39 research outputs found
Multiuser Switched Diversity Scheduling Schemes
Multiuser switched-diversity scheduling schemes were recently proposed in
order to overcome the heavy feedback requirements of conventional opportunistic
scheduling schemes by applying a threshold-based, distributed, and ordered
scheduling mechanism. The main idea behind these schemes is that slight
reduction in the prospected multiuser diversity gains is an acceptable
trade-off for great savings in terms of required channel-state-information
feedback messages. In this work, we characterize the achievable rate region of
multiuser switched diversity systems and compare it with the rate region of
full feedback multiuser diversity systems. We propose also a novel proportional
fair multiuser switched-based scheduling scheme and we demonstrate that it can
be optimized using a practical and distributed method to obtain the feedback
thresholds. We finally demonstrate by numerical examples that
switched-diversity scheduling schemes operate within 0.3 bits/sec/Hz from the
ultimate network capacity of full feedback systems in Rayleigh fading
conditions.Comment: Accepted at IEEE Transactions on Communications, to appear 2012,
funded by NPRP grant 08-577-2-241 from QNR
Secure Layered Transmission in Multicast Systems with Wireless Information and Power Transfer
This paper considers downlink multicast transmit beamforming for secure
layered transmission systems with wireless simultaneous information and power
transfer. We study the power allocation algorithm design for minimizing the
total transmit power in the presence of passive eavesdroppers and energy
harvesting receivers. The algorithm design is formulated as a non-convex
optimization problem. Our problem formulation promotes the dual use of energy
signals in providing secure communication and facilitating efficient energy
transfer. Besides, we take into account a minimum required power for energy
harvesting at the idle receivers and heterogeneous quality of service (QoS)
requirements for the multicast video receivers. In light of the intractability
of the problem, we reformulate the considered problem by replacing a non-convex
probabilistic constraint with a convex deterministic constraint. Then, a
semidefinite programming relaxation (SDR) approach is adopted to obtain an
upper solution for the reformulated problem. Subsequently, sufficient
conditions for the global optimal solution of the reformulated problem are
revealed. Furthermore, we propose two suboptimal power allocation schemes based
on the upper bound solution. Simulation results demonstrate the excellent
performance and significant transmit power savings achieved by the proposed
schemes compared to isotropic energy signal generation.Comment: 7 pages, 3 figures, accepted for presentation at the IEEE
International Conference on Communications (ICC), Sydney, Australia, 201
Joint Power and Resource Allocation for Block-Fading Relay-Assisted Broadcast Channels
We provide the solution for optimizing the power and resource allocation over
block-fading relay-assisted broadcast channels in order to maximize the long
term average achievable rates region of the users. The problem formulation
assumes regenerative (repetition coding) decode-and-forward (DF) relaying
strategy, long-term average total transmitted power constraint, orthogonal
multiplexing of the users messages within the channel blocks, possibility to
use a direct transmission (DT) mode from the base station to the user terminal
directly or a relaying (DF) transmission mode, and partial channel state
information. We show that our optimization problem can be transformed into an
equivalent "no-relaying" broadcast channel optimization problem with each
actual user substituted by two virtual users having different channel qualities
and multiplexing weights. The proposed power and resource allocation strategies
are expressed in closed-form that can be applied practically in centralized
relay-assisted wireless networks. Furthermore, we show by numerical examples
that our scheme enlarges the achievable rates region significantly.Comment: IEEE Transactions on Wireless Communications, June 201
Power Efficient MISO Beamforming for Secure Layered Transmission
This paper studies secure layered video transmission in a multiuser
multiple-input single-output (MISO) beamforming downlink communication system.
The power allocation algorithm design is formulated as a non-convex
optimization problem for minimizing the total transmit power while guaranteeing
a minimum received signal-to-interference-plus-noise ratio (SINR) at the
desired receiver. In particular, the proposed problem formulation takes into
account the self-protecting architecture of layered transmission and artificial
noise generation to prevent potential information eavesdropping. A
semi-definite programming (SDP) relaxation based power allocation algorithm is
proposed to obtain an upper bound solution. A sufficient condition for the
global optimal solution is examined to reveal the tightness of the upper bound
solution. Subsequently, two suboptimal power allocation schemes with low
computational complexity are proposed for enabling secure layered video
transmission. Simulation results demonstrate significant transmit power savings
achieved by the proposed algorithms and layered transmission compared to the
baseline schemes.Comment: Accepted for presentation at the IEEE Wireless Communications and
Networking Conference (WCNC), Istanbul, Turkey, 201
Cross-Layer Optimal Rate Allocation for Heterogeneous Wireless Multicast
Heterogeneous multicast is an efficient communication scheme especially for multimedia applications running over multihop networks. The term heterogeneous refers to the phenomenon when multicast receivers in the same session require service at different rates commensurate with their capabilities. In this paper, we address the problem of resource allocation for a set of heterogeneous multicast sessions over multihop wireless networks. We propose an iterative algorithm that achieves the optimal rates for a set of heterogeneous multicast sessions such that the aggregate utility for all sessions is maximized. We present the formulation of the multicast resource allocation problem as a nonlinear optimization model and highlight the cross-layer framework that can solve this problem in a distributed ad hoc network environment with asynchronous computations. Our simulations show that the algorithm achieves optimal resource utilization, guarantees fairness among multicast sessions, provides flexibility in allocating rates over different parts of the multicast sessions, and adapts to changing conditions such as dynamic channel capacity and node mobility. Our results show that the proposed algorithm not only provides flexibility in allocating resources across multicast sessions, but also increases the aggregate system utility and improves the overall system throughput by almost 30% compared to homogeneous multicast
Thresholds Optimization for One-Bit Feedback Multi-User Scheduling
We propose a new one-bit feedback scheme with scheduling decision based on
the maximum expected weighted rate. We show the concavity of the -user case
and provide the optimal solution which achieves the maximum weighted rate of
the users. For the general asymmetric M-user case, we provide a heuristic
method to achieve the maximum expected weighted rate. We show that the sum rate
of our proposed scheme is very close to the sum rate of the full channel state
information case, which is the upper bound performance
Augmented Driver Behavior Models for High-Fidelity Simulation Study of Crash Detection Algorithms
Developing safety and efficiency applications for Connected and Automated
Vehicles (CAVs) require a great deal of testing and evaluation. The need for
the operation of these systems in critical and dangerous situations makes the
burden of their evaluation very costly, possibly dangerous, and time-consuming.
As an alternative, researchers attempt to study and evaluate their algorithms
and designs using simulation platforms. Modeling the behavior of drivers or
human operators in CAVs or other vehicles interacting with them is one of the
main challenges of such simulations. While developing a perfect model for human
behavior is a challenging task and an open problem, we present a significant
augmentation of the current models used in simulators for driver behavior. In
this paper, we present a simulation platform for a hybrid transportation system
that includes both human-driven and automated vehicles. In addition, we
decompose the human driving task and offer a modular approach to simulating a
large-scale traffic scenario, allowing for a thorough investigation of
automated and active safety systems. Such representation through Interconnected
modules offers a human-interpretable system that can be tuned to represent
different classes of drivers. Additionally, we analyze a large driving dataset
to extract expressive parameters that would best describe different driving
characteristics. Finally, we recreate a similarly dense traffic scenario within
our simulator and conduct a thorough analysis of various human-specific and
system-specific factors, studying their effect on traffic network performance
and safety
Efficient Transmission of H.264 Video over Multirate IEEE 802.11e WLANs
The H.264 video encoding technology, which has emerged as one of the most promising compression standards, offers many new delivery-aware features such as data partitioning. Efficient transmission of H.264 video over any communication medium requires a great deal of coordination between different communication network layers. This paper considers the increasingly popular and widespread 802.11 Wireless Local Area Networks (WLANs) and studies different schemes for the delivery of the baseline and extended profiles of H.264 video over such networks. While the baseline profile produces data similar to conventional video technologies, the extended profile offers a partitioning feature that divides video data into three sets with different levels of importance. This allows for the use of service differentiation provided in the WLAN. This paper examines the video transmission performance of the existing contention-based solutions for 802.11e, and compares it to our proposed scheduled access mechanism. It is demonstrated that the scheduled access scheme outperforms contention-based prioritized services of the 802.11e standard. For partitioned video, it is shown that the overhead of partitioning is too high, and better results are achieved if some partitions are aggregated. The effect of link adaptation and multirate operation of the physical layer (PHY) is also investigated in this paper