4,631 research outputs found
Two-Layered Superposition of Broadcast/Multicast and Unicast Signals in Multiuser OFDMA Systems
We study optimal delivery strategies of one common and independent
messages from a source to multiple users in wireless environments. In
particular, two-layered superposition of broadcast/multicast and unicast
signals is considered in a downlink multiuser OFDMA system. In the literature
and industry, the two-layer superposition is often considered as a pragmatic
approach to make a compromise between the simple but suboptimal orthogonal
multiplexing (OM) and the optimal but complex fully-layered non-orthogonal
multiplexing. In this work, we show that only two-layers are necessary to
achieve the maximum sum-rate when the common message has higher priority than
the individual unicast messages, and OM cannot be sum-rate optimal in
general. We develop an algorithm that finds the optimal power allocation over
the two-layers and across the OFDMA radio resources in static channels and a
class of fading channels. Two main use-cases are considered: i) Multicast and
unicast multiplexing when users with uplink capabilities request both
common and independent messages, and ii) broadcast and unicast multiplexing
when the common message targets receive-only devices and users with uplink
capabilities additionally request independent messages. Finally, we develop a
transceiver design for broadcast/multicast and unicast superposition
transmission based on LTE-A-Pro physical layer and show with numerical
evaluations in mobile environments with multipath propagation that the capacity
improvements can be translated into significant practical performance gains
compared to the orthogonal schemes in the 3GPP specifications. We also analyze
the impact of real channel estimation and show that significant gains in terms
of spectral efficiency or coverage area are still available even with
estimation errors and imperfect interference cancellation for the two-layered
superposition system
V2X Meets NOMA: Non-Orthogonal Multiple Access for 5G Enabled Vehicular Networks
Benefited from the widely deployed infrastructure, the LTE network has
recently been considered as a promising candidate to support the
vehicle-to-everything (V2X) services. However, with a massive number of devices
accessing the V2X network in the future, the conventional OFDM-based LTE
network faces the congestion issues due to its low efficiency of orthogonal
access, resulting in significant access delay and posing a great challenge
especially to safety-critical applications. The non-orthogonal multiple access
(NOMA) technique has been well recognized as an effective solution for the
future 5G cellular networks to provide broadband communications and massive
connectivity. In this article, we investigate the applicability of NOMA in
supporting cellular V2X services to achieve low latency and high reliability.
Starting with a basic V2X unicast system, a novel NOMA-based scheme is proposed
to tackle the technical hurdles in designing high spectral efficient scheduling
and resource allocation schemes in the ultra dense topology. We then extend it
to a more general V2X broadcasting system. Other NOMA-based extended V2X
applications and some open issues are also discussed.Comment: Accepted by IEEE Wireless Communications Magazin
Massive MIMO for Internet of Things (IoT) Connectivity
Massive MIMO is considered to be one of the key technologies in the emerging
5G systems, but also a concept applicable to other wireless systems. Exploiting
the large number of degrees of freedom (DoFs) of massive MIMO essential for
achieving high spectral efficiency, high data rates and extreme spatial
multiplexing of densely distributed users. On the one hand, the benefits of
applying massive MIMO for broadband communication are well known and there has
been a large body of research on designing communication schemes to support
high rates. On the other hand, using massive MIMO for Internet-of-Things (IoT)
is still a developing topic, as IoT connectivity has requirements and
constraints that are significantly different from the broadband connections. In
this paper we investigate the applicability of massive MIMO to IoT
connectivity. Specifically, we treat the two generic types of IoT connections
envisioned in 5G: massive machine-type communication (mMTC) and ultra-reliable
low-latency communication (URLLC). This paper fills this important gap by
identifying the opportunities and challenges in exploiting massive MIMO for IoT
connectivity. We provide insights into the trade-offs that emerge when massive
MIMO is applied to mMTC or URLLC and present a number of suitable communication
schemes. The discussion continues to the questions of network slicing of the
wireless resources and the use of massive MIMO to simultaneously support IoT
connections with very heterogeneous requirements. The main conclusion is that
massive MIMO can bring benefits to the scenarios with IoT connectivity, but it
requires tight integration of the physical-layer techniques with the protocol
design.Comment: Submitted for publicatio
Physical Uplink Control Channel Design for 5G New Radio
The next generation wireless communication system, 5G, or New Radio (NR) will
provide access to information and sharing of data anywhere, anytime by various
users and applications with diverse multi-dimensional requirements. Physical
Uplink Control Channel (PUCCH), which is mainly utilized to convey Uplink
Control Information (UCI), is a fundamental building component to enable NR
system. Compared to Long Term Evolution (LTE), more flexible PUCCH structure is
specified in NR, aiming to support diverse applications and use cases. This
paper describes the design principles of various NR PUCCH formats and the
underlying physical structures. Further, extensive simulation results are
presented to explain the considerations behind the NR PUCCH design.Comment: 6 pages, 11 figures, accepted in IEEE 5G World Forum 201
A Multi-Service Oriented Multiple-Access Scheme for Next-Generation Mobile Networks
One of the key requirements for fifth-generation (5G) cellular networks is
their ability to handle densely connected devices with different quality of
service (QoS) requirements. In this article, we present multi-service oriented
multiple access (MOMA), an integrated access scheme for massive connections
with diverse QoS profiles and/or traffic patterns originating from both
handheld devices and machine-to-machine (M2M) transmissions. MOMA is based on
a) stablishing separate classes of users based on relevant criteria that go
beyond the simple handheld/M2M split, b) class dependent hierarchical spreading
of the data signal and c) a mix of multiuser and single-user detection schemes
at the receiver. Practical implementations of the MOMA principle are provided
for base stations (BSs) that are equipped with a large number of antenna
elements. Finally, it is shown that such a
massive-multiple-input-multiple-output (MIMO) scenario enables the achievement
of all the benefits of MOMA even with a simple receiver structure that allows
to concentrate the receiver complexity where effectively needed.Comment: 6 pages, 3 figures, accepted to the European Conference on Networks
and Communications (EuCNC 2016
Fairness Comparison of Uplink NOMA and OMA
In this paper, we compare the resource allocation fairness of uplink
communications between non-orthogonal multiple access (NOMA) schemes and
orthogonal multiple access (OMA) schemes. Through characterizing the
contribution of the individual user data rate to the system sum rate, we
analyze the fundamental reasons that NOMA offers a more fair resource
allocation than that of OMA in asymmetric channels. Furthermore, a fairness
indicator metric based on Jain's index is proposed to measure the asymmetry of
multiuser channels. More importantly, the proposed metric provides a selection
criterion for choosing between NOMA and OMA for fair resource allocation. Based
on this discussion, we propose a hybrid NOMA-OMA scheme to further enhance the
users fairness. Simulation results confirm the accuracy of the proposed metric
and demonstrate the fairness enhancement of the proposed hybrid NOMA-OMA scheme
compared to the conventional OMA and NOMA schemes.Comment: 6 pages, accepted for publication, VTC 2017, Spring, Sydne
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