7,683 research outputs found
Frame Structure Design and Analysis for Millimeter Wave Cellular Systems
The millimeter-wave (mmWave) frequencies have attracted considerable
attention for fifth generation (5G) cellular communication as they offer orders
of magnitude greater bandwidth than current cellular systems. However, the
medium access control (MAC) layer may need to be significantly redesigned to
support the highly directional transmissions, ultra-low latencies and high peak
rates expected in mmWave communication. To address these challenges, we present
a novel mmWave MAC layer frame structure with a number of enhancements
including flexible, highly granular transmission times, dynamic control signal
locations, extended messaging and ability to efficiently multiplex directional
control signals. Analytic formulae are derived for the utilization and control
overhead as a function of control periodicity, number of users, traffic
statistics, signal-to-noise ratio and antenna gains. Importantly, the analysis
can incorporate various front-end MIMO capability assumptions -- a critical
feature of mmWave. Under realistic system and traffic assumptions, the analysis
reveals that the proposed flexible frame structure design offers significant
benefits over designs with fixed frame structures similar to current 4G
long-term evolution (LTE). It is also shown that fully digital beamforming
architectures offer significantly lower overhead compared to analog and hybrid
beamforming under equivalent power budgets.Comment: Submitted to IEEE Transactions for Wireless Communication
Spectrum Sharing in Wireless Networks via QoS-Aware Secondary Multicast Beamforming
Secondary spectrum usage has the potential to considerably increase spectrum utilization. In this paper, quality-of-service (QoS)-aware spectrum underlay of a secondary multicast network is considered. A multiantenna secondary access point (AP) is used for multicast (common information) transmission to a number of secondary single-antenna receivers. The idea is that beamforming can be used to steer power towards the secondary receivers while limiting sidelobes that cause interference to primary receivers. Various optimal formulations of beamforming are proposed, motivated by different ldquocohabitationrdquo scenarios, including robust designs that are applicable with inaccurate or limited channel state information at the secondary AP. These formulations are NP-hard computational problems; yet it is shown how convex approximation-based multicast beamforming tools (originally developed without regard to primary interference constraints) can be adapted to work in a spectrum underlay context. Extensive simulation results demonstrate the effectiveness of the proposed approaches and provide insights on the tradeoffs between different design criteria
Secure Full-Duplex Device-to-Device Communication
This paper considers full-duplex (FD) device-to-device (D2D) communications
in a downlink MISO cellular system in the presence of multiple eavesdroppers.
The D2D pair communicate sharing the same frequency band allocated to the
cellular users (CUs). Since the D2D users share the same frequency as the CUs,
both the base station (BS) and D2D transmissions interfere each other. In
addition, due to limited processing capability, D2D users are susceptible to
external attacks. Our aim is to design optimal beamforming and power control
mechanism to guarantee secure communication while delivering the required
quality-of-service (QoS) for the D2D link. In order to improve security,
artificial noise (AN) is transmitted by the BS. We design robust beamforming
for secure message as well as the AN in the worst-case sense for minimizing
total transmit power with imperfect channel state information (CSI) of all
links available at the BS. The problem is strictly non-convex with infinitely
many constraints. By discovering the hidden convexity of the problem, we derive
a rank-one optimal solution for the power minimization problem.Comment: Accepted in IEEE GLOBECOM 2017, Singapore, 4-8 Dec. 201
Secure Full-Duplex Device-to-Device Communication
This paper considers full-duplex (FD) device-to-device (D2D) communications
in a downlink MISO cellular system in the presence of multiple eavesdroppers.
The D2D pair communicate sharing the same frequency band allocated to the
cellular users (CUs). Since the D2D users share the same frequency as the CUs,
both the base station (BS) and D2D transmissions interfere each other. In
addition, due to limited processing capability, D2D users are susceptible to
external attacks. Our aim is to design optimal beamforming and power control
mechanism to guarantee secure communication while delivering the required
quality-of-service (QoS) for the D2D link. In order to improve security,
artificial noise (AN) is transmitted by the BS. We design robust beamforming
for secure message as well as the AN in the worst-case sense for minimizing
total transmit power with imperfect channel state information (CSI) of all
links available at the BS. The problem is strictly non-convex with infinitely
many constraints. By discovering the hidden convexity of the problem, we derive
a rank-one optimal solution for the power minimization problem.Comment: Accepted in IEEE GLOBECOM 2017, Singapore, 4-8 Dec. 201
Robust Transmissions in Wireless Powered Multi-Relay Networks with Chance Interference Constraints
In this paper, we consider a wireless powered multi-relay network in which a
multi-antenna hybrid access point underlaying a cellular system transmits
information to distant receivers. Multiple relays capable of energy harvesting
are deployed in the network to assist the information transmission. The hybrid
access point can wirelessly supply energy to the relays, achieving multi-user
gains from signal and energy cooperation. We propose a joint optimization for
signal beamforming of the hybrid access point as well as wireless energy
harvesting and collaborative beamforming strategies of the relays. The
objective is to maximize network throughput subject to probabilistic
interference constraints at the cellular user equipment. We formulate the
throughput maximization with both the time-switching and power-splitting
schemes, which impose very different couplings between the operating parameters
for wireless power and information transfer. Although the optimization problems
are inherently non-convex, they share similar structural properties that can be
leveraged for efficient algorithm design. In particular, by exploiting
monotonicity in the throughput, we maximize it iteratively via customized
polyblock approximation with reduced complexity. The numerical results show
that the proposed algorithms can achieve close to optimal performance in terms
of the energy efficiency and throughput.Comment: 14 pages, 8 figure
A survey and tutorial of electromagnetic radiation and reduction in mobile communication systems
This paper provides a survey and tutorial of electromagnetic (EM) radiation exposure and reduction in mobile communication systems. EM radiation exposure has received a fair share of interest in the literature; however, this work is one of the first to compile the most interesting results and ideas related to EM exposure in mobile communication systems and present possible ways of reducing it. We provide a comprehensive survey of existing literature and also offer a tutorial on the dosimetry, metrics, international projects as well as guidelines and limits on the exposure from EM radiation in mobile communication systems. Based on this survey and given that EM radiation exposure is closely linked with specific absorption rate (SAR) and transmit power usage, we propose possible techniques for reducing EM radiation exposure in mobile communication systems by exploring known concepts related to SAR and transmit power reduction in mobile systems. Thus, this paper serves as an introductory guide to EM radiation exposure in mobile communication systems and provides insights toward the design of future low-EM exposure mobile communication networks
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