27 research outputs found
Resource allocation for licensed/unlicensed carrier aggregation MIMO systems
In this paper a novel Carrier Aggregation (CA) scheme is proposed for downlink MIMO LTE-A Systems. The proposed approach achieves increased transmission rates by establishing the communication links via both licensed and unlicensed bands without generating or experiencing interference to/from the users of the latter bands. To that end, a rate optimization problem is defined and solved subject to the previous zero interference constraints, a total power constraint and a maximum number of aggregated bands constraint
Channel modelling of human tissues at terahertz band
In this paper, the channel model is proposed to compute the path loss, delay and noise at THz band of interest (0.5 THz ~ 1.5 THz). The results shows that THz band channel is strongly dependent on both the type of the medium and the distance while the concentration of water have a lot of influence because it not only causes attenuation to the THz wave but also introduces non-white noise. Therefore, the proposed model paves the way to the further studies considering more body structures and tissue properties
Enhancing Physical Layer Security in AF Relay Assisted Multi-Carrier Wireless Transmission
In this paper, we study the physical layer security (PLS) problem in the dual
hop orthogonal frequency division multiplexing (OFDM) based wireless
communication system. First, we consider a single user single relay system and
study a joint power optimization problem at the source and relay subject to
individual power constraint at the two nodes. The aim is to maximize the end to
end secrecy rate with optimal power allocation over different sub-carriers.
Later, we consider a more general multi-user multi-relay scenario. Under high
SNR approximation for end to end secrecy rate, an optimization problem is
formulated to jointly optimize power allocation at the BS, the relay selection,
sub-carrier assignment to users and the power loading at each of the relaying
node. The target is to maximize the overall security of the system subject to
independent power budget limits at each transmitting node and the OFDMA based
exclusive sub-carrier allocation constraints. A joint optimization solution is
obtained through duality theory. Dual decomposition allows to exploit convex
optimization techniques to find the power loading at the source and relay
nodes. Further, an optimization for power loading at relaying nodes along with
relay selection and sub carrier assignment for the fixed power allocation at
the BS is also studied. Lastly, a sub-optimal scheme that explores joint power
allocation at all transmitting nodes for the fixed subcarrier allocation and
relay assignment is investigated. Finally, simulation results are presented to
validate the performance of the proposed schemes.Comment: 10 pages, 7 figures, accepted in Transactions on Emerging
Telecommunications Technologies (ETT), formerly known as European
Transactions on Telecommunications (ETT
Implementation and Evaluation of a Cooperative Vehicle-to-Pedestrian Safety Application
While the development of Vehicle-to-Vehicle (V2V) safety applications based
on Dedicated Short-Range Communications (DSRC) has been extensively undergoing
standardization for more than a decade, such applications are extremely missing
for Vulnerable Road Users (VRUs). Nonexistence of collaborative systems between
VRUs and vehicles was the main reason for this lack of attention. Recent
developments in Wi-Fi Direct and DSRC-enabled smartphones are changing this
perspective. Leveraging the existing V2V platforms, we propose a new framework
using a DSRC-enabled smartphone to extend safety benefits to VRUs. The
interoperability of applications between vehicles and portable DSRC enabled
devices is achieved through the SAE J2735 Personal Safety Message (PSM).
However, considering the fact that VRU movement dynamics, response times, and
crash scenarios are fundamentally different from vehicles, a specific framework
should be designed for VRU safety applications to study their performance. In
this article, we first propose an end-to-end Vehicle-to-Pedestrian (V2P)
framework to provide situational awareness and hazard detection based on the
most common and injury-prone crash scenarios. The details of our VRU safety
module, including target classification and collision detection algorithms, are
explained next. Furthermore, we propose and evaluate a mitigating solution for
congestion and power consumption issues in such systems. Finally, the whole
system is implemented and analyzed for realistic crash scenarios
Reinforcement Learning Exploration Algorithms for Energy Harvesting Communications Systems
Prolonging the lifetime, and maximizing the throughput are important factors in designing an efficient communications system, especially for energy harvesting-based systems. In this work, the problem of maximizing the throughput of point-to-point energy harvesting communications system, while prolonging its lifetime is investigated. This work considers more real communications system, where this system does not have a priori knowledge about the environment. This system consists of a transmitter and receiver. The transmitter is equipped with an infinite buffer to store data, and energy harvesting capability to harvest renewable energy and store it in a finite battery. The problem of finding an efficient power allocation policy is formulated as a reinforcement learning problem. Two different exploration algorithms are used, which are the convergence-based and the epsilon-greedy algorithms. The first algorithm uses the action-value function convergence error and the exploration time threshold to balance between exploration and exploitation. On the other hand, the second algorithm tries to achieve balancing through the exploration probability (i.e. epsilon). Simulation results show that the convergence-based algorithm outperforms the epsilon-greedy algorithm. Then, the effects of the parameters of each algorithm are investigated
Receiver Algorithms for Single-Carrier OSM Based High-Rate Indoor Visible Light Communications
In intensity-modulation and direct-detection (IM/DD) multiple-input and multiple-output (MIMO) visible light communication (VLC) systems, spatial subchannels are usually correlated, and spatial modulation is a good choice to achieve the advantages of MIMO technology. Peak-to-average power ratio (PAPR) is a key issue in VLCs due to the limited linear dynamic range of light emitting diodes (LEDs). Single-carrier communication systems have a lower PAPR than orthogonal frequency division multiplexing (OFDM) communication systems. However, it is challenging to design a single-carrier spatial modulation for high-rate transmissions because of the time domain intersymbol interference. This paper develops an optical spatial modulation (OSM) scheme based on bipolar pulse amplitude modulation (PAM) and spatial elements for high-rate indoor VLC systems. Multiple data streams can be transmitted simultaneously in the proposed scheme. Based on the transmit strategy, we develop a low-complexity receiver algorithm that achieves better bit-error rate performance than reference schemes, and the proposed OSM scheme has a much lower PAPR than OFDM based OSM schemes. When the spatial subchannels are highly correlated, a spatial area division strategy is applied, and the receiver algorithm is investigated. The symbol-error rate expression of the proposed OSM scheme is derived, and the computational complexity is analyzed
Optimization of a Power Splitting Protocol for Two-Way Multiple Energy Harvesting Relay System
Energy harvesting (EH) combined with cooperative communications constitutes a
promising solution for future wireless technologies. They enable additional
efficiency and increased lifetime to wireless networks. This paper investigates
a multiple-relay selection scheme for an EH-based two-way relaying (TWR)
system. All relays are considered as EH nodes that harvest energy from
renewable energy and radio frequency (RF) sources. Some of them are selected to
forward data to the destinations. The power splitting (PS) protocol, by which
the EH node splits the input RF signal into two components for EH and
information transmission, is adopted at the relay nodes. The objective is to
jointly optimize i) the set of selected relays, ii) their PS ratios, and iii)
their transmit power levels in order to maximize data rate-based utilities over
multiple coherent time slots. A joint-optimization solution based on geometric
programming (GP) and binary particle swarm optimization is proposed to solve
non-convex problems for two utility functions reflecting the level of fairness
in the TWR transmission. Numerical results illustrate the system's behavior
versus various parameters and show that the performance of the proposed scheme
is very close to that of the optimal branch-and-bound method and that GP
outperforms the dual problem-based method