GSM/UMTS/LTE Basics

1 Introduction
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Chapter 1Chapter 1Chapter 1Chapter 1
IntroductionIntroductionIntroductionIntroduction
TopicTopicTopicTopic PagePagePagePage
Cellular concept ................................................................................................. 7
Analogue and digital signals............................................................................ 16
PCM/E1 Link................................................................................................... 21
Wireline transmission ...................................................................................... 22
Microwave radio relay..................................................................................... 24
Switching ......................................................................................................... 26

GSM/UMTS/LTE Basics
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1 Introduction
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Cellular conceptCellular conceptCellular conceptCellular concept
In 1940s the first fully commercial mobile telephony systems DPLM
Domestic Public Land Mobile were launched in United States. However,
these systems were not cellular networks. There was just one Base Station
(BS) that was using the whole available bandwidth.
f1,f2,f3,f4
Figure 1-1 Non-cellular mobile system
The only way to increase the capacity (the number of simultaneous call
connections) was to add extra radio channels. This solution is very
inconvenient, as the licenses for radio frequencies are very expensive and also
the bandwidth for any application is limited as radio resources are also used
for other services than a mobile telephony.
f1,f2,f3,f4+f5,f6
Figure 1-2 Non-cellular mobile system (capacity increase)
The second disadvantage of single cell systems is a limited coverage. The
only way of increasing the coverage is to increase the output power, both of

GSM/UMTS/LTE Basics
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Base Station (BS) and Mobile Station (MS). However it is only possible to
increase the output power of the MS to a certain level defined by the national
regulations, as around very powerful transmitters there should be the closed
zone, to protect people against radiation.
f1,f2,f3,f4+f5,f6
PP
P
P
P
Figure 1-3 Non-cellular mobile system (coverage increase)
Due to limited capacity and coverage, the single cell systems were very
expensive and they have never been popular (less than 1 million of users
around the world)
The cellular concept was envisioned at Bell Laboratories in 1947. However
due to its complexity, the first such systems were putted into operation in the
late 70s.
Figure 1-4 Cellular mobile system

1 Introduction
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Cellular network comprises of a number of BSs. The radio coverage areas
given by the neighbouring BSs are partially overlapping each other, allowing
for the handover of the call connection from one cell to another, when the
subscriber is roaming through the network.
The available radio channels are organized in sets. The same set of
frequencies can be allocated to a number of cells if only the distance between
them is far enough to prevent interferences. This way, it is possible to cover
an unlimited area by using a limited number of radio channels. The maximum
number of simultaneous calls in the cell still is equal to the number of
channels allocated to that cell.
Figure 1-5 Cellular mobile system (frequency re-use)
However by decreasing the cell size, it is possible to place at the same area
more cells. Assuming that the number of frequencies per cell is constant, the
number of simultaneous calls increases. The unlimited coverage and a very
high capacity are the great advantages of the cellular networks.
Figure 1-6 Cellular mobile system (capacity increase)

GSM/UMTS/LTE Basics
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At the same time the cellular networks have same disadvantages; these are:
difficult radio network planning, necessity of automatic tracing of the
subscriber movement in the geographical cell structure, necessity of
handovers and the complex technology.
CellsCellsCellsCells
A cell is defined as the area of radio coverage given by one BS antenna
system. Typically, cells are represented graphically by hexagons. However
these are the type of antenna and the environment parameters, which
determines the actual BS radiation pattern.
equal signal
strength from both BS
Figure 1-7 Cell – hexagon shape
Figure 1-8 Cell – hexagon and real radiation pattern example

1 Introduction
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There are two main types of cells:
• Omini directional cell – served by antenna, which transmits equally in
all directions,
• Sector cell – served by antenna, which transmits in a given direction
only (e.g. 120º or 180º).
omni directional directional
Figure 1-9 Antenna types
The group of BSs that are serving sector cells can be installed at one site,
leading to terms such as two-sectored site and more commonly used three-
sector site. In such case usually the functionality of all BSs at the site resides
in a single hardware network node.
Omni directional cell 3 sector cells
Figure 1-10 Types of cells

GSM/UMTS/LTE Basics
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Figure 1-11 3-sectors site
Frequency reuse and clustersFrequency reuse and clustersFrequency reuse and clustersFrequency reuse and clusters
Groups of frequencies can be placed together into pattern of cells called a
cluster. A cluster is a group of cells in which all available frequencies have
been used once and only once. Clusters have such shapes that they fit one to
another so it is possible to cover the whole area of the network without any
gaps. The frequency re-use distance between cells that are using the same set
of frequencies in two neighbouring clusters are kept constant, therefore the
interference conditions in all cells within the network are the same.
f1f1f1f1
Figure 1-13 4/12 Frequency re-use pattern

1 Introduction
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In Fig. 1-13 the 4/12 frequencies re-use pattern is shown. 4/12 means that
there are four three-sector sites supporting twelve cells using twelve
frequency groups.
The 4/12 cell pattern is commonly used by GSM operators. GSM also can
work with other patterns providing higher capacity. The example of such
pattern is 3/9 where the entire set of available frequencies is divided only
between nine cells in the cluster in comparison to 12 in 4/12 pattern.
Unfortunately at the same time the signal quality in the network using 3/9
pattern is lower due to decreased frequency re-use distance.
f1f1 f1f1
Figure 1-14 3/9 Frequency re-use pattern
36/1=3636/3=1236/9=436/12=3# frequencies per cell
3/9 1/3
36# frequencies
1/14/12pattern
36/1=3636/3=1236/9=436/12=3# frequencies per cell
3/9 1/3
36# frequencies
1/14/12pattern
tighter frequency re-use → higher capacity
tighter frequency re-use → shorter re-use distances →
higher interferences
Figure 1-15 Frequency re-use pattern and capacity

GSM/UMTS/LTE Basics
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Other frequency re-use patterns, such as 7/21, with long frequency re-use
distance, are recommended for analogue networks, which are more sensitive
to interference. In contrast, the newest cellular systems, like UMTS, LTE and
the future 4G system (currently known under name advanced-LTE) are using
commonly 1/1 frequency re-use pattern. In those systems the interferences
caused by lack of frequency re-use distances are minimised by other methods
than frequency planning (more in the following chapters).
LTE
UMTS
GSM
1/11/33/94/12
LTE
UMTS
GSM
1/11/33/94/12
Figure 1-16 Frequency re-use patterns for cellular systems
In the real network the allocation of channels to cells and the cell size will not
be as uniform as in the presented examples. Cells where locally there is a
higher traffic will require more frequencies than the cells with smaller traffic
than average level in the network. In the big cities where there is a huge
population density the cell size will be reduced to increase the capacity,
whereas in the rural areas the cells can be quite large.
Increase of capacity in cellular systemIncrease of capacity in cellular systemIncrease of capacity in cellular systemIncrease of capacity in cellular system
If the number of subscribers in a system continues to increase, at some point it
becomes necessary to increase the capacity of the system.
There are several ways to increase the capacity of the system:
• increase the frequency band (for example, a GSM 900 operator might
buy GSM 1800 licenses),
• make frequency reuse tighter (for example, going from a 4/12 reuse
pattern to a 3/9 reuse pattern),
• make the cells smaller and smaller (cell split).
The examples of a cell split are shown in Fig. 1-17, 1-18 and 1-19. Initially,
the omni directional cells, giving the maximum range are used (Fig. 1-17).
The next step is to introduce three cells per site (Fig. 1-18), using the original
sites and feeding the cells from the corners. Now, the number of sites is still
the same, but there are three times as many cells as before. In the following
step it is possible to split existing cells again, but it is necessary to add new
sites (Fig. 1-19).

1 Introduction
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Figure1-17 Before cell split
Figure 1-18 Cell split phase 1
Figure 1-19 Cell split phase 2

GSM/UMTS/LTE Basics
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Cellular networkCellular networkCellular networkCellular network
The cellular network is not only comprising from BS and cells but also it
includes fixed elements and interfaces to which the BS are connected to.
The role of fixed elements, including, exchanges, switches, routers, databases,
servers and interfaces is to trace the terminal location and establish connection
between terminals in case one is calling to another.
VLR
RNC MSC
VLR
GMSC
GGSN
HSS
MSCBSC
BSC SGSN
Figure 1-20 Cellular network
Analogue and digital signalsAnalogue and digital signalsAnalogue and digital signalsAnalogue and digital signals
A signal is an impulse or a fluctuating electric quantity, such as voltage,
current, or electric field strength, whose variations represent coded
information.
Signal to be transmitted through any transmission medium can be analogue or
digital. Analogue signal is continuous and can take any value over time. An
example of analogue signal is human voice. Digital signal is not continuous,
as it changes its value only at the predefined time instances. The values of
digital signal are taken from the finite set of values. An example of digital
signal is the light in case when the lamp is used for transmission of Morse
Code symbols. There are only two possible values (shine or darkness) and the
change of value can be done only at certain time instances as the duration of
dot, dash and space between these two symbols is specified.

1 Introduction
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analogue
digital
Figure 1-21 Analogue and digital signal
Both analogue and digital signals are distorted during the transmission
process. In case of the analogue signal it is not possible to regenerate the
original signal at the receiver side, as it can take any value over the time,
which the receiver system cannot predict. In case of the digital binary signal,
the receiver can make a decision to which of two possible values the received
signal level is closer. If only the distortions are not very severe, by doing this
the receiver can regenerate the original signal.
transmitted received regeneratedtransmitted received regenerated
Figure 1-22 Regeneration of digital signal
The possibility of regeneration is a great advantage of using digital
transmission. In digital system it is possible to implement additional coding in
order to protect the information against transmission errors and ciphering to
protect information against overhearing by third parties. Very often the
analogue information such as human speech or music is transmitted or stored
in the digital form (digital telephony ISDN/GSM, CD), because digital signals
provide better quality for transmission of analogue information than analogue
signals.
Analogue to digital conversionAnalogue to digital conversionAnalogue to digital conversionAnalogue to digital conversion
One of the primary functions of an mobile terminal is to convert the analogue
speech information into digital form for transmission using a digital signal.
The Analogue to Digital (A/D) conversion process outputs a collection of bits:
binary ones and zeros which represent the speech input.

GSM/UMTS/LTE Basics
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Digital
System
analogue
A/D
digital
Figure 1-23 A/D conversion
The A/D conversion is performed by using a process called Pulse Code
Modulation (PCM). PCM involves three main steps:
• sampling,
• quantisation,
• coding.
SampSampSampSamplinglinglingling
Sampling is measurement of the signal level at the specific time intervals. The
signal is described by the set of samples that can still take any value, however
the signal is discrete in time domain. Sampling introduces a loss of
information. However, the more often the samples are taken, the closer the
resulting digital values will be to a true representation of the analogue
information. The sampling theory states that:
“To reproduce an analogue signal without distortion, the signal must be
sampled with at least twice the frequency of the highest frequency component
in the analogue signal spectrum”.
Speech contains frequencies from the range 300Hz - 3400Hz. That means that
to truly represent speech in the digital system the sampling frequency must be
at least equal to 2 x 3400kHz = 6800Hz or 6.8 kHz. Telecommunication
systems usually use the sampling frequency of 8 kHz to assure good speech
quality.
Figure 1-24 Sampling

1 Introduction
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QuantisationQuantisationQuantisationQuantisation
The next step in A/D conversion is quantisation. The amplitude of the signal
at the time of sampling is measured and approximated to one of the finite set
of values. Quantisation introduces errors, as the approximated value is hardly
ever equal to the value of the sample. The degree of accuracy depends on the
number of quantisation levels used. In common telephony, 256 levels are
used, while in GSM/UMTS/LTE 8192 levels are used.
QuantisationQuantisation
Figure 1-25 Quantisation
CodingCodingCodingCoding
Coding involves converting the quantised values into binary values. In case of
fixed ISDN when 256 quantisation levels are used, 8 bits represent each
value. In GSM due to the fact that 8192 quantisation levels are used, 13 bits
are needed to represent each sample.
9
8
7
6
5
4
3
2
1
5
4
3
2
1
0
1
1
1
1
1
1
Coding
00→0000
01→0001
02→0010
03→0011
04→0100
05→0101
06→0110
07→0111
08→1000
09→1001
10→1010
11→1011
12→1100
13→1101
14→1110
15→1111
1000 1100 1110 1111 1111 1111 1111 1011
0110 0011 0010 0001 0001 0001 0001 0010 0100 1000
1110 1101
9
8
7
6
5
4
3
2
1
5
4
3
2
1
0
1
1
1
1
1
1
Coding
00→0000
01→0001
02→0010
03→0011
04→0100
05→0101
06→0110
07→0111
08→1000
09→1001
10→1010
11→1011
12→1100
13→1101
14→1110
15→1111
Coding
00→0000
01→0001
02→0010
03→0011
04→0100
05→0101
06→0110
07→0111
08→1000
09→1001
10→1010
11→1011
12→1100
13→1101
14→1110
15→1111
1000 1100 1110 1111 1111 1111 1111 1011
0110 0011 0010 0001 0001 0001 0001 0010 0100 1000
1110 11011000 1100 1110 1111 1111 1111 1111 1011
0110 0011 0010 0001 0001 0001 0001 0010 0100 1000
1110 1101
Figure 1-26 Coding
After coding, in the traditional telephony, human voice is represented by a bit
stream of 64 kbits/s (8 bits * 8 kHz = 64 kbits/s) and in GSM/UMTS/LTE 104
kbits/s (13 bits * 8 kHz = 104 kbits/s)1
.
1
for AMR-WB 224 kbps (14 bis * 16 kHz)

GSM/UMTS/LTE Basics
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Segmentation and speech codingSegmentation and speech codingSegmentation and speech codingSegmentation and speech coding
The key to reducing the bit rate is to send information about the speech
instead of the speech itself.
In GSM, the speech coding process analyses speech samples and outputs
parameters of what the speech consists of the tone, length of tone, pitch, etc.
This is then transmitted through the network to another MS, which generates
the speech based on these parameters.
The human speech process starts in the vocal chords or speech organs, where
a tone is generated. The mouth, tongue, teeth, etc. act as a filter, changing the
nature of this tone. The aim of speech coding in GSM is to send only
information about the original tone itself and about the filter.
FR speechFR speechFR speechFR speech
SegmentationSegmentationSegmentationSegmentation
Given that the speech organs are relatively slow in adapting to changes, the
filter parameters representing the speech organs are approximately constant
during 20 ms. For this reason, when coding speech in GSM, a block of 20 ms
is coded into one set of bits. In effect, it is similar to sampling speech at a rate
of 50 times per second instead of the 8,000 used by A/D conversion.
Speech codingSpeech codingSpeech codingSpeech coding
Instead of using 13 bits per sample as in A/D conversion, GSM FR speech
coding uses 260 bits. This calculates as 50 x 260 = 13 kbits/s. This provides a
speech quality which is acceptable for mobile telephony and comparable with
wire line PSTN phones.
20 ms
010001010…11101101
260 bits
Figure 1-27 Segmentation and speech coding

1 Introduction
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Other types of spOther types of spOther types of spOther types of speech coderseech coderseech coderseech coders
The GSM FR is not the only speech codec to be used in the mobile network
environment. Other types of standard speech codes are presented in Fig. 1-28.
6,6 – 23,85 kbps224 kbpsAMR-WB
4,75 – 12,2 kbps104 kbpsAMR
12,2 kbps104 kbpsEFR
13 kbps104 kbpsFR
5,6 kbps104 kbpsHR
64 kbps64 kbpsG.711
LTEUMTSGSM
PSTN
/ISDN
bitrate afterbitrate beforecodec
6,6 – 23,85 kbps224 kbpsAMR-WB
4,75 – 12,2 kbps104 kbpsAMR
12,2 kbps104 kbpsEFR
13 kbps104 kbpsFR
5,6 kbps104 kbpsHR
64 kbps64 kbpsG.711
LTEUMTSGSM
PSTN
/ISDN
bitrate afterbitrate beforecodec
Figure 1-28 Speech codecs (used across air interface)
PCM/E1 LinkPCM/E1 LinkPCM/E1 LinkPCM/E1 Link
In telephony network a number of users (subscribers) can share the same
physical connection (e.g. coaxial cable), thanks to the time division
multiplexing, see Fig. 1-29.
1111 0101
0101 1101
TS 1 TS 2
TS 3TS 4
A/D
A/D
A/D
A/D
0111 0001
0101 0100
MUX 0101 0111 0101 1111 1101 0001 0100 0101
Figure 1-29 Time division multiplexing

GSM/UMTS/LTE Basics
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The physical resources of the transmission medium are divided in time
domain into several time slots. A time slot is a time duration during each a
certain user can send the data. In case of PCM/E1 link there are 32 timeslots,
however the TS=0 is reserved for synchronisation to ensure that the
transmitter and receiver work with the same frequency. The remaining time
slots can be used for other purposes, for example for speech transmission.
During one time slot the user can send 8 bits (one octet) of data. Each TS is
transmitted 8000 times per second. This means that the bit rate for each PCM
TS (PCM channel) is equal to 64 kbits/s. And the bit rate for the whole
PCM/E1 link is 2048 kbits/s (32 * 64 kbits/s = 2048 kbits/s).
TDMA frame
0 311 2
Time Slot
synchronisation data
Figure 1-30 PCM/E1 link 2048 kbits/s
Wireline transmissionWireline transmissionWireline transmissionWireline transmission
There are two ways of transmitting the information over a wire. The signal
can be either electrical or optical. In the first case the transmission medium
has to consist of at least two metallic conductors to create closed loop for the
current. In the second case, the transmission medium is optical fibre that
makes propagation of the light possible.
Copper wiresCopper wiresCopper wiresCopper wires
Copper wires are mainly used in the analogue telephony systems, although
digital transmission with high bit rates for short distances is also possible.
There are two main types of copper cables:
• Twisted pair,
• Coaxial cable.

1 Introduction
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A twisted pair consists of two insulated copper wires, typically about 0.4 mm
to 1 mm thick. The wires are twisted together in the helical form. Twisting of
the wires is done to reduce electrical interferences and losses of signal.
Twisted pairs may be used individually, like in home telephone line
connections, or may be grouped in bigger cables. Such cables may consist
from 2 up to even 500 twisted pairs. Twisted pairs may run for several
kilometres without amplification, but for longer distances repeaters are
needed.
plastic covering
outer conductor
insulating material
metal core
Figure 1-31 Twisted pair (left) and coaxial cable (right).
If better performance of the cable is needed, a coaxial cable is usually used. It
consists of copper wire as a core surrounded by an insulating material. The
insulator is encased by a cylindrical conductor covered by a protective plastic
sheath. Coaxial cable has better shielding than twisted pair, which results in
lower attenuation and wider bandwidth. It allows the transmission for longer
distances and with higher bit rates. For 1 km long cable a bit rate of 1 to 2
Gbps is feasible.
Optical fibreOptical fibreOptical fibreOptical fibre
An optical transmission system has three components: the light source, the
transmission medium and the detector. The transmission medium which is
optical fibre (optical cable) has great transmission capacity.
The optical cable consists of several thin glass fibres, as shown in the
Fig. 1-32.

GSM/UMTS/LTE Basics
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jacket
cladding (glass)
core (glass)
Figure 1-32 Side view of the optical fibre
In the centre of the cable, there is a glass core. Depending on the type of fibre,
it has a diameter of 8, 10 or 50 µm. The core is surrounded by the glass
cladding, of which diameter is usually 125 µm. The cladding with the core,
are protected against chemicals, moisture etc. by the primary coating. This
structure is surrounded by a secondary coating ensuring final mechanical
protection. It may be fixed to the primary cladding or loose. A number of such
single optical fibres is usually grouped and create optical cable. Such cables
are additionally protected against excessive stress, bending, moisture etc.
Metal, Kevlar or plastic solutions are used depending on the cable
requirements.
Microwave radio relayMicrowave radio relayMicrowave radio relayMicrowave radio relay
Microwave radio relay is a technology for transmitting telecommunication
signals between two locations on a line of sight radio path. In microwave
radio relay, radio waves are transmitted between the two locations with
directional antennas, forming a fixed radio connection between the two
points. Because of the high frequencies used, an optical line of sight between
the stations is generally required.
Because a line of sight radio link is made, the radio frequencies used occupy
only a narrow path between stations. Antennas used must have a high
directive effect; these antennas are installed in elevated locations such as large
radio towers in order to be able to transmit across long distances. Typical
types of antenna used in radio relay link installations are parabolic reflectors,
shell antennas and horn radiators, which have a diameter of up to 4 meters.
Highly directive antennas permit an economical use of the available
frequency spectrum, despite long transmission distances.

1 Introduction
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Figure 1-33 Microwave radio relay
Figure 1-34 Microwave antenna at GSM site’s tower
Obstacles, the curvature of the Earth, the geography of the area and reception
issues arising from the use of nearby land (such as in manufacturing and
forestry) are important issues to consider when planning radio links. High
intensity rain and snow must also be considered as an impairment factor,
especially at frequencies above 10 GHz.

GSM/UMTS/LTE Basics
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SwitchingSwitchingSwitchingSwitching
Circuit switchingCircuit switchingCircuit switchingCircuit switching
Circuit switching is historically the oldest type of switching, so it may serve
as an explanation of the term switching itself.
The simplest definition of switching in telephony is: to set up a connection
between two subscribers to enable them to talk to each other. We have to
switch the communication path in the exchanges on the way in order to
complete this operation.
In the old days of telephony operators in the exchanges were setting up such
connections by manually switching circuits (cables). Even with the
introduction of automatic switching the concept of a circuit remained
unchanged. However, the meaning of the word changed very much with the
successive introduction of digital transmission in early 1970s.
Nowadays, circuit switching is regarded as switching of timeslots;
representing 64 kbits/s transmission channels in which user information is
delivered to digital exchanges, see Fig. 1-35.
group switch0 31
0
3
27 31
3
27
Figure 1-35 Telephone connections in a PSTN network
The process of switching is performed in the switching part of the exchange,
whose main functional part is the group switch, controlled by a digital
processor. With the growth of complexity of switching systems this processor
evolved very quickly into a set of processors, cooperating in performing
various more or less complicated tasks.

1 Introduction
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The circuit-switched mode of communication is connection-oriented. This
means that the communication phase is preceded by a set-up phase, when
signalling is performed.
The process of connection set-up between two subscribers is done according
to information provided by the calling subscriber (A-subscriber) which
includes the called subscriber (B-subscriber) telephone number and the
routing tables defined in the exchanges involved in the connection.
B-no B-no
B-no
12488
32443
74783
76868
64388
68684
84620
58543
74683
Figure 1-36 Connection set-up
In a Circuit-Switched (CS) network the information is transferred with the
constant bit rate 64 kbits/s. The communication channel is reserved for the
entire time of the connection and it cannot be used for any other purpose even
if the subscribers (or one of them) are not talking at the moment. This means
that the bandwidth is used in a very inflexible way; however, thanks to this
the transmission delay is kept constant. The CS connection is suitable for
voice and video transmission (real-time applications). It is not very suitable
for data applications (e.g. e-mail) because usually data traffic is transmitted in
bursts (not continuous) and CS networks do not support any mechanisms for
error detection and correction.
Packet switchingPacket switchingPacket switchingPacket switching
The Packet Switching (PS) is a technology widely used in the data networks.
The information to be transferred is divided into packets of variable length.
Each packet includes the recipient address. When the data packet arrives at a
network node, it is stored in a buffer. The address is read and the packet is
forwarded to the recipient or to the next node according to the routing table
defined in each network node.

GSM/UMTS/LTE Basics
28
There is no dedicated channel for each user. The available transmission
capacity may be shared by several connections without any of them having
reserved capacity. If no bandwidth is available at the moment, the packets
remain in the buffer until there is sufficient bandwidth. This results in delays
in the transfer process, however the utilization of resources is very high.
22
11
11
2 1
22
11
22 22
22
22
11
11
Figure 1-37 Packet switching
The PS is most suitable for the applications that do not require a constant data
flow (e.g. e-mail, file transfer), due to variable bit rate and variable delay in
PS networks. PS is not suitable for real time applications like voice and video
transmission.
In the packet-switched network error correction is possible. When the packet
arrives corrupted, the receiving node can send the negative acknowledgement
and ask for retransmission.
GPRSGPRSGPRSGPRS –––– wireless packetswireless packetswireless packetswireless packets
The data bearer services that are available in the traditional GSM network are
based on the CS technology. However majority of subscribers used them for
dial-in access to packet data networks such as Internet and other IP networks.
In case of typical applications (e-mail, web browsing) the data transfer is not
continuous. For example, subscriber that is browsing the web, downloads the
content of the page, then reads it and downloads the next one. The data
transfer in this case is suspended several times during the connection. Very
often even during the downloading process there could be some longer gaps
in transmission if the external network cannot deliver them in continuous
way. It is also important to note that usually the amount of data send on
downlink is larger then on uplink. In the described example the traffic channel
is reserved for the whole duration of the session and cannot be used by
another terminal even if it is not utilized at the moment. That situation is

1 Introduction
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disadvantageous for both network operator and subscriber, because the radio
recourses are used in a very un-efficient way and the subscriber has to pay for
the whole duration of session, rather then for the amount of transmitted data.
The General Packet Radio Service (GPRS) is a data service that overcomes
the disadvantages of old CS data services. In GPRS physical channel is
assigned only for the duration of packet transfer, and immediately after it is
finished, the same channel can be assigned for another terminal. This solution
allows a number of terminals to share one physical channel (statistical
multiplexing). The network also can allocate radio resources for a certain user
on more than one channel, which allows higher transmission bit rates.
LTE
UMTS
GSM
packet switching
(GPRS)
circuit switching
(CSD)
telephony
telephony
telephony
from R96
LTE
UMTS
GSM
packet switching
(GPRS)
circuit switching
(CSD)
telephony
telephony
telephony
from R96
Figure 1-38 CS and PS services in mobile networks

GSM/UMTS/LTE Basics

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