Chapter10_4G Network Planning

8/12/2019 Chapter10_4G Network Planning

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104G Network Planning

10 1 INTRODUCTIONTO 4GMOBILE NETWORKSWith th e third-generation network deployment yet to pick up speed, fourth-generationtechno logy is already in view. If the predictions of the mobile in dustry experts prove to betrue, fourth-generation network deployment may start at any time in the coming decade.Trials have already being conducted by some mobile operators and vendors. But why isthis4G technology needed wh en 3G networks seem to be sufficient to cater for subscriberdemands fo rhigh data rates andqualityo f service?Theanswer isthat present 3Gcapability isconsidered to besubstantiallyless than pre-dicted future requirements and applications. Also, future systems should be much cheaperfor consumers. Thus, th econcepts can be summarized as:

Fourth-generation networks will provide subscribers with a higher bandwidth and amobile data rate of l O O M b p sand more.Itis expected th at third-ge neration netw orks will not be able to meet the needs of serviceslike video-con ferencing,fullmotion video etc. in terms of QoS.There willbe greater m ob ility and lower costs.Itwillbe possible to integrate W LAN and W AN.

M oreover, fourth-gene ration networkswillnot be by-product only of the m obile indus tryThe firstresearch began around th e early 1990s so as to develop technology that couldcaterfor very high data rates, with simultaneous guaranteed QoS. Thetechnology may seesome pec uliar features, suchascell phones operatinginvery high speed veh icles (e.g. train srunning at more than 200km/h). Present subscriber requirements include downloadingvideos and music etc., but the future seems to be moving towards applications like on-line games that demand immense capacity, greater QoS and very low costs In short, aFundamentals of Cellular Network Planning OptimisationA.R. Mishra. 2004 John Wiley&Sons, Ltd. ISBN : 0-470-86267-X


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Table 1 0.1 Com parison of 3G and 4G network technologiesKey featuresData rateFrequency bandBandwidthSwitching techniqueRadio accesstechnologyIP

3G networks384kbpsto 2M bps1.8-2.4GHz5 MHzCircuit- and packet-switchedWCDMA, CDMA-2000 etc.IPv4.0, IPv5.0, IPv6.0

4G networks20- 100M bps2-8 GHzAbout 100 M HzCompletely digital with

packet voiceOFDMA, MC-CDMA etc .IPv6.0

4G system must be capable of providing highly efficient and cost-effective solutions fo rwireless network users.Table 10.1 givesacomparison of few keyfeaturesof 3G and 4G technologies.

10 2 KEY TECHNOLOGIES FOR FOURTH GENERATIONNETWORKSAlthough thereare a fewtechnologiesvyingfor the topstopforfourth-generation netw orks,OFDM and M C-CDM A may turn out to be the key competitors for the physical interface,and All-IP and WLAN for the upper layers. This section introduces OFDM (orthogonalfrequency-division multiplexing)for theair-interfaceandAll-IPfor theupper layer.Laterin the chapter, an overview of WL AN systems and network plann ing is given.

10.2.1 OrthogonalFrequency divisionMultiplexingOFDM is afrequency-division multiplexin g technique thatisusedtotransm it large amoun tsof data on a radio sign al. Basica lly, a 'big' radio signal is subdivid ed into smaller signalsand then transmitted to thereceiverusing different frequencies.

It is thought that OFDM will be able to fulfil th e three most important requirementsof 4G mobile networks: higher coverage an d capacity, with desired QoS at m inim um ost

Thebiggest advantageof theOFDM techniqueis them utual orthogonali tyof itscarriers,which provides ahigh spectral efficiency.This is possible becausethere is no guard bandand carriers can be packed very close together. M ost of the alternative techn iqu es requireguard bands. In OFDM, even without a guard band, there is no interference because thecarriers are orthogonal. The spectrum for OFDM lies between 200 M Hz and about 3.5 GHz,with a spectral efficiency of about 1bit/s/Hz.Coverage in CDM A systems is limited by the phenomenon ofcell breathing (describedelsewhere in this book), as an increasin g num be r of users decreases the area covered ow ingto anincreaseininterference.In anOFDM system,th ecell overlay techniquei sused (similarto that in GSM ), thereby reducing co-channel interference.

Network planningfor anOFM D system isquite similar tothatfo rGSM/GPRS. This isbecause frequency re-use isreintroduced (unlikein WCDMA, whereth efrequency re-usefactorwas 1, theoretically). For this reason, the power control feature in O FDM netwo rks is


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Figure 10.1 Capacity increase using M IM O antenna systemsnot as essential as in WDCMA networks. In WCDMA radio networks, power control andspread spectrum are required for reducin g interference. In OFDMradio networks, accurateestimationoffrequencyoffset is required.Increasing the number of transmitting and receiving antennas can increase capac-ity. M ult iple-input/mult iple-output (M IM O ) antenna systems can be used, as shown inFigure 10.1.

Network planning fo r OFDM networks is simpler than fo r CDMA networks. OFDMreduc es the am ou nt of crosstalk in signal transmissions. Thu s, in a nutshell, we can see thatOFDM clearly has an edge over CD M A, m aking it the preferred air-interface technologyfo r future mobile networks.

10.2.2 All IP NetworksStructureThe All-IP network has been tipped as the most probable technology to be synonymouswith fourth -gen eration network s. A sim plified All-IP network is shown in Figure 10.2.The most important difference between the All-IP network and existing 2G and 3Gnetworksis in thefunctionalityof the RNC and BSC, which is now distributed to the BTSanda set of servers and gateways. Various elements in this network are described below.

Figure 10.2 Example of an All-IP network


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IP-BTS:The functionality of the IP base station in this network is more than the func-tionality of base stations seen in earlier chapters. This base station performs also as amini-RNC/BSC, generally capable ofperforming layer1, 2 and 3functions. There aretwo types: serving BTS and drift BTS (equivalent to serving RNC and drift RNC in aWCDMA radio network).(IP) servers: The IP base station is not capable of performing all the RNC/B SC func tions,which are of network level. These servers handle the signalling between the networkelements. They are capable also of auto-tuning the parameters of the radio network,leading to better utilization of radio resources. As there are multiple technologies to behandled, a common server improves the performance and efficiency of the network incomparison with separate servers for each of the radio interfaces.Gateways (GW): These are responsible for the interactionof the IP-RAN and IP-Corenetworks. They are usually of two types, CS-GW and PS-GW, based on the type of call(circuit-switched or packet-switched) it is capable of handling.

Network Planning for theAll IP Netwo rkNetworkplan ning covers the access (transmission) network and thepacketcore network.Figure 10.3 sh ows a small box with the core network as a subset of the packet core netw ork,indicating th at voice traffic willstillbe apart of mobile communications,but itwill travelon thepacket core network(asopposed to thecircuit corein 2G and 3Gnetworks).

Figure 10.3 Network plan ning for an All-IP network

Processand Protocol OverviewThe transm ission netw ork plan nin g process is similar to that discussed in Chapter 8. Theprocess th us startswithdim ensioning and pre-planning, followed by detailed plann ing andimplem entation. The m ain steps in pre-planning w ill be:

dim ension ing the nu m ber of netw ork elements such as IP base stations, servers, PS- (andCS-) core network elements etc.dimensioning th ecapacities of open interfacestackling inter-operability issues between the GSM /UM TS/W LAN networks.Transmission and core network planning are more dependent on each other compared

with 3G network planning.As thedata traffic willb ehigher inquanti tyand quality,delaystudywill constitute an important part of the planning process.


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Figure 10.4 Protocol structure in an All-IP networkThemajor changein thetransmission networkis the use ofAll-IPfor the flow of traffic.Third-generation transmission networks use an ATM (asynchronous transfer mode) layer for

the flow oftraffic, whileanAll-IP network willnothavean ATM layer (see Figure 10.4).The major impact of this on transmission network dimensioning is reduced overheads.Overheads in thedata link layer will depend on the media. The IP (version 6)layer takesoverfrom ATM layerinthese networks.

10.2.3 WirelessLocal area NetworksPerformanceA wireless local-area network (WLAN) is a flexible datacommunication system, beingan alternate to existing wired LANs. This technology removes the hassel of taking wiresan d cables to and from equipmentin an office environment.The Instituteof Electrical &Electronic Engineers developed the standards for WLAN, specified in IEEE 802.11. Theinitial stan dards specified an operating frequen cy band of 2.4 GHz and a theoretical datarateof up to 11M bps. S ubsequent issuesof thestan dards have increased thecapacityof theW LAN to 54 M bps, in the same frequency band.W hat is the expected role of W LA Ns in fourth-generation networks? It is expected thatW L A N s will complement the existing 3G and All-IP 4G networks in high-density areanetworksby providing similar services at an even higher bandwid th (compared w ith mature3G and 4G radio networks). The technology isconsidered to be best suited to low-usagemobileuserswhow ant high data ratesin anindoor setting. This also mean s thatthemobileequipment should have the flexibility to choose the access technology at any given time,dependingon theenvironm ent.Network Planning for a WLANNetworkplanningisexpected tofocus mainlyonindoor coverage.Theprincipal aspectsofth epre-plan ning phase are:

the area for which the network is plannedsubscriber database information


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coverage and capacity requirementsthenumber ofchannelsthatcan beused (e.g. 13 inEuropeand 11 in the USA)the num ber of channels that can be used simu ltaneously with out interferencepropagation conditions (e.g. multipath in an indoor environment)equipment data (e.g. antenna gains and transmitted pow er)th eair-interface radiolinkbudget.

Based on these factors, coverage, capacity and q uality can be calculated.A WLAN network should provide coverage for 100% of the area for which it is beingplanned. M ostof theissues tha twehave seeninearlier chapterson radionetwork planning -such ascoverage thresho ld, signal quality,C/Ietc.- willbeinvolvedinplan nin g coverage,butwith more stringent requirements. M ethods to improve coverage in clude increasing thepower levels, incorporating diversity schemes etc.Frequency planning is another area of challenge in WLAN networks. As the numberof channels available is less than the capacity likely to be demanded, frequency planningbecomes a crucial task. As frequencyre-use becom es lower, thequality(and hence through-put)becomes lower. One rule of thum b could be to plan these n etworks with a frequencyre-use ofmore thanunity.

10 3 CHALLENGESIN 4GWIRELESS NETWORKSTwo main challenges need to be addressed before fourth-generation networksbecome areality. The first concerns accessibility to different types of cellular network. The secondconcerns how to maintain the desired end-to-end QoS for traffic that has varying require-ments of bandwidth, bit rates, channel characteristics etc., and especially the handoverdelays, which are a cause ofworry. During th e handover process, mobile subscribers areexpected tofaceadrop in the QoS level.Fourth-generation networksare still 'unclear' from th eperspective ofdefining th e net-work planning processes.This is partly because the evolution of these 4G networks is notdriven only by the mobiles indu stry. M oreover, stand ards-d efining bodies like th e IEEEare still in the process of producing standard recommendations. A major challenge is theplann ing of handovers not only between different generations of netwo rks but also betweendifferent technologies of the same generation (All-IP to WLAN etc.), while maintainingthe QoS standards.

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Chapter10_4G Network Planning