The road and the buildings on each side of the road can

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his 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 RF design activity, as well as during the implementation and operations phases of network life.

Five solutions for coverage deficiency problems are described 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 implementation notes. The options demonstrate the flexibility that needs to be present in RF designs. These examples also provide valuable points of comparison. General recommenda-tions are provided in the Conclusion. Although the exam-ples are described using U.S. measurement units, the principles are easily transferred to international applica-tions and metric units.

Example of Coverage Objective and Limitations

A hypothetical town that stretches 1,000 yards along a relatively straight portion of a two-lane road is chosen as the example for coverage deficiency. The portion of the road that runs through the town, as well as the first row of shops on both sides of the road, should be covered with street level coverage at -95 dBm with 95 percent reliability. It will be assumed that the rest of the road is covered at -95 dBm level or better. Access to the light poles along the road has been granted, but every other type of installation is prohibited by the town.

Solutions Are Versatile

Even though the methods are applied in this paper to a GSM (global system mobile) telecommunications sys-tem in the 1900 MHz PCS (personal communication service) band for ease of comparison, in principle, these methods can be used successfully for a range of wireless systems in PCS and other bands.

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he road and the buildings on each side of the road can be covered with a 5W microcell. This solution provides omni coverage, with maximum coverage in the middle of the town and minimum coverage at the town edges.

Configuration

One 5W microcell should be installed in the middle of the town at the base of the light pole. One ½-in. coax cable will run up to 20 feet on the light pole to the single 3-foot omni antenna. See Table 1 for the detailed link budget.

According to this prediction, the RSSI (received signal strength indicator) level of -95 dBm can be expected at 600 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 corresponding link budget should be used to plan the real system.)

Implementation Notes

This design is part of the regular RF planning/design process, as well as Implementation process, except for the following stealthing requirements: The coax cable should be ordered in a specific color to match the light pole, while the antenna and microcell outdoor cabinet can be painted for stealthing.

See Figure 1 for an example of the installation.

Alternative RF Planning Solutions

for

Coverage Deficiency

Aleksey A. Kurochkin

aakuroch@bechtel.com

Issue Date: December 2002

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ff-air repeaters are bi-directional power amplifiers with gains varying from 50 to 90 dB. They provide coverage by repeating the frequency of the base station in areas that lack coverage. There may be some overlap, but this overlap should be minimal. This solution requires two off-air repeaters and the assumption that there is sufficient signal level from the two donor cells on each side of the town for the repeaters to operate.

Configuration

One off-air repeater should be set up in the area of the reliable signal received on the donor antenna outside of the town. The transceiver coverage antenna of the repeater should be directed toward the town center. If one repeater does not provide satisfactory coverage, the second repeater should be installed using the other cell as a donor.

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

Project Name: 1000 Yard Town 4.00 <-- Site Area Type

Site Name or Sector Name: Microcell Area Coverage Reliability (60-99): 95% BTS Rx Band Frequencies, MHz: 1895 SU Rx Band Frequencies, MHz: 1980

MHz: 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 Outside

What Kind of CU is Used?: 2

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

Number of RF per antenna: 2

Height 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): 0

BTS RF Cable: 4 SU RF Cable: 9

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

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

Penetration Loss (dB): 0 0

Fade 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 1800.0 RF to Hatchplate Cable loss (dB) 0.0

Two connectors (dB) 0 3m antenna jumper loss (dB) 0

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

Combiner loss (dB) 2.2

BTS 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) 126.1 Sugg. 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) 4.7 Balanced 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) 126.1

Karea 8.3 Min RSSI for the Model (dBm): -88.3

Approx. Cell Site Radius, km

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Min RSSI for the System (dBm): -94.4

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Figure 1. Microcell Solution

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Figure 3. Off-Air Repeater Solution

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Implementation Notes

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

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

• The isolation requirements should be at least 15 dB more than the gain setting of the repeater. • As much vertical and horizontal separation as

pos-sible should be provided between the capture and coverage antennas of the repeater.

• Better isolation would be obtained if the capture antenna could be shielded from the coverage antenna.

• 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 isolation between antennas.

There are no means of predicting either the location of the repeater or its coverage during the standard desktop RF planning/design process. The town and the donor cells coverage will need to be drive-tested to select the best location for the repeaters.

The repeater installation should follow the standard implementation process. Stealthing would usually not be required 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 be adjusted to ensure the coverage. This could be an itera-tive process to achieve best results.

See Figure 3 for an example of the installation.

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he 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. This is normally used for campus and/or indoor installations. There are two options for this solution: a single repeater location and a distributed antenna system.

Single FO/RF Repeater Option

Figure 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 to optical signals and sent across fiber to the repeater loca-tion. At the repeater location, the optical signal is con-verted to RF and up-concon-verted to the same RF frequency and transmitted to the repeater coverage antenna. Configuration

Assume 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 splitter to an RF-to-fiber converter. A fiber string is run from this converter to the fiber-to-RF converter, which has a nomi-nal 5W of RF power output and will be installed on the light pole in the middle of the town. A ½-in. coax cable connects this converter with 3-foot omni antenna.

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

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

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Radio Tower RF/Optical converter Base Station RF Coupler 2ft - 3 dBd Omni Antenna Jumper cable between

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Implementation Notes

A team with a system engineering specialist and an RF engineer will be needed to design this system. A system vendor will be needed to install the RF/fiber system and components. The system installation should follow the standard implementation process. The coax cable can be ordered in a color to match the color of the light pole, while the antenna and fiber-to-RF outdoor box can be painted for stealthing.

See Figure 5 for an example of the installation.

Distributed Antenna System Option

Distributed antenna systems make use of telephone poles, lamp poles, or other lower height structures that do not present any zoning/permitting issues. This system is basically extending a base station antenna's reach where coverage would otherwise be lacking. This system is most useful in towns where zoning/permitting is very difficult and for areas that are blocked by terrain or buildings. Configuration

As shown in Figure 6, the RF path is sampled at the antenna port of the base station and sent to an optical hub located at the base station. This RF signal is first converted to data stream and then converted to optical signals. 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's reach into uncovered areas. The manufacturers indicate that more hubs can be daisy chained to support many

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

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

Implementation Notes

A team with a system engineering specialist and an RF engineer will be needed to design this system. A system vendor usually installs the RF/fiber system and compo-nents. The system installation should follow the standard implementation process. The coax cables can be ordered in a color to match the light pole color, and the antennas and remote antenna unit box can be painted for stealthing. Some implementation advantages of this method are: • A low mobile station transmits power throughout

most of the coverage area.

• There is flexible traffic capacity planning and ease of future system/traffic capacity expansion. • Strong protection is provided against blocking from

uncoordinated mobiles.

• There is low environmental impact of electronic equipment and antennas.

Two implementation concerns are:

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

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Diagram Showing Connectivity of Different TMAs

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MAs can extend the range of the uplink of cell sites into areas that would otherwise lack coverage with comparatively very little additional cost. They are typically low noise amplifiers with band pass filters, duplexers, and dc blocks.

TMAs are normally used to enhance the receive signal strength 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 might result in a decrease in the number of base stations where there is some difficulty in obtaining additional sites.

There are basically three types of TMAs:

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

2. Duplex TMA (Figure 8) allows separated transmit and receive feeder cables to be connected to the same antenna port, thus eliminating the require-ment for additional antenna ports or antennas. 3. Dual duplex TMA (Figure 9) allows a combined

Tx/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.

Configuration

If the system link budget is uplink limited and trans-mission line losses are higher than 3 dB, one TMA should be installed on each of the sites adjacent to the town cell sites. This allows an increase in the output power of the respective 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 noise figure and 0.5 dB to the insertion loss. If each of the sites increases its coverage by 800 yards, the town will be cov-ered by both cell sites with some overlap.

Implementation Notes

A team with a system engineering specialist and an RF 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 beyond the town limits.

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

Care must be taken to utilize TMAs properly. A good rule of thumb for using a TMA is when the maximum power of the BTS is greater than the balanced output power of the BTS. That way, additional Tx power is avail-able to balance the link when the uplink signal is increased 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

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lthough leaky coax cable is used mostly for tunnels and indoor applications, there could be two viable options for this solution. One option is based on one microcell located in the middle of the town, with two leaky coax cables run from the center of the town to the town edges. The other solution is based on two microcells installed at the town limits, with two leaky coax cables run from the town edges to the center of the town.

Central Option Configuration

A 5W microcell should be set up in the middle of the town at the base of the light pole. A splitter will split the signal into two ½-in. coax jumper cables, which will run up to 10 feet on the light pole to connect the microcell with 7/8-in. leaky coax cables suspended horizontally from the light poles. Two 7/8-in. leaky coax cables will cover up to 1,200 feet via the light poles to the edges of the town. Link budgets can be calculated similar to those presented in previous sections.

Implementation Notes

The RF planning engineer should design this system. A special implementation plan should be developed that includes the leaky coax installation on the light poles and the stealthing requirements. The microcell outdoor cabi-net can be painted for stealthing. See Figure 11 for an example of the installation.

Edge Option Configuration

Two 5W microcells should be set up at the base of the light poles beyond the town limits. Two ½-in. coax jumper cables will run up to 10 feet on the light pole to connect the microcells with the respective 7/8-in. leaky coax cables suspended horizontally from the light poles. Two 7/8-in. leaky coax cables will run up to 1,200 feet on the light poles to the center of the town. Link budgets can be cal-culated similar to those presented in previous sections. Implementation Notes

The RF planning engineer should design this system. A special implementation plan should be developed that includes the leaky coax installation on the light poles. There are no stealthing requirements, because both microcells are installed outside the town limits.

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Figure 12. Leaky Coax Edge Option Solution Figure 11. Leaky Coax Central Option Solution

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he examples show that many methods can be used to solve a particular coverage deficiency problem. Some solutions are better suited to a particular situation than others. Therefore, the more methods that are available to an RF planning team, the more flexibility the team has in the design, and the more optimal their design can be from the standpoint of cost and coverage.

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

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Aleksey Kurochkin is currently director, Wire-less Planning, in the Bechtel Telecommuni-cations Technology group, a group that he originat-ed. Aleksey has experi-ence in international te l e c o m m u n i c a t i o n s business management and network implemen-tation. Between engi-neering and marketing positions, he has both theoretical and hands-on experience with most wireless technologies. Aleksey came to Bechtel from Hughes Network Systems, where he built an efficient multi-product team focused on RF planning and system engineering.

Aleksey is an electrical engineer, specializing in telecommunications and information systems, with an MSEE/CS degree from Moscow Technology University.

Acknowledgment: Figures 2, 4, 6, 7, 8, 9, and 10 were created by Mustapha Mohammed, formerly associated with Bechtel Telecommunications.

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