Mobile Communication 1G to 4G

7/27/2019 Mobile Communication 1G to 4G

1/27

Mobile Communication: From 1G to 4G

Any radio telephone capable of operating while moving at any speed, battery operated and

small enough to be carried by a person comes under the mobile communication systems.

These communication systems may have different facilities. The different types of mobilecommunication systems are mobile two-way radio, public land radio, mobile telephone andamateur (HAM) radio.

Mobile two-way radios are one-to-many communication systems that operate in half-duplexmode, i.e., push to talk. The most common among this type is citizen band (CB) radio,

which uses amplitude modulation (AM). It operates in the frequency range of 26-27.1 MHzhaving 40 channels of 10 kHz. It is a non-commercial service that uses a press-to-talk

switch. It can be amplitude-modulated having double-sideband suppressed carrier or single-sideband suppressed carrier.

Public land mobile radio is a twoway FM radio system, used in police, fireand municipal

agencies. It is limited to small geographical areas.

Mobile telephones offer full-duplex transmission. These are one-to-one systems that permittwo simultaneous transmissions. For privacy, each mobile unit carries a unique telephonenumber.

Amateur (HAM) radios cover a broad frequency band from 1.8 MHz to above 30 MHz. Theseinclude continuous wave (CW), AM, FM, radio teleprinter, HF slow-scan still picture TV, VHFor UHF slow-scan or fast-scan TV, facsimile, frequency-shift keying and amplitude-shift

keying.

Present and past of mobile communications

Before I narrate the journey from 1G to 4G, let me explain the important technologies

behind the phenomenal growth of mobile communication systems. Since the commercialintroduction of advanced mobile phone system (AMPS) service in 1983, mobilecommunication systems have witnessed an explosive growth. The most important

breakthrough was the cellular concept.


2/27

Cellular concept. The advent of cellular operation brought frequency reuse capabilities.

Advances in wireless access, digital signal processing, integrated circuits, increased batterylife, etc led to exponential growth of personal communication services.

Cellular system works as follows: An available frequency spectrum is divided into discretechannels, which are assigned in groups to geographic cells covering a service area. Thediscrete channels are capable of being reused in different cells with diameters ranging from

2 to 50 km. The service area is allotted a radio frequency (RF) transmitter, whereas

adjacent cells operate on different frequencies to avoid interference.

Cellular telephones began as a simple two-way analogue communication system using

frequency modulation for voice and frequency-shift keying for transporting control andsignaling information. Other cellular systems are digital cellular system, cordless telephony,satellite mobile and paging. Analogue cellular systems fall in the first-generation(1G)

category and digital cellular low-power wireless fall in the second-generation (2G) category.

Analogue cellular phone. In 1970, Bell Labs in New Jersey proposed a cellular telephoneconcept as advanced mobile telephony system (AMPS). AMPS is a standard cellular

telephone service placed into operation on October 13, 1983 by Illinois Bell. It uses narrow-band FM with a usable audio frequency band of 300-3 kHz and maximum frequencydeviation of 12 kHz for 100 per cent modulation. According to Carsons rule, this

corresponds to 30 kHz.

AMPS uses frequency-division multiple access (FDMA), where transmissions are separated in

the frequency domain. Subscribers are assigned a pair of voice channels (forward and

reverse) for the duration of their call. Analogue cellular channels carry both voice using FMand digital signaling information using binary FSK.

Digital cellular system. It provides improvements in both capacity and performance.

FDMA uses a frequency canalisation approach to spectrum management, while time-division


3/27

multiple access (TDMA) utilises a time-division approach. The entire available cellular RF

spectrum is sub-divided into narrow-band radio channels to be used as a one-way

communication link between cellular mobile units and base stations.

Multiple access technologies for cellular systemsGenerally, a fxed amount of frequency spectrum is allocated to a cellular system. Multiple

access techniques are deployed so that the users can share the available spectrum in anefficientmanner.

For wireless communication, multiplexing can be carried out in three dimensions: Time

(TDMA), frequency (FDMA and its variation OFDMA) and code (CDMA).

FDMA, TDMA , and CDMA multiple-access techniquesIn TDMA the available spectrum is partitioned into narrow frequency bands or frequency

channels, which, in turn, are divided into a number of time slots. In case of North Americandigital cellular standard IS-136, each frequency channel (30 kHz) is divided into three timeslots, whereas in European digital cellular system GSM each frequency channel (200 kHz) is

divided into eight time slots. Guard bands are needed both between frequency chan-nels

and time slots.

In FDMA, users share the available spectrum in a frequency band called trafficchannel.

Different users are assigned different channels on demand basis. The users signal power is

concentrated in a relatively narrow frequency band. All the analogue cellular systems used


4/27

FDMA system.

OFDM is a multi-cellular transmission technique where a data stream is carried with manylower-rate subcarrier tones. It has been adopted in mobile communications to combat

hostile frequency-selective fading and has been incorporated into wireless networkstandards.OFDM is a multi-cellular transmis-sion technique where a data stream is carried

with many lower-rate sub-carrier tones. It has been adopted in mobile communications tocombat hostile frequency-selective fading and has been incorporated into wireless network

standards.

OFDM combines the advantages of coherent detection and OFDM modulation and has many

merits that are critical for future high-speed transmission systems. By using up/downconversion, electrical bandwidth requirement can be greatly reduced for the OFDM

transceiver, which is extremely attractive for high-speed circuit design where electrical

signal bandwidth dictates the cost. Lastly, signal processing in the OFDM transceiver cantake advantage of efficient algorithm of fat Fourier transform (FFT)/inverse FFT, whichsuggests that OFDM has superior scalability over channel dispersion and data rate.

Digital modulation keying

Communication systems often involve modulation of a carrier, which results in a bandpasswaveform. A digital signal can be used to modulate the amplitude, frequency or phase of a

sinusoidal carrier producing three different forms of digital modulation: amplitude-shiftkeying (ASK), frequency-shift keying (FSK) and phase-shift keying (PSK). In addition tothese basic techniques, there are some modulation schemes that employ a combination of

amplitude and phase modulation. It may be noted that unlike ASK signal, PSK transmission

is polar. At the same time, ASK is a linear modulation scheme, whereas PSK is a non-linearmodulation scheme. PSK has a superior performance over ASK.

Quadrature phase-shift keying (QPSK). Digital modulation techniques mentioned aboveare spectrally inefficientin the sense that the available channel bandwidth is not fully used.Spectral efficiencycan be improved by using QPSK. It is a system for two message sources.

In this system modulation carriers in phase quadrature are combined to form the outputwaveform. In QPSK the amplitude of the modulator waveform and modulator gains aremade as nearly equal as possible.

Differential phase-shift keying (DPSK). DPSK is a modification of PS that avoids theneed to provide synchronous carrier required for detection of PSK signals. It is an ingenioustechnique whereby the carrier reference is derived from the received waveform in the

preceding bit interval by use of a 1-bit delay. In essence, the received waveform delayed by

1-bit duration serves as its own reference.

Data transmission using packet switching

This is done by supplying various addressed packets, which are interconnected to have theconversation. New dedicated paths are created for sending the data. From the multiple

paths to the destination, any path can be used to send data. Cellular digital packet data wasdesigned for optimal operation with an analogue cellular system, especially AMPS.

Short message service. Short message service is the most common packet service that is

supported on digital cellular networks like GSM, IS-136, EDGE and PDC (packet data

service). It is a store-and-forward/packet mode service that provides inter-working with thevarious applications and services within a fixednetwork. For message transfer betweenrelevant network entities, control and signaling channels (instead of normal traffic channels)

ar generally used for data transmission.


5/27

General packet radio service (GPRS). GPRS essentially represents add-on capabilities to

the basic voice-optimised cellular network that nevertheless maintain the essentialcharacteristics of radio-access technology.

Enhanced data rates for GSM evolution (EDGE). In order to enhance the data handling

capabilities of 2G service, radio-access portion had to be modifed. This modifcation wasevolved in Europe in the form of EDGE. EDGE also supports a link adaptation mechanism

that selects the best combination of modulation and encoding schemes based on thetimevarying link quality.

EDGE concept applies to both circuit-mode and packet-mode data and is sufficiently genericfor appliction to other digital cellular systems. It works in the 200kHz bandwidth with one or

more high-level modulation schemes and a range of efficient coding methods. Modulation

schemes are offset QPSK and offset 16 QAM.

Spread spectrum

It is a special communication technique that purposefully uses much more RF bandwidth

than necessary to transmit a signal. This helps in improving the signal-to-noise (S/N) ratio.

The main advantages of this technique are secure communication and resistance tointentional jamming. There are 75 channels in the 2400-2483.3MHz band.

There are two methods of perform-ing spread spectrum:Frequency hopping. This technique spreads the narrow-band signal as a function of time.

The transmitted frequency is changed to a different pre-assigned channel several times per

second (hopped). The order in which the pre-assigned channels are selected is pseudorandom. In other words, the channel order is seemingly random but actually repeats itselfat a definedinterval. The specificorder in which frequencies are occupied is a function of

code sequence and the rate of hopping from one frequency to another is a function ofinformation rate.

Direct sequence. This technique spreads a signal by expanding the signal over abroadband portion of the radio band. It uses a locally generated pseudo noise (PN) code toencode digital data to be transmitted. The most practical all-digit version is direct sequence.Binary phase-shift keying is the simplest and most often used modulation technique.

One of the most important features of spread-spectrum signals is that these contain a largenumber of very different signaling formats, used for communicating data symbols. It means

that the receiver which detects one of these formats cannot detect any other format within

a single message. The number of formats used in a spread-spectrum system is calledmultiplicity factor of the communication link and amounts to thousands.

CDMA. CDMA is a form of direct-sequence spread-spectrum technology that allows manyusers to occupy the same time and frequency allocations in a given band/space. CDMA

assigns each user a unique spreading code to spread the baseband data beforetransmission, in order to help differentiate signals from various users in the same spectrum.

It is the platform on which 2G and advanced 3G services are built.

After speech, the codec converts voice into digital signal. CDMA spreads the voice stream

over the full 1.25MHz bandwidth of the CDMA channel, coding each stream separately. Thereceiver uses a correlator to despread the wanted signal, which is passed through abandpass filter.Unwanted signals are not despread and not passed through the filter.


6/27

The rate of the spreading signal is known as the chip rate as each bit in the spreading

signal is known as chip. All 2G networks support only single-user data rates of the order of

10 kbps, which is too slow for rapid e-mail and Internet browsing.

CDMA provides more than ten times the capacity of the analogue AMPS and fivetimes thecalling capacity of GSM and TDMA systems. It requires fewer cell sites than GSM and

TDMA.

Personal communication systemPersonal communication system (PCS) is a new class of cellular telephone system such as

AMPS. PCS systems are a combination of cellular telephone network and intelligent network,

which is the entity of super-simple transfer (SST) inter-office protocol tha distinguishesphysical components of the switching network such as signal service point, signal control

point and signal transfer point from the services provided by SST network.

In essence, PCS is the North American implementation of European GSM standard. GSMutilised its own TDMA access methods and provided expanded capacity and unique services

such as caller ID, call forwarding and short messaging. A critical feature was seamless

roaming, which allowed subscribers to move across provider boundaries. The effort was

directed towards second-generation cellular systems.

In 1990, a second frequency band was specified. This band included twodomains1710-1785 MHz and 1805-1880 MHz, i.e., twice 75 MHz; three times as much as the primary900MHz band.

Digital enhanced cordless telecommunication (DECT). DECT is a type of PCS system.DECT standard was developed by European Telecommunication Standards Institute (ETSI)for wireless PABX data LAN applications that represent closed environments requiring

minimal open cordless access, since it was essential that products from different vendorsnot only coexist but interwork with each other.

DECT system has a TDMA/TDD frame structure with 24 slots that are equally allocated fordownlink and uplink operation. DECT specifiesboth simplex (half-slots) and duplex (full slot)operation. Higher data rates are achieved by utilising multilevel modulation. The basicmodulation scheme is a two-level Gaussian filled frequency-shif keying (GFSK), which is

supplemented with 8-level modulation scheme leading to as high as 2.88 Mbps per carrier.

GSM

Global system for mobile communications (GSM) was developed by the Groupe Special

Mobile, which was an initiative of the Conference of European Post and Telecommunications(CEPT) administrations. GSM was firs devised as a cellular system in a specific 900MHz bandcalled the primary band. This primary band includes two sub-bands of 25 MHz each, 890-

915 MHz and 935-960 Mhz.

GSM systems like Iridium, Globalstar and ICO use constellations of low-earth orbit (LEO) ormedium-earth orbit (MEO) satellites and operate as overlay networks for existing cellular

and PCS networks. Using dual-mode, these extend the coverage to any and all locations onthe earths surface.


7/27

GPSa reliabl e navigational aid anywhere on the earth

International Mobile Telecommunication-2000 (IMT-2000) is a standard developed by ITUfor 3G. It ensures global mobility in terms of global seamless roaming and service delivery.

An appreciation of the role of numbering and identities in mobility management,international roaming, call delivery, and billing and charging is important in understanding

the operation of mobile and personal communication networks.

Personal communication satellite service (PCSS) uses LEO satellite repeaters incorporating

QPSK modulation and both FDMA and TDMA.

The main advantages of GSM are international roaming (in harmony with ISDN principles

assuring inter-working between ISDN and GSM) and features like privacy and encryption,frequency hopping, discontinuous transmission and short message service. Other facilitiesinclude call forwarding, barring, waiting, hold and teleconferencing.

The basic architecture comprises a network sub-system, base station sub-system, mobilestations, and system interworking and interfaces.

A subscriber identity module (SIM) is required to activate and operate a GSM terminal. TheSIM may be contained within the mobile station or it may be a removable unit that can beinserted by the user in his mobile set.

New developments along the wayBefore we proceed to evolution from 1G to 4G, let me touch upon the new developments

that took place in 1G to 4G.

Global positioning system (GPS). GPS is a reliable navigational aid available anywhereon the earth, operating in all weather conditions 24 hours a day. It can be used by marine,

airborne and land users. GPS technology was developed in 1983.


8/27

GPS consists of three segments:

Space segment. GPS consists of 24 NAVSTAR satellites along with three spare satellites

orbiting at 20,200 km above the earths surface in six circular orbital planes with a 12-hourorbital period each. These satellites operate at L1 band (1.575 GHz) continuously

broadcasting navigational signals called coarse acquisition code. These codes can bereceived by anyone for decoding and findingnavigational parameters like longitude, latitude,

velocity and time.

Control segment. It consists of a master control station (MCS) and a number of smallerearth stations called monitoring stations located at different places in the world. Monitoring

stations track satellites and pass on the measured data to the MCS. The MCS computes

satellite parameters (called ephemeris) and sends them back to the satellite, which, in turn,broadcasts to all GPS receivers.

User segment. The user segment consists of all moving and stationary objects with GPSreceivers. A GPS receiver is a multi-channel satellite receiver that computes every secondits own location and velocity.

Bluetooth. Compared to WLAN technologies, Bluetooth technology aims at so-called ad-hoc

piconets, which are local-area networks with a very limited coverage and without the needfor an infrastructure. The term piconet is a collection of Bluetooth devices that are

synchronised to the same hopping sequence. One device in the piconet can act as masterand all other devices connected to the master act as slaves. The master determines thehopping pattern and the slaves have to synchronise to this pattern. The hopping pattern is

determined by the device IDa 48-bit worldwide unique identifier.The phase in the hopping

pattern is determined by the masters clock. All active devices are assigned a 3-bit activemember address.

All parked devices use an 8-bit parked member address. Devices in standby mode do notneed an address. The goal for Bluetooth development was to use a single-chip, low-cost,radio-based wireless network technology for laptops, notebooks, headsets, etc.

Bluetooth operates in the 2.4GHz ISM band. However, MAC, physical layer and the offeredservices are completely different. Bluetooth transceivers use Gaussian FSK for modulationand are available in three power classes: Class 1 (max. power 100 mW), class 2 (max.

power 2.5 mW) and class 3 (max. power 1 mW).

Journey from 1G to 4G

1G system. 1G specifications were released in 1990 to be used in GSM. 1G systems are

analogue systems such as AMPS that use FDM to divide the bandwidth intospecificfrequencies that are assigned to individual calls.

2G system. These second-generation mobile systems are digital and use either TDMA orCDMA method. Digital cellular systems use digital modulation and have several advantages

over analogue systems, including better utilisation of bandwidth, more privacy, andincorporation of error detection and correction.

2.5G system. It was introduced mainly to add latest bandwidth technology to the existing

2G generation. It supports higher-data-rate transmission for Web browsing and also

supports a new browsing format language called wireless application protocol (WAP). Thedifferent upgrade paths include high-speed circuit-switched data (HSCSD), GPRS and EDGE.

HSCSD increases the available application data rate to 14.4 kbps as compared to 9.6 kbps


9/27

of GSM. By using four consecutive time slots, HSCSD is able to provide a raw transmission

rate of up to 57.6 kbps to individual users.

GPRS supports multi-user network sharing of individual radio channels and time slots. Thus

GPRS supports many more users than HSCSD but in a bursty manner. When all the eighttime slots of a GSM radio channel are dedicated to GPRS, an individual can achieve as much

as 171.2 kbps. But this has not brought any new evolution.

EDGE introduces a new digital modulation format called 8-PSK (octal phase-shift keying). Itallows nine different air interface formats, known as multiple modulation and coding

schemes, with varying degree of error control and protection. These formats are

automatically and rapidly selectable. Of course, the covering range is smaller in EDGE thanin HSCSD or GRPS.

3G system. To overcome the short-comings of 2G and 2.5G, 3G has been developed. Ituses a wideband wireless network that offers increased clarity in conversations. Countriesthroughout the world are currently determining new radio spectrum bands to accommodate

3G networks. ITU has established 2500-2690MHz, 1700-1855MHz and 806-960MHz bands.

Here the target data rate is 2 Mbps. The data is sent through packet switching. Voice calls

are interpreted through circuit switching.

3G W-CDMA (UMTS). Universal Mobile Telecommunication System (UMTS) or W-CDMAassures backward compatibility with 2G and 2.5G TDMA technologies. W-CDMA, which isan air interface standard, has been designed for always-on packet-based wireless service,

so that computers and entertainment devices may all share the same wireless network and

connect to the Internet anytime, anywhere.

W-CDMA supports data rates of up to 2.048 Mbps if the user is stationary, thereby allowing

high-quality data, multimedia, streaming audio, streaming video and broadcast typeservices to consumers. With W-CDMA, data rates from as low as 8 kbps to as high as 2Mbps can be carried simultaneously on a single W-CDMA 5MHz radio channel, with each

channel supporting between 100 and 350 simultaneous voice calls at once, depending onantenna sectoring, propagation conditions, user velocity and antenna polarisation.

Time slots in W-CDMA are not used for user separation but to support periodic functions.

(This is in contrast to GSM where time slots are used to separate users). The bandwidth perW-CDMA channel is 4.4 to 5 MHz.

Since the global standard was diffiult to evolve, three operating modes have been

specified:A 3G device will be a personal, mobile, multimedia communication device (e.g., TVprovider redirects a TV channel directly to the subscribers phone where it can be watched).Second, it will support video conferencing, i.e., subscribers can see as well as talk to each

other. Third, it will also support location-based services, where a service provider sendslocalised weather or trafficconditions to the phone or the phone allows the subscriber to

findnearby businesses or friends.

3.5G. It supports a higher through-put and speed at packet data rates of 14.4 Mbps,supporting higher data needs of consumers.

4G system. It offers additional features such as IP telephony, ultrabroadband Internetaccess, gaming services and HDTV streamed multimedia. Flash-OFDM, the 802.16e mobileversion of WiMax (also known as WiBro in South Korea), can support cellular peak data

rates of approx. 100 Mbps for high-mobility communications such as mobile access and up


10/27

to 1 Gbps for low-mobility communications such as nomadic/local wireless access, using

scalable bandwidths of up to 40 MHz. The infrastructure for 4G is only packet-based (all-IP).

Telecom Revolution: 4G and BeyondThis year, Bharti Airtel launched a 4G service in Kolkata and Bengaluru, making India one

of the first nations to adopt the newest baby in the wireless world. 4G or IMT-Advanced is

the fourth generation in telecommunications, characterised by reliable lightning-speed

broadband wireless access (BWA)a dream come true for not just the young and raging

population but also businesses, media agencies, governments and many more stakeholders.

It is hoped that 4G will catalyse national development, as it means wireless communications

to the nooks and corners, even across rugged terrains and the poorest of villages.

With the launch of Bharti Airtels service, umpteen questions have arisen in the minds of

consumers across the countrywhat really is 4G, what sets it apart as a new generation, is

Bharti Airtels service (based on the TDD-LTE standard) really 4G, what are the competing4G standards, how is 4G doing worldwide, what are the pros and cons of this generation,

and what is next in the pecking order? Here we try to answer these questions.

The fourth generation has just begun

Some service providers in countries like South Korea and Scandinavia started terming their

service as 4G as early as 2006. Others started doing so in the US a few years later. Humbug

and marketing tricks!


11/27

Customers get hands-on experience with Verizon Wireless flexible digital showcase of 4G

With the availability of chipsets that support both 3G and 4G technologies, the market is beginning to see 4G LTE smartphones (Image courtesy:

www.digitaltrends.com) 4G is a very nascent technology and there are very few deployments worldwide that qualify

as 4G todayeven by a very liberal definition. If we keep to the true definition of IMT-

Advanced, 4G is not even here yet.

In the mid 2000s, as 3G systems were being deployed, there was the initial definition of 4G

as providing 100Mbps bandwidth. Subsequent to 2006, many systems which exceeded 40-

50 Mbps started using 4G as a marketing ploy for their networks and some providers called

their advanced 3G networks as 4G Lite with Lite written in small print. This included

WiMAX and HSPA+ systems. There were even legal litigations in the US courts by operators

against each other for false advertising. It is interesting to note that the early versions of

Long Term Evolution (LTE) were being dubbed as 3.99G in published literature. ITU finally

provided a more definitive definition of 4G, explains Dr Suresh Borkar, a member of faculty

at the Illinois Institute of Technology, Chicago. Dr Borkar has wide consulting experience in

commercial and public safety systems, telecom strategy formulation, spectrum and

regulatory policies, and dynamic spectrum management.

In addition to general specifications on inter-working, handovers and quality of service, the

key attributes defined by the ITU included an all-IP packet core and (downlink) bandwidth of

100 Mbps for mobile applications and 1 Gbps for nomadic and quasi-stationary applications.

Taking into account the estimates and techniques like carrier aggregation and wider

spectrum, there is now a general consensus in the telecommunications community that

3GPPs LTE-Advanced (Release 10) and WiMAX 2.0 (IEEE 802.16m) can be classified as 4G

systems.

LTE vs WiMaxA no-brainer!

The third generation of mobile communications is characterised mainly by HSPA+ and EV-


12/27

DO. Similarly, two technologies qualifytechnicallyto be called as 4G. These are 3GPPs

LTE-Advanced and IEEEs 802.16m (WiMAX 2.0). However, the race seems to be a no-

brainer. With WiMAX 2.0 failing to take off, it looks like LTE is going to dominate the 4G

world.

WiMAX 802.16m has not been commercially successful. Hence deployment of 4G will bebased on LTE-Advanced technology. These implementations are in a nascent stage

worldwide. Large-scale deployment of 4G will take place only next year, says Dr Abhay

Karandikar, professor and head-Department of Electrical Engineering, IIT Bombay. IIT

Bombay has made several contributions to IEEE 802.16m 4G standards, including

bandwidth reservations, quality of service (QoS), relay, etc.

Thumbs-up 4GCompletely Internet protocol (IP) based architecturea simpler, scalable, flatter and lower-

cost network architecture that eases management and service deployment, and converges

cellular communications with fixed-line InternetAdvanced and efficient air-interface based on OFDM, which provides a much higher spectral

efficiency (in bps/Hz)Multi-carrier OFDM modulation; multiple antennae

Multi-layer, multiple-input, multiple-outputdownlink and uplinkSpectrum-agnostic design, which can support higher bandwidth, bandwidth aggregation,

and time-division duplexing and frequency-division duplexing modesOperates on scalable spectrum bandwidths from 1.25 to 20 MHzthe most prevalent ones

being 5 and 10 MHzBandwidth of 100 Mbps for mobile applications and 1 Gbps for nomadic and quasi-stationary

applicationsImproved coverage and reliabilityCarrier aggregation, which allows network operators to make use of several blocks of

spectrum and aggregate the usage in the mobile terminal. This results in higher data rates

for consumer, and enhanced spectral efficiency and increasing capacity for operators. It

enables a range of wider transmission bandwidths up to 100 MHz.Low latency due to improved radio access protocols, and more efficient support for cloud-

based services and online gaming applicationsSelf-organisation, relay and many other features to enhance spectral efficiency

Experts agree that LTE-Advanced (LTE Releases 10 and 11) is the main technology on the

4G horizon. It is being standardised to use up to 100MHz channel bandwidth to achieve up

to 1Gbps downlink throughput.

In our opinion, it is okay to consider LTE (Releases 8 and 9) also to be 4G technology as it

makes a radical breakthrough by adopting multi-carrier orthogonal frequency-division

multiplexing (OFDM) technology. LTE has retained some level of backward compatibility to

benefit from the UMTS experience and coexist with UMTS, says Harpinder S. Matharu,

senior product marketing manager-Communications Division, Xilinx.


13/27

LTE technology is a completely packet-based protocol and radio access technology. Its core

network, leveraging flexible bandwidth, achieves much better spectral efficiency (bps/Hz)

and delivers a throughput of greater than 100 Mbps (for 20MHz FDD system using 22

spatial multiplexing) by using higher-order modulation and multiple-input multiple-output

(downlink and uplink).

4G antenna (Image courtesy: www.techwireasia.com)Matharu adds, In light of the above argument, niche deployments of 20MHz WiMAX cellular systems

should also be considered 4G. However, LTE framing structure is better for achieving a higher throughput

and lower latency, besides the benefits of a more power-efficient user terminal uplink technology. We

expect LTE to replace majority of the WiMAX deployments in the coming years.

Dr Borkar concurs, The initial LTE-Advanced systems are expected to deploy by the year-end. Whereas

WiMAX may have its niche applications like backhaul, from access viewpoint, LTE will become the norm

of the future. Even the current 3GPP2 US standard based 3G operators like Verizon have abandoned the

CDMA2000 evolutionary path and embraced the 3GPP LTE 4G standard.

The flavours of LTETDD and FDD

Globally, there is one harmonised standard for LTE that encompasses two modesTDD and FDD,

remarks Dr Lakshminath Dondeti, director, engineering-technical standards, Qualcomm India.

LTE involves duplexing of uplink and downlink radio signals. The duplexing scheme is responsible for

managing simultaneous transmission and reception without interference between the two. To handle this,signals for transmission and reception can be separated using either time or frequencythe former is

called time-division duplexing (TDD), while the latter is frequency-division duplexing (FDD).

FDD uses a paired set of frequency blocksone for downlink transmission and the other for uplink

transmission. TDD works on only one frequency block, but uses short alternating bursts of transmission

and reception.


14/27

FDD and TDD are different technologies. FDD is better suited for voice, while TDD is better suited for

data. In data, there is usually more of reception or download than upload, and the system can be tweaked

to allow greater download time and shorter upload time.

Most deployments of cellular systems including LTE use FDD operation because of its simplicity of

transceiver designs. Some countries like India (Bharti Airtel) and China (Chine Mobile) have selected

TDD for the 4G LTE network because of its capabilities of dynamic adaptation of downlink and uplink

bandwidths. WiMAX deployments from their early version have embraced TDD operation, explains Dr

Borkar.

In India, LTE TDD has been deployed initially in the 2.3GHz spectrum band. The Global TD -LTE

Initiative (GTI) has been formed to support closer network and device integration of LTE TDD and FDD. It

is driven by several major wireless operators from around the world, working closely with GSMA and

NGMN. Qualcomm has multimode chipsets that integrate both LTE TDD and LTE FDD, and inter-work

with 3G HSPA and EV-DO, says Dr Dondeti.

IP-based architecturepros and cons

Circuit-switched networking is inefficient for data traffic. With Internet data constituting a significantfraction of mobile traffic, it is more efficient to deploy packet-switched IP technology. IP also enables

seamless network convergence. There are really no disadvantages of IP or packet switch, except

perhaps that network security issues need to be more tightly managed in an IP network, says Dr

Karandikar, who is emphatically in favour of packet-switching.

4G problem areasHigher susceptibility to inter-cell interference

Higher variation in the instantaneous power (due to OFDM-based architecture) that impacts power

amplifier efficiency

Incompatibility with previous generationsOver 40 frequency bands make global roaming difficult

Poor voice support

High cost of embracing LTE, including high auction costs for acquiring spectrum, lack of economy of

scale to make available reasonably-priced user devices, and putting together the backhaul infrastructure

Need to set up newer operations and management systems, including provisioning, performance

optimisation, revenue realisation, fault handling and maintenance, security management, etc An all-IP network can very effectively handle multiple applications and services, e.g., voice, video and

data. The power of a unified IP multimedia system architecture can be exploited to efficiently support the

QoS requirements of such varied applications and services. Packet transport provides much better

resource utilisation than circuit-switched network.

However, all-IP systems have a flipside too. The primary disadvantages for all-IP systems are how to

recover the huge investments in legacy 2G and 3G systems, not stranding the vast number of existing

user devices in the marketplace, and inability to provide the high bar of voice reliability and quality. The

VoIP alternative is primarily statistical in nature and lacks the advantages of traditional circuit-switched

based voice, e.g., quality, deterministic behaviour in terms of latency and routing, and advanced

supplementary services, says Dr Borkar.


15/27

Since 4G LTE has an all-IP core (enhanced packet core), it cannot directly support voice applications until

voice-over-IP (VoIP) becomes the norm. Moreover, all operators have already invested heavily in 2G and

3G systems which use circuit-switching for voice support.

A quick clarification1. Going strictly by ITUs IMT-Advanced definition, only LTE-Advanced (Releases 10 and 11) and WiMAX

2.0 (IEEE 802.16m) can be considered as 4G services. These are not yet operational anywhere in the

world. We can expect to see the first deployments only by the year-end or in 2013.

2. Countries like India, China, Japan and Brazil have deployed LTE (Releases 8 and 9) in recent months.

Many players in the telecom industry tend to accept this as 4G as it uses multi-carrier OFDM technology

and can be considered a major jump in technology and user/operator experience. The general approach that current LTE operators are using is circuit switch fallback to a 2G or 3G

network via the memory management entity in the enhanced packet core. This is transparent to the user

device. In addition to the circuit switch fallback, the 4G user devices are designed to be multi-mode so

that they can connect to a 2G or 3G system in case the LTE system is not present or the LTE signals are

too weak.

The 4G technology evolved and standardised by 3GPP has multiple options of supporting voice. O ne is

circuit-switched voice. LTE supports circuit switch fallback to 3G/2G network for voice support.

Advantages are definitely there for multi-service operators like Airtel, as it can offer varied services and

bundle service plans to meet the requirements of the customers, says Rajiv Rajgopal, CEO -

broadband/data, Bharti Airtel.

Looking into the future, David Maidment, mobile segment manager, ARM, comments: Moving forward,

operators will want to break their dependency on circuit-switched services and move to an all-LTE

deployment. As such, they are working to standardise and deploy voice-over-LTE (VoLTE), which allows

voice to be carried over the packet network. VoLTE handsets are already available, and in the next one ortwo years we will begin to see the growth of these services.

Availability of 4G devices

True 4G equipment are not widely available today. LTE Release 8 systems have been deployed since

2010, but these are not 4Gmerely 3.5G. As is expected in a family of standards like LTE, device and

infrastructure manufacturers will provide migration and compatibility between different releases. Current

LTE smartphones and other devices will operate in future LTE networks but may not be able to exploit the

advanced and new features like carrier aggregation. Real 4G devices compatible with LTE-Advanced

specifications may be available by the year-end.

With the current technologies, many advanced features can be effected in the devices via provisioning

and software updates, points out Dr Borkar.

Initially, 4G user equipment targeted notebooks and tablets for data services. With the availability of

chipsets that support both 3G and 4G technologies, the market is beginning to see 4G LTE

smartphones, adds Matharu of Xilinxa company that provides silicon devices, intellectual property

solutions and design services for wireless infrastructure.

Rajgopal notes: Bharti Airtel through its GTI, along with other partners like CMCC and Softbank, is taking


16/27

a lead in ensuring that the device ecosystem rapid ly matures to the operators and consumers

requirements. Currently, we have an array of compatible devices like dongles and CPE devices that

support TDD-based LTE. Smartphone and tablet users can access 4G LTE services over Wi-Fi networks,

from CPE devices. We are working with the OEMs in ramping up the device ecosystem in the country.

That said, there is also the issue of devices made for one region not working in others. To this, Rajgopal

responds, At present, 4G LTE devices available in the open market or USA are not compatible in India.

We are working with OEMs and chipset vendors to ensure that this will not be an impediment. As a matter

of fact, Bharti Airtel is one of the founding members of the GTI that is working on standards for TD LTE.

Roaming issues

Frequency bands and duplex operation are the two primary reasons why equipment used in one

continent are not compatible in others.

LTE as a standard can be deployed in over 40 different frequency bands. This is a benefit as it makes

the standard flexible, but its also a weakness from a fragmentation and roaming point of view. We have

already seen issues around band support in LTE with current-generation devices that are unable to roam

outside their home networks. Multi-band support is nothing new in cellular applications. From 2G onwardsequipment vendors have been producing multi-band phones. The issue with LTE has been the sheer

number of bands as well as the fact that it supports two duplexing methods FDD and TDD, explains

Maidment.

From a signal processing point of view it is already possible to implement a world phone that can span

FDD and TDD. The issue is in the radio hardware, which needs to be band-specific in order to receive

and transmit at the required frequency. We expect to see innovation in this space as manufacturers work

to solve this issue and produce programmable band selection in the hardware that will, in turn, allow

devices to be produced that cover all the major bands worldwide, he adds.

During the early stages of LTE growth, 3G HSPA or EV-DO will be the primary global roaming

technologies given the global harmonisation of 3G spectrum. Over time, some common LTE bands

across the world that facilitate international roaming will start to emerge. In fact, 3G and LTE will inter-

work and coexist for a long time, says Dr Dondeti.

Facilitating international roaming is not a great problem, according to Dr Karandikar. ITU has defined

band plans for various technologies and standards. Various countries do harmonise their spectrum

allocation accordingly. ITU holds World Radio Communications Conference every three to four years

where frequency harmonisation may be achieved, he informs.

Global roaming issues have been solved in the past using multi-standard chipsets and multi-band radios.

A similar solution might be helpful here too. Qualcomm has developed the worlds first multi-mode (HSPA,

EV-DO, FDD/TDD LTE) chipsets that integrate both TDD and FDD. The commercial LTE TDD networklaunched by Bharti Airtel uses multi-mode dongles based on Qualcomms MDM 9x00.

Huawei, ZTE, BandRich and Quanta have announced LTE TDD multi -mode devices based on the

Qualcomm MDM9x00 chipset in August 2011, indicating commercial availability this year, adds Dr

Dondeti.

When will 4G phase out 3G?

Standards are quick to arrive and slow to leave. We have lived with 2G services for around 20 years


17/27

now, for example. The question of when 4G will phase out 3G should instead be phrased when will 4G

phase out 2G, quips Maidment.

Airtel 4G LTE USB modemToday, in most territories, 2G and 3G services run side by side with 2G often covering less-densely

populated regions and 3G services deployed in towns and cities. From a network perspective, we are

seeing a growing trend towards heterogeneous network architectures which combine multiple carriers

with varying access technologiessuch as small cells to deliver capacity and coverage where it is

needed most, and larger, more traditional macro cells providing wide-area coverage in rural areas.

As LTE is deployed both in the wide area through macro cells as well as in small cells, we expect to see

operators looking to free up their existing 2G spectrum to move across to LTE services. This is a slow

process which is highly dependent upon regulatory approval and will differ from region to region.

While some operators might consider leapfrogging directly from 2G to 4G, those who have deployed 3G

are likely to continue enhancing and using those networks for at least five to ten years to get justifiable

returns on their investments.

We can expect to see the continued adoption and rapid uptake of LTE services around the world. As a

key part of that, we will see new low-power, multi-band capable devices that deliver the economies of

scale required to make LTE commercially viable. From a standards perspective, device vendors are

working to implement the first-generation LTE-Advanced terminals, which we would probably see a yearor two down the line. These devices will be capable of supporting data rates up to 300 Mbps enabled by

carrier aggregation and multi-layer multiple-input multiple-output.

In addition to LTE-Advanced, there are plans within 3GPP to look at how LTE can be employed to

enable machine-type communications. The rise of machine-to-machine communications is anticipated to

be a key growth area and it is essential that we have in place the right standards to support that need.

Being an all-IP based technology, LTE is well positioned to serve this emerging space during the next 20+

years, says Maidment.

Beyond 4G

While 4G, according to its true definition, is not even here yet, we are already talking of what is yonder,

beyond the big blue mountain.

Dr Borkar provides some futuristic food for thought: Consistent with the general historical trend of a new

technology standard every ten years, it is expected that 5G specifications will likely be in place in the

2018-20 timeframe.

The framework for 5G includes higher-efficiency operation with lower battery consumption, higher system

reliability, more uniform, high data rates across the coverage area, low infrastructure deployment costs,


18/27

and higher spectral efficiency and capacity.

Some of the features being considered include advanced multi-cell coordination for enhanced system

performance and end-user service quality, efficient infrastructure for machine-to-machine communications

to support the vast number of connected devices, direct user device-to-device communications especially

for performance and network outage situations, and new ways of using and adapting to the available

spectrum based on the use of cognitive radios.

How is Mobile Number Portability Achieved

There has been rapid growth in the penetration of telephony services in the last few years.

But the growth has not been exponential in the quality of service offered or openness of

business. Consumers are not satisfied with the operators services and schemes.

Traditionally, consumers are required to give up their mobile number on changing service

providers. As a result, they are hugely inconvenienced by having to inform everyone about

the change in their number. Besides there is likelihood of important calls (from people who

didnt have the new number) being missed out, and so on. The picture has now changeddramatically with the introduction of mobile number portability (MNP).


19/27

Fig. 1: (a) Decentralised and (b) centralised database solution

Fig. 2: Signaling relay approachMobile number portability

Mobile number portability enables consumers to retain their mobile numbers when changing

service providers, service types and/or locations. The Internet Engineering Task Force(IETF) has defined three types of number portability: service provider portability, location

portability and service portability.

Service provider portability. It enables a customer to retain his existing mobile number

when changing from one service provider to another in the same area.

Location portability. It enables a customer to retain his existing mobile number without


20/27

impairment of quality, convenience or reliability when shifting from one geographic location

to another.

MNP terminologyDonor operator.Operator from whose network the customer is porting out.Recipient operator.Operator who will be providing services to the customer after porting.

Number portability database.Collection/repository of all the ported numbers. Provides a

unique routing number in response to a query from any network operator.

Routing number.A unique number stored in the number portability database that is used

to route the call to the recipient operator.Service portability. It enables a customer to retain his existing mobile number without

impairment of quality, convenience or reliability when switching from one service technology

to another service technologyfor example, from CDMA to GSM.

A combination of different kinds of portability options can also be used, which enables

customers to retain their mobile number across different service providers, service

technologies, geographical regions and national boundaries.

Many regulatory authorities have made number portability mandatory or are about to

introduce it so as to ensure better quality of service to customers. The worlds first country

to introduce mobile number portability was Singapore (1997). It was followed by the UK,

Hong Kong and the Netherlands (1999), Spain (2000) and Australia (2001). As of today,

there are many countries (including India) that have introduced number portability.

Implementation of MNP

Mobile number portability can be implemented using either decentralised database or

centralised database approach (Fig. 1). Decentralised database solution requires each

operator to maintain its own number portability database. It is useful if there are few

operators. If there are many operators, centralised database solution is better.


21/27

Fig. 3: Signaling relay using LRN


22/27

Fig. 4: Tromboning call set-up

Signaling relay approach. This approach is based on decentralised database solution. In this

implementation, the donor operator identifies the correct terminating network (recipientoperator) and routes the call to that network. The originating network receives a call from

the caller and routes the call to the donor operator. Upon receiving the call, the donor

operator network identifies that the dialed number has been ported out. Now the donor

operator routes the call to the recipient operator network.

In this routing scheme, there is no need of a central database, and only the donor and

recipient operators need to know about the porting of a number.

Direct relay. In this approach, the originating network contacts the gateway mobile

switching centre to establish a call. The gateway mobile switching centre detects that the

dialed number is ported out and relays signaling information to the home location register toget the mobile station routing number. After getting the mobile station routing number, the

gateway mobile switching centre sets up trunk to the serving mobile switching centre to

establish the call (Fig. 2).

In this routing approach, the originating, donor and recipient operators are kept busy to

establish a call. So it may not be considered as an efficient mobile number portability

scheme.


23/27

Relay using location routing number. In this scheme, a location routing number is used to

route the call to the correct terminating network. The call flow is shown in Fig. 3. Again, in

this method of number portability, all the network elements of originating, donor and

recipient networks are kept busy for the entire duration of call. Further, this approach is

susceptible to establishing a tromboning call set-up when the originating network is also arecipient network (Fig. 4).

Basically, tromboning is where a call originates at a certain point, and follows a path out

into the network and back to a destination close to where the call originated. In this way,

several networks and their entities are kept busy unnecessarily. So this mobile number

portability scheme is not recommended.

All-call-query approach. This is a direct routing scheme that utilises a centralised ported

database. In this scheme, the originating network directly queries the central ported

database to determine the routing number required to transfer the call to the recipient

operator. After determining the routing number, the call from the originating network isdirectly routed to the recipient operator network. In this way, the involvement of donor

operator is eliminated.

Fig. 5: All-call-query approach for MNP


24/27

Fig. 6: MNP process

In this approach, the originating network directly queries a central portability database to

get the location routing number in order to route the call to the gateway mobile switching

centre of the correct terminating network. Further, the gateway mobile switching centre

sets up trunk to the serving mobile switching centre to establish the call (Fig. 5).

The donor network does not take part in the call process and utilises network resources

most efficiently to route a call. Thus this scheme is considered to be the most efficient

routing scheme for large interconnected networks and a large number of ported numbers.

MNP in India

On March 8, 2006, the Telecom Regularity Authority of India (TRAI) issued draft regulations

to facilitate mobile number portability in India and submitted its recommendations to the

Department of Telecommunication (DoT). Finally, the DoT recommended service provider

number portability including service portability (portability between GSM and CDMA) for all

mobile service operators. It was decided to implement the all-call-query approach for mobile

number portability.

The DoT has divided the whole country into two zones for MNPnorth-west zone and south-

east zoneand awarded licences to two vendors to work as MNP clearing house

administrators. The north-west zone comprises Gujarat, Haryana, Himachal Pradesh,

Jammu and Kashmir, Maharashtra, Punjab, Rajasthan, UP (East), UP (West), Delhi and

Mumbai. The south-east zone comprises Andhra Pradesh, Bihar, Assam, Karnataka, Kerala,

Madhya Pradesh, North East, Orissa, Tamil Nadu, West Bengal and Kolkata.


25/27

MNP clearing house administrators manage a central mobile number portability database

that keeps record of all ported-in and ported-out numbers. Further, the operators also

maintain their own MNP database called local number portability database.

The originating network will perform number portability database query to get the locationrouting number to route the call directly to the recipient network. Location routing number

is a 4-digit unique number allotted by DoT to all mobile operators for each circle to identify

individual networks. All ported number calls are routed on the basis of location routing

number. So when the MNP database receives a query for a given mobile station

international subscriber directory number (MSISDN), the database returns the MSISDN

prefixed with location routing number.

Mobile number portability was started as a pilot project in Haryana on November 25, 2010

and has been implemented across the nation from January 20, 2011. The detailed MNP

process is shown in Fig. 6.

At present, the only restriction is that mobile number portability is allowed within the same

circle (intracircle operators). Recently, the government of India approved New Telecom

Policy-2012 (NTP), which aims to abolish roaming charges across the country and facilitate

nationwide (inter-circle) mobile number portability, i.e., one-nation-one-number with free

roaming. This will allow users to change the operator without changing their mobile number

even if they move from one circle to another. DoT has been asked to start nationwide MNP

implementation and it is expected that the inter-circle MNP will start very soon.

Network architecture for MNP

Network architecture for MNP is shown in Fig. 7. The network is deployed in a redundant

and synchronised way in two different geographical areasone as a production site and theother as a disaster recovery siteto avoid interruption in service due to failure of one site.


26/27

Fig. 7: Network architecture for MNP

Depending upon the requirement and network topology, the service provider can either

directly connect to the central number portability database (CNPDB) or deploy separate

local number portability database (LNPDB) and connect it to the CNPDB through its number

portability gateway. The CNPDB and LNPDB should be syn-chronised.

When a call is originated, the visited mobile switching centre interrogates an internal

(LNPDB) or external database (CNPDB) to get the location routing number of the correctterminating network. The CNPDB can be integrated with the signaling transfer point and

accessed via an application programming interface locally, or a query can be made to a

remote CNPDB through number portability gateway using protocols like simple object access

protocol and extensible markup language. Here MNP translations are performed by the

signaling transfer points. The signaling transfer point receives the location routing number

query from the visited mobile switching centre and routes it to the appropriate signal control

point.

The signal control point is a high-transaction-oriented server that receives number

portability requests from the visited mobile switching centre and passes on the mobile

station routing number information to the gateway mobile switching centre handling thecall. The gateway mobile switching centre then routes the call to the currently serving

visited mobile switching centre of the recipient operator.

The road ahead

About a year into its operation in India, the service provider number portability has failed to

enthuse customers. It is expected to gain momentum once the National Telecom Policys


27/27

proposals of abolishing the inter-circle roaming charges and extending MNP to national level

are implemented.

Documents

Mobile Communication 1G to 4G