30,996 research outputs found
Power allocation in multi-hop OFDM transmission systems with amplify-and-forward relaying: A unified approach
In this paper, a unified approach for power allocation (PA) in multi-hop orthogonal frequency division multiplexing (OFDM) amplify-and-forward (AF) relaying systems is presented. In the proposed approach, we consider short and long term individual and total power constraints at the source and relays, and devise low complexity PA algorithms when wireless links are subject to channel path-loss and small-scale Rayleigh fading. To manage the complexity, in the proposed formulations, we adopt a two-stage iterative approach consisting of a power distribution phase among distinct subcarriers, and a power allocation phase among different relays. In particular, aiming at improving the instantaneous rate of multi-hop transmission systems with AF relaying, we develop (i) a near-optimal iterative PA algorithm based on the exact analysis of the received SNR at the destination; (ii) a low complexity suboptimal iterative PA algorithm based on an approximate expression of the received SNR at high-SNR regime; and (iii) a low complexity non-iterative PA scheme with limited performance loss. Simulation results show the superior performance of the proposed power allocation algorithms
Practical Resource Allocation Algorithms for QoS in OFDMA-based Wireless Systems
In this work we propose an efficient resource allocation algorithm for OFDMA
based wireless systems supporting heterogeneous traffic. The proposed algorithm
provides proportionally fairness to data users and short term rate guarantees
to real-time users. Based on the QoS requirements, buffer occupancy and channel
conditions, we propose a scheme for rate requirement determination for delay
constrained sessions. Then we formulate and solve the proportional fair rate
allocation problem subject to those rate requirements and power/bandwidth
constraints. Simulations results show that the proposed algorithm provides
significant improvement with respect to the benchmark algorithm.Comment: To be presented at 2nd IEEE International Broadband Wireless Access
Workshop. Las Vegas, Nevada USA Jan 12 200
Green Communication via Power-optimized HARQ Protocols
Recently, efficient use of energy has become an essential research topic for
green communication. This paper studies the effect of optimal power controllers
on the performance of delay-sensitive communication setups utilizing hybrid
automatic repeat request (HARQ). The results are obtained for repetition time
diversity (RTD) and incremental redundancy (INR) HARQ protocols. In all cases,
the optimal power allocation, minimizing the outage-limited average
transmission power, is obtained under both continuous and bursting
communication models. Also, we investigate the system throughput in different
conditions. The results indicate that the power efficiency is increased
substantially, if adaptive power allocation is utilized. For instance, assume
Rayleigh-fading channel, a maximum of two (re)transmission rounds with rates
nats-per-channel-use and an outage probability constraint
. Then, compared to uniform power allocation, optimal power
allocation in RTD reduces the average power by 9 and 11 dB in the bursting and
continuous communication models, respectively. In INR, these values are
obtained to be 8 and 9 dB, respectively.Comment: Accepted for publication on IEEE Transactions on Vehicular Technolog
Optimal Power Control for Analog Bidirectional Relaying with Long-Term Relay Power Constraint
Wireless systems that carry delay-sensitive information (such as speech
and/or video signals) typically transmit with fixed data rates, but may
occasionally suffer from transmission outages caused by the random nature of
the fading channels. If the transmitter has instantaneous channel state
information (CSI) available, it can compensate for a significant portion of
these outages by utilizing power allocation. In a conventional dual-hop
bidirectional amplify-and-forward (AF) relaying system, the relay already has
instantaneous CSI of both links available, as this is required for relay gain
adjustment. We therefore develop an optimal power allocation strategy for the
relay, which adjusts its instantaneous output power to the minimum level
required to avoid outages, but only if the required output power is below some
cutoff level; otherwise, the relay is silent in order to conserve power and
prolong its lifetime. The proposed scheme is proven to minimize the system
outage probability, subject to an average power constraint at the relay and
fixed output powers at the end nodes.Comment: conference IEEE Globecom 2013, Atlanta, Georgia, U
Convergence Analysis of Mixed Timescale Cross-Layer Stochastic Optimization
This paper considers a cross-layer optimization problem driven by
multi-timescale stochastic exogenous processes in wireless communication
networks. Due to the hierarchical information structure in a wireless network,
a mixed timescale stochastic iterative algorithm is proposed to track the
time-varying optimal solution of the cross-layer optimization problem, where
the variables are partitioned into short-term controls updated in a faster
timescale, and long-term controls updated in a slower timescale. We focus on
establishing a convergence analysis framework for such multi-timescale
algorithms, which is difficult due to the timescale separation of the algorithm
and the time-varying nature of the exogenous processes. To cope with this
challenge, we model the algorithm dynamics using stochastic differential
equations (SDEs) and show that the study of the algorithm convergence is
equivalent to the study of the stochastic stability of a virtual stochastic
dynamic system (VSDS). Leveraging the techniques of Lyapunov stability, we
derive a sufficient condition for the algorithm stability and a tracking error
bound in terms of the parameters of the multi-timescale exogenous processes.
Based on these results, an adaptive compensation algorithm is proposed to
enhance the tracking performance. Finally, we illustrate the framework by an
application example in wireless heterogeneous network
Learning and Management for Internet-of-Things: Accounting for Adaptivity and Scalability
Internet-of-Things (IoT) envisions an intelligent infrastructure of networked
smart devices offering task-specific monitoring and control services. The
unique features of IoT include extreme heterogeneity, massive number of
devices, and unpredictable dynamics partially due to human interaction. These
call for foundational innovations in network design and management. Ideally, it
should allow efficient adaptation to changing environments, and low-cost
implementation scalable to massive number of devices, subject to stringent
latency constraints. To this end, the overarching goal of this paper is to
outline a unified framework for online learning and management policies in IoT
through joint advances in communication, networking, learning, and
optimization. From the network architecture vantage point, the unified
framework leverages a promising fog architecture that enables smart devices to
have proximity access to cloud functionalities at the network edge, along the
cloud-to-things continuum. From the algorithmic perspective, key innovations
target online approaches adaptive to different degrees of nonstationarity in
IoT dynamics, and their scalable model-free implementation under limited
feedback that motivates blind or bandit approaches. The proposed framework
aspires to offer a stepping stone that leads to systematic designs and analysis
of task-specific learning and management schemes for IoT, along with a host of
new research directions to build on.Comment: Submitted on June 15 to Proceeding of IEEE Special Issue on Adaptive
and Scalable Communication Network
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