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(GPRS, EDGE, UMTS, LTE and…)

Global System for Mobile communications

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GSM HistoryYear Events

1982CEPT establishes a GSM group in order to develop the standards for a pan-European

cellular mobile system

1985 Adoption of a list of recommendations to be generated by the group

1986Field tests were performed in order to test the different radio techniques proposed for

the air interface

1987TDMA is chosen as access method (in fact, it will be used with FDMA) Initial

Memorandum of Understanding (MoU) signed by telecommunication operators (representing 12 countries)

1988 Validation of the GSM system

1989 The responsibility of the GSM specifications is passed to the ETSI

1990 Appearance of the phase 1 of the GSM specifications

1991 Commercial launch of the GSM service

1992Enlargement of the countries that signed the GSM- MoU> Coverage of larger

cities/airports

1993 Coverage of main roads GSM services start outside Europe

1995 Phase 2 of the GSM specifications Coverage of rural areas

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GSM world coverage map

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Differences Between First and Second Generation Systems

• Digital traffic channels – first-generation systems are almost purely analog; second-generation systems are digital

• Encryption – all second generation systems provide encryption to prevent eavesdropping

• Error detection and correction – second-generation digital traffic allows for detection and correction, giving clear voice reception

• Channel access – second-generation systems allow channels to be dynamically shared by a number of users

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GSM network

The GSM network can be divided into four subsystems: • The Mobile Station (MS). • The Base Station Subsystem (BSS). • The Network and Switching Subsystem (NSS). • The Operation and Support Subsystem (OSS).

GSM Network Architecture

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Mobile Station• Mobile station communicates across Um interface (air

interface) with base station transceiver in same cell as mobile unit

• Mobile equipment (ME) – physical terminal, such as a telephone or PCS– ME includes radio transceiver, digital signal

processors and subscriber identity module (SIM)• GSM subscriber units are generic until SIM is inserted

– SIMs roam, not necessarily the subscriber devices

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Base Station Subsystem (BSS)• BSS consists of base station controller and one or more base

transceiver stations (BTS)• Each BTS defines a single cell

– Includes radio antenna, radio transceiver and a link to a base station controller (BSC)

• BSC reserves radio frequencies, manages handoff of mobile unit from one cell to another within BSS, and controls paging

• The BSC (Base Station Controller) 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.

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Network Subsystem (NS)• NS provides link between cellular network and public

switched telecommunications networks– Controls handoffs between cells in different BSSs– Authenticates users and validates accounts– Enables worldwide roaming of mobile users

• Central element of NS is the mobile switching center (MSC)

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Mobile Switching Center (MSC) Databases

• Home location register (HLR) database – stores information about each subscriber that belongs to it

• Visitor location register (VLR) database – maintains information about subscribers currently physically in the region

• Authentication center database (AuC) – used for authentication activities, holds encryption keys

• Equipment identity register database (EIR) – keeps track of the type of equipment that exists at the mobile station

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The Operation and Support Subsystem (OSS)

• 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 transferred to the BTS. This transfer decreases considerably the costs of the maintenance of the system.

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GSM Channel Types• Traffic channels (TCHs)

carry digitally encoded user speech or user data and have identical functions and formats on both the forward and reverse link.

• Control channels (CCHs)

carry signaling and synchronizing commands between the base station and the mobile station. Certain types of control channels are defined for just the forward or reverse link.

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How a Cellular Telephone Call is Made• All base stations continuously send out identification

signals (ID) of equal, fixed strength. When a mobile unit is picked up and goes off-hook, it senses these identification signals and identifies the strongest. This tells the phone which cell it is in and should he associated with. The phone then signals to that cell's base station with its ID code, and the base station passes this to the MSC, which keeps track of this phone and its present cell in its database. The phone is told what channel to use for talking, is given a dial tone, and the call activity proceeds just like a regular call. All the nontalking activity is done on a setup channel with digital codes.

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• Mobile unit initialisation

• Mobile-originated call

• Paging• Call accepted• Ongoing call• Handoff

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GSM Radio interface • Frequency allocation • Two frequency bands, of 25 Mhz each one, have been

allocated for the GSM system: • The band 890-915 Mhz has been allocated for the uplink

direction (transmitting from the mobile station to the base station).

• The band 935-960 Mhz has been allocated for the downlink direction (transmitting from the base station to the mobile station).

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Multiple access scheme • In GSM, a 25 MHz frequency band is divided, using a

FDMA, into 124 carrier frequencies spaced one from each other by a 200 kHz frequency band.

• Each carrier frequency is then divided in time using a TDMA. This scheme splits the radio channel into 8 bursts.

• A burst is the unit of time in a TDMA system, and it lasts approximately 0.577 ms.

• A TDMA frame is formed with 8 bursts and lasts, consequently, 4.615 ms.

• Each of the eight bursts, that form a TDMA frame, are then assigned to a single user.

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GSM bands

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Maximum number of simultaneous calls = [(124) × 8] / N = 330 (if N=3)

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Multiframe components

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GSM frame format

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TDMS format

Trail bits: synchronisation between mobile and BS.

Encrypted bits: data is encrypted in blocks, Two 57-bit fields

Stealing bit: indicate data or stolen for urgent control signaling

Training sequence: a known sequence that differs for different adjacent cells. It indicates the received signal is from the correct transmitter and not a strong interfering transmitter. It is also used for multipath equalisation. 26 bits.

Guide bits: avoid overlapping, 8.25 bits

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Data rate• channel data rate in GSM

(1/120 ms) × 26 × 8 × 156.26 = 270.8 33Kbps • User data rate

Each user channel receives one slot per frame

kbps8.22amms/multifr 120

iframeslots/mult 24bits/slot 114

kbps13amms/multifr 120

iframeslots/mult 24bits/slot data65

With error control

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Traffic Channels

full rate channels offer a data rate of 22.8 kBit/s:• speech data: used as 13 kBit/s voice data plus FEC data• packet data: used as 12, 6, or 3.6 kBit/s plus FEC data

half rate channels offer 11.4 kBit/s:• speech data: improved codecs have rates of 6.5 kBit/s,

plus FEC• packet data: can be transmitted at 3 or 6 kBit/s

Two half rate channels can share one physical channel Consequence: to achieve higher packet data rates, multiple logical channels have to be allocated =) this is what GPRS does

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Speech codingThere are 260 bits coming out of a voice coder every 20 ms. 260 bits/20ms = 13 kbpsThese 260 bits are divided into three classes:

• Class Ia having 50 bits and are most sensitive to errors

3-bit CRC error detection code 53, then protected by a Convolutional (2,1,5) error correcting code.

• Class Ib contains 132 bits which are reasonably sensitive to bit errors--protected by a Convolutional (2,1,5) error correcting code.

• Class II contains 78 bits which are slightly affected by bit errors– unprotected

• After channel coding: 260 bits 456bits

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Channel coding: block coding Then Convolutional coding

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Signal Processing in GSM

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Global Wireless Frequency Bands

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Evalution to 2.5G mobile Radio Networks

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• Newer versions of the standard were backward-compatible with the original GSM phones.

• Release ‘97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS). GPRS provides data transfer rates from 56 up to 114 kbit/s.

• Release ‘99 introduced higher speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE), Enhanced GPRS (EGPRS), IMT Single Carrier (IMT-SC), four times as much traffic as standard GPRS. accepted by the ITU as part of the IMT-2000 family of 3G standards

• Evolved EDGE standard providing reduced latency and more than doubled performance e.g. to complement High-Speed Packet Access (HSPA). Peak bit-rates of up to 1Mbit/s and typical bit-rates of 400kbit/s can be expected.

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GSM-GPRS

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• the Base Station Subsystem (the base stations and their controllers).

• the Network and Switching Subsystem (the part of the network most similar to a fixed network). This is sometimes also just called the core network.

• the GPRS Core Network (the optional part which allows packet based Internet connections).all of the elements in the system combine to produce many GSM services such as voice calls and SMS.

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ITU’s View of Third-Generation Capabilities• Voice quality comparable to the public switched telephone

network• High data rate. 144 kbps data rate available to users in high-

speed motor vehicles over large areas; 384 kbps available to pedestrians standing or moving slowly over small areas; Support for 2.048 Mbps for office use

• Symmetrical / asymmetrical data transmission rates• Support for both packet switched and circuit switched data

services• An adaptive interface to the Internet to reflect efficiently the

common asymmetry between inbound and outbound traffic• More efficient use of the available spectrum in general• Support for a wide variety of mobile equipment• Flexibility to allow the introduction of new services and

technologies

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Third Generation Systems (3G)

The dream of 3G is to unify the world's mobile computing devices through a single, worldwide radio transmission standard. However,

3 main air interface standards:

W-CDMA(UMTS) for Europe

CDMA2000 for North America

TD-SCDMA for China (the biggest market)

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UMTS (Universal Mobile Telecommunications System ) Services

UMTS offers teleservices (like speech or SMS) and bearer services, which provide the capability for information transfer between access points. It is possible to negotiate and renegotiate the characteristics of a bearer service at session or connection establishment and during ongoing session or connection. Both connection oriented and connectionless services are offered for Point-to-Point and Point-to-Multipoint communication.Bearer services have different QoS parameters for maximum transfer delay, delay variation and bit error rate. Offered data rate targets are:

144 kbits/s satellite and rural outdoor384 kbits/s urban outdoor2048 kbits/s indoor and low range outdoor

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UMTS Architecture

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Core Network

The Core Network is divided in circuit switched and packet switched domains. Some of the circuit switched elements are Mobile services Switching Centre (MSC), Visitor location register (VLR) and Gateway MSC. Packet switched elements are Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). Some network elements, like EIR, HLR, VLR and AUC are shared by both domains.

The Asynchronous Transfer Mode (ATM) is defined for UMTS core transmission. ATM Adaptation Layer type 2 (AAL2) handles circuit switched connection and packet connection protocol AAL5 is designed for data delivery.

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Summary of UMTS frequencies:

• 1920-1980 and 2110-2170 MHz Frequency Division Duplex (FDD, W-CDMA) Paired uplink and downlink, channel spacing is 5 MHz and raster is 200 kHz. An Operator needs 3 - 4 channels (2x15 MHz or 2x20 MHz) to be able to build a high-speed, high-capacity network.1900-1920 and 2010-2025 MHz Time Division Duplex (TDD, TD/CDMA) Unpaired, channel spacing is 5 MHz and raster is 200 kHz. Tx and Rx are not separated in frequency.1980-2010 and 2170-2200 MHz Satellite uplink and downlink.

Universal Mobile Telephone System (UMTS)

47W-CDMA Parameters

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Base station finder: http://www.sitefinder.ofcom.org.uk/

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Frequency Spectrum in UK(Sep 2007)

900MHz 1800MHz 2100MHz ( 3G ) Vodafone Vodafone Vodafone

O2 O2 O2 Restricted to 2G

services only T-Mobile T-Mobile

  Orange Orange     Three

   Restricted to 3G

services only

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GSM frequency allocations

Mobile phone transmit  frequency MHz

Base station transmit frequency MHz

Vodafone GSM 900 890 - 894.6        935 - 939.6

O2 (BT) GMS 900 894.8 - 902 939.8 - 947

Vodafone GSM 900 902 - 910 947 - 955

O2 (BT) GMS 900 910 - 915 955 - 960

Vodafone GSM 1800 &      O2 GSM 1800:

1710 - 1721.5 1805 - 1816.5

T Mobile GSM 1800 1721.5 - 1751.5 1816.5 - 1846.5

Orange GSM 1800: 1751.5 - 1781.5 1846.5 - 1876.5

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The UMTS/3G frequency allocationsFrequency (MHz) Bandwidth (MHz) licence holder1900 - 1900.3 Guard band

1900.3 - 1905.2 4.9 licence D T-Mobile

1905.2 - 1910.1 4.9 licence E Orange

1910.1 - 1915.0 4.9 licence C O2

1915.0 - 1919.9 4.9 licence A 3

1919.9 - 1920.3 Guard band

1920.3 - 1934.9 14.6 licence A 3

1934.9 - 1944.9 10 licence C O2

1944.9 - 1959.7 14.8 licence B Vodafone

1959.7 - 1969.7 10 licence D T-Mobile

1969.7 - 1979.7 10 licence E Orange

2110 - 2110.3 Guard band

2110.3 - 2124.9 14.6 licence A 3

2124.9 - 2134.9 10 licence C O2

2134.9 - 2149.7 14.8 licence B Vodafone

2149.7 - 2159.7 10 licence D T-Mobile

2159.7 - 2169 10 licence E Orange

2169.7 - 2170 Guard band

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Signal level measured at T701

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MVNO

A mobile virtual network operator (MVNO) is a mobile phone operator that provides services directly to their own customers but does not own key network assets such as a licensed frequency allocation of radio spectrum and the cell tower infrastructure.

The UK mobile market has 5 main mobile network operators and has a total of more than 60 MVNOs.

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Market share per mobile provider

Everything Everywhere (T-mobile+ Orange, inc Virgin Mobile) 38%O2 (inc Tesco) 30%, Vodafone (inc ASDA, 25%, 3UK 7% (end 2010) (from Ofcom | The Communications Market Report: United Kingdom 2011)

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LTE (Long Term Evolution)• Initiated in 2004• focused on enhancing the Universal Terrestrial Radio

Access (UTRA)• Downlink (100Mbps), OFDM, support data modulation

schemes QPSK, 16QAM, and 64QAM • Uplink (50Mbps) Single Carrier-Frequency Division

Multiple Access (SC-FDMA), support BPSK, QPSK, 8PSK and 16QAM

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• 4 x Increased Spectral Efficiency, 10 x Users Per Cell• Multiple Input / Multiple Output (MIMO) antenna • both paired (FDD) and unpaired (TDD) band operation is

supported • LTE can co-exist with earlier 3GPP radio technologies • 3GPP’s core network has been undergoing System

Architecture Evolution (SAE), optimizing it for packet mode and in particular for the IP-Multimedia Subsystem (IMS) which supports all access technologies – even wire-line

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International Mobile Telecommunications (IMT) Advanced

Key features of ´IMT-Advanced´• a high degree of commonality of functionality worldwide while

retaining the flexibility to support a wide range of services and applications in a cost efficient manner;

• compatibility of services within IMT and with fixed networks; • capability of interworking with other radio access systems; • high quality mobile services; • user equipment suitable for worldwide use; • user-friendly applications, services and equipment; • worldwide roaming capability; and, • enhanced peak data rates to support advanced services and

applications (100 Mbit/s for high and 1 Gbit/s for low mobility were established as targets for research)*.

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The Forth Generation• 4G is mainly a marketing buzzword at the moment. Some

basic 4G research is being done, but no frequencies have been allocated.

• Smart antennas• Multiple-Input-Multiple-Output Systems • Space-Time Coding • Dynamic Packet Assignment• Wideband OFDM

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OFDM for 4G Wireless

OFDM is being increasingly used in high -speed information transmission systems:

• European HDTV• Digital Audio Broadcast (DAB)• Digital Subscriber Loop (DSL)• IEEE 802.11 Wireless LAN

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Key Features of 4G W-OFDM• IP packet data centric• Support for streaming, simulcasting & generic data • Peak downlink rates of 5 to 10 Mbps• Full macro-cellular/metropolitan coverage • Asymmetric with 3G uplinks (EDGE)• Variable bandwidth - 1 to 5 MHz• Adaptive modulation/coding• Smart/adaptive antennas supported• MIMO/BLAST/space-time coding modes• Frame synchronized base stations using GPS• Network assisted dynamic packet assignment