Alternate RF Planning for Coverage Deficiancy

December 2002 • Volume 1, Number 1

IINNTTRROODDUUCCTTIIOONN

This paper introduces a few of the more common alter-natives to the usual RF (radio frequency) planning

solutions for coverage deficiency problems. These meth-ods are being applied after or concurrently with the RFdesign activity, as well as during the implementation andoperations phases of network life.

Five solutions for coverage deficiency problems aredescribed in this paper, namely:

• Microcell Solution - 1• Off-Air Repeater Solution - 2• FO (Fiber Optic)/RF Solution - 3 (with two options)• TMA (Tower-Mounted Amplifier) Solution - 4• Leaky Coax Solution - 5 (with two options)

Each of the solutions is presented in a general descrip-tion with an illustrative diagram and/or figure, a configu-ration to suit the proposed example, and implementationnotes. The options demonstrate the flexibility that needsto be present in RF designs. These examples also providevaluable points of comparison. General recommenda-tions are provided in the Conclusion. Although the exam-ples are described using U.S. measurement units, theprinciples are easily transferred to international applica-tions and metric units.

Example of Coverage Objective and LimitationsA hypothetical town that stretches 1,000 yards along a

relatively straight portion of a two-lane road is chosen asthe example for coverage deficiency. The portion of theroad that runs through the town, as well as the first rowof shops on both sides of the road, should be coveredwith street level coverage at -95 dBm with 95 percentreliability. It will be assumed that the rest of the road iscovered at -95 dBm level or better. Access to the lightpoles along the road has been granted, but every othertype of installation is prohibited by the town.

Solutions Are VersatileEven though the methods are applied in this paper to

a GSM (global system mobile) telecommunications sys-tem in the 1900 MHz PCS (personal communicationservice) band for ease of comparison, in principle, thesemethods can be used successfully for a range of wirelesssystems in PCS and other bands.

MMIICCRROOCCEELLLL SSOOLLUUTTIIOONN - 11

The road and the buildings on each side of the road canbe covered with a 5W microcell. This solution provides

omni coverage, with maximum coverage in the middle ofthe town and minimum coverage at the town edges.

ConfigurationOne 5W microcell should be installed in the middle of

the town at the base of the light pole. One ½-in. coaxcable will run up to 20 feet on the light pole to the single3-foot omni antenna. See Table 1 for the detailed linkbudget.

According to this prediction, the RSSI (received signalstrength indicator) level of -95 dBm can be expected at600 yards from the antenna location with 95 percent reli-ability. (This link budget is provided only as an example.The RF design software package with its correspondinglink budget should be used to plan the real system.)

Implementation NotesThis design is part of the regular RF planning/design

process, as well as Implementation process, except forthe following stealthing requirements: The coax cableshould be ordered in a specific color to match the lightpole, while the antenna and microcell outdoor cabinetcan be painted for stealthing.

See Figure 1 for an example of the installation.

37

Alternative RF Planning Solutionsfor

Coverage Deficiency

Aleksey A. Kurochkin

[email protected]

Issue Date: December 2002

Bechtel Telecommunications Technical Journal

OOFFFF-AAIIRR RREEPPEEAATTEERR SSOOLLUUTTIIOONN - 22

Off-air repeaters are bi-directional power amplifierswith gains varying from 50 to 90 dB. They provide

coverage by repeating the frequency of the base stationin areas that lack coverage. There may be some overlap,but this overlap should be minimal. This solution requirestwo off-air repeaters and the assumption that there issufficient signal level from the two donor cells on eachside of the town for the repeaters to operate.

ConfigurationOne off-air repeater should be set up in the area of the

reliable signal received on the donor antenna outside ofthe town. The transceiver coverage antenna of therepeater should be directed toward the town center. Ifone repeater does not provide satisfactory coverage, thesecond repeater should be installed using the other cellas a donor.

Figure 2 shows a system drawing of an off-air repeatersystem.

38

Project Name: 1000 Yard Town 4.00 <-- Site Area TypeSite Name or Sector Name: Microcell Area Coverage Reliability (60-99): 95%

BTS Rx Band Frequencies, MHz: 1895 SU Rx Band Frequencies, MHz: 1980MHz: 1900 MHz: 1985

Forward Link Reverse Link

What Kind of System is Used?: 5 What Kind of SU is Used?: 8

What Kind of Amplifier is Used?: 4 SU Antenna is OutsideWhat Kind of CU is Used?: 2

BTS Antenna Gain (dBd): 4 SU Antenna Gain (dBd): 0Max Amplifier Output per Ch. (dBW): 7 Amplifier Output max (W): 1.2

Number of RF per antenna: 2Height of Cell Site Antenna (m): 7 Height of SU Antenna (m): 1.5

Antenna to Hatchplate Cable Run (m): 7 SU to Antenna Cable Run (m): 0BTS RF Cable: 4 SU RF Cable: 9

RF to Hatchplate Cable (m): 0Duplexors Included?: N

SU Diversity Gain (dB): 0.0 BTS/4-way Diversity Gain (dB): 0.0BTS Receive Sensitivity (dBm): -106 SU Receive Sensitivity (dBm): -103

Penetration Loss (dB): 0 0Fade Margin for 95% Area Coverage 14.7 Reliability (s=10), (dB): 14.7

Total Margin (dB): 14.7 14.7

LINK BUDGET CALCULATION AREA

Central RF for Calc. (MHz) 1800.0 1800.0RF to Hatchplate Cable loss (dB) 0.0

Two connectors (dB) 03m antenna jumper loss (dB) 0

BTS Duplexor Tx loss (dB) 0 BTS Duplexor Rx loss (dB) 0BTS Tx filter loss (dB) 0 BTS Rx filter loss (dB) 0

Combiner loss (dB) 2.2BTS RF Cable loss (dB) 0.7 SU RF cable loss (dB) 0.0

FW Max Allowable Path Loss (dB) 126.4 RV Max Allowable Path Loss (dB) 126.1Sugg. Amplifier Output/1 ch. (dBW) 6.7 Closest Amplifier Setting (dBW) 6.7

Sugg. Amplifier Output/1 ch. (W) 4.7 System Amplifier Output/1 ch. (W) 4.7Balanced Model ERP (dBm) 37.8 System ERP (dBm) 37.8

Balanced Model ERP (W) 6.1 System ERP (W) 6.1

Hata Model Calculation Output Balanced Link (dBm) 126.1Karea 8.3 Min RSSI for the Model (dBm): -88.3

Approx. Cell Site Radius, km 0.6 Min RSSI for the System (dBm): -94.4

LDF4-50A ½" None

Suburban High Dense

DMCU

MICROStandard PortablePCS-1900 BTS

Table 1. Microcell Link Budget

December 2002 • Volume 1, Number 1 39

'

Figure 1. Microcell Solution

VerticalAntenna

SeparationRequirement

Radio tower

Antenna

Antenna Antenna

latigid

Ba Net wor ks

RepeaterCoverageAntenna

RepeaterDonor

Antenna

Base StationTX/RX

Antenna

RepeaterBaseStation

Base Station Coverage Area Repeater Coverage Area

F1F1

Radio Tower

Anten

na

Anten

na

Anten

na

latigid

Ba Net wor ks


RepeaterDonor

Antenna

Base StationTX/RX

Antenna

RepeaterBaseStation

Base Station Coverage Area Repeater Coverage Area

F1F1

Figure 2. Off-Air Repeater Diagram

Bechtel Telecommunications Technical Journal 40

Figure 3. Off-Air Repeater Solution

Radio tower

latigid

Bay Net wor ks


Base StationTX/RX

Antenna

RepeaterBaseStation

Base Station Coverage AreaRepeater Coverage Area

F1F1

RF CouplerRF/Opticalconverter

RF/OpticalConverter

Fiber

Antenna

Antenna Antenna

Radio Tower

latigid

Bay Net wor ks

latigid

Bay Net wor ks


Base StationTX/RX

Antenna

RepeaterBaseStation

Base Station Coverage AreaRepeater Coverage Area

F1F1

RF CouplerRF/OpticalConverter

RF/OpticalConverter

Fiber

Anten

na

Anten

na

Anten

na

Figure 4. Single FO/RF Repeater Option Diagram

December 2002 • Volume 1, Number 1

Implementation Notes

• The capture antenna (repeater donor antenna inFigure 2) must be highly directional and have afront-to-back ratio of more than 25 dB.

• The coverage antenna should have a front-to-backratio of more than 25 dB.

• The isolation requirements should be at least 15 dBmore than the gain setting of the repeater.

• As much vertical and horizontal separation as pos-sible should be provided between the capture andcoverage antennas of the repeater.

• Better isolation would be obtained if the captureantenna could be shielded from the coverageantenna.

• The coverage overlap should be minimized.• Balance of the uplink and downlink should be

ensured.• An attenuator at the capture antenna port of the

repeater should be used to increase isolationbetween antennas.

There are no means of predicting either the location ofthe repeater or its coverage during the standard desktopRF planning/design process. The town and the donorcells coverage will need to be drive-tested to select thebest location for the repeaters.

The repeater installation should follow the standardimplementation process. Stealthing would usually not berequired because both repeaters would be installed out-side of the town limits.

Once installed, the town area would need to be drive-tested again, and the repeater direction may need to beadjusted to ensure the coverage. This could be an itera-tive process to achieve best results.


FFOO//RRFF SSOOLLUUTTIIOONN - 33

The FO/RF solution is based on a wireline repeater sys-tem. Wireline repeater systems use a hardwire con-

nection between the base station and the repeater. Thisis normally used for campus and/or indoor installations.There are two options for this solution: a single repeaterlocation and a distributed antenna system.

Single FO/RF Repeater OptionFigure 4 shows that the RF is sampled via a coupler

between the base station and the base station antenna,then sent to an optical converter where it is converted tooptical signals and sent across fiber to the repeater loca-tion. At the repeater location, the optical signal is con-verted to RF and up-converted to the same RF frequencyand transmitted to the repeater coverage antenna.

ConfigurationAssume that one of the neighboring cells has access

to a dark fiber installed along the road of interest. A ½-in.coax jumper connects BTS (base transceiver station)amplifier output with a splitter and connects the splitterto an RF-to-fiber converter. A fiber string is run from thisconverter to the fiber-to-RF converter, which has a nomi-nal 5W of RF power output and will be installed on thelight pole in the middle of the town. A ½-in. coax cableconnects this converter with 3-foot omni antenna.

The link budget for this application is the same asshown in Table 1.

According to this prediction, the RSSI level of -95 dBm canbe expected at a 600-yard distance from the antenna locationwith 95 percent reliability. The link budget is provided forexample only. The RF design software package with its corre-sponding link budget should be used to plan the real system.

41

'

BTS

Figure 5. Single FO/RF Repeater Option Solution


Radio Tower

RF/Optical converter

Base Station

RF Coupler

2ft - 3 dBd OmniAntenna

Jumper cable betweenRAU and Antenna

28 ft highTelephone Pole

Remote AntennaUnit

Composite fiber and power cable

C om3 Co m3 Co m3 Co

Extended Coverage Area

AntennaFeeder Cable

Site 2 Site 3 Site 20

Distributed Antenna System Using Fiber Transport

Equipment at the BTS Location

Site 1

RF/Optical Converter

Base Station

RF Coupler

2ft - 3 dBd OmniAntenna

Jumper cable betweenRAU and Antenna

Remote AntennaUnit

Composite fiber and power cable

C om3C om3 Co m3Co m3 Co m3Co m3 CoCo

Extended Coverage Area

AntennaFeeder Cable

Site 2 Site 3 Site 20

Distributed Antenna System Using Fiber Transport

Equipment at the BTS Location

Site 1

Figure 6. Distributed Antenna System Option Diagram


Implementation NotesA team with a system engineering specialist and an RF

engineer will be needed to design this system. A systemvendor will be needed to install the RF/fiber system andcomponents. The system installation should follow thestandard implementation process. The coax cable can beordered in a color to match the color of the light pole,while the antenna and fiber-to-RF outdoor box can bepainted for stealthing.


Distributed Antenna System OptionDistributed antenna systems make use of telephone

poles, lamp poles, or other lower height structures thatdo not present any zoning/permitting issues. This systemis basically extending a base station antenna's reachwhere coverage would otherwise be lacking. This systemis most useful in towns where zoning/permitting is verydifficult and for areas that are blocked by terrain or buildings.

ConfigurationAs shown in Figure 6, the RF path is sampled at the

antenna port of the base station and sent to an opticalhub located at the base station. This RF signal is firstconverted to data stream and then converted to opticalsignals. The optical signals are sent along optical chan-nels to the remote antenna system, where the optical sig-nals are reconverted to RF and transmitted over a low-gain small omni antenna.

Each hub can support 20 to 24 remote antenna units.This means that 24 remote antenna units can be simul-casting at the same time to extend the base station'sreach into uncovered areas. The manufacturers indicatethat more hubs can be daisy chained to support many

more remotes. Information to confirm the limitation ofthis has not yet been obtained.

The power to the remote antenna unit can be providedby a composite power and fiber cable. The distance fromthe main hub will be limited by the power deterioration,which, for most manufacturers, is about 12 km. If poweris available at the remote end, then the distance will belimited by the single mode fiber run.


engineer will be needed to design this system. A systemvendor usually installs the RF/fiber system and compo-nents. The system installation should follow the standardimplementation process. The coax cables can be orderedin a color to match the light pole color, and the antennasand remote antenna unit box can be painted for stealthing.

Some implementation advantages of this method are:

• A low mobile station transmits power throughoutmost of the coverage area.

• There is flexible traffic capacity planning and easeof future system/traffic capacity expansion.

• Strong protection is provided against blocking fromuncoordinated mobiles.

• There is low environmental impact of electronicequipment and antennas.

Two implementation concerns are:

• Power must be available to the remote antenna unit.• Overlap must be minimized.

Ant

TMA

Rx

Rx Cable

To BTS

RX BP

LNA

Ant

TMA

Tx/Rx

Rx Cable

Duplex

LNA

Tx Cable

Ant

TMA

Tx/Rx

Tx/Rx Cable

Duplex

LNA

Duplex

Ant

TMA

Rx

Rx Cable

To BTS

RX BP

LNA

Ant

TMA

Rx

Rx Cable

To BTS

RX BP

LNA

Ant

TMA

Tx/Rx

Rx Cable

Duplex

LNA

Tx Cable

Ant

TMA

Tx/Rx

Rx Cable

Duplex

LNA

Tx Cable

Ant

TMA

Tx/Rx

Tx/Rx Cable

Duplex

LNA

Duplex

Ant

TMA

Tx/Rx

Tx/Rx Cable

Duplex

LNA

Duplex

Figure 7. Simplex TMA Figure 8. Duplex TMA Figure 9. Dual Duplex TMA


TX RX

SimplexTMA

TX/RX

RX

DuplexTMA

TX/RX RX

SimplexTMA

TX

RXTX RXTX RXTX/RX

Antenna

Antenna

Antenna

RXTX/RX

latigid

BTSlatigid

BTSlatigd

BTS

Use of Simplex TMA Use of Duplex TMA Use of Dual DuplexTMA

Dual PolarizedAntenna

Dual PolarizedAntenna

Diagram Showing Connectivity of Different TMAs

RX BP

LNA

Duplex

LNA

RX BP

LNA

Duplex

LNA

Duplex

TX RX TX/RX

RX

TX/RX RX

TX

RXTX RXTX RXTX/RX

Anten

na

Anten

na

Anten

na

RXTX/RX

latigid

BTSlatigid

BTSlatigid

BTSlatigid

BTSlatigd

BTS

Use of Simplex TMA Use of Duplex TMA Use of Dual DuplexTMA

Dual DuplexTMA

RX BP

LNA

RX BP

LNA

RX BP

LNA

Duplex

LNA

Duplex

LNA

Duplex

LNA

RX BP

LNA

RX BP

LNA

RX BP

LNA

Duplex

LNA

Duplex

Duplex

LNA

Duplex

Figure 10. TMA Usage Diagram


TTMMAA SSOOLLUUTTIIOONN - 44

TMAs can extend the range of the uplink of cell sitesinto areas that would otherwise lack coverage with

comparatively very little additional cost. They are typicallylow noise amplifiers with band pass filters, duplexers,and dc blocks.

TMAs are normally used to enhance the receive signalstrength at the antenna where the uplink signal is weak.Installation of a TMA leads to:

• A decrease in dropped calls • An increase in in-building coverage• An increase in in-car coverage • A decrease in output power of the mobile, and

hence an increase in battery life

TMAs can be used to optimize networks, which mightresult in a decrease in the number of base stationswhere there is some difficulty in obtaining additional sites.

There are basically three types of TMAs:

1. Simplex TMA (Figure 7) is basically a low noiseamplifier. It amplifies the receive signal at theantenna. This type of TMA is used in the receivedirection only, where the signal at the antenna isweak enough to cause dropped calls or is close tothe receiver threshold. This is connected to a sepa-rate antenna port.

2. Duplex TMA (Figure 8) allows separated transmitand receive feeder cables to be connected to thesame antenna port, thus eliminating the require-ment for additional antenna ports or antennas.

3. Dual duplex TMA (Figure 9) allows a combinedTx/Rx cable to be used at both ends of the TMA,which decreases the number of cables and antennas.

Figure 10 illustrates sample connections for TMAs.

ConfigurationIf the system link budget is uplink limited and trans-

mission line losses are higher than 3 dB, one TMA shouldbe installed on each of the sites adjacent to the town cellsites. This allows an increase in the output power of therespective BTSs. This, in turn, increases cell site coverage.

Once a TMA is installed, it cancels the receive trans-mission cable loss but adds 1 dB to the BTS receive noisefigure and 0.5 dB to the insertion loss. If each of the sitesincreases its coverage by 800 yards, the town will be cov-ered by both cell sites with some overlap.


engineer will be needed to design this system. The sys-tem installation should follow the standard implementa-tion process. There are no stealthing requirements,because TMAs will be installed on the cell sites beyondthe town limits.

Where possible, avoid using TMAs where the feederloss is less than 3 to 4 dB. The reason for this is that in-band interference will be amplified with the incoming signaland deteriorate the sensitivity of the receiver in the BTS.

Care must be taken to utilize TMAs properly. A goodrule of thumb for using a TMA is when the maximumpower of the BTS is greater than the balanced outputpower of the BTS. That way, additional Tx power is avail-able to balance the link when the uplink signal isincreased by the TMA.

Here are some guidelines for using TMAs:

• Feeder loss greater than 3 dB• BTS maximum power greater than BTS balanced

output power• Weak receiver signal strength at the BTS

LLEEAAKKYY CCOOAAXX SSOOLLUUTTIIOONN - 55

Although leaky coax cable is used mostly for tunnelsand indoor applications, there could be two viable

options for this solution. One option is based on onemicrocell located in the middle of the town, with two leakycoax cables run from the center of the town to the townedges. The other solution is based on two microcellsinstalled at the town limits, with two leaky coax cablesrun from the town edges to the center of the town.

Central Option ConfigurationA 5W microcell should be set up in the middle of the

town at the base of the light pole. A splitter will split thesignal into two ½-in. coax jumper cables, which will runup to 10 feet on the light pole to connect the microcellwith 7/8-in. leaky coax cables suspended horizontallyfrom the light poles. Two 7/8-in. leaky coax cables willcover up to 1,200 feet via the light poles to the edges ofthe town. Link budgets can be calculated similar to thosepresented in previous sections.

Implementation NotesThe RF planning engineer should design this system. A

special implementation plan should be developed thatincludes the leaky coax installation on the light poles andthe stealthing requirements. The microcell outdoor cabi-net can be painted for stealthing. See Figure 11 for anexample of the installation.

Edge Option ConfigurationTwo 5W microcells should be set up at the base of the

light poles beyond the town limits. Two ½-in. coax jumpercables will run up to 10 feet on the light pole to connect themicrocells with the respective 7/8-in. leaky coax cablessuspended horizontally from the light poles. Two 7/8-in.leaky coax cables will run up to 1,200 feet on the lightpoles to the center of the town. Link budgets can be cal-culated similar to those presented in previous sections.

Implementation NotesThe RF planning engineer should design this system. A

special implementation plan should be developed thatincludes the leaky coax installation on the light poles.There are no stealthing requirements, because bothmicrocells are installed outside the town limits.



Figure 12. Leaky Coax Edge Option Solution

Figure 11. Leaky Coax Central Option Solution

CCOONNCCLLUUSSIIOONN

The examples show that many methods can be used tosolve a particular coverage deficiency problem. Some

solutions are better suited to a particular situation thanothers. Therefore, the more methods that are available toan RF planning team, the more flexibility the team has inthe design, and the more optimal their design can befrom the standpoint of cost and coverage.

Although these methods are not being used to designentire networks and cannot be used as a single standardapplication, there is a place for each in the system.Moreover, the individual flexibility of these methods, aswell as their combined flexibility brings value to any pro-fessional RF network and operations.

BBIIOOGGRRAAPPHHYY

Aleksey Kurochkin iscurrently director, Wire-less Planning, in theBechtel Telecommuni-cations Technology group,a group that he originat-ed. Aleksey has experi-ence in internationalte lecommunicat ionsbusiness managementand network implemen-tation. Between engi-neering and marketingpositions, he has both

theoretical and hands-on experience with most wirelesstechnologies. Aleksey came to Bechtel from HughesNetwork Systems, where he built an efficient multi-productteam focused on RF planning and system engineering.

Aleksey is an electrical engineer, specializing intelecommunications and information systems, with anMSEE/CS degree from Moscow Technology University.

Acknowledgment: Figures 2, 4, 6, 7, 8, 9, and 10 werecreated by Mustapha Mohammed, formerly associatedwith Bechtel Telecommunications.


Aleksey Kurochkin

Documents

Alternate RF Planning for Coverage Deficiancy