Earth Station Design Objectives in Satellite Communications

Slide Number 1Rev -, July 2001

Technical Introduction to Geostationary Satellite Communication Systems Original Prepared by Telesat Canada

Earth Station Earth Station Design Objectives

Design Objectives

Section 2

Vol 4: Earth Stations



Contents

4.2.1 Four Design Objectives

4.2.2 Reliability & Availability

4.2.3 Link Budget Considerations

4.2.4 Customer Driven Design Objectives

4.2.5 Special Considerations Applying to Teleports

4.2: Earth Station Design ObjectivesVol 4: Earth Stations




Four Design ObjectivesPart 1



Introduction

Sec 2: Earth Stations Design Objectives

This section identifies the areas of principle concern when designing an Earth Station.

Earth Station Major SystemsAn Earth Station consists of the following major subsections:

Antenna System Transmit System Receive System Power Systems Monitoring Systems Terrestrial Interface Equipment

4.2.1: Four Design Objectives




The Four Principle Design Objectives


Four factors tend to drive Earth Station design. These are: Reliability and Availability Link Budget Considerations Customer Driven Objectives Special Considerations Applying to Teleports

These considerations may sometimes be in conflict, and compromise decisions must be made.

As always, cost is also an issue, and all design choices must make good business sense.

4.2.1: Four Design Objectives





Reliability and AvailabilityPart 2



Reliability is defined as the probability that a system will perform a specified function or mission under specified conditions for a specified time.

The reliability of a complete satellite communications system depends on the reliability of the satellite and the ground stations

Availability is the probability that a system will operate satisfactorily at any point in time, where time includes not only operating life but also active repair time and administrative and logistic time.

The conventional equation for availability is

A = MTBF / (MTBF + MTTR)

Definition

Part 2: Reliability and Availability

4.2.2.1: Introduction

Vol 4: Earth Stations, Sec 2: Earth Station Design Objectives



General The main Contributors to Unavailability are

• Equipment Failure

• Primary Power Failure

• Propagation (fading or interference)

• Maintenance and Human Error

• Unlocated

Satellite frequency selection, UPS systems, diesel backups, redundant equipment, diversity and link budgets are all factors involved in designing a reliable and available system.

Changing link availability in the Link Budget directly impacts space segment utilization.




Typical Availability NumbersC-Band 99.95%Ku-Band 99.80%



What Frequency Should be Used?There are many tradeoffs to be considered in choosing a frequency band for a proposed Earth Station.

First, Ku-Band is susceptible to rain fades to a much greater degree than C-Band. Consequently, for link availability reasons, C-Band may be the necessary choice.

However, the C-Band and extended Ku-Band frequency ranges are susceptible to terrestrial interference. Typically, if an Earth Station is to use these frequencies, a Radio Frequency Interference (RFI) study is required for the proposed site location prior to final site selection. This study can determine if any RFI present can be mitigated, or it could even eliminate the proposed location as unsuitable.


4.2.2.2: Frequency Band Selection




Since the normal Ku-Band range is not susceptible to terrestrial interference and does not require an RFI analysis, time and money can be saved during the site selection process if Ku-Band is used.

Another cost saving reason to select Ku-Band is that, depending on the bandwidth requirement, Ku-Band may offer smaller antenna sizes and thus lower costs.

The EIRP antenna pattern of the target satellite may determine if a C-Band or Ku-Band system should be selected.

If the Earth Station is located at a weak location in the satellite’s footprint, then one band may need to be chosen over another in order to meet the required link availability.

What Frequency Should be Used?

4.2.2.2: Frequency Band SelectionPart 2: Reliability and Availability




Additionally, C-Band is susceptible to longer sun transit periods than Ku-Band. This can have design implications in terms of availability.


4.2.2.2: Frequency Band Selection


What Frequency Should be Used?

Figure 4.2.2.2. Antenna vs. Degradation (C-Band and Ku-Band)



UPS


4.2.2.3: UPS


The prime power outage is the single largest contributor to the degradation of Earth Station availability.

UPS systems provide continuous power to telecommunications equipment during periods of transfer from one power system to another.When should a UPS system be purchased?

• If AC power is unreliable (over-under voltage, spikes, loss etc).

• If service availability is critical (cannot afford outages).

• If equipment is sensitive to AC noise, level or frequency fluctuations.

A UPS offers peace of mind, equipment protection from premature failure, and filters the incoming AC to improve conditions.



Diesel BackupIn small Earth Stations, UPS systems are the only backup power source available, and some UPSs only provide 15 to 60 minutes of power backup.

If this is not sufficient, a diesel generator can be installed to provide a source of power until primary power returns.


4.2.2.4: Diesel Backup


Diesel backup requires a transfer switch and adds cost to an Earth Station design.

Diesel backup is typically used only for very important Earth Stations, where much revenue would be lost in the event that a prime power outage exceeded the backup time available from UPS batteries alone.

If very high availability figures are to be met, a diesel generator is almost always required.



Redundancy OptionsTo satisfy the objectives of reliability and specified availability, it is often necessary to provide backup equipment.

Several types of redundancy options are available:• Individual module switching (1 for 1 switching systems)

• 1 for many (1 for n) switching systems

• Entire chain switching

All redundancy systems operate on the same principle. First, one or more pieces of equipment are monitored for certain specified fault or traffic conditions. When a given failure criteria is met, a “hot standby” unit is automatically switched into service in place of the failed unit.

Redundancy switching time is usually very short, typically less than 1 second.


4.2.2.5: Redundancy Options




4.2.2.5: Redundancy OptionsPart 2: Reliability and Availability


Redundancy OptionsOutages greater than 10 seconds are usually associated with failures in subsystems such as primary power, antenna tracking systems, and HPA’s.

The most common redundancy configuration is 1 for 1, entire chain switching, or a combination of both.

Redundancy choices are normally customer driven, as the customer must be willing to pay the added expense for the higher availability redundancy offers.



DiversityDiversity is based on the provision of separate paths for transmit and receive information.

The most commonly used methods to minimize the effects of multipath fading are:

• Frequency diversity

• Space diversity

Multipath fading is typically a terrestrial phenomenon, not a satellite problem.

Satellite Diversity is available but not commonly used.


4.2.2.6: Diversity




4.2.2.6.1: Frequency DiversityFrequency diversity is the process of duplicating a radio communication link by putting the same information onto two carriers, each one at a different frequency.

The receive system then monitors both carriers and chooses which to use based on signal strength, or some other quality indicator.

For best effect, the frequencies should be separated as much as possible from each other. This way, if RFI or some other condition reduces the level or quality of one carrier, the chances are good that the second carrier will not be affected.


4.2.2.6: Diversity





4.2.2.6: Diversity


4.2.2.6.1: Frequency DiversityFrequency diversity has the advantage of providing a fully redundant path and an alternate set of operating frequencies, improving equipment reliability.

However, since space segment is expensive, frequency diversity is not common in satellite systems and is left for terrestrial applications due to their need to compensate for multipath fading.

Some governments prohibit frequency diversity on centimetric bands on terrestrial systems to reduce frequency congestion.

In Ku-Band, rain attenuation is the largest contributor to fading.

Due to this, space diversity is more advantageous than frequency diversity.



4.2.2.6.2: Space Diversity

Space diversity is not common to satellite communications, but is more common to the terrestrial environment.

To implement space diversity, an alternate Earth Station with some vertical and geographic separation is required.

When RFI, or an atmospheric condition such as rain, affects one location, chances are good that the other Earth Station will remain unaffected.


4.2.2.6: Diversity




4.2.2.6.2: Space DiversityA typical diversity option would be for a Ku-Band Earth Station to have a companion Earth Station 40 kilometers away. The chance that both sites receive high rain fall at the same time is low.

Achieving this type of diversity is very expensive as a second Earth Station is required. In addition, duplicate backhaul facilities must be in place to provide for customer interface to both Earth Stations.

In C-Band systems in the far north, diffraction of the signal can occur due to atmospheric effects at very low elevation angles. Fading in the area of 10 to 12 dB is typical.


4.2.2.6: Diversity




4.2.2.6.3: Satellite Diversity Satellite diversity is provided when the same service is required on two separate satellite systems.

Should a satellite fail, satellite diversity would ensure continuity of service

Satellite diversity is very seldom used, as space segment costs are doubled.

Satellite diversity is required when the customer cannot tolerate link outages of more than a few minutes a year.

One advantage that satellite diversity shares with space diversity—provided space diversity employs significant separation—is that the effects of sun transit can be avoided.


4.2.2.6: Diversity




Cost• Cost significantly increases as the

availability of the communication link is increased.

• Adding redundancy, diversity, UPS etc, all significantly increases the cost as equipment is added to maintain the communications link availability.

• At some point it will no longer be cost effective to maintain a high availability figure.

• Typically the cost versus affordable downtime parameter is customer driven.

• How much is a customer willing to pay to keep downtime to a minimum?


4.2.2.7: Cost


Figure 4.2.2.7 Link Cost as a Function of Availability




Link Budget ConsiderationsPart 3



IntroductionLink Budget design is covered in detail in Volume 5 of this course. This section will discuss how Earth Station design is affected by link budget concerns, and will not cover the link budgeting process itself.

A link budget is composed of primarily three segments:1) The transmitting Earth Station and uplink characteristics

2) The satellite (transponder characteristics)

3) The receiving Earth Station and downlink characteristics

There are no “right answers” to questions involving the design of two-way satellite Earth Stations. Different solutions are a testament to individual ingenuity within the design group.

Part 3: Link Budget Considerations





Design Factors

These factors affect the engineering of satellite Earth Station uplinks:


4.2.3.2: Design Factors


• Receive Earth Station antenna size

• Noise temperature

• Satellite transponder parameters

• Modulation scheme

• Bandwidth

• Data rate

• Error correction coding

• Frequency

• Path loss

• Adjacent satellite interference

• Operational reliability

• Kinds of environmental ingredients



Operational reliability and environmental contingencies are joined in the establishment of fade margins. Fade margins are reliability over-designs that compensate for unpredictable changes in signal strength resulting from a variety of factors.

To minimize signal outages, allowances are made for rain fade and antenna pointing deflections caused by wind, installation errors, and controller pointing accuracy.


4.2.3.2: Design Factors


Design Factors



EIRP

A link budget is a computational aid in which each contribution is added to a spread sheet.

When totaled, what is left is an algebraic equation relating uplink Effective Isotropic Radiated Power (EIRP) to an appropriate signal quality measure such as video carrier-to-noise ratio (C/N) or data energy per bit (Eb/No)


4.2.3.3: EIRP


• Earth Station antenna size• Transmitter HPA power Manipulated to obtain an EIRP value• Waveguide run losses



Utilization - Bandwidth & PowerThe link budget equation results in two numbers, one for bandwidth utilization and one for power utilization.

Bandwidth utilization is manipulated by the modulation scheme and coding rate.

Power utilization is manipulated by many factors, but a short list of these would include:

• Antenna gain

• Mode—single or multicarrier (affects HPA backoff)

• Earth Station HPA output power variation

• End of life parameters for the transponder

• Uplink power control, if used

• Inter Facility Link (IFL) losses


4.2.3.4: Utilization - Bandwidth & Power




A few other factors affect these numbers, however these usually remain fixed within a given design such as LNA noise temperature, satellite EIRP, SFD and G/T transponder parameters for the specific site location, uplink, downlink and adjacent satellite interference.

The idea is to blend the power and bandwidth utilization numbers so that they become balanced, or as close to balanced as possible.

Balancing these numbers produces the most efficient use of transponder capacity for a given link.

Utilization - Bandwidth & Power






Example Site A Site B

Two-WayLink Availability (%) 99.950 99.950 98.336Power Utilization (%) 0.268 0.253 0.521Bandwidth Utilization(%) 0.250 0.250 0.500Occupied Bandwidth (kHz) 70.000 70.000 140.000




In this example the 64kb data circuit is quite balanced utilizing 0.521 % of a transponder. In this example the data circuit is just slightly power dominant.



Transponder parameters play a significant role in link budgeting, and consequently affect Earth Station design.

Satellite transponder performance is available, and is mapped geographically, in terms of three antenna patterns, or footprints:

• Saturating Flux Density (SFD)

• Satellite G/T (may be combined with SFD pattern)

• Downlink EIRP

Earth Stations must, of course, be within the footprint of the satellite antenna.

Satellite operators offer EIRP and G/T coverage patterns of their satellites. These maps must be obtained by the engineers who will be designing the links.

Satellite & Transponder Targeted


4.2.3.5: Satellite and Transponder Targeted




ArabsatKu-Band EIRP Coverage (48-44)dbw

ArabsatKu-Band G/T Coverage (0.2 to –3.8 db/k)

Eutelsat W1Ku-Band EIRP Coverage

Eutelsat W1Ku-Band G/T Coverage

Example: EIRP & G/T Maps




Figure 4.2.3.5. Example of EIRP and G/T Satellite Coverage Maps

EUTELSAT CopyrightEUTELSAT Copyright EUTELSAT CopyrightEUTELSAT Copyright

ARABSAT CopyrightARABSAT Copyright ARABSAT CopyrightARABSAT Copyright

All graphics All graphics used by used by permissionpermission



Transponder Gain StepsTransponders are assigned and set up for specific uses such as video, partial channel or occasional use.

Many satellites employ an adjustable SFD setting for individual transponders (called a gain step).

Transponders with higher gain step settings produce higher SFD’s.

From an Earth Station design perspective, higher SFD’s permit the use of smaller antennas and SSPA’s. Satellite communication networks with large numbers of transmit stations can achieve significant cost savings by the reduction in HPA and antenna sizes.






Hardware MatchingThe RF equipment purchased for an Earth Station should match the satellite’s frequency range. That is, if the satellite offers either Extended C- or Ku-Band ranges, Earth Station equipment should be selected to cover that range as well. This allows full Earth Station flexibility.

All satellite operators issue access agreements that impose certain minimum performance requirements on Earth Stations that will uplink to their satellites. Many of these requirements are dependent upon antenna performance. Therefore, antenna systems purchased should match satellite access parameters.









Hardware MatchingFactors to consider when selecting an antenna system:

• Designed for the correct band (C- or Ku-Band).

• Equipped for the correct polarization (linear or circular).

• Sized correctly in accordance with link budget requirements.

• De-ice equipped, if necessary.

• Meets performance specified in satellite access agreement.

• Depending on the satellite provider, selection of an Intelsat pre-approved antenna can save time and money by eliminating up-front antenna qualification testing.



4.2.3.6.1: Modem Options Perhaps the most flexible piece of equipment in an Earth Station is the satellite modem. Selecting the right modem is essential to ensure that link budget performance requirements are met. Modem parameters that effect link budget performance are:

Modulation Scheme

Modulation schemes have direct effect on bandwidth over the satellite. Most modems offer both QPSK and BPSK, and engineers should consider very carefully before buying a modem offering only BPSK.

QPSK is typically used rather than BPSK because, for a given bit rate and BER, only half the bandwidth is required.

Newer modems offer 8 PSK and 16 QAM and handle data rates of DS3 & higher.


4.2.3.6: Modems and Performance Requirements




4.2.3.6.1: Modem OptionsCoding SchemeIt is best to buy a modem that offers all the modern Forward Error Correction (FEC) rates and schemes. Sequential and Viterbi FEC schemes are the most common, but investing in modems that also offer Reed Solomon and Turbo codes is recommended. Turbo outperforms even Reed Solomon.

All FEC coding has the effect of reducing Eb/No through a concept known as coding gain, covered in Section 3.5. They do this at the expense of bandwidth and latency, but usually the tradeoff in satellite utilization is advantageous.

Reduction in Eb/No, in turn, leads to reduction in HPA power requirements and antenna sizes, reducing Earth Station costs.






4.2.3.6.1: Modem OptionsOther performance requirements, not related to link budgets themselves, are best met by procuring highly optioned modems. The modem selected should be very flexible in the following areas:




• Baseband interface type: RS232, V.35, EIA530, RS442, X.21 etc.

• IF bandwidth: 70 MHz or 140 MHz IF, or L-Band second IF

• Frequency step size: 100 Hz now common (more of a problem with older modems ex 25 kHz)

• Variable data rate 2.4 kbps to 2.048 kbps

• M&C functionality (required to connect to a central MAC)



[kb/s] Turbo Viterbi Sequential Vit + RS Seq + RS56 90 14 121 307 63464 80 106 267 555128 41 6.5 * 53 133 276.75*200 178256 26 3 26 67 138400 89500 12

1000 6 1 7 17 361544 4.5 2000 3 3 9 18

Data rate Test Data from COMTECH CDM-550 Modem

Notes:

• All data from test done at R3/4, with FB6000 using: data pattern > data rate x delay.

• Delay measured with modem Tx IF BNC connected to modem Rx IF BNC.

• Delay represents the one way delay contribution of the modems in a link in milliseconds

• Typical satellite delay is 1/4 second, typically 270 ms one way space only.

* These values for 128kb/s were extrapolated from the 64kb/s and 256kb/s values.

4.2.3.6.2: Latency vs Types of FEC Coding




In addition to slight increases in bandwidth, FEC coding also increases overall system delay. This chart compares the delay inherent in different FEC schemes.

Figure 4.2.3.6. Latency vs Types of FEC Coding



4.2.3.6.3: Application-Specific ConcernsData Buffer

Modern data links require buffers to compensate for the effect of doppler shift on data communication.

Since analog communication does not require buffers, older modems may not have buffers at all, or may have buffers of inadequate size.

It is recommended that modems selected for use on Earth Stations have adequate, and fully adjustable, buffers.

In case an old modem must be used, it is possible to buy an additional, external buffer.






4.2.3.6.3: Application-Specific ConcernsIP Modems

Because of the data acknowledgement structure of the TCP/IP protocol, it is usually not possible to carry it over satellite without compensations.

Consequently, TCP/IP applications require IP acceleration over satellite. (Acceleration could be a hardware solution, or a combination hardware/software solution.)

New IP modems have acceleration built in.

Some modems can have ethernet as a new interface.

Engineers making equipment selections for an Earth Station must be aware that a modern modem, no matter of what quality, will not be adequate for IP traffic unless it is specifically equipped with an acceleration scheme.






Terrestrial Interference is only a concern with Extended Ku-Band and C-Band frequencies.

RFI analysis can be made based on a computer interference study to predict any potential interference at an Earth Station.

The analysis considers the locations, antennas, antenna pointing directions, transmit powers, receive powers, traffic and equipment types of all stations concerned in the analysis. It also considers any existing or planned terrestrial microwave station in the vicinity.

The analysis also takes into consideration all possible traffic types (analog, digital, or a mix, etc.).



Terrestrial Interference

4.2.3.7: Terrestrial Interference



Once the Interference level is calculated, the result is compared against known objectives based on mutual agreement between affected parties and/or ITU Recommendation.

A path profile analysis can be performed to eliminate as many of the interference causes as possible.

The path profiles are based on the terrain which is taken from topographic maps and/or from a digital topographic database.

RFI field measurements may be necessary to further evaluate the interference environment if the computer/path profile approach cannot clear all interference causes.

On-site field measurement can be done to accurately assess the suitability of the station to operate in the desired band.







Even if the initial computer/path profile assessment finds the proposed Earth Station location unsuitable, field tests may still be warranted.

Because of the cost, field tests are only conducted if there is a reasonable expectation that the RFI condition at the station can be cleared by some mitigation method.

Field tests are generally done with a suitable calibrated antenna, an LNA, and a spectrum analyzer, along with appropriate computer analysis software tools to predict any interference to and from the Earth Station.







If the interference computer/path profile/field test analysis clears the station of potential interference, the proposed Earth Station will be frequency-coordinated as stipulated by the local radio licensing and governing body.

With the satisfactory completion of the frequency coordination process, the results will be filed as per the local radio licensing body's regulations.

Within standard Ku-Band frequencies (14.0 to 14.5 GHz), an RFI analysis and a radio application license are not required.







Selecting the right antenna and HPA for an Earth Station is a complicated matter.

Antennas and HPAs are both costly items; generally, keeping their size down is a major factor in controlling Earth Station costs.

This is especially true of antennas. Small antennas are relatively inexpensive. Costs magnify with larger antennas, however, not only because of the initial cost of the item but also because of the infrastructure they require.

There is a tradeoff between antennas and HPAs: larger antennas will permit the use of smaller HPAs, and larger HPAs will permit the use of smaller antennas.

Antenna and HPA Sizing



4.2.3.8: Antenna and HPA Sizing



It must be kept in mind, however, that antennas, unlike HPAs, are part of the receive system as well as the transmit system and, as such, they must be sized to provide the necessary G/T for the site.

To complicate matters further, the improved G/T of larger antennas permits the link to meet its performance criteria with smaller, lower powered carriers, thus reducing space segment costs.

This results in another tradeoff, this time between initial capital cost and monthly recurring cost. Lower monthly recurring space segment charges could pay for the additional antenna cost within 6 months to 2 years of service.







Engineers might also consider the use of Uplink Power Control (UPC), if warranted by the rain zone in which the Earth Station is located. A UPC compensates for path losses due to rain and thus permits links to be designed with less margin, again reducing antenna costs.

Because of the number of factors involved, and in spite of the cost of larger antennas, it is often cheaper to simply increase the antenna size to meet performance demands.

Engineers are reminded to place HPAs and LNAs as close to the antenna as possible in order to reduce waveguide losses and system noise. This, too, will permit the use of smaller HPAs and antennas.

Only multiple link budget calculations will determine what the best scenario is for a specific customer application.







The receive Figure of Merit, Gain to Noise Temperature (G/T), is defined at the station receiver input. It is the ratio of the composite receive gain (G), to the system noise temperature (T) of the Earth Station

Gain of an antenna increases with increasing frequency for a fixed antenna size.

Antenna gain is determined largely by the electrical area of coverage, which appears larger at shorter wavelengths.

Antenna C-Band Ku-Band9.3m 32.47.6m 29.7 36.14.6m 24.7 324.5m 25 30.83.7m 23.6 30.32.4m 18.5 26.31.8m 16.5 23.6

Antenna DataG/T C-Band 30ºK LNA elev angle=10ºG/T Ku-Band 90ºK LNA elev angle=10º

Typical Antenna G/T Performance

Antenna G/T



4.2.3.9: System Noise Temperature - Antenna G/T



Antenna gain & LNA noise temperature have the most influence on G/T.

System noise temperature is calculated as follows:

TSYS = TANTENNA + TLNA + TMisc

(where TMisc includes things like waveguide and receiver noise.)

Antenna G/T






The noise temperature of the antenna is dependent in part upon the elevation angle at which the antenna will be used. For design purposes, this value is usually drawn from manufacture’s data.

A typical LNA Noise Temp is 40° K for C-Band and 80°K to 100°K for Ku-Band

Miscellaneous temperature is typically 6°K for every 0.1 db of loss in the antenna feed and several degrees for every waveguide flange.

If the LNA is installed directly at the antenna feed, a miscellaneous noise temperature of 20 degrees can be assumed for design engineering purposes.

System Noise Temperature






Example: Andrew 4.5m C-Band antenna

Noise temperature = 32° K at 10° elevation.

Gain = 44.0db at 4.0 GHz

TSYS = TANTENNA + TLNA + TMisc

= 32 + 40 + 20

= 92° K

G/T = Antenna Gain – 10Log(TSYS)

= 44.0 – 10Log(92)

= 24.36 db/K

System Noise Temperature







Customer Driven Design ObjectivesPart 4



Proximity to Customer Facilities

Earth Stations are often built directly at a customer’s facility.

This is the best solution, eliminating the need for costly backhauls.

Elimination of backhauls figures into overall availability figures as well, by eliminating the effect of backhaul outages.

Locating with the customer can also involve the benefits of facility sharing. The power, staffing and security already in place at a customer’s premise can be extended to include the new Earth Station.

Part 4: Customer Driven Design Objectives


4.2.4.1: Proximity to Customer Facilities



Proximity to Customer’s Interface MethodWhen constructing a new Earth Station, access to the terrestrial environment should be considered. Is line of sight available? Can a tower be installed to receive a terrestrial signal?

A teleport may require cable access for video services.

Fiber access may be required for high bandwidth requirements.

Copper cable access may not be critical unless one of the above services is unavailable.



4.2.4.2: Proximity to Customer’s Interface Method



In the VSAT world, Earth Stations have been installed at strip plazas and shopping malls.

A VSAT can be installed and shared among multiple customers.

This offers a cost saving to all involved customers.

But this solution also creates a problem for servicing. • Where does the IDU get installed (must be installed were all

customers sharing the facility have access for repair and servicing)?

• Servicing costs must also be shared among the users?

Co-location with other Customer Traffic



4.2.4.3: Co-location With Other Customer Traffic



Large corporations may charge for roof access to place antennas. This is not common, but it does happen.

Finally, considering space segment, an existing customer base may have its entire network on a single transponder, served from an existing Earth Station.

If the customer now wishes to add a new service from a different location, the best solution is probably not to build a new Earth Station, but to add the service to the existing Earth Station, even at the expense of long backhauls.

In this case, as a logistical convenience, efforts would be made to place the new service on the same transponder.

Co-location with other Customer Traffic



4.2.4.3: Co-location With Other Customer Traffic




Special ConsiderationsApplying to Teleports

Part 5



GeneralTeleports differ from other Earth Stations primarily by being, at least in part, speculative ventures.

Other Earth Stations are built to serve an existing, clearly defined specific need. Teleports are built when a positive business case can be made for their existence, and usually not until at least a few customers have signed contracts to use the new facility.

At its inception, then, market decisions must be made with respect to the future growth potential of the Teleport, and these decisions should be reflected in the design.

This always results in an initial over-design in the hope that paying services will expand into the available capacity.

Uplink power, frequency range, physical space, interface, and utility power are all areas in which expansion is anticipated.


4.2.5: Special Considerations Applying to Teleports




With Respect to Uplink PowerIn a Teleport, HPA’s typically carry a number of combined services.

This requires high power HPA’s.

HPA’s are typically chosen to provide for at least double their initial workload.

Waveguide networks, often including contiguous phase combiners, are made available to take the output of several HPA’s and direct this combined output to the desired antenna.

HPA redundancy (1:n) is typical in Teleports, where a standby HPA is available to take the service from a failed HPA. The backup unit must be equal in power to the largest unit in its domain.

Part 5: Special Considerations Applying to Teleports


4.2.5.1: With Respect to Uplink Power



With Respect to FrequencyPlanners must consider what satellites are likely to be accessed in the future of the Teleport.

Certainly, full C- and Ku-Band coverage must be anticipated, with provision of extended coverage packages seriously considered.

Additionally, line of sight to multiple satellites, provision of linear and circular poles, and interfacility radio interference must be carefully considered.



4.2.5.2: With Respect to Frequency



With Respect to FrequencySince C- and extended Ku-Band frequencies may suffer RFI from terrestrial sources, full and comprehensive RFI studies must be performed.

Should terrestrial interference exist, mitigation methods must be designed (see Figure 4.2.5.2 on the following slide).

Applications must be placed well in advance for all frequencies the Teleport will handle.

Raised banks of earth—called berms—can be constructed to minimize interference. Refer to photo on the following slide.






RFI Mitigation

This Berm was constructed to minimize Terrestrial Interference from the largest free standing tower in the world. The CN Tower in Toronto, with a 160 km view and carrying a wide variety of radio services, is only 6 km away from this Telesat’s Toronto Teleport.



With Respect to Frequency


Figure 4.2.5.2. CN Tower, Toronto Canada and berm construction

Photo used by permission of TheMegacity.Com



With Respect to Physical SpaceTeleports can become overcrowded, and room for equipment and antennas can become very limited. Proper space for expansion, and for support functions, must be anticipated during the design stage.

Antenna placement becomes very critical to allow for future expansion.

Often, antennas are installed on roofs and walls due to limited real-estate.

Antennas that will be used in a multi-satellite capacity, as with occasional use facilities, must have unrestricted visibility over the whole anticipated arc.

Rack space should always be conserved during equipment installations.



4.2.5.3: With Respect to Physical Space



With Respect to Physical SpaceTeleports normally have a dollar amount associated to one rack unit of rack space. In this way the available “real estate” can be factored into the cost of new services.

In addition to equipment rooms, it is not uncommon for Teleports to house office and support space—such as a shipping and receiving area, for instance.

It is also a good idea to include floor space to be used as equipment rooms by specific, large customers. Some customers will be glad to lease this additional space to house their own baseband processing equipment.



4.2.5.3: With Respect to Physical Space



With Respect to Multi-customer InterfaceAntennas, high power amplifiers and converters can be shared among many users, depending on the type of service.

For example, because it can amplify the entire satellite bandwidth of 500 MHz, a TWTA could be shared among different customers, therefore requiring only the addition of converters for new customers.

Shared services reduce costs to the end user, but some customers will always want exclusive use of facilities.

Exclusive-use Teleport facilities must always be sold at a very high premium due to the effect this has on the capacity available to others.



4.2.5.4: With Respect to Multi-customer Interface



With Respect to Backhaul Availability

Because Teleports are speculative ventures that must attract new services to become economically viable, they must be located very close to large cities.

As a consequence, they are typically located where backhaul facilities already exist.

Backhaul facilities to the local Telco, and directly to the customer, must both be available.



4.2.5.5: With Respect to Backhaul Availability



With Respect to Backhaul Availability

Teleports are typically served by fiber, copper, cable and microwave backhauls, providing the amount of interface bandwidth they require.

It is a good idea to pre-wire all unused backhauls to baseband equipment racks, making them easily available as services come on board.

Telco channel banks or muliplexers are installed with expansion capabilities so additions and deletions can be executed quickly.



4.2.5.5: With Respect to Backhaul Availability



With Respect to Main PowerTeleports must be designed where commercial power is stable and readily available.

Teleports consume large quantities of power (200 Kilowatts to 1 Megawatt).

UPS systems, diesel generators and installed switchgear must be sized to consider future demands.

This always represents high initial costs, which only future business can justify.



4.2.5.6: With Respect to Main Power



Capital Versus Operating Cost TradeoffsTeleport services are leased to customers as packages that include backhaul costs, power, equipment repair, spares, and 24-hour maintenance services. To the customer, this represents an operating cost.

If a customer chooses to install their own Earth Station, they incur the capital cost for the installation. However, their monthly operating costs are lower.

To reduce operating costs still further, some customers with their own Earth Stations even forgo scheduled maintenance services in favor of a pay-as-you-go maintenance arrangement which is billed by the hour.



4.2.5.7: Capital versus Operating Cost Tradeoff



Capital Versus Operating Cost Tradeoffs

Other customers opt for 24-hour-per-day, 7-day-per-week (24/7) maintenance services, for which they pay a monthly premium.

Ultimately, leasing offers higher monthly costs with low, or no, capital costs, while purchasing offers lower monthly costs, but at higher capital costs.

It is important that satellite providers offer both, and let the customer decide which best suits their needs.



4.2.5.7: Capital versus Operating Cost Tradeoff

Engineering

Earth Station Design Objectives in Satellite Communications