Earlier this month, the Federal Communication Commission (FCC) decided to allocate nearly 11 GHz of spectrum for 5G mobile broadband use. If you need some good bedtime reading, try the 278-page document;
for a concise summary, see “FCC OKs sweeping Spectrum Frontiers rules to open up nearly 11 GHz of spectrum.”
The FCC made this bold move to get out in front of the coming 5G technology wave- and its decision will help the rest of us focus our energies on the crucial innovations that will enable 5G.
The commissioners wisely chose to include 3.85 GHz of licensed spectrum and 7 GHz of unlicensed spectrum, supporting both types of business innovation. The newly allocated spectrum sits at 28 GHz, 37 GHz, 39 GHz and 64-71 GHz, and the FCC will seek additional comment on the bands above 95 GHz. The new unlicensed band (64 to 71 GHz) is adjacent to the existing 57 to 64 GHz ISM band, creating a 14 GHz band of contiguous unlicensed spectrum (57 to 71 GHz).
I am struck by the huge amount of high-frequency spectrum that has been allocated for future wideband mobile use. For an interesting comparison, look back at the spectrum that launched the first analog cellular systems in the US: the Advanced Mobile Phone System (AMPS) used 824-849 MHz and 869-894 MHz for a total spectrum 50 MHz wide. The FCC’s 5G spectrum decision allocates more than 200 times that amount, underlining the kind of bandwidth required to meet the aggressive goals of 5G.
FCC Chairman Tom Wheeler was very clear about the how the FCC is approaching the 5G opportunity. In a recent speech, he said, “With today’s Order, we are repeating the proven formula that made the United States the world leader in 4G: one, make spectrum available quickly and in sufficient amounts; two, encourage and protect innovation-driving competition; and three, stay out of the way of market-driven, private sector technological development.”
To open up wide chunks of spectrum, the FCC had to reach for higher frequencies, which bring with them plenty of technical challenges. Millimeter-wave (mmWave) frequencies have higher path loss and undergo different effects from scattering, diffraction and material penetration. Also, mmWave components and subsystems are harder to design due to significant tradeoffs between energy efficiency and maximum power level. Compounding the difficulty, frequency bands below 6 GHz will also be critical for 5G deployment, working in concert with the mmWave bands. From this perspective, I see three areas that will require significant innovation on the path to 5G:
New channel models: Today, millimeter frequencies are often used for fixed terrestrial communication links and satellite communications. These tend to be stationary point-to-point links that don’t have to deal with radio mobility. At Keysight, we have been working with communications researchers at higher frequencies to develop channel models that are appropriate for mobile broadband use at mmWave. The higher-frequency, wideband nature of the channel and the dynamics of the mobile environment require more robust modeling approaches than those used for lower frequencies.
Beamforming needs to work: The remedy for higher signal loss is to increase the antenna gain and make it steerable, a technique commonly known as beamforming. This method focuses radio signals from an array of multiple antenna elements into narrow beams that can be pointed for maximum overall system performance. Wireless LAN at 60 GHz (802.11ad) offers 7 Gbps connectivity for short-distance or “in room” applications—and 802.11ad does implement beamforming to optimize signal strength. While some of this work will leverage into 5G, 802.11ad is neither mobile nor multiple access (handling multiple diverse users simultaneously). There’s more work to be done here.
New air interface: Not to be overlooked is the need for a new air interface to take advantage of wide spectrum (when available). This interface must be scalable by design so that it can deliver unprecedented high bandwidth while still performing well for lower-bandwidth applications. The aggressive goals for 5G also include improved spectral efficiency, low battery drain for mobile devices and low latency for IoT devices.
We’ve been here before: you may recall the difficult list of challenges associated with LTE (4G) technology. Just like 5G, LTE was an aggressive technology development pursued by the wireless industry. Somehow we got it done. Challenges like this drive innovation in electronic communications.