01 Tm2106euo1_eg0001 Theway to Cdma

The Way to CDMA Technology Siemens

Contents

11.11.21.3233.1

Introduction to Cellular TechnologyProgress in Radio CommunicationsThe Growth in Cellular Market & its demandsWhy it is called cellular?Advantages of Digital CommunicationsWireless Digital Transmission ProblemsBit Error Rate

3468

1115

The Way to CDMA Technology

1

Siemens The Way to CDMA Technology

44.14.2566.16.26.2.16.2.26.2.2.16.2.36.3788.18.28.2.18.3

Solutions against Air transmission ProblemsChannel codingInterleavingCellular System ArchitectureCellular System ComponentsDigital SystemsMultiple Access Systems Frequency Division Multiple Access “FDMA” Time Division Multiple Access “TDMA” The GSM NETWORK Code Division Multiple Access “CDMA”Duplex Transmission: FDD & TDDData TransmissionThe General Packet Radio System (GPRS)Timescales for GPRSGPRS Architecture GPRS Reference ArchitectureGPRS Applications

18212426293740424248505658616770727480

TM2106EU01EG_00012


3


TM2106EU01EG_0001

1 Introduction to Cellular Technology

4


5


The quest to know the unknown and see the unseen is inherent in human nature.

It is this restlessness that has propelled mankind to ever higher pinnacles and ever deeper depths. This insatiable desire led to the discovery of light as being electromagnetic, paving the way to discovery of the radio.

The origin of radio can be traced back to the year 1680 to Newton theory of composition of white light of various colors. This theory brought the importance as light as an area of study to the attention of many scientists, especially those in Europe, who began to pursue experiments with light which lead to importantdiscoveries connected to the eventual development of the radio.

These discoveries are the foundation of today’s wireless cimmunicaton systems.

Experiments with light are still being carried out today in many universities, and industries. One of the outcomes of light experiments in the 1970s is the optical fiber, which is currently being used for long – haul voice and data transmission. It is believed that the use of optical fiber technology will increase dramatically the introduction of wideband networks for voice, data, and video transmission, which is based on the Asynchronous Transfer Mode (ATM) switch.

1.1 Progress in Radio Communications Radio connections were first used for Wireless Communications in the late 19th century; information was sent via "ether" as follows: -

TM2106EU01EG_00016


7


Progress in Radio communications

1873 Electromagnetic wave theory J.C. Maxwell

1887 Experimental proof of the existence of electromagnetic waves H. Hertz

1895 First receiver with antenna for weather reports A. Popow

1895 First wireless transmission using spark inductor generated G. M. Marconi

1897 Marconi Wireless Telegraphy Company founded

1901 First transatlantic transmission Marconi

1909 First radio broadcast New York, Caruso

Fig.1

TM2106EU01EG_00018


9


1.2 The Growth in Cellular Market & its demands

The cellular telephone industry has enjoyed phenomenal growth since its inception in 1983. In just one more example of the impossibility of projecting the adoption of new technologies, a widely accepted 1985 prediction held that the total number of cellular subscribers might reach as many as 900,000 by the year 2000. In fact, by the end of 1994 there were well over 20 million subscribers in the United States alone, and approximately 50 million worldwide. Recent annual subscriber growth rates have been as high as 40%, and it is believed that this growth rate could continue through the rest of the 1990s.

In order to meet this increasing demand for service, new digital cellular telephone systems have been introduced during the first half of the 1990s. As today's cellular operators move to adopt these new technologies in their systems, they demand:

Increased capacity within their existing spectrum allocation and easy deployment of any technology it takes to get them that capacity increase.

Higher capacities and lower system design costs (plus lower infrastructure costs) which will lead to a lower cost per subscriber.

A lower cost per subscriber, combined with new subscriber features, which will help the operators to increase their market penetration.

An increased market penetration, which will lead to an increase in number of subscribers and a system, which offers support for that, increased capacity.

High quality calls must be maintained during the change to or migration to any new digital technology.

TM2106EU01EG_000110


11


Avdantages of cellular communications

Fig.2

TM2106EU01EG_000112

• A lower cost per subscriber • An increased market penetration • Higher capacities and lower system

design costs


13


1.3 Why it is called cellular?

Everyone is familiar with the usage of the term “cellular” in describing mobile radio systems. You probably know that it is called cellular because the network is composed of a number of cells. Mobile radio systems work on the basis of cells for two reasons.

The first reason is that radio signals at the frequencies used for cellular travel only a few kilometers (kms) from the point at which they are transmitted.

They travel more or less equal distances in all directions; hence, if one transmitter is viewed in isolation, the area around it where a radio signal can be received is typically approximately circular. If the network designer wants to cover a large area, then he must have a number of transmitters positioned so that when one gets to the edge of the first cell there is a second cell overlapping slightly, providing radio signal. Hence the construction of the network is a series of approximately circular cells.

The second reason has to do with the availability of something called radio spectrum. Simply, radio spectrum is what radio signals use to travel through space.

Using a mobile radio system, it consumes a certain amount of radio spectrum for the duration of the call. An analogy here is car parks. When you park your car in a car park it takes up a parking space. When you leave the car park, the space becomes free for someone else to use. The number of spaces in the car park is strictly limited and when there are as many cars as there are spaces nobody else can use the car park until someone leaves.

Radio spectrum in any particular cell is rather like this. However, there is an important difference. Once you move far enough away from the first cell, the radio signal will have become much weaker and so the same bit of radio spectrum can be reused in another cell without the two interfering with each other. By this means, the same bit of radio spectrum can be reused several times around the country. So splitting the network into a number of small cells increases the number of users who can make telephone calls around the country.

So, in summary, cellular radio systems are often called “cellular” because the network is composed of a number of cells, each with radius of a few kilometers, spread across the country. This is necessary because the radio signal does not travel long distances from the transmitter, but it is also desirable because it allows the radio frequency to be reused, thus increasing the capacity of the network.

TM2106EU01EG_000114


15


Fig. 3

TM2106EU01EG_000116


17


TM2106EU01EG_000118


1 Advantages of Digital Communications

19


First of all we can say that a digital communication system is one where the voice signal has been digitized prior to wireless transmission.

TM2106EU01EG_000120


Digitizing is aprocess where the voice signal is sampled and discrete, numiric representation of the signal are transmitted ,rather than the original signal itself.

This is much different from analog systems where the original,continuous voice signal is transmitted using a standard form of FM modulation.

As the term „Digital“ implies, the voice signal is digitized for transmission within the cellular networks.Once digitized, Advanced coding , transmission,and error correction techniques are employed. These additional techniques make it possible to detect and correct transmission errors at the receiving end.

21


Another advantage of digital wireless communications is that digital provides more traffic capacity per given RF spectrum. This is made possible by using the channel bandwidth more efficiently .

In digital systems, multible users occupy the same frequency, and they are separated by time or codes. This is more efficient than assigning each user to a separate frequency , which is efficient than assigning each user to a separate frequency, which is common in analog systems.

Digital systems also use techniques to reduce, or compress the amount of information to be transmitted over the air from each user.

These compression techniques can take advantage of the probability that not every user needs maximum bandwidth at exactly the same moment.

Another advantage of digital communication system is that they have ah inherent level of security . Unothorized listeners must have complex receivers, they must decode the digital information, and then they must convert the digital signal into analog signal.

Digital has better built-in support for non-voice services and user data traffic.

By bypassing the voice signal compression process, user data can be processed directly in their digital formats.

With digital systems, there is no need to convert the signal. The data is simply passed through as digital information. This digital information can usually be processed through the system at higher speeds.

Lastly , Analog sytems, on the other hand, use much simpler transmission techniques, which require a receiver no more complex than an inexpensive FM radio.

TM2106EU01EG_000122


Figure 4

23


TM2106EU01EG_000124


25


TM2106EU01EG_0001

2 Wireless Digital Transmission Problems

26


27


Wireless communication channels suffer from severe attenuation and signal fluctuations. Large attenuation is due to the user’s mobility through the propagation environment that causes almost no direct signal from the transmitter can reach the receiver. Even if so, the line-of-sight signal may be superimposed by its reflected or scattered duplicates that reach the receiver at different time instant causing signal fluctuations. When a mobile station moves from one location to another, all propagation scenario may change completely and the received signal changes accordingly. Three different models that are commonly used to characterise a wireless channel are:

Propagation path loss (near-far attenuation) .

Shadowing (variation on the average power) .

Multipath fading (fast signal fluctuation).

Propagation path loss

Propagation path loss occurs when the received signal becomes weaker and weaker due to increasing distance between MS and BTS . Path loss is propprtional to the square of the distance and the square of the transmitted frequency .

Shadowing

Shadwing is due to obstacles being between the MS and the BTS , like buildings, hills etc. When the MS moves around , the signal fluctuates normally around a mean value depending on the obstacles .

Multipath fading

Multipath fading occures when there is more than one transmission path to the MS

or BTS , and therefore more than one signal is arriving at the receiver .This may be

due to buildings or mountains , either close to or far from the reciving device.

Rayleigh fading and time dispersion are forms of multipath fading.

*Rayleigh fading :-

This occures when the signal takes more than one path between the MS and BTS . In this case, the signal is not received on a line of sight path directly from the Tx. Antenna . Rather , it is reflected off buidings, for example , and is received from several different indirect paths . Rayleigh fading occurs when the obstacles are close to the receiving antenna .

*Time dispersion :-

It is another problem relating to multiple paths to the Rx. Antenna of either MS or BTS . However , in contrast to Rayleigh fading , the reflected signal comes from an object far away from the Rx. antenna .Since the bit rate on the air is 270 kbit/sec , one bit corresponds to 3.7 μ sec or 1.1 km . If an obstacle is further than 500 m away, then the reflected bit will interfere with the next transmitted bit (ISI).

TM2106EU01EG_000128


29


Fig. 5

Fig. 6

Fig. 7

1.4 Bit Error Rate

Sometimes, when you are using a mobile phone, you will notice that the speech quality “breaks up” or disappears completely for short periods of time. By moving toward a window you can sometimes improve the situation. This loss of speech quality is caused by errors. That is, the transmitter might send 1011, but because of

TM2106EU01EG_000130


propagation problems, such as fast fading, the receiver might think that 1001 was sent. The third bit is said to be in error. This is a little like spelling something over the phone.You might say “S” but the person at the other end might respond “was that F?” An error was made because the line was not of sufficient quality.

Mobile phones contain advanced systems for correcting errors that. However, these systems are not always able to remove all the errors. Without error correction, the speech quality would always be so terrible that you would never be able to understand the other person.

Interference, fading, and random noise cause errors to be received, the level of which will depend on the severity of the interference. The presence of errors can 31


cause problems. For speech coders such as ADPCM, if the bit error rate (BER) rises above 10-3 (that is, 1 bit in every 1000 is in error, or the error rate is 0.1%) then the speech quality becomes unacceptable.

For near-perfect voice quality, error rates of the order of 10-6 are required. For data transfers, users expect much better error rates, for example on computer files, error rates higher than 10-9 are normally unacceptable.

If the only source of error on the channel was random noise, then it would be possible, and generally efficient, to simply ensure that the received signal power was sufficient to achieve the required error performance without any need for error correction. However, where fast fading is present, fades can be momentarily as deep as 40 dB. To increase the received power by 40 dB to overcome such fades would be highly inefficient, resulting in a significantly reduced range and increased interference to other cells. Instead, error correction coding accepts that bits will be received in error during fades but attempts to correct these using extra bits (“redundant” bits) added to the signal.

How to face BER?

TM2106EU01EG_000132


33


Fig. 8

TM2106EU01EG_000134


35


TM2106EU01EG_0001

3 Solutions against Air transmission problems

36


37


Antenna Diversity

It increases the received signal strength by taking advantage of the nature properties of radio waves , there are two diversity methods, they are :-

1. Space diversity .

2. Polarization diversity .

*Space diversity

can be achieved by mounting two receivers instead of one . If the two receivers are physically separated , the probability that both of them are affected by a deep fading dip at the same time is low .

*Polarization diversity

With this technique the two space diversity receivers are replased by one dual polarized antenna , the antenna contains two differently polarized antenna arrays.

Time Advance

Time Advance is introduced to overcome the effect of time alignment. When the MS is moving far away from the BTS , this BTS tells the MS how much time ahead of the synchronization time it must transmit the burst .

TM2106EU01EG_000138


39


Fig. 9

TM2106EU01EG_000140


41


Fig. 10

1.5 Channel Coding

Error correction is widely deployed in mobile radio, where fast fading is almost universally present. Error correction systems all work by adding redundancy to the transmitted signal. The receiver checks that the redundant information is as it would have expected and, if not, can make error correction decisions. An extremely simple error correction scheme would repeat the data three times. The first bit in each of the three repetitions is compared and, if there is any difference, the value that is present in two of the three repetitions is assumed to be correct. This is repeated for all bits. Such a system could correct one error in every three bits but triples the bandwidth required. Considerably more efficient schemes than this are available. Similarly to error correction systems, there are schemes that detect errors but do not correct them. In the preceding simple example, if the message was only repeated twice, then if the repetition of a given bit was not the same as the original transmission it is clear that an error occurred but it is not possible to say which transmission was in error. In an error detection scheme, the receiver then requests that the block that was detected to be in error is retransmitted. Such schemes are called automatic request repeat (ARQ). They have the advantage of often reducing the transmission requirements (even accounting for the bandwidth needed for retransmission of errored blocks) but add a variable delay to the transmission while blocks are repeated. This variable delay is unsuitable for speech but typically acceptable on computer file transfer. Some of the more advanced coding systems can perform error correction and also detect if there were too many errors for it to be possible to correct them all and hence request retransmission in this case. Error correction methods broadly fall into two types: block or convolutional coding. Both are highly involved and mathematical, and the treatment here will no more than scratch the surface. Block coding basically works by putting the information to be transmitted in a matrix and multiplying this by another matrix, whose contents are fixed for the particular coding scheme and known to both the transmitter and the receiver, as shown in Figure .

TM2106EU01EG_000142


The result of the matrix multiplication forms the codeword. This codeword is then transmitted after the information, which is left unchanged. At the receiver, the information is loaded into another identical matrix, multiplied by the known matrix and the results compared with the received codeword. If there are differences, then complex matrix operations (which are processor intensive) can be used to determine where the error lies and it can be corrected. If no solution can be found, then more errors than can be corrected have occurred

43


TM2106EU01EG_000144


45


1.6 Interleaving

Signals traveling through a mobile communication channel are susceptible to fading . The error-correcting codes are designed to combat errors resulting from fades and, at the same time, keep the signal power at a reasonable level. Most error-correcting codes perform well in correcting random errors. However, during periods of deep fades, long streams of successive or burst errors may render the error-correcting function useless. Interleaving is a technique for randomizing the bits in a message stream so that burst errors introduced by the channel can be converted to random errors. In Figure , we want to send the message “ARE YOU SURE THAT THEY ARE COMING TO LUNCH WITH US” over a fading channel. One way to interleave the message is to load it into a matrix of four rows and ten columns. We truncate the message into four parts and load them into the four rows. Then we read the message out from the top, column by column. The resulting randomized message is sent through the channel.The channel introduces several burst errors into the message. As a result, the underlined alphabets are received in error. At the receiving end, a deinterleaver reconstructs the message using the same matrix, except in this case the deinterleaver loads the received message into columns first, then reads the message out from the rows. As we can see, the burst errors are indeed converted to scattered random errors.

For example in GSM systems, Interleaving is used to separate consecutive bits of a message so that these are transmitted in a non-cosecutive way. Each 20 ms of speach gives 456 bits of information . These are divided in 8 blocks of 57 bits each and transmitted in 4 bursts , 2 blocks in each burst . To reduce the probability of losing information , the 57 bit blocks are transmitted in 8 bursts . So each burst contains blocks from different speech segments .

TM2106EU01EG_000146


47


TM2106EU01EG_0001

4Cellular System Architecture

48


49


Increases in demand and the poor quality of old service led mobile service providers to research ways to improve the quality of service and to support more users in their systems. Because the amount of frequency spectrum available for mobile cellular use was limited, efficient use of the required frequencies was needed for mobile cellular coverage. In modern cellular telephony, rural and urban regions are divided into areas according to specific provisioning guidelines.

Deployment parameters, such as amount of cell-splitting and cell sizes, are determined by engineers experienced in cellular system architecture.

Provisioning for each region is planned according to an engineering plan that includes cells, clusters, frequency reuse, and handovers.

CellsA cell is the basic geographic unit of a cellular system.The term cellular comes from the honeycomb shape of the areas into which a coverage region is divided. Cells are base stations transmitting over small geographic areas that are represented as hexagons. Each cell size varies depending on the landscape. Because of constraints imposed by natural terrain and man-made structures, the true shape of cells is not a perfect hexagon.

ClustersA cluster is a group of cells in which all available frequencies have been used once. No channels are reused within a cluster. Figure illustrates a seven-cell cluster.

Frequency ReuseBecause only a small number of radio channel frequencies were available for mobile systems, engineers had to find a way to reuse radio channels in order to carry more than one conversation at a time. The solution the industry adopted was called frequency planning or frequency reuse. Frequency reuse was implemented by restructuring the mobile telephone system architecture into the cellular concept.

The concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area. Cells are assigned a group of channels that is completely different from neighboring cells. The coverage area of cells are called the footprint. This footprint is limited by a boundary so that the same group of channels can be used in different cells that are far enough away from each other so that their frequencies do not interfere (see Figure ).Cells with the same number have the same set of frequencies. Here, because the number of available frequencies is 7, the frequency reuse factor is 1/7. That is, each cell is using 1/7 of available cellular channels.

TM2106EU01EG_000150


51


Fig.12

Fig.13

TM2106EU01EG_000152


53


Cell SplittingUnfortunately, economic considerations made the concept of creating full systems with many small areas impractical. To overcome this difficulty, system operators developed the idea of cell splitting. As a service area becomes full of users, this approach is used to split a single area into smaller ones. In this way, urban centers can be split into as many areas as necessary in order to provide acceptable service levels in heavy-traffic regions, while larger, less expensive cells can be used to cover remote rural regions (see Figure ).

HandoffThe final obstacle in the development of the cellular network involved the problem created when a mobile subscriber traveled from one cell to another during a call. As adjacent areas do not use the same radio channels, a call must either be dropped or transferred from one radio channel to another when a user crosses the line between adjacent cells. Because dropping the call is unacceptable, the process of handoff was created. Handoff occurs when the mobile telephone network automatically transfers a call from radio channel to radio channel as a mobile crosses adjacent cells.

During a call, two parties are on one voice channel. When the mobile unit moves out of the coverage area of a given cell site, the reception becomes weak. At this point, the cell site in use requests a handoff. The system switches the call to a stronger frequency channel in a new site without interrupting the call or alerting the user. The call continues as long as the user is talking, and the user does not notice the handoff at all.

TM2106EU01EG_000154


55


Fig.14

Fig.15

Fig.15

TM2106EU01EG_000156


Types of cells

57


The density of population in a country is so varied that different types of

cells are used:

- Macrocells

- Microcells

- Selective cells

- Umbrella cells

Macrocells

The macrocells are large cells for remote and sparsely populated areas.

Microcells

These cells are used for densely populated areas. By splitting the existing areas into smaller cells, the number of channels available is increased as well as the capacity of the cells. The power level of the transmitters used in these cells is then decreased, reducing the possibility of interference between neighboring cells.

Selective cells

It is not always useful to define a cell with a full coverage of 360 degrees. In some cases, cells with a particular shape and coverage are needed. These cells are called selective cells.

A typical example of selective cells is the cells that may be located at the entrances of tunnels where coverage of 360 degrees is not needed. In this case, a selective cell with coverage of 120 degrees is used.

Umbrella cells

A freeway crossing very small cells produces an important number of handovers among the different small neighboring cells. In order to solve this problem, the concept of umbrella cells is introduced. An umbrella cell covers several microcells. The power level inside an umbrella cell is increased comparing to the power levels used in the microcells that form the umbrella cell. When the speed of the mobile is too high, the mobile is handed off to the umbrella cell. The mobile will then stay longer in the same cell (in this case the umbrella cell). This will reduce the number of

TM2106EU01EG_000158


handovers and the work of the network .A too important number of handover demands and the propagation characteristics of a mobile can help to detect its high speed.

59


ex is ting ce lls1< R < 2 k m

m ic ro ce llsR < 3 00 m

Fig.16

TM2106EU01EG_000160


61


TM2106EU01EG_000162


5 Cellular System Components

63


The cellular system offers mobile and portable telephone stations the

same service provided fixed stations over conventional wired loops. It has the capacity to serve tens of thousands of subscribers in a major metropolitan area. The cellular communications system consists of the following four major components that work together to provide mobile service to subscribers (see Figure):-

1. Public switched telephone network (PSTN)

2. Mobile telephone switching office (MTSO)

3. Cell site with antenna system

4. Mobile Station (MS)

PSTN

TM2106EU01EG_000164


The PSTN is made up of local networks, the exchange area networks, and the long-haul network that interconnect telephones and other communication devices on a worldwide basis.

Mobile Telephone Switching Office (MTSO)The MTSO is the central office for mobile switching. It houses the mobile switching center (MSC), field monitoring and relay stations for switching calls from cell sites to wireline central offices (PSTN). In analog cellular networks, the MSC controls the system operation. The MSC controls calls, tracks billing information, and locates cellular subscribers. 65


The Cell SiteThe term cell site is used to refer to the physical location of radio equipment that provides coverage within a cell. A list of hardware located at a cell site includes power sources, interface equipment, radio frequency transmitters and receivers, and antenna systems.

Mobile Station (MS)The mobile subscriber unit consists of a control unit and a transceiver that transmits and receives radio transmissions to and from a cell site. Three types of MSUs are available:

1. The mobile telephone (typical transmit power is 4.0 watts)

2. The portable (typical transmit power is 0.6 watts)

3. The transportable (typical transmit power is 1.6 watts)

The mobile telephone is installed in the trunk of a car, and the handset is installed in a convenient location to the driver. Portable and transportable telephones are hand held and can be used anywhere. The use of portable and transportable telephones is limited to the charge life of the internal battery.

TM2106EU01EG_000166


67


Fig.17

1.7 Digital Systems

As demand for mobile telephone service has increased, service providers found that basic engineering assumptions borrowed from wireline (landline) networks did not hold true in mobile systems. While the average landline phone call lasts at least ten minutes, mobile calls usually run ninety seconds. Engineers who expected to assign fifty or more mobile phones to the same radio channel found that by doing so they increased the probability that a user would not get dial tone—this is known as call-

TM2106EU01EG_000168


blocking probability. As a consequence, the early systems quickly became saturated, and the quality of service decreased rapidly.

The critical problem was capacity. The general characteristics of TDMA, GSM,

PCS1900, and CDMA promise to significantly increase the efficiency of cellular telephone systems to allow a greater number of simultaneous conversations.

Figure 9 shows the components of a typical digital cellular system.

The advantages of digital cellular technologies over analog cellular networks include increased capacity and security. Technology options such as TDMA and CDMA offer more channels in the same analog cellular bandwidth and encrypted voice and data. 69


Because of the enormous amount of money that service providers have invested in AMPS hardware and software, providers look for a migration from AMPS to DAMPS by overlaying their existing networks with TDMA architectures.

Extended Time Division Multiple Access (E–TDMA)

The extended TDMA (E–TDMA) standard claims a capacity of fifteen times that of analog cellular systems. This capacity is achieved by compressing quiet time during conversations. E–TDMA divides the finite number of cellular frequencies into more time slots than TDMA. This allows the system to support more simultaneous cellular calls.

Personal Communications Services (PCS)

The future of telecommunications includes personal communications services.

PCS at 1900 MHz (PCS1900) is the North American implementation of DCS1800 (Global System for Mobile communications, or GSM). Trial networks were operational in the United States by 1993, and in 1994 the Federal Communications Commission (FCC) began spectrum auctions. As of 1995, the FCC auctioned commercial licenses. In the PCS frequency spectrum the operator's authorized frequency block contains a definite number of channels.

The frequency plan assigns specific channels to specific cells, following a reuse pattern which restarts with each nth cell. The uplink and downlink bands are paired mirror images. As with AMPS, a channel number implies one uplink and one downlink frequency: e.g., Channel 512 = 1850.2 MHz uplink paired with 1930.2 MHz downlink.

TM2106EU01EG_000170


71


Fig.18

1.8 Multiple Access Systems

Wireless telecommunications has dramaticall increase in popularity, resulting in the need for technologies that allow multiple users to share the same spectrum, called Multiple Access techniques.

Let’s take a closer look at the differences between the major cellular technologies in use today.

FDMA, TDMA and CDMA are the three major technologies available, along with variations of each.

TM2106EU01EG_000172


All three technologies have one goal in common that is the most important concept to any cellular telephone systems which is “Multiple Access”, meaning that multiple, simultaneous users can be supported. In other words, a large number of users share a common pool of radio channels. The “MA” in each technology stands for “Multiple Access” which is a difinition of how the radio spectrum is divided into channels and how channels are allocated to the many users of the system.

The technologies differ significantly in the manner by which they accomplish this sharing.

73


1.8.1 Frequency Division Multiple Access “FDMA”

FDMA is used for standard analog cellular. Each user is assigned a discrete band of the RF spectrum.The voice signal of each user is modulated on a separate channel frequency, which is assigned 100% of the time to that user.

The traditional analog cellular systems, such as those based on the Advanced Mobile Phone Service (AMPS) and Total Access Communications System (TACS) standards, use Frequency Division Multiple Access (FDMA). FDMA channels are defined by a range of radio frequencies, usually expressed in a number of kilohertz (kHz), out of the radio spectrum.

For example, AMPS systems use 30 kHz "slices" of spectrum for each channel. Narrowband AMPS (NAMPS) requires only 10 kHz per channel. TACS channels are 25 kHz wide. With FDMA, only one subscriber at a time is assigned to a channel. No other conversations can access this channel until the subscriber's call is finished, or until that original call is handed off to a different channel by the system. In order to overcome this inefficiency, digital access technologies were introduced.

FDMA requires NO system timing.

FDMA requires NO timing accuracy.

FDMA –based Analog system generally considered as a low capacity system.

TM2106EU01EG_000174


75


Fig.19

North American Analog Cellular Systems

Originally devised in the late 1970s to early 1980s, analog systems have been revised somewhat since that time and operate in the 800-MHz range. A group of government, telco, and equipment manufacturers worked together as a committee to develop a set of rules (protocols) that govern how cellular subscriber units (mobiles) communicate with the "cellular system." System development takes into consideration many different, and often opposing, requirements for the system, and often a compromise between conflicting requirements results. Cellular development involves some basic topics:

1. Frequency and channel assignments

2. Type of radio modulation

3. Maximum power levels

4. Modulation parameters

5. Messaging protocols

TM2106EU01EG_000176


6. Call-processing sequences

The Advanced Mobile Phone Service (AMPS)

AMPS was released in 1983 using the 800-MHz to 900-MHz frequency band and the 30 kHz bandwidth for each channel as a fully automated mobile telephone service. It was the first standardized cellular service in the world and is currently the most widely used standard for cellular communications. Designed for use in cities, AMPS later expanded to rural areas. It maximized the cellular concept of frequency reuse by reducing radio power output. The AMPS telephones (or handsets) have the familiar telephone-style user interface and are compatible with any AMPS base station. This 77


makes mobility between service providers (roaming) simpler for subscribers. Limitations associated with AMPS include:

1. Low calling capacity

2. Limited spectrum

3. No room for spectrum growth

4. Poor data communications

5. Minimal privacy

6. Inadequate fraud protection

AMPS is used throughout the world and is particularly popular in the United States, South America, China, and Australia. AMPS uses frequency modulation (FM) for radio transmission. In the United States, transmissions from mobile to cell site use separate frequencies from the base station to the mobile subscriber.

TM2106EU01EG_000178


79


Narrowband Analog Mobile Phone Service (NAMPS)

Since analog cellular was developed, systems have been implemented extensively throughout the world as first-generation cellular technology. In the second generation of analog cellular systems, NAMPS was designed to solve the problem of low calling capacity. NAMPS is now operational in 35 U.S. and overseas markets and NAMPS was introduced as an interim solution to capacity problems.

NAMPS is a U.S. cellular radio system that combines existing voice processing with digital signaling, tripling the capacity of today's AMPS systems. The NAMPS concept uses frequency division to get three channels in the AMPS 30-kHz single channel bandwidth. NAMPS provides three users in an AMPS channel by dividing the 30-kHz AMPS bandwidth into three 10-kHz channels. This increases the possibility of interference because channel bandwidth is reduced.

TM2106EU01EG_000180


81


TM2106EU01EG_000182


83


1.8.2 Time Division Multiple Access “TDMA”

The key point to make about TDMA is that users are still assigned a discrete slice of RF spectrum, but multiple users now share that RF channel on a time slot basis. Each of the users alternate their use of the RF channel . Frequency Division is still used, but these carriers are now further subdivided into some number of time slots ber carrier.

A user is assigned a particular time slot in a carrier and can only send or receive information at those times. This is true wether or not the other time slots are being used. Information flow is not continuous for any user, but rather is sent and received in „bursts“ . The bursets are re-assembled at the receiving end , and appear to provide continuous sound because the process is very fast.

TDMA digital standards include North American Digital Cellular (known by its standard number IS-54), Global System for Mobile Communications (GSM), and Personal Digital Cellular (PDC).

For example, IS-54 based TDMA system, a 30 kHz channel is divided into 6 time slots each with 30 kHz band modulated signal. Although there are 6 time slots, each user needs 2 time slots, so there are a total of 3 users per 30 kHz channel. This is three times more efficient than AMPS

PDC divides 25 kHz slices of spectrum into three channels.

GSM system uses both FDMA and TDMA operates with a 200 Khz bandwidth, divided into 8 timeslots, where each user is assigned a single timeslot, thus allowing 8 users per channel frequency.

TDMA requires timing synchronization so that users only transmit during their assigned time slot. In order to do that, all users must have a common, relatively accurate, time reference. TDMA typically acquires its timing from a clock associated with the T1 or E1 span line which connects the cell to the system.

TDMA requires millisecond accuracy.

GSM and TDMA are about 3 times more spectral efficient than analog.

TM2106EU01EG_000184


85


Fig.19

TM2106EU01EG_000186


87


1.8.2.1 The GSM network

The GSM technical specifications define the different entities that form the GSM network by defining their functions and interface requirements.

The GSM network can be divided into four main parts:

The Mobile Station (MS).

The Base Station Subsystem (BSS).

The Network and Switching Subsystem (NSS).

The Operation and Support Subsystem (OSS).

The architecture of the GSM network is presented in figure

Mobile Station MS

A Mobile Station consists of two main elements:

The mobile equipment or terminal.

The Subscriber Identity Module (SIM) .

The Mobile Equipment Terminal

There are different types of terminals distinguished principally by their power and application: The `fixed' terminals are the ones installed in cars. Their maximum allowed output power is 20 W.The GSM portable terminals can also be installed in vehicles. Their maximum allowed output power is 8W.

The handhels terminals have experienced the biggest success thanks to their weight and volume, which are continuously decreasing. These terminals can emit up to 2 W. The evolution of technologies allows decreasing the maximum allowed power to 0.8 W.

The SIM (Subscriber Identity Module)

The SIM is a smart card that identifies the terminal. By inserting the SIM card into the terminal, the user can have access to all the subscribed services. Without the SIM card, the terminal is not operational. The SIM card is protected by a four-digit Personal Identification Number (PIN). In order to identify the subscriber to the system, the SIM card contains some parameters of the user such as its International Mobile Subscriber Identity (IMSI).

TM2106EU01EG_000188


Another advantage of the SIM card is the mobility of the users. In fact, the only element that personalizes a terminal is the SIM card. Therefore, the user can have access to its subscribed services in any terminal using its SIM card.

89


Fig.20

TM2106EU01EG_000190


91


The Base Station Subsystem

The BSS connects the Mobile Station and the NSS. It is in charge of the transmission and reception. The BSS can be divided into two parts:

The Base Transceiver Station (BTS) or Base Station.

The Base Station Controller (BSC).

The Base Transceiver Station: -

The BTS corresponds to the transceivers and antennas used in each cell of the network. A BTS is usually placed in the center of a cell. Its transmitting power defines the size of a cell. Each BTS has between one and sixteen transceivers depending on the density of users in the cell.

The Base Station Controller: -

The BSC controls a group of BTS and manages their radio ressources. A BSC is principally in charge of handovers, frequency hopping, exchange functions and control of the radio frequency power levels of the BTSs.

TM2106EU01EG_000192


93


Fig.21

TM2106EU01EG_000194


95


The Network and Switching Subsystem

Its main role is to manage the communications between the mobile users and other users, such as mobile users, ISDN users, fixed telephony users, etc. It also includes data bases needed in order to store information about the subscribers and to manage their mobility. The different components of the NSS are described below.

The Mobile services Switching Center (MSC)

It is the central component of the NSS. The MSC performs the switching functions of the network. It also provides connection to other networks.

Home Location Register (HLR)

The HLR is considered as a very important database that stores information of the suscribers belonging to the covering area of a MSC. It also stores the current location of these subscribers and the services to which they have access. The location of the subscriber corresponds to the SS7 address of the Visitor Location Register (VLR) associated to the terminal.

Visitor Location Register (VLR)

The VLR contains information from a subscriber's HLR necessary in order to provide the subscribed services to visiting users. When a subscriber enters the covering area of a new MSC, the VLR associated to this MSC will request information about the new subscriber to its corresponding HLR. The VLR will then have enough information in order to assure the subscribed services without needing to ask the HLR each time a communication is established. The VLR is always implemented together with a MSC; so the area under control of the MSC is also the area under control of the VLR.

The Authentication Center (AuC)

The AuC register is used for security purposes. It provides the parameters needed for authentication and encryption functions. These parameters help to verify the user's identity.

The Equipment Identity Register (EIR)

The EIR is also used for security purposes. It is a register containing information about the mobile equipments. More particularly, it contains a list of all valid terminals. A terminal is identified by its International Mobile Equipment Identity (IMEI). The EIR allows then to forbid calls from stolen or unauthorized terminals (e.g, a terminal which does not respect the specifications concerning the output RF power).

The Operation and Support Subsystem (OSS)

TM2106EU01EG_000196


The OSS is connected to the different components of the NSS and to the BSC, in order to control and monitor the GSM system. It is also in charge of controlling the traffic load of the BSS. However, the increasing number of base stations, due to the development of cellular radio networks, has provoked that some of the maintenance tasks are transfered to the BTS. This transfer decreases considerably the costs of the maintenance of the system.

97


Fig.21

TM2106EU01EG_000198


99


1.8.3 Code Division Multiple Access “CDMA”The third major multiple access technology, which is also digital, is Code Division Multiple Access “CDMA”.

CDMA is a general category of digital wireless radio technologies that uses spread spectrum techniques to modulate information across given bandwidth.

IS-95 was an interim standard that defined the operation of the first application of CDMA.

In CDMA, information signals from all users are simultaneously modulated across the entire channel band width (1.23 Mhz).

Unique digital codes keep users separated on the 1.23 Mhz channel.

All the three” MA” technologies take advantage of the fact that radio signals travel only a finite distance. The result is that frequencies can be reused with minimal interference after a minimum distance. The resulting assignment of frequencies is referred to “reuse pattern.”

CDMA doesn’t require frequency reuse pattern i.e. every code can be used in every sector of every cell; this is one of the most significant advantages of CDMA as frequency reuse planning is very complex.

In CDMA, timing is critical and aquired from the Global Positioning system”GPS” as accurate synchronization between cells is critical to CDMA operation.

CDMA also requires microsecond accuracy.

The major advantage of CDMA when compared to the other technologies is its efficient use of available spectrum, as bandwidth efficiecy directly to system capacity. The greater the efficiency, the more users can share the same spectrum, but it also can impact the amount of infrastructure equipment required to support a given number of users. This indirectly impacts the cost of operation.

CDMA is a form of spread-spectrum, a family of digital communications techniques that have been used in military applications for years. Originally there were two motivations for using CDMA: either to resist enemy efforts to jam the communications, or to hide the fact that communication was even taking place. The use of CDMA for civilian mobile radio applications was proposed 40 years ago, but did not take place till recently.

TM2106EU01EG_0001100


In March 1992, the Telecommunications Industry Association (TIA) established the TR-45.5 subcommittee with the charter of developing a spread-spectrum digital cellular standard. In the July of 1993, the TIA gave its approval to the CDMA IS-95 standard.

In recent times, CDMA has gained widespread international acceptance by cellular radio system operators as an upgrade that will increase both their system capacity and the service quality.

101


Fig.22

TM2106EU01EG_0001102


103


1.9 Duplex Transmission: FDD & TDDTwo duplex methods are used for coordinating the uplink (UL) and downlink (DL) components of a transmission between a base station and a mobile station, namely Frequency Division Duplex (FDD) and Time Division Duplex (TDD).

UL and DL are implemented for FDD in different frequency bands. The gap between the two frequency bands for UL and DL is known as the duplex distance. It is constant for all mobile stations in a standard. Generally the DL frequency band is positioned at the higher frequency than the UL band.

In the case of TDD, UL and DL are implemented in the same frequency band. This is done by dividing the band into timeslots (TS) and frames. A frame contains a specific number, n, of timeslots, TS. A number, n, of these timeslots is reserved for UL transmission (half of the timeslots in 2G systems) and the remaining for DL transmission. The duration of a frame determines the cyclical repetition of the corresponding UL / DL transmission. The UL and DL transmission occurs almost simultaneously – i.e., the duration of a frame is generally in the range of a number of ms. TDD transmission is mainly used as of the 2nd mobile communications generation (in digital transmissions). Digital transmission simplifies speech and data compression.

As a result, only a fraction of the time needed for analog transmission is required for digital transmission of subscriber data.

TM2106EU01EG_0001104


105


Fig.23

TM2106EU01EG_0001106


Fig.24

107


TM2106EU01EG_0001108


6 Data Transmission

109


One of the problems of data transmission using GSM is posed by the

current comparatively user-unfriendly usage of data services in the terminals (e.g. SMS) or the complicated connection of terminal equipment via adapter.

Terminal equipment in which different functions are integrated, as well as displays optimized for each individual data transmission form provide an answer to this.

A decisive problem is posed by the comparatively low data transmission rates of

GSM Phase 1 and 2. Data transmission rates of 0.3 -9.6 kbit/s compared to 64 kbit/s using ISDN are considerably too low.

To increase the data transmission rates, new bearer services are being developed in

TM2106EU01EG_0001110


GSM Phase 2+, which will adapt the data transmission rates to the ISDN transmission rates in various usage areas or even, be considerably above them.

_ High Speed Circuit Switched Data HSCSD

_ General Packet Radio Service GPRS

_ Enhanced Data rates for the GSM Evolution EDGE

111


TM2106EU01EG_0001112


113


Fig.25

In Phases 1 and 2 GSM allows data transfers at rates of only 0.3 to 9.6

kbit/s. Three different principles are introduced in GSM Phase 2+ for increasing the data rate:

HSCSD, GPRS and EDGE.

HSCSD: High Speed Circuit Switched Data

HSCSD in theory allows up to 8 physical channels of a carrier to be bundled together (multilinking) to a single subscriber. In practice, however, only up to 4 channels are bundled together. The maximum transfer rate per physical channel was increased from 9.6 kbit/s to 14.4 kbit/s with the introduction of a new codec. As a result, up to

TM2106EU01EG_0001

GSM Evolution to UMTS: Date Transmission / Network Elements & Protocols

114


57.6 kbit/s can be reached (or theoretically, 115.2 kbit/s). HSCSD, like conventional GSM, only transfers circuit-switched (CD) data. Only minor modifications to the GSM network are required to introduce HSCSD.

GPRS: General Packet Radio ServicesGPRS also allows bundling (multilinking) of up to 8 physical channels to a subscriber.

Four new coding methods enable transfers at rates of 9.05 /13.4 / 15.6 / 21.4 kbit/s per physical channel. GPRS introduces packet-switched (PS) data transmission, which allows efficient use of resources and direct access to packet data networks 115


(PDN). New network elements and protocols are being introduced that will pave the way for UMTS. GPRS is therefore of major importance for launching UMTS.

EDGE: Enhanced Data Rate for the GSM Evolution

EDGE introduces a new modulation method over the radio interface –8PSK (8-Phase Shift Keying). In theory, this allows transfer rates three times faster than those for the conventional GSM modulation method, GMSK (Gaussian Minimum Shift Keying). In this way, EDGE increases the performance of GPRS and HSCSD, and transmission at up to 69.2 kbit/s per physical channel is achievable. A maximum rate of 553.6 kbit/s is possible with 8 channels multilinking.

UTRA (N): UMTS Terrestrial Radio Access (Network)

Fully new transmission methods (WCDMA, ATM) are used in UMTS for

the UTRA radio access and the UMTS Terrestrial Radio Access Network (UTRAN). New network elements and a new protocol architecture are needed. The maximum transmission rate via the radio access will approach 1920 kbit/s.

TM2106EU01EG_0001116


117


Fig.26

Fig.27

TM2106EU01EG_0001118


119


TM2106EU01EG_0001

7 The General Packet Radio System (GPRS)

120


121


The General Packet Radio System (GPRS) is a new service that provides

actual packet radio access for mobile Global System for Mobile Communications (GSM) and time-division multiple access (TDMA) users. The main benefits of GPRS are that it reserves radio resources only when there is data to send and it reduces reliance on traditional circuit-switched network elements. The increased functionality of GPRS will decrease the incremental cost to provide data services, an occurrence that will, in turn, increase the penetration of data services between consumer and business users. In addition, GPRS will allow improved quality of data services as measured in terms of reliability, response time, and features supported. The unique applications that will be developed with GPRS will appeal to a broad base of mobile subscribers and allow operators to differentiate their services. These new services will increase capacity requirements on the radio and base-station subsystem resources. One method GPRS uses to alleviate the capacity impacts is sharing the same radio resource among all mobile stations in a cell, providing effective use of the scarce resources. In addition, new core network elements will be deployed to support the high burstiness of data services more efficiently. In addition to providing new services for today's mobile user, GPRS is important as a migration step toward third-generation (3G) networks. GPRS will allow network operators to implement IP-based core architecture for data applications, which will continue to be used and expanded upon for 3G services for integrated voice and data applications. In addition, GPRS will prove a testing and development area for new services and applications, which will also be used in the development of 3G services.

TM2106EU01EG_0001122


123


Fig.28

TM2106EU01EG_0001124


125


1.10 Timescales for GPRS

When a new service is introduced, there are a number of stages before it becomes established. GPRS service developments will include standardization, infrastructure development, network trials, contracts placed, network roll out, availability of terminals, application development, and so on. These stages for GPRS are:

Like the GSM standard itself, GPRS will be introduced in phases. Phase 1 is expected to be available commercially in the year 2000/1. Point to Point GPRS (sending information to a single GPRS user) will be supported, but not Point to Multipoint (sending the same information to several GPRS users at the same time). GPRS Phase 2 is not yet fully defined, but is expected to support higher data rates through the possible incorporation of techniques such as EDGE (Enhanced Data rates for GSM Evolution), in addition to Point-to-Multipoint support.

TM2106EU01EG_0001126


127


Date Milestone

Throughout 1999 - 2000

Network operators place trial and commercial contracts for GPRS infrastructure.Incorporation of GPRS infrastructure into GSM networks

Summer of 2000

First trial GPRS services become available. Typical single user throughput is likely to be 28 kbps.For example, T-Mobil is planning a GPRS trial at Expo2000 in Hanover in the Summer of 2000

Start of 2001 Basic GPRS capable terminals begin to be available in commercial quantities

Throughout 2001

Network operators launch GPRS services commercially and roll out GPRS.Vertical market and executive GPRS early adopters begin using it regularly for nonvoice mobile communications

2001/2

Typical single user throughput is likely to be 56 kbps. New GPRS specific applications, higher bitrates, greater network capacity solutions, more capable terminals become available, fuelling GPRS usage

2002 Typical single user throughput is likely to be 112 kbps.GPRS Phase 2/ EDGE begins to emerge in practice

2002GPRS is routinely incorporated into GSM mobile phones and has reached critical mass in terms of usage. (This is the equivalent to the status of SMS in 1999)

2002/3 3GSM arrives commercially

Fig.29

TM2106EU01EG_0001128


129


1.11GPRS Architecture

From a high level, GPRS can be thought of as an overlay network onto a second-generation GSM network. This data overlay network provides packet data transport at rates from 9.6 to 171 kbps. Additionally, multiple users can share the same air-interface resources.

GPRS attempts to reuse the existing GSM network elements as much as possible, but in order to effectively build a packet-based mobile cellular network, some new network elements, interfaces, and protocols that handle packet traffic are required. Therefore, GPRS requires modifications to numerous network elements, as summarized in the next Figure.

TM2106EU01EG_0001130


131


GSM Network Element

Modification or Upgrade Required for GPRS

Subscriber Terminal (TE) A totally new subscriber terminal is required to access GPRS

services. These new terminals will be backward compatible with GSM for voice calls.

BTS A software upgrade is required in the existing base transceiver site (BTS).

BSC The base station controller (BSC) will also require a software upgrade, as well as the installation of a new piece of hardware called a packet control unit (PCU). The PCU directs the data traffic to the GPRS network and can be a separate hardware element associated with the BSC.

Core Network The deployment of GPRS requires the installation of new core network elements called the Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN).

Databases (VLR, HLR, and so on)

All the databases involved in the network will require software upgrades to handle the new call models and functions introduced by GPRS.

Fig.30

TM2106EU01EG_0001132


133


1.11.1 GPRS Reference Architecture

A GPRS terminal can be one of three classes: A, B, or C. A Class A terminal supports GPRS and other GSM services (such as SMS and voice) simultaneously. This support includes simultaneous attach, activation, monitor, and traffic. As such, a Class A terminal can make or receive calls on two services simultaneously. In the presence of circuit-switched services, GPRS virtual circuits will be held or placed on busy rather than being cleared.

A Class B terminal can monitor GSM and GPRS channels simultaneously, but can support only one of these services at a time. Therefore, a Class B terminal can support simultaneous attach, activation, and monitor, but not simultaneous traffic. As with Class A, the GPRS virtual circuits will not be closed down when circuit-switched traffic is present. Instead, they will be switched to busy or held mode. Thus, users can make or receive calls on either a packet or a switched call type sequentially, but not simultaneously.

A Class C terminal supports only nonsimultaneous attach. The user must select which service to connect to. Therefore, a Class C terminal can make or receive calls from only the manually (or default) selected service. The service that is not selected is not reachable. Finally, the GPRS specifications state that support of SMS is optional for Class C terminals.

GPRS Subscriber TerminalsNew terminals (TEs) are required because existing GSM phones do not handle the enhanced air interface, nor do they have the ability to packetize traffic directly. A variety of terminals will exist, as described in a previous section, including a high-speed version of current phones to support high-speed data access, a new kind of PDA device with an embedded GSM phone, and PC Cards for laptop computers. All these TEs will be backward compatible with GSM for making voice calls using GSM.

GPRS BSSEach BSC will require the installation of one or more PCUs and a software upgrade. The PCU provides a physical and logical data interface out of the base station system (BSS) for packet data traffic. The BTS may also require a software upgrade, but typically will not require hardware enhancements.

When either voice or data traffic is originated at the subscriber terminal, it is transported over the air interface to the BTS, and from the BTS to the BSC in the

TM2106EU01EG_0001134


same way as a standard GSM call. However, at the output of the BSC the traffic is separated; voice is sent to the mobile switching center (MSC) per standard GSM, and data is sent to a new device called the SGSN, via the PCU over a Frame Relay interface.

135


Fig.31

TM2106EU01EG_0001136


137


GPRS Core NetworkIn the core network, the existing MSCs are based upon circuit-switched central-office technology, and they cannot handle packet traffic. Thus two new components, called GPRS Support Nodes, are added:

Serving GPRS Support Node (SGSN).

Gateway GPRS Support Node (GGSN).

The SGSN can be viewed as a "packet-switched MSC;" it delivers packets to mobile stations (MSs) within its service area. SGSNs send queries to home location registers (HLRs) to obtain profile data of GPRS subscribers. SGSNs detect new GPRS MSs in a given service area, process registration of new mobile subscribers, and keep a record of their location inside a given area. Therefore, the SGSN performs mobility management functions such as mobile subscriber attach/detach and location management. The SGSN is connected to the base-station subsystem via a Frame Relay connection to the PCU in the BSC.

GGSNs are used as interfaces to external IP networks such as the public Internet, other mobile service providers' GPRS services, or enterprise intranets. GGSNs maintain routing information that is necessary to tunnel the protocol data units (PDUs) to the SGSNs that service particular MSs. Other functions include network and subscriber screening and address mapping. One (or more) GGSNs may be provided to support multiple SGSNs. More detailed technical descriptions of the SGSN and GGSN are provided in a later section.

TM2106EU01EG_0001138


139


Fig. 32

TM2106EU01EG_0001140


141


GPRS Mobility Management

Mobility management within GPRS builds on the mechanisms used in GSM networks; as a MS moves from one area to another, mobility management functions are used to track its location within each mobile network. The SGSNs communicate with each other and update the user location. The MS profiles are preserved in the visitor location registers (VLRs) that are accessible by the SGSNs via the local GSM MSC. A logical link is established and maintained between the MS and the SGSN in each mobile network. At the end of transmission or when a MS moves out of the area of a specific SGSN, the logical link is released and the resources associated with it can be reallocated.

TM2106EU01EG_0001142


143


TM2106EU01EG_0001144


1.12 GPRS Applications

145


GPRS will enable a variety of new and unique services to the mobile

wireless subscriber. These mobile applications contain several unique characteristics that enhance the value to the customers. First among them is mobility—the ability to maintain constant voice and data communications while on the move. Second is immediacy, which allows subscribers to obtain connectivity when needed, regardless of location and without a lengthy login session. Finally, localization allows subscribers to obtain information relevant to their current location. The combination of these characteristics provides a wide spectrum of possible applications that can be offered to mobile subscribers. The core network components offered by Cisco enable seamless access to these applications, whether they reside in the service provider's network or the public Internet.

In general, applications can be separated into two high-level categories: corporate and consumer. These include:

Communications: -E-mail; fax; unified messaging; intranet/Internet access

Value-added services (VAS): -Information services; games

E-commerce: -Retail; ticket purchasing; banking; financial trading

Location-based applications: -Navigation; traffic conditions; airline/rail schedules; location finder

TM2106EU01EG_0001146

Date post:	20-Jul-2016
Category:	Documents
Upload:	mohamedsalah
View:	12 times
Download:	2 times

01 Tm2106euo1_eg0001 Theway to Cdma

Documents