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2Authors Suppressed Due to Excessive Lengthternational cellular network, Nordic Mo-bile Telephone (NMT) systems, came tooperation in Nordic countries. In 1983,two other 1G systems, Advanced Mo-bile Phone System (AMPS) and TotalAccess Communication System (TACS)were introduced in the US and other Eu-ropean countries including the UK, Italy,respectively.Through a journey which startedabout 40 years ago, cellular commu-nications have experienced dramaticchanges and upgrades from 1G to 4G.Those transitions include the systemchange from analog to digital, the corenetwork evolution from circuit-switchedto packet-switched technologies andits further transfer towards all InternetProtocol (IP) networks.First Generation CellularSystemsThe 1G mobile systems were designedfor providing voice services only andwere developed based on analog tech-nologies. For medium access of multipleusers, Frequency Division MultipleAccess (FDMA) schemes were adopted.For carrying voice traffic, FrequencyModulation (FM) was employed as themodulation scheme.Nordic Mobile Telephone SystemsNMT is a mobile telephone networkcovering first the five Nordic countries,Denmark, Finland, Norway, Sweden,and Iceland and later quiet a few othercountries. NMT has two variants basedon the operational frequency bands,known as NMT-450 and NMT-900respectively. NMT-450 was developedin order to establish a compatibletelephone system in the Nordic coun-tries (Nordic Mobile Telephone Group1995). Initially NMT-450 targeted atdeploying macro cells at the 450 MHzband to provide larger cell coverage andlater it was modified to operate in the900 MHz band by considering the sizeand transmission power constraint ofhandsets. NMT systems were initiallylaunched in Norway and Sweden asa national service, and later on it wasenhanced with roaming services acrosscountries. NMT-900 bears more chan-nels than the NMT-450 network, able toserve a higher number of subscribers.Advanced Mobile Phone SystemThe AMPS systems were deployedin North America. It has 2x20 MHzbandwidth within the 800-900 MHz fre-quency band (825-845 MHz for uplinkand 870-890 MHz for downlink trafficrespectively) allocated by the FederalCommunications Commission (FCC).With 30 kHz bandwidth for each chan-nel, it provides 832 duplex channels.This system employs 7-cell clustersfor frequency reuse and uses mainly120◦sector antennas. Three sectors fora single AMPS cell site were designedtoachieveacarrier-to-interferenceratio of 18 dB with satisfactory voicequality. In 1991, an improved versionof AMPS named as narrowband AMPS(N-AMPS) was developed to furtherincrease AMPS capacity with additionaladvanced features such as authenticationand caller ID.Total Access Communication SystemsTACS was the first standard that usedthe 900 MHz band and was deployed

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Title Suppressed Due to Excessive Length3in other European countries (Goldsmith2005). TACS was operated at a higherfrequency than AMPS and adopted nar-rower bandwidth per channel (25 kHz inTACS versus 30 kHz in AMPS). Withnarrower bandwidth for each channel,the total number of channels is increasedfor a band with fixed bandwidth. Op-erated at a higher frequency, the cover-age for each cell will be reduced giventhe same transmission power and chan-nel condition. In other words, this sys-tem was designed for having higher ca-pacity rather than coverage by deploy-ing a larger number of cells and allow-ing lower transmission power for mobilestations. Indeed, TACS was proved to beefficient and economical for highly den-sity urban areas. A variant of TACS, J-TACS, was also adopted in Japan.Second Generation CellularSystemsThe core network of both 1G and 2Gcellular networks was built based oncircuit-switched technologies and theservice was mainly targeted at voicetraffic. However, unlike 1G systems,2G employedall-digitaltransmissiontechnologies for both control signalingand data traffic. The introduction ofdigital communication provides a seriesof important features such as the supportof advanced source and channel coding,more efficient spectrum utilization, anda high degree of resistance against inter-ference and channel fading. In addition,the handling of control information ismore efficient in digital systems.2G cellular networks were deployedworldwide. They are represented byfour major standards, i.e, Global Systemfor Mobile Communications (GSM),Interim Standard (IS)-136 or DigitalAMPS (D-AMPS), IS-95 or cdmaOne,and Personal Digital Cellular (PDC).ExceptcdmaOne,theotherthreesystems are based on Time DivisionMultiple Access (TDMA) mechanismsfor medium access. TDMA allowsmultiple users share the same channelin the frequency domain by allocatinga specific short period of time, knownas time slot, to each user for theirchannel access. Among these fourstandards, GSM is the most popular 2Gtechnology. Given the fact that 3G and4G are already widely deployed in theworld as of 2017, GSM still occupiesapproximately 39% of the global mobilemarket share.Global System for MobileCommunicationsIn 1982, a committee calledGroupeSp ́ecial Mobilewas established in orderto design a Pan-European digital cellularstandard for mobile communicationswhich would replace the incompatible1G analog systems. The EuropeanTelecommunications Standards Institute(ETSI) initiated the development of thefirst version of GSM and the first GSMcall was made in 1991. The success ofGSM is represented by its over 90%market share in the 2G world, coveringglobally around 200 countries andterritories.GSM is operated mainly in threefrequency bands, i.e., GSM-900, GSM-1800, and GSM-1900 with 124, 374,and 299 radio channels respectively. Theoriginal GSM network was developedfor voice communication supporting avariety of voice codecs. The bandwidthfor each GSM channel is 200 kHz andthere are 8 time slots in each frame

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4Authors Suppressed Due to Excessive Lengthwhich lasts for 4.615 ms. The raw datatransmission rate achieved at each chan-nel is 270.833 kbps and it is shared by 8users. With the combination of TDMAand FDMA, GSM provides the capabil-ity of simultaneous conversations at thesame frequency through different timeslots. Other salient features of GSMinclude data encryption, subscriberidentity module (SIM) card which givesa unique identity to each mobile station,and global roaming (Ebersp ̈acher et al2009). Furthermore, GSM is enhancedto provide short message service (SMS),however, still based on circuit-switchedtechnologies.GPRS and EDGETo support higher data transmissionrates in GSM networks and provide IPservices without replacing the networkinfrastructure, developments were madeto upgrade GSM networks into GeneralPacket Radio Service (GPRS) in year2000. GPRS is also known as 2.5Gand there are two major enhancementsfor the evolution from GSM to GPRS.At the radio access network, a useris allowed to occupy up to 5 timeslots so that 114 kbps and 20 kbps areachieved for downlink and uplink trafficrespectively. At the core network, twoentities, Serving GPRS Support Node(SGSN) and gateway GPRS SupportNode (GGSN) are introduced. With thesupport of Packet Data Protocol (PDP)and GPRS Tunneling Protocol (GTP),end-to-end IP services can be provided.In 2003, there was another im-provement in GSM systems with thedeployment of Enhanced Data ratesfor GSM Evolution (EDGE) networks.EDGE is regarded as an extensionof the GPRS radio access networkthrough advanced modulation schemes.It increased the data rates to 384 kbpsfor downlink and 60 kbps for uplinkrespectively.Third Generation CellularSystemsWhile GSM was in its early stage, thestandardization of the next generationmobiletelecommunicationnetworkwas also initiated by ETSI aiming todevelop a new system called UniversalMobile Telecommunications System(UMTS). High spectrum efficiency, datarates up to 2 Mbps, variable bit rates,QoS requirements based on servicetypes, support of asymmetric uplink anddownlink traffic and co-existence with2G systems are the main requirementsfor 3G systems (Holm and Toskala2007). Meanwhile ITU commencedproposing recommendations for 3Gsystems known as International MobileTelecommunications 2000 (IMT-2000)and started to investigate suitablespectrum for 3G. The establishment ofthe 3rd Generation Partnership Project(3GPP) in 1998 became a milestonefor the standardization of cellular net-works as aglobalstandard from 3Gand beyond. In Tab. 1, we summarize3GPP releases and their main features.Note that current 4G and upcoming5G standards are also standardized by3GPP.The key mechanism used for mediumaccess in 3G is CDMA which allowsmultiple mobile stations transmit at thesame time and in the same frequencyband. In a CDMA cell, each subscriberis assigned a unique code and the codesassigned to different stations are orthog-onal to each other. As such, the number

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Title Suppressed Due to Excessive Length5Table 13GPP release dates and features3GPP Release Start/Release Date Summary of Key FeaturesR991996/2000First release of the UMTS standardR41998/2001This release added features including an all-IP core network. Itwas originally referred to as Release 2000R52000/2002IP Multimedia Subsystem and High Speed Downlink PacketAccess (HSDPA)R62000/2004Integrate the operation of UMTS with wireless LAN networksand added enhancements to IMS (including Push to talk overCellular), and it added High Speed Uplink Packet Access(HSUPA).R72003/2007Detailed improvements to QoS for applications such as VoIPand upgrades for High Speed Packet Access Evolution,HSPA+, as well as changes for EDGE Evolution.R82006/2008Provide details for the LTE System Architecture Evolution,SAE, an all-IP flat network architecture providing the capac-ity and low latency required for Long Term Evolution (LTE)and future evolutions.R92008/2009Further enhancements to the SAE as well as allowing forWiMax and LTE/UMTS interoperability.R102009/2011Up to 3 Gbps downlink and 1.5 Gbps uplink, carrier aggre-gation (CA), relay nodes to support Heterogeneous Networks,higher order MIMO antenna configurations.R112010/2012Enhancements to Carrier Aggregation, MIMO, relay nodes, co-ordinated multipoint transmission and reception to enable si-multaneous communication with multiple cells, introduction ofnew frequency bands.R122011/2015Enhanced small cells for LTE, inter-site carrier aggregation, in-terworking between LTE and WiFi or HSDPA.R132012/2016LTE-U, LTE for machine-type communication (MTC), full-dimension MIMO, LTE-Advanced Pro.R142015/2017Energy efficiency, location services, mission critical data andvideo, massive IoT.R152016/20185G Phase 1 (new radio).R162017/2019-20205G Phase 2.

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6Authors Suppressed Due to Excessive Lengthof simultaneous calls in a CDMA cellis soft limited (based on the interferencelevel), not hard limited as in GSM.UMTS WCDMAWideband CDMA (WCDMA) was theair interface for the UMTS standardoriginally proposed by ETSI in 1998. Toprovide peak data rates from 384 kbpsto 2.048 Mbps, the WCDMA systemoperates on wider channels each with5 MHz bandwidth. However, the corenetwork architecture of UMTS remainsthe same as the existing GSM/GPRSnetworks.WCDMA is a Direct SequenceSpread Spectrum (DSSS) system whichinitially operates in the 1885-2025 MHzand 2110-2200 MHz frequency bandsfor uplink and downlink respectively.It supports operation modes of bothFrequency Division Duplex (FDD)when symmetric uplink/downlink chan-nels are available and Time DivisionDuplex (TDD) when only asymmetricspectrum is available. In addition toachieving higher data rate, the supportfor multi-code operation, larger numberof spreading factors, and enhancedtransmission diversity are the key fac-tors which lead WCDMA to the mostpopular 3G technology. Moreover, forthe purpose of leveraging the GSMcoverage for WCDMA, seamless han-dovers between GSM and WCDMA arealso supported as well as dual-modehandsets.High-Speed Packet Access (HSPA)HSPA includes two phases as thebeyond UMTS WCDMA enhance-ments by 3GPP, i.e., HSDPA in R5and HSUPA in R6. The main idea ofHSDPA is to increase downlink data ratethrough techniques including AdaptiveModulation and Coding (AMC), HybridAutomatic Repeat reQuest (HARQ),and fast packet scheduling. Unlike inthe previous standards, the MediumAccess Control (MAC) layer of HSDPAsystems is installed at the base station,i.e.,NodeB.Thusretransmissionscan be controlled directly by NodeB,leading to faster retransmission and ac-cordingly shorter delay with packet dataoperation (Holm and Toskala 2007).HSDPA is capable of supporting up to14.4 Mbps peak theoretical throughput.Similarly HSUPA is developed to sup-port enhanced packet data throughputfor uplink. HSUPA enables additionalfeatures such as fast power control andvariable spreading factors which aredisabled in HSDPA. However, HSUPAdoes not support AMC. It is capableof providing up to 5 Mbps peak uplinkthroughput.Fourth Generation CellularSystemsThe data rate provided by 3G networkswas not able to meet the growingdemand for Internet access via mobilephones. From 2008, ITU’s Radiocom-munications Sector (ITU-R) initiatedthe process for developing a new systemknown as IMT-Advanced. The mainrequirements for this new system in-clude supporting 100 Mbps and 1 Gbpspeak data rate for high and low mobil-ity scenarios respectively, bandwidthscalability up to 100 MHz, mobilitysupport with up to 350 km/h, 10 ms user

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Title Suppressed Due to Excessive Length7plane latency and 100 ms control planelatency, worldwide roaming capability,inter-networking with other 2G and3G systems, and improved spectralefficiency (Korhonen 2014). Radiotechnologies that could meet theserequirements are termed as 4G systems.LTE-advanced (LTE-A) developed by3GPP is regarded as the de facto 4Gmobile communications system from aglobal perspective. Although LTE doesnot meet the requirements for 4G asspecified by ITU, it is often marketed asa 4G technology.LTELTE is presented here under the 4G um-brella considering the fact that both LTEand, theTrue4G technology, LTE-A,are based on Orthogonal Frequency-Division Multiplexing (OFDM)/OFDMAccess (OFDMA) mechanisms formedium access. LTE supports bothFDD and TDD operations and providesflexible operations in both symmetricand asymmetric spectrum. To enhanceuplink power efficiency, LTE adoptsSingle Carrier Frequency Division Mul-tiple Access (SC-FDMA). To achievehigher data rate, LTE offers flexiblebandwidth allocation up to 20 MHz.Moreover, much shorter frame sizes (10ms frames and 1 ms sub-frames) areintroduced. With a configuration of 20MHz spectrum and 4x4 MIMO, 326Mbps on the downlink and 86 Mbps onthe uplink can be achieved in LTE radionetworks.To upgrade LTE core networks,3GPP R8 introduced Evolved PacketCore (EPC) which was designed to pro-vide higher capacity, all-IP support andreduced latency. Unlike the hierarchicalarchitecture used in GPRS and UMTScore networks, the main design principlein EPC was to keep the architecturesimple and flat.LTE AdvancedThe LTE-A standard ratified by 3GPPR10 is the major standard for 4G. Manyof the existing features in R8 are in-herently supported in LTE-A. In addi-tion, carrier aggregation up to five com-ponent carriers, use of relays, higher or-der MIMO and enhanced Inter-Cell In-terference Coordination (eICIC) servedas new features in LTE-A. Furthermorein R11, Coordinated Multi-Point trans-mission and reception (CoMP) and en-hanced Self-organizing Network (SON)are designed as parts of the LTE-A net-works.The same as in LTE, the mediumaccess mechanism in LTE-A adoptsOFDMA for downlink and SC-FDMAfor uplink. The main advantages ofOFDMA include the ability to gainmuchfrequencydiversitythroughrandomlydistributedsub-carriers,multi-user diversity via assigning con-tiguous sets of sub-carriers, and adaptivebandwidth allocation. To increase trans-mission power efficiency and reducethe cost of power amplifiers for mobilestations, SC-FDMA is employed thanksto its low peak-to-average power ratio.At the physical layer, adaptive codingand modulation (ACM) is adopted in4G systems. With ACM, the modulationorder and the coding rate are fine-tunedbased on the channel state informationto gain the full use of radio channels.

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8Authors Suppressed Due to Excessive LengthAnother technique for data rateenhancement is channel aggregationwhich assembles multiple channelstogether to perform data transmissionover wider bandwidth. Furthermore,LTE-A continues to improve capacityand reliability through more advancedMIMO technologies. While single-siteMIMO introduces beamforming, spatialmultiplexing and transmit diversity intothe system, cooperative MIMO facili-tates CoMP transmission and reception.Under CoMP, a mobile station is ableto receive signals from multiple basestations and likewise for the uplinktransmission. By adopting a propercoordination scheme, the received signalquality is greatly improved.Due to the fact that mobile stationscannot support MIMO with manyantennas, cell-edge users may not obtain4G-level quality of service althougha large number of antennas can beinstalled at the base station. To improvethe performance of these users, relayingis adopted as a cooperative communi-cation technique where single-antennamobile stations transmit their signalsto the base station via a relay stationthat is located much closer to thecell-edge (Sesia et al 2011). Anothercritical requirement for IMT-Advancedis effective power management. Theaforementioned techniques includingSC-FDMA,advancedmulti-antennadesign, and relaying collectively con-tribute to significant reduction of mobilestation power consumption.Key ApplicationsOn its journey from 1G to 4G, cellularnetworksexperiencedFDMA-basedanalog systems (NMT, AMPS, TACS),TDMA-based digital systems (GSM,GPRS),CDMA-basedIP-enabledsystems(WCDMA,HSPA),andOFDM-based broadband mobile sys-tems (LTE/LTE-A). The core network ofcellular systems has gradually evolvedfromacircuit-switchedtelephonenetwork to a packet-switched mobilenetwork with all-IP capability. Anothertrend along with this evolution is thatnowadays cellular technologies arebeing developed as a global commonstandard in lieu of multiple regionalstandards developed in the early yearswhich were not compatible with eachother.Cross-ReferencesAnalog and Digital CommunicationsRandom Access Technology in CellularNetworksKey Technologies in 4G/LTE NetworkReferencesEbersp ̈acher J, V ̈ogel HJ, Bettstetter C, C Hart-mann C (2009) GSM Architecture, Proto-cols and Services. Wiley, West Sussex, UKGoldsmith A (2005) Wireless Communications.Cambridge University Press, Cambridge,UKHolm H, Toskala A (2007) WCDMA forUMTS: HSPA Evolution and LTE. Wiley,West Sussex, UKKorhonen J (2014) Introduction to 4G MobileCommunications. Artech House, London,UKNordic Mobile Telephone Group (1995) NordicMobile Telephone. Stockholm, SwedenSesia S, Toufik I, Baker M (2011) LTE - TheUMTS Long Term Evolution: From Theoryto Practice. Wiley, West Sussex, UK

(10) (PDF) Cellular Networks: An Evolution from 1G to 4G. Available from: https://www.researchgate.net/publication/327437086_Cellular_Networks_An_Evolution_from_1G_to_4G [accessed May 03 2020].