LTE RF: Complicated by Design
Band fragmentation and a host of other radio frequency (RF)-related issues could derail the 4G LTE experience, making life particularly tricky for mobile antenna vendors, according to a new Heavy Reading report, "LTE RF Design: Challenges and Opportunities".
Everyone wants great LTE coverage across the globe on a sleek, thin device with an enormous screen and days-long battery life. However, none of this is possible without multi-band RF capabilities built into the smartphones, and the big problem is that the available space to squeeze antennas into these mobile devices is shrinking by 25 percent annually, according to antenna vendor Ethertronics. (See Next-Gen Challenges of LTE RF Design.)
"With a bigger screen, you'd think there's more space for antennas, but the screen sucks it up and the battery gets bigger," Kridel says. "Antennas are low on the pecking order."
What's more, device makers are used to paying pennies for RF antennas, so the more sophisticated antenna and RF systems required for LTE are a hard sell for the antenna makers.
The reason LTE is such a game changer is that, while the underlying technology is a global standard, the spectrum being licensed for 4G services around the world comprises multiple disparate bands. Antenna makers are therefore being required to cost-effectively support more than 40 potential bands, 19 of which are currently in use, in addition to 3G/2.5G/2G fallback, Bluetooth, NFC (near-field communications), Wi-Fi and GPS, as well as designing products that will fit into increasingly thin smartphones.
By comparison, the antennas for 3G devices were required to support just four or five bands. (See The Myth of LTE Global Roaming.)
To be called a truly global LTE phone, a device would need to support 12 to 13 of the 19 bands, Kridel says. That still wouldn't match 3G's footprint, but it'd be good enough for most.
Antenna makers are starting to address this spectrum support challenge by developing active antennas that are tunable based on environmental conditions. Changes in the physical environment can mess with a device's antenna -- remember "antennagate"? -- but tunable, multiple input multiple output (MIMO) antennas help alleviate that issue.
Kridel says active antennas are still a niche play right now, but they are a good fit for LTE and operators' heterogeneous networks (het-nets), which will see customers spending more time connected via small cells at the fringes of mobile networks. Qualcomm Inc.'s forthcoming RF360 front-end solution is an early example of an active antenna: It currently supports 40 bands and uses a dynamic antenna matching tuner to work around external issues. (See Qualcomm Unveils Single Global LTE Chip and Qualcomm: Multiband Chips Will Take LTE Global.)
RF vendors will just have their work cut out convincing the handset makers to take on the premium cost. The vendors' goal will be to retain as few SKUs (stock keeping units) as possible for each device model while still reaching the widest possible market, including price-sensitive developing markets. But they'll have to find a solid business reason to do so.
"Price is a consideration, but performance is the big one," Kridel says. "You're paying for LTE and you expect certain things. You think it'll be superfast, and if it doesn't deliver great performance, you question it. Everyone's reputation takes a hit."
— Sarah Reedy, Senior Editor, Light Reading