650 research outputs found
Indoor wireless communications and applications
Chapter 3 addresses challenges in radio link and system design in indoor scenarios. Given the fact that most human activities take place in indoor environments, the need for supporting ubiquitous indoor data connectivity and location/tracking service becomes even more important than in the previous decades. Specific technical challenges addressed in this section are(i), modelling complex indoor radio channels for effective antenna deployment, (ii), potential of millimeter-wave (mm-wave) radios for supporting higher data rates, and (iii), feasible indoor localisation and tracking techniques, which are summarised in three dedicated sections of this chapter
Towards the Next Generation of Location-Aware Communications
This thesis is motivated by the expected implementation of the
next generation mobile networks (5G) from 2020, which is being
designed with a radical paradigm shift towards millimeter-wave
technology (mmWave). Operating in 30--300 GHz frequency band
(1--10 mm wavelengths), massive antenna arrays that provide a
high angular resolution, while being packed on a small area will
be used. Moreover, since the abundant mmWave spectrum is barely
occupied, large bandwidth allocation is possible and will enable
low-error time estimation. With this high spatiotemporal
resolution, mmWave technology readily lends itself to extremely
accurate localization that can be harnessed in the network design
and optimization, as well as utilized in many modern
applications. Localization in 5G is still in early stages, and
very little is known about its performance and feasibility.
In this thesis, we contribute to the understanding of 5G mmWave
localization by focusing on challenges pertaining to this
emerging technology. Towards that, we start by considering a
conventional cellular system and propose a positioning method
under outdoor LOS/NLOS conditions that, although approaches the
Cram\'er-Rao lower bound (CRLB), provides accuracy in the order
of meters. This shows that conventional systems have limited
range of location-aware applications. Next, we focus on mmWave
localization in three stages. Firstly, we tackle the initial
access (IA) problem, whereby user equipment (UE) attempts to
establish a link with a base station (BS). The challenge in this
problem stems from the high directivity of mmWave. We investigate
two beamforming schemes: directional and random. Subsequently, we
address 3D localization beyond IA phase. Devices nowadays have
higher computational capabilities and may perform localization in
the downlink. However, beamforming on the UE side is sensitive to
the device orientation. Thus, we study localization in both the
uplink and downlink under multipath propagation and derive the
position (PEB) and orientation error bounds (OEB). We also
investigate the impact of the number of antennas and the number
of beams on these bounds. Finally, the above components assume
that the system is synchronized. However, synchronization in
communication systems is not usually tight enough for
localization. Therefore, we study two-way localization as a means
to alleviate the synchronization requirement and investigate two
protocols: distributed (DLP) and centralized (CLP).
Our results show that random-phase beamforming is more
appropriate IA approach in the studied scenarios. We also observe
that the uplink and downlink are not equivalent, in that the
error bounds scale differently with the number of antennas, and
that uplink localization is sensitive to the UE orientation,
while downlink is not. Furthermore, we find that NLOS paths
generally boost localization. The investigation of the two-way
protocols shows that CLP outperforms DLP by a significant margin.
We also observe that mmWave localization is mainly limited by
angular rather than temporal estimation.
In conclusion, we show that mmWave systems are capable of
localizing a UE with sub-meter position error, and sub-degree
orientation error, which asserts that mmWave will play a central
role in communication network optimization and unlock
opportunities that were not available in the previous generation
Robust NOMA-assisted OTFS-ISAC Network Design with 3D Motion Prediction Topology
This paper proposes a novel non-orthogonal multiple access (NOMA)-assisted
orthogonal time-frequency space (OTFS)-integrated sensing and communication
(ISAC) network, which uses unmanned aerial vehicles (UAVs) as air base stations
to support multiple users. By employing ISAC, the UAV extracts position and
velocity information from the user's echo signals, and non-orthogonal power
allocation is conducted to achieve a superior achievable rate. A 3D motion
prediction topology is used to guide the NOMA transmission for multiple users,
and a robust power allocation solution is proposed under perfect and imperfect
channel estimation for Maxi-min Fairness (MMF) and Maximum sum-Rate (SR)
problems. Simulation results demonstrate the superiority of the proposed
NOMA-assisted OTFS-ISAC system over other systems in terms of achievable rate
under both perfect and imperfect channel conditions with the aid of 3D motion
prediction topology
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