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3G, 4G, LTE, WiMAX: what do they all mean?
When shopping for technology products, consumers typically have at their disposal a wide array of technical specifications that allow for meaningful side-by-side comparisons of competing products. Shopping for a computer? Compare processor speeds, hard drive capacity, quantity of RAM and the number of USB ports. Looking at digital cameras? Check out the number of megapixels, memory card capacity, and the optical zoom. It's true that you cannot simply assume a "bigger is better" mentality and get the best product by grabbing the device with the largest specs – any informed shopping requires consumer education. But these metrics make product comparisons, at least across any single feature, relatively easy and transparent.
Now try shopping for mobile phones and cell phone service. 3G, 4G, LTE, WiFi, WiMAX – the "technical" acronyms are certainly plentiful, and seem to denote some qualitative or quantitative differences across services and devices – 4G is better than 3G, right? But is there actually any meaning behind these terms? Most of them actually have no specific technical underpinnings, at least not in the eyes of US wireless carriers, but the terms do carry some meaning.
International Telecommunications Union
First and foremost, understanding these terms as used by US wireless carriers requires, first, a recognition that they typically refer to marketing/advertising gimmicks, not to any technical specifications. In many countries around the world, but not in the US, wireless service is subject to a set of standards set by the International Telecommunications Union (ITU). The ITU describes itself as "the United Nations specialized agency for information and communication technologies – ICTs. [The ITU] allocate[s] global radio spectrum and satellite orbits, develop the technical standards that ensure networks and technologies seamlessly interconnect, and strive to improve access to ICTs to underserved communities worldwide."
When examining terms like "4G" in the US, it is critical to understand that the standards-based meaning for that term that exists elsewhere in the world simply does not apply in this country. The US wireless industry has adopted the terminology of the international standards body, but not their precise ITU meanings. These concepts are used mainly for marketing purposes, and in the US, are not analogous to technical terms with precise meanings, like megapixels, bits per second, gigahertz, and kilobytes. In general, it is thus safer to assume that any standardized international meaning of a wireless term, at least in a technological sense, does not apply here, although there are exceptions.
3G vs. 4G Networks
A casual observer would be correct to assume that a 4G network is supposed to be better than a 3G network, but there is no easy way to translate the incremental increase in speeds and quality as a network switches over from 3G to 4G. In this case, 3G simply stands for "Third Generation" and 4G is, you guessed it, "Fourth Generation." 4G networks are presumed to be faster and more robust than 3G networks. However, the increase from 3 to 4 does not imply a direct quantitative increase (4G is not simply 33% better than 3G). The terms 3G and 4G also don't have a technical meaning from the standpoint of network construction. 3G and 4G don't imply any specific type of tower or antenna, radio technology in handsets, service type (such as GSM or CDMA), cell site capacity, specific spectrum allocation, or an industry standard bandwidth capacity. Consumers are on their own to investigate how each US carrier provisions its advertised 3G and 4G services, and how that will affect their end-user experience.
One thing is clear: all of the US carriers are advertising 4G as the latest and greatest service, and are making efforts to transition from 3G to 4G service. Accordingly, we will focus just on the major 4G network rollouts in the US. But before we look at each of these technologies, it is helpful to understand the network architecture inherent in any wireless network, and the constraints that this architecture can impose upon bandwidth regardless of 4G technology.
Wireless Network Architecture: Backhaul
Most mobile phone users only directly see mobile telephony as a wireless experience between their handset or data card and the end point of their communications. In reality, the wireless portion of "wireless" service is actually quite small; calls and data are transmitted wirelessly for only a short distance to the nearest cell tower, at which point the call is sent over wired backhaul transmission lines to a switching center and ultimately routed over wireline transmission and switching facilities to its ultimate destination. The wireless network is critically dependant upon these traditional wireline telecom services, which typically consist of high capacity "Special Access" services (e.g., DS-1, DS-3, or higher) provided by wireline incumbent local exchange carriers.
Even as wireless technologies evolve to make more efficient use of spectrum and to provide better and faster wireless transmission between the end user and the cell tower, each tower must see corresponding upgrades to the wireline backhaul facilities, which can easily bottleneck traffic between the tower and the ultimate destination of the data. For example, even if a 4G device is capable of providing wireless transmission at speeds of 100 mbps, its effective data rate would be limited to that of the backhaul facility interconnecting the cell site transceiver with the cellular switching office.
As such, 4G wireless network upgrades must be accompanied by corresponding advanced wireline backhaul upgrades in the 4G coverage area in order to provide noticeable service improvements. Carriers such as AT&T often footnote their advertisements about their need to upgrade backhaul facilities to achieve their advertised speeds and, as such, do not actually guarantee that 4G speeds will, in practice, be available.
One other element needs to be considered when evaluating the claims of the wireless carriers. Radio technologies of all kinds represent a tradeoff between transmission speed and possible transmission distances. The greater the transmission distance (i.e., the distance between the end user and the closest cell site), the slower the service must be to provide quality transmission. So the maximum speeds theoretically possible using any given technology will almost never be achievable unless the end user is immediately adjacent to the site antenna. As the user moves farther away from the cell site, data speeds will necessarily decrease, resulting in average experienced speeds of well below the maximum possible.
Wireless Network Architecture: Backhaul
Sprint was, at least in a chronological sense, the frontrunner of the major US wireless carriers for 4G deployment. Sprint announced its adoption of "WiMAX" in early 2007, with plans to build a network capable of reaching 100-million users by the end of 2008. In 2008, Sprint, along with a coalition of other companies, pooled spectrum to be used by Clearwire to launch a nationwide WiMAX network. WiMAX, short for "Worldwide Interoperability for Microwave Access" is one of several competing standards for both fixed wireless backhaul and advanced mobile data services. At the time that Sprint announced its commitment to WiMAX and forged ahead to be first to market with 4G service provided using WiMAX, a classic VHS vs. Betamax "format war" was brewing, with AT&T and Verizon making ovations about a competing wireless standard known as LTE (discussed in depth below). Sprint committed to its WiMAX choice both because it was, at least in its view, the superior technology, and also to gain the first mover advantage.
Sprint's WiMAX launch was marred by setbacks, and initial plans to cover 100-million people by the end of 2008 were replaced with the reality that the first 4G/WiMAX handset, the HTC EVO, didn't hit the market until mid-2010, and then only worked in test markets. The original WiMAX standard calls for download speeds of as fast as 40 mbps, and currently calls for potential end-user speeds of as much as 100 mbps. ETI has tested a Sprint 4G data card at numerous locations across the country, and has yet to identify any location on Sprint's network where such speeds can be achieved in practice.
Although Sprint achieved its goals of being first to market with a true 4G network, it has struggled to expand the coverage nationwide, and WiMAX has not lived up to its potential, at least for the mobile applications launched by Sprint. In the time since Sprint's 2007 adoption of WiMAX, other clearly superior alternatives for providing 4G service have emerged, and Sprint has announced partnerships to migrate to one such alternative, LTE, over the coming years. Customers currently buying a WiMAX device should expect to experience only moderate coverage, slower than anticipated speeds, and the likely orphaning of the technology as Sprint migrates to LTE.
LTE: AT&T and Verizon
LTE, short for Long Term Evolution, is an upgrade to current UMTS (Universal Mobile Telecommunications System) 3G standards being marketed in the US as 4G, even though it does not meet international standards for 4G service. Nonetheless, LTE is a major upgrade over existing 3G data services, and ranks well above WiMAX in consumer tests. The "Evolution" portion of LTE does include a roadmap (called LTE-A "Advanced") to eventually get up to true 4G speeds, but several important steps — further radio advancements and massive backhaul upgrades — will be required in order to achieve these goals. LTE relies as much on backhaul upgrades as it does on new technology to improve end user speeds.
Both AT&T and Verizon have supported LTE, but to-date only Verizon has actually rolled out LTE service. In classic form, AT&T has announced its first LTE handset, though it will only work in LTE mode once AT&T makes the necessary network upgrades. Verizon meanwhile has rolled out LTE in earnest, covering 160-million potential users and offering a suite of LTE handsets and data cards.
ETI has tested a Verizon LTE data card, and has achieved download speeds in excess of 12 mbps (as advertised by Verizon) and LTE coverage in several metropolitan areas. LTE consumers can expect major upgrades from current Verizon 3G data speeds, and good and growing network coverage. AT&T's rollout is as yet unproven, but should be roughly equivalent to Verizon's from a technological standpoint, once AT&T deployment reaches parity with Verizon.
HSPA+: AT&T and T-Mobile
Both AT&T and T-Mobile have also rolled out an intermediate data product that is being marketed as 4G service but is actually only an upgrade to current 3G technologies. HSPA+ is better thought of as a 3G booster: it is powered by current hardware, but uses multiple antennas in a MIMO (multiple input, multiple output) array to boost speeds. HSPA+, like LTE, relies as much on major backhaul upgrades more than any major technological enhancement to achieve its performance boost.
However HSPA+ can only be viewed as a temporary "4G" solution—HSPA+ is the end of this particular road, with no direct roadmap to true 4G deployment. AT&T has already announced LTE 4G rollout plans, and has been using HSPA+ as a stopgap between more permanent network upgrades. T-Mobile, which has actually achieved astonishing speeds using this implementation, has acknowledged in its merger filings with the FCC that it too will need to migrate to another technology to make a full 4G transition, but claims not to have the spectrum available to accomplish this seamlessly.
Given that 3G coverage is ubiquitous in the US, consumers should expect to find such services nationwide, with HSPA+ services providing more than adequate speeds, especially on the T-Mobile network, at least in the current marketplace. Although HSPA+ is conceptually able to produce download speeds of at least 21 mbps, realistic peak download speeds fall into the 7 mbps range. As Verizon forges ahead with LTE-Advanced, and AT&T moves over to LTE, HSPA+ devices and coverage can be expected to be on the decline.
For more information, contact Colin B. Weir at firstname.lastname@example.org
Read the rest of Views and News, August 2011.
About ETI. Founded in 1972, Economics and Technology, Inc. is a leading research and consulting firm specializing in telecommunications regulation and policy, litigation support, taxation, service procurement, and negotiation. ETI serves a wide range of telecom industry stakeholders in the US and abroad, including telecommunications carriers, attorneys and their clients, consumer advocates, state and local governments, regulatory agencies, and large corporate, institutional and government purchasers of telecom services.