The Evolution of Cellular Technology: The Long Road to 5G
This is the story of Qualcomm, a company that started in sunny San Diego in the summer of 1985, and its impact on the evolution of cellular technology. Qualcomm’s success reflects its pioneering role inventing technologies with the potential to radically shape our lives, then successfully bringing them to life. What has made Qualcomm unique is its seemingly insatiable pursuit of innovation, based on a culture where ideas brew rapidly. This began with the collective vision of the founders, Irwin Jacobs and six colleagues - Andrew Viterbi, Adelia Coffman, Andrew Cohen, Franklin Antonia, Harvey White and Klein Gilhousen - who left Linkabit to start “QUALity COMMunications,” initially pursuing government R&D contracts (see Figure 1).
FROM 1G to DIGITAL COMMUNICATION
The early cellular networks in the U.S. were based on the Advanced Mobile Phone System (AMPS) standard, an analog technology which boosted cellular capacity compared to the erstwhile mobile telephone system (MTS). Once Americans knew the convenience of carrying a phone while on the move, they no longer wanted the limitation of landline telephones. This opened the initial sluicegate of cellular phone usage, prompting mobile operators to scramble to install more cell towers to add capacity. However, the operators soon realized that adding cell towers was too costly to be sustainable, so they asked the Federal Communications Commission (FCC) to allocate additional spectrum. New spectrum was only a short-term fix, though, challenging operators to find a long-term solution to meet the continuously growing demand.
Cellular was analog, while the booming computer world was digital. For the cellular industry to evolve and become a technology for the masses, it had to find a path to the digital world. At that time, not many foresaw the fledgling cellular technology converging with the computer industry to create today’s digital world. Few had explored digital communication as a viable solution for cellular, which created an opportunity for Qualcomm to apply its experience developing digital communications for military and satellite systems. This led the cellular industry to be introduced to a technology called code division multiple access (CDMA).
CDMA, A NOVEL IDEA
To support the growth of cellular, the Cellular Telecommunications Industry Association (CTIA) saw the need for a digital wireless standard to increase capacity and improve quality. Responding, Qualcomm pitched a novel and little understood technology based on CDMA. CDMA used spread-spectrum techniques, a complex and very different approach from how the airwaves were being used by better known access technologies: frequency-division multiple access (FDMA) and time-division multiple access (TDMA). With CDMA, multiple users with unique codes share a single, wide bandwidth channel, which significantly increases capacity (see Figure 2).
Many operators had difficulty visualizing CDMA, much less believing it could work in the “real world.” Some “experts” argued it was too nascent to scale commercially. While the theoretical benefits of CDMA were impressive, several technical hurdles limited it from being considered for cellular communication. First was transmit power, also referred to as the “near-far problem.” The transmit power from a CDMA user near a tower could block everyone further away. The second challenge was known as the “single channel problem.” Using the same channel on all towers, devices located between towers could cause interference to users connected to the other tower. A third issue was system acquisition time, how long it took for a device to find the network after powering on.
Qualcomm developed solutions to overcome these and other challenges, innovations such as fast power control, soft handover and a common pilot signal using GPS. However, by the time Qualcomm introduced these solutions, TDMA had established a strong foothold. The Telecommunications Industry Association (TIA) and the CTIA had announced TDMA as the cellular standard for digital communication. This was a major blow to Qualcomm, leading industry experts to predict an early exit for the company and CDMA; they believed CDMA would be limited to military and satellite communications or academia. However, Jacobs and his team believed CDMA was the right long-term solution for cellular standards because it would provide much higher capacity as well as better quality of service. For operators, this meant satisfied users and the capacity to serve more of them. Qualcomm continued researching and improving CDMA, and with persistence and persuasive demonstrations to policy drivers and regulators, the company successfully convinced the FCC to allow any operator the option to deploy CDMA.
This was a big win, and it was not long before some operators did. However, if CDMA were to become the digital communication standard in the U.S., Qualcomm did not have much time. Turning a policy win into commercial success required wide availability of cellular phone components in volume, which was challenging because of the complexity to implement CDMA. While manufacturing was not a Qualcomm core competency, the company made a strategic decision to apply its expertise with CDMA to design the ASICs which would implement the most complex elements of the technology. To further bootstrap the ecosystem, Qualcomm established a joint venture to produce mobile phones (see Figure 3), which helped convince the supply chain that CDMA technology was ready for the mass market. The decision to design its own ASICs and phones paid long-term dividends, adding valuable system knowledge which Qualcomm transformed into a leading market position in cellular modems and processors.
Although the market outlook for CDMA was improving, Qualcomm still faced challenges, including a significant cash crunch. To raise funding, the company released an initial public offering (IPO) of stock on December 16, 1991 and the price rose more than 50 percent within two weeks. However, the market’s optimism was short-lived; in January, the CTIA endorsed TDMA as the preferred cellular standard, largely erasing the gains from the IPO. Disappointed, yet undaunted, Qualcomm continued to develop and promote CDMA. By the end of 1993, the TIA had adopted CDMA as the digital cellular standard for 2G in the U.S., leading to it being selected by several operators in the U.S. and Korea. In Europe, GSM was the 2G digital standard, having been developed by the European Telecommunications Standards Institute (ETSI) and adopted in 1987 by 13 European countries as a mandatory standard for Europe.
3G AND THE MOBILE INTERNET
When the International Telecommunication Union finalized the requirements for IMT-2000 - popularly known as “3G” - CDMA’s position as the preferred technology expanded beyond the U.S. and Korea. As part of 3G, Qualcomm advanced CDMA with higher speeds and capacity in an evolved standard called cdma2000. Europe and Japan developed a 3G CDMA standard called wideband CDMA (WCDMA). Even though the cdma2000 was slightly different than WCDMA, the two standards bodies worked to harmonize key aspects. After years of technology investment and development, CDMA had been adopted as the global cellular standard, confirming Qualcomm’s early vision.
Although voice calls were the primary cellular service during the 1990s, Qualcomm had been laying the foundation for high speed data applications. “Evolution data optimized” (EV-DO) introduced an IP packet-based network design to enable high speed mobile broadband services. EV-DO adopted networking technology from the computer industry, departing from the circuit-switched standard long used for telephone service. Among other innovations, EV-DO provided an enhancement called “opportunistic scheduling,” which is still used in advanced cellular technologies. Opportunistic scheduling uses smaller data packets, exchanged “opportunistically” between a device and the base station when radio conditions are optimum. An upgrade to EV-DO enabled mobile terminals to communicate with the network using multiple RF carriers (see Figure 4). To enable these capabilities, Qualcomm envisioned combining the cellular modem with a powerful processor with graphics, making the mobile phone a handheld computer. The success of the EV-DO structure was affirmed when key aspects were integrated into high speed packet access (HSPA).
Motivating its technology development, Qualcomm realized that wireless technologies are only successful when they embrace the entire ecosystem. As well as increasing the data capacity of the network, EV-DO/HSPA was a precursor to digitally connecting the world, whether people or “things.” This capability enabled a class of new applications with a growing presence today: high speed browsing, multimedia exchange with rich media experience, low latency gaming and multicasting. Mobility with access to the Internet removed the limitation of desktop browsing and gaming, creating a more social and interactive experience we now view as normal.
The IP-based architecture of EV-DO/HSPA offered a flexible and cost-effective way to roll out applications and services. This proved a significant benefit to operators, enabling them to offer and monetize services. On-demand video and music streaming were being introduced, which accelerated data consumption on mobile devices. 3G shifted what consumers expected from their phones, renamed handsets. Internet connectivity was rapidly becoming a necessity, and EV-DO had created the enabling technology. Its IP-based architecture was best suited to support high data rates and could be deployed in tandem with voice services, giving consumers both.
4G AND THE SMARTPHONE
CDMA had proven to be very efficient for channels up to 5 MHz bandwidth. For channels greater than 10 MHz, another access technology - orthogonal frequency-division multiplexing (OFDM) - was more efficient. OFDM uses multiple, narrowband subcarriers spread over a wide channel bandwidth. Recognizing the need to strengthen its capability in OFDM, Qualcomm acquired Flarion Technologies in 2006, which provided the framework for 4G/LTE.
The proliferation of voice, broadband internet and other data services, with the convergence of these industries, offered opportunities for new services and significantly more capacity to support them. Low power computing became exceedingly important as the cellular modem, embedded camera, graphics and multimedia were bundled to support multimedia applications. This was another capability Qualcomm had anticipated, first introducing mobile devices with integrated, low power computing in 2002.
Higher data rates - well over 50 Mbps - and faster connection times were the driving forces that led to the 4G era. Smartphones, such as the iPhone, and the apps they spawned required higher data capacity. Additional antennas were integrated for both uplink and downlink, introducing the use of MIMO to significantly increase data speeds by creating multiple orthogonal data streams, called layers. MIMO could improve spectral efficiency without requiring more spectrum, scaling the network to support higher data speeds.
Launched in 2010, 4G enabled operators to offer OFDM-based services in conjunction with their existing 3G networks, creating the opportunity to expand their business models as wireless internet service providers. This convergence of networks and devices supporting both CDMA and OFDM enabled operators to assign the most appropriate access technology - 3G CDMA, 4G, Bluetooth or Wi-Fi - depending on the requested service and location. The result was a more seamless experience for users. The rapid proliferation of 4G led to a “connected world” with billions of devices communicating with each other, exchanging data and offering users unprecedented lifestyle changes. The term “internet of things” (IoT) was coined as users found themselves connected to the things in the world around them, enabled by cellular IoT connections in homes, businesses, transportation, energy infrastructure, farms, hospitals and retail stores. 4G’s all-IP architecture, inherent security and rapid global adoption further incentivized application developers to create innovative businesses using mobile devices, with Uber and Lyft as oft-cited examples.
As 4G continued to develop capabilities, defined by the roadmaps for LTE-Advanced and LTE-Advanced Pro, the need for a next-generation cellular network, named 5G, was initially met with skepticism. Qualcomm was an early proponent. As with CDMA, it saw 5G as an innovation platform for a new decade, one that could power a significant shift in how the world uses mobile devices. To support the continuing upsurge in applications and foster use cases not yet conceived, Qualcomm believed 5G could unify a diverse range of spectrum and deployment scenarios, one that would scale across these varied applications.
In 2015, the initial requirements for 5G were published as the IMT-2020 standard, and the telecommunications industry began defining the wireless networking solution to meet a core set of requirements, including ultra-fast data rates, ultra-low latency and ubiquitous connectivity to many devices, virtually anywhere. Qualcomm worked with the mobile ecosystem of standards bodies, regulatory committees, operators, mobile device and infrastructure manufacturers and technology partners to define the standards that became the first embodiment of 5G. The 5G new radio (5G NR) is designed to handle a wide range of services, deployments and spectrum bands; to do so, it uses many of the capabilities established in 3G and 4G: carrier aggregation, OFDM and MIMO. In release 15, the first standard defining the implementation of 5G, the 3GPP defined a foundation for NR that comprises five capabilities that were pioneered by Qualcomm (see Figure 5): a flexible, slot-based framework; scalable OFDM air interface; advanced channel coding; massive MIMO; and the use of mmWave spectrum for mobile and fixed wireless access. Historically, mobile communication has used spectrum below 3 GHz. 5G expands that to higher frequencies: “mid-bands” to 6 GHz and “high-bands” above 24 GHz. Adding mmWave radios at existing 4G cell sites enables operators to significantly increase data rates, with shared sites enabling faster deployment at lower cost.
mmWave was always considered unsuitable for mobile communication because of the perceived technical challenges, such as limited range, line-of-sight links and large parabolic antennas. However, Qualcomm saw mmWave as essential to realize the potential of 5G, analogous to its early belief in CDMA, and was a strong advocate. Field tests in 2015 showed robust non-line-of-sight propagation using multi-beam techniques; by 2018, Qualcomm, Ericsson, Nokia and Samsung had demonstrated 5G NR interoperability at the mmWave and mid-band frequencies; in 2019, mmWave radios began rolling out in commercial networks. In parallel, Qualcomm developed antenna front-end modules for the handset, the first and only supplier to offer a mmWave front-end. The antenna front-end module is controlled by its Snapdragon 5G modem to optimize handset performance, including battery life.
The evolution of 5G has already begun with 3GPP release 16, which will address once inconceivable vertical services, such as high-performance industrial automation and cellular vehicle-to-everything (C-V2X). Again, Qualcomm anticipated the need: in 2007, it began R&D on device-to-device proximity services, a foundation for C-V2X, integrated access and backhaul and IoT relays. Looking forward, AI will play an increasingly important role in devices and networks. Primarily concentrated in the cloud today, AI intelligence will be distributed between the device and the cloud, what is called the “intelligent wireless edge.” With its advanced network architecture, 5G can provide the framework to connect AI-powered devices with each other and the cloud, to enhance user experience, network efficiency and improve data security and privacy.
The evolution of cellular technology, from analog to 5G (see Table 1), has been a long road, requiring vision and persistence. Arguably, no company more than Qualcomm has played such a pivotal role in developing and commercializing mobile technology, leading to the connected world we enjoy today.
The 5G story will be one of momentum, evolution and transformation, leading to an even more connected world, expanding beyond consumers to industrial applications and health care. IHS Markit estimates 5G will enable $13.2 trillion in global economic output in 2035, with the 5G value chain generating $3.6 trillion and supporting 22.3 million jobs.2
Despite their belief in CDMA, Qualcomm’s founders could not have imagined its impact on the world when the company was formed.
Read Microwave Journal’s interview with Qualcomm’s Chief Technology Officer, James Thompson, at www.microwavejournal.com.
This article would not have been written without the assistance of Suranjeeta Choudhury and her team at Qualcomm, who provided technical and historic insight.
- Rashid Attar, Donna Ghosh, et al., “Evolution of cdma2000 Cellular Networks: Multi-carrier EV-DO,” IEEE Communications Magazine, February 2006.
- IHS Markit, “The 5G Economy, How 5G will Contribute to the Global Economy,” November 2019.