Signal Processing - September 2017 - 112

Evolution of radion navigation
Radio navigation has come a long way since its inception in
the early 1900s when the German companies Telefunken and
Lorenz started constructing radio beacon systems (or Funkbaken) in 1907. Circular radio beacons were set up in 1921 in
the United States for maritime navigation. Then, in 1928, a
low-frequency four-course radio range was introduced in the
United States for instrument flying. In 1932, the first aircraft
instrument landing system (or Bordfunkgeraete) was demonstrated in Germany, with the Lorenz beam using a very-highfrequency (VHF) transmitter. In 1940, the British Gee system,
which used a chain of terrestrial stations, was first tested. The
Gee system inspired the Americans to construct their longrange navigation (LORAN) system, which went live in 1942.
Around that same time period, the Decca system was invented in the United States independently of the Gee system and
offered better accuracy for navigating ships and aircrafts. It
was later developed in the United Kingdom and became operational in 1944. In 1957, the Soviet Union launched the first satellite, Sputnik I. Inspired by the Doppler shifts observed from
Sputnik I, the United States started developing in 1958 Transit
(or NAVSAT), the first global satellite-based navigation system. Transit was realized with a nominal constellation of five
satellites, but only one satellite was visible at a time, meaning that a user waited 35-100 min (depending on the latitude)
between successive satellite passes to determine its position.
The first global, continuously available radio navigation system
was the ground-based system Omega, which was developed
by the United States and six partner nations. Omega became
operational in 1971, enabling ships and aircrafts to determine
their position with a two-dimensional (2-D) root-mean square
(RMS) accuracy of 2-4 km, by receiving very-low-frequency

1)

4)

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(VLF) radio signals transmitted by a network of fixed terrestrial radio beacons transmitting at about 10 kW.
Transit's success prompted the U.S. Navy and U.S. Air Force
to develop parallel programs in the 1960s, which were eventually combined into one program: Navigation System with Timing
and Ranging (or NAVSTAR), which later became known as the
global positioning system (GPS). The nominal GPS constellation consists of 24 SVs in medium-earth orbit, the first of which
was launched in 1978, and the system was declared operational
in 1995. GPS revolutionized position determination over land,
sea, air, and even space. The system with its global coverage
is available 24 h/day every day, providing the navigator with a
highly accurate tool, which operates in all weather conditions.
The receiver, on the other hand, is compact and relatively inexpensive, allowing its use by anyone from a hiker to an airplane
pilot. The GPS inspired the development of other GNSSs such
as the Russian GLONASS (first launched in 1982), the Chinese BeiDou (2000), and the European Galileo (2011) as well
as regional navigation satellite systems including the Japanese
QZSS (2010) and the Indian IRNSS (2013).
Despite the extraordinary advances in GNSS signal processing and receiver design, GNSSs are unreliable for accurate
anytime, anywhere positioning, navigation, and timing due
to the four inherent limitations given previously. Traditional
approaches to address GNSS limitations have been to fuse
GNSS receivers with dead-reckoning systems and map-matching algorithms. These approaches typically fuse the outputs of
heterogeneous sensors, particularly inertial navigation systems
(INSs), digital map databases, and GNSS receivers, with specialized signal processing algorithms.
Motivated by the plenitude of ambient radio-frequency (RF)
signals of opportunity in GNSS-challenged environments, a

6)

9)

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12)

14)

15)

5)
8)

13)

11)

3)
16)

(a)

(b)

(c)

FIGURE 1. The evolution of radio navigation. (a) Early systems: 1) low-frequency four course radio range, 2) LORAN, 3) Gee, 4) Transit, and 5) Omega.
(b) Satellite-based navigation systems: 6) GPS, 7) GLONASS, 8) BeiDou (launch), 9) Galileo, 10) QZSS, and 11) IRNSS. (c) Signals of opportunity:
12) cellular, 13) wireless communications access point, 14) digital television, 15) FM, and 16) iridium satellite communication. (Images 1-7 and 12-16
courtesy of www.wikipedia.org. Images 8-11 courtesy of www.insidegnss.com.)

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IEEE SIGNAL PROCESSING MAGAZINE

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September 2017

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