A few images I use when describing satellite footprints and beams.
A few images I use when describing satellite footprints and beams.
Two images to help provide a gauge of orbital heights compared to the Earth’s size.
Just a few graphics on atmospheric opacity lifted from the internet to help explain why some waves get through the atmosphere while others don’t.
Satellites provide a valuable link during disasters since it requires no local terrestrial infrastructure beyond where you are setting up. Cell phones require cell towers within a few miles to be working and not overloaded. Wireline services require a connection through the disaster to where you are. Satellite systems do require a power source. Depending on the size, it can be a vehicle’s 12 volt power outlet, a portable generator or a vehicle mounted generator.
A satellite is in an orbit around the Earth. There are many different ways to position a satellite in orbit depending on the need. A common orbit for communication satellites is a geostationary orbit 22,236 miles above the Earth. Precision is needed when working with satellites at that distance. One degree off and the satellite will be missed by 388 miles. That is like aiming to land in Washington DC and really ending up in Detroit or Boston.
The antenna used makes a big difference. Let’s start by looking at a two-way radio antenna. Most handheld two-way radios have an omni-directional antenna. That means it doesn’t favor any specific direction so orientation doesn’t matter as much. This gain in flexibility is matched with a loss in “punch” or sending power. Imagine a basic light bulb in a lamp with no shade. It spreads light everywhere. That’s how an omni-directional antenna works.
What if you want that light to be focused to only project sideways? Like an all around white light on a boat. The bulb and the lens are constructed to direct the light in a specific pattern. This is similar to a high gain antenna. The main punch of the radio signal is increased perpendicular to the antenna by reducing the energy projected parallel out the top and bottom of the antenna.
Now you want to project light in a single focused direction such as a spot light or flashlight. The bulb is constructed with reflectors and other features to direct the light. The same is true with radio antenna. A directional antenna is also called a beam or Yagi-Uda antenna. Most of your neighborhood roof mount TV antennas take this form. A series of metal rods direct the radio waves to a higher focus then the use of a single rod.
Wait, a TV antenna? I thought those were receiving only? The neat thing about antennas is that they will receive with the same characteristics as they transmit. A highly directional antenna is more sensitive and will better pick up a signal from its pointed direction then an omni-directional antenna. However, if the same signal came from a different direction then where the directional antenna is pointed, then the omni-directional antenna will receive it better.
So why don’t we always use directional antennas? Think back to two-way radio repeaters. The repeater’s antenna an example of when you want to broadcast the signal widely. Directional antennas are good for communications between two known locations. Onmi-directional antennas are good when you don’t know where the other location is, or it keeps changing and moving the antenna continually is impractical.
Going back to our analogy of light to describe radio waves, now imagine that you need a highly focused light. A laser pointer; it is designed to send out a highly focused beam of light that can be seen for long distances. The radio version of this is the satellite dish. The transmitter bounces the signal off a parabolic reflector which theoretically sends all the energy in the same direction in a narrow beam. These very narrow focus antennas are called “very small aperture terminal” (VSAT).
This series of examples is just discussing the shape of the antenna relative to the direction and focus of the radio waves. It is possible to use practically any frequency with any shape of antenna so long as the antenna is properly tuned. Different radio bands are naturally more efficient for communication modes when combined with certain types of antennas.
The important thing to remember here is just because you can do something doesn’t mean you want to do it. This is where you need to rely on your radio technicians to design the most effective system using the right frequencies and modes to get the message to the final destination.
You’ll probably want to start with the entry on satellite communication and antennas before this one.
Orbits are put into four levels based on altitude. Low Earth Orbit is about 100 miles to 1240 miles. The short distance allows low-power devices with omni-directional antennas to be used. The most common example is satellite phones, like Iridium. These satellites circle the Earth in 90 minutes. From any spot on the Earth, the satellite will only be visible overhead for 10 minutes.
Being visible isn’t referring to seeing it with your naked eye. Visible means a direct line-of-sight view of a spot so communications can occur. It also assumes a large sky, such as being in Montana or the open ocean. The more clutter blocking the sky reduces the satellite visibility. This includes hills, mountains, trees, buildings and other obstructions, or being in a low spot like a valley. It is nearly impossible to use satellite equipment in downtown New York City at ground level due to all the buildings.
Medium Earth Orbits are 1240 miles to under 22,236 miles. At this altitude, the satellites orbit the earth in four to six hours. That extends the visibility overhead to about two hours. GPS satellite operate in this orbit.
Geosynchronous Orbits are satellites at 22,236 miles. It takes a full day to orbit the Earth so the satellite will appear in the same spot of the sky once a day.
Geostationary Orbits are satellites at 22,236 miles and parallel to the equator. Since the satellite is moving at the same speed the Earth is rotating and in the same plane as the rotation, the satellite is in the same spot of the sky all the time. This is the most popular orbit to park a satellite in.
High Earth Orbits are satellites above 22,236 miles. They are not commonly used for our purposes.
Footprints, beams and look angles
A satellite’s footprint is the circular area on the surface of the Earth that is visible to the satellite. This is the potential area of coverage that the satellite can communicate with. Areas directly under the satellite will receive a stronger signal then those on the fringe areas due to the increased distance and atmospheric interference.
Satellite operators want efficient use of their equipment so they use beams, or specifically focused transceivers, to cover areas within the footprint. Imagine a satellite positioned above the equator roughly centered on the United States. The satellite operator’s intended audience is maritime users. They would focus the beams toward the waters of the Atlantic, Pacific, Gulf and Great Lakes; and away from inland areas knowing that there are few oceangoing freighters in Colorado. No energy is wasted trying to fill a part of the satellite’s footprint where it will never be used. When evaluating a satellite for use, you need to consider the beams and not the total footprint.
The more transceivers a satellite has, the more traffic it can handle at simultaneously. Satellite operators rate their satellites by the total cumulative traffic it can handle simultaneously through the entire satellite. The other factor when evaluating service is how much traffic a specific beam can handle. In normal daily use, it is hard to overload a single spot beam as the resources are geographically dispersed. A catastrophic disaster will bring many of these resources to a single geographical location; all trying to use the same beam. That is when the beam will be overloaded.
Outages and overloads on satellite services are common during major hurricanes such as Katrina, Rita, Gustav and Ike. This is most common on shared satellite services. Consider the satellite user density that occurs with the convergence of local, state and Federal responders; media and observers; utility companies restoring service; private companies COOPing; and NGOs, CBOs and FBOs responding as well. Many of these rely on some form of satellite service. Paying for dedicated satellite airtime is quite costly especially when they only use it occasionally. Now that a disaster has occurred, they all want to use it at the same time. In many ways, a satellite in orbit is similar to a cell tower: they are designed to maximize revenue efficiently for normal use, and extreme circumstances quickly exceed the designed capacities.
Finding a satellite in the sky is done through look angles. These measurements are unique based on the observer’s location. With geostationary satellites, the look angles will remain constant so long as the observer’s location remains constant. A look angle is made up of three parts: the azimuth, elevation and polarization. The azimuth is the compass direction (0-360°). The elevation is how high to look up (0-90°). Polarization is rotating the transmitter to align the radio waves with the satellite.
Here’s an exercise. Imagine that we are using Intelsat’s G-18 satellite located at 123° West. This is a geostationary satellite so we know that it will be above the equator and 22,236 miles up. 123° West is near the California coast. If we are in San Francisco, the azimuth would be 180° and elevation 46°. The higher the elevation, the easier it is to clear tree and other obstacles. Move to St. Thomas, USVI; the azimuth is 258° and elevation is 22°. St. Thomas is an island with hilly peaks in the middle so a satellite shot is unlikely from the NE side of the island due to the low look angle. Change our location again to Boston; the azimuth becomes 242° and elevation drops to 19°. The same situation occurs in Maine where the elevation is very close to the horizon. We were lucky during an operation in Maine and setup headquarters at a military airbase that had a runway near the same angle we needed.
Bands and frequencies
Just as two-way radios have a number of different bands with difference characteristics, so do satellites. Satellites operate at higher frequencies then two-way radios. A number of these frequencies are shared with terrestrial services. For example, the S Band (2-4 GHz) includes both satellite radio (Sirius), and Wifi and Bluetooth signals.
Inmarsat BGANs operate on the L-band (1-2 GHz). These are small, easy to point and decent global coverage. The major issue with BGANs is the low data throughput (32 to 256 kbps) and high cost.
C-Band (3.7-8 GHz) is well known for the “direct to home” TV signals using larger dishes of 2 – 3½ meters in diameter. The downside is that C-band has power restrictions and receives interference from microwave services.
Ku-Band (12-18 GHz) doesn’t have the power restrictions of the C-band and is used by the DirecTV system. The main challenge of Ku-band is the nearness to the resonant frequency of water. This means that water absorbs radio waves reducing the strength of the signal. This is commonly called rain fade. If you have DirecTV, you’ve experienced this when your signal goes out during heavy rain storms. The wavelength absorption peaks at 22.2 GHz. For non-technical purposes, think of it this way: The subscript U representing being under this peak. The subscript A of the Ka-band represents being at or above this peak.
These characteristics are important considerations depending how satellite service will be used. A Ku-band service will not help you for communications during the storm, but it will have the fastest speeds before and after the storm. The C-band could work in the storm, but the size of the dish makes portability unlikely and temporary setups risky in high winds. L-band will get through nearly all the time, but only a relatively slow speeds and high cost.
An interview that I did and is posted originally at http://www.networkworld.com/news/2011/082911-red-cross-comm-team-ready-250197.html?page=1
Red Cross comm team ready for disasters
IT system’s design is based on experience from years of disaster experience, says Red Cross IT exec
I’m here at Satellite 2011 in Washington, DC. Like many conferences, there are new things worth seeing and trying to figure out. Here’s a few of the things that I’ve seen so far. Follow the action on the Twitter hashtag #Satellite2011.
This vendor had a neat concept that could become very useful. The auto-aquire VSAT unit is mounted in a shippable container. A national organization can maintain the VSAT in a single warehouse and use an overnight shipping company or airline freight company to get it on-scene within 24 hours. The VSAT is setup on the luggage rack of any rented SUV … and possibly just inserted in the bed of a pickup depending on look angles. The dish can be left up while driving. They claim that a connection can be established at a “quick halt”. The big advantage to this is removing the need to maintain a vehicle long-term. Shift the vehicle to a rented one and only pay for use. It would also work wonders on island operations where vehicle mounted systems can’t be sent there (easily).
Here is what really caught my eye. This is a flat panel antenna for a Ku band satellite, yet it is only 2 feet on the long side. The vendor is just the manufacturer and provides it to integrators that build the form factor around it. They said that depending on the BUC, the panel can do 1-3 Mbps speeds. The device is made from plastic and poured copper to keep the weight and cost down. With this device at the core, I can have a near-BGAN sized device that is easily portable. Add a 25-watt BUC to have transmit and receive capabilities that exceed my 1.2m dishes with 5 watt BUCs. The higher start-up costs for the smaller form factor built around it could be offset by lower shipping and deployment costs over the life of the device. Unfortunately, I haven’t seen this build out yet although I’m told it is here.
Now I need to call out the problem with many standard size booths here. Folks still do not know how to setup a booth that invites attendees to stop by. For what this convention costs the exhibitors in staff time and money, I’m amazed how many are staff by people talking to other staff and have put up barrier to conversations.
When the people in a booth are talking to each other, attendees don’t want to interupt. Tables, signs, and display cases are setup to divide the booth space from the walkway. I don’t want to talk over a barrier unless I’m really interested in what you have to show me.
On the good side, I’m seeing more and more exhibitors understanding the need to double and triple the carpet padding. Happy feet don’t leave quickly.
The International Association of Emergency Managers (IAEM) conference in November 2011 has put out a call for speakers. The deadline of February 25 is fast approaching. I decided to pitch a 1 hour breakout session loosely based on the course I teach at GWU. Below is what I sent in. Let me know your thought and make suggestions. Continue reading IAEM 2011 Conference Speaker Submittal
This interview is reposted from the Satellite 2011 Conference page.
Conference Chairman Scott Chase sat down with Keith Robertory, Disaster Services Technology Manager, American Red Cross, to discuss the relationship between government agencies and the satellite industry when a disaster strikes. You can hear more from Keith Robertory and other experts at Satellites to the Rescue on Tuesday, March 15
Scott Chase: In the event of an emergency situation of any type, how effective is coordination of government and industry satellite resources, and how does that all work?
Keith Robertory: Coordination of shared resources is going to be very important. Many organizations have satellite technology positioned as the emergency solution when terrestrial services do not work. If all these organizations pull out their satellite equipment during a disaster and try to use it, the limitations of shared bandwidth abruptly smack these organizations with reality. The satellite industry needs to work with its clients to better educate them on potential limitations.
Offers of donated satellite systems and air time are welcome at any time. That said, the worst time to engage a response organization with an offer of new equipment, new technology, and limitations unknown to them is right after a disaster occurs. The priority of key decision makers will be the response effort. Effective government and industry coordination occurs long before the emergency situation ever arises.
SC: What applications do satellites bring to support the communications requirements of users in remote locations during and after the disaster?
KR: The American Red Cross satellite infrastructure has the IP packet as a common foundation. We are not trying to push different modes and protocols through the equipment. IP allows the core network to handle the information at a very basic level, reducing the number of conversions between the source and the destination. It can be data packets, voice or video, but it is all based on the basic IP packet. The trick to be successful in disasters is to make technology transparent.
SC: What are the biggest changes you have seen in the use of satellite technology and equipment over the course of your own quarter-century in the high-tech arena?
KR: Satellite technology is becoming more and more commonplace. Imagine a couple decades ago telling someone that we’re going to send a radio signal to their car from tens of thousands of miles away. Small transceivers used to only exist in the realm of science fiction. It doesn’t seem that long ago that connectivity between computers was about as fast as you could read plain text. Now we are streaming HD video, video teleconferences, and entire site connectivity through a single satellite connection using equipment that is (relatively) easily shipped from site to site.
On the flip side, technology advances and shifts in philosophies are bringing previous “obsolete” concepts back to the mainstream. Many people consider cloud computing to be a new technology, but it isn’t. We used to call it mainframes and terminals. The current events in Egypt show that no matter how advanced the technology, technologists need to be ready to fall back to older methods to establish connectivity. Egypt is an example of how to communicate should a nationwide network be disrupted. Disaster technologists should be versed in many different tools.
SC: What would you say has been the biggest advance in satellite capability since you joined the American Red Cross nearly 15 years ago?
KR: Honestly, we have not made many substantial changes to the American Red Cross satellite system since it went live in 2000. Standing up a system of the size we have is a costly endeavor and major changes also cost more money. We’re in the maintenance mode of the IT life-cycle. We are going to keep the system running as long as possible because a poor economy is not the time to request a multi-million dollar upgrade that may not have a measureable direct impact on the mission to deliver disaster relief services to disaster survivors.
Our system has grown to have two downlink stations and nearly 80 remotes in the field, including 12 satellite trucks. It is a completely internal system behind and protected by our corporate IT systems. The only thing we don’t own is the satellite itself. What has changed is how we use satellite capability and the philosophy behind technology selection.
Consider that all the technology we have is a tool in a tool box. We are first and foremost a service delivery organization. My unit’s objective is to establish connectivity in a disaster zone. We need to leverage everything in the most mission-sensible way to balance cost with service delivery. Technology that doesn’t enhance service delivery isn’t used. The situation drives technology needs. As there is less and less local infrastructure, the selected tools shift to satellite-based technologies.
Terrestrial technology, like cellular, is giving satellite a good run for its money. Cellular is getting faster, cheaper, and more resilient to disasters then it has been in the past. Satellite is also getting faster and cheaper. The decision point between where we can expect cellular to work and when to shift to satellite is in constant motion. Both are getting better but one will never replace the other for disaster work. Use the right tool for the right job. There is no single magic bullet idea.
SC: What can the global satellite industry do better to facilitate emergency response and humanitarian efforts at the scene of major disasters of any type?
KR: The satellite industry must reach out to humanitarian and other response organizations long before disaster occurs. It is challenging to fit a new connectivity solution into an existing network that is activity being used to respond to a catastrophe somewhere. And I say “catastrophe” because it seems to take the huge disaster to get lots of companies off the bench and in the game. Taking satellite technology to an organization responding to disaster is similar to telling a freighter that you’re going to change its propellers while it is navigating a horrendous storm in the North Atlantic.
Haiti was a time when this was successfully done, and that is an exception. Haiti was the largest response of the International Federation of the Red Cross. The technology that is normally sufficient for a disaster was quickly out-scaled and couldn’t keep up with demand. Luckily, the American Red Cross domestic response team’s experience with satellite was able to screen and facilitate the offers of satellite service on behalf of the international response team who could not shift attention off the response.
SC: In your role as supervisor of literally hundreds of volunteers, many of whom may have never seen, for example, a satellite phone, what is the one thing the satellite industry could do now to simplify emergency response?
KR: A larger diagram on the satellite phone to tell them to use it outside would be a good start. Simplify, simplify, simplify. Any device that is stored “for emergency use only” will not be successful in an emergency without a lot of training. In my experience, even that can be questionable. The best “in case of emergency” device is one that a user uses every day and is resilient to disasters. The American Red Cross actually uses fewer satellite phones then you probably think. Amateur radio plays a vital role in the first couple days of a disaster, and cellular is coming back online after that. Satellite phones are used in pocket areas where we have few other working options.
It is fair to say that all the technology deployed to an American Red Cross disaster response is received, set up, managed, troubleshot, packed up and shipped back by volunteers. I’m blessed with a cadre of high caliber volunteers who can use technology and speak human. We’re the high-tech in a human-touch organization. My technical volunteers in the field are the support system for the volunteers in the field that directly touch the clients. A key to our success is a step-by-step job aid for every action that needs to be done. These range from wiring a laptop to setting up a full VSAT. As long as a new volunteer is willing to be flexible and follow directions, we can put them to use in American Red Cross Disaster Services Technology with minimal upfront training. Our more experienced volunteers can get more deployment and training opportunities.
The short answer comes back to simplifying the technology to be more reliable, set up quickly with less user intervention, and require less hands-on to keep it running.
Join Keith for Satellites to the Rescue: Industry and Government Partnership in Disaster Relief, 4:30 p.m. to 5:45 p.m. on Tuesday, March 15, Room 207A. Access to the session is included with your Full Conference registration.
Here is my “work in progress” of a syllabus for the upcoming course that I’m teaching at the George Washington University. There’s still some revisions that I plan on doing. If you were taking this course, what would you want to hear about?