Page 41 - ITU Journal, Future and evolving technologies - Volume 1 (2020), Issue 1, Inaugural issue

ITU Journal on Future and Evolving Technologies, Volume 1 (2020), Issue 1

0
10
and ideas to improve the NCDS. In particular, the multi‑
plexing of UEs in the constellation domain is not ef icient,
so an excessively high number of antennas is currently
10 -1 needed to multiplex more than two UEs [12]. There is a
need to ind new constellation designs that overcome this
limitation. A possible way to obtain these optimal designs
SER 10 -2 is to use some arti icial intelligence techniques in order to
automatically deal with the channel and multi‑user inter‑
ference effects. Not only the phases, but also the constant
amplitudes of the constellations are possible values to se‑
CDS - ZF
-3
10 CDS - ZF, PN
CDS - ZF, HPA lect, giving a more complex search space, where arti icial
NCDS intelligence can help.
NCDS, PN
NCDS, HPA Additionally, we have seen that the performance is very
-4
10 sensitive to the spatial separation of the UEs that are
0 2 4 6 8 10 12 14 16 18 20
SNR (dB) multiplexed, either in constellation or space. Therefore,
scheduling algorithms that take this into account and op‑
Fig. 7 – SER comparison for UL. timize a particular performance metric are also crucial.
0
10 The advantages of NCDS with respect to CDS vanish when
the channel is quasi‑static and with high SNR. Then, it is
10 -1 advisable to ind hybrid schemes, such as [20] where the
best of both paradigms is used according to the commu‑
-2
10
nication scenario and needs.
Finally, it is foreseen that in the future communications
10 -3
SER will be tightly integrated with sensing, which is one of the
-4 main objectives of the the Sixth Generation (6G) of mobile
10
communications [38]. In these new systems, the ef icient
-5 exploitationofCSIunderavarietyofscenarioswillplayan
10 CDS
important role, and hence, we forecast that the exploita‑
CDS, PN
CDS, HPA
-6 tion of non‑coherent techniques will be an interesting al‑
10 NCDS
NCDS, PN ternative, in order to increase the ef iciency of the overall
NCDS, HPA
10 -7 system. We hope that this review of the NCDS characteris‑
0 2 4 6 8 10 12 14 16 18 20
SNR (dB) tics, feasible implementation and performance will stim‑
ulate new research and advances in this topic.
Fig. 8 – SER comparison for DL.
ACKNOWLEDGEMENT
7
This work has been funded by project TERESA‑ADA
6
(TEC2017‑90093‑C3‑2‑R) (MINECO/AEI/FEDER, UE).
The authors would like to thank Ignasi Piqué‑Muntané
5 for his help in the elaboration of some igures.
Throughput (Msps) 4 3 REFERENCES
CDS [1] NR; Physical channels and modulation (Release 16).
2 CDS, PN Technical report, 3GPP, France, 2020.
CDS, HPA
NCDS [2] W. Guo, W. Zhang, P. Mu, F. Gao, and H. Lin.
1 NCDS, PN
NCDS, HPA High‑mobility wideband massive MIMO communi‑
cations: Doppler compensation, analysis and scal‑
0
0 2 4 6 8 10 12 14 16 18 20 ing laws. IEEE Transactions on Wireless Communica‑
SNR (dB)
tions, 18(6):3177–3191, June 2019.
Fig. 9 – Throughput comparison for DL. [3] Y. Ge, W. Zhang, F. Gao, S. Zhang, and X. Ma.
The NCDS combined with multi‑user MIMO‑OFDM is Beamforming network optimization for reducing
shown to be a feasible and very attractive technique channel time variation in high‑mobility massive
which substantially improves the performance of the co‑ MIMO. IEEE Transactions on Communications,
herent systems, especially in challenging scenarios such 67(10):6781–6795, Oct. 2019.
as systems with realistic propagation channels and high [4] M. Gao, B. Ai, Y. Niu, W. WU, P. Yang, F. Lyu, and
mobility. However, there is still need for new research X. Shen. Ef icient hybrid beamforming with anti‑

© International Telecommunication Union, 2020 21