Mobile Communication Unit IV – GSM Fundamentals :: PART I, II & III

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Mobile Communication UnIT IV – GSM FunDAmEnTALS :: PART I, II & III

Sumit Kr. Choubey March 20, 2020

1 Table of contents

1. Introduction

2. Global System for Mobile Communications

3. Characteristics of GSM standard

4. Services

5. Basic Radio Parameter

6. Application

2 Introduction

3 Mobile?

The term “mobile” has historically been used to classify all radio ter- 1 minal that could be moved during operation.

use “mobile” to describe a radio terminal that is attached to a high 2 speed mobile platform

3 e.g., a cellular telephone in a fast moving vehicle

use “portable” to describes a radio terminal that can be hand- held 4 and used by someone at walking speed

5 e.g., a walkie-talkie or cordless telephone inside a home

4 History

The first wireless networks 1 were developed in the preindustrial age.

These systems transmitted information over line- of-sight distances (later extended by telescopes) 2 using smoke signals, torch signaling, flashing mirrors, signal flares, or semaphore flags.

5 History : Radio

• Early communication networks were replaced first by the telegraph network (invented by Samuel Morse in 1838) and later by the telephone. • In 1895, Marconi demonstrated the first radio transmission. • Very high transmission power (> 200 kW) • Early radio systems transmitted analog signals. • Today most radio systems transmit digital signals composed of binary bits. • A digital radio can transmit a continuous bit stream or it can group the bits into packets. • The latter type of radio is called a packet radio and is characterized by bursty transmissions

6 History : ALOHANET

The first network based on packet radio, ALOHANET, was developed 1 at the University of Hawaii in 1971.

ALOHANET incorporated the first set of protocols for channel access 2 and routing in packet radio systems, and many of the underlying principles in these protocols are still in use today.

Lead to Ethernet and eventually wireless local area networks 3 (WLAN).

7 History : Pre-Cellular

The most successful application of wire- 1 less networking has been the cellular telephone system.

1915: Wireless voice transmission (wireless telephony) between New York and 2 San Francisco was first established by AT& T.

1946: First public mobile telephone service was introduced in 25 cities across 3 the US. The equipment was expensive at $2,000. 8 History : Pre-Cellular

• These initial systems used a single central transmitter to cover an entire metropolitan area. • High-powered transmitter & Large tower • Inefficient! • FM push-to-talk • 1976: (30 yrs after the introduction of the service in 1946), • the New York system (10M people) could only support 543 paying customers. • 3,700 on the waiting list • The mobile units weighed about 10 kilograms and put out a steady 20-25 watts. • The central transmitters that communicate with the mobile units broadcast 200 to 250 watts.

9 History : Pre-Cellular

The central station could reliably communicate with the mobile 1 units up to a radius of approximately 25 miles (50 km).

Beyond that, up to a radius of 60 to 100 miles, the signal was too 2 weak for consistent service, but strong enough to interfere with any other mobile radio system.

10 History : 1G Cellular

• A solution to this capacity problem emerged during the 50’s and 60’s when researchers at AT& T Bell Laboratories developed the cellular concept. • 1968: AT& T proposed the concept to the FCC • Cellular systems exploit the fact that the power of a transmitted signal falls off with distance.

• Thus, two users can operate on the same frequency at spatially-separate locations with minimal interference between them. • Frequency reuse

11 History : 1G Cellular

• Japan had the world’s first commercially available cellular • Nippon Telegraph and Telephone (NTT) created a cellular test system for Tokyo in 1975, with the result coming to market in 1979. ▶ Japan’s national monopoly telecoms operator/carrier • The first trial in America of a complete, working cellular system was held in Chicago in the late 1970’s. • 1983: Advanced Mobile Phone System (AMPS) • First US cellular telephone system • Deployed in 1983 by Ameritech in Chicago, IL. • Worked well. (FM, FDMA) • May even have worked too well. ▶ Its satisfactory performance lowered the demand for a better system, allowing Europe to take the lead by creating a digital cellular system first. • AMPS, RIP: 1983-2008 ▶ As of February 18, 2008, carriers in the United States were no longer required to support AMPS. 12 History : 2G Cellular

The (1G) systems introduced in the 1980s were characterized by ana- 1 log speech transmission. The (2G) of cellular systems, first deployed in the early 1990’s, were based on digital communications.

The shift from analog to digital was driven by its higher capacity and 2 the improved cost, speed, and power efficiency of digital hardware.

1991: US Digital Cellular (USDC – IS-54 > IS-136) Three times capacity 3 of AMPS via digital modulation, speech coding, and TDMA

While second generation cellular systems initially provided mainly 4 voice services, these systems gradually evolved to support data services such as email, Internet access, and short messaging. 13 Two important 2G systems

• GSM supports SMSs and user data at rates only up to 9.6 kb/s. • Security features including (for example) the encryption of data and • signaling messages on the path between the mobile phone and the BS. ▶ Subscriber identity module (SIM) ▶ A smart card ▶ Contain the subscriber’s personal details ▶ Can be moved from one handset to another. • IS-95B (cdmaOne) provides data rates in the range of 64 to 115 kb/s in increments of 8 kb/s over a 1.25 MHz channel. • Each cell uses a carrier with a bandwidth of 1.25MHz, which is divided into 64 data and signalling channels by the use of orthogonal CDMA codes.

14 GSM World Coverage Map

15 3G Cellular

• Studies started even before the earliest 2G systems arrived on the market. • International Mobile Telecommunications-2000 (IMT-2000) • A subgroup of the International Telecommunication Union (ITU) • Published a set of performance requirements of 3G (for both packet- switched and circuit-switched data): ▶ A minimum data rate of 144 Kbps in the vehicular environment. ▶ A minimum data rate of 384 Kbps in the pedestrian environment ▶ A minimum data rate of 2 Mbps in the fixed indoor and picocell environment • There are several wireless standards and systems that qualify as third generation (3G) systems. • UMTS • CDMA2000

16 4G Cellular

4G is the fourth generation of broadband cellular network technology, succeeding 3G. A 4G system must provide capabilities defined 1 by ITU in IMT Advanced. Potential and current applications include amended mobile web access, IP telephony, gaming services, high- definition mobile TV, video conferencing, and 3D television.

The first-release Long Term Evolution (LTE) standard was commercially deployed in Oslo, Norway, and Stockholm, Sweden in 2009, 2 and has since been deployed throughout most parts of the world. It has, however, been debated whether first-release versions should be considered 4G LTE.

17 Global System for Mobile Communications

18 Global System for Mobile Communications

“The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation (2G) digital cellular networks used by mobile devices such as mobile phones and tablets. It was first deployed in Finland in December 1991. By the mid-2010s, it became a global standard for mobile communications achieving over 90% market share, and operating in over 193 countries.

19 ” Global System for Mobile Communications

Origin As a result of cooperation within the European Union, a spe- cial working group for mobile telephony was established, task was to specify the objectives and the standards of a common mobile cellular telephony system.

• Scientific & industrial organizations from 17 countries signed the MoU, par- ticipated in the development of a new system • As a result of common research and discussions a series of standards has been established covering all the required layers of the OSI reference model • Most popular standard for mobile phones in the world. GSM 900 / GSM 1800 MHz are used in most parts of the world: Europe, Asia, Australia, Middle East, Africa • GSM 850 / GSM 1900 MHz are used in the United States, Canada, Mexico and most countries of S. America. 20 Global System for Mobile Communications

• GSM networks operate in a number of different carrier frequency ranges with most 2G GSM networks operating in the 900 MHz or 1800 MHz bands. • Where these bands were already allocated, the 850 MHz and 1900 MHz bands were used instead (for example in Canada and the United States). • In rare cases the 400 and 450 MHz frequency bands are assigned in some countries because they were previously used for first-generation systems. • Currently the GSM stands for Global System for Mobile Communications which stresses the fact that the application of GSM spans far beyond the European continent.

21 Features of GSM Module

• Improved spectrum efficiency • International roaming • Compatibility with integrated services digital network (ISDN) • Support for new services. • SIM phonebook management • Real time clock with alarm management • High-quality speech • Uses encryption to make phone calls more secure • Short message service (SMS) • The security strategies standardized for the GSM system make it the most secure

22 GSM Architecture

23 GSM Architecture… I

The GSM network can be divided into three broad parts ::

1 The subscriber carries the mobile station (MS)

The base station subsystem (BSS) controls the radio link with the 2 mobile station

The network subsystem performs the switching of calls between 3 the mobile users and other mobile and fixed network.

24 Mobile Station

• The mobile station consists of the mobile equipment, i.e. the handset, and a smart card called the Subscriber Identity Module (SIM).The SIM provides personal mobility • The mobile equipment is uniquely identified by the International Mobile Equipment Identity (IMEI). • The SIM card contains the International Mobile Subscriber Identity (IMSI) used to identify the subscriber to the system • The IMEI and the IMSI are independent, thereby allowing personal mobility.

25 Base Station Subsystem

• The base station subsystem is composed of two parts, the base transceiver station & the base station controller. • These communicate across a standardised “Abis” interface, allowing operation between components made by different suppliers. • The base transceiver station houses the radio transceivers that define a cell & handles the radio-link protocols with the mobile station. • The base station controller manages the radio resources for one or more base transceiver stations. It is the connection between the MS and the MSC.

26 Network Subsystem

• The central component of the network subsystem is the mobile services switching center. • This acts like a normal switching node of the PSTN (Public Switched Tele- phone Network) or ISDN (Integrated Services Digital Network) and con- nects the mobile signal to these fixed networks. • It additionally provides all the functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handovers and call routing to a roaming subscriber.

27 Radio Spectrum

• Since radio spectrum is a limited resource shared by all users, a method must be devised to divide up the bandwidth among as many users as pos- sible. The method chosen by GSM is a combination of Time and Frequency Division Multiple Access (TDMA/FDMA). • The FDMA part involves the division by frequency of the (maximum) 25MHz bandwidth into 124 carrier frequencies spaced 200kHz apart. One or more carrier frequencies are assigned to each base station. • Each of these carrier frequencies is then divided in time, using a TDMA scheme. • The fundamental unit of time in this TDMA scheme is called a burst period and it lasts 15/26 milliseconds (ms) • Eight burst periods are grouped into a TDMA frame (120/26ms, or approximately 4.615ms), which forms the basic unit for the definition of logical channels. One physical channel is one burst period per TDMA frame. 28 Additional components of the GSM I

• The area of GSM operation is divided into subareas managed by particular Mobile Switching Centers(MSC) • Each MSC connected with a respective VLR Database • GSM system is administered by a particular operator is equipped with three other data base.

HLR The data base of mobile stations permanently registered in the system by particular operator. The HLR(Home Location reg) is the central database which stores the permanent pa- rameters of the users and information on their current location.

29 Additional components of the GSM II

AUC Authentication Centre : The data base that allows checking if the user with the assigned SIM card.

EIR Equipment Identification register : The database of serial numbers of the mobile phones used in the system.

• In large systems there can be more than one HLR • The individual user’s data is stored only in one of them • The user’s record in the HLR contains his/her status, the Temporary Mobile Identification Number(TMSI) and the address of the VLR(visitor loc reg) register which is associated with the user’s current location area

30 Additional components of the GSM III

VLR The VLR is the database consisting of records describing mobile stations currently registered in the service area of a particular MSC

The data exchange between VLR and HLR allows identification of a current location of a called user by reading information on his/her current location area in the HLR and routing the connection to that MSC. • The MSC which co works with the VLR currently contains the data on the called user • The MSCs are connected with each other • One or more MSCs are called Gateway Mobile Switching Center(GMSC) play the role of a gate to the external networks such as PSTN, ISDN and packet data networks

31 Additional components of the GSM IV

• Each MSC controls at least one Base Station System(BSS) which consists of BSC and a certain number of BTS or BS The main task of MSC is to coordinate the call set-up between two mobile GSM users or between a GSM user and a user of an external network such as PSTN, ISDN. The task is realized by performing the following functions :

1 Calling the user, setting up and maintaining a connection

Dynamic network resource management in the system area man- 2 aged by that MSC

Rerouting of the connection to a new cell served by a BSC differ- 3 ent from the controller which supervised the cell which the MS has been operating so far 32 Additional components of the GSM V

• Information exchange between MSC and BSS is normalized by defining the so called A interface • Abis interface standardizes the data exchange between the base station controller and its tranceivers • A interface deals with network and switching aspects

The functions Performed by the MSC,HLR, and VLR with management of fixed links with network management, controlling and encryption of user data and signalling information with management resulting from the necessity of MS authentication and location updating caused by MS ge- ographical movement and with management due to calling the users

33 Additional components of the GSM VI

The Abis interface is associated with the information exchange related to the radio transmission, such as the distri- bution of radio channels, connection supervising, the queu- ing of messages before their transmission, carrier frequency hopping control etc.

34 The operation and maintenance Centre

• The operation and maintenance Centre (OMC) supervises the operation of particular GSM system blocks. • It is connected with all the switching blocks of the GSM system and performs management functions such as tariff accounting, traffic monitoring, management in case of failures of particular network blocks. • The most important task of OMC is HLR management • In case of large networks, there are more than one OMC and the whole network is managed by Network Management Centre(NMC).

35 Characteristics of GSM standard

36 Modulation : GMSK ··· I

The GSM uses Gaussian Minimum Shift Keying (GMSK) modulation method.

• Gaussian Minimum Shift Keying (GMSK) is a form of continuous-phase FSK (CPFSK)

That Mean The phase is changed between symbols to provide a constant envelope.

So GMSK allows efficient class C non-linear amplifiers to be used.

• The RF bandwidth is controlled by the Gaussian low-pass filter.

37 Modulation : GMSK ··· II

The degree It is expressed by multiplying the filter 3dB bandwidth (B) by of filtering the bit period of the transmission(T).

B × T = 0.3

Data rate in Gaussian Minimum Shift Keying (GMSK) modulation method is 270.8 kbps.

38 Generating a GMSK Waveform ··· I

GMSK as implemented by quadrature signal processing at baseband followed by a quadrature modulator.

39 Generating a GMSK Waveform ··· II

Modulation of GMSK

40 Generating a GMSK Waveform ··· III

Pulse • Input : Binary pulse train (+1/-1) Shaping • Each binary pulse goes through a LPF with a Gaussian impulse response • This process results in a train of Gaussian shaped pulses

Summing • The pulses are summed together (left) and Inte- • The signal is integrated over time to obtain a gration continuous waveform which captures the bit transition information (right)

41 Generating a GMSK Waveform ··· IV

42 Generating a GMSK Waveform ··· V

I& Q Signals • The resulting waveform is divided into In-Phase and Quadrature components • In-phase : Left • Quadrature : Right • The two signal components are then up-converted to the carrier frequency

43 Generating a GMSK Waveform ··· VI

Advantage • High spectral efficiency. • Reducing sideband power. • Excellent power efficiency due to constant envelope. • reducing the interference between signal carriers in adjacent frequency channels. • Self synchronizing capability

Disadvantage • causes (inter symbol interference[ISI]) • Higher power level than QPSK. • Requiring more complex channel equalization • algorithms such as an adaptive equalizer.

44 GMSK Demodulator

45 Multiple Access Techniques

• GSM devised a combination of TDMA/FDMA as the method to divide the bandwidth among the users. • FDMA part divides the frequency of the total 25 MHz bandwidth into 124 carrier frequencies of 200 kHz bandwidth. • Each BS is assigned with one or multiple frequencies, and each of this frequency is divided into eight time slots using a TDMA scheme. • Each of these slots are used for both transmission as well as reception of data.

46 Characteristics of GSM standard …

Channel Channel spacing indicates the spacing between adjacent spacing carrier frequencies. For GSM, it is 200 kHz.

Frequency • The uplink frequency range specified for GSM is 935- Band 960 MHz (basic 900 MHz band only). • The downlink frequency band 890 - 915 MHz (basic 900 MHz band only).

Speech • For speech coding or processing, GSM uses Linear Coding Predictive Coding (LPC). • The speech is encoded at 13 kbps.

47 Services ··· I

Telephone • These include emergency calling and facsimile. services • GSM also supports Videotex and Teletex.

Bearer • Data services or Bearer Services are used through a Services GSM phone to receive and send data is the essential building block leading to widespread mobile Internet access and mobile data transfer. • GSM currently has a data transfer rate of 9.6k New developments that will push up data transfer rates for GSM users are HSCSD (high speed circuit switched data) and GPRS (general packet radio service) are now available.

48 Services ··· II

Supplementary services : These are digital in nature and include call diversion, closed user groups and caller identification. • Supplementary services also include short messaging service (SMS) which allows GSM subscribers and base station to transmit alphanumeric pages of limited length • SMS provides cell broadcast also can be used for safety and advisory applications such as the broadcast of highway or weather information to all GSM subscribers.

49 Services ··· III

• Some of the supplementary services are :

Conferencing : It allows a mobile subscriber to establish a mul- 1 tiparty conversation, i.e., a simultaneous conversation between three or more subscribers to setup a conference call.

Call Waiting : This service notifies a mobile subscriber of an in- 2 coming call during a conversation. The subscriber can answer, reject, or ignore the incoming call.

Call Hold : This service allows a subscriber to put an incoming 3 call on hold and resume after a while.

50 Services ··· IV

Call Forwarding : Call Forwarding is used to divert calls from 4 the original recipient to another number

Call Barring : Call Barring is useful to restrict certain types of 5 outgoing calls such as ISD or stop incoming calls from unde- sired numbers.

51 Basic Radio Parameter ··· I

• Two 25 MHz wide bands • Uplink 890-915 MHz • Downlink 935-960 MHz • Frequency Division Duplex (FDD) is used – separate frequency band for opposite direction of communication • Both bands divided into 124 frequency intervals of 200 kHz • For each carrier time is divided into 8 slots • Multiple access is realised by assigning the connection a particular carrier frequency and a selected time slot • Thus GSM uses TDMA/FDMA scheme (Time/Frequency Division Multiple Access)

52 Basic Radio Parameter ··· II

• In TDMA/FDMA a physical channel is a sequence of time slots (denoted by the assigned slot no.) which are placed on a selected carrier • Physical channels are arranged in pairs – one physical channel in each direction – they are marked with the same time slot no and they frequency differs by 45 MHz • The time slots numbering in the downlink direction is delayed by 3 • Thus mobile station never transmits and receives signals to and from BS at the same time. • This reduces requirement for RF and DSP blocks Computation power can be shared between transmitter and receiver

53 Frequency and time structure of GSM channels ··· I

54 Frequency and time structure of GSM channels ··· II

• Presents the frequencies and time slot assignment in the GSM system • Numbering of the time slots is delayed by three in downlink as compared with uplink transmission. • Due to that, a mobile station realizing a connection to a base station in the assigned time slot never transmits and receives the signals at the same time • This way, an electromagnetic feedback between a mobile station transmitter and receiver is avoided. • Thus, the computational power can be shared between the transmitter and the receiver.

55 Logical Channel Description

• Channels arranged to organize the information exchange. • In each cell a mobile station finds a particular carrier on which in its zero time slot the system information important for all the mobile stations lo- cated within that cell is transmitted. • In turn, on the associated carrier always shifted down by 45 MHz, • In the zero time slot the mobile stations can declare their need for information exchange with the system or even their need to set up a call.

56 Application

• Smart home, smart office & Transportation • Medical field • Location tracker

Access con- Access control devices can communicate with servers and trol devices security staff through SMS messaging.

Transaction POS terminals can use SMS messaging to confirm trans- terminals actions from central servers with GSM technology. Central server can be anywhere in the world.

Supply Chain A server with GSM capability is required to manage the ap- Management plication

57 I’d love to hear your thoughts, issues, questions and comments.