Page 16 - EETimes Europe June 2021

16 EE|Times EUROPE

OPINION | BEYOND 5G, TOWARD 6G But the real breakthrough will come from
considering frequencies beyond 100 GHz. The
large bandwidths available here are of particu-
Taking 6G KPIs lar interest with, at first, D-band at about
140 GHz, and later the 300-GHz range. There
to a New Level are, of course, major challenges that will call
for technical solutions capable of pushing sil-
icon’s limits. Potential avenues include, again,
By Jean-Baptiste Doré, 5G program manager, and Eric Mercier, hybridizing silicon and III-V technologies, with
a goal of achieving transistor F
= 1 THz, and
max
manager of the Telecom & Wireless Unit, CEA-Leti co-integrating very small antennas at wafer
scale or in-package.
LIKE ANY GENERATIONAL ADVANCE in technology, the 5G-6G transition will greatly Until now, no convergence on these solutions
improve our ability to meet key performance indicators (KPIs). We’ll have the ability to link has been found, but some trends are emerging.
several-orders-of-magnitude–more devices; create zero-latency, zero-energy, ultra-reliable CEA-Leti teams are considering two specific
links; perform semantic-enhanced data mining; and seamlessly share knowledge between aspects. On the transceiver side, to avoid
humans and machines in support of artificial intelligence and other advanced applications. At large-bandwidth, power-consuming conversion,
the same time, however, achieving broad acceptance will require attention to a whole new set channel bonding/aggregation has attracted
of KPIs, such as energy efficiency, cybersecurity, and sustainability. As academic and industrial attention, and 100-Gbps throughput over
researchers have begun tackling 6G design and engineering tasks, several preliminary directions 16 channels has been demonstrated. On the
have emerged: exploration of new spectrum horizons, targeting of higher spectral efficiency antenna side, efforts have focused on a transmit
through new MIMO schemes, and improvement of the overall environmental footprint. array utilizing a single transceiver/FEM rather
The worldwide 5G rollout has resulted in some local states placing stringent limits on electro- than more classical phase-shifter architectures
magnetic field (EMF) emissions, impacting network deployment and increasing the complexity that require one transceiver/FEM per tile.
of upcoming spectrum use. Because EMF limits are calculated over the entire spectrum, the Figure 1 compares the average power of a
envisioned increase in traffic throughput will likely require more efficient spectral-use schemes. beamforming RF front end assuming 34-dBm
Recently, distributed massive multiple-input multiple-output (D-MIMO) networks, also EIRP and 100-mW RF transmitter consump-
referred to as cell-free MIMO, have gained attention. Unlike the co-located massive-MIMO tion. This would allow a transmit array with
approach used in 5G, the D-MIMO scheme involves a cooperative, dense network based on a 26-dBi gain to reach a 7.2-Gbps/2-GHz chan-
massive deployment of cost- and energy-efficient RF units, which together build a virtual large nel at 200 meters with a backoff of 6 dB and
array. This new paradigm promises efficiency gains even at low frequencies; this is hardly possi- expected power gain of a factor of 2 to 20 for
ble for co-located MIMO because of the necessary array size. The vision of a distributed network xHaul or multi-user MIMO use cases.
would lead to massively digital cells with terminal-like hardware specifications, denoted as an Another major point of concern lies in
RF-less architecture. Necessary components include digital front ends, filtering and switching the digital domain for processing of very
functions, and power amplifiers with advanced energy-efficient features such as digital pre- high-throughput data streams. Silicon CMOS
distortion (DPD) and envelope tracking. node technologies are evolving in response
Again, a continuum for new spectrum opportunities is being investigated. Spectrum resources to calls for this type of processing capacity,
below 6 GHz will still be essential to support wide-range radio coverage, and there may be ways but they come with higher prices and greater
to use frequencies currently not considered, between 6 GHz and 24 GHz, to deploy power dissipation. While this is acceptable
massive-MIMO base stations. Development will be fueled by continued hybridizing of CMOS and for backhauling, it is not suitable for edge
III-V technologies for output power in front-end modules (FEMs). applications, and optimization work to meet
6G expectations is expected. As with 5G
networks, the use of edge computing and AI
blocks is seen as a key enabler for several stra-
tegic functions: development of ever-more
complex wireless networks, reduction in data
traffic through edge processing, and enhance-
ment of signal-processing algorithms for
channel estimation, the beamforming process,
DPD, and optimization of RF settings.
Finally, there are the emerging KPIs asso-
ciated with sustainability and environmental
impact. A primary concern, energy efficiency,
is addressed in 5G by avoiding useless
resources when capacity exceeds the momen-
tary and local actual need. 6G promises to
advance this in several ways in anticipation
of the envisioned exponential traffic growth.
The use of AI to manage network power
consumption and load is being studied, as
are the impacts on equipment life cycles, as
well as novel mechanisms such as reconfigu-
rable intelligent surfaces and new MIMOs for
Figure 1: Average power consumption of a transmit array architecture and a classical an- limiting the impact of EMF radiation on both
tenna array. The photo shows a 300-GHz transmit array with 26-dBi gain. (Source: CEA-Leti) intended and non-intended recipients. ■

JUNE 2021 | www.eetimes.eu