1236039_07_P1E

WCDMA Cell Planning

Chapter 7

OBJECTIVES:Upon completion of this chapter the student will be able to:

Carry out power, frequency and code planning

Distinguish between different types of handovers

Discuss different ways of expanding the capacity by configuration modification

WCDMA Radio Network Design

ll aa nn kkBB

iioonnaall llyy

ttnneettnnII

EN/LZT 123 6039 P1E

7 WCDMA Cell Planning


Table of Contents

Topic Page

SPECTRUM REQUIREMENTS.................................................93

GUARD BAND................................................................................................93

SPECTRUM ALLOCATION............................................................................94

RADIO NETWORK DESIGN.....................................................95

POWER PLANNING.......................................................................................95

FREQUENCY PLANNING..............................................................................97

CODE PLANNING..........................................................................................97

CO-SITING.....................................................................................................98

HANDOVER...................................................................................................99

RADIO ACCESS DIMENSIONING/CAPABILITIES................106

INTRODUCTION..........................................................................................106

EXPANDING CAPACITY BY CONFIGURATION MODIFICATION..............107

EXPANDING BY ADDING SITES................................................................109

POTENTIAL ENHANCEMENTS...................................................................110

EN/LZT 123 6039 P1E – I –


ll aa nn kkBB

iioonnaall llyy

ttnneettnnII

– ii – EN/LZT 123 6039 P1E


SPECTRUM REQUIREMENTS

GUARD BAND

It is foreseen that GSM and UMTS will coexist and it is therefore essential to give guidance regarding guard band requirements between UMTS and other 2G systems like GSM.

The required guard band between WCDMA and GSM 1800 is dependent on the minimum isolation between the two systems at hand at certain performance degradation. It must be ensured that the GSM system gives an insignificant contribution to the WCDMA receiver noise. If the systems are not co-sited, a carrier spacing of typically 3 MHz between the carriers at band edge is required if the performance degradation shall be limited. This figure is however still under consideration. Necessary investigations concerning performance of 2G terminals have not been completed.

An example of a guard band situation for a WCDMA operator is shown in the figure below.

Figure 7-1 An example of UMTS deployment with three WCDMA carriers in less than 15 MHz spectrum, including guard bands.

The diagram shows a WCDMA operator deploying three WCDMA carriers, two in a macro cell layer and one in a micro

EN/LZT 123 6039 P1E – 93 –

GSMoperator

UMTS operator Other UMTSoperator

f4.4 MHz 5.0 MHz 5.0 MHz3 MHz

2.7 + 4.4 + 5.0 + 2.5 = 14.6 MHz

Macro layer Micro layer


cell layer. The carrier spacing is nominally 4.4 MHz. Between the macro and micro layer carriers, a 5.0 MHz spacing is used, the same spacing as between WCDMA operators. The spectrum below the WCDMA allocation has a GSM system deployed (with a single carrier 200 kHz guard-band), while the spectrum above is another WCDMA system. The total spectrum required for this deployment is 14.6 MHz.

SPECTRUM ALLOCATION

Each service requires a 3.84 Mcps carrier. Simulations indicate that one carrier can support four simultaneous users (384 kbps) in the outdoor to indoor and Pedestrian A environment and about five simultaneous users (144 kbps) in the Vehicular A environment. For speech services, one 5 Mbps carrier can serve more than 64 simultaneous users.

The indoor environments, outdoor to indoor and pedestrian and vehicular environments are denoted pico, micro and macro cell layers in the text below.

Operators will typically have access to 2*15 MHz frequency bands. In this case it will be straightforward to introduce a three layer HCS cell structure.

Some operators have 2*10 MHz bands available. In these cases the pico/micro cell layer may share the same frequency band with only small performance degradation. The isolation between the pico/micro cells due to the walls reduces the interference between the layers. Also the difference in user movement (users speed) between micro (e.g. a Manhattan environment) and pico environments is quite small. Therefore a micro base station can serve indoor users (on lower floors). However, there is a problem if a line-of-sight macro base station) interferes with an indoor user (e.g. on the top floors). Therefore a guard band should be used to separate the pico/micro layer and the macro layer. In several cases these operators will also have access to 5MHz unpaired spectrum that may be used when it is time to introduce the pico layer.

The conclusion is that WCDMA can support, a 2 Mbps service in an indoor office environment, a 384 kbps service in an outdoor environment and a 144 kbps service in a vehicular environment simultaneously in a total frequency band of 15 MHz for high capacity applications. A frequency band of 10 MHz could also be used with a small capacity reduction.

– 94 – EN/LZT 123 6039 P1E


RADIO NETWORK DESIGN

POWER PLANNING

In a WCDMA system, the power is the common shared resource between the different services and users. The part used for the control channel transmission reduces the overall network capacity for paying traffic. The coverage of these channels must be large compared to the traffic channels in order for the mobile station to decode other base stations before entering the soft/softer handover zone. The broadcast channel including the cell information has to be decoded before the mobile enters the coverage area of the cell. As a consequence, it is necessary to plan how the power in the downlink is distributed between the following common control channels:

SCH (Synchronisation CHannel)

Primary CCPCH (Primary Common Control Physical CHannel)

Secondary CCPCH (carrying PCH: Paging CHannel)

Secondary CCPCH (carrying FACH: Forward Access CHannel)

CPICH (Common PIlot CHannel)

AICH (Acquisition Indication CHannel)

PICH (Page Indication CHannel)

Typically, about 20-25% of the maximum base station power should be allocated for common control channels.

In WCDMA networks, synchronization between base stations is not required. Therefore the mobile station utilizes the SCH to find the Broadcast Control CHannel (BCCH) according to the cell search algorithm. This procedure is also performed to update the active set during an handover process. A critical aspect to be considered is the percentage of the maximum base station power used for SCH transmission.

The SCH consists of a Primary SCH (PSCH) to find slot synchronization and a Secondary SCH (SSCH) to find the scrambling code group and the frame synchronization. Moreover, the SCH is transmitted in the first 256 chips of each slot with a duty cycle of 10%.

EN/LZT 123 6039 P1E – 95 –


The output power for the transmission of the SCH is a trade-off between the time required for a reliable cell search procedure and the maximum allowed interference with the traffic channels

Simulation results indicate that a peak power value between 5% and 10% of the BS output power is sufficient for an efficient synchronization.

If, as an example, 25% of the maximum base station power is allocated to control channels it can be distributed e.g. as following: 0.5% for SCH (5% but with a duty cycle of 10%) and the remaining of 24.5% for the other Common Control CHannels (Primary CCPCH, PCH, FACH, CPICH, AICH and PICH).

In the power planning, the SCH/DPCH and the PCCPCH /DPCH power ratios should be also considered, since the SCH is not orthogonal to the DPCH. Simulations show that the Eb/N0 ratio decreases (compared with a reference value) 0.3 dB at a SCH/DPCH power ratio of 10 dB and between 2 and 8 dB for a PCCPCH /DPCH power ratio of 19.3 dB. According to simulations the power ratio between the SCH and PCCPCH might be in the range –10 to –2 dB. One possible value is –6 dB.

In Table 1, the power allocation example is summarized:

Table 1: Example of DL common channel power allocation.

ChannelPower relative

to max BSpower [dB]

Duty cycle

SCH -12 0.1

Primary CCPCH -12 0.9

Secondary CCPCH (carrying PCH: Paging CHannel)

-12 0.25

Secondary CCPCH (carrying FACH: Forward Access CHannel)

-12 0.25

CPICH -10 1

AICH -15 1

PICH -15 1

– 96 – EN/LZT 123 6039 P1E


FREQUENCY PLANNING

Capacity requirements may call for two carriers per cell from the start-up of the network (and thus a higher bandwidth). All carriers of a cell should have essentially the same coverage area with slight differences due to the load handled by each frequency. The addition of a new frequency implies a new optimization process of certain system features. In particular regarding inter-frequency handover, cell search and coverage overlaps.

CODE PLANNING

WCDMA codes

In a WCDMA system, two operations are applied to the physical channels: the channelization, which transforms every bit into a SF number of chips (SF: Spreading Factor) and the scrambling, where a scrambling code is applied to spread the signal. In the channelization operation, Orthogonal Variable Spreading Factor (OVSF) codes are used to preserve the orthogonality between the physical channels of connections even if operating at different rates.

In the uplink, each user has his own scrambling code and can utilize all the codes in the OVSF code-tree. Therefore, the scrambling code is related to the user while the channelization code to the type of service at a given bit rate.

In the downlink, the scrambling codes are used to distinguish the different cells while the channelization codes are related to the different services and users.

Code planning is required for scrambling codes. In particular conditions, channelization code planning is needed, but only in the downlink direction.

Downlink scrambling code planning

In the downlink, the maximum number of scrambling codes (Gold sequence of 38400 chips) are 218-1, but not all codes are used. The scrambling codes are divided into 512 sets each of a primary scrambling code and 15 secondary scrambling codes so the total codes used are 8192. To each cell is allocated one and only one primary scrambling code: as consequence the code reuse becomes 1:512. Downlink scrambling code planning is therefore a fairly straightforward task. However, the codes are

EN/LZT 123 6039 P1E – 97 –


divided into 64 different groups and if neighbouring cells are allocated codes from differenct code groups the power consumption of the UE is reduced. The primary CCPCH is always transmitted using the primary scrambling code while the other downlink physical channels can be transmitted with either the primary or secondary scrambling codes associated with the primary scrambling code of the cell.

Downlink planning of channelization codes

The maximum number of OVSF downlink spreading codes is 512. All users in a cell have to share the available channelization codes in the OVSF code tree, which is a limited resource. A limit on the number of downlink codes is imposed mainly by high bit rate services with low spreading factors, as the utilization of a code causes the unavailability of the subtree of higher SF descending from that code. Furthermore, mobiles in soft handover use more codes (one for each server). Nevertheless, the use of a single scrambling code per user implies theoretical orthogonality of different services provided by the cell. Actually, the multipath environment disrupts the orthogonality between them, hence the system is interference limited.

If there is a necessity to increase the downlink capacity in a situation where there is a risk for code limitation, the channelization codes can be increased using multiple code trees, each of them having a different scrambling code. In particular, it is possible to assign up to 15 secondary scrambling codes (code-trees) per cell.

CO-SITING

– 98 – EN/LZT 123 6039 P1E


M PM PET & T U

ET & T U

MCPA

Battery

U M T SR B S

G SM B T S

Shared A ntenna T ow er

Shared Pow er Supp ly

R x R xT x

R x R xT x

U M T SU E

G SMM S

U M T SR N C

G SMB SC

Shared T ransport

D ual M odeU E

C ore N etw ork

Figure 7-2 Co-siting

The main advantage of co-siting WCDMA with GSM is that the large cost associated with acquiring a new site is avoided. In addition to that, cost can be further reduced by being able to share antenna towers, share power supply as well as share transport network (Figure 7-2). It should also be noted that it is possible to co-site WCDMA with GSM900. However, the link budget of GSM900 differs from the link budget of GSM1800. This means that it may be necessary to add WCDMA sites in between the existing GSM900 sites, in order to achieve the desired coverage.

HANDOVER

Hard handover

Hard handover includes inter-frequency and intra-frequency handover as summarised below:

Inter-frequency:

Cells with multiple carriers for high load (Figure 7-3)

WCDMA GSM

Intra-frequency:

Channel Rate Switching

EN/LZT 123 6039 P1E – 99 –


Figure 7-3 Cells with multiple carriers

Since UMTS transmission is continuous, there are no regularly occurring idle time intervals for inter-frequencies measurements as in TDMA-based systems. Therefore, a compressed mode of operation has been introduced (see Figure 7-4) for a UE in connected mode. Measurement slots are thereby created by transmitting the data of a slot with a lower spreading factor or by a higher code rate. The rest of the slot remains idle, and is used for measurements on other carriers.

..

Figure 7-4 Compressed mode used for Inter-frequency measurements

Whereas in soft handover the UE is simultaneously connected to more than one base station, during the hard handover procedure the connection to the old base station is released before the new base station is connected. As a consequence, the hard handover events cause short interruptions that may cause speech quality deterioration and increase packet delay.

A hard handover algorithm is always based on quality measures, for example path loss or average received power. The best base station is the one with the highest value of the particular quality measure or combination of quality measures used there and then for evaluation in the RNC (Radio Network Controller). In a UMTS network, the RNC performs the handover evaluation, comparing the measurements with the handover thresholds.

– 100 – EN/LZT 123 6039 P1E


A handover hysteresis is used to limit the risk for multiple handovers back and forth between two base stations, that might occur due to signal fading. In this way, the amount of signalling is reduced. The principle is that the handover is not conducted until the difference between the output power of the new and the original base station exceeds the hysteresis value (Figure 7-5). The disadvantage of hysteresis is that the handover decision is delayed. This aspect has to be taken into account, especially for environments with fast moving users.

A

C

B

HO quality measure [dB]

TimeReplace A

by CReplace C

by AReplace A

by B

Replace hysteresis

Figure 7-5 The principle of the hard handover algorithm

An increase of the handover hysteresis reduces the number of updatings of the Active Set (the set of cells participating actively in transmission and reception with the connection) thus avoiding a degradation of the connection quality, in particular data throughput. However, an increase of the handover hysteresis also causes the increase in uplink and downlink interference, because the UE and base station transmit at maximum power for a longer amount of time before performing the handover.

Simulations of a packet data connection at a 240 kbps bearer and user mobility at 30 and 120 km/h show that an appropriate hysteresis value is 2 dB. However, for similarity with GSM, and extra safety, a suitable value should be 3 dB.

Soft/softer handover

In intra-frequency handover, the UE can be connected to more than one cell on dedicated channels but it can only be connected to exactly one cell on common channels.

EN/LZT 123 6039 P1E – 101 –


The use of macro diversity (soft and softer handover) is an opportunity for achieving improved network performance in a WCDMA system. Soft handover is the process when performed between cells of different sites, and softer the process when the cells belong to the same site.

Uplink

In the case of soft handover, the detection process for the uplink direction is based on a selective combining algorithm. This algorithm is performed in the RNC. The best frame of those that arrive from the air interface links participating in the soft handover, and that belong to the same slot transmitted from the UE, is selected according to the frame error indication. In the uplink soft/softer handover is always good since the interference generated from this connection is reduced, as the mobile follows the power control command from the base station which requires the smallest amount of output power. Less power in the air leads automatically to a capacity gain.

In the softer handover algorithm, the signals from the different sectors are combined within the receiver unit (called “rake” receiver) of the RBS with a maximum-ratio combining algorithm. This method yields a higher handover gain than that obtained with the selective combining method.

Downlink

In the downlink, the receiver unit (rake receiver) of the UE combines all the signals from the different base stations according to the maximum-ratio combining method. The capacity gain obtained in the downlink depends on the optimum active set size. This number is related to the handover thresholds, the number of available rake fingers and the radio environment. If a rake receiver is not able to collect enough energy from two or three base stations due to a limited number of rake fingers, a system capacity degradation can occur due to the extra radio links that are transmitted in the air, increasing the interference. Soft handover also consumes additional hardware.

Soft handover areas

The number of users in soft handover is also determined by the cell coverage. Thus, during the antenna system deployment, in particular for the choice of orientation and tilt, it is important to plan the possible soft handover areas, which are the cell

– 102 – EN/LZT 123 6039 P1E


coverage overlaps of different base stations, according to the type of services and users distribution.

EN/LZT 123 6039 P1E – 103 –


Soft handover algorithm

In the following, the soft handover procedure, based on the 3GPP Specifications (TS 25.302 V3.3.3), are described.

Figure 7-6 The principles of the soft/softer handover algorithm

The soft handover procedure consists of two different functions: evaluation and execution. In the evaluation function, the UE performs measurements on the cells of the monitoring set (the set of cells for which the UE has to perform measurements) and evaluates these measurements with respect to specific events. If the condition of an event is met, a measurement report will be sent to the RNC to start the handover evaluation function there (HO_eval). In the execution function, HO_eval makes the final decision on which cells to add, delete or replace in the active set (see Figure 7-6), based on the received measurement report. This decision can be based on several different criteria:

path loss L, the difference between the transmitted power on the CPICH (Primary Common PIlot CHannel) and the received power on the CPICH after despreading

received power on the CPICH after despreading CPICH_RSCP (CPICH_Received Signal Code Power)

Ec/N0, the received energy per chip of the CPICH divided by the power density in the frequency band (this is the default criterion the Ericsson system).

Simulations show that the choice of the handover decision algorithm can be crucial for the capacity of mixed systems (co-existence of macrocell and microcell). In particular, the algorithm based on the received power works better in a system

– 104 – EN/LZT 123 6039 P1E


where the base stations have different transmit power levels, as the load becomes more equal between macrocell and microcell and the soft handover region is minimised.

Inter-system handover

Due to the existing widespread coverage of GSM, it is important that UTRAN supports handover to/from GSM systems in an early stage. In the first release UTRAN shall be able to perform an Inter-system handover from UTRAN/FDD to GSM and vice versa both for speech and data services, although only due to radio coverage reasons. Later releases will also support intersystem handover for overload reasons in UTRAN.

In order to perform an intersystem handover, the network (RNC) informs the UE of the cells belonging to the monitoring set. The cells in the monitoring set are the union of all neighbour cells of all cells in the active set. The information about neighbouring cells is distributed to the UE either on FACH or DCCH when the UE is in connected mode. If the RNC decides to perform an inter-system handover, the UE is informed about which GSM cells to include in the handover monitoring set. In this case the UE works in compressed mode to be able to carry out measurements on the GSM frequencies.

A priority between different types of handover is considered in the RNC. The scope is to keep the connection with the least handover effort. That means the first decision is for intra-frequency handover, i.e. soft/softer handover, then inter-frequency handover and finally inter-system handover.

The UE can only be ordered to perform RSSI (Received Signal Strength Indicator) measurements in the first phase. Other types of measurements on GSM frequencies will be possible in later release.

Inter-system handover from GSM does not require any handover algorithms within UTRAN, only Admission Control, to decide whether an Inter-system handover shall be allowed or not.

How UTRAN and GSM can be configured in order to be able to perform inter-system handover is shown in Figure 7-7.

EN/LZT 123 6039 P1E – 105 –


UMSC MSC

RNC BSC

MAP/E

Iu A

Case A

UMSC

RNC BSC

Iu A

Case B

Figure 7-7 Configuration for handover UTRAN-to-GSM-to-UTRAN with MAP/E interface (case A) or with a combined MSC, MAP/E interface in a unique UMSC (case B).

– 106 – EN/LZT 123 6039 P1E


RADIO ACCESS DIMENSIONING/CAPABILITIES

This chapter describes different deployment scenarios of a WCDMA radio network using Ericsson’s product portfolio.Initial deployment is described as well as different possibilities to expand from the primary deployment.During the expansion phase new products as well as features that have been evolved from first product release are needed. This means that some of the expansion scenarios outlined below may not be feasible during the very first phase of initial deployment. Please consult detailed product description for products’ capabilities.

INTRODUCTION

When planning a UMTS network at this early stage, the assumed area morphology is of outmost importance. It has a major impact on the number of sites. Urban and suburban areas are often coverage limited not capacity limited.

An another important parameter for the dimensioning is the traffic model. High traffic volumes and high bit rate services has a major impact for the site configuration and number of sites.

The key initial dimensioning goal is to achieve an overall coverage. The best foundation for this aim, according to Ericsson’s experience, is to primarily use 3-sector macro sites. The macro base stations are all of the 3-sector type and based on the indoor, one-cabinet RBS 3202 solution.

In addition, there will be a need for micro cells. These will mostly be for additional local coverage and hot spots. The micro base stations will be of omni type and based on a micro RBS, which is a small, lightweight, weather proof base station with no floor space requirements.

In a WCDMA system the cell breathes, which means that when loaded with a certain amount of traffic the coverage decreases due to the increased interference in the cell. An initial value for the cell load can be determined by comparing the traffic volume of the different bearer services to the initial number of sites.

The resulting cell load will give a new link budget and thereby result in a corrected number of cells, which again will lead to a corrected load factor. This process converges at a certain number of base station sites.

EN/LZT 123 6039 P1E – 107 –


It should be noted that the number of carriers in each sector affects the iterative process described above. If two carriers are employed in a sector, the load of that sector (for a fixed traffic) decreases (regarding one carrier), which in turn means that the coverage increases. This results in a trade off between the employment of new sites and additional carriers.The rule of thumb for dimensioning scenarios is to add a carrier if the number of sites decreases by 30% or more.

EXPANDING CAPACITY BY CONFIGURATION MODIFICATION

This section deals with expansion possibilities that do not require additional sites. However, some of the solutions require additional cabinets or main units at the existing site. For detailed information regarding the configurations supported by a single cabinet, please consult [RBS].

Adding channel capacity

Ericsson offers the possibility to have sub-equipped carriers1 for RBSs covering a rather small amount of traffic. At initial deployment, the capacity requirement may be low. However, as the capacity demand grows more hardware can be added to the RBS. By allowing this approach, Ericsson offers a solution with low initial cost as well as the possibility to expand easily when more capacity is needed. Once the RBS is fully equipped, further channel capacity can be added by replacing existing hardware boards with boards having more highly integrated ASICs.

Adding power

Ericsson’s macro RBSs offer the possibility to increase the downlink output power. This is achieved as it is possible to connect two MCPAs together. Whether it is useful or not to increase the maximum allowed output power depends on the cell size, i.e. is the cell so large that the background noise has an impact? For small cells, the output power of the downlink broadcast channels have a larger impact than the background noise.

For large cell ranges the downlink improvement is substantial by using paired MCPAs.

1 A sub equipped carrier is a carrier in an RBS that has not been fully equipped with hardware, i.e. all hardware boards are not installed. Note that the W-TRU always is fully equipped.

– 108 – EN/LZT 123 6039 P1E


The increase in output power can be used to increase coverage, capacity or both of them. Further, by comparing the uplink and the downlink, regarding capacity, it can be seen that the downlink offers better capacity for systems that have been planned to provide high coverage. The possibility to use multiple MCPAs enhances this feature.

Adding new frequency carriers

An obvious and straightforward expansion method to improve the system’s performance is to add new frequency carriers. Going from one to two frequency carriers, the planned capacity is roughly doubled.

Expanding a three sector site from one to two frequency carriers can be achieved without adding a new cabinet at the site, for the indoor cabinet solution. Adding a third or a fourth carrier if that much spectrum has been assigned in the licence will of course further expand the capacity in the system.

Increase number of sectors

An alternative to adding new frequency carriers when expanding the network is to increase the number of sectors. An obvious possibility is to go from three to six sectors. The sectorisation can of course also be increased even further.

When increasing the number of sectors, the antenna beams will be narrower, which leads to higher antenna gain. By reducing the beam width to a half, the gain is increased approximately with 3 dB.

Further, adding more sectors also means that the site can handle more traffic. The improvements that are achieved, when going to six sectors, can be used to improve coverage, capacity or both of them. If the planned load in a sector exceeds 50-60%, advanced radio network functionality is needed. That type of functionality will be available in later product releases.

Using repeater solutions

Adding power, adding new frequencies and increasing the number of sectors can all be used to improve the coverage in the system. Another alternative, for increasing the coverage, is to use repeater solutions, i.e. RF repeaters or optical distribution systems. Both of them can be used for coverage gap filling as well as augmenting the coverage area of a given sector.

EN/LZT 123 6039 P1E – 109 –


The characteristic of a coverage gap filling is that the area to fill often is surrounded by the sector communicating with the repeater, e.g. indoor locations or tunnels. While when augmenting, or moving, the shape of the sector is altered, for instance when extending highway coverage.

Adding distributed antennas

Distributed antennas can be used to increase both coverage and capacity. In cases where the traffic concentration is quite low, each antenna can be allowed to transmit the same signal. While for areas with high capacity demand, more advanced functionality is required, so that the signal intended for a certain user is transmitted to the antennas close to that user. By doing that, the interference level in the system is reduced.

In areas with distributed antennas, the interference level in the system is very low, as the users always are close to at least one antenna. This means that RBSs with distributed antennas can be deployed in frequency bands that are already used by another RBS. Further, if the distributed antenna system is located indoors, the building penetration loss will act as extra shield between the cells.

EXPANDING BY ADDING SITES

In the previous chapter, the focus was on expansion by adding hardware at existing sites. Another alternative is to add new sites and that is the focus of this chapter. Note that this chapter only considers areas where WCDMA already has been deployed. Deploying WCDMA in areas without WCDMA coverage is viewed as initial deployment. Adding new sites can be used to improve the coverage, the capacity or both of them. The new sites can then also be expanded by using the approaches described in the previous chapter.

Cell split

Assuming that the number of sites in a certain area is doubled, then the area covered by each cell is half as large as previously. The added sites can be used for increasing coverage (for high bit rate services at the cell border), capacity or both of them.

If the focus is on coverage, then the system with the added sites can offer full area coverage for services using higher bit rates. This means that full area coverage for 64kbps best effort

– 110 – EN/LZT 123 6039 P1E


services can be expanded to full area coverage for 128kbps best effort services.

Layered network

A layered network simply means that there exists different cell layers in the system, i.e. macro layer, micro layer and perhaps also a pico layer. One simple approach of a layered network is to have a macro layer and then deploy micro base stations in a separate band in the high traffic demand areas.

A layered network is not deemed to be essential during the initial network build up and hence not supported in the early phases.

The traditional way to deploy a layered network is to have the different cell layers in different frequency band.

In order to maximise the performance of a layered network some additional radio network functionality is needed. The purpose of that functionality is to divide the traffic between different layers. This kind of functionality typically distributes the load between different bands and more advanced types of functionality can also consider the user speed when deciding in which layer the user connection should be handled.

One special example of a layered network is hot spot deployment. A hot spot is defined to be a very limited area, typically a few blocks, with very high load. One example of handling local hot spots is to add sites in an already used frequency band.

An alternative is to let the new site operate in a separate frequency band. This means that the hot spot cell would not have neighbour cells in it own frequency band. It can then handle a load, which is about 1.5-2.0 times higher compared to if it had neighbour cells in the same frequency band. In the downlink, capacity difference can be even higher, depending on how well the downlink orthogonality is maintained.

POTENTIAL ENHANCEMENTS

WCDMA has been designed to be future proof, which means that it efficiently supports advanced technologies like adaptive antennas and interference cancellation. These types of advanced functionality can be used to improve the system’s coverage, capacity or both of them even further.

EN/LZT 123 6039 P1E – 111 –


– 112 – EN/LZT 123 6039 P1E

Documents

1236039_07_P1E