The benfits of GPS

GPS has revolutionised positioning, navigation and timing (PNT) over the last twenty-fi ve years. During this period, we have come to rely on GPS to an unprecedented extent and GPS has gone from being an interesting research and development topic, to a professional niche market maker, to becoming the fourth utility and now to today’s mass market phenomenon.

One of GPS’s greatest strengths is its ease of use and many of today’s mass-market users neither care about nor understand the intricacies of GPS positioning. Because GPS is now embedded in so many consumer products, there is confusion about where GPS stops and the application starts. This confusion extends to GPS, on occasion, being blamed for “leading” car drivers many hundreds of miles off course.

At the same time, PNT based on GPS has become part of our critical infrastructure: finance, power, telecommunications, emergency services and transportation among others. GPS is often a small, perhaps overlooked, but very important component in the timing subsystem of a much larger system. GPS has produced a wide variety of both industrial and user benefits worldwide as a result of new applications and services.

A key cross-sector benefit has been manning efficiency savings arising from system integration and automation. In many cases, automation has resulted in a change of operational concept where reversion to the previous operational concept is almost impossible without increasing the number and skill of the people involved. This is most obvious in ship navigation, where many experienced mariners believe that reversion to visual/ radar fi xing without warning, even for a ship travelling at speed in a crowded sea lane, in low visibility and with minimal bridge manning is unrealistic for many commercial vessels. However, it also applies to many control rooms that now rely heavily on automated processing based on location.

Emerging predators

As the benefits have grown so has GPS’s value as a target.

Over the last twenty-fi ve years we have experienced and catalogued GPS errors at system, signal and user levels. Perhaps the biggest development over the last few years has been the arrival of new predators: GPS jammers. We have always known that the low-power, high-frequency GPS signals are vulnerable to interference.

In the past, unintentional interference was the main concern and intentional jamming outside military theatres of operation was largely a theoretical problem. This is no longer the case. Low-powered transmitters are readily available over the Internet for as little as $150 and can block civil and military GPS on both frequencies together with Galileo and GLONASS in a vehicle’s vicinity. They can also block all mobile phone bands used in the area. Recently, much more powerful jammers have appeared on the market. Some of these are more powerful than the 1.5W jammers used in by the General Lighthouse Authorities in offi cial UK maritime trials that denied GPS for up to 30km.

Resilient PNT: Today’s requirement

GPS interference detection and mitigation (IDM) is an emerging industry with governments discussing databases, sensor networks and funding. Detecting and locating GPS jammers in a timely fashion is not straightforward as shown by US experiences at Moss Landing and San Diego among others.

The fall-out from GPS jamming can be severe and so we cannot afford to wait for IDM teams to be set up or the delay as they search for GPS jammers. If we want to secure the GPS-based benefits that we all enjoy, then our best strategy is to ensure that PNT is resilient in the face of GPS jamming. There are four real system requirements for the solution:

1. it needs to build on GPS and be independent of it with very different failure mechanisms;
2. it needs to have compatible performance and be interoperable so that we can keep our advanced, automated operational concepts;
3. it needs to be capable of being brought into operation soon (e.g.
in the next fi ve years); and
4. it should meet the requirements of many different users (maritime,
aviation, land and timing) in order to share the costs and benefits.

Options for resilience

Twenty-fi ve years ago, we would not have this problem. No single navigation system was used to the extent that GPS is today. Positioning (P) and navigation (N) were generally treated separately to time (T). The navigation sector was much smaller with niche professional markets and there was no mass-market. We could have had a lengthy discussion as we discussed the relative merits of systems like Omega, or Loran-C, or Decca, or Syledis.

Today, natural selection based largely on cost and benefi t means that PNT options are much more limited. There are a number of Global Navigation Satellite Systems (GNSS) in existence (GPS, GLONASS) or under development (Galileo, Compass) but they all share common vulnerabilities at signal and user levels, for example to interference and jamming. Adding more GNSS systems does not increase resilience.The key is diversity. We need to augment GNSS with a solution that meets the four system requirements stated earlier. The only real option is Enhanced Loran.

Is it curtains for Loran?

So, to the exam question: is it curtains for eLoran? This question has undoubtedly been prompted by activity in the United States of America and it is important to understand what has happened in recent times:

• In 2006, the US Departments of Transportation and Homeland Security commissioned an Independent Assessment Team (IAT) on eLoran that was led by Professor Brad Parkinson, the “Father of GPS”, and comprising a high-level group of experts. This recommended unanimously to designate eLoran as primary backup for critical GPS applications, to fund its completion and to commit to 20 years of operations.

• In early 2007, there was a Federal Register Notice on Loran. This demonstrated extremely broad support for establishing Loran with potential markets in the maritime, aviation and timing sectors. Taken together with the IAT report, these remain powerful and compelling reasons for transitioning to eLoran.

• In February 2008, the US Department of Homeland Security announced that it was starting to implement eLoran as an independent national positioning, navigation and timing (PNT) system to complement the Global Positioning System (GPS) in the event of an outage or disruption.

• On 25th February 2009, the US Secretaries of Transportation, Defense and Homeland Security released the 2008 Federal Radionavigation Plan (FRP) which is the offi cial source of radionavigation policy and planning for the US Government. This noted that in March 2008 the US National Space-based PNT ExComm endorsed the Department of Transportation (DOT) / DHS decision to transition the Loran system to eLoran and that DHS was working to clarify the operational requirements.

• Finally, on 26th February 2009, the US Offi ce of Management and Budget issued the US budget proposal for 2010/11 that effectively announced its intention to terminate Loran. From an international perspective, this may look rather confusing. However, at the time of writing, the World awaits the US Congress’ decision on Loran and there is one key question to be answered: if the US decides to close Loran, will the rest of the World keep going with Loran? This question has never, to my knowledge, been put formally to the 14 other nations that provide Loran services. However, I suspect that the majority including France, Japan, Norway, the Peoples Republic of China, the Russian Federation, Saudi Arabia, South Korea and the United Kingdom may see real benefi t in system diversity and decide to keep Loran and transition to eLoran. So, is it curtains for Loran? I don’t think so but there will be a process of realignment if the US decides to close Loran. This and other questions will, I’m sure, be discussed at the International Loran Association conference at Portland, Maine in mid-October.