Page 33 - 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

NON‑COHERENT MASSIVE MIMO‑OFDM FOR COMMUNICATIONS IN HIGH MOBILITY
SCENARIOS

1
2
Kun Chen‑Hu , Yong Liu , Ana Garcia Armada 1
1 Deparment of Signal Theory and Communications of Universidad Carlos III of Madrid (Spain). E‑mails: {kchen,
2
agarcia}@tsc.uc3m.es, Shanghai Research Center, Huawei Technologies (China). E‑mail: liu.liuyong@huawei.com.

Abstract – Under scenarios of high mobility, the traditional coherent demodulation schemes (CDS) have a limited perfor‑
mance, due to the fact that reference signals cannot effectively track the variations of the channel with an affordable overhead.
As an alternative solution, non‑coherent demodulation schemes (NCDS) based on differential modulation have been proposed.
Even in the absence of reference signals, they are capable of outperforming the CDS with a reduced complexity. The literature
on NCDS laid the theoretical foundations for simpli ied channel and signal models, often single‑carrier and spatially uncorre‑
lated lat‑fading channels. In this work, the most recent results assuming orthogonal frequency division multiplexing (OFDM)
signaling and realistic channel models are explained, and the impact of some hardware impairments such as the phase noise
(PN) and the non‑linear high power ampli ier (HPA) are also considered. Moreover, new potential research lines are also
highlighted.
Keywords – 5G, channel estimation, MIMO, non‑coherent, OFDM.

1. INTRODUCTION state information (CSI). This overhead can be excessively
high for very fast time‑varying channels. In such cases, a
The Fifth Generation of mobile communications (5G) [1] signi icant number of reference signals is required for the
is the global standard for a uni ied wireless air interface, continuous tracking of the channel estimation [20].
which is capable of providing a great lexibility for a mul‑
titude of use cases. The three main requirements of those The works in the literature have provided the theoreti‑
services are enhanced mobile broadband (eMBB), mas‑ cal foundations to understand NCDS and point to some
sive machine type communications (mMTC) and ultra re‑ cases when they can outperform the traditional CDS, in
liable low‑latency communications (URLLC). Therefore, particular in scenarios with high mobility [20]. Also, re‑
the peak data‑rate is not the only feature to be improved, cent works show some combinations of NCDS with MIMO‑
but also an enormous number of connected devices and OFDM for the uplink (UL) and downlink (DL). In the
the latency‑sensitive services are taken into account. Also present work, convinced that NCDS is an idea whose time
there is an increasing interest in providing an adequate has come, we discuss the implementation of the NCDS in
service in high mobility scenarios [2] ‑ [4]. practical MIMO‑OFDM communication systems, assum‑
Orthogonal frequency division multiplexing (OFDM) with ing some realistic channels characterized by high mobil‑
multiple‑input multiple‑output (MIMO) [5] have been re‑ ity. We provide the details of how to integrate the differ‑
cently set as the radio techniques for the physical layer ential modulation [21] in the two‑dimensional resource
in 5G [1]. New frequency bands are proposed to be grid (time and frequency) provided by the OFDM. Addi‑
exploited to obtain more available bandwidth, such as tionally, we also show the performance of this combina‑
3.5 GHz and millimeter‑waves (mm‑Wave) [6], and thus, tion under the effects of the phase noise (PN) [22], [23] or
the existing services can be improved and new ones can high power ampli ier (HPA) [24], for both UL and DL, and
be implemented. The integration of massive MIMO is a its bene its as compared to the traditional CDS. Finally, a
must, not only to improve the average capacity of the discussion related to challenges and opportunities is pro‑
link, but also for the implementation of beam‑steering vided together with some concluding remarks, in order to
and beamforming to mitigate propagation losses in these stimulate the research on this promising topic.
new higher bands. Furthermore, the complexity of the
signal processing techniques need to be bounded to re‑ The remainder of the paper is organized as follows. Sec‑
duce the cost of the devices and the delay of the required tion 2 introduces the main differences between CDS and
operations. As an alternative to classical coherent de‑ NCDS, especially for high mobility scenarios. Section 3
modulation schemes (CDS), non‑coherent demodulation and Section 4 provide the details of how to integrate the
schemes (NCDS) [7–9] have been proposed recently to be NCDS with MIMO‑OFM for the UL and DL, respectively.
combined with massive MIMO systems [10] ‑ [19]. They Section 5 presents several numerical results to evaluate
are capable of avoiding the overhead produced by the ref‑ the proposed scheme under some realistic channel mod‑
erence signals due to the fact that the transmitted sym‑ els, providing an assessment of the achieved system per‑
bols can be recovered without the knowledge of channel formance. Finally, in Section 6, the conclusions follow.

© International Telecommunication Union, 2020 13