The main frequencies used in communications in the United States are CDMA, GSM, 4G and upcoming 5G. In order to give you a better understanding of various frequency bands, we will introduce the above frequency bands in detail.
Conventional frequencies in United States
3G (short for third Generation) is a mobile telecommunications system used in cell phones that grew in popularity in the 2000s in North America. 3G handles talk, text, and basic mobile internet.
4G (short for fourth Generation) is a mobile telecommunications system used in cell phones that grew in popularity in the 2010s in North America. 4G devices are backward-compatible with 3G, meaning it can handle talk, text, and data-heavy fast internet. WiMAX was one of the first 4G standards; however, popularity has shifted to LTE. Clear (owned by Sprint Nextel) will continue WiMAX support until the end of 2015 before switching to LTE. LTE is considered to be true 4G and a popular global mobile standard. Although LTE uses different frequencies and bands in different countries, a multi-band LTE-compatible phone will most likely work in different countries. While 3G handles talk, text, and basic internet, 4G can handle 3G duties and also do fast streaming internet for data-heavy services such as YouTube, Pandora, Spotify, Hulu, Netflix, Facebook, Google Chrome, Google Maps, iTunes, and other apps.
CDMA and GSM are the two radio networks used by wireless carriers and present in cell phones. CDMA stands for "code division multiple access" and GSM stands for "global system for mobiles. As you might guess, GSM networks are much more common globally than CDMA ones.
The Cellular band occupies 824–849 MHz and 869–894 MHz ranges. To issue cellular licenses, the FCC divided the U.S. into 734 geographic markets called Cellular Market Areas (CMAs) and divided the 40 MHz of spectrum into two, 20 MHz amounts referred to as channel blocks; channel block A and channel block B. A single license for the A block and the B block were made available in each market. The B block of spectrum was awarded to a local wireline carrier that provided landline telephone service in the CMA. The A block was awarded to non-wireline carriers. In 1986, the FCC allocated an additional 5 MHz of spectrum for each channel block, raising the total amount of spectrum per block to the current total of 25 MHz.
The 1850–1990 MHz PCS band is divided into six frequency blocks (A through F). Each block is between 10 MHz and 30 MHz in bandwidth. License (A or B) is granted for Major Trading Areas (MTAs). License (C to F) is granted for Basic Trading Areas (BTAs). License (G), where issued, is granted for Economic Areas (EAs). There are 51 MTAs, 493 BTAs and 175 EAs in the United States.
3G and 4G are two types of wireless networks. The "G" denotes "generation"; as you'd probably guess, 4G is a newer, faster generation of network than 3G. 4G is often up to 10x faster than 3G in real-world use — with speeds commonly between 20Mbps and 50Mbps (which is really fast).
The United States is broadly covered by both 3G and 4G LTE technology. 3G is the network that some older phones run on, and the one newer 4G LTE-capable devices fall back to when unable to reach a primary network.
In terms of their relevance to 3G and 4G LTE bands and frequencies, the thing to know is that CDMA and GSM only use 3G technology. So the CDMA vs. GSM discussion is really a 3G discussion. However, as alluded to earlier, it's important to ensure that your phone has ample 3G frequency compatibility, since this is the network your phone will jump on in the absence of a 4G signal. Otherwise, you'll simply have no reception when you can't reach a 4G network.
2G, first introduced in 1992, is the second-generation of cellular telephone technology and the first to use digital encryption of conversations. 2G networks were the first to offer data services and SMS text messaging, but their data transfer rates are lower than those of their successors.
3G networks succeed 2G ones, offering faster data transfer rates and are the first to enable video calls. This makes them especially suitable for use in modern smartphones, which require constant high-speed internet connection for many of their applications. 4G is the fourth generation of mobile phone communications standards. It is a successor of the 3G and provides ultra-broadband internet access for mobile devices.
The latest signal frequency-5G
The next generation cellular network--named, naturally, 5G--is in the works, promising speeds between 10 and 100 times faster than 4G LTE. The 5G networks being planned right now will operate in a high-frequency band of the wireless spectrum—between 30 GHz and 300 GHz, in what's known as the millimeter wave spectrum. These millimeter waves can transfer heaps of data at very high speeds, but they don't travel as far as the lower-frequency waves used in 4G networks. High-frequency millimeter waves also have difficulty getting around walls, buildings, and other obstacles. On a lower-frequency network like 4G LTE, the antennas can be farther apart, and obstacles aren't a big issue. When the 5G networks are built, the carriers will have to use more antennas—many more—to get the same coverage as our current networks. You'll see mini-antennas basically everywhere.