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Introduction to modern mobile communications

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.

 

General information

History

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.

 

Basic technologies

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.

 

1G Introduction

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.

 

2G Introduction

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.

 

GSM

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.

 

Other 2G systems than GSM

There are also other 2G systems than GSM, Those systems are generally used in more limited areas (usually country or area specific systems).

 

CDMA Based cellular phone systems information

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 phone systems

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.

 

Other cellular phone systems

4G Mobile communications

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).

 

Celluar phone design articles

Mobile phone hacking

This section gives you tips how to use yout cellular phone beyond normal speaking and SMS messages.

 

Paging

Bluetooth

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).

 

WAP

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.

 

 

iMode

iMode is a technology used in Japan to add Internet conenctivity and web features to their PDC mobile phone system. iMode is a way of providing information to mobile devices. It uses CHTML (Compact HTML) as a markup language, and uses more traditional internet protocols to deliver it. The content is served using HTTP to a so called iMode center (under the control of the developers of iMode, NTT DoCoMo). The iMode center performs protocol conversions which enable the content to be delivered to the phone.

 

Wireless Internet

Ultra Wide Band (UWB)

Ultrawideband wireless technology uses no underlying carrier wave, instead modulating individual pulses in some way. UWB operation relies on razor-thin, precisely timed pulses similar to those used in radar applications. Unlike traditional communications systems, ultrawideband wireless occupies a broad span of frequencies at very low power levels, often below the noise floor of the existing signaling environment. The secret of wide bandwidth is the use of short pulses: the shorter the time interval of a pulse, the broader its bandwidth. Because of extremely short duration of UWB pulses, these ultrawideband pulses function in a continuous band of frequencies that can span several gigahertz.

Because the UWB pulses employ the same frequencies as traditional radio services, they can potentially interfere with them. To avoid this UWB devices deliberately operate at power levels so low that they emit less average radio energy than hair dryers, electric drills, laptop computers and other common appliances that radiate electromagnetic energy as a by-product. This low-power output means that UWB's range is sharply restricted--to distances of 100 meters or less and usually as little as 10 meters. For well-chosen modulation schemes, interference from UWB transmitters is generally benign because the energy levels of the pulses are simply too low to cause problems.

As with emissions from home appliances, the average radiated power from UWB transceivers is likewise expected to be too low to pose any biological hazard to users, although further laboratory tests are needed to confirm this fully. A typical 200-microwatt UWB transmitter, for example, radiates only one three-thousandth of the average energy emitted by a conventional 600-milliwatt cell phone.

Challenging technical problem appears to be finding ways to stop other emitters from interfering with UWB devices. A UWB receiver needs to have a "wide-open" front-end filter that lets through a broad spectrum of frequencies, including signals from potential interferers. The ability of a UWB receiver to overcome this impediment, sometimes called jamming resistance, is a key attribute of good receiver design.

UWB technology has been used for some time in Ground Penetrating Radar (GPR) applications and is now being developed for new types of imaging systems that would enable police, fire and rescue personnel to locate persons hidden behind a wall or under debris in crises or rescue situations. UWB devices can be used to measure both distance and position.

UWB devices can be used for a variety of communications applications involving the transmission of very high data rates over short distances without suffering the effects of multi-path interference.

There are different possible modulation method for UWB. In a bipolar modulation scheme, a digital 1 is represented by a positive (rising) pulse and a 0 by an inverted (falling) pulse. In another approach, full-amplitude pulses stand for 1's, whereas half-amplitude pulses stand for 0's. Pulse-position modulation sends identical pulses but alters the transmission timing. Delayed pulses indicate 0's.

At present, it appears that semiconductor-based UWB transceivers will be able to provide very high data transmission speeds--100 to 500 Mbps across distances of five to 10 meters.

UWB is superior to other short-range wireless schemes in another way.

UWB's precision pulses can also be used to determine the position of emitters indoors: a UWB wireless system can triangulate the location of goods tagged with transmitters using multiple receivers placed in the vicinity.

On February 14 2003 the Federal Communications Commission gave qualified approval to UWB usage, following nearly two years of commentary by interested parties. Taking a conservative tack, federal regulators chose to allow UWB communications applications with full "incidental radiation" power limits of between 3.1 and 10.6 GHz. Despite the imposed limitations, UWB developers are confident that the wireless technology will be able to accomplish most of the data-transfer tasks its proponents envision for it.

Because of its short range, UWB is seen as the next generation Bluetooth. Capable of speeds between 400 and 500 Mbps. Intel, is taking a close look at adding UWB to its chips.

 

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