation mobile phones are fast Internet surfing, advanced value-added services and video telephony. What will be the reality we will start to see in few years. Mobile communication is promised to move from simple voice to rich media, where we use more of our senses to intensify our experiences.
There is tremendous excitement about the development of 3G wireless telecommunication systems. Two major forces are driving the development of these 3G systems. The first is the demand for higher data rate services, such as high-speed wireless Internet access. The second requirement is the more efficient use of the available radio frequency (RF) spectrum. This second requirement is a consequence of the projected growth in worldwide usage of wireless services. W-CDMA is the emerging wireless multiple access scheme for IMT-2000/UMTS.
But not all of this will happen at once. 3G is an evolution to a communications ideal that no one completely understands yet. It seems that the deployment of 3G will be slower than expected some time ago. Some analysts say that third generation W-CDMA networks will not widely deployed until the ends of year 2003 or at 2004. There are some technical problems still to be solved and many 3G operators have financial problems in deploying their networks (the licenses in some European countries were very expensive).
Europe's 3G concessions are estimated to have cost licensees in the region of GBP100 billion. Add to this the mammoth cost of rolling out new generation network infrastructure and the not insignificant outlay involved in the testing of networks and the total start-up figure may jump to GBP300 billion. The sheer size of this figure has ensured that operators - and in particular their shareholders.
Third-generation wireless systems will handle services up to 384 kbps in wide area applications and up to 2 Mbps for indoor applications. Most operators have decided to make their 3G networks to work at around 2 GHz frequency band.
The Universal Mobile Telecommunications System is a code-division multiple-access standard that contains two built-in standards: frequency-division duplex (FDD) and time-division duplex (TDD). In the case of FDD, the basestation transmit frequency and the mobile transmit frequencies are widely separated. Because of this, a handset may interfere with the signal of another handset, but never with a basestation signal. A long code is employed to randomize the transmitted signals. In TDD, the basestation and handset share the same frequency, and there is no long code.
Both standards employ CDMA to replace a transmitted symbol by an orthogonal short-code sequence. As a result, the bandwidth of the signal at 5 MHz is much wider than in a second-generation GSM system. Also, signal-correlation operations-that is, the ability to correlate signals with users-allow multiple users to transmit in the same frequency band without interference.
Typical 3G Node B base station includes analogue radio parts and theree digital parts: time slice processing, processing as symbol speed and base station controller.
Cellular service providers are slowly beginning to deploy third-generation (3G) cellular services. As access technology increases, voice, video, multimedia, and broadband dataservices are becoming integrated into the same network. The hope once envisioned for 3G as a true broadband service has all but dwindled away. While 3G hasn't quite arrived, designers are already thinking about 4G technology. To achieve the goals of true broadband cellular service, the systems have to make the leap to a fourth-generation (4G) network.
4G is intended to provide high speed, high capacity, low cost per bit, IP based services. The goal is to have data rates up to 20 Mbps. Most propable the 4G network would be a network which is a combination of different technologies (current celluart networks, 3G celluar network, wireless LAN, etc.) working together usign suitable interoperability protocols (for example Mobile IP).
This section gives you tips how to use yout cellular phone beyond normal speaking and SMS messages.
Controlling cellular phone from external electronics (computer or some other device) is usually manufacturer and cellular mode specific. This means that different manufacturers use different kind of physical and electrical interface to control their cellular phones using the accessory connector on the cellular phone (usually on the bottom of the cellular phone).
A global specification for wireless connectivity. The Bluetooth solutions promise to provide a cable replacement technology that simplifies the interaction between people and machines. It is designed to be a small form-factor, low-cost, and low-power radio communiction technology. Bluetooth technology supports a data transfer speed of 1 Mbit per second (Mbps) in the 2.4GHz band (2.400 to 2.483 GHz) and communication at a range of up to 10 meters. The downside is that Bluetooth is late the uptake and will propably be much smaller than anticipated.
Bluetooth provides two types of physical links. The Synchronous Connection Oriented (SCO) and the Asynchronous Connectionless (ACL) link. The SCO is used for voice and the ACL is used for data. Simultaneously up to three synchronous voice channels can be used. The data rate is 432 kbit/sec symmetrically and 721 / 57 kbit/s asymmetrically. 79 channels with 1MHz carrier distance are available. The channels are changed 1600 times per second (channel hopping). This is a pseudo-random sequence of 79 frequencies. In practical Bluetooth applications the transmitting only milliwatts, which gives communication distance up to around 10 meters. The Bluetooth standard defines also a higher power class of devices, which have maximum tranmission power is up to 100 mW and with that transmission distance is up to 100 meters.
Bluetooth supports the 'ad-hoc networking' between different mobile wireless devices for spontaneous networking and immediate communication. Two supported network types are piconet and scatternet. Piconet is a network consisting of one master and up to seven slaves. This means that generally one Bluetooth device can be at the same time have connection up to seven other Bluetooth devices. Scatternet is a network formed by several piconets.
Besides physical networking the Bluetooth standard defines also the application layer. All Bluetooth services must be built based on the predefined Bluetooth profiles. Bluetooth profile can be viewed as application class. There is currently 13 different Bluetooth profiles defined in Bluetooth 1.1 standard. Examples of such profiles are wireless hands-free devices, file transfer and Internet connection through cellular phone. The compatibility of Bluetooth devices depends on the supported profiles (if two devices support same profile, they are compatible with the services provided with that profile). Bluetooth supports also encryption (64 bit keys).
The Wireless Application Protocol (WAP) is an open, global specification which gives mobile users with wireless devices the opportunity to easily access and interact with information and services. It is a collection of languages and tools and an infrastructure for implementing services for mobile phones. WAP makes it possible to implement services similar to the World Wide Web. Unlike marketers claim, WAP does not bring the existing content of the Internet directly to the phone. There are too many technical and other problems for this to ever work properly.
The protocol is developed by WAP Forum http://www.wapforum.org/, an organization of some of the most powerful Internet and telecom companies. WAP is advertized as bringing "the web"on your mobile phone, but in reality the bottom line is that WAP is not "the web" on your mobile phone, but something a lot less. WAP can be used to build many mobile phone specific services and used for giving very limited web access form th mobile phones.
WAP consists of markup language (WML), scripting language (WMLScript), picture format specification (WBMP), microbrowser specification, freamework for wireless telephony applications, protocol stack and secure connections (WTLS) specifications. WML is an XML based markup language used to describe the contents of the WAP pages. WMLScript is a scripting language used with WML pages (this scripting language is loosely based on JavaScript). On the WAP server side you can use a standard web server to store wap pages and standard HTTP protocol to transfer pages from the web server to WAP gateway. A WAP gateway is a piece of software between WAP device and the web server. WAP gatway has to following functions: converting the markup language (WML) from textual format to tokenized (binary/compressed) format which is readable by the WAP device, translating the requests from the WAP device to HTTP requests for the "web" world, convert between the SSL encryption used in the "web" world and the WTLS encryption used in the WAP world and conversion from TCP protocol used in web to WDP transport protocol used in WAP world. Optionally many gateways also perform other conversions such as converting other types of files (plain text, simple HTML) into a WAP readable format.