Six Sector Antenna Strategy

CDMA

Six Sector Cell ApplicationsHandbookNBSS 7.0 Standard 01.01 September 1998

411-2133-123

CDMA

Six Sector Cell ApplicationsHandbook

Product release: NBSS 7.0Document release: Standard 01.01Date: September 1998Document Number: 411-2133-123

Copyright Country of printing Confidentiality Legal statements Trademarks

. 1998 Northern Telecom

. Printed in the United States of America

. NORTHERN TELECOM CONFIDENTIAL: The information contained in this document is the property of NorthernTelecom. Except as specifically authorized in writing by Northern Telecom, the holder of this document shall keep the informationcontained herein confidential and shall protect same in whole or in part from disclosure and dissemination to third parties and usesame for evaluation, operation, and maintenance purposes only.

. Information is subject to change without notice.

. DMS, DMS SuperNode, DMS-MTX, DMS-100, and MAP are trademarks of Northern Telecom.

iv

411-2133-123 Standard 01.01 September 1998

Publication history

September 1998

Standard 01.01

June 1998

Preliminary 01.00

May 1998

First Draft 01.00

vii

CDMA Six Sector Cell Applications Handbook NBSS 7.0

ContentsIntroduction 1-1Overview of Nortel’s CDMA System 1-1Funtionality of the BTS 1-3Functionality of the BSC 1-3Six Sector Application 1-3The BTS for a Six Sector Site 1-4Suitable Morphology Sites for Six Sector Deployment 1-5Diminishing Returns 1-6Deploying Second Carrier Over Six Sector 1-7Antennas 2-1Antenna Beamwidth 2-1Antenna Gain 2-1

Reconfiguring a Three Sector to Six Sector 2-1New Six Sector site 2-2

Diversity Options for Six Sector 2-2Antenna Orientation 2-2

Six Sector cell in a cluster of Six Sector cells. 2-2Six sector cell in a cluster of three sector cells 2-5

Transition from Three Sector to Six Sector 3-1First Step 3-1Six Sector with Space Diversity Antenna 3-1Six Sector with Dual Polarized Antennas 3-4Six Sector Capacity 4-1Forward Link Capacity 4-1

Reverse Link Capacity 4-1Three Sector Cell Calculation 4-2Fully Embedded six sector cell Calculation 4-2A six sector embedded in three sector cells 4-3Impact on the neighbor cell forward link capacity 4-4

Datafill 4-4Channel Element (CE) Usage 4-5Reverse Link Budget 4-5T1 Link Requirement 4-5References: 4-6

viii


List of Figures

High level overview of Nortel’s CDMA System 1-1High level overview of Nortel’s CDMA System functionality 1-2Arranging two BTSs to make a Six Sector fort optimum performance 1-5Deploying a Six Sector cell at a traffic Junction in downtown area with high-rises. 1-6Six Sector cell orientation for optimum capacity/coverage Performance 2-3Another type of antenna which results in poor coverage and capacity 2-4Another type of antenna which results in poor coverage and capacity 2-5A typical three sector cell 2-6Deploying a Six Sector in a cluster of three sectors 2-7Hexagonal platform for six sector antennas, using space diversity 3-3Space diversity on three sector platform IS NOT RECOMMENDED 3-4Phase 1 of the installation: the 2nd BTS is installed, but not connected to antennas 3-6Installing the Six Sector Antennas on a Triangular (Three Sector) Platform 3-6Phase 2 of the installation, the site is configured as a Six Sector site 3-7Computing the Frequency Reuse Factor of a six sector in a cluster of three sectors 4-4

List of Tables

Frequency Reuse Factor for three sector cell cluster 4-2Frequency Reuse Factor For six sector Cluster 4-2Frequency Reuse Factors of Lettered Sectors in Figure 4-1 4-3

2

v


1About this documentThis document describes the guidelines for deploying Six Sector cells in aCDMA application. It discusses and explains how to deploy a Six Sector celland the conditions and parameters that needs to be verified for a successfuldeployment. To achieve optimum performance of a Six Sector Cell, users ofthis document are advised to read through the document carefully.

This document must be treated as a general CDMA Six Sector DeploymentGuideline. It is the duty of the user of this document to work out the requiredsteps for applying this guideline for his/her own specific needs. It is one in asuite of manuals required for successful installation, commissioning,operation, and maintenance of equipment comprising the NORTEL CDMAnetwork. Consult other manuals in the suite when referenced.

This document shall not be used for deploying Six Sector Cells in othertechnologies, such as AMPS, TDMA, GSM, and any other Cellular or PCStechnologies.

Who should use this manualInformation contained in this manual is intended to provide engineers andtechnicians an overview of for deploying Six Sector cells in a CDMAapplication concepts and features.

Document revisionsThis manual is revised periodically to maintain consistency with systemhardware and software releases, operational enhancements, and to incorporatecustomer suggestions.

When changes are required, the number and scope of changes dictate whetherindividual change pages are issued or a new manual is released. Whenindividual change pages are issued, change bars appear in the right-handmargin to mark the revised text. An accompanying Page Change Noticecontains instructions regarding proper placement of the change pages. Thechange pages or complete re-release includes an updated Revision Historypage that summarizes the changes.

1

vi About this document


Conventions used in this manualThroughout this manual and others in the suite, the following symbolsprecede procedures or topics to which they apply:

Note: A policy or procedure that deserves emphasis.

GraphicsGraphics contained in this manual are preliminary. They are provided as anaid in developing concepts discussed. Future versions of this document willprovide updated graphics drawn to scale.

1

1-1


1Introduction

This chapter provides a general description of the Base Station Transceiver(BTS) and Base Station Controller (BSC) and their function in the CDMAMTX architecture. This chapter will help you understand the BTS and BSCrelationships to other CDMA MTX subsystems for inter-system soft handoffISSHO) deployment.

Overview of Nortel’s CDMA SystemIn Nortel’s CDMA network voice trunks allow users in one cellular system tocommunicate with users in another system using IS-41 messaging to accessHome Location Register/Visitor Location Register (HLR/VLR) and inter-system handoffs. An HLR is a permanent database of subscriber informationwhile a VLR is a dynamic database containing subscriber information andtheir location.

Figure 1-1High level overview of Nortel’s CDMA System

1-2 Introduction


Nortel’s CDMA System is illustrated in figure 1-1 and is comprised of thefollowing:

• MTX (Mobile Telephone Exchange) - Provides call processing functionsfor AMPS/TDMA/CDPD/and CDMA cellular systems, and connectivityto the Public Switch Telephone Network (PTSN) and cellular networks.

• BSM/MAP (Base Station Manager/Maintenance Administrative Position)- Provide graphical user interface (GUI) for operations, administration,and maintenance of the BSC, BTS, and itself to the service provider. Itcontains the MTX database and provides MTX statistics used introubleshooting.

• The BSC controls the message and signaling routing between itself, theMTX, and the BTS. It also provides the voice coding and decodingbetween the IS-95 mobiles (via the BTSs) and the PCM T1s from theMTX. The BSC provides cellular-specific call processing functions suchas power control, service optionality, and intrasystem handoffs. Only oneBSC is supported for the system and it is normally co-located with theMTX.

• BTS (Base Station Transceiver Subsystem) - Provides the air interface(RF link) between mobile subscribers and the CDMA system.

Figure 1-2High level overview of Nortel’s CDMA System functionality

1-3


Funtionality of the BTSFigure 1-2 provides a high level overview of Nortel’s CDMA systemfuntionality. The Base Station Transceiver (BTS) provides the followingfuntionality in the MTX-CDMA system:

• over-the-air RF interface with the subscriber unit.

• additional over-the-air functions such as pilot, sync, paging, and accesschannels.

• call processing functions to control the subscriber unit operation over thepaging and access channels.

• communication of subscriber information.

• control and management of BTS resources.

• control and management communication between the BTS and other basestation subsystems.

• monitoring and configuration functions.

The next chapter, Second Carrier Overlay Concepts, discusses deploymentissues. Other chapters include distributing traffic among two carriers, secondarchitecture, installation, and specifications.

Functionality of the BSCThe Base Station Controller (BSC) provides the following functionality in theMTX-CDMA system:

• Data routing

— routes signaling and control message packets

– Messages are routed internally, to/from the LPP/FLIS of the MTXand the BTS

• System interface i.e. the voice PCM/IS-95A interface

• Mobility management

— intra-system handoff (soft), power control and service

Six Sector ApplicationSix Sector is a solution to provide service in areas where there is a higher thanaverage demand for service. The original Three Sector site is configured to aSix Sector site by adding another BTS and reconfiguring the antennaarrangement.

Six Sectorcell deployment is a good solution for small hot spots. Hot spots aresmall areas, where the capacity demand is higher than average. SecondCarrier Overlay is a good solution for large areas within which the demandfor service is higher than the network can provide. For this reason, if servicedemand is high in a small area, Six Sector can be a good option. This

1-4 Introduction


statement should be taken with consideration that there are cases wheredeploying a single Six Sector cell may not be advantagous.

The BTS for a Six Sector SiteCurrently Nortel does not have a true Six Sector BTS. To deploy a Six Sectorcell, two BTSs are deployed back to back. There are a number of ways thatthe 6 sectors (2x3 sectors of each BTS) of the two BTSs can be configured.All 3 sectors of one BTS can also be placed on one side (180o) and the secondBTS on the other side. Another option is to mix them, where a sector of oneBTS will be adjacent to two sectors of the 2nd BTS (interleaving the sectors).The way these sectors are arranged impacts the performance of the Six Sector.Of the two options stated here, the first one yields the best performance,resulting in the least amount of channel element usage, more softer handoffthan soft handoff (compared to the latter option), improved signaldemodulation and lower power requirements, all resulting in improvedperformance. This option is shown in Figure 1-3. Please note that a patent hasbeen filed for this type of Six Sector BTS configuration.

An argument can be made that by interleaving the sectors of the two BTSs,some redundancy is provided. That is, if one BTS goes down, then the secondBTS provides coverage, and everything is not lost. This is partially true, sincethe antennas of the Six Sector are narrow beam (about 33 degrees), resultingin having coverage holes, if one BTS of the interleaved Six Sector goes down.However, the BTSs are robust enough compared to degradation on capacity(if interleaved), that the benefit of having partial coverage does notoverwhelm the benefits of having better performance.Therefore, it isimperative that the BTSs are arranged as shown in Figure 1-3, if we want toachieve the best performance.

1-5


Figure 1-3Arranging two BTSs to make a Six Sector fort optimum performance

Suitable Morphology Sites for Six Sector DeploymentThere are some restrictions regarding the deployment of Six Sector cells. SixSector cells may cause extra pilot pollution, and for this reason care must begiven as to where they are deployed. The rule of thumb is that a site should bechosen where the antenna mast ismuch taller than buildings around it. Forexample, there might be some difficulty in deploying a Six Sector cell indowntown areas with high rise buildings where antennas are deployed on theside (face) of the buildings. Assuming that the building has 2 sides facing thestreets (if located on a traffic junction) or one side facing the street (in themiddle of the road), with buildings with similar heights, then putting 6antennas on the side of the building to cover an area is a difficult task,generally resulting in extreme pilot pollution. This point is highlighted inFigure 1-4, where each sector of the BTS covers one end of the street wherethe BTS is deployed. Such a scenario requires a 4 sector cell and not a 6sector cell. Overall the best sites are urban or suburban sites where antennamasts are generally taller than most of the buildings. Note that the termsurban or suburban refer to the morphology (building heights/types and theirconcentration). It is quite possible to have a suburban/urban morphology withhigh capacity demand. It is not anticipated to deploy Six Sector in rural areas,where there is no capacity demand.

α1

β1 γ1

γ2β2

α2

BTS #2

BTS #1

1-6 Introduction


Figure 1-4Deploying a Six Sector cell at a traffic Junction in downtown area with high-rises.

Diminishing ReturnsThere are two options available to service providers if there is a capacityproblem. One solution includes re-configuring an existing three sector cell toa six sector cell. The second option is to deploy a second carrier overlay onthe top of the first carrier. This advances the question of when to deploy a SixSector and when to deploy a second carrier overlay.

If hot spots are isolated, a three sector site can be reconfigured to a six sectorsite using dual polarized antennas. As demand for service grows andneighbour cells reach maximum capacity, the six sector cell and its neighbourcells can be configured as a second carrier overlay.

Sector #1

Sector #2

Sector #3

Sector #4

1-7


Note: The six sector site can be configured as two three sector sites (firstand second carrier) or two six sector sites overlayed on the top of eachother (which requires two extra BTSs), provided that the six sector cell isnot a border cell in second carrier deployment.

The primary disadvantage of six sector over second carrier is that the sixsector capacity improves by about 1.7-1.8 times, while the second carrierimproves by two times that of the first carrier. This is provided that the secondcarrier is not a border cell. In border cell, the second carrier will lose part ofits capacity advantage, which is dependent on the size of the cell, and theRTD distance from the border cell. Please note that the second carrieradvantage (2 times capacity improvement Vs. 1.7 times for Six Sector) comesat a cost, which is, the use of 2.5 MHz in two carriers Vs. 1.25 MHz in a sixsector. Another disadvantage of a six sector over second carrier is that the sixsector degrades the capacity of its first tier neighbour sectors in the range of 5to 10%.

Six sector does have certain advantages over the second carrier. The first isthat the second carrier has hardhandoff at the border cells, which is unreliablein comparison with the soft handoff in six sector deployment. Anotheradvantage is that the second carrier does not make full use of its capacity atthe border cell caused by the shrinkage of the usable area due to hardhandofflimitations.

If six sector has limitations with deployment in Dense Urban areas, secondcarriers cannot be deployed with its border cell passing through dense urbanareas. These points are raised to show that there is no rule to stress where todeploy a six sector and where to deploy a second carrier. Field engineers areresponsible for determining impacts and future growth in consultation withthe service provider and the decision to deploy a six sector or a second carrier.

Deploying Second Carrier Over Six SectorTechnically a second carrier can overlay a six sector first carrier provided thatthe overlay is not a border cell. The reason for this constraint is thathardhandoff has limited success and six sector overlay adds to the problem oftarget ambiguity resulting in more hardhandoff failures. This condition shouldbe corrected after the introduction of multi-pilot hardhandoff, which isexpected to improve the hardhandoff performance.

The antennas of the six sector underlay can be shared with the antennas of thesecond carrier overly (which is also a Six Sector)as in a normal Three Sectoroverlay, where the antennas are shared.

1-8 Introduction


2-1


2Antennas

Antenna BeamwidthThe choice of antennas for six sector is depends upon whether achievingmaximum capacity or good coverage is the goal. To increase capacity,narrower beamwidth antennas are used. The recommended antennabeamwidth is 33 degrees for this type of deployment. Both space diversity orpolarization diversity can be used. However, polarization diversity may causesome degradation in the forward link; especially if deployed in rural areas orsome suburban areas where there is inadequate cluttering. Cluttering causescross polarization, resulting in the mobile to receiving the signal in eitherplane. In rural application it is not recommended to use polarization diversity.

Note: The general expectation is that in rural deployment the coverageand not the capacity, is the main objective in most cases.

Narrow beam antennas, such as 33 degrees, may cause holes within thecoverage area if the antenna orientation is not performed properly. If theintention is to achieve good coverage by sacrificing improvement in capacity,then wider beam antennas such as 45 degree antenna can be deployed. Thischoice must be made in consultation with the service provider, and theyshould be made aware of the impact on the capacity of the Six Sector cell.Using a 45 degree antenna may result in 10% drop in the capacity of the SixSector cell vs. its capacity with 33 degree antenna. Please note that with usingproper cell orientation (see Figure 2-1), it is possible to reduce the risk ofcreating holes within the coverage area using 33 degree antennas.

Antenna GainThe choice of antenna gain depends upon whether the site is being re-configured from a three sector to six sector, or the site was configuredoriginally as a six sector.

Reconfiguring a Three Sector to Six SectorWhen a three sector site is re-configured to a six sector site, the antenna gainshould be chosen as close to the antenna gain of the original three sector siteas possible. This ensures that the link budgets are similar for the original threesector as well as for the six sector.

2-2 Antennas


New Six Sector siteWhen the site is new and chosen to operate as a six sector, the antenna gainchosen should be close to the antenna gain of its neighbour cells (which inmost cases happen to be three sector site). Otherwise, the guide on theantenna gain is the link budget, which includes the assumed antenna gain forthe majority of sites.

Diversity Options for Six SectorTwo types of diversity can be used in six sector applications. These are: spacediversity and dual polarization diversity. Both options have advantages anddisadvantages:

Space diversity has a small diversity gain advantage (around 0.2 to 0.5 dB)compared to dual polarization diversity. This gap may be larger in rural areaswhere there is less cluttering (resulting in less cross polarization between thepolarized antennas). In rural areas or some suburban areas (very flat withscattered low rise houses) where there is less cluttering on the forward link,dual polarization may be degraded further than space diversity by the lack ofcluttering.

Cost-wise, the space diversity is more expensive than the dual-polarizedoption. In space diversity 12 single polarization antennas are needed, while indual polarization only 6 antennas are needed. Furthermore in mast mountapplications, space diversity needs hexagonal platforms, while dualpolarization can use the original triangular platform of the three sector cell.The hexagonal platform is bigger than the triangular (see Figure 2-1 forcomparison), which will make it more expensive. Additionally, withstandingwind, size, and other environmental and mechanical issues related to thelarger size will make the hexagonal platform more expensive. Time-wise, it iseasier and faster to deploy dual polarized antennas, especially, since there isno need to dismantel the original triangular platform. This significantlyreduces the interruption in service, a major issue with the service provider.

Antenna OrientationSix Sector cell in a cluster of Six Sector cells.

To achieve best performance (capacity and coverage) the antenna of a sixsector cell must be oriented in so that the sectors do not face each other.Figure 2-1 shows the orientation which achieves the best performanceregarding both capacity and coverage. This type of orientation is useful whennarrow beam antennas are used since every antenna is beaming in a directionwithout facing directly other antennas. A patent has been filed for this type ofSix Sector antenna orientation.

Figure 2-2 shows a sub-optimum antenna orientation resulting in poorcoverage areas (coverage holes). In this configuration each sector of eachBTS is directly facing a sector of a neighbour BTS resulting in greater

2-3


interference and a reduction in capacity. There are also locations at theintersecting edges of the three antennas which may result in coverage holes.

Figure 2-3 shows another sub-optimum antenna orientation, which results inpoor coverage areas (coverage holes), as well as areas with high pilotpollution. In this configuration, three sectors of adjacent BTSs are directlyfacing each other resuling in greater interference and lower capacity numbers.There are also locations at the intersecting edges of the three antennas whichmay result in coverage holes.

It is preferred to deploy the antennas as close as possible to the orientationshown in Figure 2-1.

Figure 2-1Six Sector cell orientation for optimum capacity/coverage Performance

Antenna Beamfor Each Sector

2-4 Antennas


Figure 2-2Another type of antenna which results in poor coverage and capacity


Antennas facing each other, increasinginterference and reducing capacity

poor coverage area

2-5


Figure 2-3Another type of antenna which results in poor coverage and capacity

Six sector cell in a cluster of three sector cellsIn most cases a single Six Sector cell or a very limited number of six sectorcells will be deployed in a cluster of three sector cells. Figure 2-4 shows acluster of three sector cells with the central cell configured as a six sector cell.One option available to orient antennas to optimize performance is to divideeach sector of the three sector cells into two sectors to establish a six sectorcell. This option is shown in Figure 2-5, option A. This type of Six Sectororientation results in a condition where none of the antennas of the six sectorsdirectly face any antenna of the neighbour three sector cells. This is importantin controlling interference and achieving good capacity numbers. However,there are coverage holes where no antenna is radiating as highlighted inFigure 2-5, option A.


poor coverage area

pilot pollution area

2-6 Antennas


A solution is to rotate (in horizontal plane) the six sector antennas by 30o(clockwise or counterclockwise) as shown in Figure 2-5, option B to coverthe holes. However, three sectors of the six sector cell will directly faceneighbour sectors, increasing the interference between them and those sectorsthat they are facing. An option is todowntilt these antennas so that thecoverage area of these sectors shrinks, reducing interference intoneighbouring sectors.

The diagrams shown here, depict a very uniform and perfect cell layout. Inreality cells are not layed out perfectly, and their antenna orientation is not sowell defined. Field engineers must consider the antenna angles andorientation of surrounding three sector cells with those of the six sector cell.The antennae of the six sector cell must be oriented so that no coverage holesare created between the six sector cell and its neighbour. This helps in usingnarrower beam antennas to improve capacity. If by rotating the antennas,some of the six sector antennas directly face neighbouring three sectorantennas, then those six sector antennae should be downtilted (only those thatare directly facing the neighbour Three Sector cells).

Figure 2-4A typical three sector cell


This cell will beconfigured to aSix Sector Cell

2-7


Figure 2-5Deploying a Six Sector in a cluster of three sectors



poor coverageArea

Sectors facing eachother, increasinginterference to eachother.

A

B

Downtilt these Sectorsto reduce interference

2-8 Antennas


3-1


3Transition from Three Sector to SixSector

Certain procedures must be followed to successfully deploy a six sector cellin a cluster of three sector cells. These steps are required to ensure that thereis minimum service interruption where the six sector is being deployed. If theantennas are roof-mounted where no special platform is needed, fieldengineers can choose either the space diversity or dual polarization option,since deployment of both types of antennas is much easier than a mast-mounted condition. The roof mount condition is simple and variable (in termsof the position of the antenna w.r.t., the roof, and where they are deployed).For this reason the transition for the “roof mount condition” is not coveredhere. The following sub-sections discuss the transition from a three sector to asix sector for mast-mount antennas.

First StepThe first step is to find out whether the six sector with the recommendedantenna provides proper coverage. To achieve this some analysis can be doneusing PLANET. If PLANET is used, orient the antenna w.r.t. to the neighbourcells. The analysis should indicate if there are coverage holes. For a goodcomparison, run an analysis for the cell when it was configured as a threesector cell to see if there is degradation or improvement in coverage if the cellis configured as a six sector. While PLANET is used for analysis, ensure thatcapacity is not sacrificed for coverage.

Six Sector with Space Diversity AntennaIf space diversity antennas are installed, then the platform should be modifiedto a hexagonal type as shown in Figure 3-1. Here the platform is larger thanthe normal triangular platform since there is a minimum required spacingbetween the main antenna and the diversity antenna.

The minimum distance between the antennas (main vs. diversity) of the samesector should follow the following equation: d> h/11, where d is the antennaseparation and h is the antenna height. Also note that the antennas of theadjacent sector at the vertex should be mounted in such a way that the bestisolation is achieved between the two antennas. Sometimes, antennas have

3-2 Transition from Three Sector to Six Sector


high peak sidelobes which may fall into the neighbour sector antenna. Thismay reduce the margin of antenna isolation. Some tuning of the positionwhere the antennas are mounted may be needed with respect to the neighboursector to ensure that there is enough isolation between the two antennas.

As shown in Figure 3-1, in order to meet the minimum requirement for spacediversity antenna separation, the edge of the hexagonal platform will be thesame length as that of the triangular platform. Mounting such a huge platformmay cause some problems, especially in meeting the wind and loadrequirements of the mast. It is recommended that before installing such aplatform that the issues of wind, weight, and other mechanical metrics areinvestigated and approved to reduce the delay in installing the BTS and costto the service provider.

Use of the three sector platform to mount space diversity antennas is NOTrecommended (see Figure 3-2 for details). The reason for this is that byinstalling the six sector antenna on three sector platform, the spacing betweenthe main antenna and the diversity is significantly reduced. Furthermore,antennas mounted in the central part of the platform need to be extendedsignificantly outward so that they see the cell edge, further complicating thewind and other mechanical issues.

Note: Antennas for six sector are rotated by 30 degrees.

Steps to be taken:

1. Before installation, ensure that the direction of the six sector antennaswith respect to its neighbour are worked out to achieve best capacity/coverage performance.

2. Install the 2nd BTS in the cell-site which will be configured as a sixsector.

3. Wilt and disconnect the three sector from its antennas.

4. Mount the six sector platform (the three sector platform may requiredismantling).

5. Install the antennas of the six sector.

6. Update the neighbour list to include the PN number of the second BTS.

7. Connect the RFFEs of both BTSs to six sector antennas.

8. Blossom both BTSs and verify bydrive testing that:

• both BTSs are operational.

• coverage is provided by both BTSs (six sector).

• handoff occurs between the six sector cell and its neighbour.

• there are no excess access failures near the antenna mast of the six sectorcell.

3-3


Note: The above steps will result in severe service interruption while thethree sector antennas and their platform are dismantled and the six sectorantennas (with their new platform) are mounted.

Figure 3-1Hexagonal platform for six sector antennas, using space diversity

six sectorAntennas

three sectorAntennas

three sectorPlatform six sector

Platform

Equ

al s

ide

plat

form

s



Figure 3-2Space diversity on three sector platform IS NOT RECOMMENDED

Six Sector with Dual Polarized AntennasIf dual polarized antennas are installed, the triangular platform of the threesector can be used to install the six sector dual polarized antennas. Thefollowing steps explain how to install the six sector with minimuminterruption:

Phase 1:Installing the Second BTS:

1. Install the 2nd BTS (in the cell-site which will be configured as a sixsector).Do not connect the second BTS to any antenna, see Figure 3-3.

2. Modify the datafill so that new datafill includes the PNs of the new sectorsof the second BTS.

six sectorAntennas


three sectorPlatform

Shrin

kage

of

Ante

nna

Spac

eNot Recommended

3-5


3. Connect the 2nd BTS to a dummy load and verify that it is functional inall its three sectors.

Phase 2:Configuring the site as a six sector BTS:

1. Before installation ensure that the direction of the six sector antennas withrespect to its neighbour are worked out to achieve the best capacity/coverage performance.

2. If the results of Phase 1 are positive and satisfactory, in a maintenancewindow wilt the first BTS and disconnect it’s RFFE cable from the threesector antennas (all three sectors and both diversity and main antenna).

3. Update the neighbour list to include the PN number of the second BTS.

4. Next install the narrow-beam dual polarized six sector antennas, as shownin Figure 3-4.

5. Connect all sectors of the two BTSs (the six sector) to the six sectorantennas as shown in Figure 3-5.

6. Blossom the two BTSs.

7. Ensure that the two BTSs are functional and verify by drive testing that:

• both BTSs are operational.

• coverage is provided by Both BTSs (six sector).

• handoff takes place between the six sector cell and its neighbour.

• that there are noEXCESS access failure near the antenna mast of the sixsector cell.

8. The antennas of the three sector (the old antennas) can be removed or beleft on the antenna mast. This action should be taken in consultation withthe customer. If the decision is to leave the three sector antennas on themast, then the mechanical issues of the extra load on the mast should bereviewed.



Figure 3-3Phase 1 of the installation: the 2nd BTS is installed, but not connected to antennas

Figure 3-4Installing the Six Sector Antennas on a Triangular (Three Sector) Platform

BTS #2

RFFESect #1

RFFESect #2

RFFESect #3

BTS #1

RFFESect #1

RFFESect #2

RFFESect #3


Only BTS #1 is connected to the antennas.BTS#2 is installed,but it IS NOT CONNECTED to the antennas.

Dummy Load

six sectorAntennas

six sector antennas (Dual polarized) are mounted


on brackets and tilted by 30 degree, if necessary.

Sector #1 Sector #2

Sector #3

Sector #4Sector #5

Sector #6

Brackets

3-7


Figure 3-5Phase 2 of the installation, the site is configured as a Six Sector site

six sectorAntennas

Both BTS #1 and BTS #2 are connected to the six sector antennas.three sector antennas are either removed or left disconnected.

BTS #1

RFFESect #1

RFFESect #2

RFFESect #3

BTS #2

RFFESect #1

RFFESect #2

RFFESect #3




4-1


4Six Sector Capacity

Forward Link CapacityAnalysis show that the forward link capacity of a six sector embedded in acluster of six sector cells (using 33 degree antennas) is approximately 1.7times that of a three sector cell. This number was confirmed in a series of testscarried out in Kansas City. The test in Kansas City was carried out for apartially embedded six sector cell in a cluster of three sector Cells (4 threesector cells). The tests in kansas City showed a capacity increase of 1.8 timesfor 33 degree antenna beam width.

Reverse Link CapacityThe Reverse Link Pole capacity of a CDMA cell is given by:

W/R is the processing gain, Eb is the energy per bit, No is the noise powerspectral density, v is the voice activity factor, G is the sectorization gain, andF is the frequency reuse factor. From the equation, it is obvious that thereverse link capacity has a linear relation with the frequency reuse factor.Analysis shows that the re-configuration of a three sector cell to a six sectorcell results in a decrease in Frequency Reuse factor F. In the following sectionthe frequency reuse factor of a three sector cell, as well as that of a six sectorcell (in a cluster of six sector cells as well as in a cluster of three sector cells)are tabled. In these calculations G is assumed to be equal to 3 (and not 2.55 asquoted in some other CDMA literature, which inherently has the reduction inF factor). Furthermore, the frequency reuse factors are calculated based on theHata model, which works out to a path loss exponent of about 3.5.

NWR----- 1

Eb

No------

------------• 1

v---• F• G•=

4-2 Six Sector Capacity


Three Sector Cell CalculationThe following table summarizes the Frequency Reuse Factor for athreesector Cell (calculated for different antenna Beam width):

The results indicate that in order to have the best reverse link capacitynumber, it is important to use narrower beam width antennas. This pointshould be taken with caution, and that in planning the cells and their antennaorientation, the designer should attempt to orient the antennas in such a waythat the antennas of the neighbor cells do not face each other. This way,narrower beam antennas has a better chance in providing better coverage.Otherwise, we may face having some holes within our coverage area, forcingus to use wider beam antennas, which will result in lower reverse linkcapacity numbers.

Fully Embedded six sector cell CalculationThe following table summarizes the Frequency Reuse Factor for asix sectorCell embedded in a cluster of six sector cells (for different antenna beamwidth):

Table 4-1Frequency Reuse Factor for three sector cell cluster

Antenna Beam width(Horizontal)

Frequency ReuseFactor

60o 0.55

70o 0.53

80o 0.51

90o 0.49

100o 0.47

110o 0.45

120o 0.43

Table 4-2Frequency Reuse Factor For six sector Cluster

Antenna Beam width(Horizontal)

Frequency ReuseFactor

30o 0.51

40o 0.49

50o 0.44

60o 0.40

4-3


Six sector cells require narrower beam width antennas than that of the threesector cells. For this reason the analysis for six sector is restricted to beamwidth from 30o to 60o range. Like for three sector cell, the results indicate thatunder similar conditions, the 30o antenna would provide about 5% morereverse link capacity than the 40o antenna.

A six sector embedded in three sector cellsThe following table summarizes the Frequency Reuse Factor for asix sectorCell embedded in a cluster of three sector cells (for different antenna beamwidth. The results show the frequency Reuse Factor of the sector (c), andSector (d) of the six sector cell (see Figure 4-1), as well the frequency ReuseFactor of the sector (a), and Sector (b) of the three sector cell as shown inFigure 4-1.

The results indicate a drop in the Frequency Reuse Factor of the three sectorcell, while the central six sector cell shows an increase. Please note that theFrequency Reuse Factor of those three sector Cells facing the six sector celldecreases. The reason for this decrease and increase is that each Sector of thesix sector cell is now facing half of a Sector of the three sector cell (hence lessinterference seen by the six sector, and better Frequency Reuse Factor), whilejust the opposite happens, where each Sector of a three sector cell faces 2sectors of a six sector cell (more interference seen by the three sector, andworse Frequency Reuse Factor).

Table 4-3Frequency Reuse Factors of Lettered Sectors in Figure 4-1

Horizontal Antenna BW3 sectors/6 sectors

Frequency Reuse Factor of Sectors

three sector six sector

Sector a Sector b Sector c Sector d

60o(in 3 sector)/30o(in 6 sector) 0.43 0.49 0.65 0.62





Figure 4-1Computing the Frequency Reuse Factor of a six sector in a cluster of three sectors

Impact on the neighbor cell forward link capacityAnalysis indicate that the forward link capacity of the neighbor cells willdecrease by about 5 to 10%, when a three sector is configured as a six sector.These numbers are based on simulation only. Attempts have been made in thefield to measure the impact, but no conclusion could be made on the impact,due to the data corruption. This section will be updated, once more reliablefield information is collected.

DatafillThe deployment of a six sector should be treated like adding a new cell site,as far as the datafill is concerned. For this reason the six sector deployment


d

c

b

a

Freq Reuse factors of theseSectors of a three sectorcell is computed.

Freq Reuse factors of theseSectors of a six sectorcell is computed.

4-5


involves a small amount of work. The following issues/steps must be takenfor the datafill:

• PN Numbers for the second BTS.

• Cell_id numbers for the second BTS.

• Pilot database updated to include the new PN numbers

• Ports on CIS allocated.

Channel Element (CE) UsageThe CE usage of a six sector site is about 10% more than that of a three sectorsite. However, the number of users in a sector of a six sector site is about 10%less than of a Sector of a three sector. For this reason, the combined CE usagewill not change for a six sector site. This statement is valid as far as a sixsector is deployed using two three sector BTSs.

Reverse Link BudgetThere is no change in the reverse link budget of the cell site, when the sixsector is being deployed, provided the antenna gain and feeder loss are thesame. If any of these factors change, then the link budget should be verified,to ensure that the link budget is valid for the new cell condition. Please notethat the statement in Section on Frequency Reuse Factor of the reverse linkcapacity should not be confused with the reverse link budget.

T1 Link RequirementAt present a six sector is made by putting two three sectors back to back. Byre-configuring a three sector to a six sector, there is a greater load on the T1link, and for this reason, 2 T1s are required (1 for each BTS). It is notrecommended to daisy chain the two BTSs to one T1 link.

The following inputs and calculations were used to determine if one (daisychained BTSs) or two T1s should be deployed to support a six-sectorconfiguration. Since this configuration is typically deployed inhigh trafficregions, the inputs reflect heavy loading almost to the point of blocking due toa lack of power on the RF air link on two sectors of the six sector cell.

Inputs:

2. 2 BTSs configured a six sector cell.

3. 2.2 CE/user (average)

4. 11 users/sector on 2 sectors (see note below)

5. 5.2 users/sector on 4 sectors (see note below)

6. T1 Capacity (13K vocoder, 1.344Mbps effective BW) = 86 Calls (Eachcall uses one CE on a single BTS)



Note: When determining the users/sector, 5.2 is used as the average valueon all 6 sectors. However, for traffic loading that approaches a blockingpoint (from a lack of RF power), at most two sectors may peak to a valueof 11 while the other four remain near the average.

Calculations:

Total CEs = (11)*(2)*(2.2) + (5.2)*(4)*(2.2) = 94 > 86.

Therefore, based on the inputs,two T1s should be deployed.

Note: One T1 could be deployed if the expectation is that the six sectorsite will not provide service to higher than average number of users, or ifthe CE usage is improved. Please also note that there is no DISCO portadvantage since two ports must be assigned no matter if one or two T1sare used.

References:1. “six sector Analysis”, issue 0.1, 25 February 1998, by Ashvin Chheda.

2. “Diminishing Return of six sector and Second Carrier”, by FarhadBassirat, 10 September 1997.

3. Mobile Communications Engineering, by W.C.Y. Lee, McGraw-HillBook co.

4. “Communication System Having Optimum Resource Arrangement in aMulti-Sectored Environment and Method Therefor”, by Ashvin Chhedaand Farhad Bassirat, Attorney Docket No. RR-2063, 28 May 1997.

5. “Enhanced Cellular Layout for CDMA Networks Having six sectoredCells”, by Ashvin Chheda and Farhad Bassirat, Attorney Docket No. RR-2057, 20 May 1997.

6. PLANET is a simulation Tools by MSI International.

7. NTP 411-2133-121; Inter-system/Inter-BSC Soft Handoff (ISSHO)Handbook

8. NTP 411-2133-122; Second Carrier Overlay Handbook

Family Product Manual Contacts Copyright Confidentiality Legal statements DocInfo

CDMA

Six Sector CellApplicationsHandbook

Nortel,Department 34314300 EmperorMorrisville, NC 27560Phone: 1-800-684-2273Fax: (919) 905-5854 attn: Wireless documentation

Copyright 1998 Northern Telecom

NORTHERN TELECOM CONFIDENTIAL: Theinformation contained in this document is the property ofNorthern Telecom. Except as specifically authorized in writingby Northern Telecom, the holder of this document shall keep theinformation contained herein confidential and shall protect samein whole or in part from disclosure and dissemination to thirdparties and use same for evaluation, operation, andmaintenance purposes only.

Information is subject to change without notice.DMS, DMS SuperNode, DMS-MTX, DMS-100, and MAP aretrademarks of Northern Telecom.411-2133-123NBSS 7.0Standard 01.01September 1998Printed in the United States of America

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