As operators roll out 5G
The communications industry began to consider other modulation methods for radio signals
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In 2017,
members of the mobile communications industry group 3GPP were still debating whether to accelerate the development of 5G standards.
The proposal first proposed by Vodafone was eventually agreed by other members of the group, promising to develop 5G technologies in multiple directions simultaneously, so as to deliver 5G networks earlier.
Adopting this recommendation may also mean driving some other decisions.
One of these decisions has to do with the encoding of the wireless signals in 5G networks.
The 3GPP Release 15 standard (which lays the foundation for 5G) ultimately chose orthogonal frequency division multiplexing (OFDM), which is inherited from 4G, as the encoding technology.
Release 16, expected to be released by the end of this year, will include the findings of a research team tasked with exploring alternatives.
Wireless standards are updated frequently, and in the next release of 5G communications standards, the communications industry may address the problem of OFDM's high power consumption in 5G devices and base stations.
This is an inevitable problem because 5G networks are expected to require many base stations to provide services and connect billions of mobile devices and IoT devices.
“I don’t think the carriers really understand the impact this is going to have on the phone and battery life,
” said James Kimery, marketing director for radio frequency and software-defined radio research at National Instruments. “5G comes at a price, and that price is battery life.
”
Kimery pointed out that it's not just 5G phones that have power consumption issues.
China Mobile has been "very vocal about the power consumption of base stations," he said.
It is estimated that a 5G base station will consume about three times as much power as a 4G base station.
To cover the same area, more 5G base stations are needed.
So how is 5G a potential power-hungry monster?
OFDM is a big factor.
OFDM transmits data by splitting it into multiple parts and sending them simultaneously at different frequencies, so that the parts are "orthogonal" (meaning they don't interfere with each other).
The trade-off with OFDM is a high peak-to-average power ratio (PAPR).
Generally speaking, the orthogonal parts of an OFDM signal actively transmit energy, which means that the very properties that prevent the signals from canceling each other also prevent the energy of the parts from canceling out.
This means that any receiver must be able to absorb a large amount of energy at once, and the transmitter must be able to send a large amount of energy at once.
This high energy situation results in a high peak-to-average power ratio for OFDM, making this method less energy efficient than other coding schemes.
For some emerging 5G applications, high peak-to-average power ratios are unacceptable, said Yuan Yifei, chief engineer for wireless standards at ZTE Corp.
and rapporteur of the 3GPP study group on 5G non-orthogonal multiple access possibilities
, pointing specifically to large machine-type communications such as large-scale IoT deployments.
Typically, if multiple users (such as a group of IoT devices) are communicating using OFDM, the system will organize the communications using orthogonal frequency-division multiple access (OFDMA), which allocates a large block of spectrum to each user.
(To avoid confusion, note that OFDM is how each device's signal is encoded, while OFDMA is how one device's signal doesn't interfere with the others overall.
) The logic of each device using a different spectrum would cause large IoT networks to spiral out of control, but the Release 15 standard defines OFDMA for 5G connected machines, largely because it was used in 4G communications.
Yuan’s team is considering a promising alternative:
non-orthogonal multiple access (NOMA), which would maintain the advantages of OFDM while allowing overlapping users to use the same spectrum.
Yuan Yifei currently believes that OFDM and OFDMA meet the early needs of 5G.
He believes that the earliest application of 5G will be smartphones, and the Release 16 standard is scheduled to be launched in December 2019. 5G will not be used in large-scale machine-type communications for at least one or two years.
However, if network providers want to upgrade their equipment to fully offer NOMA, the cost will be high.
"It will definitely cost money,
" Yuan Yifei said, "especially the base stations.
" Handling NOMA will require at least a software update, and may also require more advanced receivers, more processing power, or even hardware upgrades.
Kimery is not optimistic that the industry will adopt any non-OFDMA approach.
“It’s possible there will be alternatives,
” he said, “but they’re unlikely.
Some things are very difficult to change once they’re in place.
”
*Disclaimer: This article is originally written by the author. The content of the article is the author's personal opinion. Semiconductor Industry Observer reprints it only to convey a different point of view. It does not mean that Semiconductor Industry Observer agrees or supports this point of view. If you have any objections, please contact Semiconductor Industry Observer.
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