LTE & Wi-Fi: Options for Uniting Them for a Better User Experience

2

Most national governments consider the radio spectrum a valuable national resource and heavily regulate its commercial use. Governments typically auction off licenses for the right to transmit over a portion of the spectrum, which can be very expensive.

The traditional business model for cellular carriers is based on access to this licensed spectrum. They license slices of spectrum from the local regulator and sell their customers access to it. After decades of parallel evolution on the two sides of the Atlantic through multiple generations of technologies, the business has coalesced worldwide around a single 4th generation (4G) radio technology standard called Long Term Evolution, commonly referred to as LTE.

However, if a wireless device promises to “play nice,” most regulators will allow it to transmit on a slice of spectrum set aside for that purpose: the license-exempt, license-free or simply unlicensed bands. Playing nice means adhering to certain rules that will be verified when the device is certified. The rules are derived from basic human civility: I will not shout too loudly—there is a limitation on transmit power, with the Effective Isotropic Radiated Power (EIRP) limited to anything between 4W (36 dBm) to 25 mW (14 dBm). I will share the resource, not monopolize it—these are rules about the duty cycle, the maximum duration of transmit bursts, minimum duration of silence after transmission, and an obligation to “listen before talk (LBT).” I will yield to users who have been deemed by society to be serving a higher need than I have—as we would pull over to give way to a fire engine or ambulance, unlicensed spectrum users must move away from a frequency if they detect equipment like airport weather radar operating on it.

While the exact situation varies by country, generally speaking there are three unlicensed

bands of greatest interest today when it comes to wireless broadband: The 2.4 GHz band (λ ≈ 12 cm) has 83 MHz between 2.400 and 2.483 GHz. This band is almost uniformly available worldwide and is heavily used by consumer devices. The 5 GHz band (λ ≈ 5½ cm) has 775 MHz between 5.150 and 5.925 GHz. This band is gaining popularity in consumer devices—mostly in premium and high-end devices for now—but its allocation is fragmented and less uniform across countries. The 60 GHz band (λ ≈ ½ cm) has 9,000 MHz between 57 and 66 GHz. This band is relatively new and promising, though the laws of physics put some limitations on the ways it can be used.

The dominant wireless broadband technology in these three bands is Wi-Fi, which is based on the IEEE 802.11 wireless LAN standard. Wireless LAN technology is now heavily used for private networks in homes as well as in the workplace. Then there is public Wi-Fi, which is common in cafés, restaurants, airports, hotels, shopping malls, and increasingly on trains and planes. Sometimes it is complimentary, and sometimes we have to pay for it. In fact, in several small, densely populated developed nations such as Singapore, Wi-Fi can be found almost anywhere.

While cellular carriers have been good at providing coverage—especially outdoors—they face both coverage and capacity challenges as the demand for broadband internet access grows. There can be a coverage problem at the network’s edge, in locations where installing radio infrastructure, such as towers, cannot be justified financially. There is a coverage problem indoors, because the materials a building is made of—especially stone, concrete, steel and metallized sun-control film—can block radio signals to and from the carrier’s cell tower outdoors. There can be a capacity problem in “hotspots” where many people congregate. This isn’t a problem if the carrier has enough licensed spectrum to address this demand. However, spectrum licenses are expensive, and budgeting spectrum for the capacity demands of hotspots would leave most of that spectrum unused