Qualcomm is proposing a suite of OFDM techniques for a variety of 5G use cases except large IoT deployments.
A consensus is brewing the Phase I 5G spec will not use LTE’s SC-FDMA as its primary waveform but will use a variant of OFDM for both up and downlinks. “One operator at the last plenary referred to it as ‘LTE Advanced Pro, Olympics Edition,’ and others were even more negative,” said the engineer who asked not to be named.
Despite the emerging consensus, no final decisions have been reached on coding schemes except that LDPC likely will be used for large block sizes. Contentious debates over coding schemes forced some of the latest meetings held in Lisbon to drag on well past midnight, sometimes arguing over “tenths of decibels,” the engineer said.
Figure 1: The 3GPP originally aimed to finish 5G specs in in 2018 and 2019 for service roll outs in 2020 and beyond. (Source: Qualcomm)
Qualcomm is proposing a suite of OFDM techniques for a variety of 5G use cases except large Internet of Things deployments. Final decisions on all the attributes of the new air interface are expected from 3GPP by March.
“The new 5G air interface will bring both new capabilities, flexibility and efficiency below 6GHz. Although it is OFDM-based, we would not call it a variant of LTE,” a Qualcomm representative said.
Carson of Qualcomm said engineers are down to “about three flavours of OFDM as the basis for the Phase I 5G spec with higher order modulation beyond 256QAM under consideration.
“We can leverage a lot of what we know from LTE Pro and 802.11.ad” which already support 60GHz links with 32-element antenna arrays, he added.
Figure 2: Qualcomm highlighted in a white paper its preferred OFDM variants for a 5G air interface. (Source: Qualcomm)
Wireless specialists outside the 3GPP took a balanced view of the situation.
Given 5G adds several new cellular use cases with sometimes competing requirements, “standardisation for such a complex system will take time and should not be hurried,” said Arogyaswami Paulraj, a professor emeritus in Stanford’s EE department.
On the other hand, real-world results are helpful to characterise millimetre wave bands. “I hope—unlike in the previous standards process when simulations were the primary basis for decision making—5G will use field trials also to help pick the right technology choices,” he said.
He applauded work by AT&T, Facebook, KT and Verizon on developing mm-band back-haul technologies. “This is certainly not 5G, but they serve an urgent market need and the significant learning they will bring can enhance the final 5G standard,” he said.
Standards bodies and developers appreciate real-world data, said Phil Marshall, chief research officer at Tolaga Research. He noted with 5G “from a marketing perspective the industry is getting ahead of itself, but this is something that we see with every technology generation.”
Separately NetGear announced a consumer device that delivers Gbit-class speeds over LTE. The Mobile Router MR1100 uses a Snapdragon X16 LTE modem supporting 3x carrier aggregation, a combination of 2x2 and 4x4 MIMO and 256QAM.
Telstra and other carriers plan to use the system in a commercial service launching in 2017. Qualcomm aims to integrate the X16 modem in an SoC it will launch next year.