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Cellular systems have evolved significantly since the first handheld cell phone was demonstrated by John F. Mitchell and Martin Cooper of Motorola in 1973. The first commercially automated cellular network was launched in Japan by Nippon Telegraph and Telephone (NTT) in 1979. This first generation (1G) was analog and used frequency division multiple access (FDMA). The second generation (2G) transitioned to digital and mostly used time‐division multiple access (TDMA), which later evolved into 2.5G: General Packet Radio Service (GPRS) and 2.75G: Enhanced Data Rates for GSM Evolution (EDGE). The third generation (3G) upgraded 2G networks for faster Internet speed and used CDMA. The fourth generation (4G), commonly referred to as LTE, was introduced to allow for even faster data rates. LTE used orthogonal frequency division multiple access (OFDMA) and featured multiple‐input multiple‐output (MIMO), that is, antenna arrays. Figure 38.1 summarizes the existing cellular generations and their corresponding predominant modulation schemes.

This chapter focuses on using cellular CDMA and LTE signals for PNT. Table 38.1 compares the main characteristics of (i) GPS coarse/acquisition (C/A) code, (ii) CDMA pilot signal, and (ii) three LTE reference signals: primary synchronization signal (PSS), secondary synchronization signal (SSS), and cell‐specific reference signal (CRS).

Figure 38.1 Cellular systems generations.

Source: Adapted from A. Elnashar, “Wireless Broadband Evolution,” http://www.slideshare.net/aelnashar/ayman‐el‐nashar, June 2011, accessed on: June 2019.

Table 38.1 GPS versus cellular CDMA and LTE comparison

Standard	Signal	Possible number of sequences	Bandwidth (MHz)	Code period (ms)	Expected ranging precision (m)*
GPS	C/A code	63	1.023	1	2.93
CDMA	Pilot	512	1.2288	26.67	2.44
LTE	PSS	3	0.93	10	3.22
	SSS	168	0.93	10	3.22
	CRS	504	up to 20	0.067	0.15

^* 1% of chip width

In 2012, the International Telecommunication Union Radiocommunication (ITU‐R) sector started a program to develop an international mobile telecommunication (IMT) system for 2020 and beyond. This program set the stage for 5G research activities. The main goals of 5G compared to 4G include (i) higher density of mobile users; (ii) supporting device‐to‐device, ultra‐reliable, and massive machine communications; (iii) lower latency; and (iv) lower battery consumption. To achieve these goals, millimeter wave bands were added to the current frequency bands for data transmission. Other salient features of 5G include millimeter waves, small cells, massive MIMO, beamforming, and full duplex [30, 31].