Tag Archives: GPS

Network Timing

One element that is key to all networks rarely gets discussed. Network timing (or network clocks) involves hardware or processes to make sure that all parts of a network are in synch.

Timing and synchronization are critical for network services that depend on precise, synchronized timing on network devices. Accurate and reliable synchronization of any network device helps manage the security, availability, and efficiency of the network devices. Timing is essential for the function of telephone, cellular, and broadband networks.

There are multiple kinds of timing in use.

Frequency Synchronization. This makes sure that all electronics inside a network operate using the same clock rate or frequency. Many kinds of network gear come with built-in clocks, and having different parts of a network using different clocks will result in data loss, corruption, or misinterpretation of bits. Frequency synchronization forces all of the clocks inside the network to operate in unison by matching the frequency of each clock to a source clock. There are different sources for frequency synchronization:

  • Synchronous Ethernet (SyncE) chooses one clock and forces the other clocks to match.
  • Networks can be synchronized to external clocks such as BITS or the GPS satellites. BITS can choose any reliable external clock.
  • Many networks use Precision Time Protocol (PTP), which eliminates the danger of losing the connection to an external clock.
  • A network can use a free-running internal oscillator chip that holds an accurate clock.

Many networks have used GPS for frequency synchronization. A GPS satellite carries a highly stable atomic clock that provides precise time signals, which can be converted into frequency references by a GPS receiver. While the atomic clock provides highly precise time and frequency information, GPS is not as reliable when there isn’t a clear view of the sky during weather events.

Phase Synchronization makes sure that the phase of network signal is consistent throughout the network. Phase refers to a specific point in time on a waveform cycle. Phase synchronization ensures that electronics agree on the timing of the start and end of each bit in a data stream. This is critical in applications where data from multiple sources have to be combined or compared, such as in a cellular network.

Time Synchronization, also called Time of Day (ToD) ensures that all electronics agree on the current time, which is critical in applications where timing is crucial. Networks differ in the need for precise time. Network Time Protocol (NTP) can be used to provide millisecond accuracy, while PTP can provide nanosecond accuracy along with phase synchronization.

Alternatives to GPS?

The FCC plans to hold a vote in April to consider alternatives to GPS, the U.S. location technology. The aviation industry has reported an increase in GPS spoofing, where a fake GPS signal shows a pilot the wrong location of a plane. GPS spoofing has been common around conflict zones, but airlines are reporting it happening in other places.

There are national security concerns because GPS is now used extensively by airlines, shipping, the military, and by the public for a wide range of uses. There is growing fear of the negative impact of something going wrong with GPS due to malicious attacks, technical malfunctions, or natural phenomenon like solar flares.

GPS technology was developed by the U.S. and is currently controlled by the U.S. Space Force. The technology was first designed in 1973 and became fully functional when a constellation of 24 satellites was in place in 1993. The U.S. government first made GPS available for civilian uses after Korean Air Lines Flight 007 was shot down in 1983 when it entered Russian air space. Over time, the government allowed wider use of GPS, and the technology is familiar to everybody who uses it as the basis for driving directions.

We’ve already begun to modernize the GPS network. There are currently 18 new GPS satellites in orbit that use the L5 frequency band that can provide accuracy for functions like surveying within 2 centimeters. The new satellite constellation will be completed in 2024 when it reaches 24 satellites.

GPS is not the only location network in the world. Russia has a GLONASS network, China a BeiDou network, and the European Union operates its Galileo locating network.

The purpose of GPS is supply geolocation information and the time anywhere on earth. Folks in the telecom business are familiar with GPS because we use it to mark the location of network outdoor components. GPS can help to lead a technician directly to the source of a network problem.

The FCC wants to open an exploration into other locating technologies so that we aren’t dependent on the GPS satellites. There are alternatives to GPS that can be explored, and it seems likely that a second locating system would be used in conjunction with GPS so that there wouldn’t be a single network providing the service. Some of the alternate technologies that might be considered include:

  • GNSS (Global Navigation Satellite System). LORAN (Long Range Navigation) technology is already used in conjunction with current GPS. This is a land-based network that use low-frequency radios that allow a calculation of position. Today LORAN supplements GPS in areas where reception is poor, and it can enhance accuracy where GPS is being used. Some are proposing that an updated eLORAN network be built as more extensive alternative to GPS. The downside is the cost of build a large numbers of LORAN towers around the world.
  • INS (Inertial Navigation System) is a self-contained system that keeps track of the location of an INS device through continuous motion tracking – the device constantly calculates where it is at. The technology is already used today in airplanes, ships, and by the military. The devices are fairly expensive but could become more affordable with mass production. The downside is what is called sensor drift where a device has to occasionally be recalibrated by connecting to GPS or another location system.
  • Quantum Clocks are still in the research and development phase but hold promise for timekeeping and location calculations. Quantum clocks are far more accurate than the atomic clock that is currently used as our time standard. The lab devices today are complex, and the challenge to make this into a usable technology is miniaturization and mass production.

An Alternative to GPS?

Outdoor-GPS-Unit1A few weeks ago DARPA (Defense Advanced Research Projects Agency) issued a request to the electronics and aviation industries to consider if there can and ought to be an alternative to GPS (Global Positioning System). DARPA has several concerns about GPS: It doesn’t work underground or underwater. It can be severely degraded by solar flares. And, since GPS is satellite-based, it is susceptible to being jammed or knocked out of commission by an enemy. And so DARPA asks if we should be exploring an alternative to GPS that overcomes these deficiencies. Since a lot of things we do relies on GPS any replacement has to be at least as accurate as GPS, which can pinpoint anything within 25 feet anywhere on earth 95% of the time. When coupled with land-based GPS augmentation technologies the accuracy can be narrowed in the best cases to within a few centimeters for land-based locations.

GPS was developed by the military in the late 1970s as a needed component of more accurately firing missiles from atomic submarines. The submarines needed to know exactly where they were located in order to calculate the desired path of a missile. But in 1983 after the Soviet Union shot down a civilian airliner KAL 007 that had strayed into their airspace, Ronald Reagan ordered that GPS be made available to all commercial aircraft.

GPS basically works by triangulation. Today there are a series of thirty GPS satellites at about 12,500 miles above the earth. To get the most accurate reading a location must be able to see at least four of these satellites. Each GPS satellite contains a very accurate clock which is almost as accurate as the atomic clock that is the basis for keeping official time. Each GPS satellite continuously transmits a message that includes the time the message was transmitted and the position of the satellite at the time it was sent. On the earth, a GPS device reads these transmissions and does a calculation to determine the coordinates of the GPS device. The math is somewhat complex in that a sphere is calculated around each of the received GPS signals and where those spheres intersect is the location of the GPS device.

In 1996 President Clinton authorized GPS to be used for any commercial use and by around 2000 it became widely adopted. Since then the number of ways that GPS is used has mushroomed. Following are some of the more important uses today of GPS, with the telecom uses listed first:

  • Cellular telephony. GPS is essential today in cellular roaming in handing cell phone calls from one tower to the next. GPS is also used for determining the caller location for cellular calls to 911.
  • Telematics. GPS is used to determine the location of moving vehicles. Telematics enables technologies like using Siri to help you with driving directions. This is also used for tracking and locating ships. This same technology enables stores to track the location of shoppers based upon their cellphone signal.
  • Geotagging. This is used in modern mapping systems to overlay photographs over maps.
  • Surveying and mapping. We now use GPS when mapping the routes of proposed fiber or other utilities and to determine property boundaries.
  • Geofencing. This is the technology used in fitness trackers, dog collars and other systems used today to track the location and travel history of a GPS device.
  • Clock synchronization. The accuracy of GPS time signals (±10 ns) is second only to the atomic clocks upon which they are based and many of our telecom devices get their timing from the GPS satellites.
  • Automated vehicles. GPS is going to be key in developing automated vehicle and drones.
  • Meteorology. GPS is used in sensors and balloons used measure and calculate atmospheric pressure, wind speed and direction in the upper atmosphere.
  • Aircraft tracking and navigation.
  • Tectonics. GPS enables direct fault motion measurements to pinpoint the epicenter of an earthquake.

This partial list shows you how quickly GPS has been integrated into our everyday lives in just the last decade. GPS is now a key component of huge number of industry and functions that we count on daily. I can see why DARPA is concerned about the security of GPS. The thought that the GPS system could be disabled in an attack on the country is scary. Luckily DARPA thinks there are alternatives and suggest some possibilities including “electro-optic/infrared (EO/IR) and radio frequency (RF) imaging (active or passive imaging), active/semi- active/passive guidance by EO/IR and/or RF signals, and tracking by exploitation of signals of opportunity.”