Civilian GPS Receivers

Civil receivers rapidly caught up with military receivers, before surpassing them in many ways such as lower cost, size, weight, and power (CSWaP); sensitivity; and user interface. The first commercially available receiver used analog electronics to perform dual-frequency sequential processing of C/A-signals and P(Y)-signals. A codeless receiver, the Macrometer, was also developed, exploiting the cyclos- tationarity of GPS signals to produce sinusoidal waveforms that could be tracked for relative positioning without use of the spreading codes.

The Texas Instruments TI 4100 NAVSTAR Navigator was the first widely used commercial GPS receiver. Sold from 1981 to 1989, it was distinctive for its use of digital circuitry, processing C/A-signals and P-signals on L1 and L2 from four satellites. A geodetic version was also available that provided higher-accuracy differential positioning. These receivers were used for surveying even when four Block I satellites were in view only for several hours a day.

The Macrometer and TI-4100 were primarily used for professional applications such as geodesy and surveying, pioneering the concepts of single- and doubledifference measurements that are widely used in precision satnav applications today.

The first handheld GPS receiver was marketed in 1989, using sequential processing of C/A-signals from different satellites. Consumer receivers became more common in the 1990s, with the first GPS receiver in a mobile phone introduced in 1999. Figure 3.8 shows some of these pioneering civil GPS receivers.

Figure 3.8. TI-4100 (left; image courtesy of Mr. Phil Ward); Magellan NAV 1000, the first handheld receiver (Navigation, Division of Work & Industry, National Museum of American History, Smithsonian Institution); Benefon!, the first commercially available mobile phone with GPS (right). Source: (Left) Reproduced with permission of Institute of Navigation. (Center) Reproduced with permission of Smithsonian National Museum of American History

Professional civil receivers also matured during the 1990s, with more receiver channels, “semicodeless” processing of the encrypted P(Y)-signal for dual-frequency ionospheric measurements, use of carrier phase differential processing for decimeter accuracy, and the addition of GLONASS signals for geometric diversity. Use of GPS for civil aviation also increased during the 1990s, becoming increasingly popular in the United States as WAAS became operational in 2003.

As described in Chapter 1, Section 1.1, the FCC’s E911 mandate in 1994 stimulated low-power, low-cost GPS chipsets that revolutionized GPS in consumer devices, facilitated by assisted-GPS techniques. Billions of GPS receivers are now in use worldwide, with new chipsets increasingly capable of also receiving signals from SBAS, GLONASS, Galileo, BeiDou, and QZSS.

Modern civil receivers employ a front-end integrated circuit that inputs RF signals from the antenna and outputs digitized samples at low IF or baseband, followed by a digital integrated circuit that products PVT measurements. The newest receivers employ tens or even hundreds of channels to process signals from GPS as well as other satnav systems at one, two, or three different carrier frequencies. Their low CSWaP makes them suitable for embedding in many devices.