Radio network planning and optimisation for umts 2nd edition phần 4 ppsx

To start operating the network, one would begin typically with just one carrier in amacro-cellular layer to provide continuous coverage.. How the performance of a hierarchical WCDMA netw

which means that the MS generates only a very small noise rise compared with the noisefloor of about103.1 dBm (assuming a noise figure of 5 dB).

The MCL problem can naturally also be encountered when an MS of a secondoperator is coming too close to the first operator’s BS The difference, however, isthat the MS is not power-controlled by the BS it is approaching If the twooperators have co-sited their BSs this is not critical, since then the second operator’s

BS will command the MS to lower its power In an ideal case there would not be anyproblems, since the operators are using different frequency carriers and there would be

no interference between them In reality, however, there are only finite values for ACSand ACLR (see Section 3.2.4) Assuming values of 33 dB and 45 dB, respectively, thecoupling, C, between the carriers becomes:

C¼ 10
log10ð1033=10þ 1045=10Þ dB ¼ 32:7 dB ð3:73ÞThis means that if the own MS and the other operator’s MS are transmitting with thesame power, the interference received from the latter is about 32.7 dB less than thatgenerated by the MS of the own system The worst case scenario in the MCL problem,however, happens when some MS of the second operator is transmitting with itsmaximum power at the MCL distance from the BS of the other operator Thishappens, for example, when the sites are not co-located In an extreme situation onesite is at the border of a cell of the other operator’s network If then an MS is movingtowards that border and in doing so it is approaching the first operator’s BS, it istransmitting with full power in the near vicinity of the first operator’s BS, as can beseen in Figure 3.26

With a maximum MS power of 21 dBm, 53 dB for MCL to the micro-BS andcoupling between the carriers of C¼ 32.7 dB, the received level at the micro-BS can

be estimated as:

21 dBm 53 dB  32:7 dB ¼ 64:7 dBm ð3:74Þ

Operator 2 Micro cell high TX power

Operator 1 Macro cell

Signal

ACI

Operator 1 MS dead

zone

Operator 2 Micro cell

Signal

ACI

Operator 1 MS, max TX power

If the background noise level is103.1 dBm, the micro-BS would suffer a 38.4 dBnoise rise from one macro-user, which is located in the radio sense at the MCL distancefrom the micro-BS – i.e., such a macro-user would completely block the micro-BS.Next we calculate the situation on the downlink: consider that the micro-BS istransmitting with even minimum power of 0.5 W (27 dBm); then the received interfer-ence at the MS in the adjacent channel is:

27 dBm 53 dB (MCL)  32:7 dB (ACS) ¼ 58:7 dBm ð3:75ÞAssuming a speech service (processing gain of Gp¼ 25 dB) with an Eb=N0requirement at the MS of 5 dB and an allowed noise rise in the macro-cell of 6 dB,the maximum allowed propagation loss, Lp, to keep the uplink connection working is:

Lp¼ 21 dBm  5 dB þ 25 dB  ð103 dBm þ 6 dBÞ ¼ 138 dB ð3:76ÞAssuming a downlink transmit Eb=N0 requirement of 8 dB, the transmit power, Ptx,would need to be:

Ptx¼ 58:7 dBm þ 8 dB  25 dB þ 138 dB ¼ 62:3 dBm ð3:77ÞThis simple example shows that clearly in these cases the downlink is the weaker link –i.e., before coming too close to a micro-BS, the connection of a macro-MS will bedropped due to insufficient downlink power and it cannot block the micro-BS

Dead zones are another problem that can occur due to MCL problems A dead zone is

an area in which either the BS in the downlink or the MS in the uplink does not haveenough transmit power to maintain the QoS requirements of the other end Whenentering such an area an existing connection is lost and it is not possible to establish

a connection from that area One possible scenario where a dead zone can arise is again

in a multi-operator environment, if an MS from one operator is approaching at the celledge a (micro-) BS from another operator that is transmitting with full power Then theown BS does not have enough transmit power to overcome the interference generatedfrom the second BS This will be the case in a certain area around the second BS.Alternatively, or simultaneously, it might happen that the MS can no longer reachits own BS Due to a smaller MCL, the problem is more severe around a micro-BSthan around a macro-BS Additionally, the link loss from the cell edge to the BS isbigger in macro-environments Therefore, the most typical case for a dead zone will befor an MS of a macro-operator around the BS of a micro-operator However, itdepends on the scenario whether this MS will first lose its connection or whether itwill first block the uplink of the micro-BS An example of dead zones can be seen inFigure 3.27

3.6.4.1 Two Macro-cellular WCDMA Networks in an Urban Environment

In earlier work published in the field [41] and [42] the simulation scenario has beenrather unrealistic It is rather unlikely that in an (dense) urban area one operator would

choose to employ a micro-cellular network modelled with a Manhattan grid, whileanother operator would see it feasible to provide services with a macro-cellularnetwork.

This section describes the network simulation results of a study on the mutualinfluence of two macro-cellular WCDMA radio networks when operating in thesame area Both operators’ networks were of macro-cellular type, located in anurban environment in the city centre of Helsinki (Finland) Both operators wereassumed to have the same traffic and QoS requirements

The first phase of the analysis considered the two operators’ networks to beindependent from each other – i.e., without experiencing the influence of externalinterference from the other operator’s network In the second phase, the influence ofthe interference leaking from one operator’s network to the other’s was taken intoaccount by filtering the transmit powers from one operator to the other In thewhole study the two operators were considered to operate in immediately adjacentchannels separated by 5 MHz No other neighbouring channel interference was takeninto account The values of the minimum transmit power for the mobiles and the filtersettings were chosen on a best guess basis, as their standardisation was not finished atthe time of the study

Urban Simulation Case

In the urban simulation case a 9 km2 area in the city centre of Helsinki was analysed.The dimensioning proposed 13 sites (38 sectors) for the coverage and the requiredcapacity Because in reality some 20% of the total area is water, the actual networkplanning was done with 32 sectors, of which 31 used 65/17.5 dBi sector antennas andone 11 dBi omni-antenna The selected antenna installation height was from 16 m to

Figure 3.27 Example of downlink link power needed for a macro-operator’s network Alsovisible are some dead zones, where the maximum link power is not sufficient for good enoughquality of service

20 m and the propagation loss was calculated with the Okumura–Hata model, with anaverage area correction factor of6.3 dB For users inside the buildings an additionalpropagation loss of 12 dB was added Two independent network layouts were created.The network scenarios can be seen in Figure 3.28.

The system features used in the simulations are from [37], except the chip rate whichwas modified to 3.84 Mcps The multi-path channel profile was the ITU Vehicular Achannel [29] For the soft handover window a value of5 dB was used – i.e., all sectorswhose received P-CPICH are received within5 dB of the strongest P-CPICH are inthe active set The maximum allowed uplink loading was set to 75% Other relevantparameters applied in the simulations are listed in Table 3.31 The traffic requirementswere as in Table 3.9

Simulation Results

In this section results from the urban simulation case are collected The numberspresented are averages over three different MS distributions following the trafficrequirements of Table 3.9 Table 3.32 lists the uplink coverage probabilities Therequirements are well-met, except that the 384 kbps coverage is slightly too small

If a second operator is present, coverage does not drop significantly

Table 3.33 gives an overview on the MS transmit powers in terms of maximum andminimum powers used, as well as the 50, 75 and 95 percentiles In this case, too, nosignificant increase is noticed when introducing the influence of a second operator.Mobiles using their minimum allowed transmit powers indicate that there could besome problems in the network arising from excessive MCL, though no consequences,such as downlink dead zones, have been observed

Table 3.34 shows the transmit powers in the downlink Statistics from both thesingle-link powers and the total transmit powers are collected If a second operator is

Figure 3.28 Used network scenarios in the urban case

introduced, transmit powers increase slightly, though no dramatic effects could benoticed.

In Table 3.35 the average number of users per cell, the uplink load, the averagenumber and type of links per cell and the soft handover overhead are given Again,these results indicate that with the chosen filter values no significant influence from theneighbouring operator is experienced

Table 3.32 Uplink coverage in urban case

Table 3.33 Mobile station transmit powers in the urban case

Reproduced by permission of IEEE.

Table 3.31 Parameters used in the simulations

Shadow fading correlation between sites/sectors 50%/80%

Filter settings – Equations (3.58) and (3.60)

a In this study, the minimum transmit power of the mobile station was 44 dBm In 3GPP standards this value was adjusted later to 50 dBm.

Reproduced by permission of IEEE.

In this study the influence of two operators on each other in a macro-cellularenvironment was investigated for an urban area Owing to the relatively tight filtersettings describing the mutual influence, network performances did not suffersignificant degradation Almost the same performance with and without the secondoperator was achieved The biggest degradation was observed for the outageprobabilities, but the changes were not too dramatic as the outage was only slightlyincreased In this urban study none of the so-called dead zones could be observed Oneexplanation for this could be that the link losses were calculated using an Okumura–Hata model without LOS check, so the minimum link losses were bigger than theminimum coupling loss required to avoid the problem The result could, however, bedifferent if an LOS check were used, especially in a scenario where there are BSs of twooperators aligned along streets or even highways The same reason lies behind theobservation that there was no significant difference in performance whether cells ofdifferent operators were almost co-located or whether they were positioned at eachother’s cell edge Another case in which networks are located in a suburban area can

be found in [43] Those results indicate the same behaviour in terms of ACI

3.6.4.2 Macro- and Micro-cellular WCDMA Networks in an Urban Environment

In this ACI exercise the two networks comprised one macro- and one micro-cellularlayout, operated on adjacent carriers servicing the same urban area (downtown

Table 3.35 Other results from the urban case

handover12.2 kbps 64 kbps 144 kbps 384 kbps overhead

Reproduced by permission of IEEE.

Table 3.34 Base station transmit powers in the urban case

Helsinki) as in the previous section with sufficient capacity and coverage Thedimensioning in this case suggested that the macro-operator has 32 cells and themicro-operator 46 cells in an area of about 4 km2 In the simulations the basic ideawas that each operator optimises its network first so that the outage was below 2%,without considering the other operator Therefore, the cell plans are totallyindependent In the real case the parameters could be optimised in a more efficient way.The propagation environments were calculated using a ray-tracing program for themicro-cell scenario and the Okumura–Hata model for the macro-cell scenario In thestudy the micro-/macro-scenarios were first analysed independently Then the scenarioswere combined and the interaction of these two operators in the form of interferencewas deduced Both network-based indicators and cell-based indicators were of interest.The general simulation parameters are listed in Table 3.36 These serve as defaultvalues, if not stated otherwise, in the simulation cases.

3.6.4.3 Simulations in Helsinki with 32 Macro-cells and 46 Micro-cells

Figure 3.29 shows the cell plans used in the simulation together with the studied area.For each simulated case three snapshots with random positions of MSs were used Onaverage, 20, 25, 30 and 35 users per cell were input for the macro-operator and 55, 65,

75 and 85 users per cell on average for the micro-operator

Table 3.36 Some general simulation parameters

Shadowing standard deviation/correlation between BSs 7 dB/0.5 7 dB/0.5

6674400 6674800 6675200 6675600 6676000

Figure 3.29 The macro- and micro-operators’ cell plans

Simulation Results

This section and the figures that follow give the main simulation results for macro- andmicro-operators with and without the other operator present Service probability(number of users served after iterations divided by initial number of users), uplinknoise rise and BS total transmit power are shown In addition, performance has beenstudied with two settings of the maximum traffic channel power for a single link in thedownlink: 5.5 dB below CPICH (left diagrams) and 0 dB below CPICH (rightdiagrams) The latter corresponds to an aggressive parameter setting to avoid deadzones All the curves show averages from all three snapshots and the powersaveraged over the cells The x-axis is always ‘Number of users’ or ‘Number of servedusers’: this means on average per cell, as the traffic was generated uniformly onto thearea For the macro-cells only ‘inner cells’ on the area were included in the cell-basedanalysis to avoid bias from border effects

From the simulation results one can see that there is always a significant loss ofdownlink performance for the macro-operator If the loading in the macro-operator’snetwork is low, an aggressive parameterisation (allowing high transmit power for thetraffic channels) may help slightly and make the micro-operator’s life slightly moredifficult, but for high loading it does not help Also one can see that if the macro-operator uses aggressive parameterisation the micro-operator can suffer in the uplinkbecause of a slightly bigger noise rise

Simulation Results for the Macro-operator (Figures 3.30–3.32)

Number of users per cell (input)

obability (%) Macro aloneMacro with micro

Figure 3.30 Service probability of the macro-operator when alone and with the micro-operator

Macro with micro

Figure 3.31 Uplink noise rise of the macro-operator when alone and with the micro-operator

30 35 40

Figure 3.32 Total base station transmit power of the macro-operator when alone and with themicro-operator

No pure capacity effects can be seen from these simulations – i.e., moving thepole capacity – but according to the results one could think of adding the effect

of the adjacent carrier, if cell planning between the macro- and micro-layers is coordinated, as an offset to the noise level in dimensioning In the optimisationprocess the other operator on the adjacent carrier should be taken into account toavoid local dead zones

un-Simulation Results for the Micro-operator (Figures 3.33–3.35)

85 90 95 100

Figure 3.33 Service probability of the micro-operator when alone and with the macro-operator

0 1 2 3 4 5

Number of served users per cell

Micro alone Micro with macro

Figure 3.34 Uplink noise rise of the micro-operator when alone and with the macro-operator

25 30 35

Figure 3.35 Total base station transmit power of the micro-operator when alone and with themacro-operator

Conclusions

The operator is more affected by the micro-operator than vice versa The operator can lose downlink coverage near the micro’s BSs The micro-operator’s uplinknoise rise can be slightly higher because of the macro’s MSs if the macro-operator usesaggressive downlink power allocation (giving high power for a single MS) No clearcapacity effects were found but only coverage effects Downlink dead zones can occur insuch places where the macro-cell boundary is close to the micro-operator’s BS (themicro–micro case is probably easier, since in most cases the cell boundaries areinside buildings for both operators) The problem is made worse by a larger averagepath loss difference

The simulations in Section 3.6.4 prove that with proper radio network planning theseverest problems with ACI within WCDMA can be avoided to such a level that theWCDMA network performance does not suffer significant degradation This sectiongives a summary of the most popular radio network planning means to alleviate ACIproblems

BS and antenna locations:

e in macro-cellular-only environments, the natural distance between the MS and BS

is normally large enough to provide sufficient decoupling In mixed environments,however, when micro-cells and pico-cells are present, the minimum coupling loss isusually not enough to avoid interference problems In such cases it is desirable thatoperators try to co-locate BSs, since then there is no possibility that an MS that isclose to the cell edge of one operator comes close to the BS of the other operator;

e if co-location is not achievable then one means to increase the MCL is to deploy theantennas in a position as high as possible above the MS;

e other possibilities to reduce interference between operators are proper selection ofthe antenna direction and the correct tilting of the antennas

Base station configuration:

e after selection of the correct sectorisation to meet the coverage and capacityrequirements, for each configuration there exists an optimum antenna beamwidth

Antennas that are too wide cause too much interference to adjacent sectors,naturally not only in the same frequency but also in adjacent ones;

e in case other means are not possible or do not achieve the required coupling loss, it

is still possible to reduce artificially the sensitivity of the BS receiver by increasingthe noise figure This technique, called desensitisation, reduces the effect of ACI butunfortunately also makes the receiver less sensitive to wanted signals, which results

in reduction of coverage area and increased battery consumption in the MS Thisapproach, therefore, is normally applicable only in small micro- and pico-cellswhere coverage is not an issue

Inter-frequency Handovers (IF-HOs):

e an operator can apply a second frequency in interference problematic areas and,for example, provide the possibility of Inter-frequency Handover (IF-HO) tothe less interfered frequency, such as for services with especially high QoSrequirements (service-based IF-HO)

Inter-system Handovers (IS-HOs):

e if there is a neighbouring system, such as a 2G GSM system, available, system Handovers (IS-HOs) can be performed in such areas where there aredead zones Of course, this requires the affected mobiles to be multi-system-capable

Inter- Guard bands:

e the standards allow the centre frequencies of the different channels to be adjusted

in a 200 kHz raster If at least one operator has two or more frequencies available,

he can decide to select a different carrier spacing than the nominal 5 MHz between

at least the two frequencies closest to the other operator By applying this method aguard band to the frequency band of the neighbouring operator’s frequency bandcan be generated, which can help to alleviate ACI problems (see Figure 3.36)

3.7 CELL DEPLOYMENT STRATEGIES

As outlined in previous sections of this chapter, there are certain issues to be taken intoaccount when deploying multiple frequencies and layers in a network This sectiondiscusses tasks that need to be done for deploying operational 3G RANs, and the

Figure 3.36 Reduction of ACI by creating a guard band with reduced carrier spacing

strategies for utilising frequencies if Hierarchical Cell Structures (HCSs) are used.Section 3.7.1 highlights the general process of rolling out a network and presentssome differences between the strategies for an operator who is starting anew in anarea (a ‘greenfield’ operator) and those for an operator already running a networkfrom a previous generation – e.g., a GSM system.

In 3G systems, due to the variety of services and different capacities of differentlayers, an operator needs to have a clear vision about the deployment strategy of thedifferent cell layers Micro-cells, for example, may be necessary to accommodatehotspots with increased capacity requirements, but they may also be needed tosupport higher bit rates On the other hand, before taking micro-cells into use, it isvery likely a continuous macro-cell layer is already present The simplest way to operatedifferent cell layers is to have them on different frequency carriers, but this is not theonly possible scenario that can be deployed Section 3.7.2 discusses various issues ofhierarchical cell structures and studies the influence of different scenarios on networkperformance when two frequencies are available with and without reusing them indifferent layers of a hierarchical WCDMA network

Rollout refers to a process that has to be completed in order to generate an operationalnetwork 3G systems set high requirements for rollout, since effective and rapid rolloutconfers competitive advantage The performance of UMTS must be at least as high asthat provided by current systems The services provided by UMTS must outperform theservices provided currently Therefore, effective means for integrating WCDMAnetworks are required The prompt startup of network operation and aggressiveintroduction of new services could be the differentiating factor between twooperators Rollout and network development-related issues to be considered early inthe business planning phase include:

Services to be provided

Evolution of the services and the network (see Section 3.7.2):

e usage of carriers;

e usage of HCSs

Provisioning of indoor coverage and services

Services to be provided will have a direct impact on site density Furthermore,capacity limited networks should be planned with multiple carriers or with HCSs.The extension plan for the network must be considered so that new services will beintroduced as seamlessly as possible, preferably without major changes in the networkconfiguration

For 3G greenfield operators, rollout includes radio network planning, site acquisition,packet core network planning, construction work, commissioning and integration ofthe network elements In the radio network planning phase, dimensioning and siteacquisition information is combined with the traffic and service quality requirements,see Section 3.1 The site density and configuration for the network regions aredetermined, and the work schedule and instructions for civil engineering andequipment installation are generated for site deployment Transmission requirements

are estimated and transmission planning is performed A part of the radio network andtransmission planning is the preparation of parameter files and templates for the ATMlayer and RNC After installation, the sites can be commissioned with the parameterfiles and commissioning reports The result of the installation and commissioning visit

to each site is an operating network element with a connection to an Operation andMaintenance Centre (OMC), enabling effective networkwide mass operations for theradio network part Now the radio parameters can be downloaded and the sites madeoperational When the network plans are ready and the rollout project tasks are inplace, effective tools are required to implement the plans quickly, cost-effectively andwithout manual errors A successful rollout ends when the network is ready andoperational, and the monitoring of the network performance can start As the config-uration of installed network elements is based on predicted network behaviour anddefault parameter settings, it is usually necessary not only to monitor and report on theactual performance but also to react fast with appropriate performance optimisation.Immediate feedback from network performance is also needed for providing informa-tion for network development tasks and plans More about measurement-based con-figuration tuning in a Network Management System (NMS) can be found in Sections7.3.3 and 9.3

For GSM operators the radio network planning phase is slightly different tion (location, height, possible antenna directions, etc.) on sites that will be reused isneeded as input for 3G planning Data from the existing GSM network can be effec-tively utilised GSM traffic density information can be used to indicate traffic hotspotsalso in WCDMA IS-HO (see Section 4.3.4) gives an opportunity to start WCDMAimplementation selectively GSM can be used to extend coverage, introducingWCDMA initially only in areas where service requirements so demand, such as citycentres or high-density business areas Furthermore, experience of the cell coverageareas and interference situation in GSM can be used in planning WCDMA In thecase of co-siting, GSM interference problems will indicate possible interference andthus also capacity problems in the WCDMA network More about co-siting can befound in Chapter 5

In most UMTS frequency allocations done until today, operators have been allocatedtwo or more Frequency Division Duplex (FDD) carriers Spectrum allocation affectsthe operators’ WCDMA deployment scenarios, and the use of HCSs In principle, anallocation of one pair of FDD carriers allows the operation of only a single networklayer Two paired carriers can cater for a two-layer structure, such as a macro-cell layertogether with a micro-cell or pico-cell layer A full hierarchical cell structure, with eachlayer operating on its own carrier, can be built with three carriers With four or morecarriers additional capacity and flexibility in network design is achieved In hotspotareas highly loaded cells can be given extra capacity by adding another carrier to thecell, which would be more effective than increasing the BS transmission power (seeSection 6.4) In order to support HCSs and handovers between carriers, IF-HOs arerequired An example for a typical evolution path in a 3G network is presented inFigure 3.37

To start operating the network, one would begin typically with just one carrier in amacro-cellular layer to provide continuous coverage This applies especially to agreenfield operator who cannot rely on an existing GSM network for coverage orcannot partner with an existing GSM operator Later, a second carrier (and possiblymore) is deployed to enhance capacity This second carrier can then be added to themacro-cellular layer to create high-capacity sites or can be used to build a micro-layer.

In its first phase, the micro-layer typically is deployed only in traffic hotspots or wherehigh bit rates are needed In a further stage of the network, then, both layers are givingcontinuous coverage in a specific area, and if further capacity is needed more carriersmust be deployed Again, the simplest way is to use a third frequency and assign iteither to the macro- or the micro-layer In cases, however, when an operator will belimited to two frequencies only, he will need to start to reuse a carrier that has alreadybeen used in another network layer

The required capacity and coverage tradeoff needs to be carefully considered Within

an HCS in a WCDMA network, the micro-layer provides a very high capacity in alimited area, whereas the macro-layer can offer full coverage but with reducedthroughput only Typical air interface capacities are about 1 Mbps/carrier/cell for athree-sectored macro-BS and 1.5 Mbps/carrier/cell for a micro-BS

Another important issue is whether to support mobiles moving at high speeds

If there is no such need, the easiest way to continue is to sacrifice the macro-layerand assign both frequencies to the micro-layer This alternative might, however,result in increased investment, which has to be evaluated carefully If high-mobilityusers have to be supported in a micro-cell layer there would be too many handoversbetween the cells, and it is therefore always beneficial to have an ‘umbrella’ macro-layerfor those users Then the strategy to further increase capacity is to reuse one frequency

in the other layer How the performance of a hierarchical WCDMA network is affected

by reusing carrier frequencies in different layers is the subject of the study inSection 3.7.2.2

continuous macro layer with frequency f1 continuous micro layer with frequency f2

continuous macro layer with frequency f1 continuous micro layer with frequency f2

3.7.2.1 Network Operation Aspects

There are certain aspects of WCDMA characteristics whose consideration is crucialfrom the point of view of frequency reuse They are next recapped briefly

Interference

It is impossible to consider any part of a WCDMA system in isolation Changes to apart of the system may induce changes over a large area For example, GSM systemsare basically ‘hard blocking’ so that their ultimate capacity is limited by the number ofchannel elements, and blocking occurs when all frequencies and timeslots are fullyoccupied WCDMA systems differ fundamentally from GSM in that the samespectrum is shared between all users

In WCDMA, capacity limits can be reached before all channel elements in all cellsare in use The limit is reached when the QoS of the network degrades to a minimumacceptable level that depends on the interference levels in the system In WCDMA,capacity and coverage can be limited by uplink and downlink interference In the uplinkthe interference comes from other MSs, and in the downlink from adjacent BSs.Although the number of sources for downlink interference is low, the interferingpower is relatively high As the interference level experienced by a mobile depends onthe path loss to all BSs, users suffer from different interference depending on theirlocations in the network [44] Downlink interference levels are high even if cell load

is low, because the BSs always have to transmit the downlink common channels

In the downlink, the total transmitted power is shared between the users In theuplink, there is a maximum interference level tolerable at the BS receiver Each usercontributes to the interference, and it is shared between the users in the cell If theperformance of some links can be improved, the power levels required in both theuplink and downlink and the interference generated are immediately reduced With acommon shared power resource, this results in reduced interference levels for all users,which can be further utilised as increased capacity and coverage, or improved linkquality

Soft Handover

In soft handover a mobile is located in an area where cell coverage of two (or more)sectors overlap, and the communication between the mobile and the BS occur via two(or more) air interface channels Soft handover improves the performance of hardhandover through the exploitation of macro-scopic diversity In the downlink, signalsreceived from different BS sectors are combined in the MS by MRC in RAKEprocessing In the uplink, the signal from the MS is received at different sectors,which are combined in softer handover by using MRC and in soft handover byusing selection combining

Soft handover improves WCDMA system performance by minimising the receivedand transmitted powers when mobiles are close to cell boundaries Typically, softhandover probability is targeted to keep below 20–30%, since excessive softhandover connections decrease downlink capacity Each soft handover connectionincreases downlink interference to the network, and, if the increased interference

exceeds the diversity gain, soft handover cannot provide any benefits for system formance [45].

per-Pilot Power Adjustment

P-CPICH power allocation is another important task in WCDMA network design.Optimum pilot powers ensure coverage with minimum interference to neighbouringcells Excessive pilot powers will easily take too large a proportion of the totalavailable BS transmission power so that not enough power is left for traffic channels.The cell can collect distant users whose mobile transmission power is not enough toconnect to the BS, and which would more optimally be served by some other BS On theother hand, pilot powers that are too low may not provide wide enough pilot coverageand result in very small dominance areas Moreover, if link power limits are definedwith respect to pilot power levels, low pilot powers also restrict link powers Typically,approximately 5% of the total BS power is allocated to the pilot channel, and roughlythe same amount to other common channels

If the same carrier frequency is used at different network layers, a cell with higherpilot power easily blocks a nearby cell with lower pilot power As the micro- andmacro-BS total and pilot powers normally differ from each other by several decibels,micro- and macro-layer users on the same carrier may cause undesirable performancedegradation – e.g., due to the near–far effect This is shown in Figure 3.38

The mobile is connected to the macro-cell BS with higher pilot power, although thepath loss to the nearby micro-BS would be smaller Higher transmission power isneeded to compensate for the higher path loss, and the mobile introduces additionalinterference to the adjacent micro-cell (and the whole network) Therefore, it is nottrivial to assign a carrier used in one network layer to another one

Figure 3.38 A mobile is connected to the macro-cell base station (BS2) with higher received pilotpower, and increases uplink interference at the micro-cell base station (BS1)

If a mobile is in a location where numerous pilots are received with relatively equalsignal strengths, it may happen that none of the pilot signals is dominant enough toenable the mobile to start a call Pilot coverage from neighbouring BSs must overlap incell border areas to accommodate handovers However, each cell that has significantpower in the soft handover area will increase I0 and decrease Ec=I0 (energy of the pilotsignal divided by the total channel power) The total power in the channel includes themeasured pilot signal, pilots from other BSs, traffic and other channels from BSs andthermal noise Receiving too many pilot signals can degrade both capacity and quality,and can be prevented to a large extend by proper radio network planning It is essential

to create a network plan, where cells have clear dominance areas Some pilot tion aspects are discussed in more detail in [44] and [46]

optimisa-3.7.2.2 Case Study – Frequency Reuse in Micro- and Macro-cellular NetworksThe basic issue in WCDMA network design is to determine the cell and carrierconfigurations at which the interference and QoS targets for given traffic are met.Since capacity and coverage in WCDMA networks are coupled with each otherthrough interference, it is very difficult to consider any parts of a WCDMA networkseparately Simple analytical studies, such as in [2] and [47], can be used to estimateasymptotic limits or study regular and simplified network scenarios, but have limitedapplicability in actual radio network planning Such analyses often assume unrealisticassumptions or simplifications on traffic distributions, propagation models or cellpatterns that do not reflect the complexity of real planning In reality, uplink anddownlink interference levels are affected by each mobile with different propagationconditions, service in use, Eb=N0 requirements, soft handover situation, etc.Moreover, micro- and macro-cells and traffic distributions in urban areas do notreadily form a regular pattern that could easily be handled by analytical means.Some factors, such as soft handover probabilities, are treated as input parameters foranalytical approaches, although in reality one more often would expect them as outputs

of the planning process, or factors to be optimised Therefore, simulation methodsoften appear more appealing for network planning purposes In the following section

we have also adopted a simulation approach

Network Configurations

In this study a static radio network simulator supporting IF-HOs between carriers wasused to examine frequency reuse between micro- and macro-cellular layers in aWCDMA network It is described in [16] and [48] and in more detail in its specifications

at the weblink (www.wiley.com/go/laiho) The two-layered network this study is based

on is shown in Figure 3.39 It consists of a micro-layer of 31 cells (sectors), and amacro-layer of 18 cells (six three-sectored sites) Micro- and macro-layers have beenplanned independently of each other without considering the other layer’s sitelocations The average micro- and macro-cell densities are 2,respectively Both network layers provide (nearly) continuous coverage, so thatmicro-cells are not used only as capacity fill-ins under the macro-cellular network,which could initially be planned to provide coverage (in GSM, for example) Hencethe network can be considered to be in rather a mature deployment phase (see Figure

3.37) In case of continuous micro-layer coverage, macro-cells serve more like umbrellacells, which are best suited for high-speed users to minimise the number of handovers.Alternatively they can fill micro-cell coverage holes or collect users who, for loadreasons, for example, cannot be served by micro-cells Propagation data for link losstables for both micro- and macro-cells were calculated using a 3D ray-tracing model[49] Initially all users were connected to (micro-) carrier 1 If not heard, mobiles wereallowed to make an inter-frequency handover to carrier 2, if its pilot (P-CPICH) Ec=I0was sufficient In this study no code limitation (hard blocking) was considered.Initially, the micro- and macro-cellular networks were examined individually, andthereafter load balancing through inter-frequency handovers was allowed in a two-layerHCS A key finding characterising the network operation in both cases was thatmicro-cells were first limited in the downlink by the total available BS power,whereas in macro-cells the uplink loading was the first factor restricting the perform-ance Figure 3.40 shows the reference scenario and the frequency reuse scenariosstudied.

Performance of WCDMA networks where a macro-carrier is reused in micro-cells,and a micro-carrier is reused on macro-cells, are compared with that of a network with

an HCS, where micro- and macro-layers operate on their own carriers Tables 3.37 and3.38 show parameters used for mobiles and BSs in basic micro- and macro-cellnetworks, respectively When reusing a carrier on a different network layer, the pilotand total BS transmission powers were modified Cases and modifications are listedseparately in Table 3.39

Figure 3.39 Micro (m) and macro (M) base station locations Mobiles are uniformly distributed

in the polygon in all cases

Simulation Results

Figure 3.41 shows the service probabilities and Figure 3.42 the reasons for not servingmobiles As such, the figures are not fully transparent regarding the feasibility ofdifferent carrier reuse cases

User distributions among the carriers, other-to-own-cell-interference levels in theuplink, soft handover overheads, uplink loading and downlink transmission powersare shown in Figures 3.43–3.47 to give insight into the network operation in eachcase They are presented as functions of users served per sector, ‘sector’ referring toboth micro- and macro-sectors To avoid confusion, the number of sectors remainsunchanged throughout this study – i.e., 49 – although the number of cells changeswhen carriers are added to sectors In Table 3.40 some cell-specific results are alsogiven

f2f1,f2 f1,f2 f1,f2 f1,f2

Reuse of micro frequency in macro layer

continuous macro layer with frequencies f1 and f2 continuous micro layer with f1

Reuse of macro frequency in micro layer

continuous micro layer with frequencies f1 and f2 continuous macro layer with frequency f2

Reuse of macro frequency in selected microcells

continuous macro layer with frequency f2 continuous micro layer with frequency f1 selected microcells reusing macro frequency f2

Reference scenario

Reuse of micro-frequency in macro-layer

Reuse of macro-frequency in micro-layer

Reuse of macro-frequency in selected micro-cells

Figure 3.40 Hierarchical cell structures used in the study

Table 3.37 Parameters for mobiles (common in all simulations)

Table 3.39 Base station parameters in frequency reuse cases Note that in reality the total basestation power is pooled rather than split between the carriers.

(a) Micro f1, macro f2 (reference case)

(b) Micro f1, macro f1þ f2

(c) Micro f1þ f2, macro f2

Power for other common channels 21 dBm (per carrier) 30 dBm

(d) Micro f1þ f2 on selected cells, macro f2

Power for other common channels 24 dBm (per carrier) 30 dBm

Table 3.38 Parameters used in the simulations for micro- and macro-cells

Table 3.40 Served users, other-to-own-cell interferences, i, soft handover overheads, uplinkloadings and base station transmission powers for the cases listed in Table 3.39 The initialnetwork loading was 90 mobiles per micro-sector In cells with two carriers f1 is on the leftand f2 is on the right hand.

(a) Micro f1, macro f2

BS ID Downlink i Soft handover Uplink BS transmit

(c) Micro f1þ f2, macro f2 (cont.)

(d) Micro f1þ f2 on selected cells, macro f2

Figure 3.43 Served users on different cell layers (a), (b), (c) and (d) refer to the base stationconfigurations given in Table 3.39

Figure 3.44 Other-to-own-cell-interference, i (a), (b), (c) and (d) refer to the base stationconfigurations given in Table 3.39.

Figure 3.45 Average soft handover overheads (a), (b), (c) and (d) refer to the base stationconfigurations given in Table 3.39

Micro f1, Macro f1þ f2

In the reference HCS case 95% service probability can be provided for up to 110users per micro-sector Reusing a micro-carrier on all macro-cells does not bring anyimprovements in network performance Microcell users are mostly in the line of sight tothe base station, and interference levels are lower than in macro-cells due to betterphysical cell isolation (Figure 3.44) Consequently, throughputs in micro-cells aregreater than in macro-cells When a micro-carrier is reused on macro-cells, the bettercapacity of micro-cells is sacrificed for a worse solution, since an additional carrier onmacro-cells cannot compensate for the capacity reductions at micro-cells Users caninitially be connected also to macro-carrier 1 with higher pilot power, as depicted inFigure 3.38 Micro-carrier 1 now serves only

loading) of the users it serves in the reference HCS case (Figure 3.43) However, itsuplink loading and downlink transmission power levels have not decreased in the sameproportion as the number of users, as seen in Figures 3.46 and 3.47 and Table 3.40.Mobiles connected to macro-cells are required to transmit with higher power levels, astypically the minimum link losses to micro-cells are 53–55 dB, and to macro-cells over

70 dB Higher transmission powers increase the uplink interference experienced atmicro-cell BSs In addition, micro-layer users are seen as additional uplink interference

in macro-cells operating on carrier 1 As soon as carrier 1 macro-cells become fullyloaded in the uplink (Figure 3.46), macro-cells operating on carrier 2 and micro-cellsstart to collect more users Also, in the downlink the maximum transmission power isreached in many macro-cells (Figure 3.47), which pushes users to other carriers andlayers These can be seen in Figure 3.42 as major reasons for outages

Another factor deteriorating network performance, if a micro-carrier is reused inmacro-cells, is increased soft handover overhead (Figure 3.45) In this context softhandover overhead for a cell is defined as Number_of_secondary_users/Number_of_primary_users Secondary users are those mobiles in soft handover to the sector, towhich the sector is not the best server Primary users refer to the users to whom thesector is the best server Although in soft handover a mobile is using less transmit powerand therefore introducing less uplink interference, the call is handled by two BSs Ifused excessively, soft handovers decrease the overall capacity, as in the downlink theinterfering power is increased If a micro-carrier is reused in macro-cells, the softhandover overhead in macro-cells can be as high as 50–70%, and also micro-layersoft handover is increased to

comparison with the reference case Also the single-link power in the downlink hasbecome an important factor resulting in outages The macro-cell pilot power isdecreased by 3 dB when a micro-carrier is reused in macro-cells As maximum linkpowers in our examples are defined with respect to the pilot power level, consequentlythe link powers are affected In principle more power can be granted for a connection inthe downlink than in the uplink, because BS transmission power is much higher thanmobile output power Therefore, services requiring high bit rates can be given bettercoverage in the downlink, if desired By setting the link power limits properly, theuplink and downlink coverage areas can be balanced

Micro f1þ f2, Macro f2

In our example micro-cells as such are inherently limited by the available downlinkpower earlier than by uplink loading Also in the reference HCS case BS transmission

Figure 3.46 Average uplink loading (a), (b), (c) and (d) refer to the base station configurationsgiven in Table 3.39.

Figure 3.47 Average base station transmission powers (a), (b), (c) and (d) refer to the basestation configurations given in Table 3.39

power is clearly the most limiting factor reducing the network performance, as seen inFigure 3.42 Therefore, sharing the total available BS transmission power between themicro-cell carriers (Table 3.39(c)) increased the number of outages due to downlinktransmission power On the other hand, the number of outages due to link powerlimitations and uplink loading was decreased At a 95% service probability operatingpoint, the network where a macro-carrier is reused on all micro-cells can servemore users than in the reference HCS case The macro-layer is barely affected by theunderlying micro-cells operating on the same carrier Macro-cells serve more or less thesame number of users, as in the reference HCS case (Figure 3.43), and the soft handoveroverhead and other-to-own-cell-interference levels have not drastically changed (seeFigures 3.44 and 3.45).

Despite the users being handed over at a lower network loading to the other carrier,the reused macro-carrier on micro-cells is able to collect them, and the total number ofusers served on the micro-layer has slightly increased at a higher network loadingcompared with the reference HCS case, as can be seen in Figure 3.43 and Table 3.40.The situation is somewhat different from the scenario where a micro-carrier is reused

in macro-cells: now micro-cells operating on carrier 1, which is the network layer towhich the users are initially connected, are not interfered by macro-cells Therefore,their capacity can be fully exploited before inter-frequency handovers are made tocarrier 2 micro- and macro-cells, which are more subject to increased interferencelevels due to carrier reuse Micro-layer capacity could be best exploited if the total

BS power is not shared between the carriers, but instead the power is doubled whenanother carrier is added However, in terms of cost this is a much more expensivesolution, as another power amplifier is required, which also affects the BS size andinstallation efforts The problems of reusing a macro-carrier in a micro-cell are verylike those involved in embedding micro-cells in hotspot areas under a macro-cell layer,

as studied in [50] and [51]

Micro f1þ f2 on Selected Cells, Macro f2

Micro-cells do not benefit from the other carrier reused from macro-cells, if they stillhave unused capacity on their own carrier In that case those cells with the reusedcarrier that do not collect traffic only generate additional downlink interference, sincethey still have to transmit the power for CPICH and other common channels Figure3.48 shows the users served, BS powers and uplink loadings at relatively high networkloadings, when a macro-carrier is reused on all micro-cells In this case the micro-cellpower was doubled when the other carrier was added We see that only about 20% ofthe micro-cells benefit from the other carrier This is because inter-frequency handover

is made to carrier 2 only when carrier 1 cannot serve users, and many cells shown inFigure 3.48 have unused capacity

Micro-cells 8, 19, 21, 25, 28 and 31 (circulated in Figure 3.50) are selected to have asecond carrier reused from the macro-layer The BS configurations were given in Table3.39 The selected cells can also collect traffic on carrier 2, and are not located in theimmediate vicinity of a nearby macro-sector Sufficient distance (attenuation) from amacro-sector is required to ensure that, if inter-frequency handover is made, the reusedmacro-carrier is likely to collect those mobiles The selected cells can also establishreasonable dominance areas on carrier 2 Achieving clear cell dominance areas is

essential for efficient WCDMA network operation Dominance areas based on highestreceived pilot powers are shown in Figure 3.49 for micro-cells, and in Figure 3.50 forcarrier 2 cells, when a macro-carrier is reused on micro-cells.

In the plain micro-cell network cells are easily distinguishable from each other, as thesurrounding buildings provide good physical isolation When a macro-carrier is reused

on micro-cells, the cells are more fragmented in shape, have unequal sizes and mayoverlap each other The effects of pilot power differences between micro- and macro-cells are distinguishable, for example, in micro-cells 7 and 12 They suffer from thenearby macro-sector, showing diminished dominance areas compared with the network

Figure 3.49 Downlink dominance areas based on highest received pilot power for f1 micro-cells

in a hierarchical cell structure network

Figure 3.48 Served users, uplink loadings and downlink transmission powers for a networkwhere a macro-carrier is reused in all micro-cells The black line across the right-hand figuredenotes the minimum power level required for pilot and other common channels The networkwas initially loaded with 4340 users – i.e., 140 users per micro-sector The service probability inthis case was 93%

with HCS It is noticeable that reusing a macro-carrier only on selected micro-cellshardly increases the soft handover and other-to-own-cell-interference levels in macro-cells compared with the HCS network, as seen in Figures 3.44 and 3.45 Micro-cells oncarrier 2 are affected more than macro-cells, but they still have rather moderate softhandover overheads and other-to-own-cell-interference levels at higher network loading– i.e., over 50–60 served users per sector – when they start to collect traffic If a micro-cell collects a lot of traffic, but is located very close to a macro-cell, macro-carrier reuse

is not worthwhile Micro-cell 12 is an example of such a situation Although it collectsplenty of users, the nearby macro-sectors 13 and 15 nearly fully disable carrier 2 onmicro-cell 12, see Table 3.40 If BS transmit power limits micro-cell performance,decreasing the micro-cell pilot power could be a better solution instead If the pilotpower coverage is still adequate, the benefit is twofold With smaller pilot power themicro-cell dominance area is reduced, and it attracts less users Moreover, by decreasingpilot power, more power is left for traffic channels

3.7.2.3 Concluding Remarks

This study indicates that the HCS of a WCDMA network can be divided in certainmicro- and macro-cell scenarios, which could occur during WCDMA networkdeployment phases The most important thing to avoid is excessive increase ofinterference levels in both the uplink and downlink, and it is essential to keep soft

Figure 3.50 Downlink f2 dominance areas for f2 micro- and macro-cells, when macro-carrier f2

is reused on the micro-layer Circulated cells are examples of micro-cells, which can establish cleardominance areas and collect traffic under the overlying macro-layer The pilot power differencebetween micro- and macro-cells is 6 dB Dominance areas of, for example, micro-cells 7 and 12(shown with arrows) have shrunk considerably compared with Figure 3.49

handover areas restricted so that carrier reuse is able to bring some performanceimprovements Therefore, the selection of cells for carrier reuse may be limited inorder to avoid increased interference levels in the network In the reuse scenariosstudied, the best capacity enhancements were achieved by reusing a macro-layercarrier in such highly loaded micro-cells, which were far enough away from macro-cells operating on the same carrier By this, the interference levels could be keptreasonable, and the micro-cell load could be balanced between the two carriers Theresults are based on snapshots of a static network simulator, and therefore do not takeinto account true mobility effects In reality, problems may be encountered when, forexample, a high-speed mobile connected to a macro-cell moves towards a micro-celloperating on the same carrier frequency As the handover is a relatively slow process,the mobile may get deep into the micro-cell before the handover is completed The fastand accurate operation of power control is crucial so that micro-cell users can quicklyadjust their transmit powers to cope with the high-power interferer In the radionetwork planning phase, operators can design different network layers to accommodatedifferent types of traffic; handovers between cells can be directed, restricted or evencompletely prohibited.

[3] Sipila¨, K., Laiho-Steffens, J., Ja¨sberg, M and Wacker A., Modelling the impact of the fastpower control on the WCDMA uplink Proc VTC 1999 Spring Conf., Houston, Texas,May 1999, pp 1266–1270

[4] Sipila¨, K., Ja¨sberg, M., Laiho-Steffens, J and Wacker, A., Soft handover gains in fastpower controlled WCDMA uplink Proc VTC 1999 Spring Conf., Houston, Texas, May

[9] 3GPP, Technical Specification 25.141, Base Station (BS) conformance testing (FDD),v.5.9.0, September 2004

[10] Pedersen, K.I., Toskala, A and Mogensen, P.E., Mobility management and capacityanalysis for high speed downlink packet access in WCDMA Proc VTC 2004 FallConf., Los Angeles, California, September 2004, pp 3388–3392

[11] 3GPP, Technical Specification 25.213, Spreading and Modulation (FDD), v.5.5.0,December 2003

[12] 3GPP, TSG RAN Technical Report 25.858, High-speed Downlink Packet Access: PhysicalLayer Aspects 3G, v.5.0.0, March 2002

[13] Holma, H and Toskala A (eds), WCDMA for UMTS: Radio Access for Third GenerationMobile Communications(3rd edn) John Wiley & Sons, 2004, chapter 11.

[14] Kolding, T.E., Pedersen, K.I., Wigard, J., Frederiksen, F and Mogensen, P.E., High-speeddownlink packet access: WCDMA evolution IEEE Vehicular Technology Society (VTS)News, 50(1), February 2003, pp 4–10

[15] http://www.3gpp.org/

[16] Wacker, A., Laiho-Steffens, J., Sipila¨, K and Ja¨sberg, M., Static simulator for studyingWCDMA radio network planning issues Proc VTC 1999 Spring Conf., Houston, Texas,May 1999, pp 2436–2440

[17] Dehghan, S., Lister, D., Owen, R and Jones, P., WCDMA capacity and planning issues.IEE Electronics & Communication Engineering Journal, June 2000, 101–118

[18] Labedz, G and Love, R., A new time-based outage criterion for the forward and reverselinks of DS-CDMA cellular systems Proc VTC 1998 Conf., Ottawa, Canada, May 1998,

pp 2182–2186

[19] Okumura, Y., Ohmori, E., Kawano, T and Fukuda, K., Field strength and its variability

in the VHF and UHF land mobile service Review Electronic Communication Laboratories,16(9/10), 1968, pp 825–873

[20] Urban transmission loss models for mobile radio in the 900 and 1800 MHz bands COST

[23] Berg, J.E., Path loss and fading models for micro-cells at 900 MHz COST 231, TD(92)95,Helsinki, September 1992

[24] Wei, Q.X., Gong, K and Gao, B.X., Ray-tracing models and techniques for coverageprediction in urban environments Proc APMC 1999 Conf., Singapore, November/December 1999, pp 614–617

[25] Erricolo, D and Uslenghi, L.E Two-dimensional simulator for propagation in urbanenvironments IEEE Transactions on Vehicular Technology, AP-50(4), July 2001,

pp 1158–1168

[26] Daniele, P., Frullone, M., Heiska, K., Riva, G and Carciofi, C., Investigation of adaptive3D micro-cellular prediction tools starting from real measurements Proc ICUPC 1996Conf., Cambridge, Massachusetts, September/October 1996, pp 468–472

[27] Ji, Z., Li, B.H., Wang, H.X., Chen, H.Y and Sarkar, T.K Efficient ray-tracing methodsfor propagation prediction for indoor wireless communications IEEE Antennas andPropagation Magazine, AP-43(2), April 2001, pp 41–49

[28] Rajala, J., Sipila¨, K and Heiska, K., Predicting in-building coverage for micro-cells andsmall macro-cells Proc VTC 1999 Conf., Houston, Texas, May 1999, pp 180–184.[29] Guidelines for Evaluation of Radio Transmission Technologies for IMT-2000, Recom-mendation ITU-R M 1225, 1997

[30] Laiho-Steffens, J., Sipila¨, K and Wacker, A., Verification of 3G radio network ing rules with static network simulations Proc VTC 2000 Spring Conf., Tokyo, Japan,May 2000, pp 478–482

dimension-[31] Ha¨ma¨la¨inen, S., Slanina, P., Hartman, M., Lappetela¨inen, A., Holma, H and Salonaho,O., A novel interface between link and system level simulations Proc ACTS Summit 1997,Aalborg, Denmark, October 1997, pp 509–604

[32] Ha¨ma¨la¨inen, S., Holma, H and Sipila¨ K., Advanced WCDMA radio network simulator.Proc PIMRC 1999, Aalborg, Denmark, October 1997, pp 509–604.

[33] Brady, P.T., A model for generating on–off speech patterns in two-way conversation BellSystems Technical Journal, 48(9), September 1969, pp 2445–2472

[34] Wacker, A., Sipila¨, K and Kuurne, A., Automated and remote optimisation of antennasub-system based on radio network performance Proc WPMC 2002 Symposium, Waikiki,Hawaii, October 2002, pp 752–756

[35] Wacker, A., Laiho-Steffens, J., Sipila¨, K and Heiska K., The impact of the base stationsectorisation on WCDMA radio network performance Proc VTC 1999 Fall Conf.,Amsterdam, Netherlands, September 1999, pp 2611–2615

[36] Laiho-Steffens, J., Wacker, A and Aikio, P., The impact of the radio network planningand site configuration on the WCDMA network capacity and Quality of Service Proc.VTC 2000 Spring Conf., Tokyo, Japan, May 2000, pp 1006–1010

[37] Toskala, A., Holma, H and Muszynski, P., ETSI WCDMA for UMTS Proc of ISSSTA

1998, South Africa, September 1998, pp 616–620

[38] 3GPP, Technical Specification 25.101, UE Radio Transmission and Reception (FDD),v.5.13.0, December 2004

[39] Spurious Emissions, Recommendation ITU-R SM.329-7

[40] 3GPP, Technical Specification 25.104, UTRA (BS) FDD; Radio Transmission andReception, v.5.9.0, September 2004

[41] Ha¨ma¨la¨inen, S., Lilja, H and Ha¨ma¨la¨inen, A., WCDMA adjacent channel interferencerequirements Proc VTC 1999 Fall Conf., Amsterdam, Netherlands, September 1999,

[44] Akl, R.G., Hedge, M.V., Naraghi-Pour, M and Min P.S., Cell placement in a CDMAnetwork IEEE Wireless Communications and Networking Conf., 1999, Vol 2, pp 903–907.[45] Gorricho, J.-L and Paradells, J., Evaluation of the soft handover benefits on CDMAsystems 5th IEEE International Conf on Universal Personal Communications, 1996,Vol 1, pp 305–309

[46] Love, R.T., Beshir, K.A., Schaeffer, D and Nikides R.S., A pilot optimisation techniquefor CDMA cellular systems Proc VTC 1999 Fall Conf., Amsterdam, Netherlands,September 1999, pp 2238–2242

[47] De Hoz, A and Cordier, C., WCDMA downlink performance analysis Proc VTC 1999Fall Conf., Amsterdam, Netherlands, September 1999, pp 968–972

[48] Holma, H and Toskala A (eds), WCDMA for UMTS: Radio Access for Third GenerationMobile Communications(3rd edn) John Wiley & Sons, 2004, chapter 8

[49] Wo¨lfle, G., Gschwendtner, B.E and Landstorfer, F.M., Intelligent ray tracing: A newapproach for field strength prediction in micro-cells Proc VTC 1997 Conf., Phoenix,Arizona, May 1997, pp 790–794

[50] Wu, J.-S., Chung, J.-K and Yang Y.-C., Performance study for a micro-cell hot spotembedded in CDMA macro-cell systems IEEE Transactions on Vehicular Technology,VT-48(1), January 1999, pp 47–59

[51] Shapira, J., Micro-cell engineering in CDMA cellular networks IEEE Transactions onVehicular Technology, VT-43(4), November 1994, pp 817–825

Radio Resource Utilisation

Achim Wacker, Jaana Laiho, Toma´sˇ Novosad, David Soldani,

Chris Johnson, Tero Kola and Ted Buot

4.1 Introduction to Radio Resource Management

The expression Radio Resource Utilisation (RRU) covers all functionality for handlingthe air interface resources of a Radio Access Network (RAN) These functions togetherare responsible for supplying optimum coverage, offering the maximum plannedcapacity, guaranteeing the required Quality of Service (QoS) and ensuring efficientuse of physical and transport resources The Radio Resource Management (RRM)function consists of Power Control (PC), Handover Control (HC), congestioncontrol – typically subdivided into Admission Control (AC), Load Control (LC) andPacket data Scheduling (PS) – and the Resource Manager (RM) PC is presented inSection 4.2 Since many users in a Wideband Code Division Multiple Access(WCDMA) network are operating on the same frequency, interference is a crucialissue and PC is responsible for adjusting the transmit powers in uplink and downlink

to the minimum level required to ensure the demanded QoS HC, presented in Section4.3, takes care that a connected user is handed over from one cell to another as he ismoving through the coverage area of a mobile network AC and LC, together with PS,ensure that the network stays within the planned condition AC, handled in Section4.4.2, lets users set up or reconfigure Radio Access Bearers (RABs) only if these wouldnot overload the system and if the necessary resources are available LC takes care that

a system temporarily going into overload is returned into a non-overloaded situation,and is the subject of Section 4.4.4 The main task of PS is to handle all NRT traffic –i.e., allocate optimum bit rates and schedule transmission of the packet data, keepingthe required QoS in terms of throughput and delays The functionality of PS istreated in Section 4.4.3 The RM is in charge of controlling the physical and logicalradio resources under one Radio Network Controller (RNC) Its main tasks are tocoordinate the usage of the available hardware resources and to manage the code tree.The RM is presented in Section 4.5 Most of the Release ’99 RRM functionality islocated in the RNC Only part of the PC, LC and the RM can also be found in the Node

B, and in the User Equipment (UE) only PC functionality is included For Release 5RRM involving High-speed Downlink Packet Access (HSDPA) transmission, big parts