Wireless communications networks have evolved dramatically from their humble beginnings. The first-generation (1G) wireless network, the Advanced Mobile Phone Service (AMPS) cellular communications standard, was based on analog technology from Bell Labs. But users liked the convenience of carrying a communications device such as a telephone wherever they went, and the number of users grew quickly. Subsequently, second-generation (2G) wireless networks saw the adoption of GSM and CDMA technologies as the first digital standards.
Still, users wanted more functions from their cell phones, so third-generation networks eventually arrived as the first mobile broadband wireless systems. With 3G UMTS technology integrated as the high-speed digital standard, they could send e-mails and data as well as make voice calls,. The fourth-generation (4G) wireless network, equipped with Long Term Evolution (LTE) and LTE Advanced digital technologies, was thought to be the last wireless communications network that anyone would ever need—until the need arose for the fifth generation (5G).
In spite of digital techniques and advanced modulation formats, wireless communications generations 1 through 4 have worked with essentially limited bandwidth, trying to serve a fast growing number of users wanting more services that consume ever-increasing bandwidth.
For example, current 4G LTE wireless network infrastructure equipment in the U.S. operates at 800 MHz, 1900 MHz, 1.7 to 2.1 GHz, and 2.5 to 2.7 GHz. However, it also employs a variety of additional communications technologies, such as wired Ethernet and fiber-optic cables, to transfer data at the highest rates possible. Both fixed and mobile wireless users now expect data rates in excess of 1 Gb/s. With the coming of 5G in approximately two years, data rates are expected to reach 10 Gb/s.
The mmWave Bandwidth Solution
Even with the advances of 4G LTE, the network is running out of bandwidth. The solution, as seen by 5G wireless network developers, is to add more bandwidth by using frequency spectrum in the millimeter-wave frequency range (Fig. 1). With hundreds of megahertz of wireless transmission bandwidth available at center frequencies such as 24, 28, and 38 GHz, 5G wireless networks will be capable of almost zero-latency phone calls and extremely high data speeds. Although mmWave frequencies, according to their wavelengths, range from 30 to 300 GHz, 5G innovators such as Qualcomm and other members of the Third Generation Partnership Program (3GPP) working on 5G network solutions typically refer to the mmWave frequency range as starting at about 24 GHz.