130 research outputs found
Energy Efficiency and Sum Rate Tradeoffs for Massive MIMO Systems with Underlaid Device-to-Device Communications
In this paper, we investigate the coexistence of two technologies that have
been put forward for the fifth generation (5G) of cellular networks, namely,
network-assisted device-to-device (D2D) communications and massive MIMO
(multiple-input multiple-output). Potential benefits of both technologies are
known individually, but the tradeoffs resulting from their coexistence have not
been adequately addressed. To this end, we assume that D2D users reuse the
downlink resources of cellular networks in an underlay fashion. In addition,
multiple antennas at the BS are used in order to obtain precoding gains and
simultaneously support multiple cellular users using multiuser or massive MIMO
technique. Two metrics are considered, namely the average sum rate (ASR) and
energy efficiency (EE). We derive tractable and directly computable expressions
and study the tradeoffs between the ASR and EE as functions of the number of BS
antennas, the number of cellular users and the density of D2D users within a
given coverage area. Our results show that both the ASR and EE behave
differently in scenarios with low and high density of D2D users, and that
coexistence of underlay D2D communications and massive MIMO is mainly
beneficial in low densities of D2D users.Comment: 30 pages, 10 figures, Submitte
Energy Efficiency and Sum Rate when Massive MIMO meets Device-to-Device Communication
This paper considers a scenario of short-range communication, known as
device-to-device (D2D) communication, where D2D users reuse the downlink
resources of a cellular network to transmit directly to their corresponding
receivers. In addition, multiple antennas at the base station (BS) are used in
order to simultaneously support multiple cellular users using multiuser or
massive MIMO. The network model considers a fixed number of cellular users and
that D2D users are distributed according to a homogeneous Poisson point process
(PPP). Two metrics are studied, namely, average sum rate (ASR) and energy
efficiency (EE). We derive tractable expressions and study the tradeoffs
between the ASR and EE as functions of the number of BS antennas and density of
D2D users for a given coverage area.Comment: 6 pages, 7 figures, to be presented at the IEEE International
Conference on Communications (ICC) Workshop on Device-to-Device Communication
for Cellular and Wireless Networks, London, UK, June 201
Performance Evaluation and Enhancement in 5G Networks : A Stochastic Geometry Approach
PhDThe deployment of heterogeneous networks (HetNets), in which low power nodes (LPNs)
and high power nodes (HPNs) coexist, has become a promising solution for extending
coverage and increasing capacity in wireless networks. Meanwhile, several advanced technologies
such as massive multi-input multi-output (MIMO), cloud radio access networks
(C-RAN) and device-to-device (D2D) communications have been proposed as competent
candidates for supporting the next generation (5G) network. Since single technology
cannot solely achieve the envisioned 5G requirements, the e ect of integrating multiple
technologies in one system is worth to be investigated. In this thesis, a thoroughly theoretical
analysis is conducted to evaluate the network performance in di erent scenarios,
where two or more 5G techniques are employed.
First, the downlink performance of massive MIMO enabled HetNets is fully evaluated.
The exact and asymptotic expressions for the probability of a user being associated
with a macro cell or a small cell are presented. The analytical expressions for the
spectrum e ciency (SE) and energy e ciency (EE) in the K-tier network are also derived.
The analysis reveals that the implementation of massive MIMO in the macro cell can
considerably improve the network performance and decrease the demands for small cells
in HetNets, which simpli es the network deployment.
Then, the downlink performance of a massive MIMO enabled heterogeneous C-RAN is
investigated. The exact expressions for the SE and EE of the remote radio heads (RRHs)
tier and a tractable approximation approach for evaluating the SE and EE of the macrocell
tier are obtained. Numerical results collaborate the analysis and prove that massive
MIMO with dense deployment of RRHs can signi cantly enhance the performance of
heterogeneous C-RAN theoretically. Next, the uplink performance of massive MIMO enabled HetNets is exploited with interference
management via derived SE and EE expressions. The numerical results show that
the uplink performance in the massive MIMO macrocells can be signi cantly improved
through uplink power control in the small cells, while more uplink transmissions in the
macrocells have mild adverse e ect on the uplink performance of the small cells. In addition,
the SE and EE of the massive MIMO macrocells with heavier load can be improved
by expanding the small cell range.
Lastly, the uplink performance of the D2D underlaid massive MIMO network is investigated
and a novel D2D power control scheme is proposed. The average uplink achievable
SE and EE expressions for the cellular and D2D are derived and results demonstrate
that the proposed power control can e ciently mitigate the interference from the D2D.
Moreover, the D2D scale properties are obtained, which provide the su cient conditions
for achieving the anticipated SE. The results demonstrate that there exists the optimal
D2D density for maximizing the area SE of D2D tier. In addition, the achievable EE of
a cellular user can be comparable to that of a D2D user.
Stochastic geometry is applied to model all of the systems mentioned above. Monte
Carlo simulations are also developed and conducted to validate the derived expressions
and the theoretical analysis
Recommended from our members
Integrated cellular and device-to-device networks
textDevice-to-device (D2D) networking enables direct discovery and communication between cellular subscribers that are in proximity, thus bypassing the base stations (BSs). In principle, exploiting direct communication between nearby mobile devices will improve spectrum utilization, overall throughput, and energy consumption, while enabling new peer-to-peer and location-based applications and services. D2D-enabled broadband communication technology is also required by public safety networks that must function when cellular networks are not available. Integrating D2D into cellular networks, however, poses many challenges and risks to the long-standing cellular architecture, which is centered around the BSs. This dissertation identifies outstanding technical challenges in D2D-enabled cellular networks and addresses them with novel models and fundamental analysis. First, this dissertation develops a baseline hybrid network model consisting of both ad hoc nodes and cellular infrastructure. This model uses Poisson point processes to model the random and unpredictable locations of mobile users. It also captures key features of multicast D2D including multicast receiver heterogeneity and retransmissions while being tractable for analytical purpose. Several important multicast D2D metrics including coverage probability, mean number of covered receivers per multicast session, and multicast throughput are analytically characterized under the proposed model. Second, D2D mode selection which means that a potential D2D pair can switch between direct and cellular modes is incorporated into the hybrid network model. The extended model is applied to study spectrum sharing between cellular and D2D communications. Two spectrum sharing models, overlay and underlay, are investigated under a unified analytical framework. Analytical rate expressions are derived and applied to optimize the design of spectrum sharing. It is found that, from an overall mean-rate perspective, both overlay and underlay bring performance improvements (vs. pure cellular). Third, the single-antenna hybrid network model is extended to multi-antenna transmission to study the interplay between massive MIMO (multi-input multiple-output) and underlaid D2D networking. The spectral efficiency of such multi-antenna hybrid networks is investigated under both perfect and imperfect channel state information (CSI) assumptions. Compared to the case without D2D, there is a loss in cellular spectral efficiency due to D2D underlay. With perfect CSI, the loss can be completely overcome if the number of canceled D2D interfering signals is scaled appropriately. With imperfect CSI, in addition to pilot contamination, a new asymptotic underlay contamination effect arises. Finally, motivated by the fact that transmissions in D2D discovery are usually not or imperfectly synchronized, this dissertation studies the effect of asynchronous multicarrier transmission and proposes a tractable signal-to-interference-plus-noise ratio (SINR) model. The proposed model is used to analytically characterize system-level performance of asynchronous wireless networks. The loss from lack of synchronization is quantified, and several solutions are proposed and compared to mitigate the loss.Electrical and Computer Engineerin
Wearable Communications in 5G: Challenges and Enabling Technologies
As wearable devices become more ingrained in our daily lives, traditional
communication networks primarily designed for human being-oriented applications
are facing tremendous challenges. The upcoming 5G wireless system aims to
support unprecedented high capacity, low latency, and massive connectivity. In
this article, we evaluate key challenges in wearable communications. A
cloud/edge communication architecture that integrates the cloud radio access
network, software defined network, device to device communications, and
cloud/edge technologies is presented. Computation offloading enabled by this
multi-layer communications architecture can offload computation-excessive and
latency-stringent applications to nearby devices through device to device
communications or to nearby edge nodes through cellular or other wireless
technologies. Critical issues faced by wearable communications such as short
battery life, limited computing capability, and stringent latency can be
greatly alleviated by this cloud/edge architecture. Together with the presented
architecture, current transmission and networking technologies, including
non-orthogonal multiple access, mobile edge computing, and energy harvesting,
can greatly enhance the performance of wearable communication in terms of
spectral efficiency, energy efficiency, latency, and connectivity.Comment: This work has been accepted by IEEE Vehicular Technology Magazin
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